Vibrational spectra of crystalline n-paraffins: II. Intermolecular effects

An artificial nose based on a micromechanical cantilever array

Thermoreversible gelation of relatively short n-alkanes and a variety of other organic liquids has been accomplished using low concentrations of long n-alkanes (chain lengths from 24 to 36 carbon atoms) as gelators The stability of the gels is discussed in terms of gelator concentration, gelation temperature, and the duration of time gels persist without bulk phase separation Generally, stability increases with the chain length of the gelator n-Alkanes are structurally the simplest organic gelators possible and their gels with n-alkanes as liquids are the simplest organogels that can be made Their existence demonstrates that London dispersion forces alone can provide colloidal networks whose strength is sufficient to immobilize liquids against the pull of gravity

n-Alkanes Gel n-Alkanes (and Many Other Organic Liquids)

Fourier transform infrared spectroscopy has been used to study the infrared-active acyl chain vibrational modes of fully hydrated multibilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (L-DPPC) over the temperature range 0-55 degrees C. Frequencies, bandwidths, and other spectral parameters were measured as a function of temperature for the methylene scissoring, rocking, and wagging modes, as well as for the C-H stretching modes, and they were used to monitor the packing of the acyl chains. Particular emphasis was placed on determining the nature of the pretransition event. It is shown that between 36 and 38 degrees C the spectral changes are indicative of a phase change in the acyl chain packing from an orthorhombid to a hexagonal subcell. It is also concluded that in the gel phase, at all temperatures below the main transition, the acyl chains are predominantly in all-trans conformations and that the temperature-dependent variations of spectral parameters result from changes in interchain interactions.

Characterization of the pretransition in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine by Fourier transform infrared spectroscopy.

Experiments on the chain melting thermal transition in simple biological membranes are briefly reviewed and shown to indicate that a microscopic order‐disorder model may be appropriate to describe the thermodynamics of the transition. To test this conclusion further a pair of two dimensional lattice models (A and B) are introduced and the statistical mechanics is solved exactly using dimer techniques. The phenomenological parameters required by the models are evaluated from experiments on other systems. The more realistic of the two models (model A) has a second order transition at a temperature of 353°K compared to 315°K for dipalmitoyl‐L‐α‐lecithin membranes. However, the specific heat peaks do not have the same shape and the transition is broader for model A than for the experiment. In comparison, the less realistic model B has a first order transition at 925°K, considerably higher than the experimental transition temperature. From these results it seems likely that the points of disagreement between m...

C. J. Busso

Papers

Properties of Pure Normal Alkanes in the C17 to C36 Range