ARTICLE pubs.acs.org/Langmuir
Macroscopic Observations of Molecular Recognition: Discrimination of the Substituted Position on the Naphthyl Group by Polyacrylamide Gel Modified with β-Cyclodextrin Yongtai Zheng,† Akihito Hashidzume,† Yoshinori Takashima,† Hiroyasu Yamaguchi,† and Akira Harada*,†,‡ † ‡
Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Japan Science and Technology Agency (JST), Core Research for Evolutional Science and Technology (CREST), 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
bS Supporting Information ABSTRACT: Macroscopic molecular recognition observations were realized using polyacrylamide-based gels modified with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), 1-naphthylmethyl (1Np), and 2-naphthylmethyl (2Np) moieties, which are denoted as αCD(x)-gel, βCD(x)-gel, 1Np(y)-gel, and 2Np(y)-gel, where x and y indicate the mol % of CD and Np moieties, respectively. The αCD(5)-gel did not adhere to either the 1Np(5)-gel or 2Np(5)-gel, whereas the βCD(5)-gel interacted with both to form alternating or checkered assemblies. Although the difference in the association constants of βCD for the model polymers was small, the βCD(x)-gel successfully discriminated between 1Np(y)-gel and 2Np(y)-gel at the appropriate x and y.
’ INTRODUCTION In biological systems, macroscopic supramolecular assemblies, which sustain living activities, are formed from macromolecules (e.g., nucleic acids, proteins, and polysaccharides) and amphiphiles (e.g., lipids) that assemble hierarchically through molecular recognition based on microscopic interactions.13 On the other hand, the construction of macroscopic assemblies based on microscopic interactions has been a challenge in artificial systems. Although some reports have examined macroscopic assemblies based on macroscopic interactions, for example, capillary effect,46 electrostatic interaction,79 magnetic interaction,1012 and hydrophobic interaction,1316 to the best of our knowledge, macroscopic supramolecular assemblies based on molecular recognition have not been investigated. Cyclodextrins (CDs) are cyclic oligomers with D-(+)-glucopyranose units linked through an α-1,4-glycoside bond. CDs of 6, 7, and 8 glucopyranose units are called α-CD, β-CD, and γ-CD, respectively. CDs are toroidal with a narrower primary hydroxyl and wider secondary hydroxyl sides. The most important features of CDs are their hydrophilic exterior and hydrophobic cavity. CDs recognize hydrophobic compounds by size and shape matching their cavity to form inclusion complexes in aqueous media. Hence, CDs have received considerable interest as a simple molecular recognition motif.1720 Recently, we were the first to demonstrate macroscopic assemblies based on molecular recognition by CDs using relatively simple systems, which consisted of polyacrylamide gels modified with CDs and linear, branched, or cyclic aliphatic moieties.21,22 These studies have indicated that gels possessing α-CD moieties form gel assemblies only with gels possessing r 2011 American Chemical Society
linear aliphatic moieties, but gels possessing β-CD or γ-CD moieties form assemblies only with gels possessing branched or cyclic aliphatic moieties. More recently, we have focused our efforts on aromatic moieties, which are promising systems that can transfer electrons and/or energy based on molecular recognition because they absorb and emit UV and visible light. Herein we report the formation of gel assemblies of polyacrylamide gels possessing α-CD and β-CD (αCD(x)-gel and βCD(x)-gel, respectively, where x denotes the mol % of the CD moiety, Scheme 1) with polyacrylamide gels possessing 1-naphthylmethyl (1Np) and 2-naphthylmethyl (2Np) moieties (1Np(y)gel and 2Np(y)-gel, respectively, where y denotes the mol % of the Np moiety, Scheme 1) at various x and y.
’ EXPERIMENTAL SECTION Measurements. 1H NMR spectra were measured on a JEOL JNMECA500 spectrometer, and chemical shifts were referenced to the solvent (2.49 and 4.79 ppm for DMSO-d6 and D2O, respectively). IR spectra were recorded using a JASCO FT/IR-410 spectrometer. Fluorescence spectra were obtained on a HITACHI F-2500 spectrophotometer using a 1 cm quartz cuvette. The slit widths for both excitation and emission sides were 2.5 nm. Stressstrain curves for gel assemblies were recorded using a Yamaden RE-33005 Rheoner creep meter; each sample (5 10 mm2 in size) was measured at a rate of 0.1 mm/sec at room temperature. Received: July 16, 2011 Revised: September 27, 2011 Published: October 06, 2011 13790
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Langmuir Scheme 1. Chemical Structures of αCD(x)-gel, βCD(x)-gel, 1Np(y)-gel, and 2Np(y)-gel
Materials. 1-Naphthylmethylamine was purchased from SigmaAldrich Co., Ltd. 2-Naphthylmethylamine hydrochloride and acryloyl chloride were purchased from Wako Pure Chemical Industries, Ltd. Triethylamine, acrylamide (AAm), ammonium peroxodisulfate (APS), N,N,N0 N0 -tetramethylethylenediamine (TMEDA), N,N0 -methylenebis(acrylamide) (MBA), dimethyl sulfoxide (DMSO), acetone, methanol, NaHCO3, and NaOH were purchased from Nacalai Tesque, Inc. N,NDimethylformamide (DMF) and tetrahydrofuran (THF) were purified utilizing a Glass Contour solvent dispending system, whereas water was purified by using a Millipore Milli-Q system. Cyclodextrins (α-CD and β-CD), which were purchased from Junsei Chemical Co., Ltd., were recrystallized twice from water prior to use. Other reagents were reagent grade and used without further purification. Preparation of Monomers. N-1-Naphthylmethylacrylamide (A1Np), N-2-naphthylmethylacrylamide (A2Np), mono(6-deoxyacrylamido)-α-cyclodextrin (A6αCD), and mono(6-deoxyacrylamido)-β-cyclodextrin (A6βCD) were prepared by previously reported procedures with slight modification.23,24 a. Preparation of N-1-Naphthylmethylacrylamide (A1Np). To a solution of 1-naphtylmethylamine (630 mg, 4.0 mmol) and triethylamine (665 μL, 4.8 mmol) in THF (35 mL), a solution of acryloyl chloride (378 μL, 4.8 mmol) in THF (5 mL) was added dropwise at 0 °C under an argon atmosphere while stirring. After stirring overnight, the resulting precipitate was removed via filtration. The crude product, which was obtained by evaporating the solvent, was purified by silica gel column chromatography using a mixed solvent of ethyl acetate and hexane (1/3, v/ v). A1Np was obtained as a crystalline product: yield 680 mg, 81%; mp 122123 °C; 1H NMR (500 MHz, DMSO-d6, 30 °C) δ 8.58 (brs, 1H, NH), 8.087.84 (m, 3H, naphthyl), 7.587.43 (m, 4H, naphthyl), 6.29 (dd, J = 17.1 and 10.2 Hz, 1H, vinyl), 6.15 (dd, J = 17.0 and 2.3 Hz, 1H, vinyl), 5.61 (dd, J = 10.1 and 2.3 Hz, 1H, vinyl), 4.80 (d, J = 5.5 Hz, 2H, CH2). Anal. Calcd for C14H13NO: C, 79.59; H, 6.20; N, 6.63. Found: C, 79.54; H, 6.10; N, 6.62.
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b. Preparation of N-2-Naphthylmethylacrylamide (A2Np). To a solution of 2-naphthylmethylamine hydrochloride (775 mg, 4.0 mmol) and acryloyl chloride (630 μL, 8.0 mmol) in DMF (35 mL), a solution of triethylamine (1.66 mL, 12 mmol) in DMF (5 mL) was added dropwise at 0 °C. After stirring overnight, the resulting precipitate was removed via filtration. The crude product, which was obtained by evaporating the solvent, was purified by silica gel column chromatography using a mixed solvent of ethyl acetate and hexane (1/3, v/v). A2Np was produced as a crystalline product: yield 550 mg, 65%: mp 121122 °C; 1H NMR (500 MHz, DMSO-d6, 30 °C) δ 8.67 (brs, 1H, NH), 7.917.85 (m, 3H, naphthyl), 7.75 (s, 1H, naphthyl), 7.527.41 (m, 3H, naphthyl), 6.32 (dd, J = 17.1 and 10.2 Hz, 1H, vinyl), δ 6.15 (dd, J = 17.1 and 2.2 Hz, 1H, vinyl), δ 5.64 (dd, J = 10.2 and 2.2 Hz, 1H, vinyl), δ 4.52 (d, J = 5.5 Hz, 2H, CH2). Anal. Calcd for C14H13NO: C, 79.59; H, 6.20; N, 6.63. Found: C, 79.51; H, 6.13; N, 6.68. c. Preparation of Mono(6-deoxyacrylamido)-α-cyclodextrin (A6αCD). Mono(6-deoxyamino)-α-CD (0.58 g, 0.6 mmol) and NaHCO3 (0.5 g, 6 mmol) were dissolved in water (50 mL), and the pH was adjusted to about 10 using saturated NaOH. Then a solution of acryloyl chloride (90 μL, 1.2 mmol) was added dropwise at 0 °C with vigorous stirring. After 6 h, the reaction mixture was poured into acetone (500 mL) to obtain the crude product as a precipitate. After recovery by filtration, the crude product was dried under vacuum. A6αCD was purified by reversed phase chromatography (DIAION HP-20) using a mixed solvent of methanol and water (1/4, v/v) as the eluent. The product was recovered by lyophilization: yield 330 mg, 54%; mp > 300 °C; 1H NMR (500 MHz, DMSO-d6, 30 °C) δ 8.00 (t, J = 6.0 Hz, 1H, NH), 6.26 (dd, J = 17.0 and 10.2 Hz, 1H, vinyl), 6.01 (dd, J = 17.1 and 2.2 Hz, 1H, vinyl), 5.585.33 (m, 13H, O2,3H of CD and vinyl), 4.894.73 (m, 6H, C1H of CD), 4.574.36 (m, 5H, O6H of CD), 3.823.20 (m, 36H, C26H of CD). Anal. Calcd for C39H63NO30(H2O)3.9: C, 42.73; H, 6.51; N, 1.28. Found: C, 42.72; H, 6.40; N, 1.44. Positive ion MALDITOF-MS: m/z = 1025.3, [M + Na]+ 1046.8, [M + K]+ 1065.3. d. Preparation of Mono(6-deoxyacrylamido)-β-cyclodextrin (A6βCD). Mono(6-deoxyamino)-β-CD (0.68 g, 0.6 mmol) and NaHCO3 (0.5 g, 6 mmol) were dissolved in water (50 mL), and the pH was adjusted to around 10 using saturated NaOH. Then a solution of acryloyl chloride (90 μL, 1.2 mmol) was added dropwise at 0 °C with vigorous stirring. After 6 h, the reaction mixture was poured into acetone (500 mL) to obtain the crude product as a precipitate. After recovery by filtration, the crude product was dried under vacuum. A6βCD was purified by reversed phase chromatography (DIAION HP-20) using a mixed solvent of methanol and water (1/4, v/v) as the eluent. The product was recovered by lyophilization: yield 400 mg, 56%; mp > 300 °C; 1H NMR (500 MHz, DMSO-d6, 30 °C) δ 7.91 (t, J = 5.5 Hz, 1H, NH), 6.27 (dd, J = 17.0 and 10.3 Hz, 1H, vinyl), 6.04 (dd, J = 17.1 and 2.1 Hz, 1H, vinyl), 5.805.60 (m, 14H, O2,3H of CD), 5.54 (dd, 1H, J = 10.2 and 2.1 Hz, vinyl), 4.904.79 (m, 7H, C1H of CD), 4.464.38 (m, 6H, O6H of CD), 3.823.15 (m, 42H, C26H of CD). Anal. Calcd for C45H73NO35(H2O)5.70: C, 41.87; H, 6.59; N, 1.09. Found: C, 41.84; H, 6.39; N, 1.24. Positive ion MALDI-TOFMS: m/z = 1187.4, [M + Na]+ 1211.5, [M + K]+ 1229.1. Preparation of Model Polymers. The model polymers, i.e., polyacrylamide modified with 1 mol % 1Np and 2Np moieties, were prepared by conventional radical copolymerization. A predetermined amount of AAm and a naphthyl monomer (A1Np or A2Np) were dissolved in DMSO. After purging with dry argon for 30 min, APS (3 mg, 13 μmol) was added to the monomer solution. The reaction mixture was placed into a cuvette equipped with a stirrer and sealed. The cuvette was warmed in a 60 °C oil bath overnight. The reaction mixture was poured into an excess of methanol to give a precipitate. The obtained polymer was recovered by filtration and dried under vacuum. Preparation of Guest and Host Gels. Guest and host gels were also prepared by conventional radical terpolymerization. A predetermined amount of AAm, MBA, and a naphthyl monomer (A1Np or 13791
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Scheme 2. Chemical Structure of pAAm/1Np and pAAm/ 2Np
A2Np) were dissolved in DMSO (1.5 mL). After purging with dry argon for 30 min, APS (3 mg, 13 μmol) was added to the monomer solution. The reaction mixture was placed into a 1 cm quartz cuvette and sealed. The cuvette was set into a 60 °C oven for 6 h. The gel was soaked in water for several days to remove DMSO, unreacted monomers, and initiators. 1Np(y)-gel and 2Np(y)-gel were dyed with yellow (food pigment yellow no. 4) and green dyes (cyan no. 1 and yellow no. 4), respectively, by immersing into a solution of the corresponding dye. A predetermined amount of AAm, MBA, and a CD monomer (A6αCD or A6βCD) were dissolved in water (2 mL) in a 1 cm quartz cuvette. After addition of APS (3 mg, 13 μmol) and TMEDA (2.5 μL, 16 μmol), the reaction mixture immediately turned into a gel, which was washed with water to remove unreacted monomers and initiators. αCD(x)-gel and βCD(x)-gel were dyed with blue (Coomassie brilliant blue R-250) and red dyes (food pigment red no. 102), respectively, by immersing into a solution of the corresponding dye. x and y denote the mol % of the CD and Np moieties in the feed, respectively. Elemental analyses confirmed the CD and Np content in the gels.
Figure 1. Steady-state fluorescence spectra for 0.4 g L1 pAAm/1Np (a) and pAAm/2Np (b) at various β-CD concentrations.
’ RESULTS Preparation of Model Polymers and Guest and Host Gels. The model polymers, pAAm/1Np and pAAm/2Np, were prepared by conventional radical copolymerization of AAm and a naphthyl monomer (A1Np or A2Np) in DMSO, a common solvent, using APS as an initiator. The polymers were purified by reprecipitation. The guest gels, 1Np(y)-gel and 2Np(y)-gel, were also prepared by radical terpolymerization of AAm, MBA (a cross-linker), and a naphthyl monomer (A1Np or A2Np) in DMSO using APS as an initiator. The guest gels obtained were soaked in water for several days to remove DMSO, unreacted monomers, and initiators. The host gels, αCD(x)-gel and βCD(x)-gel, were prepared by radical terpolymerization of AAm, MBA, and a CD monomer (A6αCD or A6βCD) in water initiated by a redox pair of APS and TMEDA. The host gels obtained were washed with water to remove unreacted monomers and initiators. The guest and host gels were dyed with conventional dyes for visualization. Interaction of CDs with Model Polymers Possessing Np Moieties. Prior to investigating the interactions of the βCD(x)gel with the 1Np(y)-gel or 2Np(y)-gel, the association constants (K) of the β-CD moiety with polymer-carrying 1Np and 2Np moieties were estimated using model systems. The model systems consisted of native β-CD with soluble polyacrylamides modified with 1 mol % 1Np or 2Np moieties (Scheme 2). Figure 1 shows the steady state fluorescence spectra measured for
Figure 2. I/I0 as a function of [β-CD] for the β-CDpAAm/1Np (square) and β-CDpAAm/2Np systems (circle). Best fitting curves using eq 1 are also drawn.
0.4 g L1 pAAm/1Np and pAAm/2Np at various β-CD concentrations ([β-CD]). The intensity of the fluorescence maxima for pAAm/1Np and pAAm/2Np increased with increasing [βCD], but tended to become saturated at higher [β-CD]. Using these spectra, the ratios (I/I0) of the fluorescence intensities in the presence and absence of β-CD were calculated, and Figure 2 is a plot of the intensities as a function of [β-CD]. For both polymers, I/I0 increased with [β-CD], but became slightly saturated at higher [β-CD]. For both the cases, the BenesiHildebrand plots (data not shown) exhibited linear relationships, suggesting 1:1 complexation of β-CD with the 1Np or 2Np group. Therefore, fitting the plots in Figure 2 with I 1 þ aK½β-CD ¼ I0 1 þ K½β-CD
ð1Þ
where a is a constant provided apparent K values of (1.2 ( 0.5) 102 and (2.7 ( 0.5) 102 M1 for complexation of the β-CD pAAm/1Np and β-CDpAAm/2Np systems, respectively. These association constants indicate that β-CD includes both 13792
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Figure 5. Conceptual illustration for macroscopic molecular recognition of βCD(x)-gel with 1Np(y)-gel and 2Np(y)-gel.
Figure 3. Macroscopic assembly of gels through molecular recognition: βCD(5)-gel and 1Np(5)-gel (a), and βCD(5)-gel and 2Np(5)-gel (b). βCD(5)-gel and 2Np(5)-gel adhere strongly (c).
Figure 4. Pictures for macroscopic discrimination by βCD(1)-gel (pink) between 1Np(5)-gel (yellow) and 2Np(5)-gel (green) (a) and by βCD(5)-gel (red) between 1Np(2)-gel (yellow) and 2Np(2)-gel (green) (b).
1Np and 2Np moieties, but similar to the data reported for ester analogues25,26 β-CD has a slight preference for the 2Np moiety. Macroscopic Observations of the Interaction of CD(x)gels with Np(y)-gels. The interactions of the host gels (i.e., αCD(5)-gel and βCD(5)-gel) with the guest gels (i.e., 1Np(5)gel and 2Np(5)-gel) were first investigated by mixing and shaking gel pieces in water for several minutes. The αCD(5)-gel did not adhere to either 1Np(5)-gel or 2Np(5)-gel (data not shown).
On the other hand, the βCD(5)-gel interacted with both 1Np(5)gel and 2Np(5)-gel to form alternating or checkered assemblies (Figure 3). The entire assembly formed from βCD(5)-gel and 2Np(5)-gel pieces could be picked up with tweezers due to the strong interaction (Figure 3c). The formation of gel assemblies based on inclusion complexes was confirmed by competitive experiments using 1-admantanamine as a competitor because β-CD interacts strongly with 1-adamantanamine.27 In an aqueous solution of 2 mM 1-adamantanamine, βCD(5)-gel did not adhere to either 1Np(5)-gel or 2Np(5)-gel. This observation demonstrates that gel assemblies are not formed when a competitive guest masks the binding site, supporting the hypothesis that inclusion complexes are responsible for the formation of gel assemblies. The noteworthy is that βCD(x)-gel could discriminate between 1Np(y)-gel and 2Np(y)-gel under optimized conditions (Figure 4). For example, after βCD(1)-gel, 1Np(5)-gel, and 2Np(5)-gel pieces were shaken in water for several minutes, the βCD(1)-gel pieces formed a gel assembly with 2Np(5)-gel pieces but not with 1Np(5)-gel pieces (Figure 4a). Similarly, βCD(5)-gel pieces formed a gel assembly with 2Np(2)-gel pieces, but not with 1Np(2)-gel pieces (Figure 4b). Although the difference in the association constants of β-CD for the model polymers, that is, pAAm/1Np and pAAm/2Np, is small (Figure 5), these observations demonstrate that the βCD(x)gel recognizes the substituted position on the naphthyl group. Estimation of the Adhesion Strength of βCD(x)-gels with Np(y)-gels. To investigate semiquantitatively the adhesion strength of the gel samples, the adhesion strengths for gel assemblies of βCD(x)-gel with 1Np(y)-gel and with 2Np(y)gel were evaluated by rupture stressstrain measurements (Tables S1 and S2, Supporting Information). Because the gel samples for these rupture stressstrain measurements were prepared in a 1 cm quartz cuvette, all the gel samples were equally smooth. Thus, the differences in roughness (i.e., smoothness) of the gel surfaces had a negligible effect on these measurements. Figure 6a and b demonstrate the stress at rupture as a function of x at y = 5 mol % and as a function of y at x = 5 mol %, respectively. Figure 6a indicates that the stress at rupture increased with increasing x and had a slight tendency to become 13793
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Figure 6. Stress at rupture as a function of x for the βCD(x)-gel/ 1Np(5)-gel (square) and βCD(x)-gel/2Np(5)-gel systems (circle) (a) and as a function of y for the βCD(5)-gel/1Np(y)-gel (square) and βCD(5)-gel/2Np(y)-gel systems (circle) (b). All gel samples are prepared in a 1 cm quartz cuvette.
Scheme 3. Equilibrium for the Complexation of β-CD Moieties with Np Moieties
Figure 7. Concentration of complex ([β-CD 3 Np]) calculated by eq 2 as a function of x at y = 5 mol % (a) and as a function of y at x = 5 mol % (b): 1Np (dark yellow) and 2Np moieties (green).
respectively). Tables S3 and S4 in the Supporting Information list the concentrations calculated using the amounts of β-CD and Np moieties in the feed and the volumes of the gel in water. The concentration of the β-CD moiety ([β-CD]) is proportional to the mol % content of the β-CD moiety in the feed (x) because βCD(x)-gel samples were prepared in water: ½β-CD ¼ ð1:5 102 Þx
saturated higher x for both 2Np(5)-gel and 1Np(5)-gel. Figure 6b shows that the stress at rupture also increased with increasing y, but plateaued at y g 4 mol % for both 2Np(y)-gel and 1Np(y)-gel.
’ DISCUSSION It is likely that the adhesion strength of the gel samples is proportional to the number of inclusion complexes and the strength sustained by an inclusion complex at the gel interface. Both factors may depend on the stability of the inclusion complex (i.e., the association constant). Assuming that complexation of β-CD moieties with Np moieties is in equilibrium (Scheme 3), the concentration of β-CD/Np complex ([β-CD 3 Np]) can be calculated as ½β-CD 3 Np
¼
1 ½β-CD þ ½Np þ K
ffi sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 2 ½β-CD þ ½Np þ 4½β-CD½Np K 2
ð2Þ where [β-CD] and [Np] denote the concentrations of the β-CD and Np moieties, respectively, and K is the association constant (i.e., 1.2 102 and 2.7 102 M1 for 1Np and 2Np moiety,
ð3Þ
On the other hand, the concentrations of the 1Np and 2Np moieties ([Np]) strongly depend on the swelling ratio in water because 1Np(y)-gel and 2Np(y)-gel samples were prepared using DMSO as a solvent and subsequent replacement of the solvent. In the present study, the swelling ratios for the 1Np(y)gel and 2Np(y)-gel were almost identical for a given y. From the relationship of [Np] with the mol % content of Np in the feed (y) (Figure S1, Supporting Information), it is assumed that [Np] can be calculated as ½Np ¼ ð 9:1 106 Þy4 þ ð1:2 103 Þy3 þ ð 1:6 103 Þy2 þ ð3:8 103 Þy
ð4Þ
Using eqs 24, Figure 7 plots the obtained [β-CD 3 Np] values against x and y. [β-CD 3 Np] increases with increasing x, but has a weak tendency to become saturated at higher x (Figure 7a). Similarly, [β-CD 3 Np] also increases with y, but due to smaller swelling ratios (Table S4, Supporting Information), the Np moieties concentrate a higher y, causing a plateau at y > ca. 4.5 (Figure 7b). It is noteworthy that Figures 6 and 7 display similar tendencies, indicating that the dependencies of the stress at rupture on x and y are explained partly by the equilibrium for complexation of the β-CD moieties with the 1Np and 2Np moieties. Figure 6 differs from Figure 7, because the data points in Figure 6 do not pass through the origin and the variance between the data for 1Np(y)-gel and 2Np(y)-gel is larger. These differences between the figures may be due to variations between 13794
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Langmuir the interactions in homogeneous solutions and on the interface (e.g., cooperativity in the interaction on the interface). As described earlier, the strength sustained by an inclusion complex is an important factor for gel assemblies, but the strength should be further evaluated in the future.
’ CONCLUSION In the present study, we investigated the formation of gel assemblies of CD(x)-gels Np(y)-gels with various x and y. αCD(5)-gel did not adhere to either 1Np(5)-gel or 2Np(5)gel. In contrast, βCD(5)-gel interacted with both to form alternating or checkered assemblies. The formation of gel assemblies based on inclusion complexes was confirmed by competitive experiments using 1-admantanamine. Although the association constants of β-CD for the model polymers were similar, the βCD(x)-gel successfully discriminated between 1Np(y)-gel and 2Np(y)-gel at the appropriate x and y. The adhesion strengths for gel assemblies of βCD(x)-gel with 1Np(y)-gel and with 2Np(y)-gel were evaluated by rupture stress strain measurements; the stress at rupture increased with increasing x and y, but tended to become saturated at higher x and y for both Np(y)-gels. The dependencies of the stress at rupture on x and y were explained partly by the equilibrium for complexation of β-CD moieties with 1Np and 2Np moieties. ’ ASSOCIATED CONTENT
bS
Supporting Information. Additional experimental results. This material is available free of charge via the Internet at http:// pubs.acs.org.
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’ AUTHOR INFORMATION Corresponding Author
*Telephone/Fax: +81-6-6850-5445. E-mail
[email protected]. osaka-u.ac.jp.
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