Ultrafast Raman loss spectroscopy: a new approach to vibrational structure determination

The rapid data acquisition, natural fluorescence rejection and experimental ease are the advantages of the ultra-fast Raman loss scattering (URLS) which makes it a unique and valuable molecular structure-determining technique. URLS is an analogue of stimulated Raman scattering (SRS) but far more sensitive than SRS. It involves the interaction of two laser sources, viz. a picosecond (ps) pulse and white light, with the sample leading to the generation of loss signal on the higher energy (blue) side with respect to the wavelength of the ps pulse, unlike the gain signal observed on the red side in SRS. These loss signals are at least 1.5 times more intense than the SRS signals. Also, the very prerequisite of the experimental protocol for signal detection to be on the higher energy side by design eliminates the interference from fluorescence, which always appears on the red side. Unlike coherent anti-Stokes Raman scattering, URLS signals are not precluded by non-resonant background under resonance condition and also being a self-phase matched process, it is experimentally easier.

N-Acetylglycyl-L-lysine methyl ester acetate

C llH22 N 30 + . C2H302, orthorhombic, P2~2~2~, a = 5.511(2), b = 14.588(4), c = 21.109 (4)A, Z = 4. The structure has been solved using MULTAN and refined to R = 0.079 for 993 observed reflections. The fully extended lysine side chain in the molecule is staggered between the main-chain amino and carbonyl groups. The dipeptide molecules in the crystal structure are arranged in twofold helices centred on 21 screw axes. These helices are interconnected through interactions involving the acetate and the side-chain amino groups. Each acetate group bridges two adjacent side-chain amino groups, related by an a translation, giving rise to an infinitely long chain of alternating negatively charged carboxylate and positively charged amino groups.

Structure of a new crystal form of 2- ([3-(trifluoromethyl)phenyl] amino)benzoic acid (flufenamic acid)

C14Ht0F3NO2, P2.Jc, a = 12.523 (4), b = 7.868(6), c = 12.874 (3)A, fl = 95.2 (2) ° , O,,, = 1.47 (4), D e = 1.47 Mg m -3, Z = 4. Final R = 0.074 for 2255 observed reflections. The carboxyl group and the phenyl ring bearing the carboxyl group are nearly coplanar whereas the two phenyl rings are inclined with respect to each other at 52.8 ° . The difference between the two polymorphs of flufenamic acid lies in the geometrical disposition of the [3-(trifluoromethyl)- phenyl]amino moiety with respect to the benzoic acid moiety. As in other fenamate structures, the carboxyl group and the imino N atom are connected through an intramolecular hydrogen bond; also, pairs of centrosymmetrically related molecules are connected through hydrogen bonds involving carboxyl groups.

Structural studies of analgesics and their interactions. VII. Stereoisomerism and disorder in the structure of oxyphenbutazone monohydrate

Oxyphenbutazone, C19H20N203, a metabolite and perhaps the active form of phenylbutazone, is a widely used non-narcotic analgesic and anti-inflammatory pyrazolidinedione derivative. The monohydrate of the compound crystallizes in the triclinic space group Pi with two molecules in a unit cell of dimensions a -- 9.491 (4), b = 10.261 (5), c = 11.036 (3)A and ¢~ = 72.2 (1), fl = 64.3 (1), 7 = 73.0 (1) °. The structure was solved by direct methods and refined to an R value of 0.107 for 1498 observed reflections. The butyl group in the molecule is disordered. The hydroxyl group occupies two sites with unequal occupancies. On account of the asymmetry at the two N atoms and one of the C atoms in the central five-membered ring, the molecule can exist in eight isomeric states, of which four are sterically unfavourable. The disorder in the position of the hydroxyl group can be readily explained on the basis of the existence, with unequal abundances, of all four sterically favourable isomers.The bond lengths and angles in the molecule are similar to those in phenylbutazone. The crystal structure is stabilized by van der Waals interactions, and O-H... O hydrogen bonds involving the carbonyl and the hydroxyl groups as well as a water molecule.

Structure-thermal behaviour studies on the salicylato complex of cobalt

The salicylato complex of cobalt was synthesized and its structure established to be [Co(sal)2] · 4 H2O, where, sal =, from elemental analysis, IR spectroscopy, magnetic susceptibility, cryoscopy and conductivity. The X-ray diffractogram of the complex has been given. Thermal decomposition has been studied in air by thermogravimetry (TG), differential thermal analysis and differential scanning calorimetry. TG shows three main steps of decomposition. The intermediates formed at various stages were collected and analysed. From the TG results and chemical analysis of the intermediates, a mechanism has been proposed for the thermal decomposition of the complex, leading to the oxide formation in the final stage.

A neutron diffraction investigation of the structure of PBO-PBCL2 glasses

Neutron diffraction techniques have been employed to investigate the structure of PbO-PbCl2 glasses as a function of composition in the nominal range PbO.PbCl2 to 9PbO.PbCl2. It is concluded that, whereas the first Pb-O distance is well defined, the distribution of Pb-Cl distances is much broader, in agreement with a previous EXAFS study.

Structure of (6S,13bR)-1,2,3,5,6,13b-hexahydro-6-isopropyl-8H-pyrrolo[1',2':1,2]pyrazino[3,4,-b]quinazoline-5,8-dione

C17H19N302, monoclinic, P21, a = 5.382 (1), b = 17.534(4), c = 8.198(1)/L ,8 = 100.46(1) °, Z= 2, d,, = 1.323, dc= 1.299 Mg m-3, F(000) = 316, /~(Cu .Ka) = 0.618 mm -1. R = 0.052 for 1284 significant reflections. The proline-containing cispeptide unit which forms part of a six-membered ring deviates from perfect planarity. The torsion angle about the peptide bond is 3.0 (5) ° and the peptide bond length is 1.313 (5)A. The conformation of the proline ring is Cs-Cf~-endo. The crystal structure is stabilized by C-H... O interactions.

Interaction of Metal Ions with 2'-Deoxyribonucleotides. Crystal and Molecular Structure of a Cobalt(l1) Complex with 2'-Deoxyinosine 5'-Monophosphate

The crystal structure of the cobalt( 11) complex with 2'-deoxyinosine 5'-monophosphate (5'- dlMP), [Co(5'-dlMP) (H,0),]-2H20, has been analysed by X-ray diffraction. The complex crystallizes in the space group P2,2,2, with a = 6.877(3), b = 10.904(2), c = 25.421 (6) A, and Z = 4. The structure was solved by the heavy-atom method and refined to an R value of 0.043 using 1 776 unique reflections. The cobalt ion binds only to the 6-oxopurine base of the nucleotide at the N(7) position, the octahedral co-ordination of the metal being completed by five water oxygens. The phosphate oxygens are involved in hydrogen bonding with the co-ordinated water molecules. The structure is closely similar to that of the corresponding ribonucleotide complex. The nucleotide has the energetically preferred conformation: an anti base, a C(3') -endo sugar pucker, and a gauche-gauche conformation about the C(4')-C( 5') bond. The significance of sugar puckering in the monomeric complexes of general formula [ M (5'-nucleotide) (H20),] is explained in terms of the structural requirements for metal-water-phosphate bridging interactions.

Molecular structure of a cyclic tetrapeptide disulfide. A novel 310 helical conformation with an S-S bridge

The crystal structure of the cyclic peptide disulfide Boc-Cys-Pro-Aib-Cys-NHMe has been determined by X-ray diffraction. The peptide crystallizes in the space group P212121, with A = 8.646(1), B = 18.462(2), C = 19.678(3)Å and Z = 4. The molecules adopt a highly folded compact conformation, stabilized by two intramolecular 4→ 1 hydrogen bonds between the Cys (1) and Pro (2) CO groups and the Cys (4) and methylamide NH groups, respectively. The backbone conformational angles for the peptide lie very close to those expected for a 310 helix. The S-S bridge adopts a right handed twist with a dihedral angle of 82°. The structure illustrates the role of stereochemically constrained residues, in generating novel peptide conformations. Aib, α-aminoisobutyric acid; Z, benzyloxycarbonyl; Boc, t-butyloxycarbonyl; OMe, methyl ester; OBz, benzyl ester; NHMe, N-methylamide; Tosyl, p-toluenesulfonyl.

Infrared and Mössbauer spectroscopic study of the metal-insulator transition in some oxides of perovskite structure

The IR spectra of some LaNi1−xBxO3 (B = Cr, Fe, and Co) compounds having perovskite structure have been studied in the range 1000−300 cm−1. An investigation of the changes in the metal-oxygen stretching frequency as x → xc from the insulating side has been carried out. An important feature is that as x → xc the vibrational features in the infrared spectra disappear when the resistivity is not, vert, similar10−1 Ω cm which is of two orders of magnitude more than the value of varrho0 at which the temperature coefficient of resistance changes sign. Mössbauer studies on Fe-containing samples with various conductivities show that the isomer shift decreases as conductivity increases which is indicative of larger Fe---O overlap.

Self Assembly and Electronic Structure of ZnO Nanocrystals

In this paper, we report the synthesis and self assembly of various sizes of ZnO nanocrystals. While the crystal structure and the quantum confinement of nanocrystals were mainly characterized using XRD and UV absorption spectra, the self assembly and long range ordering were studied using scanning tunneling microscopy after spin casting the nanocrystal film on the highly oriented pyrolytic graphite surface. We observe self assembly of these nanocrystals over large areas making them ideal candidates for various potential applications. Further, the electronic structure of the individual dots is obtained from the current-voltage characteristics of the dots using scanning tunneling spectroscopy and compared with the density of states obtained from the tight binding calculations. We observe an excellent agreement with the experimentally obtained local density of states and the theoretically calculated density of states.

Structure of disodium guanosine 5'-phosphate heptahydrate

Abstract is not available.

Electronic Structure of some Substituted azolidines.CNDO/2, NMR and vibratational spectoroscopic studies

The 1H and 13C chemical shifts, characteristic vibrational frequencies and force constants for some substituted azolidines are correlated with the results of the CNDO/2 calculations. The influence of the exo and endo heteroatoms on the electronic structure of the heterocyclic ring are discussed.

Conformational Analysis and Electronic Structure of Monothiodiacetamide: Normal Coordinate Analysis and Molecular Orbital Study

The infrared spectra of monothiodiacetamide (MTDA, CHaCONHCSCH3) and its N-deuterated compound in solution, solid state and at low temperature are measured. Normal coordinate analysis for the planar vibrations of MTDAd o and -dl have been performed for the two most probable cis-trans-CONHCSor -CSNHCO-conformers using a simple Urey-Bradley force function. The conformation of MTDA derived from the vibrational spectra is supported by the all valence CNDO/2 molecular orbital method. The vibrational assignments and the electronic structure of MTDA are also given.