Swelling behavior of poly(sodium acrylate) gels crosslinked by aluminum ions

The cylindrical poly(sodium acrylate) gel (SA gel) was synthesized in the glass capillary using aluminum ions as the crosslinker. The swelling ratio of the gel was measured after the repeated exchange of solvent (distilled deionized water, about pH 5.8). The gel exhibited two relaxation processes; at first the gel swells rapidly as exchange of water (the swelling process), then shrinks very slowly (the shrinking process). In order to reveal the microscopic structural change (especially, the formation of hydrogen bonding) by water exchange, attenuated total refraction (ATR) Fourier transform infrared (FT-IR) spectroscopy was applied to the gels with different swelling ratio. The IR absorption peaks of the gel were assigned based on those of poly(sodium acrylate) aqueous solutions at different pH. On the swelling process, the carboxyl groups were gradually protonated, and the intermolecular hydrogen bonding started to form in the gel with maximum swelling ratio. On the shrinking process, the formation of hydrogen bonding gradually increased with long-time repeated water exchange which resulted in the shrinkage of the gel. Effects of the repeated water exchange on the swelling behavior were discussed in terms of the exchange of counter ions and the formation of hydrogen bonding.     

Molecular structure of guanine-quartet supramolecular assemblies in a gel-state based on a DFT calculation of infrared and vibrational circular dichroism spectra

The infrared (IR) and vibrational circular dichroism (VCD) spectra of guanosine-5'-hydrazide ( G-1), a powerful hydrogelator, have been measured and analyzed on the basis of ab initio modeling. B3LYP/6-31G** DFT calculations predict that G-1, forming a clear solution in deuterated DMSO, is present in monomeric form in this solvent, whereas strong gelation in a phosphate buffer is due to the formation of a guanine-quartet structure, ( G-1)4, in which the four G-1 are linked by hydrogen-bonded guanine moieties and stabilized by an alkali metal cation. The B3LYP/6-31G** IR and VCD spectra of the nearly planar G-quartet, whose structure is slightly distorted from the C4h symmetry, in which the G-bases interact via four Hoogsteen-type hydrogen bonds and a sodium cation is positioned in the middle of the G-quartet, are in very good agreement with the experimental spectra, indicating that this structure is the predominant structure in the gel state. The geometric parameters are discussed. This study is the first to use IR and VCD spectroscopies coupled with DFT calculations to elucidate the structure of a supramolecular species in a gel state and shows the VCD spectroscopy as a powerful method for investigating the structure of complex supramolecular self-assemblies where the use of other structural methods is limited.     

Hydrogen bonds and molecular complexes in solutions of cellulose nitrate

Intermolecular hydrogen bonds in the systems based on cellulose nitrate and a number of low-molecular solvents were studied by IR spectroscopy. The majority of the systems under study are characterized only by redistribution of intensities of the spectral bands corresponding to the pure polymer accompanied by their minor shift. In this case, acceptors of cellulose nitrate become sterically accessible for the redistribution of hydrogen bonds, and only an insignificant portion of them forms hydrogen bonds with a solvent. New spectral bands in the IR spectra were observed only for solutions containing diethyldiphenyl carbamide, suggesting the formation of a molecular complex. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 484–487, March, 1999.     

Spectroscopic study of the interactions of alkali fluorides with D-xylose.

The interactions of alkali fluorides with D-xylose have been studied by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR, 1H and 13C) and atomic absorption spectrophotometry. KF and CsF form complexes with D-xylose in a 1:1 molar ratio. These complexes can be obtained by solid state milling the reactants in an agate mortar or from methanolic solutions of the sugar and the salt. LiF and NaF do not form complex with D-xylose. IR and XRD prove the identical nature of the complexes obtained by milling and from solution. IR spectra indicate strong perturbation of the OH stretching vibrations with considerable shifts to lower frequencies, which must be caused by strong hydrogen bond formation to the fluorine anion. The perturbations of C-O bond are weak, indicating that cation binding to the oxygen atoms is not the main interaction responsible for the complex formation. 1H NMR spectra of the D-xylose-KF complex dissolved in deuterium oxide is equal to that of pure D-xylose, indicating the destruction of the complex in solution. The complex is stable in DMSO, and 13C spectra of the complex in DMSO-d6 and in solid state (CPMAS) spectra are in accordance with the observed interactions in the IR spectra. As far as we know, this is the first report of a sugar-halide salt complex in which the anion instead of the cation provides the binding forces.     

Intermolecular hydrogen bonding between neutral transition metal hydrides (eta(5)-C5H5)M(CO)3H (M = Mo, W) and bases

The interaction of CpM(CO)3H (M = Mo, W) hydrides as proton donors with different bases (B = pyridine, (n-Oc)3PO, ((CH3)2N)3PO, H3BNEt3) was studied by variable temperature IR spectroscopy and theoretically by DFT/B3LYP calculations. The data obtained show for the first time the formation of intermolecular hydrogen bonds between the neutral transition metal hydrides and bases in solutions of low polarity. These M-H...B hydrogen bonds are shown to precede the hydrides' deprotonation.     

Small-angle neutron-scattering study on a structure of microemulsion mixed with polymer networks

The structure of a microemulsion mixed with polymer networks was investigated by means of small-angle neutron scattering (SANS). The system consists of nonionic surfactant, polymer network, oil, and water. The microemulsion and the polymer network employed in this work are known to undergo temperature-induced structural transition and volume phase transition, respectively. Polymer solutions and gels were made by polymerizing monomer solutions in the presence of microemulsion droplets. In the case of a mixture of an N-isopropylacrylamide (NIPA) monomer solution and a microemulsion, the NIPA monomer was found to behave as a cosurfactant. However, polymerization resulted in a phase separation to polymer-rich and -poor phases. Interestingly, SANS results indicated that a well-developed ordered structure of oil domains was formed in polymer network and the structure was very different from its parent systems. Furthermore, the system underwent two different types of structural transitions with respect to temperature. One was originated from the structural transition of microemulsion due to the change of the spontaneous curvature and the other from the volume phase transition of the NIPA gel.     

甲基氰乙基纤维素／二氯乙酸液晶溶液的红外研究

本文用FTIR研究了甲基氰乙基纤维素/二氯乙酸溶液相转变过程中分子间相互作用的变化。发现溶液中分子之间的相互作用随溶液结构的改变而变化。随着浓度的增大,溶液由各向同性态向各向异性态转变,分子产生有序排列,导致某些氢键被增强或削弱,使基团的红外吸收谱带发生位移。当加热液晶溶液时,各向异性态向各向同性态转变,也使基团的红外吸收谱带位移。     

Nanostructural characterization of the dehydrated (NIPA/SA+additive ion) gels

In the present study, the authors have investigated ion-absorption effects on a nanoscopic structure of a dehydrated N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel.

First of all, the authors compared small-angle X-ray scattering (SAXS) profile of a dehydrated NIPA/SA gel with that dehydrated after absorbing Cu²⁺ ion. Then, in order to examine copper-ion distribution structure in the NIPA/SA gel dehydrated after absorption of copper-ion, an incident-X-ray energy-dependence of a small-angle X-ray scattering profile was observed, in which the anomalous dispersion effect was clearly perceived especially around a distinct SAXS-peak. Because the SAXS-peak is thought to come from a dehydration-induced microphase separation between hydrophilic and hydrophobic network-polymers in the NIPA/SA gel, such a feature indicates that the copper-ions gather in the dehydration-induced hydrophilic domains.

In addition to this interesting copper-ion nanostructure in the dehydrated NIPA/SA gel, a difference in the SAXS-peak position between the dehydrated NIPA/SA gels with and without absorbing the copper-ion has shown a possibility of a controlling method of the nanostructure in relatively gentle conditions without special instruments. Along this line, in order to get further information on the ion-absorption effects on the nanostructure, the authors have compared the SAXS profiles of the several NIPA/SA gels which were dehydrated after absorbing respectively different kinds of ions. In the observation, the SAXS-peak positions have shown characteristic features which are different with the kind of the absorbed ions and found to be classified into several kinds according to the periodic-table group of the absorbed ion.     

Two-dimensional infrared spectroscopy study on phase transition and structural variations of a hydrogen-bonded liquid crystal

Infrared (IR) spectra have been measured for a liquid crystal (LC) consisting of one trans-butene diacid (BD) molecule as a proton donor and two 4-(2,3,4-tridecyloxybenzoyloxy)-4'-stilbazoles (DBS) molecules as a proton acceptor (DBS:BD:DBS) linked together with each other by inter-molecular hydrogen bonds over a temperature range from 20 to 120 degrees C to explore its phase transition and heat-induced structural variations. The temperature-dependent IR spectra have shown that the inter-molecular hydrogen bonds are stable in the liquid crystalline phase but become slightly decoupled with temperature increasing. Two kinds of two-dimensional (2D) correlation spectroscopy, variable-variable (VV) and sample-sample (SS) 2D spectroscopy, have been employed to analyze the observed temperature-dependent spectral variations more efficiently. The SS 2D correlation analysis in the spectral range of 2700-1800 cm(-1) has demonstrated that a change in hydrogen bonds in the LC starts from 40 degrees C, which is not clarified by differential scanning calorimetry (DSC) and conventional IR and Raman spectroscopic analyses. On the other hand, the phase transition of LC revealed by SS 2D spectroscopy in the specific spectral regions of 1750-1650 and 3000-2700 cm(-1) is in a good agreement with that revealed by DSC for the heating process. The VV 2D correlation spectroscopy analysis has provided information about the structural variations of inter-molecular hydrogen bonds. The different species of hydrogen-bonded and free -COOH and -COO- groups in the LC have been clarified by the VV 2D correlation analysis. It has also elucidated the specific order of the temperature-induced structural changes in the intra- and inter-molecular hydrogen bonds concerning with the -COOH and/or -COO- groups in the LC.     

Explanation of Ionic Sequences in Various Phenomena. VI. The Formation and Destruction of Helices in Bovine Plasma Albumin in Neutral and Acidic Solutions

Abstract

The structure of bovine plasma albumin (BPA) was examined by optical rotatory dispersion studies at both low (pH 1.5 and 2.0) and high (pH 9.0) pH values in various aqueous salt solutions. The resulting cationic sequences were compared to those observed by Pedersen for values of the sedimentation constant. At pH 9.0 the destruction of the “helix” produces an acidic sequence. The relative pH position of the “helix” transition, the fact that addition of salt increases the apparent helical content of BPA, and the observed acidic-type of sequence rule out the possibility of (1)ionic bonds between carboxylate and ?-amino groups, (2) hydrophobic bonds, or (3) hydrogen bonds between peptide linkages as major contributing forces in the formation of the helix. The stability of the “helix” in BPA between pH 3.0 and 9.0 must therefore be due to hydrogen bonds between carboxylate ions and hydroxyl groups such as those of serine, threonine, and tyrosine. Repulsive forces between the positively charged groups on BPA strengthen these bonds by preventing the expanded form of BPA from collapsing. At pH 2.0 two types of sequences were observed: The s⁰ _{20, w}, [α]_D and a₀ values gave an acidic-type cationic sequence. The b₀ (helix content), λ_c and [λ]₂₃₃ values gave essentially a nonpolar sequence. The nonpolar or hydrophobic salting-out sequences show that the formation of hydrophobic bonds at pH 2.0 hinders the formation of the helix or folded structure. The acidic sequences show that hydrogen bonds between carboxylic acid groups stabilize both the apparent helix or helices and the intermolecular aggregation of the BPA molecules. From a comparison of the S⁰ ₂₀,w values and the helical content of BPA at pH 9.0 it is also concluded that the formation of these apparent helices or folded structures expands or stiffens the BPA molecule.     

An acetonitrile‐solvated cocrystal of piroxicam and succinic acid with co‐existing zwitterionic and non‐ionized piroxicam molecules

This work reports a new acetonitrile (ACN)‐solvated cocrystal of piroxicam (PRX) and succinic acid (SA), 2C₁₅H₁₃N₃O₄S·0.5C₄H₆O₄·C₂H₃N or PRX:SA:ACN (4:1:2), which adopts the triclinic space group P. The outcome of crystallization from ACN solution can be controlled by varying only the PRX:SA ratio, with a higher PRX:SA ratio in solution unexpectedly favouring a lower stoichiometric ratio in the solid product. In the new solvate, zwitterionic (Z) and non‐ionized (NI) PRX molecules co‐exist in the asymmetric unit. In contrast, the nonsolvated PRX–SA cocrystal contains only NI‐type PRX molecules. The ACN molecule entrapped in PRX–SA·ACN does not form any hydrogen bonds with the surrounding molecules. In the solvated cocrystal, Z‐type molecules form dimers linked by intermolecular N—H…O hydrogen bonds, whereas every pair of NI‐type molecules is linked to SA via N—H…O and O—H…N hydrogen bonds. Thermogravimetry and differential scanning calorimetry suggest that thermal desolvation of the solvate sample occurs at 148 °C, and is followed by recrystallization, presumably of a multicomponent PRX–SA structure. Vibrational spectra (IR and Raman spectroscopy) of PRX–SA·ACN and PRX–SA are also used to demonstrate the ability of spectroscopic techniques to distinguish between NI‐ and Z‐type PRX molecules in the solid state. Hence, vibrational spectroscopy can be used to distinguish the PRX–SA cocrystal and its ACN solvate.     

Effect of amino acid surfactants on phase transition of poly(N-isopropylacrylamide) gel

The volume phase transition behavior of a poly(N-isopropylacrylamide) gel (NIPA gel) in solutions of N-acyl amino acid surfactants were studied as a function of surfactant concentration. The addition of a surfactant beyond the critical micelle concentration (cmc) produced elevation in the transition temperature of the NIPA gel and its swelling. The changes in the volume phase transition temperature and in the swelling of the NIPA gel became more significant with the decreasing size of the amino acid side chain. This result could almost be explained only by the binding amount of surfactant onto the NIPA gel regardless of molecular structure of the amino acid. The binding amount increased in the order of sodium N-lauroyl-glycinate>-alaninate>-valinate>-leucinate>or=-phenylalaninate. For an N-acyl amino acid surfactant to bind onto the NIPA gel, to increase the transition temperature, and to facilitate swelling of the gel, the steric hindrance of the amino acid side chain was more effective than its hydrophobicity.     

pH dependence of the electronic structure of glycine

The carbon, nitrogen, and oxygen K-edge spectra were measured for aqueous solutions of glycine by total electron yield near-edge X-ray absorption fine structure (TEY NEXAFS) spectroscopy. The bulk solution pH was systematically varied while maintaining a constant amino acid concentration. Spectra were assigned through comparisons with both previous studies and ab initio computed spectra of isolated glycine molecules and hydrated glycine clusters. Nitrogen K-edge solution spectra recorded at low and moderate pH are nearly identical to those of solid glycine, whereas basic solution spectra strongly resemble those of the gas phase. The carbon 1s --> pi*(C=O) transition exhibits a 0.2 eV red shift at high pH due to the deprotonation of the amine terminus. This deprotonation also effects a 1.4 eV red shift in the nitrogen K-edge at high pH. Two sharp preedge features at 401.3 and 402.5 eV are also observed at high pH. These resonances, previously observed in the vapor-phase ISEELS spectrum of glycine, have been reassigned as transitions to sigma* bound states. The observation of these peaks indicates that the amine moiety is in an acceptor-only hydrogen bond configuration at high pH. At low pH, the oxygen 1s --> pi*(C=O) transition exhibits a 0.25-eV red shift due to the protonation of the carboxylic acid terminus. These spectral differences indicate that the variations in electronic structure observed in the NEXAFS spectra are determined by the internal charge state and hydration environment of the molecule in solution.     

Electronic and infrared vibrational analysis of cyanidin-quercetin copigment complex

Copigment complex formation between cyanidin and quercetin, in aqueous buffered solutions, was studied by electronic absorption and infrared vibrational spectroscopies. It was found that the association of cyanidin with quercetin occurred at pH 3.0 and pH 5.0 including cyanidin flavylium ion and anhydrobase transformation forms, respectively. Obtained copigmentation constant values of K=2726.7 (pH 3.0) and K=1093.1 (pH 5.0) indicated good association ability of the investigated molecules. Infrared spectra revealed the existence of hydrogen bonds in the copigment complexes structures. The analysis of the deconvoluted infrared spectra indicated several types of hydrogen bonds, differently formed: the H--O...H bonds with the corresponding bands around 3500 cm(-1) and bonds formed via H(3)O(+), oxonium, ion of the molecules with the corresponding bands below 3000 cm(-1).     

Time‐dependent density functional theory study on the electronic excited‐state geometric structure,infrared spectra,and hydrogen bonding of a doubly hydrogen‐bonded complex

The geometric structures and infrared (IR) spectra in the electronically excited state of a novel doubly hydrogen‐bonded complex formed by fluorenone and alcohols, which has been observed by IR spectra in experimental study, are investigated by the time‐dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in both ground state and the S₁ state of this doubly hydrogen‐bonded FN‐2MeOH complex are calculated using the DFT and TDDFT methods, respectively. Two intermolecular hydrogen bonds are formed between FN and methanol molecules in the doubly hydrogen‐bonded FN‐2MeOH complex. Moreover, the formation of the second intermolecular hydrogen bond can make the first intermolecular hydrogen bond become slightly weak. Furthermore, it is confirmed that the spectral shoulder at around 1700 cm^?1 observed in the IR spectra should be assigned as the doubly hydrogen‐bonded FN‐2MeOH complex from our calculated results. The electronic excited‐state hydrogen bonding dynamics is also studied by monitoring some vibraitonal modes related to the formation of hydrogen bonds in different electronic states. As a result, both the two intermolecular hydrogen bonds are significantly strengthened in the S₁ state of the doubly hydrogen‐bonded FN‐2MeOH complex. The hydrogen bond strengthening in the electronically excited state is similar to the previous study on the singly hydrogen‐bonded FN‐MeOH complex and play important role on the photophysics of fluorenone in solutions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Gel-sol transition in gellan aqueous solutions

Gel-sol transition of sodium type gellan solutions with and without salts is studied by dynamic viscoelastic measurements and differential scanning calorimetry (DSC). Mechanical spectra show that gellan aqueous solutions behave as an entangled polymer solution in the concentration range around 2 wt.-% at temperatures >15°C and as a weak gel below this temperature. Concentrated solutions (> 3 wt.-%) show a true gel behavior below 30°C. The two step transition is observed for 2∼3 wt.-% gellan aqueous solutions in thermal scanning rheological (TSR) measurements; the transition at a higher temperature is attributed to a coil-helix transition whilst the transition at a lower temperature is attributed to sol-gel transition. The transition observed in dilute solutions of gellan is attributed to the coil-helix transition whilst the sol-gel transition occurs simultaneously with coil-helix transition in more concentrated solutions (>3 wt.-%). The sol-gel transition temperature shifts to higher temperatures with increasing concentration of the added salts. Junction zones formed in the presence of divalent cations are far more heat resistant than those with monovalent cations judging from both DSC and TSR, however, the possibility of the formation of junction zones by covalent bonds or by ionic bonds is excluded.     

The structure of 2,4,6-tris[di(tert-butoxycarbonyl)methylidene]-hexahydro-1,3,5-triazine

The structure of 2,4,6-tris[di(tert-butoxycarbonyl)methylidene]hexahydro-1,3,5-triazine was studied by quantum chemistry, NMR and IR spectroscopy, and X-ray diffraction. This compound exists exclusively in the hexahydro-1,3,5-triazine form both in solution and in the solid phase, although due to the loss of the aromatization energy, this structure should be less stable than a 1,3,5-triazine structure. The formation of strong intramolecular hydrogen bonds confirmed by NMR and IR spectroscopy and X-ray diffraction data may be a main reason for stabilization of the hexahydro-1,3,5-triazine isomer. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1022–1026, June, 2006.     

Complex formation of boric acids with DI- and TRI- carboxylic acids and poly(vinyl alcohol) in aqueous solutions

Complexation of dihydroxyboryl compounds such as dihydroxyboryl phenylalanine and boric acid with polycarboxylic acids as well as polyols was studied by infrared spectroscopy and zone electrophoresis. By consulting the results obtained, gel formation of poly(vinyl alcohol) (PVA) in aqueous solutions of boric acids (BA) and borax was studied. The IR spectra of aqueous PVA-BA gels indicate that BA mainly assumes a planar triangle form, while the local conformation of PVA in the gel is different from that in aqueous solutions.     

三聚氰胺和环三酮氢键复合物的理论研究

用AM1和PM3方法对三聚氰胺和环三酮衍生物的超分子复合物进行理论研究, 得到稳定化能和相对生成焓; 在AM1优化构型的基础上, 分别用INDO/SCI和AM1方法计算复合物的电子光谱和红外光谱. 结果表明, 两个单体通过氢键形成多聚体, 导致体系能量降低, 单体的电性和位阻差异能改变体系的稳定化能. LUMO-HOMO能隙的减小使电子光谱吸收峰发生红移, 氢键的形成削弱了单体原来的N-H键, 使红外振动频率变小.     

IR spectroscopy investigation of molecular association in the acetone-trichlormethane mixture

A significant increase in the stretching band intensity of trichloromethane in IR spectra of its solutions in acetone with increasing acetone mole fraction indicates the formation of hydrogen bonds between their molecules. The integral absorption coefficient (α) of this vibration is calculated. Experimental values of α are approximated by a theoretical dependence using the nonlinear least-squares method; association parameters are obtained. The relative volume fractions of H-bonded and free trichloromethane molecules are calculated depending on the total trichloromethane volume fraction in solution. The structure of the H-bonded associate is determined by quantum chemical calculations.