Molecular dynamics simulation of infrared spectra for potassium palmitate B-form crystal

Abstract

The intra- and intermolecular potentials of potassium palmitate B-form crystal were estimated by a normal mode analysis and a molecular dynamics simulation. Based on these potentials, we calculated the time history of the dipolemoment in the nine unit cells (3a×3b) containing 18 molecules and obtained the polarized infrared spectra by a Fourier transformation. The frequencies and the intensities of the intense bands agreed well with the observed ones, and were consistent with the crystal structure.

Vibrational Spectra and Structural Transitions of Potassium Caprate A-Form Crystal

“…The observed infrared and Raman spectra at room temperature are shown in Figures 1, 2, and 3, respectively. Hence, our force field for potassium palmitate B-form crystal 18 was successfully applied to potassium caprate A-form crystal, although the two crystal structures were different especially in the packing form of the alkyl chains. We first discuss the assignments of the bands ascribed to the carboxylate group and then describe the assignments of the alkyl chain briefly.…”

“…[13][14][15] We have made normal-mode analyses and a molecular dynamics simulation concerning the assignments, deducing the structural changes of several potassium soaps. [16][17][18] A similar analysis will be carried out in the present system with high purity over 99%.…”

Ionic Liquid Crystals

“…Ishioka and co-workers investigated the phase transitions of potassium soaps by infrared and Raman spectroscopy. [286][287][288][289][290] A compilation of the thermal and transport data of the alkali metal alkanoates is available. 291 The alkali metal salts of fatty acids are well-known examples of ionic liquid crystals, but it is less wellknown that also the alkali metal salts of short chain alkanoic acids (with less than seven carbon atoms) can form mesophases.…”

Molecular Dynamics Simulation of the Vibrational Spectra of Stearic Acid Monolayers at the Air/Water Interface

“…Thus, for a system consisting of N ‘ atoms, where V is the corresponding potential energy. We use the intramolecular potential function expressed by a set of internal coordinates S t as where S t 's represent the bond stretching, the bend angles, the out-of-plane angles, and the torsion angles.…”

“…The time step was chosen for the convenience of the computational program of the Fourier transformation in the IR spectral simulation described below. The initial values of the translational velocities, the angular momenta of the molecules, and the amplitudes of each normal vibrations were chosen from normal random numbers based on the Maxwell−Boltzmann distribution . The number of the molecules, N , the volume of the unit cell, V , and the temperature, T = 293 K, were always constant in each simulation.…”