Synthesis of certain 1-β-D-ribofuranosyl-1,2-dihydro-2-oxopyridines structurally related to nicotinamide ribonucleoside

Several substituted 1-β-D-ribofuranosyl-1,2-dihydro-2-oxopyridines have been prepared as congeners of nicotinamide ribonucleoside. Direct glycosylation of the silylated 3-ethylcarboxylate 5 or 3-carbamoyl 6 derivative of 1,2-dihydro-2-oxopyridine with 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose ( 7 ) in the presence of trimethylsilyl triflate gave the corresponding blocked nucleosides 8 and 9 , respectively in good yield. Ammonolysis of 8 and 9 with methanolic ammonia furnished 1-β-D-ribofuranosyl-1,2-dihydro-2-oxopyridine-3-carboxa-mide ( 10 ), the structure of which was established by single-crystal X-ray diffraction analysis. Thiation of 9 with Lawesson's reagent and subsequent deacetylation of the thiated product 11 with methanolic ammonia furnished 1-β-D-ribofuranosyl-1,2-dihydro-2-oxopyridine-3-thiocarboxamide ( 12 ). Modification of the carbo-nitrile function of 1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-1,2-dihydro-2-oxopyridine-4-carbonitrile ( 13 ) gave a series of 4-substituted-1-β-D-ribofuranosyl-1,2-dihydro-2-oxopyridines, in which the 4-substituent is a thiocarboxamide 15 , carboxamide 16 , carboxamidoxime 17 , carboxamidine 18 and aminomethyl 19 group. None of these compounds exhibited any significant antitumor or antiviral effects in vitro.     

New lignans from the heartwood of cleistanthus collinus

The isolation and characterisation of five new compounds and nine known compounds from the heartwood of Cleistanthus collinus are reported. The new compounds are wodeshiol 16,3,4-dihydrotaiwanin C 20, and three new glycosides 24, 25 and 26 of diphyllin and taiwanin E The ¹H and ¹³C NMR spectra of these compounds are also reported.     

Indirect complexometric determination of cadmium(II) using 1,10-phenanthroline as selective masking agent

An indirect complexometric method is described for the determination of cadmium(II), 1,10-phenanthroline being used as masking agent. Cadmium(II) in a given sample solution is initially complexed with an excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. An excess of 1,10-phenanthroline is then added and the EDTA released from the Cd-EDTA complex is titrated with standard lead nitrate solution. Results are obtained for 1.5–57 mg of Cd with relative errors 0.90% and standard deviations 0.06 mg. Cu(II), Co(II), Hg(II), Ni(II), Zn(II), Pd(II), Tl(III), Au(III) and Sn(IV) interfere, but can be easily masked. The method is applied for the determination of cadmium in synthetic alloy solutions.     

Structural and dielectric characterization of Sr substituted Ba(Zr,Ti)O<Subscript>3</Subscript> based functional materials

Single phase Sr substituted BaZr_0.1Ti_0.9O₃ (also known as BZT) ceramics with a formula Ba_1-xSr_xZr_0.1Ti_0.9O₃ (x=0.10, 0.20, 0.30, 0.40 and 0.50) are prepared using a solid state reaction of mixed oxides at 1250 °C for 15 h. Analysis of XRD patterns of the ceramic powders show that Sr substitutes into Ba sites and reduces the lattice parameter. The powders are sintered at 1600 °C for 6 h to investigate the microstructure and functional properties. It is found that strontium substitution significantly modifies the microstructure and greatly influences the dielectric properties. The increase in Sr content reduces the ceramic grain size and results in spherical grains. With an increase in Sr content, the Curie temperature is lowered, and the relative permittivity maximum is increased and broadened. In Ba_1-xSr_xZr_0.1Ti_0.9O₃ with x=0.30, the relative permittivity reached a maximum of 26600 and with further increase of Sr content, the relative permittivity is lowered and the phase transition is found to be broad and diffused. The ferroelectric hysteresis characteristics are discussed in detail. PACS 77.84.-s; 77.80.Bh; 77.22.Ch; 77.84.Dy; 77.22.-d     

Fourier phase microscopy for investigation of biological structures and dynamics

By use of the Fourier decomposition of a low-coherence optical image field into two spatial components that can be controllably shifted in phase with respect to each other, a new high-transverse-resolution quantitative-phase microscope has been developed. The technique transforms a typical optical microscope into a quantitative-phase microscope, with high accuracy and a path-length sensitivity of lambda/5500, which is stable over several hours. The results obtained on epithelial and red blood cells demonstrate the potential of this instrument for quantitative investigation of the structure and dynamics associated with biological systems without sample preparation.     

Coexistence curve and rectilinear diameter in the critical liquid system carbon disulphide+nitromethane

The phase boundary of the binary liquid system CS₂+CH₃NO₂ is studied over nearly six decades in reduced temperature 3×10⁻⁶<ε=(T _C−T)/T _C<2×10⁻¹ and over the composition range 8-98 mole % of CS₂. The critical parameters areT _C=335.13₂K andx _C=57.3₄ mole % of CS₂. A single critical exponentβ=0.315±0.004 fits the observations over the entire range with no indication ofβ increasing to the classical value of 1/2 far away fromT _C. The diameter of the coexistence curve shows a rectilinear behaviour only far away fromT _C. NearT _C, the deviation ΔX from the rectilinear law seems to fit a curve of the form ΔX=fε^7/8 exp (−gε ^h), the derivative of which has a singularity like that of specific heat. An ambiguity in the analysis of the data in terms of mole fractions and volume fractions is pointed out. It is also suggested that the curvature of the diameter may be much weaker in a liquid-gas system and hence might have escaped detection.     

Heat transfer in a MHD flow between eccentric disks rotating at different speeds

Heat transfer in a MHD flow between two infinite eccentric disks rotating with different speeds is considered when the plates are maintained at different temperatures. The results for the corresponding nonmagnetic case presented wrongly by Banerjee and Borkakati [7] are corrected. It is observed that the eccentric rotation reduces the heat transfer on the disks.