Molecular mechanics for phase transition and melting ofn‐alkanes: A spectroscopic study of molecular mobility of solidn‐nonadecane

Infrared spectra of 1 -monopalmitin- or 1-monostearin-water systems in the gel phase

The infrared spectra of 1-monopalmitin- or 1-monostearin-water systems in the gel phase were observed at room temperature. In both systems the infrared intensities of the bands parallel and perpendicular to the paraffin chain are relatively reduced and enhanced, respectively, on going from the crystalline phase to the gel phase. These spectral changes are explained in terms of the interaction among oscillating dipoles, which is sensitive to the morphology change from the three-dimensional crystalline phase to the two-dimensional lipid bilayers. The non-planar lipid bilayers are proposed for the gel phase in monopalmitin-water systems with x > or = 35 (x: wt.% water).

Infrared intensity of 1-monolaurin-water systems in the gel phase

The infrared spectra of 1-monolaurin-water systems, where KSCN is added as the intensity standard, were observed and the infrared intensity of the bands due to acyl groups measured relatively to that of the CN stretching. The infrared intensities of the bands parallel and perpendicular to the paraffin chains decrease and increase, respectively, on going from the crystalline 1 phase to the gel phase, confirming that these intensity changes result from the long-range interaction among oscillating dipoles. The infrared spectra with no CH2 rocking and the splitting of the CH2 rocking are also discussed with the same interaction model.

Infrared intensity and morphology of l-monolaurin-water systems

The infrared spectra for some metastable states in 1-monolaurin water systems were observed at room temperature, where the relative intensity of bands due to paraffin chains changed considerably, especially in the CH2 rockings, which disappear in some cases. It is considered that the spectral changes result from the morphology change on going from the crystal to the liquid crystal, smectic B phase, so-called gel phase, which consists of the lipid bilayers with ordered paraffin chains alternating with water layers. The model for explaining the intensity change is proposed on the basis of the interaction among oscillating dipoles.

Phase transitions of reversed-phase stationary phases. Cause and effects in the mechanism of retention

We provide a somewhat historical perspective on the work that has been accomplished that supports the suggestion of phase transitions in reversed-phase liquid chromatographic bonded phases. In addition to this general review, we consider from both a practical and theoretical viewpoint the implications of such transitions in the rational design of improved reversed-phase separations. Analytical theory and molecular simulation approaches to chromatographic stationary phases and related systems are reviewed. Initial results are presented on the temperature, density and chain length dependences of stationary phase properties. The role of computer simulation in analyzing transition behavior and retention processes is discussed.

The stratum corneum lipid thermotropic phase behavior

The stratum corneum, the outermost layer of mammalian skin, is considered the least permeable skin layer to the diffusion of water and other solutes. It is generally accepted that the intercellular lipid multilayer domain is the diffusional pathway for most lipophilic solutes. Fluidization of the lipid multilayers is believed to result in the loss of barrier properties of the stratum corneum. Current investigations address the lipid thermotropic phase behavior in terms of lipid alkyl chain packing, mobility and conformational order as measured by Fourier transform infrared (FTIR) spectroscopy. A solid-solid phase transition is observed with increased alkyl chain mobility followed by a gel to liquid-crystalline phase transition near 65 degrees C. These results further elucidate the role of lipid fluidity that may contribute to the transport properties of the stratum corneum.