Search PubMed⌕ Search

Biomedical subjects

Henk Schenk

Publications and source records attributed to Henk Schenk.

18 recordsLinked to original sources
PubMed2006

Structures of mono-unsaturated triacylglycerols. I. The beta1 polymorph.

The crystal structures of the beta1 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 (beta1-MOM), 1,3-dipalmitoyl-2-oleoylglycerol (beta1-POP), 1,3-distearoyl-2-oleoylglycerol (beta1-SOS), 1-palmitoyl-2-oleoyl-3-stearoylglycerol (beta1-POS), 1-stearoyl-2-oleoyl-3-arachidoylglycerol (beta1-SOA) and three mixtures: the co-crystallized 1:1 molar mixture of SOS and POP [beta1-SOS/POP (1:1)] and two cocoa butters from Bahia and Ivory Coast, both in their beta-VI (=beta1) polymorph. All eight beta1 structures crystallized in the space group (P2(1)/n) and have two short cell axes (5.44-5.46 and 8.18-8.22 A), as well as a very long b axis (112-135 A). 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 beta1 structures is a step forward towards understanding the mechanism of fat-bloom formation in dark chocolate and has led to a reexamination of the beta2 structural model [see van Mechelen et al. (2006). Acta Cryst. B62, 1131-1138].

Crystallization↗
PubMed2006

Structures of mono-unsaturated triacylglycerols. II. The beta2 polymorph.

An improved crystal structure model has been established for the beta2 polymorph of the symmetric mono-unsaturated triacylglycerol 1,3-distearoyl-2-oleoylglycerol (SOS) and the equivalent beta-V polymorph of Ivory Coast cocoa butter. In addition, the crystal structures of the beta2 polymorphs are reported for the triacylglycerols 1,3-dipalmitoyl-2-oleoylglycerol (POP) and 1-palmitoyl-2-oleoyl-3-stearoylglycerol (POS), which are, together with SOS, the major components of cocoa butter, and that of 1-stearoyl-2-oleoyl-3-arachidoylglycerol (SOA). The existence of beta2-POS and beta2-SOA has not been previously reported in the literature. All structures have been solved from high-resolution laboratory or synchrotron powder diffraction data with the direct-space parallel-tempering program FOX and refined with the Rietveld module of GSAS. All compounds crystallize in similar monoclinic unit cells (Cc) with very long b axes (>127 A). The oleic chains are packed together and sandwiched between saturated chain layers, forming acyl-chain three-packs. An analysis of the beta2 polymorphs and beta1 polymorphs [van Mechelen et al. (2006). Acta Cryst. B62, 1121-1130] shows that they contain the same three-packs and differ only in the symmetry relation between the three-packs. The three-pack build-up provides an explanation of the mechanism of the phase transition that causes the formation of fat bloom on dark chocolate.

Crystallization↗
PubMed2006

High-spin- and low-spin-state structures of [Fe(chloroethyltetrazole)6](ClO4)2 from synchrotron powder diffraction data.

The spin-crossover complex [Fe(teec)(6)](ClO(4))(2) (teec = chloroethyltetrazole) exhibits a 50 % incomplete spin crossover in the temperature range 300-30 K. Time-resolved synchrotron powder diffraction experiments have been carried out to elucidate its structural behavior. We report crystal structure models of this material at 300 K (high spin) and 90 K (low spin), as solved from synchrotron powder diffraction data by using Genetic Algorithm and Parallel Tempering techniques and refined with Rietveld refinement. During short synchrotron powder diffraction experiments (five minutes duration) two distinguishable lattices were observed the quantities of which vary with temperature. The implication of this phenomenon, that is interpreted as a structural phase transition associated with the high-to-low spin crossover, and the structural characteristics of the high-spin and low-spin models are discussed in relation to other compounds showing a similar type of spin-crossover behavior.

Journal Article↗
PubMed2006

Crystal structure of carnidazole form II from synchrotron X-ray powder diffraction: structural comparison with form I, the hydrated form and the low energy conformations in vacuo.

The crystal structure of carnidazole form II, O-methyl [2-(2-methyl-5-nitro-1H-imidazole-1-yl)ethyl]thiocarbamate, has been determined using synchrotron X-ray powder diffraction in combination with simulated annealing and whole profile pattern matching, and refined by the Rietveld method. For structure solution, 12 degrees of freedom were defined: one motion group and six torsions. Form II crystallizes in space group P2(1)/n, Z=4, with unit cell parameters after Rietveld refinement: a=13.915(4), b=8.095(2), c=10.649(3) A, beta=110.83(1) degrees, and V=1121.1(5) A3. The two polymorphic forms, as well as the hydrate, crystallize in the monoclinic space group P2(1)/n having four molecules in the cell. In form II, the molecules are held together by forming two infinite zig-zag chains via hydrogen bonds of the type N--H...N, the same pattern as in form I. A conformational study of carnidazole, at semiempirical PM3 level, was performed using stochastic approaches based on modification of the flexible torsion angles. The values of the torsion angles for the molecules of the two polymorphic forms and the hydrate of carnidazole are compared to those obtained from the conformational search. Form I and form II are enantiotropic polymorphic pairs this agrees with the fact that the two forms are conformational polymorphs.

Calorimetry, Differential Scanning↗
PubMed2005

Low-spin state structure of [Fe(chloroethyltetrazole)6](BF4)2 obtained from synchrotron powder diffraction data.

The complex [Fe(teec)6](BF4)2 (teec = chloroethyltetrazole) shows a two-step complete spin-crossover transition in the temperature range 300-90 K. Time-resolved synchrotron powder diffraction experiments have been carried out in this temperature range, and crystal structure models have been obtained from the powder patterns by using the parallel tempering technique. Of these models, the low-spin state structure at 90 K has been refined completely with Rietveld refinement. Its structural characteristics are discussed in relation to the high-spin state model and other spin-crossover compounds. The complex shows a remarkable anisotropic unit-cell parameter contraction that is dependent on the applied cooling rate. In addition, the possible important implications for the interpretation of spin-crossover behavior in terms of structural changes are discussed.

Journal Article↗
PubMed2005

Structural analysis of a melaminium polyphosphate from X-ray powder diffraction and solid-state NMR data.

The crystal structure of the environmentally friendly flame retardant melaminium polyphosphate (MPoly) (2,4,6-triamino-1,3,5-triazinium x PO(3))(n)was determined by a direct-space global optimization technique from X-ray powder diffraction data. Solid-state NMR was used to corroborate the proposed hydrogen-bonding model and to determine the average degree of polymerization (n > 100). An analysis of the crystal structure of MPoly reveals aspects of molecular geometry and packing that are characteristic for melamine-containing compounds and polyphosphate salts. A comparison of MPoly with the crystal structures of its precursors melaminium orthophosphate (MP) and melaminium dihydrogenpyrophosphate (MPy) provides insight in the mechanism of the endothermic dehydration processes that takes place in the reaction path MP --> MPy --> MPoly. Solid-state NMR characterization of various samples of the same batch showed inhomogeneities in the MPoly composition. Various quantities of orthophosphates were found, which cannot be assigned to be MP.

Journal Article↗
PubMed2005

Structural characterization of [1,4]diazepino[6,5-b]indoles by powder diffraction.

As part of a systematic structural study of potentially pharmacologically active [1,4]diazepino[6,5-b]indoles, the crystal structures of nine compounds have been determined from laboratory powder diffraction data. The investigated compounds are: 2-oxo-1-(4-nitrophenyl)-1,2,3,6-tetrahydro[1,4]diazepino[6,5-b]indole-4-oxide, C(17)H(12)N(4)O(4) (1a); 2-oxo-1-phenyl-1,2,3,6-tetrahydro[1,4]diazepino[6,5-b]indole-4-oxide, C(17)H(13)N(3)O(2) (1b); 2-oxo-1-(4-ethoxyphenyl)-1,2,3,6-tetrahydro[1,4]diazepino[6,5-b]indole-4-oxide, C(19)H(17)N(3)O(3) (1c); 2-oxo-1-(4-chlorophenyl)-1,2,3,6-tetrahydro[1,4]diazepino[6,5-b]indole-4-oxide, C(17)H(12)N(3)O(2)Cl (1d); 2-oxo-1-(4-cyanophenyl)-1,2,3,6-tetrahydro[1,4]diazepino[6,5-b]indole-4-oxide, C(18)H(12)N(4)O(2) (1e); 6-methyl-2-oxo-1-phenyl-1,2,3,6-tetrahydro[1,4]diazepino[6,5-b]indole-4-oxide, C(18)H(15)N(3)O(2) (1f); 2-formyl-3-[N'-(omega-chloracetyl)-N'-(4-nitrophenyl)]aminoindole, C(17)H(12)N(3)O(4)Cl (2a); 2-formyl-3-[N'-(omega-chloracetyl)-N'-(4-nitrophenyl)]aminoindole solvate with toluene (2:1), C(17)H(12)N(3)O(4)Cl.0.5C(7)H(8) (2as); 2-formyl-3-[N'-(omega-chloracetyl)-N'-(4-cyanophenyl)]aminoindole, C(18)H(12)N(3)O(2)Cl (2e). Compounds (1a)-(1f) crystallize in non-centrosymmetric triclinic, monoclinic and orthorhombic space groups. The three-dimensional structures of (1a)-(1e) demonstrate identical intermolecular NH(indole)...O<--N hydrogen bonds, which form linear chains of connected molecules. A comparison of the crystal structures (2a), (2e) and (2as) shows that the solvent used in the re-crystallization of (2a) and (2e), which are intermediates in the synthesis of (1a) and (1e), affects the intermolecular hydrogen-bond formation and, as a result, leads to essentially different yields of the goal products.

Journal Article↗
PubMed2004

Structures of Fe(II) spin-crossover complexes from synchrotron powder-diffraction data.

Crystal structure determination and analysis have been carried out for the two spin-crossover compounds [Fe(teeX)(6)](BF(4))(2) (teeX is haloethyltetrazole; X = I: teei; X = Br: teeb), in both their high-spin (near 300 K) and their low-spin states (T = 90 K), using high-resolution powder-diffraction data collected at the ESRF (Grenoble, France) and SPring8 (Japan) synchrotron radiation facilities. The structures of teei have been solved using various direct-space structure determination techniques (grid search, genetic algorithm and parallel tempering) and refined with the Rietveld method using geometrical restraints. In the case of teeb, a structural model was found but a full refinement was not successful because of the presence of a significant amount of an amorphous component. Analysis of the structures (space group P2(1)/c, Z = 2) and diffraction data, and the absence of phase transitions, show the overall structural similarity of these compounds and lead to the conclusion that the gradual spin-crossovers are likely to be accompanied by small structural changes only.

Journal Article↗
PubMed2004

N-Methylpyridinium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate.

The crystal structure of the title compound, C(6)H(8)N(+).C(8)HN(4)O(2)(-), is characterized by three independent ion pairs (A, B and C) in the asymmetric unit. Each ion pair consists of an anion and a cation, and the three ion pairs have similar geometric parameters. All the anions are arranged as dianion dimers via two N-H.O hydrogen bonds and the dimers form one-dimensional columns parallel to the b axis as a result of pi-pi interactions. The cations are also stacked, in two different ways: one type of stacking consists of alternating A and B cations, while the other type consists of C cations only. Each dianion dimer stack is surrounded by eight stacks of cations and is not connected directly to other dianion stacks.

Journal Article↗
PubMed2003

N,N-dimethylanilinium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate.

In the title compound, C(8)H(12)N(+).C(8)HN(4)O(2)(-), the anion and cation lie on a crystallographic mirror plane and form planar ribbons via N-H...O [N...O = 2.933 (4) A, H...O = 2.01 A and N-H...O = 170 degrees] and N-H...N [N...N = 3.016 (5) A, H...N = 2.15 A and N-H...N = 169 degrees] hydrogen bonds. The ribbons are further linked via weak C-H...O and C-H...N hydrogen bonds. In adjacent planes, anions lie opposite cations; pi-pi interactions (separation a/2 = 3.520 A) exist between the anions and the cations, and stacks are formed, running along the a axis. The cations are disordered over two interpenetrating sites, with occupancies of 0.833 (5) and 0.167 (5).

Journal Article↗
PubMed2003

KHCoP2O7.2H2O: a novel acidic pyrophosphate.

Potassium cobalt hydrogenpyrophosphate dihydrate, KHCoP(2)O(7).2H(2)O, crystallizes in the orthorhombic space group Pnma. This salt is isotypic with KHMP(2)O(7).2H(2)O (M = Mn and Zn). The structure consists of alternating layers, built from HP(2)O(7)(3-) acidic pyrophosphate groups and CoO(6) octahedra, joined by potassium ions and bridging hydrogen bonds. The Co, K and water O atoms lie on mirror planes. The pyrophosphate group consists of two symmetry-related PO(4) groups, with the bridging O atom on a mirror plane.

Journal Article↗
PubMed2002

Crystal structure of the inclusion complex of beta-cyclodextrin with mefenamic acid from high-resolution synchrotron powder-diffraction data in combination with molecular-mechanics calculations.

The crystal structure of the inclusion complex of beta-cyclo-dextrin with mefenamic acid has been determined from a combination of high-resolution synchrotron powder-diffraction data and molecular-mechanics calculations. A grid search indicates two possible solutions, which are corroborated by molecular-mechanics calculations, while Rietveld-refinement results suggest the crystal structure that is more likely to be formed in the solid state. Mefenamic acid is partially included in beta-cyclodextrin with either the xylyl or the benzoic-acid moiety being inside its cavity. In both solutions mefenamic acid and beta-cyclodextrin form a monomeric complex in a herringbone packing scheme.

Journal Article↗
PubMed2002

Lead tartrate from X-ray powder diffraction data.

The structure of lead tartrate, Pb(2+).C(4)H(4)O(6)(2-), has been solved from X-ray powder diffraction data. The cation exhibits ninefold coordination and the tartrate groups are linked through Pb.O contacts to form a three-dimensional network.

Journal Article↗
PubMed2002

Novel selective phosphodiesterase (PDE4) inhibitors. 4. Resolution, absolute configuration, and PDE4 inhibitory activity of cis-tetra- and cis-hexahydrophthalazinones.

Recently, we reported that 4-catechol-substituted cis-(+/-)-4a,5,6,7,8,8a-hexa- and cis-(+/-)-4a,5,8,8a-tetrahydro-2H-phthalazin-1-ones show potent inhibition of phosphodiesterase (PDE4) activity, while the corresponding trans racemic mixtures exhibit only weak to moderate activity. To determine the absolute configuration and PDE4 inhibitory activity of the individual cis-enantiomers, several optically active phthalazinones have been synthesized. The enantiomers of the various gamma-keto acids, used as starting materials, were resolved in a classical way by the formation of diastereomeric salts, and each was converted to optically active phthalazinone in an enantioselective manner. The absolute configuration of the (+)-enantiomer of cis-hexahydrophthalazinone (+)-12 was determined by X-ray crystallography. The carbon atoms at the 4a and 8a positions were found to have the S- and R-configuration, respectively. In the present series of hexa- and tetrahydrophthalazinones, stereoselectivity for PDE4 inhibition is observed; the cis-(+)-enantiomers of the phthalazinones display high inhibitory activity, whereas their (-)-counterparts exhibit only weak to moderate activity. It is likely that all cis-(+)-phthalazinones have a (4aS,8aR)-configuration and vice versa for the cis-(-)-analogues. In the current series, the N-adamantan-2-yl analogue (+)-14 shows the most potent inhibition of PDE4 (pIC(50) = 9.3); the corresponding (-)-enantiomer is 250-fold less active. In addition, the N-substituted tetrahydrophthalazinones under study were investigated for their in vivo antiinflammatory activities by examining the suppression of arachidonic acid (AA) induced mouse ear edema formation. In this assay analogues (+)-14 and (+)-15 were found to be potent antiinflammatory agents showing about 50% inhibition at 30 micromol/kg po.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2002

5,5-Dimethyl-2-[6-methyl-2-(methylsulfanyl)pyrimidin-4-yloxy]-1,3,2-dioxaphosphorinane-2-thione.

The title compound, C(11)H(17)N(2)O(3)PS(2), is a cyclic thiophosphoryl pyrimidine derivative exhibiting insecticidal properties. The crystal structure determination gives evidence for the presence of the thione isomer of the compound. The pyrimidine nucleus is planar and its substituents have small deviations from the least-squares plane. The dioxaphosphorinane ring adopts a chair conformation. The lack of classical hydrogen bonds and the weak intermolecular interactions lead to a 'loose' packing characterized by channels in the structure.

Crystallography, X-Ray↗
PubMed2001

Structure of C15-, C17- and C19-mono-acid beta-triacylglycerols.

The crystal structures of beta-1,2,3-tris(pentadecanoyl)glycerol (beta-C15C15C15), beta-1,2,3-tris(heptadecanoyl)glycerol (beta-C17C17C17) and beta-1,2,3-tris(nonadecanoyl)glycerol (beta-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 beta-1,2,3-tris(tridecanoyl)glycerol (beta-C13C13C13) and the even-numbered mono-acid triacylglycerols, all three odd-numbered monoacid triacylglycerols crystallize in space group P1 with Z = 2 in an asymmetric tuning-fork conformation and have a lateral acyl chain packing resulting in a layered structure.

Journal Article↗