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Organic Crystals (organic + crystal)
Selected AbstractsVibrational, optical and microhardness studies of trimethoprim DL -malateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2009S. Franklin Abstract Trimethoprim malate, an organic crystal, has been synthesized using slow evaporation method from its aqueous solution. Structural, optical and the mechanical properties of the grown crystal have been investigated by various characterization techniques which include FTIR spectra, single crystal XRD, UV-Vis spectra and Vickers microhardness testing. The structure of the compound predicted by analysing the recorded FTIR spectrum compliments the structure determined using single crystal X-ray diffraction. Single crystal X-ray diffraction study reveals that the crystals are monoclinic [P21/c, a=12.9850 Å, b=9.3038 Å, c=15.6815 Å and ,=111.065°]. The UV-Vis spectrum exhibits maximum transparency (98%) for a wide range suggesting the suitability of the title compound for optical applications. The optical constants have been calculated and illustrated graphically. Microhardness tests have been performed on the cystal under study and the Vicker hardness number has been calculated. The work hardening coefficient is found to be 2.85 which suggest that the crystal belongs to the family of soft materials. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Developing 100,ps-resolved X-ray structural analysis capabilities on beamline NW14A at the Photon Factory Advanced RingJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2007Shunsuke Nozawa NW14A is a newly constructed undulator beamline for 100,ps time-resolved X-ray experiments at the Photon Factory Advanced Ring. This beamline was designed to conduct a wide variety of time-resolved X-ray measurements, such as time-resolved diffraction, scattering and X-ray absorption fine structure. Its versatility is allowed by various instruments, including two undulators, three diffractometers, two pulse laser systems and an X-ray chopper. The potential for the detection of structural changes on the 100,ps time scale at NW14A is demonstrated by two examples of photo-induced structural changes in an organic crystal and photodissociation in solution. [source] Modeling the crystallization of proteins and small organic molecules in nanoliter dropsAICHE JOURNAL, Issue 1 2010Richard D. Dombrowski Abstract Drop-based crystallization techniques are used to achieve a high degree of control over crystallization conditions in order to grow high-quality protein crystals for X-ray diffraction or to produce organic crystals with well-controlled size distributions. Simultaneous crystal growth and stochastic nucleation makes it difficult to predict the number and size of crystals that will be produced in a drop-based crystallization process. A mathematical model of crystallization in drops is developed using a Monte Carlo method. The model incorporates key phenomena in drop-based crystallization, including stochastic primary nucleation and growth rate dispersion (GRD) and can predict distributions of the number of crystals per drop and full crystal size distributions (CSD). Key dimensionless parameters are identified to quickly screen for crystallization conditions that are expected to yield a high fraction of drops containing one crystal and a narrow CSD. Using literature correlations for the solubilities, growth, and nucleation rates of lactose and lysozyme, the model is able to predict the experimentally observed crystallization behavior over a wide range of conditions. Model-based strategies for use in the design and optimization of a drop-based crystallization process for producing crystals of well-controlled CSD are identified. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Thermal expansion of organic crystals and precision of calculated crystal density: A survey of Cambridge Crystal DatabaseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2007Changquan Calvin Sun Abstract True density is a physical property of both fundamental and practical importance to the study of pharmaceutical powders. True density may be calculated from crystal structure. However, precision of such calculated density is not well understood. Furthermore, thermal expansion properties of organic crystals have rarely been characterized. A survey of Cambridge Crystal Database is conducted to assess (1) precision of calculated crystal density from crystal structure; (2) thermal expansion properties of organic crystals. It is shown that calculated crystal density exhibits, on average, a relative standard deviation (RSD) of ,0.4%. It is found that crystal density generally increases linearly with decreasing temperature provided no phase change occurs. Slope of the line, termed thermal density gradient, of organic crystals ranges between 0.04 and 1.74 mg,cm,3,K,1 with an average of ,0.2 mg,cm,3,K,1. It is shown that majority polymorph pairs exhibit significantly different thermal expansion behavior and their density,temperature lines can cross. This likely contributes to the less than perfect prediction of relative stability of polymorphs at ambient temperature using the density rule. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1043,1052, 2007 [source] The effect of disorder on the chemical reactivity of an organic solid, tetraglycine methyl ester: Change of the reaction mechanismJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2002Evgenyi Shalaev Abstract Many drugs undergo chemical changes in the solid state, and understanding chemical reactivity of organic crystals is a critical factor in the drug development process. In this report, the impact of milling on the thermal chemical reactivity of an organic solid, tetraglycine methyl ester, was studied using DSC, isothermal calorimetry, chemical analysis (HPLC and insoluble residue determination), and powder X-ray diffraction. Significant changes in both X-ray diffraction patterns and DSC curves were detected after very brief milling (5 s). The changes were interpreted as the formation of a disordered phase. The disordered phase was tentatively identified as a crystal mesophase that combines properties of both crystalline (i.e., long-range order) and amorphous (i.e., glass transition) states. In the disordered material, the reaction mechanism changed from the methyl transfer reaction, which was observed in the intact crystal, to a polycondensation reaction when the reaction was performed at 165°C. Such changes in the reaction mechanism occurred in materials milled for >,30 s. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:584,593, 2002 [source] Structural transformations in organic crystals during photochemical reactionsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2004Ilona Turowska-Tyrk Abstract In the 1980s and 1990s, x-ray studies of the photochemical reaction course in crystals dealt with the analysis of changes in cell constants or movements of atom groups inside molecules. This review presents the results of crystallographic studies on the monitoring of the behaviour of whole molecules in organic crystals during photochemical reactions. Papers on this subject started to appear only a few years ago. The studies showed quantitatively that reactant and product molecules do not take a fixed position in a crystal during the reaction. The product molecules move smoothly to a position assumed in the pure product crystal and the reactant molecules move from a position occupied in the pure reactant crystal. Moreover, with the reaction progress the adjacent reactant molecules gradually come closer and change their mutual orientation to resemble the product. The analysis of the photoreaction kinetics in crystals is also presented. Copyright © 2004 John Wiley & Sons, Ltd. [source] Potassium and ammonium hydrogen phthalates KHC6H4(COO)2 and (NH4)HC6H4(COO)2 , new organic crystals for Raman laser converters with large frequency shiftLASER PHYSICS LETTERS, Issue 7 2009A.A. Kaminskii Abstract Raman-induced many-phonons Stokes and anti-Stokes generation in a orthorhombic crystals KHC6H4(COO)2 and (NH4)HC6H4(COO)2 under picosecond pumping has been observed. All recorded nonlinear lasing lines in the visible and near-IR regions are identified and attributed to the ,(3) -promoting vibration modes of these orthorhombic phthalates. (© 2009 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] The lines-of-force landscape of interactions between molecules in crystals; cohesive versus tolerant and `collateral damage' contactACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Angelo Gavezzotti A quantitative analysis of relative stabilities in organic crystal structures is possible by means of reliable calculations of interaction energies between pairs of molecules. Such calculations have been performed by the PIXEL method for 1108 non-ionic and 98 ionic organic crystals, yielding total energies and separate Coulombic polarization and dispersive contributions. A classification of molecule,molecule interactions emerges based on pair energy and its first derivative, the interaction force, which is estimated here explicitly along an approximate stretching path. When molecular separation is not at the minimum-energy value, as frequently happens, forces may be attractive or repulsive. This information provides a fine structural fingerprint and may be relevant to the mechanical properties of materials. The calculations show that the first coordination shell includes destabilizing contacts in ,,9% of crystal structures for compounds with highly polar chemical groups (e.g. CN, NO2, SO2). Calculations also show many pair contacts with weakly stabilizing (neutral) energies; such fine modulation is presumably what makes crystal structure prediction so difficult. Ionic organic salts or zwitterions, including small peptides, show a Madelung-mode pairing of opposite ions where the total lattice energy is stabilized from sums of strongly repulsive and strongly attractive interactions. No obvious relationships between atom,atom distances and interaction energies emerge, so analyses of crystal packing in terms of geometrical parameters alone should be conducted with due care. [source] Universal prediction of intramolecular hydrogen bonds in organic crystalsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Peter T. A. Galek A complete exploration of intramolecular hydrogen bonds (IHBs) has been undertaken using a combination of statistical analyses of the Cambridge Structural Database and computation of ab initio interaction energies for prototypical hydrogen-bonded fragments. Notable correlations have been revealed between computed energies, hydrogen-bond geometries, donor and acceptor chemistry, and frequencies of occurrence. Significantly, we find that 95% of all observed IHBs correspond to the five-, six- or seven-membered rings. Our method to predict a propensity for hydrogen-bond occurrence in a crystal has been adapted for such IHBs, applying topological and chemical descriptors derived from our findings. In contrast to intermolecular hydrogen bonding, it is found that IHBs can be predicted across the complete chemical landscape from a single optimized probability model, which is presented. Predictivity of 85% has been obtained for generic organic structures, which can exceed 90% for discrete classes of IHB. [source] On the mechanism of some first-order enantiotropic solid-state phase transitions: from Simon through Ubbelohde to MnyukhACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2006Frank H. Herbstein The first (so-called) lambda transition in solids was found in the specific heat measurements for NH4Cl at 242,K by F. Simon in 1922 [Simon (1922). Ann. Phys.68, 241,280]. Analogous phenomena found in many other solids gave rise to doubts (expressed most clearly by A. R. Ubbelohde some 50 years ago) about the applicability of classical thermodynamics to some phase transitions [Ubbelohde (1956). Brit. J. Appl. Phys.7, 313,321]. However, Y. Mnyukh's studies of enantiotropic phase transitions in eight organic crystals showed that all proceed by a nucleation-and-growth mechanism [summarized in Mnyukh (2001), Fundamentals of Solid State Phase Transitions, Ferromagnetism and Ferroelectricity. 1st Books]. Nucleation is localized at defects in the parent phase; growth can be epitaxic and oriented if parent and daughter phases have closely similar structures, or random (not oriented) if there are substantial structural differences. This conclusion is supported by a critical review of Mnyukh's eight examples and other results published in the interim. It seems that Ubbelohde's invocation of `hybrid crystals' and `smeared transitions' can mostly be accounted for by lack of equilibrium in the phase-transition studies cited by him. However, the intermediate phase in 4,4,-dichlorobenzophenone appears to have structural resemblances to Ubbelohde's' `hybrid crystal'. [source] How precise are measurements of unit-cell dimensions from single crystals?ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2000Frank H. Herbstein The results of single-site and many-site measurements of cell dimensions from single crystals are compared for Bond and four-circle diffractometers using samples of corundum (essentially pure rhombohedral ,-Al2O3, aluminum oxide) of high diffraction quality, where the effects of small changes in temperature and composition (Cr2O3, chromium oxide, in solid solution) can be taken into account. Similar comparisons are made for four-circle diffractometer measurements on ruby (,-Al2O3, with 0.46 wt % Cr in solid solution). The precisions are some parts in 105. There is partial support for the Taylor,Kennard [Acta Cryst. (1986), B42, 112,120] dictum that standard uncertainties (s.u.s) of cell parameters from routine four-circle diffractometer measurements are less than those for many-site measurements by factors of 5 for cell lengths and 2.5 for cell angles. For organic crystals, independent repetitions of adequate quality for comparison and analysis of routine four-circle diffractometer measurements are available only for ,-oxalic acid dihydrate and anthracene. The experimental standard uncertainties given for these two crystals agree reasonably well with the sample s.u.s at room temperature, but appreciably less well at ,100,K, again giving partial support to the Taylor,Kennard dictum. The relation between specimen characteristics and attainable precision is emphasized; the precisions for routine measurements on good quality organic crystals are some parts in 104. Area-detector measurements of cell dimensions have also been appraised; currently published s.u.s from such measurements appear to be highly unreliable, and this is supported by a recent analysis of the operation of such diffractometers [Paciorek et al. (1999). Acta Cryst. A55, 543,557]. Formulation of a standard protocol for such measurements is badly needed. The dangers inherent in high degrees of replication are illustrated by recounting Kapteyn's Parable of the Chinese Emperor. Attention is drawn to the fact that there has been little improvement in claimed precisions over the past 40,60 years. [source] Recrystallization and Shape Control of Crystals of the Organic Dye Acid Green 27 in a Mixed SolventCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2007Huai-Ping Cong Abstract Recrystallization of the unstructured dye acid green 27 (AG27) in a mixed solvent of alcohol (ethanol or methanol) and water was systematically studied. The results demonstrated that AG27 crystals with uniform sizes and controllable shapes can be produced by simply changing the volume ratio of ethanol (or methanol) and deionized water (DIW). Rodlike and shuttlelike AG27 crystals can be selectively synthesized. The XRD analyses revealed the periodic structures of the organic crystals. Furthermore, crystallization in another mixed solvent of N,N -dimethylformamide (DMF) and DIW results in the formation of longer fibers with high aspect ratio, which further validates the remarkable effects of mixed solvent on the shape of the AG27 crystals. This method of recrystallization in a mixed solvent is expected to facilitate the synthesis of other functional organic crystals with unusual shapes. [source] | |||||||||||||