Synthesis and crystal chemistry of NH3(MoO3)3

NH₃(MoO₃)₃ crystallizes with hexagonal symmetry, space group $\text{P6}{}_3\text{m}$, lattice constants a = 10.568 Å, c = 3.726 Å, and Z = 2. The crystal structure has been determined by Patterson synthesis and refined assuming isotropic temperature factors to a final conventional R value of 0.085. The structure shows a three-dimensional arrangement built up of double chains of distorted MoO₆ octahedra, parallel to the [001] direction. The octahedral double chains are linked among each other through common oxygen atoms. In addition to the shared oxygen atoms, each molybdenum is coordinated to one terminal oxygen. MoO distances range from 1.645 to 2.378 Å and OMoO angles from 74.3 to 114.3°. These results are consistent with the fact that molybdenum in high-valence states shows octahedral coordination with terminal oxygens.     

Raman spectroscopic and structural studies of indigo and its four 6,6'-dihalogeno analogues

The Raman and electron impact mass spectra of synthetic indigo and its four 6,6'-dihalogeno analogues are reported and discussed. The influence of varying the halogen on these Raman spectra is considered. Particular emphasis is laid on distinguishing indigo from 6,6'-dibromoindigo and differentiating between the dihalogenocompounds, so as to develop protocols for determining whether artefacts are coloured with dyes of marine or terrestrial origin and whether such artefacts are dyed with genuine "Tyrian Purple" or with dihalogenoindigo substitutes that do not contain bromine. The value of even low resolution electron impact mass spectrometry in a forensic context as a means of identifying authentic 6,6'-dibromoindigo and distinguishing it from its dihalogenoanalogues is emphasised     

Benzylic cleavage and McLafferty rearrangement under electron ionization conditions in the fragmentation of 5,6-dialkyl-2, 4-diarylpyrimidines

Several 5,6-dialkyl-2,4-diarylpyrimidines were prepared and their electron ionization (EI) mass spectra reported. The benzylic cleavage takes place easily together with an important McLafferty rearrangement. The involvement of the nitrogen atom appears to be important in the fragmentation of 5-methyl-substituted pyrimidines. In contrast, the 6-methyl-substituted pyrimidines undergo benzylic cleavage without hydrogen transfer. Thus, the difference in the mass spectrometric behaviour allows the identification of these isomeric compounds which, in contrast, exhibit only small differences in their NMR spectra. Copyright 1999 John Wiley & Sons, Ltd.     

Accurate Gaussian basis sets for the H2O molecule generated with the molecular improved generator coordinate Hartree–Fock method

The molecular improved generator coordinate Hartree–Fock (MIGCHF) method is used to generate accurate basis sets of primitive Gaussian-type functions for the H₂O molecule. Sequences of increasing size atom centered basis sets are employed to explore the accuracy that can be achieved with this method. Using the O(24s14p8d5f2g1h);H(22s9p5d2f1g) basis set, the HF and second-order electron correlation energies of the H₂O ground state at the experimental geometry are computed as −76.0674680 and −0.3491935 hartree, respectively. The HF energy is in error by 20 μhartree and the second-order correlation energy corresponds to 96.5% of an estimate of the limiting value. The relevance of the present calculations is to show the accuracy that can be achieved in studies of small polyatomic molecules with the MIGCHF method.     

The structure of the FeNO group in two metastable states (MS1 and MS2) of the nitroprusside anion in Na2[Fe(CN)5NO].2H2O. Infrared spectra and quantum chemistry calculations for the normal and the 15NO and N18O isotopic substituted substance

Low temperature infrared spectra of light induced metastable states MS1 and MS2 of the nitroprusside anion in Na(2)[Fe(CN)(5)NO].2H(2)O, isotopically normal and substituted with (15)NO and N(18)O, are presented and discussed. As a consequence of the relatively high population of the MS2 state achieved by further irradiation with 1064 nm light of samples previously irradiated with 488.0 nm light, new bands were seen for the first time, and others, previously reported, were confirmed. The comparison of the spectral data obtained for the FeNO moiety of the isotopically normal as well as of the (15)NO and N(18)O substituted anion with the results of quantum chemical (DFT) calculations support the assignment of the bands which appear after successive irradiations to MS1, the linear Fe(eta(1)-ON) linkage isomer, and to MS2, the side-bound Fe(eta(2)-NO) isomer.     

Theoretical study of p‐methacryloyl‐aminophenylarsonic acid

Conformations of p‐methacryloylaminophenylarsonic acid (p‐MAPHA) are determined through molecular mechanics and DFT/B3LYP calculations. Solvation effects are studied within the self‐consistent isodensity continuum model (SCI‐PCM). The stationary points were found to correspond to minima as verified by the analysis of vibrational frequencies in the molecule. The molecular optical absorption was obtained by using different solvent environments. The present results are in good agreement with the available experimental data. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Functionalization of substituted 2-(1H)pyridones. II. Synthetic pathways to c-6 modified 3-cyano- and 3-carboxy-2-(1H)pyridones from a common precursor

Starting from readily available 1,2-dihydro-6-methyl-2-oxo-3-pyridinecarbonitrile, 1, viable synthetic pathways to a number of C-6 functionalized 1,2-dihydro-2-oxo-3-pyridinecarbonitriles and corresponding acids are presented. Through the utilization of dianion chemistry, the C-6 methyl substituent is selectively functionalized to three different oxidation levels.     

On the origin of optical activity in tris-diamine complexes of Co(III) and Rh(III): a simple model based on time-dependent density function theory

Time-dependent density functional theory (TD-DFT) is applied to the CD spectra of Lambda(deltadeltadelta)-(+)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Lambda(deltadeltadelta)-(+)-[Co(en)3]3+ as well as the stereoisomers Delta-((delta)n(lambda)(3-n))-(-)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Delta(deltadeltadelta)-(-)-[Co(en)3]3+. Theory is able to reproduce the major differences in the CD spectra of the species with a Lambda-configuration and their isomers with a Delta-configuration in both the d-d and ligand-to-metal CT region. It is further possible to rationalize the trend in terms of a larger azimuthal distortion away from the octahedral geometry in the Lambda-conformation compared to the Delta-configuration. Considerations were also given to the CD spectra of the lel3-isomer, Delta(lambdalambdalambda)-(-)-[Rh(R-pn)3]3+ and the ob-isomer, Lambda(lambdalambdalambda)-(+)-[Rh(S-pn)3]3+.     

Prostaglandin D2 synthase and its post-translational modifications in neurological disorders

Prostaglandin D2 synthase (PGDS) (beta-trace protein) is a highly abundant cerebrospinal fluid (CSF) glycoprotein. A number of studies have been performed to determine the potential value of this protein for the diagnosis of various neurological disorders. The measurement of total PGDS levels in CSF has proved marginally useful for this purpose, but promising results were obtained while investigating changes in the posttranslational modifications (PTM) pattern. Using 2-DE analysis, we previously showed that PGDS is differentially expressed in ante- and post mortem CSF samples. In the present study, we examined whether the PGDS isoforms may help to distinguish stroke and neurodegenerative disease patients from healthy subjects. The pattern of PGDS PTM was analyzed in CSF from patients with various neurological disorders (n = 44) using IEF/immunoblotting techniques. Strong alterations of this pattern were detected in patients with different forms of degenerative dementia. These findings are consistent with PGDS being altered in some neurological diseases and provide new opportunities for clinical applications.