Chemisorption theory

The aim of chemisorption theory is to achieve for any adsorbateladsorbent system complete quantum predictions of the equilibrium positions of all the nuclei, the ground-state (electronically adiabatic) potential energy surface, the electronic excitation spectrum, and the response of the system to external probes. We are still a very long way from this goal, but some simplified models can now be explored in depth. Serious quantitative work begins with Toya,^1,2 and my review ends with the work of Appelbaum and Hamann³ These works provide examples of two of the three approaches to chemisorption theory. Toya's is a configuration interaction (CI) approach, using the states of the noninteracting adsorbate/solid system as basis states; Appelbaum and Hamann try to integrate Schrodinger's equation directly. The third approach is the linear combination of atomic orbitals molecular orbital (LCAO-MO) theory, and I begin with it because it is generally familiar in its simpler forms through its widespread use in molecular quantum mechanics. However, I remark at this stage that the direct integration of Schrodinger's equation may be more economical in computer time than the traditional quantum chemistry approach; it is certainly more economical if the nonlocal Hartree-Fock exchange potential is replaced by a local approximation to it.     

Electronic energy transfer in actinyl crystals V. Non-resonant mechanisms in Cs2UO2Cl4

Measurements are reported of the rate of non-resonant energy transfer in single crystals of caesium uranyl chloride over a range of temperatures down to 0.5 K. The dependence of the rate upon temperature and energy defect is used to identify the mechanism of phonon assistance. Comparison with the thermal line broadening and lineshift gives a value of the intersite coupling of ～0.02 cm^-1. Dilution shifts support this value. It is argued that both quadrupole-quadrupole coupling and exchange interactions contribute. The electron-phonon coupling parameters are also discussed. Unlike other examples where the mechanism has been established the transfer is controlled by a two-phonon Raman process.     

Novel seco-dibenzopyrrocoline alkaloid from Cryptocarya oubatchensis

[structure: see text] A novel seco-dibenzopyrrocoline alkaloid, named oubatchensine 6, and five phenanthroindolizidines (1-5) were isolated from Cryptocarya oubatchensis, and their structures were elucidated. Displacement centrifugal partition chromatography was used to purify compounds 1 and 6. Structure determination of the latter was carried out by mass spectrometry, NMR spectroscopy, quantum chemistry, and computer-assisted structure determination. Cytotoxic activity against KB cells was then investigated.     

Conformation study of HA(306-318) antigenic peptide of the haemagglutinin influenza virus protein

Several HLA-DR alleles present the immunodominant HA(306-318) peptide of haemagglutinin of the influenza virus to T cells. NMR data of the peptide in various water solutions exclude any alpha-helix or turn conformations. Circular dichroism and Fourier transform infrared spectroscopies indicate an estimated beta-extended structure in water of 31% and 28%, respectively, with spectra shape similar to the ones observed for beta-sheet containing proteins. The H/D amide exchange suggests a stable length-dependent interchain hydrogen-bonding. The partially beta-extended conformation of HA(306-318) in solution might be close to the one found in HA(306-318)-HLA-DR1 complex. These results suggest different interconverting extended conformations of HA(306-318), depending on the microenvironment of the solution medium. This flexibility emphasizes the ability of some peptides to fit more easily the binding site of several HLA-DR molecules. Similar results were obtained on the HIV P25(263-277) peptide which has been previously shown to be a good DR1 binder. From a vibrational point of view, infrared Amide I frequencies of secondary structures in peptides were ascertained. As previously demonstrated for proteins in solution, Fourier transform infrared and circular dichroism spectroscopies appear to be valuable tools for conformational properties of peptides. Their use may contribute to the detection of peptide conformation-binding relationship which has to be further tested by biochemical and biological studies.     

Minimizing makespan for a bipartite graph on a single processor with an integer precedence delay

We consider the makespan minimization for a unit execution time task sequencing problem with a bipartite precedence delays graph and a positive precedence delay d. We prove that the associated decision problem is strongly NP-complete and we provide a non-trivial polynomial sub-case. We also give an approximation algorithm with ratio .     

Raman studies on anticancer inorganic ring–dna interactions: Part 1. HexaziridmocyclotriphosphazeneN3P3(NC2H4)6

A Raman investigation of hexaziridinocyclotriphosphazene3D?NA interactions in vitro suggests that the alkylating sites on DNA for this powerful antitumour agent are the N(7) and NH₂ positions of adenine.     

Smoothing out positively curved metric cones by Ricci expanders

We investigate the possibility of desingularizing a positively curved metric cone by an expanding gradient Ricci soliton with positive curvature operator. This amounts to study the deformation of such geometric structures. As a consequence, we prove that the moduli space of conical positively curved gradient Ricci expanders is connected.     

Resonance-enhanced,multiphoton-ionization spectroscopy of NH3

The multiphoton-ionization spectroscopy of NH₃ has been explored using three-photon ionization through a two-photon resonant intermediate state. This method provides greatly increased sensitivity when compared to three-photon excitation to the intermediate state.     

Pilot‐scale ion‐exchange centrifugal partition chromatography: Purification of sinalbin from white mustard seeds

The purification of p‐hydroxybenzylglucosinolate (sinalbin) on a multigram scale from a crude aqueous extract of white mustard seeds (Sinapis alba var. concerta) was successfully achieved by scaling up a strong ion‐exchange centrifugal partition chromatography (SIXCPC) laboratory procedure. Thus, the one‐step sinalbin purification was performed with 2.35 g of crude extract in ?170 min (830 mg/h) up to 70.3 g in ?160 min (26.3 g/h) by switching from a 200 mL laboratory scale column to a 5.7 L pilot‐scale column. The required biphasic solvent system contained ethyl acetate, n‐butanol, and water in 3:2:5 v/v/v proportions, Aliquat 336® (trioctylmethyl ammonium chloride) was added to the organic stationary phase (80 mM) and acted as ion‐exchanger. Potassium iodide in the aqueous mobile phase (80 mM) was used as sinalbin displacer. The 28.5 mass scale factor arose from the increase in mobile phase flow‐rate (from 2 to 50 mL/min), from the higher mass of injected white mustard seed extract (from 12 to 350 g), and from the calculated productivity (from 830 mg to 26.3 g). These results demonstrate that industry scale production of glucosinolates is easily performed by SIXCPC, thus providing pure reference standards for pharmacology studies.