Koichi Fukuhara

Conformational analysis of poly(oxyethylene) chain in aqueous solution as a hydrophilic moiety of nonionic surfactants

Abstract Conformational states of poly(oxyethylene) chain in aqueous solution are examined in connection with hydrophilic property of nonionic surfactants. The Raman spectra in various states are analyzed on the basis of comprehensive normal coordinate treatment. The poly(oxyethylene) chain is more ordered in more dilute aqueous solution. This conformational ordering is further promoted by lowering temperature. The ordered structure, which is similar, at least in part, to that in the solid state, is substantiated by the hydrogen bonds making the gauche conformation of the OCH 2 -CH 2 O group more favorable. The hydration has no significant effect on the conformation of the CH 2 O-CH 2 CH 2 group.

Raman spectra of perdeuterated ethylene glycol dimethyl ether and diethylene glycol dimethyl ether and the molecular force field of oxyethylene compounds

Abstract Raman spectra of ethylene glycol dimethyl ether-d 10 and diethylene glycol dimethyl ether-d 14 were measured in the liquid and solid states, and spectral analysis was made on the basis of normal-coordinate treatment. The previous force field for the oxyethylene group was refined in the light of the newly obtained experimental data for these compounds together with those for the undeuterated oligo(oxyethylene) compounds. The present study has demonstrated the importance of the use of experimental data for the deuterated compounds in deriving the molecular force field from the vibrational wave-numbers.

Raman spectroscopic studies of molecular conformation of α-alkyl-ω-alkoxyoligo-(oxyethylene)s: Part I. α-butyl-ω-butoxymono-, bis- and tris(oxyethylene)s

Abstract Raman spectra of α-butyl-ω-butoxymono-, bis- and tris(oxyethylene)s, CH 3 (CH 2 ) 3 (OCH 2 CH 2 ) m O(CH 2 ) 3 CH 3 ( m = 1–3), were measured in the solid state at liquid nitrogen temperature. The molecular conformation of these substances was determined on the basis of a spectral analysis in combination with normal coordinate treatment. The mono(oxyethylene) molecule takes the all- trans extended conformation, while the bis- and tris(oxyethylene) molecules take the repeated trans-gauche-trans helical conformation. The chain-length dependent conformational behavior of the triblock oligomers is explained by a conformational competition between the alkyl and oxyethylene groups which intrinsically favor the extended and the helical conformation, respectively, and the conformation of the molecule is most likely determined by subtle balance of the conformational competence of the respective constituent groups.

Raman spectroscopic study of the conformational equilibria in 18-crown-6 in water: Predominant D3d conformation

Abstract The conformational equilibria in 18-crown-6 in water have been studied by Raman spectroscopy. The Raman bands for aqueous solutions of 18-crown-6 with 20–100 wt% concentrations have been assigned to particular conformational forms or conformational fragments of the crown ring. The spectral changes with varying concentration indicate that the conformational equilibria in 18-crown-6 depend significantly on the composition of the solution. In dilute aqueous solutions, 18-crown-6 molecules predominantly adopt the D 3 d conformation. Conformations other than D 3 d also coexist at low concentrations, although their populations are small. These experimental results are in good agreement with the theoretical prediction by Monte Carlo and molecular dynamics simulations. In the neat liquid and concentrated aqueous solutions, 18-crown-6 molecules adopt diverse conformations.

Normal coordinate analysis and force field of 18-crown-6

Abstract Normal vibrations and force field of 18-crown-6 have been studied in comparison with open-chain poly (oxyethylene). The force field was derived from the Raman and IR wavenumbers for uncomplexed 18-crown-6 and complexes with KSCN, urea and LiSCN·H 2 O, with different ring conformations. The force field for 18-crown-6 has been found to be substantially the same as that to open-chain poly (oxyethylene). The normal coordinate analysis has indicated that the Raman and IR bands of 18-crown-6 are correlated with the local conformation of the ring. The conformation-wavenumber correlations evaluated previously for open-chain poly(oxyethylene) are also applicable to cyclic compounds. The normal modes of the skeletal deformation vibrations of the 18-crown-6 ring are interpreted in terms of the circular mode, the radial mode and the out-of-plane mode in order to descending wavenumber.

Extended oxyethylene chain in triblock compounds α-octyl-ω-octyloxyoligo(oxyethylene)s studied by Raman spectroscopy

Abstract The Raman spectra of α-octyl-ω-octyloxyoligo(oxyethylene)s CH3(CH2)7(OCH2CH2)mO(CH2)7CH3 with m = 1–5 were measured in the crystalline solid state at liquid-nitrogen temperature. The molecular conformation of these triblock compounds was determined by utilizing the conformational key bands previously established and by performing normal coordinate calculations. It is shown that the oxyethylene chain in the central block has an extended structure for the compounds with m = 1 to at least 5, although the intrinsically stable structure of this chain is a helix. A stable extended structure of the oxyethylene chain composed of up to five monomeric units is observed for the first time. The structural characteristics of the triblock compounds show that the conformation of the central oxyethylene chain depends significantly on the length of the adjoining alkyl blocks. The conformational behaviour of the oxyethylene chain is elucidated by the doubled effect of the extended structure of the two long alkyl chains bonded to the oxyethylene chain at the ends.

Characteristic responses of a phospholipid molecular layer to polyols.

Polyols (sugar alcohols) are widely used in foods, pharmaceutical formulations and cosmetics, and therefore it is important to understand their effects on cell membranes and skin. To address this issue, we examined the effect of polyols (1,2-ethanediol (ethylene glycol), 1,3-butanediol, 1,2,3-propanetriol (glycerol), and 1,2,3,4-butanetetraol) on artificial membrane systems (liposomes, monolayers, or dry films) prepared from phospholipid (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)). 1,2-Ethanediol and 1,3-butanediol had little effect on the size of the DMPC liposomes or the surface pressure (π)-surface area (A) isotherm of DMPC monolayers at an air-water interface, whereas 1,2,3-propanetriol or 1,2,3,4-butanetetraol increased both liposome size and surface pressure. Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) and differential scanning calorimetry (DSC) were used to evaluate the interaction between DMPC and polyols. These experimental results suggest that the chemical structure of polyol plays an important role in the characteristic interaction between polyol and DMPC.

Chain-length dependent conformational behaviour of triblock oligomers α-octyl-ω-n-alkoxytetrakis(oxyethylene)s in the solid state studied by Raman spectroscopy☆

Abstract The Raman spectra of triblock oligomers α-octyl-ω-n-alkoxytetrakis(oxyethylene)s, H(CH2)8(OCH2CH2)4O(CH2)nH with n = 2–7, were measured in the solid state, and the conformational behaviour with changing alkyl chain length was examined. The molecular conformations of these compounds were determined by spectral analysis based on normal coordinate calculations. The conformation changes from the extended/helical/extended form to the fully extended form with increasing alkyl chain length (n). The extended structure of the oxyethylene chain is stabilised at n ≥ 3. This experimental finding suggests that the extended structure of the oxyethylene block in the triblock compounds is stabilised by the end alkyl blocks with the length comparable to or longer than that of the oxyethylene block. The results of this study, together with those of previous studies, demonstrate that the conformation of the oxyethylene chain is affected strongly by adjoining alkyl chains.

Raman spectroscopic study of conformational variety of triblock homologous oligomers α-n-alkyl-ω-n-alkoxyoligo(oxyethylene)s in the solid state☆

Abstract The Raman spectra of triblock homologous oligomers α- n -alkyl-ω- n -alkoxyoligo(oxyethylene)s, H(CH 2 ) n (OCH 2 CH 2 ) m O(CH 2 ) n H, with n = 3–7 and m = 1–5, were measured in the solid state, and the molecular conformations of these compounds were determined by spectral analysis based on normal coordinate calculations. The spectral features vary with changing lengths of the oxyethylene and alkyl chains. Some of the compounds exhibit two different spectra depending on the solidification conditions. The conformations of the homologous oligomers are classified roughly into two types; one is a highly extended form and the other is an extended/helical/extended triblock form. The former is relevant to the homologues with longer alkyl chains and a shorter oxyethylene chain. The conformational variety of the triblock oligomers in the solid state is explained by the conformational competition between the alkyl and oxyethylene chains, which implies competition in the local crystallization between the two different chains.

Vibrational spectra, force field and normal modes of 4,13-diaza-18-crown-6

Abstract Raman and IR spectra of uncomplexed 1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (4,13-diaza18-crown-6) have been measured in the solid state. Normal coordinate calculations have been carried out on the C2h conformation of this macrocyclic compound. The force field of the diazacrown ether has been determined by adjusting several important several force constants associated with the imino group, other force constants being constrained, as transferred, to those of 18-crown-6. The vibrational assignments of 4,13-diaza-18-crown-6 are made on the basis of the previous assignments of a KSCN complex of 18-crown-6 with a similar ring conformation and of the results of the normal coordinate calculations. The normal modes of low-wavenumber vibrations are depicted. The lowest two vibrations represent out-of-plane deformations of folding the macrocyclic ring double. These modes are favourable to complexation of the macrocycle with guest. It is likely that these low-wavenumber vibrations are possible paths of the inclusion of the guest by the macrocyclic ring.