Electroreduction and electrocatalytic dimerization of halogenated benzothiophenes and benzothiophene-2-oxazolines.

Use of sonication, diastereoselectivity of the coupling reaction.

Jiří Ludvíka, Michal Rejňákb, Jiří Klímaa, Jiří Svobodab

aJ. Heyrovský Institute of Physical Chemistry, Academy of Science of the Czech Republic, Dolejškova 3, 182 23 Prague 8, Czech Republic

bDepartment of Organic Chemistry, Institute of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic

Biaryls found large application as a) chiral templates for stoichiometric and asymmetric catalytic reactions b) new materials with liquid-crystalline properties. Formation of an aryl-aryl bond can be accomplished by various methods. Recently [1] we used successfully the classical Ullman reaction of methyl 3-halobenzothiophene-2-carboxylates for preparation of dimeric 3,3´-bi(benzothiophene) derivative (BT2). In addition to this, the dimerization of the chiral oxazolines [2] was newly studied in an analogous way. Generally, high reaction temperature lowers the diastereoselectivity because the transition states of diastereomer formation are of different energies. On the other hand, low temperature leads to loss of reactivity. Electrochemical reductive dehalogenation with (catalytic) dimerization is another possible method of biaryl synthesis. For this reason electrochemical behaviour of methyl 3-halobenzothiophene-2-carboxylates and oxazoline on various electrodes at various conditions has been first investigated [3] and the most effective and stereoselective dimerization procedure was searched using controlled potential reductive electrolysis. Since the blocking of electrode was observed during the preparative electrolysis, the application of sonication caused the efficient reactivation of the platinum electrode from the formed polymer film [4] . It has been found that the halogen atom can be effectively reduced at platinum and mercury electrode. Sonoassisted electrolysis increases effectivity of the process, however, without a catalyst the only product was the reduced species. The successful electroreductive dimerization of chloro ester was achieved using the [Ni-DPA] complex as an electrochemically generated catalyst and the axial chiral bis-oxazoline was prepared. Electrolysis at room temperature thus made possible to increase the diastereoslectivity of the coupling. Further investigation of the diastereoselective electrochemical dimerization is under way. Financial support of the Grant Agency of the Czech Republic (projects No. 202/02/0840 and 202/02/0983) and of the Grant Agency of the Academy of Sciences of the Czech Republic (Project No. 4040304) is gratefully acknowledged.

[1] Bennincori T, Brenna E, Sannicolo F, Trimarco L, Antognazza P, Cesarotti E, Demartin F, Pilati T, J Org Chem 1996, 61, 6244 [2] Mézlová M, Petříčková H, Maloň P, Svoboda J, Collect Czech Chem Commun 2003, 68, 1020 [3] Rejňák M, Klíma J, Svoboda J, Ludvík J, Collect Czech Chem Commun 2004, 69, 242. [4] Klíma J., Ludvík J.: Collect. Czech. Chem. Commun. 2000, 65, 941-945.

Recent applications of polarography to some problems of organic chemistry Petr Zuman Department of Chemistry, Box 5810, Clarkson University, Potsdam,NY 13699-5810, USA Limiting currents obtained by DC polarography (DCP) or RDE voltammetry are aprticularly suitable for investigation of some problems in physical organic chemistry and related areas. Opposed to techniques like cyclic voltammetry, differential , square wave or AC polarography or voltammetry, the limiting currents measured in DCP do not depend on the rate of the electrode process, but solely on the transport of the electroactive species to the electrode. Limiting currents thus depend only on the number of electrons transferred, on concentration of the electroactive species and on rate and equilibria of chemical reactions generating such species. The following examples will be discussed: 1) Absence of conjugation (delocalization) in systems containing grouping C=N-N=C. It has been demonstrated that in such groupings the N-N bond is practically a single bond. This has been later confirmed by crystallography (with J.Ludvik) 2) Sequence of the reduction of azomethine bond in heterocycles bearing the grouping HN-CO-C(R)=N-N==C<. Conjugation in the group HN=CO-CR=N-N=C< facilitates the reduction of the C=N bond adjacent to the amidic gouping, so that this reduction occurs at potentials by about 0.5V more positive than the reduction of the second azomethine group (with J.Ludvik). 3) The difference in the participation of covalent hydration in tere- ortho- and isophthalaldehydes. Strong resonance interaction of the two p-CHO groups in terephthalaldehyde results in a stronger hydration than that of the CHO group in p-nitrobenzaldehyde. In solutions of orthophthalaldehyde equilibrium exists between the unhydrated, monohydrated acyclic and cyclic hemiacetal forms. These reactions play a role in the use of orthophthalaldehyde in determination of amino acids. Isophthalaldehyde remains practically unhydrated, as the majority of substituted benzaldehydes (with. M.S.Baymak and J.Bover). 4) Proof of diprotonation of hydrazones and oxime based on change of the limiting current with pH. Role of general acid catalysis in such reactions at the electrode surface. Diprotonated form is also most probably the form which is involved in acid catalysed hydrolyses of hydrazones and oximes.(with M.S.Baymak, H.Celik and H.Lund). 5) Proof of formation of an imine as a reactive intermediate in the reductions of hydrazones and oximes Proof is based on comparison with a stable imine derived from fluorenone, on separation of two two-electron waves in acidic media and on the behavior of N,N,N--trialkylhydrazonium componds (with M.S.Baymak, H.Lund and H.Celik). 6) TYpes of electroreductions of cephalosporins. Depending on the presence of substituents in positions 3- and 7- , the reduction of cephalosporins involves either a reduction of the double bond in the C=C-COOH grouping, a cleavage of the 3-CH2X grouping or reductions in the side chain at 3-C or 7-C.An example is the elctroreduction of the antibiotic cefetamet, where the o-methyloxime group in the 7-C side chain is reduced in two two-electron steps. Most O-alkyloximes are

reuced in a single four electron step. The different behavior of cefetamet is due to a difference in protonatim of the C=NOCH3 of the starting material and the C=N group of the intermediate (with V.Kapetanovic and M.Aleksic). _______ Petr Zuman Clarkson University Department of Chemistry Box 13699-5810 Potsdm,NY,U.S.A http://www.clarkson.edu/~celikh/zuman.htm_________________________________

Electrochemical Kinetic Simulations Using Hermitian Finite-Difference Methods

L. K. Bieniasz

Institute of Physical Chemistry of the Polish Academy of Sciences, Department of Electrochemical Oxidation of Gaseous Fuels,

ul. Zagrody 13, 30-318 Cracow, Poland. Tel. /fax.: (+48 12) 266 03 41.

E-mail: nbbienia@cyf-kr.edu.pl URL: http://www.cyf-kr.edu.pl/~nbbienia

Abstract

Hermitian finite-difference methods (also known as compact finite-

difference schemes) are an attractive alternative to the conventional finite-

difference discretisations, traditionally used in electrochemical kinetic simulations.

They possess higher spatial accuracy orders, compared to conventional space

discretisations that use the same number of space grid points. For example, the

three-point compact Numerov method [1] is fourth-order accurate, in contrast to

the conventional, second-order accurate three-point approximation of the second

space derivatives of the concentrations. This makes the simulations substantially

more efficient. The principles of the Hermitian methods will be briefly

characterised, The advantages of using the Numerov method, and its various

extensions, for simulating typical electroanalytical experiments, will be

demonstrated, based on the recent studies of the author [2-4]. A Hermitian

approach to approximating electric currents at electrodes [5] will also be outlined.

References

[1] B. V. Numerov, Month. Notices Roy. Astronom. Soc. 84 (1924) 592. [2] L. K. Bieniasz, Comput. Chem. 26 (2002) 633. [3] L. K. Bieniasz, J. Comput. Chem. 25 (2004) 1075. [4] L. K. Bieniasz, J. Comput. Chem. 25 (2004) 1515. [5] L. K. Bieniasz, Comput. Biol. Chem. 27 (2003) 315.

Which digital simulation method should I use?

Dieter Britz

Abstract

Various methods for digital simulation are described,

with emphasis on their uses, advantages and disadvantages.

The choice is to some extent individual, and dependent on

the simulation problem.

Investigation of horseradish peroxidase in polyelectrolyte multilayers by means of scanning electrochemical microscopy Malte Burchardt, Gunther Wittstock

Carl von Ossietzky Universität Oldenburg, School of Mathematics and Science, D-26111

Oldenburg, Germany

Polyelectrolyte multilayers are built up by alternating adsorption of polyanions and

polycations on charged surfaces. Starting from surfaces which are only charged on certain

areas, it is possible to build up localized polyelectrolyte multilayers.

Topic of our research is the fabrication and characterization of continuous and structured

polyelectrolyte multilayers containing horseradish peroxidase. The amount of immobilized

enzyme can be adjusted in a broad range by varying the number of adsorption cycles. Locally

charged surfaces as primers were built by microcontact printing with terminal functionalised

alcane thiols on gold surfaces. Using a simple programmable robot it was possible to simplify

fabrication process of the multilayer. In order to avoid unspecific adsorption in between of the

polyelectrolyte multilayers and to achieve reproducible growth of the films, the adsorption

conditions and the primers were optimised.

Using scanning electrochemical microscopy (SECM) the continuous and structured

polyelectrolyte multilayers were characterized. Turn over numbers for the catalytic

conversion of H2O2 depending on the number of adsorbed enzyme layers were evaluated by

means of approach curves. Mapping experiments were done to examine unspecific adsorption

between the polyelectrolyte multilayers. Furthermore the self assembled monolayers that were

uses as primers were investigated by SECM.

The morphology of the microstructured polyelectrolyte multilayers was investigated with

AFM.

Localized corrosion studies using the alternating current mode of scanning electrochemical microscopy

Kathrin Eckhard, Mathieu Etienne, Albert Schulte, Wolfgang Schuhmann*

Analytische Chemie – Elektroanalytik & Sensorik, Ruhr-Universität Bochum, D-44780 Bochum, Germany

Scanning electrochemical microscopy (SECM) is a powerful local probe technique for

imaging surface topography along with its conductivity and reactivity. As interpretation of

SECM measurements is difficult on surfaces displaying topography and conductivity

variations at the same time it is vital to maintain the tip-to-sample distance constant

throughout scanning. Recently, alternating current scanning

electrochemical microscopy (AC-SECM) was introduced

for imaging local variations in surface activity [1]. Initial

studies on lacquered tinplates [2] and nickel titanium shape

memory alloys [3] demonstrated that AC-SECM is a

suitable approach to visualize microscopic sites of localized

corrosion. However, measurements were carried out with

conventionally-sized SECM probes scanned in constant

height, hence, spatial resolution was rather limited.

In this communication the application of shear-force

based constant-distance AC-SECM for studying

localized corrosion is presented. A scheme of the employed set-up is shown in figure 1. Its

piezoelectric distance control allows to employ UME probes. Samples such as stainless steel

304 and stainless steel 316Ti surfaces have been investigated with improved resolution in

alternating current mode of SECM. Actively corroding areas could be visualized using this

technique unimpaired by topographic features of the substrate.

Keywords : scanning electrochemical microscopy, AC-SECM, shear force distance control,

localized corrosion [1] B. Ballesteros-Katemann, A. Schulte, E. J. Calvo, M. Koudelka-Hep, W. Schuhmann. Electrochem.

Commun. 4 (2002) 134. [2] B. Ballesteros-Katemann, C. Gonzalez Ichauspe, P. Castro, A. Schulte, E. J. Calvo, W. Schuhmann.

Electrochim. Acta 48 (2003) 1115. [3] A. Schulte, S. Belger, W. Schuhmann. J. Mat. Sci. Eng. A, 378 (2004) 523-526

RE/CE

WE

RE/CE

WE

Oscillator Out External Reference

Signal In

R

Lock-in amplifierAC

Trigger

Frequency generator

Signal Out

Lock-in amplifierSF

x,y,z Positionning elements

Oscillation piezo

Detection piezo

1 mM NaCl aq

Ag/AgCl

Sample

PC Hardware control and data acquisition

Potentiostat

I out

Oscillator Out

Signal In

E inR ΘΘΘΘ

(X Y)Signal Out

Fig 1: Scheme of an SECM set-up operating in alternating current mode (AC-SECM)

Study of Electrocatalytic Oxidation of Hydrazine with Pyrogallol Red as a Mediator on Glassy Carbon Electrode

Ali Asghar Ensafi*, Elham Mirmomtaz

College of Chemistry, Isfahan University of Technology, Isfahan, 84156, Iran

The anodic oxidation of hydrazine has been studied on a glassy carbon electrode by electrocatalytic effect of pyrogallol red as a homogenous mediator, using cyclic voltammetry, linear sweep voltammetry and chronoamperometry as diagnostic techniques. Cyclic voltammetry study showed that, the catalytic current of the system depends on the concentration of hydrazine. The magnitude of the peak current for pyrogallol red increased sharply in the presence of hydrazine, and proportional to hydrazine concentration. The influence of chemical and instrumental variables on the system was studied completely. The calibration curve was plotted for optimized condition which shows a good linearity between the data. The diffusion coefficient of hydrazine was also estimated using chronoamperometry. The chronoamperometry studies also were used to determine the catalytic rate constant for catalytic reaction of pyrogallol red with hydrazine. The experimental results showed that the peak current varied in the presence of different metal cations, but these effects were omitted in the presence of EDTA, while most of anions had no effect on the peak current of hydrazine. The proposed method was used for analysis of hydrazine in real samples.

This method for the determination of hydrazine is very rapid (less than one minute per sample solution), reproducible, selective and sensitive and can be used for real sample analysis. The importance of the technique is its ability to electrocatalytic determination of hydrazine with pyrogallol red as homogenous electrocatalyst, while it doesn't need to prepare as for modified electrode. The independency of the system from the interferences, and the ability of removing the effect of most of cationic interferences easily are the features of the technique. On the other hand, the kinetic parameters of the system have been calculated from the experimental results, which are in good agreement with the literatures

3D-Hybrid Networks

with Controllable Electrical Conductivity

by Electrochemical Deposition of

Terthiophene-Functionalized Polyphenylene Dendrimers

Hermann John, Pamela Espindola and Jürgen Heinze,

Institute of Physical Chemistry, University of Freiburg,

A new class of monodisperse nanostructured macromolecules which exhibit remarkable

physical and electrochemical properties are dendrimers. We have studied the

electropolymerisation and conductivities of shape-persistent polyphenylene dendrimers

decorated with peripheral terthiophene units [1].

S

S

S

S

SS

S

SS

SSS

SS S

SS

SSS

SS

S

S

S

S

S

S

SS

S

SS

S SS

SSS

SS

S SS

SS

S

S 1

Upon electrochemical oxidation the hedgehog-type core-shell system 1 forms a network

which can be charged and discharged in the potential range between 0.4 and 1.5 V. In-situ

conductivity measurements of the coupling product of 1 show an increase of the conductivity

during voltammetric charging of the thiophene chains in the deposited material. This

conductivity passes a maximum approximately at the half-charged level. At higher potentials

the conductivity increases again indicating a three-dimensional charge transport. Obviously,

the hopping processes of charge carriers are facilitated in the 3D network. The results offer

new insights into conductivity mechanisms of conjugated polymers. The great similarity

between the conductivity behaviour of this material and that of radical ion salts supports the

view of almost identical transport mechanisms. _________________________________________________________________________________________________________________

[1] H. John, R. Bauer, P. Espindola, P. Sonar, J. Heinze, K. Müllen, Angew. Chem. Int. Ed Engl., in press

0 10 20 300

50100150200-1.5

-1.0

-0.5

0

δd [n

m]

time [min]

Cd

[mA/

cm²]

Fig. 1: Current and thickness versus time for the growth of a pNIPAM layer. The thickness was determined by quartz crystal microgravimetry.

FORMATION OF THIN HYDROGEL LAYERS ON METAL SURFACES BY ELECTROCHEMICALLY INITIATED FREE-

RADICAL POLYMERIZATION

Helke Reinhardt, Johanna Reuber, Diethelm Johannsmann*P

Institute of Physical Chemistry, Clausthal-Zellerfeld, HTUwww.pc.tu-clausthal.deUTH

Thin layers of a hydrogel were formed on metal surfaces by in-situ polymerization of a

surface-attached network. The initiation occurred via a slightly negative voltage (-0.8 V SCE) in conjunction with a persulfate initiator, which ensures formation of the gel at the electrode only. Even though no strictly covalent links are formed, the adhesion of the gel to the surface is very good. The recipe is easy and robust. It has been tested with acrylamide as well as N-isopropylacrylamide.

The characterization occurred in-situ by quartz-crystal microweighing (QCM). Typical layer thicknesses are in the range of 10 – 200 nm. The water content is in the range of 30 to 70%, depending on the cross-linker concentration and other parameters of the growth process. The layers are highly permeable as evidenced by cyclovoltammetry with a solution of KB3 B[Fe(CN)]B6 B , where the electrode surface was covered with a gel layer. Polymer-metal composites were by depositing copper into the mesh formed by the hydrogel. This technique can have numerous applications for sensing, stimulated drug release, as well as surface modification in a broader sense.TP

1PT

TP

1PT Acknowledgements:

Funding by the European Graduate School: MicrostrPolymerization, as well as helpful discussions with Wacknowledged. *johannsmann@pc.tu-clausthal.de

25 30 35 40 45 50bare quartz

pNIPAM covered quartz

1 kHz

Change of bandwidth (dissipation)

temperature [°C]

Fig. 2: Temperature-induced swelling (T < 36°C) and de-swelling (T > 36 °C) of a pNIPAM gel. The swollen gel dissipates more energy, leading toa larger bandwidth of the acoustic resonance.

uctural Control In Free−Radical ilhelm Oppermann are gratefully

Investigation of the Rotating Disk Electrode for determination of diffusion coefficient in

depending of the temperature and solvent viscosity.

Ewa M. Kalisz, Günter Grampp, Stephan Landgraf

Institute of Physical and Theoretical Chemistry, Graz University of Technology,

Technikerstrasse 4/I, A-8010 Graz, Austria

Rotating Disk Electrode (RDE) is a widely used method for the study of electrode processes

because of its ability to solve many theoretical and experimental problems. The method gives

many possibilities to change the experimental conditions and its theory is described in great

detail. This method is used mainly for the determination of diffusion coefficients and the

kinetics of electrochemically induced reactions.

We will present the results from the RDE measurements of the diffusion coefficient of

N,N,N’,N’-tetramethyl-p-phenylendiamin (TMPPD) in alcohols of different viscosity. The

diffusion coefficients are determined as a function of solvent viscosity and temperature. The

experimental results will be compared to the theoretical values from different diffusion

models. The range of the diffusion coefficients vary from 1.60*10-5 to 7.00*10-6 cm2 sec-1 at

T=298K and from 9.60*10-6 to 1.40*10-5 cm2 sec-1 for one solvent within 273K � T � 308K.

Electrochemiluminescence Studies of the Iridium(III) Cyclometalated Complexes

Andrzej Kapturkiewicz

Institute of Physical Chemistry, Polish Academy of Sciences,

01-224 Warsaw, Kasprzaka 44/52, Poland, e-mail: akaptur@ichf.edu.pl

Iridium(III) cyclometalated complexes of the general formula L3Ir and L2Ir(acac) (where acac denotes

acetylacetone anion) can be straightforwardly synthesized from IrCl3 and appropriate ligand L

(substituted phenyl derivatives of N-methyl-benzimidazole, benzoxazole, benzothiazole, pyridine and

isoquinoline).

Their electrochemical, luminescence and electrochemiluminescence (ECL) properties have been studied

in acetonitrile/dioxan (1:1) solutions. The complexes investigated are strongly emissive in solutions (with

quantum efficiencies up to 0.70) with 3MLCT (or mixed 3MLCT/IL) luminescence maxima distinctly

tuned (in the range 480-650 nm) by the nature of the ligand L. The excited 3*L2Ir(acac) species can be

also efficiently generated by means of the electron transfer reactions

A− + L2Ir(acac)+ → Α + 3*L2Ir(acac) (1)

A− + L3Ir+ → Α + 3*L3Ir (2)

between electrochemically generated L2Ir(acac)+ cations and A− radical anions of aromatic nitriles and

ketones.

High yields of the excited 3*L2Ir(acac) formation (0.60-0.90) together with their high luminescence

efficiencies lead to extremely efficient ECL system with total electrochemiluminescence efficiencies

0.08-0.69 (expressed in number of photons emitted per number of the annihilating A−/L2Ir(acac)+ or

A−/L3Ir+ pairs).

References

1) A. Kapturkiewicz, G. Angulo, Dalton Trans. 2003, 3907.

2) A. Kapturkiewicz, T-M. Chen, I. Laskar, J. Nowacki, Electrochem. Commun. 6, 827 (2004).

3) A. Kapturkiewicz, J. Nowacki, P. Borowicz, Electrochim. Acta (in press).

N

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CNNC

CN CN

CN

Scanning Electrochemical Microscope for the Analysis of Microbial Activity in Biofilm

Carolina Nunes-Kirchner, Chuan Zhao, Gunther Wittstock Carl von Ossietzky University of Oldenburg, Institute for Pure and Applied Chemistry and Institute for Chemistry and Biology of Marine Environment Scanning electrochemical microscope (SECM) was designed specially for examination of Biofilm. The piezo nano-translation stages with high resolution was placed above one inversed microscope in order to make movements in horizontal and vertical directions of one amperometric Ultra Microelectrode (UME) regarding the optical focus. Therefore it is possible to determine the position of the UME on the interest part of the biofilm, whose activity can be detected through localized measurement of redox active substrate or product. Feedback Mode or Generation/Collection Mode can be used to this application. The possibility of quantification of activity by comparison with simulation of reaction and transport process will be shown in the first measurement. Local chemical reactivity of polymers particles with modified surfaces (used as model of bacteria) can be investigated with GC-Mode. The activity of galactosidase will be measured. SECM images show the topography, electric conductivity, and local activity of the surface.

Electrochemical quartz crystal microbalance study of some protein adsorption

A. Kochman,a G. Farace,b P. Vadgama,b K. Haupt,c W. Kutner a

a Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

b Queen Mary University, Mile End Road, London E1 4NS, United Kingdom c Université de Technologie de Compiègne UMR CNRS 6022 BP. 20529 60205 Compiègne

cedex, France

In human plasma albumin is responsible, among other, for isolating and removing of foreign

intruding objects. Undesirably, albumin clings to implants as well resulting in their rejection

by virtue of the same mechanism. In our effort, we tried to find conditions, in vitro, under

which adsorption of albumin on a solid substrate surface is prevented. It is known that,

virtually, albumin does not interact with avidin. Therefore, an idea was explored to coat, first,

the studied solid surface with avidin in hope that albumin will not adsorb onto it afterwards.

For effective adsorption of avidin, we used an avidin-biotin immobilization procedure and

monitored this adsorption by using piezoelectric microgravimetry with an electrochemical

quartz crystal microbalance (EQCM) under batch conditions. We used a matrix of a

conducting polymer film for biotin immobilization. That is, the surface of a gold electrode of

a 5 MHz resonant frequency quartz crystal piezoelectric resonator was coated with a

poly(pyrrole) film doped by ion exchange with either potassium salt of d-biotin or sodium salt

of d-botin 4-aminobenzoic acid. The films were prepared by electropolymerization under

cyclic voltammetry (CV) conditions in aqueous solutions. That way anions of the biotin salts

served as counterions for charge compensation of electro-oxidized poly(pyrrole).

Electropolymerization was interrupted at the positive potential limit of a CV scan so, that

anions were retained in the polymer. The avidin and albumin adsorption was studied by

EQCM under flow injection analysis (FIA) conditions. First, consecutive injections of the

avidin solution samples resulted in the negative frequency steps indicating irreversible

interaction of avidin with the biotin sites of the poly(pyrrole) film. The height of these steps

decreased with the injection number as the biotin sites became gradually saturated. Then,

adsorption of albumin on the saturated with avidin surface of the polymer film was examined.

Results of the FIA experiments indicated that the avidin layer immobilized onto the

poly(pyrrole)-biotin film effectively repelled albumin. In another EQCM studies, thin films

of either electropolymerized polymer of C60, crosslinked with a Pd acetate trimer, or

molecularly imprinted polymer was investigasted for development of biomimetical sensors

for selective determination of chosen proteins.

Physicochemical identity and electrochemical reactivity of hybrid films of conducting polymer-linked polyoxometallate-stabilized platinum nanoparticles

Malgorzata Chojak, Katarzyna Karnicka, Krzysztof Miecznikowski, Pawel J. Kulesza

Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

There has been a tremendous interest in the fabrication of organized monomolecular (monolayer) and multilayered assemblies at solid surfaces that produce functionalized interfaces with well-defined composition, structure, reactivity and thickness. Most of research concerns alkanothiols and their derivatives that can be successfully employed to obtain monolayer coverages on gold. An interesting alternative originates from the possibility of self-assembling inorganic monolayers on electrode surfaces. Inorganic (e.g. polyoxometallate) templates as design elements in nanocomposites at electrode surfaces provide potentially better stability, and they undergo reversible stepwise multielectron transfer reactions of importance to such technologies as electrocatalysis, electrochromism, molecular electronics and sensing. Heteropolyacids of molybdenum and tungsten are particularly attractive because of their ability to adsorb irreversibly on carbon and metal surfaces and to form structured films. We pursue here the concept based on multiple formation of two-dimensional arrays and three-dimensional networks composed alternately of a conducting polymer, such as polyaniline or polypyrrole, and a polyoxometallate of molybdenum or tungsten.

Dense robust monolayers of alkanothiolates are capable of passivating gold nanoparticles and to produce alkanothiolate monolayer protected clusters or nanoparticles of gold. In the present work, we explore the ability of polyoxometallates to form self-assembled monolayers on metal nanoparticles and fabricate platinum (ca. 5-10 nm) nanoparticles (clusters) covered (protected) with polyoxometallate (phosphotungstate, phosphomolybdate) monolayers. Further, we can link them together by conducting polymer (polyaniline, polypyrrole) bridges to form network polymer films on glassy carbon, platinum and gold electrodes including gold-coated quartz crystals. The formation, morphology, structural transformations and electrochemical properties of the three-dimensional network films are examined using cyclic voltammetry, potential step techniques, microgravimmetry, FTIR spectroscopy, STM and AFM. In the case of nanoscopic measurements, the respective images, corresponding to the spontaneous deposition of polyxometallate-covered Pt nanoparticles on gold or glassy carbon, clearly show uniform and dense dispersion of nanostructured Pt when phosphomolybdate has been used to stabilize metal nanoparticles.

The presence of chemisorbed polyxometallate on platinum is evident from the ex-situ FTIR examination of the surface of gold-covered glass onto which the phosphomolybdate-stabilized Pt nanoparticles have been self-assembled. Some increase in the frequencies of oxygen-bridged Mo-O-Mo stretching modes may originate from “strengthening” of the polyanion structure and the related decrease of distance between the anions upon formation of a compact phosphomolybdate monolayer on Pt. The positive shift of external (terminal) Mo=O bond frequency is presumably due to interactions between the Pt substrate and the adsorbed polyoxometallate.

The films produce molecular systems capable of charge storage in bilayer type coatings as well as organized monolayer and multilayer assemblies with specific electrocatalytic properties.

Fabrication of nanoelectrode arrays using FIB milling and their characterisation by cyclic voltammetry.

Yvonne Lanyon, Yvonne Watson, Damien Arrigan, Gianluca DeMarzi, Aidan Quinn.

Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland. Abstract The fabrication of nanoelectrodes has gained increasing interest in recent years. One of the principle motives for the development of these nano-devices, is their application for single molecule detection such as DNA and other biological molecules. A number of advantages of such electrodes over conventionally sized macro-electrodes have been proposed, including increased mass transport rates and increased signal to noise ratios (related to the prevalence of radial diffusion at the sensor surface), as well as the diverse potential use of the large number of individual electrodes that can be incorporated into a single array layout. Nanoelectrode fabrication techniques have incorporated the sputtering or evaporation of metal films, or electrochemical etching of a thin wire followed by insulation of all but the very tip. Such methods have typically created single electrode devices. Nanoelectrode arrays or ensembles have also been created by deposition of metal into the pores of a nanoporous filtration membrane, however the close proximity of the pores resulted in non-steady state voltammetric responses. In this work, arrays of nanoelectrodes have been created by focused ion beam (FIB) milling through a passivation layer of silicon nitride deposited onto a layer of platinum. Several arrays have been designed and fabricated, varying in electrode number and dimension, and have been characterised by cyclic voltammetry using ferrocenecarboxylic acid. The results have shown steady-state voltammetric responses, indicating radial diffusion characteristics at the surface of each of the individual nanoelectrodes, and an enhanced sensor signal with increasing number of electrodes in the array. A correlation between the theoretical and experimental current obtained for ferrocenecarboxylic acid has allowed the determination of the dimensions of the various nanoelectrode pores. The FIB milling technique has provided a simple and rapid technique for the fabrication of nanoelectrode array prototypes, allowing their development and potential application as analytical sensing devices.

Influence of the crystallinity on the efficiency of ZnO/dye hybrid materials in photoelectrochemical solar cells

T. Loewenstein [a], K. Nonomura [a], T. Yoshida [b], D. Schlettwein [a] [a] Institut für Angewandte Physik, Justus-Liebig Universität Gießen, Heinrich Buff Ring 16, 35392 Gießen [b] Graduate School of Engineering, Gifu University, Yanagido 1-1, Gifu 501-1193, Japan The sensitization of wide-bandgap semiconductors is an attractive approach towards a photoelectrochemical photovoltaic cell. ZnO/dye hybrid materials follow this strategy and porous thin film electrodes can be deposited in electrochemical reactions. The structure and texture (porosity) of ZnO is highly relevant for the efficiency of the hybrid electrodes. Single crystalline substrates allow investigating the film structure in great detail. For ZnO, e.g., (0001) GaN offers the possibility of epitaxial growth [1]. In this study, ZnO/dye hybrid materials were deposited on (0001) GaN. The deposition was caused by a local pH-increase at the working electrode during the oxygen reduction. The structure of the films was analysed by X-ray diffraction, rocking curves allow discussing the quality of the in-plane orientation. The morphology was analysed by scanning electron microscopy. The influence on the additive molecule in the electrochemical deposition will be discussed. [1] Th. Pauporté, R. Cortès, M. Froment, B. Beaumont, D. Lincot, Chem. Mater., 14, 4702 (2002)

Modeling & Simulation with EChem++ - The Coupling of Ecco to an

Adaptive Multilevel Finite Element Algorithm

Kai Ludwig and Bernd Speiser

Universitat Tubingen, Institut fur Organische Chemie

Auf der Morgenstelle 18

D-72076 Tubingen, Germany

Recently, Ecco - A Compiler for (Electro-)Chemistry was published1,2. Ecco enables themodeling of electrochemical processes, in particular concerning the kinetics of homogeneouschemical reactions, surface reactions and adsorptions coupled to heterogeneous electron trans-fers.We demonstrate how the output of this compiler can be integrated into numerical simulationschemes, such as a solver for stiff ordinary differential equations and a more sophisticatedsolver for nonlinear parabolic PDE systems, based on an adaptive multilevel finite elementapproach. Some results of the simulation of cyclic voltammetry will be discussed.

1K. Ludwig and B. Speiser, J. Chem. Inf. Comput. Sci. 2004, 44, 2051 – 20602http://echempp.sourceforge.net

Formation and properties of donor-acceptor dyads of Zn porphyrins and amine adducts of C60 in the Langmuir and Langmuir-Blodgett Films

R. Marczak,a K. Noworyta,b R. Nowakowski,a S. Gadde,c M. Zandler,c Benard Desbat,d W. Kutner,a and F. D’Souza,c

a Institute of Physical of Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

b Department of Mineral, Analytical and Applied Chemistry, University of Geneva, quai Ernest-Ansermet 30, CH-1211 Genova, Switzerland

c Department of Chemistry, Wichita State University, Wichita Kansas, USA d Laboratoire de Physico-Chimie Moléculaire, University Bordeaux I, 351 cours de la

Liberation, F-33405 Talence Cedex, France

In search for donor-acceptor dyads capable of photoinduced charge separation, being thus

suitable for constructing organic photovoltaic elements, we examined self assembly of

hydrophobic polar aromatic amine adducts of C60 via complex formation with Zn porphyrins

in the Langmuir and Langmuir-Blodgett (LB) films. That is, Langmuir films of C60 adducts

of imidazole (C60im) and pyridine (C60py) were prepared at the interfaces of air and aqueous

subphase solutions of water-soluble porphyrins, viz., Zn tetrakis (N-methylpyridyl)porphyrin

cation, Zn(TMPyP), or Zn tetrakis (4-sulfonatophenyl)porphyrin anion, Zn(TPPS). In effect,

relatively stable donor-acceptor dyads of C60py-Zn(TMPyP) and C60py-Zn(TPPS) as well as

C60im-Zn(TMPyP) and C60im-Zn(TPPS) were formed in the interfacial films. Simultaneously

derived isotherms of surface pressure and surface potential vs. area per molecule as well as

the in situ BAM imaging revealed that all adducts were aggregated in the films. Therefore,

limiting area per molecule at the infinite adduct dilution in films was determined by

extrapolating the actual area per molecule to the zero adduct concentration in the film

enabling us to propose orientations of the adduct molecules. The resulting area per molecule

increased in the order: water < Zn(TPPS) < Zn(TPMyP) both for the C60im and C60py films.

Thickness of the films, determined by ellipsometry, was close to that predicted by molecular

modeling for vertically oriented dyad molecules and equal to ca. 1.4 nm. The Langmuir films

were LB transferred onto quartz slides, Au plates, HOPG specimens, and quartz resonators for

characterization by UV-vis spectroscopy, STM, PM-IRRAS as well as simultaneous cyclic

voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz

crystal microbalance, respectively. It appeared that Zn porphyrins were transferred together

with the aducts onto solid substrates. Orientation of the C60im-Zn(TMPyP) dyad molecules in

the LB film was determined by PM-IRRAS. The determined by STM distance between C60

moieties in the LB film was comparable to that estimated theoretically and close to 0.9 nm.

The dyads in the LB films were both electroreductively and electro-oxidatively active.

Dimerization of Electrochemically Generated Anion Radicals under High Pressure

UV. MazineU,

Chemistry Department, Moscow State University, Russia

J.Heinze

Institute for Physical Chemistry, University of Freiburg, Germany

Anion-radicals of conjugated organic systems activated by electron-withdrawing

substituents can be generated electrochemically. In spite of the electrostatic

repulsion between equally charged particles they often demonstrate strong tendency

to form dimeric species:

−−

−+

⎯→←

⎯→←2

2 ][2 AAAA e

In aprotic media this dimerization process can be reversible in the sense that the

reoxidation of the so formed dimer leads to the initial monomer. The kinetic

parameters of the overall process are strongly dependent upon the distribution of

charge and spin density in the anion-radicals as well as upon the properties of the

reaction medium and vary in the range of many orders of magnitude. This, in many

cases, hampers correct interpretation of the experimental data and determination of

the real mechanism of the process. Performing the electrochemical experiment under

high pressure in the kilo-bar range permits to affect the equilibrium of the dimerization

reaction and, thus, gives direct insight into the mechanism of electrodimerization and

related processes.

For the first time a special experimental setup was built for the electrochemical

measurements in aprotic media under high pressure. We report here the first

example of reductive electrodimerization performed under a pressure of up to 4 kBar.

The formation of dimers is shown for a set of model compounds such as 9-

cyanoanthracene, trinitrotoluene, 2,3-naphtalenedicarbonitrile, trans-ß-nitrostyrene

and others. The activation volumes and the reaction volumes of the dimerization

reaction are determined. We discuss the important consequences of these results for

the understanding of other processes involving anion-radicals.

ERMIS8 0405 michman

Considering Homogeneous Catalysis through Electrochemistry .

Michael Michman

The Institute of Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem Israel

michman@cc.huji.ac.il

Back in the mid 1980’ies, work on several problems on electro-synthesis prompted

me to consider several routes of studying homogeneous electro-catalysis of some

electro-oxidations. The main objective has been the improvement of preparative

technology. A long research adventure starting with the apparently simple

RuCl3.3H2O through several other derivatives and ending up with RuCl3(CH3CN)3

has revealed several aspects of this field of homogeneous electro-catalysis1.

The exploration of the nature of the catalytic activity deals with the change and

lifetime of oxidation states Ru II, RuIII and RuIV as followed by voltammetry, by

EC-ESMS technique and by chemical modifications of the ruthenium compounds.

The homogeneous electro-catalytic activity is constrained within narrow potential

ranges, depends on lifetimes of intermediates and the regulation of the double

layer at the electrodes. The study of such limitations can shed light on principles of

homogeneous catalysis at large2.

The use of electrochemical analysis as a tool for catalytic studies, rare at that time,

has by now gained considerable significance thanks to the efforts of several

research groups. Still, much mystery remains to be solved.

1. L. Appelbaum, C. Heinrichs, J. Dehmtschuk, M. Michman, M. Oron, H.J. Schäfer and H. Schumann, J. Organomet. Chem. 592/2 240-250 1999 2. M. Michman, J. Mol. Cat. 107 393-398 1996.

-

Electrochemical Finishing – the Key to Develop Smart Textiles and

New Kinds of Technical Textiles?

Andreas Neudeck Textilforschungsinstitut Thüringen-Vogtland e.V. (TITV), Zeulenrodaer Str. 42, D-07973 Greiz Tel.: ++49 (0) 3661 / 611-204, Fax: ++49 (0) 3661 / 611-222, Email: a.neudeck@titv-greiz.de, Web: http://www.titv-greiz.de/

Since the seventies silver coated polyamide threads and fabrics are on the market /1/. Till now most of the applications are limited on the use of the electrostatic and antimicrobiel properties of the material. The silver coated polyamide (Ag-PA) threads and fabrics are much more promising composite materials than to be used only for such simple applications.

A simple REM image of the cross section of a single filament of a Ag-PA thread shows that the silver layer is not only a simple metal layer on the surface /1/. The silver coating is a nano struc-ture. The top metal layer of about 100 nm – 300 nm is connected with a system of very thin metal roots with the nano porous surface of the polyamide filaments. This nano structure causes an extremely strong tie together of two total different materials and results in a composite combining the textile properties of the polyamide with a metallic conductivity. The Ag-PA threads can be stretched up to 5 % - 7 % without damage of the metal coating. Such metallized threads are an interesting alternative to metal wires use in novel textile applications /2/ and can be woven, knitted much easier. Unfortunately the conductivity of the material is only in the range of 102 Scm-1 not sufficient for some applications in our focus.

However, the Ag-PA threads can be used to prepare textile pre-cursor structures. The precursor structure can be electrochemically modified by metals and even noble metals /3/, as well as by electropolymerisation /4/ and electrodeposition of paint (cf. Fig. 1). The metals can be electro-chemically oxidized to form oxide structures with semiconducting properties. The textile precur-sor structure permits to coat various zones by various metals, metal oxides and even new mate-rial as for example intrinsic conducting polymers. First applications of textile substrates struc-tured in this way will be presented (cf. Fig. 2). This treatments can be understood as an new kind of finishing of textiles.

The integration of microelectronic devices in textiles /5/ can be very useful for communication and controlling aims, especially for occupational clothes and medical applications. Till now the microelectronic devices are not really integrated into textile structures: in most cases, they are “stitched” on the fabric or hidden in the textile structure /6/. Together with the new electrochemi-cal finishing textiles become micro structures with fantastic new properties insulated metallic and semiconducting, non-rigid, flexible materials much more mechanically stable than foils.

REFERENCES : /1/ www.statex.de

/2/ H. Hieber, W. Scheibner, J. Schüler, “Textiler verdratungsträger für elektronische Baugruppen”, GMM Fachbericht 37: Elektroni-sche Baugruppen – Aufbau- und Verbindungstechnik DVS/GMM-Fachtagung 6.-7.2.2002, Fellbach.

/3/ S. Gimpel, U. Möhring, H. Müller, A. Neudeck, and W. Scheibner, “Textile Based Electronic Substrate Technology“, Journal of Industrial Textiles, 33/3 (2004) 179-189. S. Gimpel, U. Möhring, H. Müller, A. Neudeck und W. Scheibner, „Galvanische und e-lektrochemische Modifizierung von Textilien zur Integration von Mikrosystemtechnik, Sensorfunktionen und Elektrolumines-zenz“, Melliand – Band- und Flechtindustrie, 40/4 (2003) 115.

/4/ See for example: M. Maumy, P. Capdevielle, P.H. Aubert, M. Roche, P. Audebert, A. Neudeck and L. Dunsch, J. Electroanal. Chem. 470, (1999) 77 ; A. Neudeck, L. Guyard, P. Audebert, L. Dunsch, P. Guiriec and P. Hapiot, Acta Chem. Scand., 53 (1999) 867.

/5/ See for example: W.D. Hartmann, K. Steilmann, A. Ullsperger, high-tech-fashion, Heimdall Verlag, Witten, 2000 ; B. Lancaze, Funktionelle Textilien, mitttex, 1 (2000) 14 ; Rainer Klose, Denkende Kleider - automatisch wärmen oder kühlen: Ein neues Ma-terial revolutioniert die Kleiderwelt, Facts Interactiv. ; B. Müller, “Kraft aus Kunststoff”, Bild der Wissenschaft, 10 (2000) ; G. Wal-lace, “Smart bra heralds age of intelligent fabrics”, Technical Textiles International, 07/08 (2000) 32.

/6/ See for example: Klaus Rönnebeck, Patent, Notrufsystem in Kinder- und Jugendbekleidung, DP 198 43 237 2 ; Symposium of Wearable Computer (1. Meeting 1997 by Georia Tech and IEEE; 2. Meeting 1998 Pittsburg, 3. Meeting 1999 San Francisco, 4. Meeting 2000 Atlanta) ; International Meeting of Wearable Computing 2000 Washington sponsored by Xypernaut (McLean).P. Lukowitz, G. Tröster, “Wearable Computing”, Bulletin ASE/VSE, 9 (2000) 15 ; Electro Textiles Company Ltd., www.electrotextiles.co, Peratech, www.peratech.co.uk/profile/

Fig. 2

Electroluminescenting fabric with the motive of the railway bridge Göltzschtalbrücke based on an electrochemical finished fabric

Fig. 1

Photograph of the equipment used for the electrochemical finishing

ELECTROCHEMICAL BEHAVIOUR OF REDOX LIQUID MICRODROPLETS DEPOSITED ON SILICATE FILM BASED

ELECTRODE

UJ. Niedziolka UPU

a*UP, E. RoznieckaP

aP, B. Palys P

bP, R. Nowakowski P

aP, K. J. McKenzie P

cP, F. Marken P

dP and

M. OpalloP

a

P

a PInstitute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland

P

bP Department of Chemistry, University of Warsaw, Warsaw, Poland

P

cP Department of Chemistry, Loughborough University, Loughborough, United Kingdom

P

dP Department of Chemistry, University of Bath, Bath, United Kingdom

Biphasic electrodes recently emerged as a new and versatile class of modified

electrodes [1]. They are based on droplets, microdroplet arrays, or thin films of diluted or

undiluted redox liquids (neat redox active organic liquids or a redox active probe solution in

hydrophobic solvents) deposited onto a suitable electrode surface. Recently our groups

explored the possibility of an immobilisation of redox liquids within porous films as a

component of an electrode system [2-5].

Sol-gel films obtained from methyltrimethoxysilane (MTMOS) and/or 3-

mercaptopropyltrimethoxysilene (MPS) precursors were deposited on gold electrodes. The

silicate formation was confirmed by FTIRRA spectroscopy. AFM and SEM images reveals

large number of protrusions in the presence of MPS precursor. Access to the electrode surface

by various redox probes from aqueous solution is prevented by these films.

After redox liquid (t-butylferrocene) modification, the electrochemical behaviour of

these electrodes was also examined. The presence of thiol groups in the film stabilizes the

electrochemical response connected with redox reaction of t-butylferrocene. Namely, it

prevents expulsion of electrogenerated cation into aqueous solution [5]. The conversion of

redox liquid during electrochemical reaction is much below 1%. It is increased by almost two

orders of magnitude for electrodes made of MTMOS based film deposited on glass and

covered with sputtered gold.

[1] C.E. Banks, T.J. Davies, R.G. Evans, G. Hignett, A.J. Wain, N.S. Lawrence, J.D.

Wadhavan, F. Marken, R.G. Compton, Phys. Chem. Chem. Phys. 5 (2003) 4053. [2] J. Niedziolka, M. Opallo, Electrochem. Commun. 6 (2004) 475. [3] S.J. Stott, K. McKenzie, R.J. Mortimer, C.M. Hayman, B.J. Buckley, P.C. Bulman Page, F.

Marken, G. Shul, M. Opałło, Anal. Chem. 76 (2004) 5364. [4] K.J. McKenzie, J. Niedziolka, C.A. Paddon, F. Marken, E. Rozniecka, M. Opallo, Analyst

129 (2004) 1181. [5] F. Marken, K.J. McKenzie, G. Shul, M. Opałło, Farad. Discuss. in press. [6] J.D. Wadhawan, R.G. Evans, R.G. Compton, J. Electroanal. Chem. 533 (2002) 71.

REDOX AND ADSORPTION CHARACTERISTICS OF FERROCENE- AND RUTHENIUM-MODIFIED STÖBER NANOPARTICLES

F. NovakP

*P, B. Schetter, D. Straub, UB. SpeiserU

P

1PInstitut für Organische Chemie, Universität Tübingen

Auf der Morgenstelle 18, 72076 Tübingen, Germany * presenting author: filip.novak@uni-tuebingen.de

Ucorresponding author:U bernd.speiser@uni-tuebingen.de Non-porous spherical silica nanoparticles (Stöber nanoparticles)P

1P were modified with redox

active Fc- and Ru- species in order to obtain a catalytic system in interphases. Both species were characterized by means of cyclic voltammetry, EQCN and spectroscopic methods (UV-VIS, AAS, ICP-MS). A voltammetric investigation revealed a one-electron oxidation process for both systems occurring only after adsorption on an electrode surface (Pt). The values of EP

oP

evaluated for these electron transfers are very close to the values gained for Fc and Ru(II) complex in a solution. However, an analysis of peak current characteristics (iBp B/ v) suggested some kinetics limitations in the electron transfer process of the adsorbed nanoparticles ascribed to the redox communication occurring within the redox active shell (hopping process). Hence, diffusion properties of a hopping-process must be considered by voltammetric experiments of the adsorbed nanostructure performed at higher scan rates P

2P.

In addition to voltammetric characterization, the kinetics of the adsorption process was investigated by means of EQCN and SEM. A growth of the nanoparticle layer was detected in terms of mass (m) and charge density (σ) changes at a quartz crystal. Since σ reaches a plateau, the obtained curves indicate a spatially restricted electron transfer between the electrode and the nanoparticles layer. The redox communication does not exceed the monolayer of the adsorbed nanoparticles as shown by SEM images. Such results seem to be consistent with our voltammetric investigation as well as other previous worksP

2P.

1. TC. Payne, The Colloid Chemistry of Silica, American Chemical Society, 1994 2. C. Amatore, Y. Bouret, E. Maisonhaute, J. I. Goldsmith, H. D. Abruna,

ChemPhysChem, 2001, 2, 130-134

Ion Transfer Across Liquid - Liquid Interface Coupled to Electrochemical

Redox Reaction at Carbon Paste Electrode

Galyna Shul and Marcin Opallo

Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224

Warszawa, Poland

Ion transfer processes across liquid | liquid phase boundary formed at electroactive

carbon paste electrode immersed into an aqueous solution were studied by cyclic voltammetry

and differential pulse voltammetry. The electrode material consists of graphite particles and

redox probe (ferrocene, t-butylferrocene, or decamethylferrocene) solution in polar organic

hydrophobic solvent o-nitrophenyloctylether as a binder. The anion transfer from the aqueous

solution following electrooxidation of the redox probe or ejection of electrogenerated cation

from the organic phase was detected by anion dependence of the redox potential of the redox

probe dissolved in an organic phase. The contribution of both processes depends on the

hydrophobicity of the redox probe and anion present in the aqueous phase.

droplet modified electrode carbon paste electrode

These results will be compared with those obtained with droplet modified electrodes

[3] and carbon ceramic electrodes modified with hydrophobic polar solvent [4].

[1] C.E. Banks, T.J. Davies, R.G. Evans, G. Hignett, A.J. Wain, N.S. Lawrence, J.D. Wadhavan, F. Marken, R.G. Compton, Phys. Chem. Chem. Phys. 5 (2003) 4053.

[2] F. Scholz, S. Komorsky-Lovric, M. Lovric, Electrochem. Commun. 3 (2001) 112. [3] R. Gulaboski, A. Galland, G. Bouchard, K. Caban, A. Kretschmer, P.A. Carrupt, Z.

Stojek, H.H. Girault, F. Scholz, J. Phys. Chem. B 108 (2004) 4565. [4] G. Shul, M. Opallo, F. Marken, Electrochim. Acta in press

Preparation and selected properties of electrophoretic [C60]fullerene films

Amy Lea Schumacher,a Piotr Pięta,b Włodzimierz Kutner,b Francis D’Souzaa

aDepartment of Chemistry, Wichita State University, 1845 Fairmount, Wichita,

KS 67260-0051, USA bInstitute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka,

01-224 Warsaw, Poland Different conditions of solution composition and constant electric field were tested for bulk

electrophoretic preparation of C60 films from C60 suspensions. The deposition was monitored

by piezoelectric microgravimetry (PM) with the use of an electrochemical quartz crystal

microbalance, EQCM. For the deposition, a two-electrode system was used, which was

composed of a 1×1 cm Pt tab (negative) and 5-mm diameter Pt film (positive) electrode. This

Pt film was prepared by cathodic sputtering of Pt onto a 14-mm diameter, 5- or 10-MHz

quartz resonator for EQCM. Optimum solution composition was found for a mixture of the

deaerated C60 toluene solution and line ethanol at the toluene-to-EtOH ratio of 1 : 10 (v : v)

while optimum electrophoretic conditions involved 50 V dc applied to the Pt electrodes,

placed parallel 40 mm apart. The total mass of the C60 film deposited within 12 min was

1.7 µg indicating that mean electrode coverage by C60 was, Γ = 1.2×10-8 mol cm-2, and that

the film was composed of ca. 72 equivalent monolayers. The initial deposition rate was 6.9

ng s-1 being maintained for ca. 4 min. Then, the rate decreased nearly exponentially by one

order of magnitude and, finally, it was equal to 0.68 ng s-1. Presumably, this rate decrease

was caused by the growth of the C60 aggregates in solution with time resulting in the decrease

of their mobility and, hence, their ability to deposit onto the electrode surface. Consequently,

small and large aggregates were initially and finally deposited, respectively. That way, the

size of the C60 micrograins can be readily controlled by controlling the time of the deposition.

Cyclic voltammetry (CV) curves for the C60 films featured four main cathodic peaks formed

during the negative potential excursion in the accessible potential range corresponding to for

one-electron reductions. The PM curve, recorded simultaneously with the CV curve, showed

an overall decrease of the electrode mass accompanying electroreduction of the film. This

decrease was due to dissolution of the electroreduced C60 film. In the positive CV half cycle,

the anodic peaks were hardly seen as the dissolved fullerene anions diffused away from the

electrode surface. Evolution of simultaneously recorded multi scan CV and PM curves for a

narrower potential range, i.e., that for which the film was stable with respect to dissolution,

indicated some phase transition in the film.

Impedance Spectroscopy with OLEDs

Joerg Posdorfer Ormecon GmbH, Ferdinand-Harten-Str. 7, D - 22949 Ammersbek, Germany

Polyaniline was used as hole injection material (HIL) for organic light emitting devices (OLED). The devices were prepared by spin coating and curing a 80 nm layer of water based polyaniline/poly-styrenesulfonate (Pani/PSS) dispersion onto ITO patterned glass substrates followed by spin coating of a 80 nm light-emitting polymer layer. As cathode material Ba was used. Data presented here were based on blue light-emitting polymers (LEP). Depending on the applied bias voltages the devices were studied by electrical impedance spectroscopy (EIS) in a wide frequency range. Experimental data could only be fitted by applying an equivalent circuit consisting of three RC elements in series. By separating the frequency dependent bulk and interface contributions, resistance and capacitance for bulk and junctions were determined at various current densities. Variation in high interfacial capacitance was observed in the devices before and after stressing the OLEDs with a constant current of 10 mA/cmP

2P for 100 hours.

By fitting the impedance data the resistance and the capacitance of the bulk material RBb B and CBb B and the interfacial resistance and capacitance RB1 B, RB2 B, CB1 B and CB2 B were obtained. The contact resistance RBcB was independent of applied bias voltage and approximately the same for all devices. The capacities of the interfacial regions were significantly higher than the capacitance in the bulk. The sum of the resistance values RBcB, RBb B, RB1 B and RB2 B agreed very well with the numerical derivatives of the corresponding current-voltage curves. CB2 B can be related to the intermediate layer at the PAni/LEP interface. This was proven by variation of hole injection layer thickness. For a given device the values for CB2 B changed proportional to layer thickness. When the cathode consisted of LiF/Al instead of Ba only changes in CB1 B were obvious. The geometrical capacitance CBgeo PB

-1P=CBb PB

-1P+CB1 PB

-1P+CB2 PB

-1P was voltage-independent and the relative

dielectric constant was calculated. From the individual capacitances the thickness of bulk, depletion and intermediate layer were obtained depending on bias voltage. From the dielectric relaxation times τ Bi B = RBi BCBi B and the thickness of bulk, depletion and intermediate layer the charge concentrations were calculated as a function of bias voltage. Different behaviour was observed in the bias voltage dependence of charge concentrations for the stressed and unstressed state. The highly capacitive junction provides interfacial electron-hole recombination, which can lower life-time and efficiency of the displays. It is important that the charge mobility is balanced in the devices in order to maximize power conversion efficiency and minimize degradation of the material by oxidation. This may be an explanation for the unstable electroluminescence of the blue light-emitting material.

Automated electrochemical detection of transmitter release in vitro

– a plate-based assay opens novel perspectives for functional screening of cells

Sabine Reiter1, Ina Radtke2, Thomas Erichsen1, Andrea Blöchl2, Rolf Heumann2, Wolfgang Schuhmann1

1Anal. Chem. – Elektroanalytik & Sensorik; 2Mol. Neurobiochemie Ruhr-Universität Bochum; Universitätsstr. 150, D-44780 Bochum; Germany

A reproducible monitoring of in vitro changes of transmitter concentrations in the vincinity of cells upon stimulation within a reasonable period of time is a great challenge. Among different methods electrochemical quantification of transmitters at (modified) electrodes was demonstrated to be very sensitive and fast. Due to its importance as chemical mediator of neuroendocrine function and behaviour, the gaseous molecule nitric oxide (NO) [1] was chosen as analyte in this study. An electrochemical robotic system [2] was developed as a technical platform for monitoring cellular activity in-vitro aiming on applications in cell-based high-throughput screening. By means of a precise micro-positioning devices, the microtiter plate in which the cells were grown was moved in x- and y-direction. Endothelial and glioma cells were used adherently growing at the bottom of the wells of a 96-well microtiter plate. NO-selective modified electrodes were placed in close proximity to the cell layer within the individual wells using SECM approach curves[3]. The software allows the use of all electrochemical techniques and the automated supply of reagents via a pump. An automated assay sequence allows to detect the release of NO from well to well and is illustrated in scheme 1.

Scheme 1:

Assay sequence for automated detection of NO release from cells: 1. positioning of the electrodes, 2. stimulation of the cells, 3. electrochemical detection of released NO, 4. movement to the next well

The NO sensors were automatically evaluated. The cells were tested concerning their viability under assay con-ditions in the robotic system.

The resulting current signals upon stimulation are highly dependent on the number of cells and the distance between the cells and the sensor tip [4]. A distance control was integrated into the set-up. The kinetics of NO release by endothelial and glioma cells after stimulation with vascular endothelial growth factors and bradykinin, and the influences of selected inhibitors and pharma-ceuticals were investigated. In addition, other sensors e.g. for glutamate were already implemented in the robotic system. An automated electrochemical assay for the detection of released transmitters opens novel perspectives for functional in vitro screening of cells.

[1] R. J. Nelson, L. J. Kriegsfeld, V. L. Dawson, T. M. Dawson, Front. Neuroendocrin. 18: 463-491 (1997) [2] T. Erichsen, S. Reiter, W. Märkle, C. Tittel, V. Ryabova, E. M. Bonsen, G. Jung, B. Speiser, W. Schuhmann, Rev. Sci. Instr.

submitted. [3] S. Reiter, K. Eckhard, A. Blöchl, W. Schuhmann, Analyst 126: 1912-1918 (2001) [4] S. Isik, M. Etienne, J. Oni, A. Blöchl, S. Reiter, W. Schuhmann, Anal. Chem. 76: 6389-6394 (2004)

buffersolution

reference electrode

OO

NO sensor

application tube

cells 1.positioning of sensor 2.stimulation 3.detection 4.movement tonext well

+

Electroactive ceramic carbon electrode modified with ionic liquid

Ewa Roznieckaa, Galyna Shula, Juliette Sirieix-Plenetb, Laurent Gaillonb

and Marcin Opalloa

aInstitute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224

Warsaw, Poland bLaboratoire d’Electrochimie et Chimie Analytique, UMR 7575, Universite Pierre et Marie

Curie, 4, Place Jussieu, Bat F Boite 39, 75252 Paris Cedex 05, France

Ionic liquids (ILs) are media resulting from the combination of organic cations and

various anions. They have several unique properties: negligible vapour pressure, low toxicity, high chemical and thermal stability, and the ability to dissolve a wide range of organic and inorganic compounds. ILs exhibit a large potential window and high conductivities, allowing for studies without supporting electrolyte [1]. As it was recently shown, redox probe solution in IL can be used for electrode modification [2] in a similar way as a redox liquid or a solution of redox probe in polar solvent [3].

We have attempted to immobilize redox probe solution in the ionic liquid material on sol-gel carbon ceramic electrode (CCE) [4]. CCE consists of graphite powder homogeneously dispersed in a hydrophobic-hydrophilic silicate matrix. This electrode was modified with redox probe (t-butylferrocene) solution in ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate or 1-decyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide) by impregnation [5]. For comparison Au electrode was also modified with droplets of the same IL based redox solution. After immersion into an aqueous solution the electrochemical properties of these electrodes were investigated using cyclic voltammetry. They exhibits electrochemical signal connected with electrode reaction of the redox probe dissolved in ionic liquid. The heterogeneous structure of electrode material enhances substantially efficiency of the electrode process in comparison to the flat electrode surface. The midpeak potential depends on the hydrophobicity of the anion present in the aqueous solution indicating significant contribution of anion injection into the ionic liquid following electron transfer. The efficiency of electrode process is much larger than that of CCE modified with the redox probe solution in less viscous organic polar solvent. Key words: ionic liquid, carbon ceramic electrode, Au electrode, cyclic voltammetry, sol-el,

redox probe References:

1. M.C. Buzzeo, R.G. Evans, R.G. Compton, Chem. Phys. Chem., 2004, 5, 1106. 2. J.D Wadhawan, U. Schroder, A. Neudeck, S.J. Wilkins, R.G. Compton, F. Marken,

C.S. Consorti, R.F. de Souza, J. Dupont, J. Electroanal. Chem., 2000, 493, 75. 3. C.E. Banks, T.J. Davies, R.G. Evans, G. Hignett, A.J. Wain, N.S. Lawrence, J.D.

Wadhawan, F. Marken, R.G. Compton, Phys. Chem. Chem. Phys., 2003, 5, 4053. 4. M. Tsionsky, G. Gun, V. Glezer, O. Lev, Anal. Chem. 1994, 66, 1747. 5. M. Opallo, M. Saczek-Maj, Chem. Commun., 2002, 448.

Direct electrochemistry of Desulfovibrio Gigas [NiFe]-Hydrogenase covalently bound and oriented on a gold electrode. In order to study the mechanism of catalytic hydrogen evolution or consumption by Desulfovibrio Gigas [NiFe]-Hydrogenase, through direct electrochemistry, several methods of covalent oriented immobilization were studied. The distal 4Fe4S cluster, used by the protein to exchange electrons with his redox partner, was tried to face the electrode with the aim of having direct electrochemistry by the use of diverse self assembled monolayers. Near the distal cluster, the [NiFe]-Hydrogenase has a glutamate environment which creates a negative potential at basic pH, compared to the other face of the protein. This phenomenon was studied by modifying the pH of incubation and the thiol employed on the SAM.

The orientation of the protein was elucidated comparing the catalytic current obtained by direct electron transfer with the electrode and the current obtained using methyl viologen as redox mediator.

Detection of Ni2+-ions released from corroding Nickel-Titanium shape-memory alloys using an electrochemical robotic system

Dirk Ruhlig, Albert Schulte, Wolfgang Schuhmann

Analytische Chemie – Elektroanalytik & Sensorik, Ruhr-Universität Bochum, D-44780 Bochum, Germany

Due to the unique properties of nickel-titanium alloys such as e.g. superelasticity, shape

memory effect, and good resistance to fatigue and corrosion, these alloys have become very

common materials in bioengineering. However, Ni2+-ions are known to be hypo-allergenic or

potentially cancerogenic. Owing to these characteristics, the Ni2+-ion release caused by

corrosion of NiTi-alloys has to be determined in order to evaluate their biocompatibility.

A well known method for Ni2+-ion determination in trace amounts is adsorptive stripping

voltammetry (AdSV). Due to the fact that Ni2+-ions do not form an alloy with Hg cathodic

AdSV of Ni2+-complexes is generally applied. Recently, bismuth-plated electrodes have been

introduced, ensuring a high sensitivity and in contrast to mercury they are non-poisonous and

independent from dissolved oxygen. Until now, only manual analytical procedures in standard

electrochemical cells were used. However, due to the very low corrosion rate of NiTi shape-

memory alloys caused by surface passivation and the availability of a large number of

different alloys and surface treatment procedures, a reliable determination of Ni2+-ion release

was not possible.

To overcome this limitation, a previously developed electrochemical robotic system [1] was

adapted for sequential and automized determination of Ni2+-ions by means of cathodic AdSV

using the wells of a microtiter plate as electrochemical cells. Besides differential pulse

voltammetry or square-wave voltammetry for cathodic AdSV and the control of the position

of the microtiter plate, the system allows for formation of the Bi-plated working electrode,

addition of necessary reagents by means of a step-motor controlled syringe pump, standard

addition techniques, automatic sampling etc. Thus, biologically and chemically induced

corrosion of nickel-containing alloys could be successfully monitored using the electro-

chemical robotic system with significantly increased a sample throughput and improved

repeatability.

[1] T. Erichsen, S. Reiter, W. Märkle, C. Tittel, V. Ryabova, E. M. Bonsen, G. Jung, B. Speiser, W.

Schuhmann, Rev. Sci. Instr. Combinatorial microelectrochemistry - Development and evaluation of an electrochemical robotic system.

Temperature-Controlled Scanning Electrochemical Microscopy: Instrumentation and Selected Applications

Dominik Schäfer, Albert Schulte, Florin Turcu, Thomas Erichsen, Wolfgang Schuhmann

Anal. Chem. - Elektroanalytik & Sensorik, Ruhr-Universität Bochum, D-44780 Bochum, Germany

Based on basic thermodynamical considerations it is obvious that chemical and biochemical

processes show usually a strong temperature dependence. Although an ideal tool for the

(electrochemical) examination of surface properties and reactions at surfaces, scanning electro-

chemical microscopy (SECM) so far has not been used to systematically study temperature

dependences of interfacial processes.

To overcome this limitation, a SECM set-up has been developed which allows for an accurate

control of the temperature of the examined sample specimen. This is achieved by means of a

Peltier element, which is located underneath the electrochemical cell. Using a specifically

developed software module in combination with a sophisticated control unit for the Peltier

element enables the set-up to approach and maintain a desired temperature set-point with high-

precision and high speed. As a matter of fact, heating or cooling the substrate results in a

temperature dependent displacement of the sample with respect to the positioned SECM tip

which is severely changing the tip-to-sample distance even leading to tip crash or the loss of the

feedback interaction. In principal, two possibilities are straightforward to compensate for the

relative displacement between SECM tip and sample surface. On the one hand, the previously

developed optical or non-optical shearforce-dependent constant-distance mode of SECM can be

used for forcing the tip to follow the movement of the sample surface. On the other hand, z-

approach curves can be performed after each temperature change to re-position the SECM tip

within the desired working distance. The latter approach was carefully evaluated especially

concerning the variations in the SECM approach characteristics for positive as well as negative

feedback in dependence from the temperature. Due to the high dependence of the diffusion

coefficient from the electrolyte viscosity, one could expect that the feedback characteristics are

highly temperature dependent. The knowledge of the z-approach characteristics enabled to

develop a temperature compensation thus allowing to re-position the SECM tip at the same tip-

to-sample distance irrespective of the temperature. Using this system the temperature dependence

of enzymatic feedback amplification was investigated.

The design of the instrument will be shown and selected applications presented, which

demonstrate the performance of temperature-controlled SECM with respect to the above

mentioned interfacial phenomena.

"Studying the Interactions of Silver ions with Dithiol Self-Assembled Monolayers by the Scanning

Electrochemical Microscope (SECM)"

J.K.Sinha P

aP, G.WittstockP

aP*; D.MandlerP

bP∗

P

aP Carl-von-Ossietzky University of Oldenburg, FB 5 - Chemie & Iinstitute of Chemistry and

Biology of the Marine Environment, D-26111 Oldenburg, Germany P

b Department of Inorganic and Analytical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

Scanning electrochemical microscopy (SECM) has been used as a means of generating a flux of metal ions near to a gold surface modified with self assembled monolayer of dithiols by double potential step chronoamperometry (DPSC). Preliminary DPSC experiments were performed with an Ag microelectrode (25µm diameter) held at different distances (of the order of a few micrometers) above the surface. The Ag microelectrode was precisely positioned near to a glass surface using the steady state current of oxygen reduction. The flux of Ag+ ions was generated close to the inert glass surface in the 1st step of the DPSC. The ions were re-reduced at the microelectrode in the 2nd step of the DPSC. There was a considerable decrease in the collection current in comparison to generating current, due to the hindered diffusion of the ion species,which caused the depletion of the silver ions from the gap between the microelectrode and the glass surface. Comparing these chronoamperometric curves to similar experiments carried out over dithiol self assembled monolayers, the extent of metal ions binding to the thiol functions of the monolayers could be evaluated. The cyclic voltammetry of silver deposition on dithiol monolayers on Au shows a distinct additional peak, which is absent on either bare gold or gold covered with an alkanethiolate monolayer.

Boundary Element Simulation for Transient Measurements Markus Träuble, Gunther Wittstock Carl von Ossietzky University Oldenburg, School of Mathematics and Natural Sciences, D-26111 Oldenburg, Germany Numeric simulation using the boundary element method (BEM) has developed to a useful tool in the quantitative analysis of problems related to scanning electrochemical microscopy (SECM). The advantages are restriction of space discretisation to the object surface , the treatment of almost arbitrary geometry and the improvement of the simulations by the possibility of exterior Laplace formulation. The discretisation of object surfaces only allows easy repositioning of probe and sample without reconstruction and optimising a volume mesh. The formalism to shift the computations of the concentrations in the volume to the boundary is at present developed only for the mathematically homogeneous, time-independent diffusion equation. Problems including homogeneous chemical reaction, time dependent SECM response or convection lead to mathematically inhomogeneous systems. In order to solve them, one reverts so far to FDM- or FEM simulation. Also the combination of BEM for the spatial and FDM/FEM for the temporal development was suggested. All these methods have the disadvantage to lose the mentioned advantages of the volume independence of the BEM description. Here several approaches offer the possibility of taking up both reaction within the volume and transient terms to the BEM simulation. The bottleneck with the transfer of the volume problem to the boundary is to express the volume integral within the describing integral equation by boundary integrals. Therefore one can transfer the volume part of the Green function with an iterative method to the boundary. One can describe also the inhomogeneous part as a linear combination of radial basis functions (RBF) with time-dependent factors. Since the RBF have Laplace shape, the BEM can be applied to transform them (dual reciprocity BEM). A further numeric problem now arises, since the very large sets of equations change with each time step. Numeric procedures were tested in order to solve the systems effectively. In the literature there are reports about the successful implementation of the DRBEM for 2D-problems with simple geometry. In this contribution the conversion and testing on 3D-objekts is developed and tested for electrochemical problems.

Modified carbon black electrodes as the basis for the third generation biosensors Julija Razumienė, Remigijus Šimkus, Aistė Vilkanauskytė, Valdas Laurinavičius

Institute of Biochemistry, Mokslininkų 12, LT-08662 Vilnius, Lithuania

E-mail: Julija.R@bchi.lt

Direct electron transfer between redox enzymes and electrode surface is the basis for the third

generation biosensors. For the first time the direct electron transfer between pyrroloquinoline

quinone (PQQ) dependent glucose dehydrogenases (PQQ-GDH) and especially modified carbon

paste electrodes (CB) was observed. Aiming to create an optimal transducing material for

biosensors a set of different CB batches was synthesized using the matrix of Plackett-Burman

experimental design. Reagentless enzyme biosensors suitable for the determination of glucose were

developed using screen-printed carbon paste electrodes. Depending on the obtained surface

functional groups as well as the nano-scale carbon structures in CBs batches the kinetic parameters

of the biosensors were found to be different.

The plate gap model of porous enzyme-carbon electrode has been proposed and analyzed. It was

suggested that diffusion conditions of reaction in pores of bulk electrode resemble particular conditions in a

thin gap between parallel conducting plates. The model is based on the diffusion equations containing a

nonlinear term related to Michaelis - Menten kinetics of the enzymatic reaction inside the gap. Steady state

currents for the wide range of given parameters and substrate concentrations were calculated. All

dependences of current on substrate concentration were approximated by hyperbolas in order to obtain

“apparent” parameters (maximal currents and Michaelis constants) of modelled biosensors. The applicability

of theoretical plate gap model was tested for the carbon paste electrodes which were modified with two types

of PQQ dependent glucose dehydrogenases: intracellular soluble glucose dehydrogenase (s-GDH) from

Acinetobacter calcoacetics and the membrane-bound enzyme (m-GDH) from Erwinia sp. 34-1. It was found,

that s-GDH- based biosensor exhibits characteristic features of the theoretical plate gap biosensors.

Keywords: amperometric biosensors, carbon black, surface composition, PQQ-GDH, hindrances to

diffusion, modelling.

Microelectrochemically Induced Local Cell Adhesion on Oligo (ethylene glycol)-

Terminated Self-Assembled Monolayer

Chuan Zhao and Gunther Wittstock

Department of Chemistry and Institute of Chemistry and Biology of the Marine Environment,

Carl Von Ossietzky University of Oldenburg, D-26111 Oldenburg, Germany

chuan.zhao@uni-oldenburg.de

Micropatterning of localized chemical or biochemical domains has the potential to become a

powerful tool to control the behaviour of anchorage-dependent cells which is critically

important in cellular biology, tissue engineering and cell-based bioelectronics. Several

methods for patterning the immobilization of ligands or proteins, and consequently the

attachment of cells on the microscale have been described using microfabricated metal

templates, photolithography, softlithography, biopolymers, extracellular matrix proteins and

self-assembled monolayer (SAM). The existing methods to pattern SAM on surface rely on a

softlithography technique, e.g. micro-contact printing (µCP) to fabricate a cytophilic pattern

on a substrate and then fill the empty area with a cell-resistant SAM prior to the cell

cultivation. SAMs that are terminated by short oligomers of the ethylene glycol (EG) unit

(HS(CH2)11(OCH2-CH2)nOH; n = 3-7) have been found especially effective in resisting

protein adsorption and are now the most important tool for bioanalytical applications.

In this presentation, we report an alternative, simple method to create cellular patterns using

scanning electrochemical microscopy (SECM). The method is based on our finding that the

cytophobic nature of ethylene glycol-terminated SAM is rapidly switched to cell-adhesive by

exposure to some oxidants which can be in situ produced by a microelectrode. SECM has

been successfully used to characterise and modify the SAMs on the micrometer scale. By

scanning a microelectrode as a “pen” closely above the substrate oxidants are locally

generated to transform the EG-terminated SAM. The cytophobic nature of the SAM is

changed, which finally results in cell adhesion on the modified region. The surface

modification of the ethylene glycol (EG)-terminated SAM was characterized with SECM,

atomic force microscopy (AFM) and contact angle measurements. Marine bacteria T5 from

the German Wadden Sea was used to absorb on the pre-treated SAM surface.

Electron Transfer through Aib Oligopeptides

USabrina AntonelloU and Flavio Maran

Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, Padova, Italy.

Long-range electron transfer in proteins relies on the efficiency of the peptide chains in

supporting charge transfer processes. Therefore, understanding how the electron tunneling

between a donor (D) and an acceptor (A) separated by model peptide bridges takes place is an

important issue. We are currently interested on the mechanism by which certain peptide

chains support charge transfer processes. In these studies, we have focused on the use of

bridges based on α-aminoisobutyric acid (Aib) homooligomers, which are known for their

propensity to form rigid 3B10B-helices because of steric hindrance at the α-carbon and resulting

restricted torsional freedom.P

1P In the investigated molecules, the electron is first

elctrochemically injected into the D end of the peptide and then transferred intramolecularly

to the A moiety. By studying the electron-transfer rate across these well-defined peptide

bridges, we could evidence an important role played by the secondary structure of the peptide

and, particularly, by the presence and number of intramolecular hydrogen bonds.P

2P

References (1) Toniolo, C.; Crisma, M.; Formaggio, F.; Peggion, C. Biopolymers (Pept. Sci.) 2001, 60,

396. (2) Antonello, S.; Formaggio, F.; Moretto, A.; Toniolo, C.; Maran, F. J. Am. Chem. Soc.

2003, 125, 2874.