Junzo Umemura

Infrared spectroscopic evidence for the coexistence of two molecular configurations in crystalline fatty acids

Infrared spectra of 14 normal fatty acids have been obtained in the range of temperatures from room temperature to liquid‐helium temperature. Great temperature dependencies are observed in their spectra, especially in the regions of the characteristic frequencies of the carboxyl group, and the band progression of the CH2 wagging modes. Many bands decrease in intensity with decreasing temperature and disappear near liquid‐helium temperature. Close to the positions of these lost bands, alternative bands, which increase in intensity with decreasing temperature, are found. The results support the postulate proposed in our earlier work that the two distinct configurations, cis and trans forms for Cβ–Cα–C=O group, coexist in the crystalline state, and indicate that (1) the cis configuration is the lower energy (enthalpy) form for the odd acids (C3–C11) and for the acids containing four or six carbon atoms; and (2) the trans configuration is the lower energy form for the even‐numbered (C8–C20) carbon series. Dif...

Disappearances of COOH infrared bands of benzoic acid

Infrared spectra of benzoic acid and benzoic acid‐d were obtained in the range of temperatures from liquid nitrogen to liquid helium. The C=O stretching band at 1688 cm−1, the strongest absorption band of this compound in the over‐all infrared region at room temperature, decreases in intensity with decreasing temperature and disappears near liquid‐helium temperatures. Near this temperature, also lost was the band at 959 cm−1 which has been assigned to the OH out‐of‐plane vibration. For the deuterated species both bands at 1689 and 1679 cm−1, which have been interpreted as splitting due to Fermi resonance of the C=O stretching vibration, were lost. Close to the positions of these lost bands, alternative bands, which are assignable to the same modes and increase in intensity with decreasing temperature, are found. The results support the postulate proposed in our earlier work that two distinct equilibrium configurations of benzoic acid dimer coexist in the crystal.

Fourier transform infrared study on the phase transitions of an octadecyltrimethylammonium chloride-water system

Abstract Fourier transform infrared spectroscopy has been used to study thermotropic phase transitions of a 20 g% water-octadecyltrimethylammonium chloride (ODAC) system. In this system, there appear three successive phases of coagel, gel, and liquid crystal with increasing temperature. In the coagel phase, the methylene chains take the trans-zigzag conformation packed in parallel with each other. The hydrophilic part of ODAC is in a fixed state, and the presence of bound water is evident. In the gel phase, the rotational motion of the methylene chain around the chain axis occurs in the hexagonal lattice. The hydrophilic part is in a fused state. The water spectrum becomes similar to that of liquid water. In the liquid crystalline phase, both hydrophobic and hydrophilic parts of ODAC are in fused states. The water spectrum also resembles that of liquid water.

Fourier transform infrared-attenuated total reflection spectroscopy of hydration of dimyristoylphosphatidylcholine multibilayers

The effect of hydration on the structure and molecular orientation of multibilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), cast on a germanium plate, was studied by means of polarized Fourier transform infrared (FT-IR)-attenuated total reflection spectroscopy. Compared with the dry state, the antisymmetric and symmetric CH2 stretching bands of fully hydrated DMPC in the liquid-crystalline state were shifted to the higher frequency side, indicating the increase in the number of the gauche conformers. However, the dichroism of these bands revealed that the hydrocarbon chains of DMPC were still ordered and titled. The absorption bands of the glycerol ester, phosphoryl, and choline groups were broadened upon hydration, suggesting the activation of the librational or torsional motion. Furthermore, the dichroism of the polar head group bands of DMPC indicated that these groups retained a slight orientation even in the fully hydrated and fluid multibilayers.

ORIENTATION STUDIES OF HYDRATED DIPALMITOYLPHOSPHATIDYLCHOLINE MULTIBILAYERS BY POLARIZED FTIR-ATR SPECTROSCOPY

Polarized Fourier-transform infrared-attenuated total reflection spectroscopy has been applied to explore the temperature-dependence of molecular orientations in multibilayers of 1,2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) of various degrees of hydration. The order parameter of the hydrocarbon chain, evaluated from the dichroic ratios of the antisymmetric and symmetric CH2 stretching bands, was drastically decreased at the main (or gel to liquid-crystalline phase) transition temperature (Tm) irrespective of the water content, suggesting that the hydrocarbon chain is in a disordered state as a result of chain-melting associated with an increase in the number of the gauche conformers. On the other hand, the dichroic ratios of the polar bands of hydrated DPPC assignable to the symmetric PO2- stretching and asymmetric N+ (CH3)3 stretching modes were increased mainly at the pretransition temperature (Tp), except for less hydrated case. The dichroic ratios of both the OH stretching and OH2 bending bands of water showed the same temperature-dependence as those of the polar bands. These results indicate that the pretransition is ascribable mainly to the reorientation of the polar groups of the DPPC and bound water, while the main transition is due to the orientational disorder of the hydrocarbon chains. For less hydrated DPPC, the reorientation of the polar groups and water did not occur around Tp, but in the higher temperature region around Tm. This is in accord with the previously reported observation that the pretransition disappears for less hydrated DPPC. In this case, the polar groups and water may reorient following the reorientation of the hydrocarbon chains near Tm.

Raman spectral studies of ionic motion and ionic interaction in aqueous nitrate solutions

The Raman spectra of the totally symmetric ν1(A 1′) mode of an NO3 - ion have been recorded in aqueous LiNO3, NaNO3, KNO3 and NH4NO3 solutions at various concentrations. The vibrational and rotational correlation functions have been calculated from the Fourier transform of the Raman profiles. Reorientation of the symmetry axis of an NO3 - ion in the aqueous solutions may be represented by the inertial motion for short times (t ≲ 0·15 ps, jump angle 17°), and by the rotational diffusion for longer times (t ≳ 0·3 ps). An effective moment of inertia for short times has been found to be I ⊥ = 20 × 10-39 g cm2, which suggests, as compared with the free NO3 - value I ⊥ 0 = 6 × 10-39 g cm2, some association with the surrounding water molecules or cations. The mean-square torque acting on an NO3 - ion from the moment analysis has been found to increase linearly with nitrate concentration. The torque on an NO3 - ion in concentrated nitrate solutions is predominantly from other ions, while the contribution from an ...

Change of molecular configuration in crystalline decanoic acid as studied by infrared spectra and normal coordinate analysis

Infrared spectra of a well‐oriented crystalline film of decanoic acid were obtained in the range from room temperature to liquid‐helium temperature. Many absorption bands due to the carboxyl group and a band progression due to the CH2 wagging modes appear as doublets. In each doublet, one component decreases in intensity with lowering temperature and disappears near liquid‐helium temperature (type I), while another component increases in intensity with lowering temperature (type II). It is confirmed by normal coordinate analysis that the type I and II bands are ascribed to fundamental vibrations of the cis and trans isomers, respectively. The latter isomer would be produced from the former by double proton transfer in the decanoic acid dimer. From the temperature dependence of band intensities, the enthalpy and entropy differences between the two isomers are evaluated to be about 240 cal⋅mol−1 and 3.8 cal⋅mol−1⋅deg−1, respectively.

Non-resonance Raman studies on spread monolayers of stearic acid-d35 and cadmium stearate-d35 on water surfaces and thin LB films

Abstract Non-resonance Raman spectra in the CD stretching region of spread monolayers of stearic acid- d 35 and cadmium stearate- d 35 on water surfaces and of their thin LB films were measured by combining a CCD detector with the total reflection technique. From an analysis of the linewidth of the symmetric CD 2 stretching band, we discuss changes in the lateral packing and conformational disorder of the carbon chains during the process of monolayer compression on the water surface and of monolayer transfer from the water surface to a solid substrate.

Fourier transform infrared-attenuated total reflection spectra of dipalmitoylphosphatidylcholine monomolecular films

Abstract Single monomolecular films of 1,2- dipalmitoyl -3-sn- phosphatidylcholine (DPPC) were transferred onto a germanium plate by the Langmuir-Blodgett technique at various surface pressures encompassing a plateau region in a surface pressure(π)-area( A ) isotherm. Molecular orientation and structure of the monomolecular films were investigated by the Fourier transform infrared-attenuated total reflection spectroscopy. Appreciable changes in frequency and halfbandwidth of the antisymmetric and symmetric CH2 stretching bands of the palmitoyl chains were found at the onset of the plateau region in the π-A isotherm . By analyzing polarized infrared-attenuated total reflection spectra, the palmitoyl chains of DPPC films were proved to be oriented vertically to the germanium surface with all -trans conformation, irrespective of the surface pressure on the film transfer. This finding suggests the existence of islands or surface micelles on the surface throughout the surface pressure examined. The changes in the spectral parameters mentioned above were explained by changes in the state of packing of these islands. The plateau is ascribable to a transition process from a close-packed island phase to a molecularly homogeneous phase.

Negative surface potential produced by self-assembled monolayers of helix peptides oriented vertically to a surface

Abstract Self-assembled monolayers (SAMs) of helix peptides oriented vertically to a gold surface were prepared and the surface potential measured using the Kelvin technique up to 140°C. Negative surface potentials of a few hundred millivolts were observed for the helix peptide SAMs, indicating the occurrence of the large dipole moment of the helices directing toward the surface. The longer the helix peptide, the larger was the negative surface potential obtained. The absolute value of the surface potential decreased with increase in temperature due to thermal perturbation in the helical structure. However, Fourier transform infrared reflection–absorption spectroscopy revealed that perturbation is not significant and the α-helical conformation is stable even at 140°C.