Computational study of the halogen atom-benzene complexes

The structures of halogen atom-benzene complexes were investigated by modern DFT and ab initio computational methods. The spectroscopic properties of the complexes are also predicted and are in good agreement with experiment where such data have been reported. The fluorine atom-benzene complex is predicted to be a sigma complex due to the strength of a C-F bond. The chlorine atom-benzene complex is predicted to have an eta(1) pi complex structure, which is only slightly more favorable (1.1 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than a sigma complex but is significantly more stable (4.4 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than the eta(6) pi complex. The bromine and iodine benzene complexes are also predicted to prefer an eta(1) pi complex structure.     

Multisample probe for fast-atom bombardment / mass spectrometry

An inexpensive multisample fast-atom bombardment (FAB) probe assembly was designed for high-throughput analysis of samples on a VG ZAB-SE mass spectrometer. The system consists of a vacuum lock system and a FAB probe whose tip contains five or more sample wells. The probe enters the mass spectrometer source region perpendicular to the secondary ion beam axis, The probe is maintained at high voltage on contact with a spring clip attached to the screen plate of the source block. Sample throughput with the multisample probe is twice that of a coaxial probe, with about twice the sensitivity and no sample cross contamination.     

Mechanism of sorption of phenols from aqueous solutions onto surfactant-modified montmorillonite

Equilibrium and kinetic studies on the sorption of phenol, m-nitrophenol (m-NP), and o-cresol from water onto montmorillonite modified with cetyltrimethylammounium bromide (CTAB) were conducted. Experiments were carried out as a function of solution pH, sorbate concentration, and temperature (25-55 degrees C). It was shown that the sorption capacity decreased in the order phenol>o-cresol>m-NP. The Langmuir, dual-mode sorption, and Redlich-Peterson models were tested to fit the sorption isotherms of single-solute systems, whereas the Langmuir competitive model was used to describe bisolute sorption equilibria. Thermodynamic parameters (DeltaH degrees and DeltaS degrees ) and the mean free energy (E) for the sorption of phenols were determined from the temperature dependence of the distribution constant and the Dubinin-Radushkevick equation, respectively. A simplified kinetic model was proposed to confirm the sorption mechanism.     

Synthesis of 3-(3′-Acetyl-5′-aroyl-1′,3′,4′-oxadiazolyl-2′)-chromones

A general method has been proposed for synthesizing 3-(3-acetyl-5-aroyl-1,3,4-oxadiazolyl-2)-chromones that has been based on conversion of 3-formylchromones to acylhydrazones and of theacylhydrazones into the heterocyclic chromones.     

On the determination of crystallinity and cellulose content in plant fibres

A comparative study of cellulose crystallinity based on the sample crystallinity and the cellulose content in plant fibres was performed for samples of different origin. Strong acid hydrolysis was found superior to agricultural fibre analysis and comprehensive plant fibre analysis for a consistent determination of the cellulose content. Crystallinity determinations were based on X-ray powder diffraction methods using side-loaded samples in reflection (Bragg-Brentano) mode. Rietveld refinements based on the recently published crystal structure of cellulose Iβ followed by integration of the crystalline and amorphous (background) parts were performed. This was shown to be straightforward to use and in many ways advantageous to traditional crystallinity determinations using the Segal or the Ruland–Vonk methods. The determined cellulose crystallinities were 90–100 g/100 g cellulose in plant-based fibres and 60–70 g/100 g cellulose in wood based fibres. These findings are significant in relation to strong fibre composites and bio-ethanol production.     

Linear programming with entropic perturbation

In this paper, we derive an unconstrained convex programming approach to solving standard form linear programs through an entropic perturbation. The whole duality theory is established by using only one simple inequality lnz z –1 forz > 0. A curved search algorithm is also proposed for obtaining a pair of primal and dual-optimal solutions. The proposed algorithm is proven to be globally convergent with a quadratic rate of convergence. Computational results are included in support of theoretic findings.The work is partially supported by the North Carolina Supercomputing Center, the Cray Research Award, and the National Science Council of the Republic of China # NSC 81-0415-E-007-10.