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S1
Electronic Supporting Information
A quantitative appraisal of the binding interactions between anionic dye, Alizarin Red S
and alkyloxypyridinium surfactants: a detailed micellization, spectroscopic and
electrochemical study
Renu Sharma, Ajar Kamal and Rakesh Kumar Mahajan*
*Department of Chemistry, UGC-Centre for Advanced Studies-I, Guru Nanak Dev University,
Amritsar-143005, India
*To whom correspondence should be addressed:
e-mail: [email protected]; Fax: +91 183 2258820
Electronic Supplementary Material (ESI) for Soft Matter.This journal is © The Royal Society of Chemistry 2015
S2
Annexure SI
1. Methods (Detailed Description)
1.1 Conductivity measurements. Conductivity was measured using a digital Systronics
conductivity meter model 306 with a dip-type conductivity cell having a cell constant of
1.01 cm-1
at 298.15 K. The specific conductivity of deionised double distilled water used in
present study was measured to be 2.0-3.0 µS cm-1
.
1.2 Surface tension measurements. Surface tension measurements have been performed
using Kruss (Hamburg, Germany) Easy dyne tensiometer using ring detachment method with an
accuracy of ± 0.15 mN m-1
at room temperature of 298.15 K. A mixing time of two minutes
followed by an equilibration time of 5 minutes was adopted before each measurement
1.3 UV-visible measurements. The absorption spectra were recorded on a UV-1800
Shimadzu spectrophotometer with a quartz cuvette having a path length of 1 cm. The titrations
were performed at 298.15 K by successive additions of small aliquots of stock solutions of
alkyloxypyridinium surfactants directly into the quartz cuvette containing 2.0 mL of 0.02 mmol
dm-3
ARS solution. After every addition, the solution was equilibrated for 5 minutes to reach
thermal equilibrium. The spectra were recorded in the range 350-700 nm.
1.4 Voltammetric measurements. Voltammetric measurements were performed on a PC
controlled CHI660D (Austin, USA) electrochemical workstation equipped with a conventional
three electrode system comprising of a working glassy electrode (3.0 mm in diameter), a counter
Pt wire and a reference Ag/AgCl electrode. All the solutions were deoxygenated with N2 and
working electrodes were polished with slurry of alumina powder. The voltammetric
measurements were carried out in the presence of 0.1 M phosphate buffer having pH of 7.4 as a
supporting electrolyte.
1.5 Potentiometric measurements. The potentiometric measurements were carried out by
using an Equiptronics digital potentiometer, Model EQ-602 employing the following
electrochemical cell assembly:
Ag/AgCl 3M KCl Test Solution PVC
membrane
Internal Reference
Solution
3M KCl Ag/AgCl
S3
The neutral ion-pair complexes of alkyloxypyridinium surfactants and sodium
dodecylsulfate as [HECnOPy] +DS ̄ were prepared by the procedure earlier reported by our
laboratory [1, 2]. Equimolar aqueous solutions of [HECnOPyBr], n = 14, 16 and sodium
dodecylsulfate (SDS) were mixed and after continuous stirring for a considerable time, the white
precipitates of HECnOPy+DS ̄ were obtained . The precipitates so obtained were washed
repeatedly with water to remove NaCl and recrystallized thrice from acetone. The PVC (176
mg), ion-pair (5 mg) and plasticizer (550 mg) were mixed and dissolved in minimum quantity of
THF. The resulting mixture was poured in 50-mm petri dish after removing the air-bubbles. The
solvent THF was allowed to evaporate at room temperature. The resulting membrane was cut to
required size and attached to PVC tubes with PVC glue and equilibrated in 1 mmol dm-3
of
respective surfactant solution. The internal reference solution was 1mM of these surfactants in
1 mmol dm-3
NaCl. The given composition of the components used for membrane formation
represents the best system in terms of slope values, correlation coefficient, linear range and
detection limit. The EMF measurements were carried out by titration method at 298.15K in the
presence of 1 mmol dm-3
NaCl solution.
1.6 Dynamic light scattering measurements. Dynamic light scattering measurements were
performed using a Malvern Nano-ZS Zetasizer instrument employing a He-Ne laser (λ = 632
nm) at a scattering angle of 173˚ using quartz cuvette having path length of 1 cm. The
temperature of the measurements was controlled to an accuracy of ±0.1°C using a built-in
temperature controller.
1.7 1H NMR measurements.
1H NMR experiments were performed on a 500 MHz JEOL-FT
NMR-AL spectrometer using CD3CN as solvent. The NMR titration experiments were
performed by titrating one equivalent of ARS prepared in CD3CN with increasing equivalents of
alkyloxypyridinium surfactants. Chemical shifts were given on the δ scale.
S4
Annexure SII.
The maximum surface excess concentration (Гmax) and minimum area per molecule [3, 4] at the
air-solution interface can be calculated using equation (1) and (2) as follows:
(1)
Amin =1020
/ (NA. Гmax) (2)
The Gibbs free energy of adsorption (ΔG˚ads) [5] is calculated using the equation (3)
ΔG˚ads= ΔG˚mic - Пcmc/ Гmax (3)
maxln
nRTCd
d
T
S5
System C1(mmol dm-3
) C2 = cmc(mmol dm-3
)
ARS - -
[HEC14OPyBr] - 0.83
ARS+[HEC14OPyBr] 0.05 0.78
[HEC16OPyBr] - 0.16
ARS+[HEC16OPyBr] 0.02 0.13
ARS + [HEC14OPyBr]
xARS 0.0 0.1 0.3 0.5 0.7 0.9
Dh / nm 1.2 4.50 11.7 25.8 18.6 10.4
ARS + [HEC16OPyBr]
xARS 0.0 0.1 0.3 0.5 0.7 0.9
Dh / nm 1.5 6.20 13.5 28.2 21.3 12.8
Table S2. Hydrodynamic diameter (Dh) for ARS-alkoxypyridinium surfactants, [HEC14OPyBr]
and [HEC16OPyBr] mixed systems at varying mole fractions of ARS (xARS).
Table S1. The concentration corresponding to ion-pair formation (C1), critical micelle
concentration (cmc) of alkyloxypyridinium surfactants, [HEC14OPyBr] and [HEC16OPyBr]
surfactants in the absence and presence of ARS determined from potentiometric measurements.
S6
ARS-[HEC14OPyBr]
system
1H-NMR
chemical shift
range in δ
(ppm) for
aromatic
protons of
ARS
Observations
after addition
of surfactant
solution
1H-NMR
chemical shift
range in δ (ppm)
for aromatic and
aliphatic protons
of surfactants
Observations after
addition of
surfactant solution
ARS 11.52 (s, H1)
11.79 (s, H2)
3.99 (m, Hy),4.23
(t, Hn), 4.65 (m,
Hx), 8.38 (d, Hq),
8.53 (s, Hr)
1 equivalent ARS+
0.25 equivalent of
[HEC14OPyBr]
11.51 (s, H1)
12.79 (s, H1)
Upfield shift
for H1 proton.
3.96 (m, Hy),4.22
(t, Hn), 4.64 (m,
Hx), 8.37 (d, Hq),
8.51 (s, Hr)
Upfield shift for
all the protons.
1 equivalent ARS+
0.5 equivalent of
[HEC14OPyBr]
11.49 (s, H1)
12.79 (s, H1)
Upfield shift
for H1 proton.
3.98 (m, Hy),4.23
(t, Hn), 4.67 (m,
Hx), 8.40 (d, Hq),
8.57 (s, Hr)
Downfield shift
for all the protons.
1 equivalent ARS+
1.0 equivalent of
[HEC14OPyBr]
11.48 (s, H1)
12.79 (s, H1)
Upfield shift
for H1 proton.
3.98 (m, Hy),4.25
(t, Hn), 4.69 (m,
Hx), 8.42 (d, Hq),
8.60 (s, Hr)
Downfield shift
for all the protons.
1 equivalent ARS+
1.5 equivalent of
[HEC14OPyBr]
11.47 (s, H1)
12.79 (s, H1)
Upfield shift
for H1 proton.
3.99 (m, Hy),4.23
(t, Hn), 4.70 (m,
Hx), 8.43 (d, Hq),
8.61 (s, Hr)
Downfield shift
for all the protons.
Table S3. Chemical shifts and observations determined by 1H-NMR titrations of alizarin red S
(ARS) with increasing equivalents of alkyloxypyridinium surfactant, [HEC14OPyBr].
S7
ARS-[HEC16OPyBr]
system
1H-NMR
chemical shift
range in δ
(ppm) for
aromatic
protons of
ARS
Observations
after addition
of surfactant
solution
1H-NMR
chemical shift
range in δ (ppm)
for aromatic and
aliphatic protons
of surfactants
Observations after
addition of
surfactant solution
ARS 11.52 (s, H1)
11.79 (s, H2)
3.99 (m, Hy),4.23
(t, Hn), 4.65 (m,
Hx), 8.38 (d, Hq),
8.53 (s, Hr)
1 equivalent ARS+
0.50 equivalent of
[HEC16OPyBr]
11.53 (s, H1)
12.79 (s, H1)
Upfield shift
for H1 proton.
3.97 (m, Hy),4.21
(t, Hn), 4.57 (m,
Hx), 8.39(s, Hq)
Upfield shift for
all the protons.
1.0 equivalent ARS+
1.0 equivalent of
[HEC16OPyBr]
11.49 (s, H1)
12.79 (s, H1)
Upfield shift
for H1 proton.
3.98 (s, Hy),4.23
(t, Hn), 4.64 (s,
Hx), 8.35 (d, Hq),
8.52 (s, Hr)
Downfield shift
for all the protons.
1.0 equivalent ARS+
1.5 equivalent of
[HEC16OPyBr]
11.48 (s, H1)
12.79 (s, H1)
Upfield shift
for H1 proton.
3.98 (s, Hy),4.23
(s, Hn), 4.66 (s,
Hx), 8.39 (s, Hq),
8.55 (s, Hr)
Downfield and
upfield shift for
protons.
Table S4. Chemical shifts and observations determined by 1H-NMR titrations of alizarin red S
(ARS) with increasing equivalents of alkyloxypyridinium surfactant, [HEC16OPyBr].
S8
400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0
[HEC16OPyBr](A)
Ab
sorb
an
ce
Wavelength / nm
0.000mmol dm-3
0.005mmol dm-3
0.009mmol dm-3
0.015mmol dm-3
0.020mmol dm-3
0.039mmol dm-3
0.077mmol dm-3
0.095mmol dm-3
0.113mmol dm-3
0.165mmol dm-3
0.182mmol dm-3
0.214mmol dm-3
0.276mmol dm-3
0.330mmol dm-3
10-5
10-4
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
(B)
Ab
sorb
an
ce
C / mol dm-3
420
440
460
480
500
520
540
560[HEC16OPyBr]
Wa
vele
ng
th (
ma
x) / n
m
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
-0.40
-0.35
-0.30
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
[HEC16OPyBr]
A
Xsurf
(C)
-6.5 -6.0 -5.5 -5.0 -4.5 -4.0 -3.5
35
40
45
50
55
60
65
[HEC16OPyBr]
/
mN
m-1
log C / mol dm-3
0.00 mmol dm-3ARS
0.02 mmol dm-3ARS
(B)
0.0000 0.0001 0.0002 0.0003
0
10
20
30
40
50
60[HEC16OPyBr]
0.000 mmol dm-3 ARS
0.020 mmol dm-3 ARS
0.050 mmol dm-3 ARS
0.075 mmol dm-3 ARS
0.100 mmol dm-3 ARS
(A)
/
S
cm
-1
C / mol dm-3
Fig.S1 (A) Variation of specific conductivity (κ) with molar concentration of [HEC16OPyBr] in the
absence and presence of varying amounts of ARS. (B) Variation of surface tension (γ) as a function of
logarithm of molar concentration of alkyloxypyridinium surfactant, [HEC16OPyBr] in the absence and
presence of 0.02 mmol dm-3
ARS.
Fig.S2 (A) UV-visible spectrum of 0.02 mmol dm-3
ARS in the presence of increasing concentrations
of alkyloxypyridinium surfactant, [HEC16OPyBr] (B) Plot of Absorbance and λmax vs increasing
concentration of [HEC16OPyBr] (C) Job’s plot depicting 1:1 stoichiometry of ARS-[HEC16OPyBr]
mixed system.
S9
Fig.S4 (A) Linear sweep voltammograms (LSV) of 0.05 mmol dm-3
alkyloxypyridinium surfactant,
[HEC14OPyBr] in ARS at various scan rates of potential (B) LSV of 0.25 mmol dm-3
[HEC14OPyBr]
in ARS at various scan rates of potential (C) LSV of 1.0 mmol dm-3
[HEC14OPyBr] in ARS at various
scan rates of potential
-1.5 -1.0 -0.5 0.0 0.5
-1.5x10-5
-1.0x10-5
-5.0x10-6
0.0
5.0x10-6 (A) [HEC16OPyBr]
0.000mmol dm-3
0.007mmol dm-3
0.013mmol dm-3
0.020mmol dm-3
0.026mmol dm-3
0.033mmol dm-3
0.039mmol dm-3
0.046mmol dm-3
I p /
A
Potential / V
-1.5 -1.0 -0.5 0.0 0.5 1.0
-1.5x10-5
-1.0x10-5
-5.0x10-6
0.0
5.0x10-6
-0.2 0.0 0.2 0.4 0.6 0.8
2.0x10-6
4.0x10-6
6.0x10-6
I p /
A
Potential / V
[HEC16OPyBr]
I p /
A
Potential / V
(B)
Fig.S3 (A) Cyclic voltammograms of ARS in the presence of increasing concentrations of
alkyloxypyridinium surfactant, [HEC16OPyBr] (B) Linear sweep voltammograms of ARS in the
presence of increasing concentrations of [HEC16OPyBr]
-1.5 -1.0 -0.5 0.0 0.5
-1.2x10-5
-9.0x10-6
-6.0x10-6
-3.0x10-6
0.0
3.0x10-6
0.05 mmol dm-3
[HEC14OPyBr] in ARS
Ip
/ A
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
(A)
-1.5 -1.0 -0.5 0.0 0.5
-1.0x10-5
-5.0x10-6
0.0
5.0x10-6
I p /
A
Potential / V
0.25 mmol dm-3
[HEC14OPyBr] in ARS
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
(B)
-1.5 -1.0 -0.5 0.0 0.5 1.0
-1.5x10-5
-1.0x10-5
-5.0x10-6
0.0
5.0x10-6
I p /
A
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
1.0 mmol dm-3
[HEC14OPyBr] in ARS
(C)
S10
-1.5 -1.0 -0.5 0.0 0.5
-1.0x10-5
-5.0x10-6
0.0
5.0x10-6
I p /
A
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
0.01 mmol dm-3
[HEC16OPyBr] in ARS
(A)
-1.5 -1.0 -0.5 0.0 0.5
-1.5x10-5
-1.2x10-5
-9.0x10-6
-6.0x10-6
-3.0x10-6
0.0
3.0x10-6
6.0x10-6
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
0.05 mmol dm-3
[HEC16OPyBr] in ARS
I p /
A
Potential / V
(B)
-1.5 -1.0 -0.5 0.0 0.5
-1.5x10-5
-1.0x10-5
-5.0x10-6
0.0
5.0x10-6
I p /
A
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
0.35 mmol dm-3
[HEC16OPyBr] in ARS
(C)
0.10 0.15 0.20 0.25
1.0x10-6
2.0x10-6
3.0x10-6
4.0x10-6
I p /
A
v1/2
[HEC16OPyBr]
0.00 mmol dm-3
0.01 mmol dm-3
0.10 mmol dm-3
0.35 mmol dm-3
(D)
Fig.S5 (A) LSV of 0.01 mmol dm-3
[HEC16OPyBr] in ARS at various scan rates of potential (B)
LSV of 0.05 mmol dm-3
[HEC16OPyBr] in ARS at various scan rates of potential (C) LSV of 0.35
mmol dm-3
[HEC16OPyBr] in ARS at various scan rates of potential (D) Variation of Ip (A) vs v1/2
for ARS in the absence and presence of increasing concentrations of [HEC16OPyBr].
S11
Fig.S6 Binding constant determination for the ARS-[HECnOPyBr] mixed systems using (A) changes
in UV-visible spectra of ARS (B) changes in the peak current of ARS.
4.0x103
6.0x103
8.0x103
5.0x104
1.0x105
2x105
3x105
4x105
5x105
6x105
7x105
8x105
9x105
1/
p
1/C
[HEC14OPyBr]
[HEC16OPyBr]
(B)
-5.5 -5.0 -4.5 -4.0 -3.5
-0.15
-0.10
-0.05
0.00
0.05
0.10
EM
F /
V
log C / mol dm-3
[HEC16OPyBr]
0.00mmol dm-3
0.02mmol dm-3
(A)
-5.5 -5.0 -4.5 -4.0 -3.5
1.0x109
1.2x109
1.4x109
1.6x109
1.8x109
(B)
log C / mol dm-3
[HEC16OPyBr]
v
Fig.S7 (A) EMF as a function of logarithm of molar concentration of alkyloxypyridinium surfactant,
[HEC16OPyBr] in the absence and presence of 0.02 mmol dm-3
ARS (B) Binding isotherms of
binding parameter (v) versus logarithm of molar concentration of [HEC16OPyBr] in the presence of
0.02 mmol dm-3
ARS.
0 1x104
2x104
3x104
4x104
0
10
20
30
40
50
60
70
1/C
[HEC14OPyBr]
[HEC16OPyBr]
1/
(A)
S12
N+
O
HO
Br-
q
p
or
n l
k
j
i g
f d b
e c a
x
y
m
h
s
Hy
Ha
Hr
Hn
Hx
Hm
Hl
Hq
Ho
Hp
Hb-Hk
(A)
SO3Na
O
O
OH
OH
HH
H
H
H
1
2
3
4
5
6
7
H3-H4
H7
H2
H1
H6
H5
(B)
Fig.S8 (A) 1H-NMR spectra of pure alkyloxypyridinium surfactant, [HEC14OPyBr] (B)
1H-
NMR spectra of pure ARS
S13
1.0 eq.of ARS+0.50 eq.of [HEC16OPyBr]
1.0 eq.of ARS+1.0 eq.of [HEC16OPyBr]
1.0 eq.of ARS+1.5 eq.of [HEC16OPyBr]
[HEC16OPyBr]
ARS
Fig.S9 1H-NMR titrations of ARS with increasing equivalents of alkyloxypyridinium surfactant,
[HEC16OPyBr]
S14
References
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F68), using surfactant-selective sensors based on neutral ion-pair complexes. Ind. Eng.
Chem. Res. 2007, 46, 4706-4709.
2. R. K. Mahajan, A. Shaheen, Effects of various additives on the performance of a newly
developed PVC based potentiometric sensor for anionic surfactants. J. Colloid Interface
Sci. 2008, 326, 191-195.
3. D. K. Chattoraj, K. S. Birdi, Adsorption and Gibbs Surface Excess, Plenum, New York,
1984 (Chapter 3).
4. K. Anand, O. P. Yadav, P. P. Singh, Studies on the surfaces and thermodynamic
properties of some surfactants in aqueous and water+1,4-dioxane solutions. Colloids Surf.
1991, 55, 345-358.
5. P. Mukherjee, The nature of the association equilibria and hydrophobic bonding in
aqueous solutions of association colloids. Adv. Colloid Interface Sci. 1967, 1, 242-275.