Effect of pulse profile variations on measurement of eccentricity in orbits of Cen X-3 and SMC X-1

It has long been argued that better timing precision allowed by satellites like Rossi X-ray Timing Explorer (RXTE) will allow us to measure the orbital eccentricity and the angle of periastron of some of the bright persistent high-mass X-ray binaries (HMXBs) and hence a possible measurement of apsidal motion in these system. Measuring the rate of apsidal motion allows one to estimate the apsidal motion constant of the mass losing companion star and hence allows for the direct testing of the stellar structure models for these giant stars present in the HMXBs. In the present paper, we use the archival RXTE data of two bright persistent sources, namely Cen X-3 and SMC X-1, to measure the very small orbital eccentricity and the angle of periastron. We find that the small variations in the pulse profiles of these sources, rather than the intrinsic time resolution provided by RXTE, limit the accuracy with which we can measure arrival time of the pulses from these sources. This influences the accuracy with which one can measure the orbital parameters, especially the very small eccentricity and the angle of periastron in these sources. The observations of SMC X-1 in the year 2000 were taken during the high-flux state of the source and we could determine the orbital eccentricity and omega using this data set.

Selective detection of single-enantiomer spectrum of chiral molecules aligned in the polypeptide liquid crystalline solvent: Transition selective one-dimensional H-1-H-1 COSY

One-dimensional (1D) proton NMR spectra of enantiomers are generally undecipherable in chiral orienting poly-gamma-benzyl-L-glutamate (PBLG)/CDCl3 solvent. This arises due to large number of couplings, in addition to superposition of spectra from both the enantiomers, severely hindering the H-1 detection. On the other hand in the present study the benefit is derived front the presence of several couplings among the entire network of interacting protons. Transition selective 1D H-1-H-1 correlation experiment (1D-COSY) which utilizes the Coupling assisted transfer of magnetization not only for unraveling the overlap but also for the selective detection of enantiopure spectrum is reported. The experiment is simple, easy to implement and provides accurate eanantiomeric excess in addition to the determination of the proton-proton couplings of an enantiomer within a short experimental time (few minutes). (C) 2009 Elsevier Inc. All rights reserved.

Application of z-COSY experiment and its variant for accurate chiral discrimination by H-1 NMR

We report the application of z-COSY experiment and a band selected version of it by employing a selective 90 degrees pulse entitled BASE-z-COSY for precise chiral discrimination, quantification of enantiomeric excess and the analyses of the H-1 NMR spectra of chiral molecules aligned in the chiral liquid crystalline solvent poly-gamma-benzyl-L-glutamate (PBLG). We have demonstrated their applicability for obtaining very high resolution in the H-1 NMR spectra of small organic molecules. It is well known that the commonly employed z-COSY experiment disentangles the spectral complexity, provides pure phase spectra with high resolution, aids in the complete spectral analyses, in addition to yielding information on relative signs of the Couplings. The BASE-z-COSY experiment possesses all these properties, permits the measure of enantiomeric excess, in addition to large saving of instrument time.

Antibodies specific for 1-methylguanosine as a probe of tRNA conformation

Antibodies specific for 1-methylguanosine (m1G) were produced by immunization of rabbits with a bovine serum albumin conjugate of m1G. Antibodies specificity was determined by measuring the inhibition of binding of 3H-m1G trialcohol by various nucleosides or related derivatives. The relative affinities of the unpurified antibodies for various nucleosides showed that m1G trialcohol had an 8-fold higher affinity than m1G; further, guanosine and 2'-O-methylguanosine had at least a 500-fold lower affinity than m1G. The antibodies were purified on m1G-AH-Sepharose column and subsequently immobilized to Sepharose. Immobilized m1G antibodies quantitatively and exclusively retained m1G-containing oligonucleotides derived from ribonuclease A digests of 32P-labeled phage T4 tRNAPro. On the other hand, intact 32P-labeled T4 tRNAPro or its precursor RNA(s) did not bind to the same column. These findings indicate that at least a portion of m1G adjacent to the 3' end of the anticodon in intact T4 tRNAPro is not accessible for antibody binding.

1,3-Difluorobenzene

The weak electrostatic and dispersive forces between C([delta]+)-F([delta]-) and H([delta]+)-C([delta]-) are at the borderline of the hydrogen-bond phenomenon and are poorly directional and further deformed in the presence of other dominant interactions, e.g. C-H...[pi]. The title compound, C6H4F2, Z' = 2, forms one-dimensional tapes along two homodromic C-H...F hydrogen bonds. The one-dimensional tapes are connected into corrugated two-dimensional sheets by further bi- or trifrucated C-H...F hydrogen bonds. Packing in the third dimension is controlled by C-H...[pi] interactions.

1-(4-Chlorophenyl)-2-[(3-phenylisoquinolin 1-yl)sulfanyl]ethanone

The title compound, C23H16ClNOS, exhibits dihedral angles of 11.73 (1) and 66.07 (1)degrees, respectively, between the mean plane of the isoquinoline system and the attached phenyl ring, and between the isoquinoline system and the chlorophenyl ring. The dihedral angle between the phenyl and chlorophenyl rings is 54.66 (1)degrees.

Phases in the (1-x)Na0.5Bi0.5TiO3-(x)CaTiO3 system

The structures of (1 - x) Na0.5Bi0.5TiO3-(x) CaTiO3 at room temperature have been investigated using neutron powder diffraction and dielectric studies. The system exhibits an orthorhombic (Pbnm) structure for x >= 0.15 and rhombohedral (R3c) for x <= 0.05. For x = 0.10, though the neutron diffraction pattern shows features of the orthorhombic (Pbnm) structure, Rietveld refinement using this structure shows a drastic reduction in the in-phase tilt angle (similar to 4 degrees) as compared to the corresponding value (similar to 8 degrees) for a neighbouring composition x = 0.15. The neutron diffraction pattern of x = 0.10 could be fitted equally well using a two-phase model (R3c + Pbnm) with orthorhombic as the minor phase (22%), without the need for a drastic decrease in the in-phase tilt angle. The dielectric studies of x = 0.10 revealed the presence of the polar R3c phase, thereby favouring the phase coexistence model, instead of a single-phase Pbnm structure, for this composition.

Diethyl 4-(2,4-dichlorophenyl)-2,6-dimethyl 1,4-dihydropyridine-3,5-dicarboxylate

In the title compound, C19H21Cl2NO4, the dihydropyridine ring adopts a flattened boat conformation. The dichlorophenyl ring is oriented almost perpendicular to the planar part of the dihydropyridine ring [dihedral angle = 89.1 (1)degrees]. An intramolecular C-H center dot center dot center dot O hydrogen bond is observed. In the crystal structure, molecules are linked into chains along the b axis by N-H center dot center dot center dot O hydrogen bonds.

3-Methyl-5-phenyl-1-(3-phenylisoquinolin-1-yl)-1H-pyrazole

The title compound, C25H19N3, is composed of an aryl-substituted pyrazole ring connected to an aryl-substituted isoquinoline ring system with a dihedral angle of 52.7 (1)degrees between the pyrazole ring and the isoquinoline ring system. The dihedral angle between the pyrazole ring and the phenyl ring attached to it is 27.4 (1)degrees and the dihedral angle between the isoquinoline ring system and the phenyl ring attached to it is 19.6 (1)degrees.

2-[2-(Hydroxymethyl)phenyl]-1-(1-naphthyl)ethanol

The molecular conformation of the title compound, C19H18O2, is stabilized by an intramolecular O-H-O hydrogen bond. In addition, intermolecular O-H-O interactions link the molecules into zigzag chains running along the c axis.

5-Phenyl-3-(2-thienyl)-1,2,4-triazolo[3,4-a]isoquinoline

In the title molecule, C20H13N3S, the triazoloisoquinoline ring system is approximately planar, with an r.m.s. deviation of 0.045 angstrom and a maximum deviation of 0.090 (2) angstrom from the mean plane for the triazole ring C atom which is bonded to the thiophene ring. The phenyl ring is twisted by 52.0 (1)degrees with respect to the mean plane of the triazoloisoquinoline ring system. The thiophene ring is rotationally disordered by approximately 180 degrees over two sites, the ratio of refined occupancies being 0.73 (1): 0.27 (1).

Expression, purification and X-ray analysis of 1,3-propanediol dehydrogenase (Aq_1145) from Aquifex aeolicus VF5

1,3-Propanediol dehydrogenase is an enzyme that catalyzes the oxidation of 1,3-propanediol to 3-hydroxypropanal with the simultaneous reduction of NADP(+) to NADPH. SeMet-labelled 1,3-propanediol dehydrogenase protein from the hyperthermophilic bacterium Aquifex aeolicus VF5 was overexpressed in Escherichia coli and purified to homogeneity. Crystals of this protein were grown from an acidic buffer with ammonium sulfate as the precipitant. Single-wavelength data were collected at the selenium peak to a resolution of 2.4 angstrom. The crystal belonged to space group P3(2), with unit-cell parameters a = b = 142.19, c = 123.34 angstrom. The structure contained two dimers in the asymmetric unit and was solved by the MR-SAD approach.

2-(4-Chloro-3-nitrophenyl)-4-(4-chlorophenyl)-1,3-thiazole

The title compound, C15H8Cl2N2O2S, crystallizes with two molecules in the asymmetric unit. The dihedral angles between the 4-chloro-3-nitrophenyl ring and the thiazole ring are 0.5 (1) and 7.1 (1)° and those between the 4-chlorophenyl ring and the thiazole ring are 7.1 (1) and 7.4 (1)° in the two molecules. The crystal structure is stabilized by intermolecular C-H...Cl and C-H...O hydrogen bonds.

2-[(E)-(4-hydroxy-3-methoxybenzylidene)amino]-N-(2-methylphenyl)-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxamide

The title compound, C24H24N2O3S, exhibits antifungal and antibacterial properties. The compound crystallizes with two molecules in the asymmetric unit, with one molecule exhibiting 'orientational disorder' in the crystal structure with respect to the cyclohexene ring. The o-toluidine groups in both molecules are noncoplanar with the respective cyclohexene-fused thiophene ring. In both molecules, there is an intramolecular N-H...N hydrogen bond forming a pseudo-six-membered ring which locks the molecular conformation and eliminates conformational flexibility. The crystal structure is stabilized by O-H...O hydrogen bonds; both molecules in the asymmetric unit form independent chains, each such chain consisting of alternating 'ordered' and 'disordered' molecules in the crystal lattice.