Polymorphic transformation of 1,3‐distearoyl‐sn‐2‐linoleoyl‐glycerol

Abstract

Polymorphic transformation behavior of sub-α 1 , sub-α 2 , α, and γ in 1,3-distearoyl-sn-2-linoleoyl-glycerol (SLS) has been studied with X-ray diffraction, differential scanning caloremetry, and Fourier-transform infrared spectroscopy. Synchrotron radiation X-ray beam was employed to observe rapid transformation processes from the sub-α and α forms to the γ form. The chain length structures were double in sub-α 1 , sub-α 2 , and α, whereas γ was of triple chain-length structure. The subcell packing was pseudohexagonal for the two sub-α forms, hexagonal for the α form, and parallel type for the γ form. In comparison with 1,3-distearoyl-sn-2-oleoyl-glycerol (SOS), the occurrence behavior of sub-α, α, and γ of SLS was the same as that of SOS. However, the absence of β' and β was unique for SLS. The chain-chain interactions between the linoleoyl moieties may stabilize the γ form, prohibiting the transformation into β' or β forms. The presence of two cis double bonds may cause this stabilization, revealing the disordered chain conformation of the unsaturated chains.

Effect of unsaturated acyl chains on structural transformations in triacylglycerols

“…This is evidenced in both the results presented here and in the literature, e.g., for pure saturated TAG [4,5], pure unsaturated TAG [7,19], blends of saturated and unsaturated TAG [23,24], mixed saturated/unsaturated TAG [12][13][14] and their complex solutions in natural fats [26,27].…”

“…These peaks, which could be indexed to an orthorhombic unit cell (110, d = 4.13 Å; and 200, d = 3.69 Å), indicate a transformation of the hexagonal subcell into a pseudo-hexagonal subcell with a directional orientation of the zigzag planes of the acyl chains. In analogy with the a-phases, these have to be assigned to a sub-a 2 -phase [12]. Accompanying the transformation of the a 2 -phase into the sub-a 2 -phase there is a decrease of the longitudinal period (from 54.4 to 52.5 Å) and a simultaneous appearance of diffuse scattering peaks observed in the SAXS patterns (peak 1, d ,32 Å; and peak 2, d ,15 Å).…”

“…1a). However, the diffraction peaks observed at the initial stage of crystallization after quenching from the melt for mixed saturated/unsaturated TAG (1,3-distearoyl-2-oleoyl-sn-glycerol (StOSt) [11], 1,3-distearoyl-2-linoleoyl-sn-glycerol (StLSt) [12] and 1,2-dioleoyl-3-stearoyl-rac-glycerol (OOSt) [13]), even corresponding to a long period close to 2L-packing, though slightly longer than would be expected [14], show a completely different set of intensities with a very strong first-order peak and a strong second-order peak. A reconstruction of the electron density distribution along the layer normal leads to a structural model of TAG packing in this phase that is different from both 2L-and 3L-packing, but one that still contains their motives (Fig.…”

Structural models of metastable phases occurring during the crystallization process of saturated/unsaturated triacylglycerols

“…The transient metastable states are restricted to pure TAGs containing both saturated and unsaturated acyl chains (Kodali et al, 1987;Takeuchi et al, 2000;Ueno et al, 1997) or mixtures thereof (Takeuchi et al, 2002) including natural fats such as lard or cocoa butter (Loisel et al, 1998;Riiner, 1970). Thus, to understand polymorphic transformations taking place in TAGs, especially in natural fats, the structures of various unstable phases have to be determined.…”

A mathematical technique for estimating the melting points of triacylglycerols from the component fatty acid melting points

“…However, it should be noted that some anomalous crystallographic behaviors by comprising unsaturated acyl radicals have been reported. The crystal of b-SSO is stabilized in the metastable b' form and not transformed into the most stable b form [10], and another striking fact was that the crystal of b-SLS is stabilized in the unstable g form [11], which was thereafter reinvestigated in further detail and confirmed as is [12]. And a minor change in molecular structure, e.g.…”