Dc

MD

a

ARRA

KBPCO

1

twtbitoIt(mmcfmoTca

0d

Materials Chemistry and Physics 126 (2011) 278–283

Contents lists available at ScienceDirect

Materials Chemistry and Physics

journa l homepage: www.e lsev ier .com/ locate /matchemphys

NA–cyclodextrin–inorganic hybrid material for absorbent of various harmfulompounds

asanori Yamada ∗, Shinya Tabuchiepartment of Chemistry, Faculty of Science, Okayama University of Science, Ridaicho, Kita-Ku, Okayama 700-0005, Japan

r t i c l e i n f o

rticle history:eceived 23 July 2010eceived in revised form 2 October 2010ccepted 13 November 2010

eywords:iomaterialolymers

a b s t r a c t

A DNA–cyclodextrin (CD)–inorganic hybrid material was prepared by mixing the DNA, CD, and silanecoupling reagents, such as 3-aminopropyltriethoxysilane (APTES) or tetraethoxysilane (TEOS). TheDNA–PCD–APTES hybrid material possessed a high water-stability. Additionally, the tensile strength ofthe hybrid material containing the APTES was approximately two times higher than that of hybrid mate-rial without the inorganic component. These chemical and physical properties were due to the formationof a siloxane network in the hybrid material and the electrostatic interaction between the phosphategroup in the DNA and amino group in the APTES. Furthermore, the DNA–PCD–APTES hybrid material

omposite materialrganic compounds

could be immobilized on a glass filter by the coupling reaction to the silanol group in the filter. Whenan aqueous multi-component solution, which contained dibenzofuran, biphenyl, bisphenol A, diethyl-stilbestrol, and naphthalene, was applied to DNA–PCD–APTES hybrid filter, this filter could effectivelyaccumulate various harmful compounds, such as dioxin, polychlorobiphenyl (PCB), and bisphenol A.Especially, the accumulation of diethylstilbestrol was extremely high and this value was approximately

D–TEerial

85%. In contrast, DNA–PCgroups, was a fragile mat

. Introduction

DNA, one of the most important biopolymers in living sys-ems, can be purified from either salmon milts or shellfish gonads,hich are generally discarded as waste around the world. Addi-

ionally, since DNA has various functions, such as the selectiveinding of harmful compounds, the interaction with heavy metal

ons, biodegradation, etc. [1,2], DNA material has attracted atten-ion as a functional material [3,4]. We also reported the utilizationf the double-stranded DNA as an environmental material [5–7].n this study, DNA selectively accumulated harmful planar struc-ure compounds, such as dioxin-derivatives, polychlorobiphenylPCB)-derivatives, and benzo[a]pyrene [5,6], by an intercalating

echanism into the double-stranded DNA. However, the DNAaterial could not accumulate the harmful non-planar structure

ompounds, such as diethylstilbestrol and bisphenol A [5,6]. There-ore, most recently, we prepared a DNA–cyclodextrin composite

aterial by mixing of DNA and cyclodextrin (CD), which is a cyclic

ligosaccharide composed of seven d-glucopyranose residues [7].his DNA–CD composite material can accumulate various harmfulompounds, such as dioxin, PCB, and bisphenol A, by intercalationnd encapsulation in the CD cavity. However, the DNA–CD compos-

∗ Corresponding author. Tel.: +81 86 256 9550; fax: +81 86 256 9757.E-mail address: myamada@chem.ous.ac.jp (M. Yamada).

254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2010.11.026

OS hybrid, that was prepared by the mixing of TEOS without the aminoand could not use for the adsorbent of harmful compounds.

© 2010 Elsevier B.V. All rights reserved.

ite material was unstable in an aqueous solution and the elution ofDNA after a long incubation occurred. Additionally, since this mate-rial, entirely of consisting organic compounds, does not have therequired physical property, such as tensile strength, it is difficult touse it as an environmental material for practical application.

The sol–gel method is a cornerstone technique to prepareinorganic or organic–inorganic hybrid materials at a relativelylow temperature. Therefore, this method is important for thesoft matter process in the fields of nanotechnology, engineeringand material sciences [8–11]. Especially, organic–inorganic hybridmaterials with both the properties of a flexible organic material andthe physical strength of an inorganic material have been attractiveas novel functional materials for optical devices, coating materials,and sensors materials [8–11]. Additionally, the biological applica-tion of an organic–inorganic hybrid material has also been reported[12–15]. Therefore, an organic–inorganic hybrid material includ-ing the double-stranded DNA and cyclodextrin is interesting andimportant for using in the material, environmental, and biologicalsciences.

In this study, we prepared the DNA–cyclodextrin(CD)–inorganic hybrid material by mixing the DNA, CD, and

silane coupling reagents 3-aminopropyltriethoxysilane (APTES).The DNA–PCD–APTES hybrid material was extremely stable inwater and had good physical properties, such as tensile strength.Additionally, the DNA–PCD–APTES hybrid material could be immo-bilized on a glass filter by polymerization of the silanol group.

M. Yamada, S. Tabuchi / Materials Chemistry and Physics 126 (2011) 278–283 279

O

OHHO

OH

O

O

OH

HOOH

O

OOH

OH

OH

O

O

OHOH

HO

O

O

OH

OH

HO

O

OOH

OH

HO

O

O

OH

HO

HO

O

β-cyclodextrin

APTES

PCD

Si

OC2H5

OC2H5

C2H5O NH2 Si

OCH3

H3CO

OCH3

OCH3

TEOS

NHNH2 n-x

x

Spl

Faac(bDa

2

2

>wJtbwTtaeGJ

2

r[ap

OHHO

O

HO

OH

Dibenzofuran (DF) Biphenyl (Bip)

Diethylstilbestrol (DES)Naphthalene (NP)

cheme 1. Molecular structures of �-cyclodextrin (�-CD), �-CD immobilizedoly(allylamine) (PCD), 3-aminopropyltriethoxysilane (APTES), and tetraethoxysi-

ane (TEOS).

urthermore, the DNA–PCD–APTES hybrid material indicated theccumulation of various harmful compounds, such as dioxin, PCB,nd bisphenol A, from an aqueous multi-component solution. Inontrast, although we prepared the DNA–PCD–tetraethoxysilaneTEOS) hybrid material, this material was fragile and could note used for the adsorbent of harmful compounds. Therefore, theNA–PCD–APTES hybrid material has the potential to be used asn environmental material.

. Experimental

.1. Materials

Double-stranded DNA (sodium salt from salmon milt, molecular weight:5 × 106) and poly(allylamine hydrochloride) (PAA·HCl, molecular weight: 1 × 105)as obtained from Biochem Ltd., Saitama, Japan, and Nittobo Co., Ltd., Tokyo,

apan, respectively. �-Cyclodextrin (CD), 3-aminopropyltriethoxysilane (APTES),etraethoxysilane (TEOS), ethidium bromide, p-nitrophenol, dibenzofuran (DF),iphenyl (Bip), naphthalene (NP), bisphenol A (Bis-A), and diethylstilbestrol (DES)ere purchased from Wako Pure Chemical Industries, Ltd., Osaka, Japan; Nacalai

esque, Inc., Kyoto, Japan; Acros Organics, Morris Plains, NJ, or Tokyo Kasei Indus-ries Ltd., Tokyo, Japan. The molecular structures of silane coupling reagents APTESnd TEOS are shown in Scheme 1. Additionally, the molecular structures of modelndocrine disruptors and harmful compounds are shown in Scheme 2. Glass filterC-50 (thickness: 0.2 mm) was purchased from Advantec Toyo Kaisha, Ltd., Tokyo,

apan.

.2. Synthesis of ˇ-CD-immobilized poly(allylamine).

The monotosylated �-CD (CDOTs) at the 6-position was synthesized byeaction of �-CD with toluene-p-sulfonyl chloride in pyridine at 0 ◦C for 2 h16,17]. The resulting CDOTs were purified by recrystallization from water and

butanol–ethanol–water (5:4:3, v/v/v) mixed solvent. The �-CD-immobilizedoly(allylamine) (PCD) was synthesized by a reported procedure [7,18,19]. The

Bisphenol A (Bis-A)

Scheme 2. Molecular structures of model endocrine disruptors and harmful com-pounds.

molecular structure of PCD was shown in Scheme 1. The free poly(allylamine)(PAA) was prepared by a reported method [7,18,19]. The free PAA was dissolvedin water, and the CDOTs were added while stirring at 75 ◦C. This solution wasstirred for 12 h at 75 ◦C. Finally, the reaction mixture was filtered and the filtratewas transferred to a dialysis membrane (Wako Pure Chemical Industries, Ltd.) andthen dialyzed against water for 7 days. After freeze–drying, a white powder wasobtained.

The identification of the synthetic polymer PCD was demonstrated by a 1H NMRspectrum using a LNM-LA500 (JEOL Ltd., Tokyo, Japan). 1H NMR (500 MHz, D2O): ı1.3 (CH2-a); 1.6 (CH2-b); 2.3 (CH3-TsO); 2.7 (CH2-c); 3.6–3.8 (2-H, 3-H, 4-H, 5-H, and6a,6b-H); 5.0 (1-H); 7.3–7.6 (ar H). The peaks in 1H NMR spectra were consistent withthe reported spectra [7,18,19]. The degrees of �-CD substitution were estimatedfrom the integral ratio in the 1H NMR spectrum.

2.3. Preparation of DNA–PCD–APTES hybrid materials

The DNA–PCD–APTES hybrid materials were prepared as follows: aqueousPCD solution (50 �L, 100 mg mL−1) and APTES solution (0.93 �L) were mixed. ThePCD–APTES-mixed solution, which is the precursor solution, was stirred for 24 hat room temperature to hydrolyze the APTES molecules. This PCD–APTES-mixedsolution and aqueous DNA solution (200 �L, 10 mg mL−1) were mixed on a glassplate (Matsunami Glass Ind., Ltd., Osaka, Japan). The gelation was detected by theformation of a water-insoluble gel. These DNA–PCD–APTES hybrid materials wererinsed with pure water (10 mL × 5 times) to remove the DNA, PCD, and APTES, whichhad not gelled, and then stored in pure water for more than one day. On the otherhand, the DNA–PCD composite materials were prepared by a reported procedure[7].

The DNA–PAA–APTES hybrid fibers were prepared as follows: the PAA–APTES-mixed solution was put on the DNA aqueous solution without mixing and theDNA–PAA–APTES matrix at the liquid/liquid interface was drawn from the liq-uid interface by tweezers at the pulling rate of approximately 10 mm s−1. TheseDNA–PAA–APTES hybrid fibers were rinsed with pure water (50 mL × 5 times) anddried under an air at room temperature. The DNA–PAA–APTES hybrid fiber wasobserved using an optical or polarization microscope (BX50, Olympus Optical Co.,Ltd., Tokyo, Japan) with two polarizing filters. On the other hand, the DNA–PAAhybrid fibers were prepared by the similar methods.

The DNA–PCD–APTES-immobilized glass filter was prepared as follows: aque-ous PCD solution (50 �L, 100 mg mL−1) and APTES solution (0.93 �L) were mixedand incubated for 24 h at room temperature to hydrolyze the APTES molecules. ThisPCD–APTES-mixed solution and aqueous DNA solution (200 �L, 10 mg mL−1) werecast onto glass filter (�13 mm), mixed on filter, and then dried for 24 h at room tem-perature. This DNA–PCD–APTES filter was rinsed with pure water and then storedin pure water for more than one day.

2.4. Tensile strength of DNA–PAA–APTES hybrid fiber

The DNA–PAA–APTES hybrid fibers were cut into the length of approximately30 mm. The diameter of the hybrid fiber was 10–30 �m. The tensile strain and stresswere measured using a tensile machine (Autograph AGS-J, Shimadzu Corp., Kyoto,Japan) [20]. The measurement condition of the tensile strength was controlled by thelaboratory air conditioner and the temperature and humidity conditions were 25 ◦C

2 hemistry and Physics 126 (2011) 278–283

aaws

2

tutJm

batm

2

aB1wtuG(Ttm

gfiTfisdD

3

3

Cdagtratp[p

3

lTtADwihhae

2520151050

Incubation time / h

0

20

40

60

80

Am

ount of elu

ted D

NA

/ %

Fig. 1. Stability of DNA–PCD–APTES hybrid material in water. (♦), (�), (�), (©), and(×) showed DNA–PCD hybrid without the inorganic component, DNA–PCD-5 wt.%APTES hybrid, DNA–PCD-10 wt.% APTES hybrid, DNA–PCD-20 wt.% APTES hybrid,

80 M. Yamada, S. Tabuchi / Materials C

nd 50 ± 5%, respectively. The initial gauge length of the hybrid fiber was 10 mmnd the drawing speed was 10 mm min−1. The value of tensile strain and stressere expressed as an average of ten measurements. On the other hand, the tensile

trengths of DNA–PAA hybrid fiber were measured by the similar methods.

.5. Characterization of DNA–PCD–APTES hybrid materials

The stability in an aqueous solution of the hybrid material was confirmed byhe following method: the DNA–PCD–APTES hybrid materials were incubated inltra-pure water (5 mL) for various times. The absorbance at 260 nm of the solu-ion was measured by a U-2010 UV–vis spectrophotometer (Hitachi Co., Ltd., Tokyo,apan) and the eluted DNA from the hybrid material was determined [5,6,20]. In this

easurement, we used the DNA–PCD composite material for the control.The molecular structures of DNA–PCD–APTES hybrid materials were confirmed

y the infrared (IR) spectra. The IR spectra of the DNA–PCD–APTES hybrid materi-ls were measured by an attenuated total reflection (ATR) method using a Fourierransform infrared spectrometer FT-IR 8400 (Shimadzu Corp.). The IR spectrum was

easured with a resolution of 4 cm−1.

.6. Accumulation of harmful compounds from multi-component solution

The harmful multi-component solution, which contained DF, Bip, Bis-A, DES,nd NP, was prepared by mixing of the aqueous solutions. The concentrations of DF,ip, Bis-A, DES, and NP in the multiple component solution were 0.72, 0.53, 0.13,.4, and 12 �M, respectively. The DNA–PCD–APTES hybrid material (see Section 2.3)as incubated in the aqueous multi-component solutions (2 mL) for 24 h at room

emperature. This solution was analyzed by reverse-phase high performance liq-id chromatography (HPLC) using an Inertsil® ODS-P column (7.6 mm × 250 mm,L Science Inc., Tokyo, Japan) with a CH3OH/water (80:20, v/v). The detections

276 nm) of the harmful compounds used a UV-8010 UV–vis detector (Tosoh Coop.,okyo, Japan). The amounts of the accumulated compounds were determined byhe absorbance of the aqueous solutions in the absence or presence of the hybrid

aterial.The accumulation of harmful compounds by the DNA–PCD–APTES-immobilized

lass filter was demonstrated as follows: the DNA–PCD–APTES-immobilized glasslter (see Section 2.3) was placed in the filter holder (Millipore Corp., Boxboro, MA).he harmful multi-component solution (1 mL) was applied to the DNA–PCD–APTESlter by the glass syringe. This process was repeated ten times for 30 min. The treatedolution was analyzed by HPLC. The amounts of the accumulated compounds wereetermined by the absorbance of the aqueous solutions before and after of theNA–PCD–APTES-immobilized glass filter.

. Results and discussion

.1. Synthesis of ˇ-CD-immobilized poly(allylamine)

The PCD polymer was synthesized by the reaction of PAA andDOTs [18,19]. In addition, this PCD polymer was purified using aialysis membrane. The degrees of �-CD substitution (DS) to themino group of the PAA polymer were estimated from the inte-ral ratio in the 1H NMR spectrum. The DS value increased withhe molar ratio of the CDOTs (a monomer unit of PAA) (=R) andeached a constant value at R = 0.3 (data not shown). The DS valuet R ≥ 0.3 was approximately 7%. The constant value of DS is dueo the steric hindrance of the immobilized-cyclodextrin in the PAAolymer. Similar results have been reported for the PCD polymer18,19]. Therefore, for the following experiments, we used the PCDolymer at R = 0.3.

.2. Preparation of DNA–PCD–APTES hybrid materials

The DNA–PCD–APTES hybrid materials were prepared as fol-ows: the APTES solution was added to the aqueous PCD solution.he PCD–APTES mixed solution, which is the precursor solu-ion, was stirred for 24 h at room temperature to hydrolyze thePTES molecules. This PCD–APTES-mixed solution and aqueousNA solution were mixed on a glass plate. The construction of thehite hybrid material was detected by the formation of a water-

nsoluble gel. Fig. 1 shows the stability of the DNA–PCD–APTESybrid materials with various APTES mixing ratios in water. Theybrid materials were incubated in water and the absorbancet 260 nm of the solution was measured at various times. Theluted DNA from the DNA–PCD composite material without

and DNA–PCD-50 wt.% APTES hybrid, respectively. The eluted DNA from hybridmaterial was quantified by its absorbance at 260 nm. Each value represents the meanof three separation determinations.

the APTES silane coupling reagents increased with the incu-bation time and reached the constant value of approximately60% at 6 h. We next demonstrated the water-stability of theDNA–PCD–APTES hybrid material with silane coupling reagents.Surprisingly, the stability of the DNA–PCD–APTES hybrid mate-rial in water increased with the mixing of the silane couplingreagents and the amount of eluted DNA from hybrid materialat 24 h was only a few percent at ≥20 wt.%. This water-stabilityis due to the formation of a siloxane network in the hybridmaterial and similar phenomena have been reported at theDNA–bis(trimethoxysilylpropyl)amine hybrid material (mentionlater). These results suggested that the addition of silane couplingreagents to the DNA–PCD composite material was an effectivemethod for the water-stabilization.

We estimated the intercalative and encapsulative propertiesof double-stranded DNA and cyclodextrin in DNA–PCD–APTEShybrid material, respectively. When the DNA–PCD–APTES hybridmaterial was incubated in an aqueous ethidium bromide solution,which is one of the famous intercalating reagents [1,2], this whitematerial was dyed red (data not shown). Additionally, the dyed-hybrid material fluoresced under UV irradiation (� = 254 nm). Theseresults suggested that the DNA in the hybrid material maintaineda double-stranded structure and possessed the DNA’s property,such as intercalation. In contrast, this DNA–PCD–APTES hybridmaterial was dyed yellow in an aqueous p-nitrophenol solution(data not shown). Generally, the p-nitrophenol molecule is encap-sulated into the hydrophobic cavity of the cyclodextrin and thecyclodextrin-containing materials are dyed yellow [21]. Therefore,the DNA–PCD–APTES hybrid material possesses an encapsulationfunction into the CD’s cavity. Similar results have been reportedfor the DNA–PCD composite material without mixing of the APTESmolecules [7]. These results suggested that the DNA–PCD–APTEShybrid materials have functions of both the double-stranded DNAand cyclodextrin. In contrast, the DNA–PCD–APTES hybrid materialwith the dyeing by ethidium bromide or p-nitorophenol did notshow the release of these molecules in spite of a long incubationtime.

In contrast, we also prepared the DNA–PCD–TEOS hybrid mate-rial by mixing the TEOS molecules. This composite material alsoshowed functions for both the double-stranded DNA and cyclodex-

trin. However, the DNA–PCD–TEOS hybrid was a fragile material.Additionally, the TEOS hybrid material indicated the elution ofDNA from the hybrid material and was unstable in water (data notshown).

M. Yamada, S. Tabuchi / Materials Chemistry and Physics 126 (2011) 278–283 281

6008001800 1600 1400 1200 100030004000

Wavenumber / cm-1

Tra

nsm

itta

nce

(a)

(b)

(c)

FDs

3

wtmPmg1FicvattpihtabSrt

smgsoaTD

3

psecm

than that of the DNA–PAA composite or DNA–PAA–APTES hybrid

ig. 2. IR spectra of DNA–PCD–APTES hybrid material. (a) pure DNA; (b)NA–PCD–20 wt.% APTES hybrid material; (c) pure PCD. The IR spectrum was mea-

ured at the resolution of 4 cm−1.

.3. Molecular structure of DNA–PCD–APTES hybrid material

The molecular structure of the DNA–PCD–APTES hybrid materialas confirmed by IR spectrometry using an attenuated total reflec-

ion (ATR) prism. Fig. 2 shows the IR spectra of (a) the pure DNAaterial, (b) the DNA–PCD–APTES hybrid material, and (c) the pure

CD material. The absorption band at 1234 cm−1 in the pure DNAaterial, related to the antisymmetric vibration of the phosphate

roup [7,20,24,25], shifted to a lower wavenumber, approximately2 cm−1, by the hybrid with PCD and APTES (see the dashed line inig. 2). This shift to a lower wavenumber is due to the electrostaticnteraction between the phosphate group of DNA and the positivelyharged molecules, and similar phenomena have been reported forarious polyion complexes, such as the DNA–PCD hybrid materialsnd DNA–metal ion biomatrices [7,20]. Additionally, the absorp-ion band at 3100 cm−1 in the pure PCD material, attributed tohe stretching vibration of N–H [24,26], was broaden and disap-eared for the hybrid with DNA and APTES (see the dashed line

n Fig. 2). These results suggested that in the DNA–PCD–APTESybrid material, the amino group of PCD and APTES is bound tohe phosphate group of the DNA by an electrostatic interactionnd formed the acid–base salt. On the other hand, the absorbanceand at 1000–1200 cm−1, attributed to the stretching vibration ofi–O–Si [20,24,27], appeared in the DNA–PCD–APTES hybrid mate-ial. These results indicated the hydrolysis of APTES molecule andhe formation of the siloxane network in the hybrid material.

Generally, the trimethoxysilyl group, –Si(OCH3)3, hydrolyzestepwise in water to give the corresponding silanols, which ulti-ately condense to siloxanes. The hydrolysis of the methoxysilyl

roup is relatively fast, while the condensation reaction of theilanol group is much slower [28]. In this study, the silanol groupf DNA–PCD–APTES hybrid material did not appear in IR spectrumnd the siloxane network formed in all parts of hybrid material.herefore, this siloxane network provided the water-stability toNA–PCD hybrid material (see Fig. 1).

.4. Mechanical property of DNA–PAA–APTES hybrid material

Generally, organic–inorganic hybrid materials, which were pre-ared by the sol–gel method, have a high mechanical strength,

uch as tensile strength [20]. Therefore, we demonstrated theffect of adding APTES molecules to the hybrid material. Espe-ially, in this measurement, since the tensile strength of hybridaterial was related to the degree of �-CD substitution to PAA

Fig. 3. Photograph of DNA–PCD–APTES hybrid fiber. The scale bar is 10 mm.

polymer, we used the PAA polymer which was not immobilizedcyclodextrin. The DNA–PAA–APTES hybrid fibers were preparedas follows: the PAA–APTES-mixed solution was put on the DNAaqueous solution without mixing, and the DNA–PAA–APTES matrixat the liquid/liquid interface was drawn from the liquid interfaceby tweezers. The matrix was continuously produced at the inter-face by the drawing matrix. These DNA–PAA–APTES hybrid fiberswere rinsed with pure water and dried in an air at room tem-perature. Fig. 3 is a photograph of the DNA–PAA–APTES hybridfibers. The diameter of the hybrid fiber was 10–300 �m. This hybridfiber was flexible and did not snap, even if rounded. These hybridfiber constructions at the liquid/liquid interface are due to thepolyion complex, and similar results have been reported for theDNA–metal ion complex [22] and DNA–chitosan complex fibers[23]. Additionally, we observed the DNA–PAA–APTES hybrid fibersunder the crossed nicols condition (data not shown). As a result,the images under the crossed nicols condition were obtained in allparts of the hybrid fiber. Therefore, the DNA–PAA–APTES hybridfiber has an ordered structure with a molecular orientation inthe drawing direction. Similar images under the crossed nicolscondition were obtained for the DNA–metal ion complex fiber[22].

The mechanical property of DNA–PAA–APTES hybrid fiberwas measured using a tensile machine. Fig. 4(a) shows thetensile strength and the elongation at the break point of theDNA–PAA–APTES hybrid fibers. The tensile strength increased withthe mixing ratio of APTES and showed the maximum value, approx-imately 50 MPa, at 30 wt.%. This value of the DNA–PAA–APTEShybrid fiber was approximately two times higher than that of theDNA–PAA composite fiber without the silane coupling agent. Addi-tionally, the elongation at the break point of the DNA–PAA–APTEShybrid fiber was as same as that of the composite material withoutthe APTES. These results suggested that the addition of inorganiccomponents, such as APTES, to the composite material increasesthe physical property without any decrease in the elongation. Incontrast, we prepared the DNA–PAA–TEOS hybrid fibers. Fig. 4(b)shows the tensile strength and the elongation at the break pointof the DNA–PAA–TEOS hybrid fiber. The tensile strength of theDNA–PAA–TEOS hybrid fiber was approximately 50 MPa and wasthe same as that of the DNA–PAA–APTES hybrid fiber. How-ever, the elongation at the break point of the DNA–PAA–TEOShybrid fiber was approximately 5%, and this value was lower

fibers. These results suggested that although the DNA–PAA hybridmaterial with the addition of TEOS rises to increase the phys-ical property, this hybrid material became fragile. Additionally,similar phenomena were obtained for the water-stability of the

282 M. Yamada, S. Tabuchi / Materials Chemistry and Physics 126 (2011) 278–283

Fig. 4. Tensile strengths and elongations of DNA–PAA–inorganic hybrid material. (a)Drit

Dfr

atGcIwgastctc

3D

fDriaaoDcde

demonstrated the accumulation of various harmful compounds bythe DNA–PCD–APTES hybrid material with the cyclodextrin. Thediagonal bar in Fig. 6 shows the accumulated amount of harmfulcompounds by the DNA–PCD–APTES hybrid material. The accu-

NA–PAA–APTES hybrid material. (b) DNA–PAA–TEOS hybrid material. Each valueepresents the mean of ten separation determinations. The solid and diagonal barsndicate the tensile strength and the elongation, respectively. The error bars indicatehe standard deviations.

NA–PCD–TEOS hybrid material (see Section 3.2). Therefore, forollowing experiments, we used the DNA–PCD–APTES hybrid mate-ial.

The increase of tensile strength is due to the formation of silox-ne network by the addition of silane coupling reagents. In contrast,he elongation is based on the shearing of polymer network.enerally, the elongation decreases, since the addition of otheromponent material weakens the interaction between polymers.n fact, the elongation value of DNA–PAA–TEOS hybrid material

ith TEOS decreased. However, APTES molecules with the aminoroup not only form the siloxane network in hybrid material butlso can connect each polymer, such as DNA, through the electro-tatic interaction between phosphate and amino groups. Therefore,he shearing of polymer network in DNA–PAA–APTES increased inomparison with the TEOS hybrid. As a result, the addition of APTESo DNA–PAA hybrid material increases tensile strength withouthanging the elongation.

.5. Accumulation of harmful compounds by theNA–PCD–APTES hybrid material

We demonstrated the accumulation of harmful compoundsrom an aqueous multi-component solution, which containedF, Bip, Bis-A, DES, and NP. The DNA–PCD–APTES hybrid mate-

ial was added to the aqueous multi-component solution andncubated for 24 h at room temperature (batch method). Thisqueous solution was analyzed by reverse phase HPLC. Fig. 5(a)nd (b) shows the chromatogram in the absence and presence

f the DNA–PCD–APTES hybrid material, respectively. When theNA–PCD–APTES hybrid material was added to the aqueous multi-omponent solution, the absorbance of the harmful compoundsecreased. The accumulated amounts of harmful compounds werestimated from the absorbance in the absence and presence of the

Fig. 5. Chromatograms of absence (a) and presence (b) of the DNA–PCD–APTEShybrid material. This chromatogram was measured by HPLC using an Inertsil® ODS-P column with a CH3OH/water (80:20, v/v). The harmful compounds were detectedby the absorbance at 276 nm.

hybrid material. In contrast, we used the DNA–PAA–APTES hybridmaterial without the cyclodextrin for the control.

Fig. 6 shows the accumulated amount of harmful com-pounds from the aqueous multi-components solution. TheDNA–PAA–APTES hybrid material without the cyclodextrin couldaccumulate the planar-structure containing compounds, such asBip and DF (see open bar in Fig. 6). These results were due to theintercalation of the planar-structure containing compounds intodouble-stranded DNA and similar results have been reported forthe UV-irradiated DNA matrix [6] and DNA-immobilized column[6,29]. The non-planar structure containing harmful compounds,such as Bis-A and DES, cannot intercalate into the double-strandedDNA [6,30], and the DNA–PAA–APTES hybrid material did notshow any accumulation. Naphthalene has a planar structure. How-ever, since the aromatic ring of naphthalene is too small tointercalate into the double-stranded DNA, naphthalene cannotinteract with DNA. Therefore, the DNA–PAA–APTES hybrid mate-rial could not accumulate the naphthalene molecule. Next, we

Fig. 6. Accumulated amounts of various harmful compounds by DNA–PAA–APTEShybrid material (open bar) and DNA–PCD–APTES hybrid material (diagonal bar)using the batch method. Solid bar shows the accumulated amount by theDNA–PCD–APTES hybrid filter. Each value represents the mean of three separationdeterminations.

emist

mDacoDhBaccoio

vc0aaNboiDohs

3D

ppttb

otDpnmtmt8ihrta

4

r

[

[

[[[[[[

[[[[

[

[

[

[[

[

[

M. Yamada, S. Tabuchi / Materials Ch

ulated amount of harmful compounds was higher than that ofNA–PAA–APTES hybrid material without the cyclodextrin. Theccumulation of the non-planar- or small aromatic ring-containingompounds is due to encapsulation into the hydrophobic cavityf the CD in the PCD polymer. These results suggested that theNA–PCD–APTES hybrid material could accumulate not only thearmful planar structure-containing compounds, such as DF orip, but also the non-planar structure-containing compounds, suchs Bis-A or DES, from an aqueous multi-component solution. Inontrast, the accumulated amount of harmful planar structure-ontaining compounds, such as DF or Bip, increased by the additionf cyclodextrin (see open and diagonal bars in Fig. 6). This increases due to the encapsulation of DF or Bip into the hydrophobic cavityf the �-CD in PCD polymer [31,32].

On the other hand, we demonstrated the accumulation ofarious harmful compounds at the same concentrations. The con-entrations of Bis-A, DES, NP, Bip, and DF were 0.65 �M, 0.63 �M,.59 �M, 0.53 �M, and 0.72 �M, respectively. The accumulatedmounts of Bis-A, DES, NP, Bip, and DF were 54%, 45%, 56%, 81%,nd 82%, respectively. The accumulated amounts of Bis-A, DES, andP were ca. 50% and corresponded with the result of Fig. 6 (diagonalar) at the differential concentrations. The accumulated amountsf Bip and DF were higher than that of Fig. 6 (diagonal bar). Thiss because that the CD’s cavity, which can encapsulate the Bip andF molecules, increased with the decrease of initial concentrationsf DES and NP. These results suggested that the DNA–PCD–APTESybrid material can accumulate the various harmful compounds iname concentration.

.6. Accumulation of harmful compounds by theNA–PCD–APTES hybrid material-immobilized glass filter

Finally, we demonstrated the accumulation of harmful com-ounds by the DNA–PCD–APTES hybrid filter. This hybrid filter waslaced into the filter holder and the harmful multi-component solu-ion, which contained DF, Bip, Bis-A, DES, and NP, was applied tohe filter by the glass syringe. These solutions were then analyzedy reverse phase HPLC.

The closed bar in Fig. 6 shows the accumulated amountf harmful compounds in an aqueous multi-component solu-ion by the DNA–PCD–APTES hybrid filter. As a result, thisNA–PCD–APTES hybrid filter could accumulate not only thelanar structure-containing compounds, but also the harmfulon-planar structure-containing compounds from an aqueousulti-component solution. In addition, the accumulated amount by

he DNA–PCD–APTES hybrid filter was higher than that of the batchethods (see diagonal bar in Fig. 6). Furthermore, the accumula-

ion of DES was extremely high and this value was approximately5%. This increase of accumulated amount by the filter methods

s due to the increase of the surface area that can contact betweenybrid material and harmful compounds in aqueous solution. Theseesults suggested that the DNA–PCD–APTES hybrid filter is an effec-ive method to accumulate and separate harmful compounds fromn aqueous multi-component solution.

. Conclusion

We prepared a DNA–cyclodextrin (CD)–inorganic hybrid mate-ial by mixing the DNA, CD, and silane coupling reagents, such

[[[

[

ry and Physics 126 (2011) 278–283 283

as 3-aminopropyltriethoxysilane (APTES). This DNA–PCD–APTEShybrid material possessed attractive chemical and physical prop-erties, such as water-stability and tensile strength. Additionally,the DNA–PCD–APTES hybrid material could be immobilized on aglass filter by the coupling reaction to the silanol group in the filter.Furthermore, the DNA–PCD–APTES could effectively accumulatevarious harmful compounds, such as dioxin, polychlorobiphenyl(PCB), and bisphenol A, from an aqueous multi-component solu-tion. Therefore, the DNA–cyclodextrin–silane coupling reagenthybrid material has the potential to be used as an environmentalmaterial for accumulating harmful compounds from experimentaland industrial waste.

Acknowledgements

This work was supported by matching fund subsidy for privateuniversities from MEXT (Ministry of Education, Culture, Sports, Sci-ence and Technology of Japan). Additionally, the part of this workwas supported by Wesco Scientific Promotion Foundation.

References

[1] W. Saenger, Principles of Nucleic Acid Structure, Springer-Verlag, Berlin,1987.

[2] M.J. Waring, Rev. Biochem. 50 (1981) 159–192.[3] X.D. Liu, M. Yamada, M. Matsunaga, N. Nishi, Adv. Polym. Sci. 209 (2007)

149–178.[4] X.D. Liu, H.Y. Diao, N. Nishi, Chem. Soc. Rev. 37 (2008) 2745–2757.[5] M. Yamada, K. Kato, M. Nomizu, N. Sakairi, K. Ohkawa, H. Yamamoto, N. Nishi,

Chem. Eur. J. 8 (2002) 1407–1412.[6] M. Yamada, K. Kato, M. Nomizu, K. Ohkawa, H. Yamamoto, N. Nishi, Environ.

Sci. Technol. 36 (2002) 949–954.[7] M. Yamada, K. Hashimoto, Biomacromolecules 9 (2008) 3341–3345.[8] V.B. Kandimalla, H. Ju, Chem. Eur. J. 12 (2006) 1074–1080.[9] T. Uragami, T. Katayama, T. Miyata, H. Tamura, T. Shiraiwa, A. Higuchi,

Biomacromolecules 5 (2004) 1567–1574.10] Z.J. Wang, Y. Yang, J. Li, J. Gong, G. Shen, R. Yu, Talanta 69 (2006) 686–

690.11] I. Honma, H. Nakajima, O. Nishikawa, T. Sugimoto, S. Nomura, Solid State Ionics

162–163 (2003) 237–245.12] T. Coradin, J. Livage, Acc. Chem. Res. 40 (2007) 819–826.13] I. Gill, A. Ballesteros, Trends Biotechnol. 18 (2000) 282–296.14] I. Gill, A. Ballesteros, Trends Biotechnol. 18 (2000) 469–479.15] S. Satoh, B. Fugetsu, M. Nomizu, N. Nishi, Polym. J. 37 (2005) 94–101.16] K. Takahashi, K. Hattori, F. Toda, Tetrahedron Lett. 25 (1984) 3331–3334.17] N. Ito, N. Yoshida, K. Ichikawa, J. Chem. Soc., Perkin. Trans. 2 (1996) 965–

972.18] M. Hollas, M.A. Chung, J. Adams, J. Phys. Chem. B. 102 (1998) 2947–2953.19] T. Seo, T. Kajihara, T. Iijima, Makromol. Chem. 188 (1987) 2071–2082.20] M. Yamada, H. Aono, Polymer 49 (2008) 4658–4665.21] M.L. Bender, M. Komiyama, Cycrlodextrin Chemistry, Springer-Verlag, Berlin,

1978.22] M. Yamada, M. Yokota, M. Kaya, S. Satoh, B. Jonganurakkun, M. Nomizu, N. Nishi,

Polymer 46 (2005) 10102–10112.23] A. Nishida, H. Yamamoto, N. Nishi, Bull. Chem. Soc. Jpn. 77 (2004) 1783–

1787.24] R.M. Silverstein, F.X. Webster, Spectrometric Identification of Organic Com-

pounds, John Wiley & Sons, New York, 1998.25] M. Banyay, A. Sarkaräslund, Biophys. Chem. 104 (2003) 477–488.26] M. Kawahara, J. Morita, M. Rikukawa, K. Sanui, N. Ogata, Electrochim. Acta 45

(2000) 1395–1398.27] J. Vince, B. Orel, A. Vilcnik, M. Fir, A.S. Vuk, V. Jovanovski, B. Simoncic, Langmuir

22 (2006) 6489–6497.28] E.P. Plueddemann, Silane Coupling Agents, 2nd ed., Plenum Press, New York,

1991.29] M. Yamada, A. Hamai, Anal. Acta Chim. 674 (2009) 249–254.30] P.O.P. Ts’o, P. Lu, Proc. Natl. Acad. Sci. U.S.A. 51 (1964) 17–24.31] P.R. Sainz-Rozas, J.R. Isasi, G. González-Gaitano, J. Photochem. Photobiol. A 173

(2005) 248–257.32] S. Ehsan, S.O. Prasher, W.D. Marshall, Chemosphere 68 (2007) 150–158.