Thermotropic phase behavior of model membranes composed of phosphatidylcholines containing dl-methyl anteisobranched fatty acids. 1. Differential scanning calorimetric and phosphorus-31 NMR spectroscopic studies

Abstract

The thermotropic phase behavior of aqueous dispersions of nine dl-methyl branched anteisoacylphosphatidylcholines was studied by differential scanning calorimetry and 31P nuclear magnetic resonance spectroscopy. The calorimetric studies demonstrate that these compounds all exhibit a complex phase behavior, consisting of at least two minor, low-enthalpy, gel-state transitions which occur at temperatures just prior to the onset of the gel/liquid-crystalline phase transition. In addition, at still lower temperatures, anteisobranched phosphatidylcholines containing fatty acyl chains with an odd number of carbon atoms show a major, higher enthalpy, gel-state transition, which was assigned to a conversion from a condensed to a more loosely packed gel phase. No such transition was observed for the even-numbered compounds in aqueous dispersion, but when dispersed in aqueous ethylene glycol, a major gel-state transition is clearly discernible for two of the even-numbered phospholipids. The major gel-state transition exhibits heating and cooling hysteresis and is fairly sensitive to the composition of the bulk aqueous phase. 31P NMR spectroscopic studies indicate that the major gel-state transition is accompanied by a considerable change in the mobility of the phosphate head group and that, at temperatures just prior to the onset of the gel/liquid-crystalline phase transition, the mobility of the phosphate head group is comparable to that normally exhibited by the liquid-crystalline state of most other phospholipids. The temperatures at which the gel/liquid-crystalline phase transition occurs and the enthalpy change associated with this process are considerably lower than those of the saturated n-acyl-PC's of comparable acyl chain length.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential scanning calorimetric and powder X-ray diffraction studies on a homologous series of N-acyl-L-alanine esters with matched chains (n = 9-18)

“…7 Similar results were observed earlier with phosphatidylcholines containing ω-tertiary-butyl fatty acyl chains and dl-methyl anteisobranched fatty acyl chains in the hydrated state. 19,20 The H t and S t data for odd and even acyl chain length NAAEs could be fit well to expressions (2) and (3) given below 14 as reported previously with N -acylethanolamines, N -acyldopamines, and Nacylserotonins with even and odd acyl chain lengths, O-acylcholines with even chainlengths as well as N -, O-diacylethanolamines with matched as well as mixed acyl chains. [15][16][17][18][21][22][23] When the transition enthalpies and transition entropies of NAAEs are compared with those corresponding to the single chain amphiphiles derived from L-alanine (N -acyl-L-alnines and L-alanine alkyl esters), 6,7 it is seen that NAAEs exhibit higher values of H t and S t for the solid to liquid transition, which could be attributed to the high molecular weight of the NAAEs.…”

Self-assembly, supramolecular organization, and phase transitions of a homologous series of N-acyl-l-alanines (n=8–20)

“…This observation is rather unusual since for many other homologous series such as long chain fatty acids, hydrocarbons, alcohols, N-acylethanolamines, N-acyldopamines, N-acylserotonins, and N-,O-diacylethanolamines the values of thermodynamic parameters for the odd chain length series are lower as compared to those of the even chain length series [29][30][31][32][33]. However, this type of odd-even alteration was observed earlier with phosphatidylcholines bearing -tertiary-butyl fatty acyl chains and phosphatidylcholines containing dl-methyl anteisobranched fatty acyl chains in the hydrated state [34,35]. The enthalpy and entropy data for NAAs of even and odd acyl chain lengths could be fit well to expressions (2) and (3) [29] given below as observed previously with N-acylethanolamines, Nacyldopamines, and N-acylserotonins with even and odd acyl chain lengths, O-acylcholines with even chain lengths as well as N-,Odiacylethanolamines with matched as well as mixed acyl chains [31][32][33][36][37][38][39].…”

Branched phospholipids render lipid vesicles more susceptible to membrane-active peptides

“…The degree of branching and the position of the branch point influences the main phase transition temperature ( T m ) of hydrated phospholipid vesicles (11–16). Symmetric di-anteiso-branched phosphatidylcholines (PC) with C16 hydrocarbon chains or shorter show a main T m below 0°C, whereas di-ai17PC melts around 10°C.…”