Reactions of hydroxyalkyl radicals with nickel(II) and copper (II) complexes of 2-methyl-5-nitro-1H-imidazole-1-ethanol: A steady-state gamma-radiolysis and flash photolysis study

The yields for the loss of chromophore of Ni(II) and Cu(II) complexes of metronidazole,G(-Ni(II)M) andG(-Cu(II)M), reached almost zero when their aqueous solutions were -irradiated in the presence, of 0.4 mol·dm^–3 of MeOH, EtOH,i-PrOH andt-BuOH in aerated medium. However, under N₂O saturated conditions, these yields attained limiting values which suggests that the hydroxyalkyl radicals, derived from the alcohols by reaction with OH, react with the complexes in deaerated medium. But in aerated medium they react preferentially with O₂. The rate constants for the reactions of the different hydroxyalkyl radicals with the complexes have been determined by the flash photolysis technique and the plausible mechanisms for the reactions have been suggested.     

Molecules in an electric field: Some structural and spectroscopic consequences

It is theoretically shown that under the influence of an appropriately directed external electric field (ε) in H₂CO or a similar molecule (of the XYC = O type), the barrier to planar inversion in the ³n π* state decreases as the field strength increases. The molecule assumes a forced planar geometry in the ³n π* state rather abruptly when ε_(applied) > ε_(critical). This phenomenon of field-induced change of structure of an isolated molecule has the attributes of a first order phase transition. The effects should be spectroscopically detectable in the inversion spectrum. The existence of another critical field strength at which the molecule makes a more or less continuous transition from the normal convalent to a purely ionic structure is demonstrated and rationalized through a simple model.     

The INDO/2-AHP (average hole potential) method for excited states: Comparison with the simple INDO/2-HP (hole potential) method

The INDO/2 version of the average hole potential (AHP) model is analyzed. The model is applied to study the geometric features, molecular inversion barriers, singlet-triplet splittings, etc., of a few small carbonyl molecules (H₂CO, HFCO, F₂CO) in the ^1,3nπ* states with partial as well as complete optimization of all geometric parameters in the excited states. The results are compared with those obtained by a simple hole-potential (HP) model.     

Isoelectric focusing studies of concanavalin A and the lentil lectin

Isoelectric focusing (IEF) of metallized and demetallized preparations of concanavalin A (Con A) consisting of either intact or fragmented subunits shows different band patterns. Metallized Con A consisting of intact polypeptide chains (intact Con A) has an isoelectric point (pI) 8.35. Metallized preparations consisting of fragmented chains (fragmented Con A) show three bands with pI values 8.0, 7.8 and 7.7. Demetallized intact Con A (intact apoCon A) has a pI of 6.5, however, it undergoes pH dependent association during IEF under certain conditions, which gives rise to multiple bands. Ampholyte-mediated demetallization of intact and fragmented Con A and subsequent aggregation of the apoprotein results in multiple bands during IEF in the presence of the pH range 3 to 10 ampholytes. However, ampholytes of the pH range 7 to 9 do not demetallize the proteins and show a single band with intact Con A. The pI of intact Con A remains essentially the same in the presence of inhibitory sugar. Furthermore, different moleculars forms of Con A, including locked and unlocked conformers of intact apoCon A, and the dimeric and tetramic states of both intact Con A and intact apoCon A have been identified and their pI values determined. IEF of the lentil isoelectins, LcH-A and LcH-B, shows single bands of pI 8.5 and 9.0, respectively. However, the native lectin mixture gives rise to an additional band of pI 8.8 due to a hybrid protein formed by ampholyte-mediated subunit exchange between the isolectins.     

Terpenoids—LVII Synthesis of some germacrane derivatives

Both liquid and solid hexahydrocostunolides obtained by the pressure hydrogenation of costunolide (V) and solid dihydrocostunolide (VI) respectively, give the same optically active hexahydrogermacol (IIIa), when subjected to controlled reduction with LiAlH₄, followed by Huang-Minlon reduction. The alcohol (IIIa) on oxidation with chromic oxide gives optically active hexahydrogermacrone (IIa). Dehydration of IIIa with KHSO₄ followed by catalytic hydrogenation gives the optically inactive saturated hydrocarbon, germacrane (IV). Since the total synthesis of solid dihydrocostunolide (VI) has already been achieved the preparation of IIIa, IIa and IV from VI constitutes a total synthesis of the above three compounds.     

Solvent extraction separation of tantalum from niobium on macro scale using di(2-ethylhexyl) phosphoric acid as extractant

A solvent extraction procedure for the separation of niobium and tantalum has been developed. The method consists of extracting tantalum from its aqueous mixture with niobium, with the help of di(2-ethylhexyl)phosphoric acid (HDEHP) in n-heptane. The aqueous feed consists of niobium and tantalum in an aqueous medium containing hydrochloric and oxalic acids. The concentrations of niobium and tantalum were raised to 1 mg/ml in the aqueous solution. The extraction efficiency of tantalum under these conditions was found to be 85%. Effects of chloride and oxalate ions as well as those of the concentration of HDEHP on the extraction efficiency were studied and discussed in detail.     

Redox reactions of hydrogen adducts of thymine: Comparisons with the reactions of hydroxyl adducts

Hydrogen atoms form two kinds of adducts with thymine (oxidizing and reducing). Redox reactions of these two kinds, popularly known as 5-hydrogenated-6-thyminyl (reducing) and 6-hydrogenated-5-thyminyl (oxidizing), were investigated where ferric ions (oxidizing) and ferrous ions (reducing) were used as the corresponding redox partners. A steady-state gamma radiolytic system was chosen where hydroxyl radicals were scavenged using t-butyl alcohol in acidic (pH 1.8) solution. It is inferred that the redox potential of oxidizing hydrogenated thyminyl radicals lies between 0.77 and 1.4 V vs. NHE. The reducing hydrogenated thyminyl radical has a redox value less than 0.8 V because it efficiently undergoes electron transfer reaction with Fe(III). A probable range of redox values for hydroxyl adduct of thymine is included for comparison.     

Cosmic Antiproton Spectrum at the Top of the Atmosphere Derived from the New Scaling Model

The new scaling variable model explains the scaling behavior of p + p → p + X inclusive reactions at ISR energies. The cosmic antiproton spectrum has been derived from this model using the primary proton spectrum of RYAN et al. The derived antiproton-proton flux ratio lies within the upper limit value of BOGOMOLOV et al. and CHEN. The estimated antiproton spectrum follows the relation where the antiproton energy E_p is expressed in GeV and the intensity in units (cm² sec sr GeV)^?1.     

Sea Level Muon Spectrum Derived from Bugaev Model

The pion and kaon spectra in the atmosphere are derived from primary nucleon spectrum determined by GRIGOROV et al.; they satisfy the relations N(E_π) dE_π = 0.187 EdE_π and N(E_k) dE_k = 0.017 E dE_k, respectively. By using the pion-kaon atmospheric diffusion equation the sea level muon spectrum is calculated and the result compared with the magnetic spectrograph data of ALLKOFER et al. and AYRE et al.     

Exploiting the interdependence of maximum entropy parameters in eigenvalue problems

We exploit the interrelation among the parameters embedded in the maximum entropy ansatz to develop a scheme for obtaining accurate estimates of the ground‐state energy and wave function of systems for which the potential is represented by a rational function. Our scheme reduces an N‐parameter optimization problem to a two‐parameter one, leading to considerable simplification of the prevalent strategy. An indirect route for the study of excited states is also sketched. Test calculations on hydrogenic systems subject to strong or superstrong radial magnetic fields with and without electric field reveal the advantages of our approach. Additional studies on 1‐D anharmonic oscillators affirm its workability and generality. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002