Ab initio configuration-interaction investigation of optical transitions in K+He and K+H2

The potassium resonance line (4s-->4p) centered around 770 nm is a major contributor to the optical extinction in the atmospheres of certain classes of brown dwarfs and extrasolar giant planets. The resonance line is significantly broadened by collisions with He and H2, and an accurate calculation of the line profile is needed for astrophysical models of these objects. As a first step, we report an accurate ab initio study of the K+He and K+H2 potential-energy curves correlating to the K 4s and 4p atomic energy levels, together with the dipole moments governing the transitions between these potential-energy curves. The molecular calculations have been carried out using a multireference configuration-interaction method, with the molecular orbitals expanded in a large Gaussian basis set. The transition dipole moments show significant variation with the molecular geometry. Calculations for the K+H2 system have been carried out for a range of H2 orientations and internuclear separations, so that the effect of H2 rotation and vibration may be explicitly included in future calculations of the pressure-broadened line profiles.     

Analytically continued Fock space multireference coupled-cluster theory: application to the 2Pi(g) shape resonance in e-N2 scattering

The technique of Fock space multireference coupled-cluster (FSMRCC) is applied for the first time to the correlated calculation of the energy and width of a shape resonance in an electron-molecule collision. The procedure is based upon combining a complex absorbing potential with FSMRCC theory. Accurate resonance parameters are obtained by solving a small non-Hermitian eigenvalue problem. The potential-energy curve of the (2)Pi(g) state of N2- is calculated using the FSMRCC and multireference configuration-interaction (MRCI) level of theories. Comparison with the single-determinant Hartree-Fock theory indicates that correlation effects are important in determining the behavior of the resonance state.     

Synthesis of diverse β-(nitrooxy)-substituted amines by regioselective ring-opening of aziridines under neat conditions

An efficient and regioselective method was developed for the synthesis of β-(nitrooxy)-substituted amine derivatives by ring-opening of different aziridines with Zn(NO₃)₂·6H₂O without using additives or catalyst. A library of β-(nitrooxy)-substituted amine derivatives having a variety of substituents has been synthesized. Excellent regioselectivity, high yields, clean reaction, ease of product isolation, easily accessible reactants, and solvent-free as well as environment friendly reaction conditions are the notable advantages of the present methodology. The nitrooxy derivative was successfully transformed into hydroxy derivative by simple reduction. Gram-scale synthesis demonstrates the potential applications of the present method.     

Efficient method to perform CAP/CI calculations for temporary anions

Electronically metastable states can efficiently be investigted using ??² techniques, such as the complex absorbing potential (CAP) or the stabilization method; but, the study of autodetaching systems is nonetheless far more expensive than the investigation of comparable bound states. The costly step of the ??² methods for resonances involves the repeated diagonalization of a parameterized Hamilton operator, and in this communication we investigate representations of the needed operators in very small basis set consisting of a few eigenstates of the physical Hamiltonian. It is shown that CAP calculations can indeed be performed using a very small eigenstate basis set, whereas basis sets of comparable size are unsuitable for stabilization calculations. Our results allow us to study the frequently employed energy selection procedure in the context of Siegert energies. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 218–226, 2001     

Combination of NH2OH·HCl and NaIO4: a new and mild oxidizing agent for selective oxidation of alcohols to carbonyl compounds

A new method for oxidation of alcohols to carbonyl compounds has been developed using NH₂OH·HCl and NaIO₄ under mild reaction conditions at room temperature. Application of the method for the synthesis of diiodo compound from α,β-unsaturated carbonyl compound is also described.     

Modeling the Biomass Growth and Enzyme Secretion by the White Rot Fungus Phanerochaete chrysosporium: a Stochastic-Based Approach

The white rot fungus Phanerochaete chrysosporium has been identified to be an environmentally useful microorganism for the degradation of various hazardous pollutants, mainly because of its ligninolytic enzyme system, particularly the lignin peroxidase (LiP) secreted by the fungus. In the present work, the behavior of the fungus in liquid medium due to variation in physico-chemical parameters, i.e., glucose concentration, nitrogen concentration, agitation, etc., was studied. Increment of the initial concentration of glucose in the medium increases the biomass growth and LiP activity, when cultured under controlled conditions. The biomass growth and LiP activity by the fungus was modeled following stochastic approach. The behavior of growth and enzyme activity of the fungus observed from the model were found to be in agreement with the experiments qualitatively.     

Precise determination of the unperturbed 8B neutrino spectrum

A measurement of the final state distribution of the (8)B β decay, obtained by implanting a (8)B beam in a double-sided silicon strip detector, is reported here. The present spectrum is consistent with a recent independent precise measurement performed by our collaboration at the IGISOL facility, Jyv?skyl? [O. S. Kirsebom et al., Phys. Rev. C 83, 065802 (2011)]. It shows discrepancies with previously measured spectra, leading to differences in the derived neutrino spectrum. Thanks to a low detection threshold, the neutrino spectrum is for the first time directly extracted from the measured final state distribution, thus avoiding the uncertainties related to the extrapolation of R-matrix fits. Combined with the IGISOL data, this leads to an improvement of the overall errors and the extension of the neutrino spectrum at high energy. The new unperturbed neutrino spectrum represents a benchmark for future measurements of the solar neutrino flux as a function of energy.     

Pyrene excimer fluorescence of yeast alcohol dehydrogenase: a sensitive probe to investigate ligand binding and unfolding pathway of the enzyme

The cysteine residues of yeast alcohol dehydrogenase (YADH) were covalently modified by N-(1-pyrenyl) maleimide (PM). A maximum of 3.4 cysteines per YADH monomer could be modified by PM. The secondary structure of PM-YADH was found to be similar to that of the native YADH using far-UV circular dichroism. The covalent modification of YADH by PM inhibited the enzymatic activity indicating that the active site of the enzyme was altered. PM-YADH displayed maximum excimer fluorescence at an incorporation ratio of 2.6 mol of PM per monomeric subunit of YADH. Nucleotide adenine dinucleotide (NAD) divalent zinc and ethanol reduced the excimer fluorescence of PM-YADH indicating that these agents induce conformational changes in the enzyme. Guanidinium hydrochloride (GdnHCl)-induced unfolding of YADH was analyzed using tryptophan fluorescence, pyrene excimer fluorescence and enzymatic activity. The unfolding of YADH was found to occur in a stepwise manner. The loss of enzymatic activity preceded the global unfolding of the protein. Further, changes in tryptophan fluorescence with increasing GdnHCl suggested that YADH was completely unfolded by 2.5 M GdnHCl. Interestingly, residual structures of YADH were detected even in the presence of 5 M GdnHCl using the excimer fluorescence of PM-YADH.