Hydrocarbon chain trans-gauche isomerization in phospholipid bilayer gel assemblies

Abstract

The vibrational Raman spectra of dimyristoyl (DMPC)-, dipalmitoyl (DPPC)-, and distearoylphosphatidycholine (DSPC)-water bilayer system were used to probe lipid hydrocarbon chain trans-gauch isomerization dynamics below the gel-liquid crystalline phase transition temperature. In addition to the 1090-1085 cm-1 vibrational transitions, which appear with increasing temperatures and are characteristic of gauche conformers within the acyl chains, a new feature arises in all three bilayer systems at approximately 1122 cm-1. This carbon-carbon stretching mode is associated with the formation of the gauche bond rotation of the terminal methyl group oriented toward the center of the bilayer. Estimates of the enthalpy differences (deltaH) between hydrocarbon chains in an all-trans conformation and chain configurations containing gauche forms may be made from peak height intensities of vibrational features associated with the appropriate rotational isomers. For the DMPC-H2O, DPPC-H2O, and DSPC-H2O assemblies, the Raman data yield enthalpy differences of 2.9 +/- 0.6, 3.4 +/- 0.5, and 9.9 +/- 1.2 kcal/mol, respectively. These values are interpreted to reflect approximately two gauche bonds per lipid molecule for the DMPC-H2O and the DPPC-H2O gels and six gauche bonds per molecule for the DSPC-H2O gels.

On the relationship between the order parameter and the shape of orientation distributions

“…However, several studies by infrared (6,(33)(34)(35), NMR (36,37), and Raman (38, 39) spectroscopy have shown that approximately a 2-7% fraction of gauche conformers is probably already present at temperatures below the transition, accounting for an average of 0.5-1.0 gauche bond per chain. The gauche rotamers are probably located mostly in kinks (gtg') or jogs (gttg') (34,40,41), which are not too disruptive of side-to-side order in the bilayer, or form end-gauche methyl groups (38). Moreover, the insertion of peptides or proteins in membranes can also introduce conformational disorder in the phospholipid acyl chains.…”

Lipid-protein interaction in the glycophorin-dipalmitoylphosphatidylcholine system: Raman spectroscopic investigation

“…The set of vibrational frequencies for gel phase phospholipid hydrocarbon chains is quite distinct from that of liquid crystalline hydrocarbon. The Raman technique has been used to probe phospholipid conformation in one-or two-component lipid systems (10)(11)(12). Although preliminary studies of intact membranes have appeared (13,14), no detailed temperature dependence has been reported for intrinsic membrane proteins reconstituted into single-component lipid systems.…”

Ein Kinkenblock-Modell für die Hauptumwandlung in Phospholipidschichten

“…Die wichtigsten davon sind R6ntgenbeugung [13,14], Differentialkalorimetrie [3], Volumendilatometrie, Kernresonanz-und RamanSpektrometrie [14] und Messungen mit Fluoreszenzsonden [1]. Die Interpretation der experimentellen Resultate wird durch die einfache Unterteilung einer Lipidschicht in die sog.…”

“…Die Bildung dieser thermisch angeregten Rotationsisomere kann direkt mittels Raman-Spektroskopie beobachtet werden [14]. Wie die Schwingungsanalyse der kettenst~indigen CH2-Gruppen mit dieser Methode zeigt, erh6ht sich in Lipiden, deren Alkylketten n = 14, 16 bzw.…”