Hiroatsu Matsuura

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.

Conformational properties of short poly(oxyethylene) chains in water studied by IR spectroscopy

Conformational properties of short-chain poly(oxyethylene) (POE) compounds in water have been studied by IR spectroscopy. The compounds examined are CH3(OCH2CH2)mOCH3 (m = 1–4), CH3CH2(OCH2CH2)2OCH2CH3, CH3(OCH2CH2)mOH (m = 2–4), CH3CH2(OCH2CH2)mOH (m = 2 and 3), CH3(CH2)3(OCH2CH2)mOH (m = 2 and 3), H(OCH2CH2)mOH (m = 1–4 and 6), PEG 600 and PEG 2000. The relative intensities of the gauche and trans conformational key bands of the C–C and C–O bonds have been measured with varying solution concentration, and the effects of the chain length and the terminal group on the conformation around the respective bonds have been studied. The relative population of the gauche conformation around the C–C bond increases significantly with increasing water fraction. The rate of increase in the gauche population does not depend practically on the length of the POE chain and the length of the terminal alkyl group as long as it is a butyl or shorter group. The terminal hydroxy group greatly restrains the preference of the gauche conformation around the C–C bond in water. The conformational change of the C–O bond with varying solution concentration is much smaller than that of the C–C bond. The population of the trans conformation around the C–O bond increases only slightly with increasing water fraction for the compounds with alkyl terminals, but no substantial conformational changes are observed for the compounds with hydroxy terminal(s). The conformational behaviour of the C–C bond suggests the presence of several types of hydrogen bonds between the POE chain and water. One is a hydrogen-bonded bridge by a water molecule between the adjacent ether oxygen atoms, and the others are bridges by one or more water molecules between the ether oxygen atoms separated by two oxyethylene units. The restrained gauche preference of the terminal O–CH2–CH2–OH segment may be accounted for by the destabilised hydration structure around the terminal part of the chain. The present results have shown the importance of both the hydrogen bonding and the structural matching between the POE chain and the water in the conformational stabilisation of the POE chain in water.

Importance of an intramolecular 1,5-CH…O interaction and intermolecular interactions as factors determining conformational equilibria in 1,2-dimethoxyethane: a matrix-isolation infrared spectroscopic study

Abstract The infrared spectra of 1,2-dimethoxyethane in an argon matrix have been measured. Spectral analysis based on ab initio molecular orbital calculations and normal coordinate treatment has shown that the conformers TTT, TGT and TGG′ (T: trans, G: gauche) coexist in the matrix, the TTT being the most stable. The experimental conformational stability agrees with the theoretical prediction from the molecular orbital calculations. The stability of the TGG′ conformer is explained by an intramolecular 1,5-CH…O interaction. The stabilization of the TGT conformer in the liquid and crystalline states is shown to be caused by possible intermolecular interactions.

The microwave spectra of deuterated silanes, germanes, and stannanes

Abstract A previous measurement of the rotational spectra of SiH3D, SiH2D2, and SiHD3 has been extended in frequency region to determine rotational constants and quartic centrifugal distortion constants. Similar observations have been performed on GeH3D, GeH2D2, and GeHD3, consisting of five, three, and three Ge isotopes, respectively, and also on SnH3D, SnH2D2, and SnHD3 with seven, three, and three Sn isotopes, respectively. The observed rotational constants were analyzed to estimate the equilibrium internuclear distance for the three molecules.

Conformational stabilities of 1-methoxy-2-(methylthio)ethane and relevant intramolecular CH⋯O interaction studied by matrix-isolation infrared spectroscopy and density functional calculations

Abstract Conformational stabilities of 1-methoxy-2-(methylthio)ethane were studied by matrix-isolation infrared spectroscopy, and the relevant intramolecular 1,5-CH⋯O interaction was examined by density functional calculations. The conformer with trans–trans–gauche± around the CH3O–CH2–CH2–SCH3 bonds is the most stable in an argon matrix and the conformer with trans–gauche±–gauche∓ is the second most stable. The energy difference between the two conformers was determined to be 0.7±0.4 kJ mol −1 using thermal effusive sources. The 1,5-CH⋯O interaction is responsible for the high stability of the trans–gauche±–gauche∓ conformer, since the nonbonded (C)H⋯O distance associated with this interaction is shorter than the corresponding van der Waals separation by 0.15 A. The energy of the 1,5-CH⋯O interaction was evaluated to be 4.0 kJ mol −1 .

Infrared and Raman spectra of N-acetyl-l-amino acid methylamides with aromatic side groups

Abstract Infrared and Raman spectra of N -acetyl- l -phenylalanine methylamide, N -acetyl- l -tyrosine methylamide and N -acetyl- l -tryptophan methylamide, as model compounds of aromatic amino acid residues in proteins, were measured in the solid state and in methanol solutions. Vibrational assignments of the spectra were made by utilizing the deuteration effect and by comparison with the spectra of related compounds which include toluene, p -cresol and 3-methylindole. The amide I, III and IV bands were strong in Raman scattering, but other characteristic amide bands were ill-defined. In the Raman spectra of methanol solutions, only the bands due to the aromatic side group vibrations were markedly observed, but those due to the peptide backbone vibrations were very weak, suggesting the coexistence of various molecular conformations in solution.

The microwave spectra of deuterated silanes: SiH3D, SiH2D2, and SiHD3

Abstract The pure rotational spectrum was measured for the deuterated silanes in the ground vibrational states by microwave spectroscopy. The J = 1 ← 0 transition was observed for each of the 28 Si, 29 Si, and 30 Si species of the two symmetric tops, SiH 3 D and SiHD 3 , whereas 1 R -branch and 19 Q -branch transitions were observed for 28 SiH 2 D 2 and 1 R -branch and 3 Q -branch transitions for each of 29 SiH 2 D 2 and 30 SiH 2 D 2 in the region 100 to 140 GHz, and were analyzed to derive the rotational and the quartic and sextic centrifugal distortion constants. From the observed rotational constants the equilibrium SiH distance was estimated to be 1.4741 A, by taking into account only the third-order anharmonic potential constant of − 12.54 md/A 2 for the SiH stretching coordinate. The intensity of the SiH 2 D 2 spectrum was found to exhibit a rotational dependence, which was qualitatively discussed in terms of centrifugal distortion effects on the dipole moment.

Vibrational spectra and molecular conformation of taurine and its related compounds

Abstract IR and Raman spectra have been measured for taurine (2-aminoethanesulfonic acid) and its sodium salt in the solid state and Raman spectra for aqueous solutions of taurine with different pH values. Normal coordinate treatment has been carried out. The analysis of the spectra has indicated that, in the solid state, the molecule of taurine takes the gauche form while that of the sodium salt takes the trans form, and that the trans and gauche forms coexist in both acidic and basic aqueous solutions. The CS stretching bands for the gauche and trans forms were observed at 742 cm −1 and 803 cm −1 respectively. These bands were applied to a conformational analysis of other compounds containing a taurine skeleton; sodium taurocholate takes the gauche conformation about the bond axis NCCS.

Anomalous conformational behavior of short poly(oxyethylene) chains in water: An FT-IR spectroscopic study

Abstract Conformational behavior of short poly oxyethylene) (POE) chains in water has been studied by FT-IR spectroscopy. The spectra of aqueous solutions of CH 3 (OCH 2 CH 2 ) m OCH 3 with m = 2–6 were measured for various concentrations by using a horizontal ATR accessory. The observed spectra show that, with increasing water fraction, the population of the gauche conformation about the OCCO bond increases, but the direction of the conformational preference is reversed for lower concentrations. The observed maximum of the gauche population is interpreted as a consequence of anomalous enhancement of the gauche population in a specific concentration region. This effect is more significant for shorter POE chains. These observations suggest that there exist some specific interactions, which highly favor the gauche conformation of the OCH 2 CH 2 O segment, for limited composition regions of the binary systems of short POE chains and water.

The vibration-rotation spectrum of C-fluorophosphaethyne FCP: Fermi resonance and harmonic force field

The vibration-rotation bands of all the fundamentals and several overtone and combination vibrations of F12CP have been recorded. The C-F stretching fundamental ν3 was observed in strong Fermi resonance with the overtone 2ν20; a similar resonance was also observed between ν1 + ν3 and ν1 + 2ν10. The spectral analysis gave fundamental wavenumbers: ν1 = 1670.842 (9), ν2 = 375.428 (6), and ν3 = 780.10 (22) cm−1. The value of the equilibrium rotational constant Be was found to be 0.1758943 (81) cm−1. The harmonic force field for this molecule was derived from the wavenumbers of the three fundamentals and the l-doubling constant.