Conformation Intermediate (conformation + intermediate)

Distribution by Scientific Domains

Selected Abstracts

Vibrational spectral studies and the non-linear optical properties of a novel NLO material L -prolinium tartrate

L. Padmaja
Abstract Vibrational spectral analysis of the novel non-linear optical (NLO) material, L -prolinium tartrate (LPT) was carried out using NIR-FT-Raman and FT-IR spectroscopy. The density functional theoretical (DFT) computations have been performed at B3LYP/6,31G (d) level to derive equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The reasonable NLO efficiency, predicted for the first time in this novel compound, has been confirmed by Kurtz,Perry powder second-harmonic generation (SHG) experiments. The charge-transfer interaction between the pyrrolidine ring and the carbonyl group of the tartrate anion through the intramolecular ionic hydrogen bonds is confirmed by the simultaneous activation of ring modes in IR and Raman spectra. The splitting of the ring-breathing mode, pseudo-rotational ring puckering modes and the NH2 modes of the pyrrolidine ring lead to the conclusion that the pyrrolidine ring adopts a conformation intermediate between the envelope (bent) form and the half-chair (twisted) form, resulting in the lowering of symmetry from C2 to Cs. The lowering of the methylenic stretching wavenumbers and the enhancement of the stretching intensities suggest the existence of the electronic effects of back-donation in LPT. The positional disorder of the pyrrolidine ring, the presence of blue-shifting H-bonds as well as other non-bonded interactions in LPT, low frequency H-bond vibrations and the role of intramolecular charge transfer and the hydrogen bonds in making the molecule NLO active have been analysed on the basis of the vibrational spectral features. Copyright © 2006 John Wiley & Sons, Ltd. [source]

rac -5-Diphenylacetyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine and rac -5-formyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine

Thanikasalam Kanagasabapathy
rac -5-Diphenylacetyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine, C26H27NOS, (I), and rac -5-formyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine, C13H17NOS, (II), are both characterized by a planar configuration around the heterocyclic N atom. In contrast with the chair conformation of the parent benzothiazepine, which has no substituents at the heterocyclic N atom, the seven-membered ring adopts a boat conformation in (I) and a conformation intermediate between boat and twist-boat in (II). The molecules lack a symmetry plane, indicating distortions from the perfect boat or twist-boat conformations. The supramolecular architectures are significantly different, depending in (I) on C,H...O interactions and intermolecular S...S contacts, and in (II) on a single aromatic ,,, stacking interaction. [source]

Conformational and configurational disorder in 6-(3,4,5-trimethoxyphenyl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8(5H)-one and 6-(1,3-benzodioxol-5-yl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8-one: a hydrogen-bonded chain of rings and ,-stacked hydrogen-bonded chains

Paola Cuervo
In 6-(3,4,5-trimethoxyphenyl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8(5H)-one, C19H19NO6, (I), the six-membered heterocyclic ring adopts a conformation intermediate between envelope and half-chair forms; it is disordered over two enantiomeric configurations, with occupancies of 0.879,(3) and 0.121,(3), leading to positional disorder of the 3,4,5-trimethoxyphenyl unit. In 6-(1,3-benzodioxol-5-yl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8-one, C17H13NO5, (II), the molecules are similarly disordered, with occupancies of 0.866,(4) and 0.134,(4). The molecules in (I) are linked by one three-centre N,H...(O)2 hydrogen bond and one two-centre C,H...O hydrogen bond to form a complex chain of rings whose formation is reinforced by two independent aromatic ,,, stacking interactions. In (II), a single N,H...O hydrogen bond links the molecules into a simple chain, and pairs of chains are linked by a single aromatic ,,, stacking interaction. [source]

1-Deoxy-1-(4-fluoro­phenyl)-,- d -ribo­furan­ose, its hemihydrate, and 1-­deoxy-1-(2,4-di­fluoro­phenyl)-,- d -ribo­furan­ose: structural evidence for intermolecular C,H,F,C interactions

Jan W. Bats
The structures of 1-deoxy-1-(4-fluoro­phenyl)-,- d -ribo­furan­ose in two crystal forms, (Ia) and (Ib) (C11H13FO4), 1-deoxy-1-(4-fluoro­phenyl)-,- d -ribo­furan­ose hemihydrate, (Ic) (C11H13­FO4·0.5H2O) and 1-deoxy-1-(2,4-di­fluoro­phenyl)-,- d -ribo­furan­ose, (II) (C11H12F2O4), show two-dimensional networks of intermolecular hydrogen bonds between the hydroxyl groups. Weak intermolecular C,H,F,C and C,H,,arene interactions complete the packing in the third dimension. The ribo­furan­ose ring has a conformation intermediate between a C1,- exo,C2,- endo twist and a C2,- endo envelope for (Ia) and (Ic), a conformation intermediate between a C2,- endo,C3,- exo twist and a C2,- endo envelope for (Ib) and an unsymmetrical C2,- exo,C3,- endo twist conformation for (II). [source]

Substrate analogs induce an intermediate conformational change in Toxoplasma gondii adenosine kinase

Yan Zhang
Adenosine kinase (AK) is a key enzyme in purine metabolism in the ubiquitous intracellular parasite Toxoplasma gondii and is a potential chemotherapeutic target for the treatment of T. gondii infections. To better understand the structure,activity relationship of 6-substituted purine ribosides, the structures of the T. gondii AK,N6,N6 -dimethyladenosine (DMA) complex, the AK,DMA,AMP-PCP complex, the AK,6-­methyl mercaptopurine riboside (MMPR) complex and the AK,MMPR,AMP-PCP complex were determined to 1.35, 1.35, 1.75 and 1.75,Ĺ resolution, respectively. These structures reveal a conformation intermediate between open and closed, with a small lid-domain rotation of 12°. Residues Gly143- X - X -Gly146 undergo torsional changes upon substrate binding, which together with a Gly68-Gly69 switch induces a hinge bending of the lid domain. The intermediate conformation suggests that ATP binding is independent of adenosine binding. Orienting the ,-phosphate group of ATP into the optimal catalytic position may be the last step before the onset of chemical catalysis and may require the translocation of Arg136 following the complete closure of the lid domain. 6-­Substituted purine-nucleoside analogs are accommodated in a hydrophobic cavity. Modification at the N6 or C6 position of the nucleoside would affect the interactions with the surrounding residues and the binding affinity. [source]