A comparative study of nitrogen physisorption on different C70 crystal structures using an ab initio based potential

Quantum mechanical calculations are performed using the recently developed hybrid method for interaction energies to determine atom site Lennard-Jones potential parameters for the interactions of molecular nitrogen with C(70) molecules. This ab initio based potential is used in grand canonical Monte Carlo simulations to predict surface adsorption properties of N(2) on five known C(70) structures: rhombohedral, fcc, ideal hcp, deformed hcp, and monoclinic crystals. Because of the presence of five-membered carbon rings and the surface curvature of C(70) molecule, the Lennard-Jones potential parameters for nitrogen-carbon interactions obtained from ab initio based calculations are found to be different from that with planar graphite. The simulation results obtained from these two sets of force fields are compared and shown to differ, particularly at low coverage, where the nitrogen-carbon interactions are more important than the nitrogen-nitrogen interactions. The surface area, monolayer capacity, and isosteric heat of adsorption are calculated for various C(70) crystals and found to change appreciably as a result of the shear-induced phase transformation from hcp to rhombohedral lattice.     

Solvent extraction of uranium(VI) into toluene by dicyclohexano-18-crown-6 from mixed aqueous-organic solutions

Extraction behaviour of uranium(VI) from mixed organo-aqueous solutions containing water-miscible protic aliphatic alcohols and several aprotic solvents was investigated by using dicyclohexano-18-crown-6(DC18C6) as an extractant. The organic phase was a binary solution of DC18C6 and toluene while the polar phase was a three component solution of uranyl nitrate, polar additive and aqueous nitric acid. Methanol, ethanol, isobutanol, dioxane, acetone, propylene carbonate and acetonitrile were used as the organic components of the mixed (polar) phase. Propylene carbonate, acetone, acetonitrile and dioxane increased the extractability of U(VI), whereas alcoholic additives showed only an antagonistic effect. The relative increase in extraction was found to be more at lower nitric acid concentrations. Possible reasons for such behaviour are briefly discussed. Recovery of U(VI) from loaded organic phase was easily accomplished using dilute perchloric acid and sulphuric acid. A sample method was standardized for the separation of plutonium(IV) from uranium(VI) based on its reductive stripping.     

TDDFT investigation on nucleic acid bases: comparison with experiments and standard approach

A comprehensive theoretical study of electronic transitions of canonical nucleic acid bases, namely guanine, adenine, cytosine, uracil, and thymine, was performed. Ground state geometries were optimized at the MP2/6-311G(d,p) level. The nature of respective potential energy surfaces was determined using the harmonic vibrational frequency analysis. The MP2 optimized geometries were used to compute electronic vertical singlet transition energies at the time-dependent density functional theory (TDDFT) level using the B3LYP functional. The 6-311++G(d,p), 6-311(2+,2+)G(d,p), 6-311(3+,3+)G(df,pd), and 6-311(5+,5+)G(df,pd) basis sets were used for the transition energy calculations. Computed transition energies were found in good agreement with the corresponding experimental data. However, in higher transitions, the Rydberg contaminations were also obtained. The existence of pisigma* type Rydberg transition was found near the lowest singlet pipi* state of all bases, which may be responsible for the ultrafast deactivation process in nucleic acid bases.     

High-performance liquid chromatographic assay of alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine butanol (BMY 14802), a potential antipsychotic drug, in monkey and rat plasma

A high-performance liquid chromatographic-fluorescence method was developed for the quantitative analysis of BMY-14802 (I) in monkey and rat plasma. After the addition of the internal standard (BMY-14853 I.S.), 250 microliters of plasma were made basic by the addition of 2 ml of saturated sodium carbonate buffer. Compound I and the I.S. were then extracted into 5 ml of methyl tert.-butyl ether. The organic phase was evaporated and the resulting residue was reconstituted in mobile phase. Final separation and quantitation of I was achieved on an octadecyl column with a 0.05 M potassium phosphate-acetonitrile-triethylamine-85% phosphoric acid (650:350:0.1:0.05, v/v) mobile phase. Fluorescence detection was used to monitor the eluent at an excitation wavelength of 240 nm and an emission wavelength of 400 nm. The limit of detection was 0.5 ng/ml. The standard curve was linear over the range 5.0-1000 ng/ml. Intra-assay and inter-assay precision values were less than 4.0% relative standard deviation and accuracy was within 12% of nominal values. Compound I was shown to be stable in monkey and rat plasma for at least six months when stored at -20 degrees C.     

Solvent extraction of metals with potassium-dihydro-bispyrazolyl-borate

The extraction of Cu(II), Ni(II), Co(II), Cd(II), Zn(II), Pb(II) and Mn(II) with potassium-dihydro-bispyrazolyl-borate (H(2)BPz(2)(-)) in dichloromethane has been studied. Extraction constants (logK(ex)) have been calculated for all metal systems and were compared with those obtained with dibenzoylmethane (DBM), thenoyltrifluoroacetone (HTTA) and 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP). The method has been used for the determination of Cu(II), Co(II), Cd(II), Zn(II), Pb(II) and Mn(II) in standard alloys and for preconcentration of metal ions in synthetic samples.     

An ab initio study of electronic spectra and excited-state properties of 7-azaindole in vapour phase and aqueous solution

The geometries of 7-azaindole (7AI), its tautomer (7AT), and 7AI–H₂O and 7AT–H₂O complexes were optimised in the ground state and some low-lying singlet excited states using the 3-21G basis set. Differences of total energies of the optimised ground and excited states and the vertical excitation energies of these systems were used to explain the observed electronic spectra. Effect of solvation of these systems in bulk water was studied using the polarized continuum model (PCM). The mode of binding of a water molecule in the S₂(n–π^*) excited state of 7AI was found to be quite different from those in its ground and π–π^* excited states. It is shown that crossing of the lowest two singlet excited-state potential surfaces S₁(π–π^*) and S₂(n–π^*) of 7AI occurs in the vapour phase under geometry relaxation while on interaction with water, the S₂(n–π^*) excited state is raised up appreciably going even above the S₃(π–π^*) excited state. Ground- and excited-state molecular electrostatic potential mapping was carried out, which led to valuable information regarding the nature of excited states of the above-mentioned systems.     

Bis(2-ethylhexyl)sulfoxide as an extractant for americium(III) from aqueous nitrate media

Solven extraction separation of americium(III) from dilute aqueous nitrate media into n-dodecane by bis(2-ethylhexyl)sulfoxide (BESO) has been investigated over a wide range of experimentgal conditioins. Very poor extractablity of Am(III), necessitated the use of calcium nitrate as the salting-out agent. Effects of certain variables such as acidity, extractant concentration, salting-out agent concentration, organic diluents on the metal extraction by BESO have been examined in detail. By increasing the concentration of BESO in organic phase or calcium nitrate in aqueous phase, nearly quantitative extraction of americium even from moderate acidity is accomplished. Slope analyses applied to Am(III) distribution experiments from acidic nitrate solutions indicate predominant formation of the risolvated organic phase complex, Am(NO₃)₃)·3BESO for which equilibrium constant is found to be, log K_x=1.99. Extraction behavior of Am(III) has also been evlauated in the presence of several water-miscible polar organic solvents to stuy their possible synergistic effects on its extraction. Extractability of americium increased 5 to 10-fold withi increasing conentration of some of these additives, with maximum enhancement being observed in the presence of acetone or acetonitrile. Recovery of BESO from loaded americium is easily obtained using dilute nitric acid as the strippant.     

Evaluation of O2 and CO2 transfer coefficients in a locally integrated tubular hollow fiber bioreactor

We have studied the transfer coefficients for O₂ transport to and CO₂ removal from a model cell-free system using microporous hydrophobic hollow fibers axially placed along a tubular bioreactor for ethanol production with immobilized yeast in the shell. In this locally integrated bioreactor, O₂ and CO₂ transfer rates depend strongly on the shell side liquid flow rate; O₂ flow rate in the fiber bore influences O₂ transport only at very low flow rates. Diffusion of CO₂ does not affect O₂ transport. Local and overall O₂ and CO₂ transfer coefficients have been determined for a wide range of Reynolds Numbers. The efficiency of such transfers has been demonstrated for alcohol fermentation.     

Second-order dispersion energy between interacting hydrogen pairs by using the Borel integral

The second-order dispersion energy between interacting hydrogen pairs has been evaluated by the Borel-integral method. The results are in complete harmony with those obtained by the method of Padé approximants.