Tohru Takenaka

Studies on built-up films by means of the polarized infrared ATR spectrum I.: Built-up films of stearic acid

Abstract The infrared attenuated total reflection (ATR) spectra of molecular layers of stearic acid built upon the germanium plate by the Blodgett method were studied by using the polarized radiations with the electric vectors parallel and perpendicular to the plane of incidence. It is concluded that the built-up films are made of an assembly of crystallites of the monoclinic system, and that the crystallites are oriented so that their crystallographical c-axis may form angles from ca. 27° to 35° with the z-axis (the axis perpendicular to germanium-stearic acid interface) depending upon the number of layers, but at random around the z -axis (uniaxial orientation with respect to the z -axis) irrespective of the direction of withdrawal of the plate in the film preparation. From penetration depth of the totally reflected radiation and changes in reflectivity with the number of layers, the thickness of a single monomolecular layer is estimated to be ca. 23.8 A, showing a good agreement with the values previously proposed by Blodgett and by Muller.

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.

Structural studies of poly-γ-benzyl-l-glutamate monolayers by infrared ATR and transmission spectra

Abstract An apparent plateau region was observed in the surface pressure (F)-area (A) isotherm of poly-γ-benzyl- l -glutamate (PBG) monolayers spread on the water surface from methylene chloride solution. Polarized infrared ATR and transmission studies were made of built-up films of PBG transferred onto a germanium plate from the monolayers compressed at 10 and 5 dyne/cm, which are above and below the plateau surface pressure (8 dyne/cm), respectively. The molecular orientation and relative thickness of the films were quantitatively examined. It was found for the thin layers compressed at both surface pressures that the PBG molecules were in the α-helical conformation and lay flat on the water surface. It was also likely that the molecular chains on the water surface were packed in parallel with each other making a certain angle with the direction of compression. On the preparation of built-up films, the thin layers were transferred onto the germanium plate so that the helix axes formed an angle of ca. 35° with the direction of withdrawal. The built-up films prepared above the plateau surface pressure were found to be almost twice as thick as those prepared below the plateau surface pressure. This result supports Malcolms proposal that the plateau region can be ascribed to a transition process from monolayer to bilayer.

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 ...

Raman study of rotational motion and vibrational dephasing dynamics of NO3 - in molten nitrates

The Raman spectra of the symmetric stretching v 1(A′1) mode of NO3 - ions have been measured in a series of molten nitrates, LiNO3, NaNO3, KNO3, RbNO3, CsNO3, AgNO3, TlNO3, at a temperature 10–20 K above each melting point. Temperature dependence of the Raman spectrum was also measured in molten NaNO3. Reorientation of the symmetry axis of an nitrate ion is represented by the inertial motion of an associated ion cluster for short times and by rotational diffusion for longer times. One observes a point of inflection between two types of rotational motion at 0·2–0·5 ps. The speeds of inertial rotation and rotational diffusion decrease in the order, CsNO3, RbNO3, KNO3, NaNO3, TlNO3, LiNO3, AgNO3. The ratio of the effective moment of inertia obtained from moment analysis to the theoretical moment of inertia for a free NO3 - ion, I/I 0, increases in the same order, from 2·0 for CsNO3 to 20 for AgNO3. The vibrational correlation functions are analysed on the basis of a model of simultaneous homogeneous and inho...

Studies of poly-γ-methyl-l-glutamate monolayers by infrared ATR and transmission spectroscopy and electron microscopy

Abstract Polarized infrared ATR and transmission spectra were studied of built-up films of poly-γ-methyl- l -glutamate (PMLG) transferred onto a germanium plate at 15 and 22 mN·m−1, which are below and above an apparent plateau region, respectively, in the surface pressure (π)-area (A) isotherm. Electron photomicrographs of these films were also obtained by using the folding method, and the film thickness was measured. It was concluded from results of these experiments that the PMLG molecules were in the α-helical conformation and helix axes lay flat on the water surface as condensed ordered arrays forming a certain angle with the compressing direction. The plateau region in the π-A isotherm was ascribed to a transition process from monolayer to bilayer, the molecular conformation as well as orientation being left unchanged.

Molecular vibrational spectra of tetracyanoquinodimethane and tetracyanoquinodimethane-d4 crystals

Abstract The infrared spectra of the TCNQ and TCNQ- d 4 crystals were observed with polarized radiations incident perpendicularly and obliquely upon the sample plane. From the results obtained, the observed bands were experimentally classified into the three infrared-active symmetry species on the assumption of the oriented gas model. The far-infrared spectra and the laser Raman spectra were also obtained for the TCNQ and TCNQ- d 4 samples. An assignment of the observed frequencies to the fundamental modes was made with the aid of the selection rule, the product rule, and the normal coordinate analysis of the in-plane vibrations carried out by using the basic and modified Urey-Bradley force fields. Some of the remaining frequencies were attributed to the overtone or combination vibrations with a good agreement between the calculated and observed values.

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.