Showing papers by "Gautam R. Desiraju published in 2004"
TL;DR: Two new stable crystal forms of the 120 year old compound sym-trinitrobenzene are reported by the use of an additive, trisindane, that can act as a mimic in the crystallization experiment.
Abstract: The most stable is not necessarily the most easy to obtain! Two new stable crystal forms of the 120 year old compound sym-trinitrobenzene are reported. These elusive forms have been obtained by the use of an additive, trisindane, that can act as a mimic in the crystallization experiment.
135 citations
TL;DR: In this paper, the authors argue that pseudopolymorphism should ideally be restricted to crystals of a single compound and that in multicomponent crystals there are too many structural variations and the term polymorphism is unnecessarily restrictive.
Abstract: The author offers a counter argument for the use of the term pseudopolymorphism. He argues that the term polymorph should ideally be restricted to crystals of a single compound. However, he notes that in multicomponent crystals there are too many structural variations and the term polymorphism is unnecessarily restrictive. The term pseudopolymorphism in this context brings to attention the fact that certain related multicomponent crystals, with slightly different chemical compositions or stoichiometries, have slightly different crystal structures in a manner reminiscent of polymorphism.
76 citations
TL;DR: It is noteworthy that the so-called "weak" acceptor, organic chlorine, is able to sustain a good intramolecular hydrogen bridge that is of an attractive and stabilizing nature and which is of potential importance in crystal engineering and supramolescular chemistry.
Abstract: The acceptor capabilities of "organic" halogen, CX (X=F, Cl, Br, I), with respect to hydrogen bonding are controversial, and unactivated organic chlorine is generally deemed to be a poor acceptor. Hydrogen bridges of the type O--H...Cl--C are uncommon and occur mainly in an intramolecular situation when the donor group is sterically hindered, so that the formation of intermolecular interactions is difficult. In this paper, intramolecular O--H...Cl--C interactions in a series of chloro-substituted gem-alkynols are studied. We describe various features of this interaction using crystallographic, spectroscopic and computational methods. The O--H...Cl--C interaction occurs in five of the six compounds under consideration here (CDDA, 14DDDA, 15DDDA, 18DDDA, 15MKA). Solution (1)H NMR spectroscopy shows that the interaction is intramolecular and that it is a true hydrogen bond. DFT calculations give a stabilisation energy around 4.0 kcal mol(-1). In the crystal structures of the compounds studied, the intramolecular O--H...Cl--C interactions fit into the overall scheme of cooperative interactions. These structures may be derived from that of the unsubstituted compound DDA by means of synthon exchange and the O--H...Cl--C interaction fares surprisingly well in the presence of competing stronger acceptors. The crystal structures show an unusual degree of modularity for compounds that generally form interactions that are weak and variable. It is noteworthy that the so-called "weak" acceptor, organic chlorine, is able to sustain a good intramolecular hydrogen bridge that is of an attractive and stabilizing nature and which is of potential importance in crystal engineering and supramolecular chemistry.
64 citations
TL;DR: In this article, the authors rationalised the difference in terms of conditional isomorphism between 4-Iodophenoxyaniline and 4-iodoaniline, and showed that 4-IDO is not isostructural to its bromo, chloro, and ethynyl counterparts.
Abstract: 4-(4′-Iodo)phenoxyaniline is isostructural to the corresponding bromo, chloro and ethynyl derivatives in contrast to 4-iodoaniline which is not isostructural to its bromo, chloro and ethynyl counterparts. This difference is rationalised in terms of conditional isomorphism.
32 citations
TL;DR: In this paper, the title compound 6-amino-2-phenylsulfonylimino-1,2-dihydropyridine, 12 phenyl-substituted derivatives were examined for polymorphism by recrystallization from a large number of solvents.
Abstract: Following up from a study of polymorphism in the title compound, 6-amino-2-phenylsulfonylimino-1,2-dihydropyridine, 12 phenyl-substituted derivatives were examined for polymorphism by recrystallization from a large number of solvents. The title compound contains hydrogen bond donor (D) and acceptor sites (A) located in a AADD juxtapositioning. Two structural families that differ in their use of the AADD hydrogen bond functionality may be identified. Methyl and chloro substitution in the ortho position or fluoro substitution in the para position leads to a catemer motif, which is related to the kinetic form of the title molecule. Meta Substitution by methyl and larger substituents in the para position block this structural option. While meta-methyl and para-chloro substitution lead to unique structures, two polymorphs of the para-methyl-substituted derivative could be crystallized and these adopt the dimer arrangement. With the larger bromo, iodo, methoxy, and trifluoromethyl substituents in the para position, dimers arranged into interconnected layers are obtained. These dimer structures are reminiscent of the thermodynamic form of the title compound. It is noteworthy that the majority of derivatives of the title compound fail to show polymorphic behavior, and this shows that our understanding of polymorphism is still far from complete.
29 citations
TL;DR: In this article, the host-guest complexes of tetranitrotetraphenylmethane (TNTPM) derivatives are characterized by O−H⋯O, C−H-O, O-H-N, C-Hπ interactions.
Abstract: Dinitro and tetracyano derivatives of tetraphenylmethane (TPM) are identified as new host materials that include THF, water and MeCN. The crystal structures of the host–guest complexes are reminiscent to those of the related host compound tetranitrotetraphenylmethane (TNTPM) studied by us previously. Guest loss has been measured quantitatively. The crystal structures are characterized by O–H⋯O, C–H⋯O, C–H⋯N and C–H⋯π interactions. It is interesting to note that while the unsubstituted TPM and some of its other derivatives form guest-free crystals, the nitro and cyano derivatives form more open structures.
23 citations
TL;DR: 4-Aminothiophenol exists as 4-ammonio-1-benzenethiolate in the solid and liquid state and is characterised by a tetrahedral beta-As type network which is the driving force for the proton transfer.
18 citations
TL;DR: In this paper, low-temperature X-ray analysis of two aminophenols reveals an interesting and novel saturated O−H···N and N−H·O hydrogen bond tube architecture.
Abstract: Low-temperature X-ray analysis of two aminophenols reveals an interesting and novel saturated O−H···N and N−H···O hydrogen bond tube architecture. This pattern is topologically similar to the anion framework in the rare zeolite narsarsukite Na2TiOSi4O10.
15 citations
TL;DR: Diethylamine has been trapped in its less stable gauche conformation in a solvate of the title diol; the staggered conformation, which is ca.
14 citations
TL;DR: Molecular complexes of 4-(4-aminophenoxy)aniline with a series of diphenols are structurally homologous and adopt the carborundum III topology, which is an unprecedented network for organic solids.
14 citations
Journal Article•
TL;DR: The importance of homology modeling in predicting the three dimensional structures of proteins has been discussed in this paper. Efforts in improving the predictive quality are outlined. Successful implementation of homological modelling has been demonstrated in predicting structure of the kinase domain of EGF Receptor (EGFR).
Abstract: The importance of homology modelling in predicting the three dimensional structures of proteins has been discussed. Efforts in improving the predictive quality are outlined. Successful implementation of homology modellinghas been demonstrated in predicting the structure of the kinase domain of Epidermal Growth Factor Receptor (EGFR). A comparison between the modelled and experimental X-ray crystal structure (C α RMSD 1.96 A) shows the accuracy of the modelling methods used.
TL;DR: The title molecular complex, 4-ammonio-cyclo-hexanol (4-hydroxycyclohexyl) carbamate, C6H14NO+·C7H12NO3−, forms an ionic column with N−H⋯O, O−H−O, and C−H-O interactions.
Abstract: The title molecular complex, 4-ammoniocyclohexanol (4-hydroxycyclohexyl)carbamate, C6H14NO+·C7H12NO3−, forms an ionic column with N—H⋯O, O—H⋯O and C—H⋯O interactions. There are two different cyclic supramolecular synthons of note. The crystal structures of ionic amino acids also have similar structural patterns.