Structural analyses of polymorphic transitions of sn-1, 3-distearoyl-2-oleoylglycerol (SOS) and sn-1, 3-dioleoyl-2-stearoylglycerol (OSO): assessment on steric hindrance of unsaturated and saturated acyl chain interactions.
Polymorphic transformations in two saturated-unsaturated mixed acid triacylglycerols, SOS (sn -1,3-distearoyl-2-oleoylglycerol) and OSO (sn -1,3-dioleoyl-2-stearoylglycerol), have been studied by FT-IR spectroscopy using deuterated specimens in which stearoyl chains are fully deuterated. A reversible phase transition between sub alpha and alpha and a series of irreversible transitions (alpha-->gamma-->beta'-->beta (beta2, beta1) for SOS and alpha-->beta'-->beta for OSO) were studied with an emphasis on the conformational ordering process of stearoyl and oleoyl chains. The alpha-->sub alpha reversible transition was due to the orientational change of stearoyl chains in the lateral directions from the hexagonal subcell to a perpendicularly packed one. As the first stage of the series of irreversible transitions from alpha to beta, the conformational ordering of saturated chains took place in the alpha-->gamma transition of SOS and in the alpha-->beta' transition of OSO; one stearoyl chain in SOS and OSO takes the all-trans conformation and the second stearoyl chain in SOS takes the bent conformation like those observed in the most stable beta-type. As the final stage, the ordering of unsaturated chains occurred in the beta'-->beta transition both for SOS and OSO. A conversion in the layered structure from bilayer to trilayer was also accompanied by the conformational ordering in the alpha-->gamma transition of SOS and in the beta'-->beta transition of OSO.
Yano
J
J
Faculty of Applied Biological Science, Hiroshima University, Higashi-Hiroshima, 739-8528 Japan.
Sato
K
K
Kaneko
F
F
Small
D M
DM
Kodali
D R
DR
D000495:Allosteric Site; D008968:Molecular Conformation; D015394:Molecular Structure; D017550:Spectroscopy, Fourier Transform Infrared; D014280:Triglycerides / Q000737:chemistry*; D014961:X-Ray Diffraction
C117423:1,3-distearoyl-2-oleoylglycerol; D014280:Triglycerides; C057439:1,3-dioleoyl-2-stearoylglycerol