Acta Crystallographica Section B

Structural Science

Volume 62, Part 6 (December 2006)

research papers

Acta Cryst. (2006). B62, 1121-1130 [ doi:10.1107/S0108768106037074 ]

Structures of mono-unsaturated triacylglycerols. I. The ₁ polymorph

J. B. van Mechelen, R. Peschar and H. Schenk

Abstract: The crystal structures of the [beta] ₁ polymorphs of mono-unsaturated triacylglycerols have been solved from high-resolution laboratory and synchrotron powder diffraction data for five pure compounds, the 1,3-dimyristoyl-2-oleoylglycerol ( [beta] ₁-MOM), 1,3-dipalmitoyl-2-oleoylglycerol ( [beta] ₁-POP), 1,3-distearoyl-2-oleoylglycerol ( [beta] ₁-SOS), 1-palmitoyl-2-oleoyl-3-stearoylglycerol ( [beta] ₁-POS), 1-stearoyl-2-oleoyl-3-arachidoylglycerol ( [beta] ₁-SOA) and three mixtures: the co-crystallized 1:1 molar mixture of SOS and POP [ [beta] ₁-SOS/POP (1:1)] and two cocoa butters from Bahia and Ivory Coast, both in their [beta] -VI (= [beta] ₁) polymorph. All eight [beta] ₁ structures crystallized in the space group (P2₁/n) and have two short cell axes (5.44-5.46 and 8.18-8.22 Å), as well as a very long b axis (112-135 Å). The dominant-zone problem in the indexing of the powder patterns was solved with the special brute-force indexing routine LSQDETC from the POWSIM program. Structures were solved using the direct-space parallel-tempering method FOX and refined with GSAS. Along the b axis, alternations of inversion-centre-related `three-packs' can be discerned. Each `three-pack' has a central oleic zone, with oleic acyl chains of the molecules being packed together, that is sandwiched between two saturated-chain zones. The conformation of the triacylglycerol molecules is relatively `flat' because the least-square planes through the saturated chains and those through the saturated parts of the olein chain are parallel. The solution of the [beta] ₁ structures is a step forward towards understanding the mechanism of fat-bloom formation in dark chocolate and has led to a reexamination of the [beta] ₂ structural model [see van Mechelen et al. (2006). Acta Cryst. B62, 1131-1138].

Keywords: powder diffraction; crystal structure; ₁ polymorph; triacylglycerol; cocoa butter.


	Structure factor file (CIF format) (63.6 kbytes) [ doi:10.1107/S0108768106037074/dr5011MOM-CH1635-B1-EXSOAP_publsup2.hkl ] Contains datablock MOM-CH1635-B1-EXSOAP_publ

	Structure factor file (CIF format) (67.6 kbytes) [ doi:10.1107/S0108768106037074/dr5011POP-B1-CH1630-EXPOSE_publsup4.hkl ] Contains datablock POP-B1-CH1630-EXPOSE_publ

	Structure factor file (CIF format) (79.3 kbytes) [ doi:10.1107/S0108768106037074/dr5011SOS-POP-B1-ENAN_publsup6.hkl ] Contains datablock SOS-POP-B1-ENAN_publ

	Structure factor file (CIF format) (80.7 kbytes) [ doi:10.1107/S0108768106037074/dr5011SOS-B1-SNBL4-ENAN_publsup8.hkl ] Contains datablock SOS-B1-SNBL4-ENAN_publ

	Structure factor file (CIF format) (79.1 kbytes) [ doi:10.1107/S0108768106037074/dr5011POS-B1-ENAN_publsup10.hkl ] Supplementary material

	Structure factor file (CIF format) (59.9 kbytes) [ doi:10.1107/S0108768106037074/dr5011SOA-B1-SNBL3-EXSOSEN_publsup12.hkl ] Supplementary material

	Structure factor file (CIF format) (70.1 kbytes) [ doi:10.1107/S0108768106037074/dr5011BAHIA-B6-CH1635-ENAN_publsup14.hkl ] Supplementary material

	Structure factor file (CIF format) (43.8 kbytes) [ doi:10.1107/S0108768106037074/dr5011IV15-B6-XPERT-STD_publsup16.hkl ] Supplementary material

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