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Additional Stabilization (additional + stabilization)

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Chemistry100%

Selected Abstracts

Nucleotide,amino acid interactions in the l -His,IMPˇMeOHˇH2O complex

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2010
Katarzyna, lepokura
In the crystal structure of the methanol-solvated monohydrated complex of l -histidine (His) with inosine 5,-monophosphate (IMP), namely l -histidinium inosine-5,-phosphate methanol solvate monohydrate, C6H10N3O2+ˇC10H12N4O8P,ˇCH3OHˇH2O, most of the interactions between IMP anions (anti/C3,- endo/gauche,gauche conformers) are realized between the riboses and hypoxanthine bases in a trans sugar-edge/sugar-edge geometry, and between the phosphate groups. The base Watson,Crick edge is involved in additional methanol-mediated IMP...MeOH...IMP contacts. Specific and nonspecific nucleotide,amino acid (IMP...His) interactions engage the Hoogsteen edges of the base and phosphate group, respectively. Additional stabilization of His...IMP contacts is provided by ,,, stacking between the imidazolium ring of His and the hypoxanthine base of IMP. The results may indicate the possible recognition mechanism between His and IMP. [source]

Structures of alkyl-substituted Tröger's base derivatives illustrate the importance of Z, for packing in the absence of strong crystal synthons

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2010
Christophe M. L. Vande Velde
Crystal structures of Tröger's base (5,11-methano-2,8-dimethyl-5,6,11,12-tetrahydrodibenzo[b,f][1,5]diazocine) analogues with the methyl groups replaced by ethyl, iso -propyl and tert -butyl groups were studied. The incidence of Z, > 1 structures increases to rather conspicuous levels. The reasons behind this trend are expanded upon, and a possible explanation is given in the flexibility of the alkyl substituents and van der Waals stabilization. In combination these effects allow for an additional stabilization of the packing by small changes in the molecular conformations, thus expanding the size of the asymmetric unit. [source]

Polymorphism of 4-bromobenzophenone

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2007
Mikhail A. Strzhemechny
A combination of single-crystal and powder X-ray diffractometry was used to study the structure of two polymorphs of 4-bromobenzophenone over the temperature range from 100 to 300,K. One of the polymorphs of the title compound was known previously and its structure has been determined at room temperature [Ebbinghaus et al. (1997). Z. Kristallogr.212, 339,340]. Two crystal growth methods were employed, one of which (a modification of the Bridgman,Stockbarger technique) resulted in single crystals of a previously unknown structure. The basic physical properties of the stable polymorph are: growth method, from 2-propanol solutions or gradient sublimation; space group, monoclinic P21/c; melting point, Tm = 355.2,K; X-ray density (at 100,K), Dx = 1.646,g,cm,3. The same properties of the metastable polymorph (triclinic ) are: growth method, modified Bridgman,Stockbarger method; X-ray density (at 100,K), Dx = 1.645,g,cm,3; Tm = 354,K. Thermograms suggest that the melting of the metastable form is accompanied by at least a partial crystallization presumably into the monoclinic form; the transformation is therefore monotropic. Analysis of short distances in both polymorphs shows that numerous weak hydrogen bonds of the C,H,, type ensure additional stabilization within the respective planes normal to the longest dimension of the molecules. The strong temperature dependence of the lattice constants and of the weak bond distances in the monoclinic form suggest that the weak bond interactions might be responsible for both the large thermal expansion within plane bc and the considerable thermal expansion anisotropy. [source]

Variable-Temperature Powder X-ray Diffraction of Aromatic Carboxylic Acid and Carboxamide Cocrystals

CHEMISTRY - AN ASIAN JOURNAL, Issue 4 2007
L. Sreenivas Reddy
Abstract The effect of temperature on the cocrystallization of benzoic acid (BA), pentafluorobenzoic acid (FBA), benzamide (BAm), and pentafluorobenzamide (FBAm) is examined in the solid state. BA and FBA formed a 1:1 complex 1 at ambient temperature by grinding with a mortar and pestle. Grinding FBA and BAm together resulted in partial conversion into the 1:1 adduct 2 at 28,°C and complete transformation into the product cocrystal at 78,°C. Further heating (80,100,°C) and then cooling to room temperature gave a different powder pattern from that of 2. BAm and FBAm hardly reacted at ambient temperature, but they afforded the 1:1 cocrystal 3 by melt cocrystallization at 110,115,°C. Both BA+FBAm (4) and BA+BAm (5) reacted to give new crystalline phases upon heating, but the structures of these products could not be determined owing to a lack of diffraction-quality single crystals. The stronger COOH and CONH2 hydrogen-bonding groups of FBA and FBAm yielded the equimolar cocrystal 6 at room temperature, and heating of these solids to 90,100,°C gave a new crystalline phase. The X-ray crystal structures of 1, 2, 3, and 6 are sustained by the acid,acid/amide,amide homosynthons or acid,amide heterosynthon, with additional stabilization from phenyl,perfluorophenyl stacking in 1 and 3. The temperature required for complete transformation into the cocrystal was monitored by in,situ variable-temperature powder X-ray diffraction (VT-PXRD), and formation of the cocrystal was confirmed by matching the experimental peak profile with the simulated diffraction pattern. The reactivity of H-bonding groups and the temperature for cocrystallization are in good agreement with the donor and acceptor strengths of the COOH and CONH2 groups. It was necessary to determine the exact temperature range for quantitative cocrystallization in each case because excessive heating caused undesirable phase transitions. [source]