Structure of β-trimyristin and β-tristearin from high-resolution X-ray powder diffraction data (original) (raw)
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Structure of mono-acid even-numbered β-triacylglycerols
Acta Crystallographica Section B Structural Science, 1999
The crystal structure of the β polymorph of tripalmitin (1,2,3-trihexadecanoylglycerol, β-PPP) has been determined by single-crystal X-ray diffraction. The molecules crystallize in space group P1¯ in an asymmetric tuning-fork conformation. This structure and the already-known crystal structures of β-tricaprin (β-CCC) and β-trilaurin (β-LLL) could be matched in an overlap model. Apart from a difference in chain length, the three structures are almost identical. The overlap model can be used to predict the crystal structure of the other members of the C n C n C n -type (n = even) TAG series reasonably accurately. This is demonstrated by predicting the crystal structure for β-trimyristin (β-MMM) and successively comparing the experimental and calculated X-ray powder diagrams.
Structure of C15-, C17- and C19-mono-acid β-triacylglycerols
Acta Crystallographica Section B Structural Science, 2001
The crystal structures of β-1,2,3-tris(pentadecanoyl)glycerol (β-C15C15C15), β-1,2,3-tris(heptadecanoyl)glycerol (β-C17C17C17) and β-1,2,3-tris(nonadecanoyl)glycerol (β-C19C19C19) have been determined from high-resolution X-ray powder diffraction data. Grid search and Rietveld refinement have been used to determine and refine the structures, respectively. As in β-1,2,3-tris(tridecanoyl)glycerol (β-C13C13C13) and the even-numbered mono-acid triacylglycerols, all three odd-numbered monoacid triacylglycerols crystallize in space group P\bar 1 with Z = 2 in an asymmetric tuning-fork conformation and have a lateral acyl chain packing resulting in a layered structure.
CrystEngComm, 2011
The crystal structure of propylthiouracil, a drug used in the treatment of hyperthyroidism, was determined by means of high-resolution synchrotron X-ray powder diffraction data. The Rietveld method was employed to refine the structure. This drug crystallizes in an orthorhombic (Pcab) space group, with unit cell parameters a 1⁄4 28.67338(23) A#, b 1⁄4 11.15287(6) A#, c 1⁄4 10.66821(5) A#, V 1⁄4 3411.59 (4) A#3, Z 1⁄4 16, Z0 1⁄4 2, M 1⁄4 170.23 g mol1, rcalc 1⁄4 1.3258(1) g cm3. The goodness-of-fit and R-factors were, respectively: c2 1⁄4 1.599, RBragg 1⁄4 1.57%, Rwp 1⁄4 8.85% and Rexp 1⁄4 5.53%. Four hydrogen bonds involving the atoms N(6)–H(12)/S(39), N(19)–H(21)/O(41), N(27)–H(33)/S(18) and N(40)–H (42)/O(20) form a network of molecular aggregates in propylthiouracil.
Structural aspects of oligothienyls from X-ray powder diffraction data
Synthetic Metals, 1993
The structures of oligothienyls (T4-T6) has been evinced from x-ray powder diffraction data using the Rietveld full-profile analysis on particularly pure samples , we were able to overcome preferred orientation effects. Both T4 and T6 molecules display no internal symmetry, are planar within 10 ° and present a herringbone arrangement, the angle between mean planes of adjacent molecules ranges from 70°(T4) to 60°(T6). Intra and intermolecular energy minimization is in progress.
Journal of Applied Crystallography
The direct-space methods software Powder Structure Solution Program (PSSP) [Pagola & Stephens (2010). J. Appl. Cryst. 43, 370–376] has been migrated to the Windows OS and the code has been optimized for fast runs. WinPSSP is a user-friendly graphical user interface that allows the input of preliminary crystal structure information, integrated intensities of the reflections and FWHM, the definition of structural parameters and a simulated annealing schedule, and the visualization of the calculated and experimental diffraction data overlaid for each individual solution. The solutions are reported as filename.cif files, which can be used to analyze packing motifs and chemical bonding, and to input the atomic coordinates into the Rietveld analysis software GSAS. WinPSSP performance in straightforward crystal structure determinations has been evaluated using 18 molecular solids with 6–20 degrees of freedom. The free-distribution program as well as multimedia tutorials can be accessed at ...
Structure of CnCn+2Cn-type (n = even) β′triacylglycerols
Acta Crystallographica Section B-structural Science, 2000
The crystal structures of the H phase of CLC (1,3-didecanoyl-2-dodecanoylglycerol) and MPM (1,3-ditetradecanoyl-2-hexadecanoylglycerol) have been determined from single-crystal X-ray diffraction and high-resolution X-ray powder diffraction data, respectively. Both these crystals are orthorhombic with space group Iba2 and Z = 8. The unit-cell parameters of H -CLC are a = 57.368 , b = 22.783 (2) and c = 5.6945 (6) A Ê and the ®nal R value is 0.175. The unit-cell parameters of H -MPM are a = 76.21 (4), b = 22.63 (1) and c = 5.673
Structure determination of riboflavin by synchrotron high-resolution powder X-ray diffraction
Acta Crystallographica Section C Structural Chemistry, 2021
The crystal structure of the stable form of vitamin B2 or riboflavin (C17H20N4O6) was solved using high-resolution powder X-ray diffraction (PXRD). The high-resolution PXRD pattern of riboflavin was recorded at room temperature at the European Synchrotron Radiation Facility (Grenoble, France). The starting structural model was generated using a Monte Carlo simulated annealing method. The final structure was obtained through Rietveld refinement. The positions of the H atoms belonging to hydroxy groups were estimated from computational energy minimizations. The symmetry is orthorhombic with the space group P212121 and the following lattice parameters: a = 20.01308, b = 15.07337 and c = 5.31565 Å.
Journal of Organometallic Chemistry, 2001
The crystal structures of orthorhombic and monoclinic diethyltin bis(1,3-dithiole-2-thione-4,5-dithiolate), [Et 2 Sn(dmit)], ortho-3 and mono-3, and dimethyltin bis(1,3-dithiole-2-thione-4,5-dithiolate) (4) have been determined. Transformation of solid ortho-3 to mono-3 occurs at 139-140°C. Molecules of ortho-3, obtained by recrystallisation from aqueous acetone, and 4, are linked into chains as a result of intermolecular Sn thione S(5) interactions: the tin centres are penta-coordinate with distorted trigonal bipyramidal geometries. The intermolecular, Sn S(5) thione bonds {3.0083(15) A , in ortho-3 at 150 K [3.037(4) at 298 K], and 3.001(2) and 2.960(2) A , in the two independent molecules of 4 at 150 K}, are considerably longer than the primary intramolecular Sn bonds to the dithiolato S atoms [between 2.440(3) and 2.5235(15) A , ]. The two independent molecules of mono-3, obtained from aqueous methanol, have quite different arrangements: tin atoms in molecule A form two relatively weak intermolecular Sn thione S bonds, 3.567(2) and 3.620(3) A , , with the formation of sheets, while those in molecule B form one similar bond, Sn S= 3.555(2) A , to give chains, with a much longer contact, Sn•••S =3.927(2) A , to another chain. The latter is only ca. 0.12 A , less than the van der Waals radii sum for Sn and S. Sulfur-sulfur contacts, within the sum of the van der Waals radii of two S atoms, 3.60 A , , in 3 and 4, not only reinforce the chains but also help to establish 3D networks.
Journal of the American Oil Chemists' Society, 2006
A comprehensive study of the isothermal crystallization kinetics of tripalmitin-tristearin mixtures was carried out using DSC, with data fitted to the Avrami equation. Polymorphs were identified by subsequent melting of samples in the differential scanning calorimeter, with additional confirmatory information obtained from wide-angle X-ray diffraction. It was found that α-, β′-, and β-forms require small (<1.0°C), moderate (3.5-8.5°C), and large (9.0-13.0°C) amounts of subcooling below their respective polymorph melting temperatures for nucleation to occur. Concurrent crystallization of β and β′ polymorphs was not observed. The β polymorphs exhibited sharper heat flow exotherms than β′, due to the higher crystallization driving forces experienced. Analysis of apparent induction times shows that the activation free energy of nucleation for the β-form is significantly higher than for the β′-form. Samples rich in either species crystallized faster (both shorter apparent induction times and sharper peaks) than samples with equivalent compositions. Driving-force arguments do not fully explain this behavior, strongly suggesting that mass transfer resistances (greatest for equivalent compositions) have a significant effect on kinetics. Multiple crystallization events were observed for 50-80% tristearin samples between 56 and 60°C and were attributed to a demixing of tripalmitin-rich and tristearin-rich β phases, in line with established phase diagrams. FIG. 1. DSC thermograms showing isothermal crystallization and melting of (a) pure tripalmitin and (b) pure tristearin. The y-axis scale divisions for crystallization and remelting thermograms are 1.0 and 10 W/g, respectively. 8 W. MACNAUGHTAN ET AL.