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Crystallization and Polymorphism of 1,3‐Acyl‐Palmitoyl‐ rac ‐Glycerols
Author(s) -
Craven R. John,
Lencki Robert W.
Publication year - 2011
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-011-1769-0
Subject(s) - crystallization , chemistry , glycerol , polymorphism (computer science) , crystallography , molecule , acyl group , myristoylation , stereochemistry , organic chemistry , group (periodic table) , biochemistry , membrane , genotype , gene
Crystallization and melting behavior, small‐angle X‐ray scattering, X‐ray powder diffraction and infra‐red absorbance were measured for nine 1,3‐acyl‐palmitoyl‐ rac ‐glycerols (1,3‐acetoyl‐, ‐butyroyl‐, ‐hexanoyl‐, ‐octanoyl‐, ‐decanoyl‐, ‐lauroyl, ‐myristoyl‐ and ‐oleoyl‐palmitoyl‐ rac ‐glycerol and 1,3‐dipalmitoyl‐glycerol). All but one of the prepared 1,3‐diacylglycerols (1,3‐DAG) were β‐stable with 1,3‐acetoyl‐palmitoyl‐ rac ‐glycerol being the exception (β′‐stable). Small‐angle X‐ray scattering indicates that molecules in β‐tending diacid 1,3‐DAG adopt a herringbone‐type configuration similar to monoacid 1,3‐DAG. In this configuration acyl chains of the same length associate and regular chain‐end matching between terminal methyl groups delineate lamellae. In contrast, molecules in crystalline 1,3‐acetoyl‐palmitoyl‐ rac ‐glycerol are oriented similar to those of 1(3)‐monoacylglycerol. Interestingly, DSC curves indicate five of the nine diacid compounds have meta‐stable forms—suggesting these forms are quite common for diacid 1,3‐DAG. Meta‐stable forms are observed in the melting curve when the difference in length between acyl chains is large (1,3‐acetoyl‐, ‐butyroyl‐ and ‐hexanoyl‐palmitoyl‐ rac ‐glycerol), and in the crystallization curve when the difference is moderate (1,3‐decanoyl‐ and ‐lauroyl‐palmitoyl‐ rac ‐glycerol).