Group Divisible Covering Designs with Block Size 4: A Type of Covering Array with Row Limit

A k‐GDCD, group divisible covering design, of type is a triple , where V is a set of gu elements, is a partition of V into u sets of size g, called groups, and is a collection of k‐subsets of V, called blocks, such that every pair of elements in V is either contained in a unique group or there is at least one block containing it, but not both. This family of combinatorial objects is equivalent to a special case of the graph covering problem and a generalization of covering arrays, which we call CARLs. In this paper, we show that there exists an integer such that for any positive integers g and , there exists a 4‐GDCD of type which in the worst case exceeds the Schönheim lower bound by δ blocks, except maybe when (1) and , or (2) , , and or . To show this, we develop constructions of 4‐GDCDs, which depend on two types of ingredients: essential, which are used multiple times, and auxiliary, which are used only once in the construction. If the essential ingredients meet the lower bound, the products of the construction differ from the lower bound by as many blocks as the optimal size of the auxiliary ingredient differs from the lower bound.     

Electrospun Hybrid Nanofibers Based on Chitosan or N‐Carboxyethylchitosan and Silver Nanoparticles

Hybrid nanofibers from chitosan or N‐carboxyethylchitosan (CECh) and silver nanoparticles (AgNPs) were prepared by electrospinning using HCOOH as a solvent. AgNPs were synthesized in situ in the spinning solution. HCOOH slowed down the cross‐linking of the polysaccharides with GA enabling the reactive electrospinning in the presence of poly(ethylene oxide) (PEO). EDX analyses showed that AgNPs are uniformly dispersed in the nanofibers. Since AgNPs hampered the cross‐linking of chitosan and CECh with GA in the hybrid fibers, the imparting of water insolubility to the fibers was achieved at a second stage using GA vapors. The surface of chitosan/PEO/AgNPs nanofibers was enriched in chitosan and 15 wt.‐% of the incorporated AgNPs were on the fiber surface as evidenced by XPS.

     

One‐Step Preparation of Electrospun Microfibrous Polystyrene Mats Having Surface Enriched in p‐tert‐Butylcalix[4]arene Fitted with Phosphinoyl Pendant Arms

Polystyrene microfibers containing lower‐rim substituted calix[4]arene with phosphinoyl pendant arms were easily prepared in one‐step procedure by electrospinning. A specific feature of the fibers is the difference in their functionality at the surface and in the bulk. The graded structure of the fibers was shown by XPS analyses. The calix[4]arene concentration in the 3–5 nm surface layer was 50% higher than the theoretically calculated if calix[4]arene was uniformly distributed in the fibers. A six‐coordinated complex was formed between the calix[4]arene included in the fibers and Ni²⁺ ions. The distribution of phosphorus along the fibers is uniform, as evidenced by X‐ray mapping.

     

H2S dissociation on the Fe(1 0 0) surface: An ab initio molecular dynamics study

The adsorption of H₂S on Fe(1 0 0) is examined using ab initio molecular dynamics at 298 and 1808 K. Dissociation of H₂S occurs at both temperatures simulated, to leave adsorbed S and two H atoms. The dissociation occurs via a two step process and the mechanism is found to be different depending on the temperature of the reaction. At 1808 K, diffusion of the dissociated H atoms into the subsurface region is also observed.     

Ab initio study of S dynamics on iron surfaces

Density functional theory was employed to examine the interactions of atomic sulfur with the Fe(1 0 0) and Fe(1 1 0) surfaces. Vibrational frequency calculations were performed to determine the nature of stationary points at the high symmetry atop, bridge and hollow adsorption sites and to indicate the direction the adsorbate would move across the surface. The values were also used in the determination of the rate constant for hopping of S from one energy minimum site to another. Ab initio molecular dynamics (MD) simulations were then performed to monitor the mobility of the S atom on the (1 0 0) surface at different temperatures up to the melting point of Fe (1808 K) and were compared to our previously obtained ab initio MD results for S/Fe(1 1 0) [N. Todorova, M.J.S. Spencer, I. Yarovsky, Australian Institute of Physics 16th Biennial Congress, 2005, Canberra, Australia, ISBN 0-9598064-8-2].     

Simultaneous Spectrophotometric Determination of Paracetamol and <Emphasis Type="Italic">p</Emphasis>-Aminophenol in Pharmaceutical Products with Tiron Using Dissolved Oxygen as Oxidant

A simple, rapid, and specific method was developed for the determination of paracetamol and p-aminophenol. The method is based on the hydrolysis of paracetamol to p-aminophenol, which, using dissolved oxygen as an oxidant in the alkaline region, was further transformed into benzoquinoneimine, capable of reacting with tiron to produce a green indophenol dye. The stabilization of indophenol dye was achieved by the addition of copper(II) solution. The absorbance was measured at 601 nm in alkaline medium, and the molar absorptivity was found to be 1.1 × 10⁴ L/(mol cm). Paracetamol (PCT) and p-aminophenol (PAP) were determined in pharmaceutical products in the 1.5–15 mg/L PAP concentration range with a detection limit of 1.2 × 10⁻⁶ M or 0.13 μg/mL PAP. The developed method can be applied to the determination of p-aminophenol in the presence of paracetamol without prior separation. The proposed method is successfully employed for determination of paracetamol and p-aminophenol in various synthetic mixtures and pharmaceutical preparations. The obtained results were statistically compared with those given by the official method and the procedures evaluated as regards to both figures of merit and ease of applicability. __________ From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 11, 2005, pp. 1147–1151. Original English Text Copyright ? 2005 by Cekic, Filik, Apak. This article was submitted by the authors in English.     

Mass spectrometric investigation of some [1]benzopyrano[3,4-c]pyrazole and [1]benzopyrano[4,3-d]isoxazole derivatives

The fragmentation behaviour of some [1]benzopyrano[3,4-c]pyrazole and [1]benzopyrano[4,3-d]isoxazole derivatives under electron impact is described.     

Discovery of new therapeutic targets by the informational spectrum method

The field of bioinformatics has become a major part of the drug discovery pipeline playing a key role in improvement and acceleration of this time and money consuming process. Here we review the application of the informational spectrum method (ISM), a virtual spectroscopy method for structure/function analysis of proteins, in identification of functional protein domains representing candidate therapeutic targets for drugs against human immunodeficiency virus (HIV)-1, anthrax, highly pathogenic influenza virus H5N1 and cardiovascular diseases.     

A Convenient Approach to Stereoisomeric Iminocyclitols: Generation of Potent Brain‐Permeable OGA Inhibitors

Pyrrolidine‐based iminocyclitols are a promising class of glycosidase inhibitors. Reported herein is a convenient epimerization strategy that provides direct access to a range of stereoisomeric iminocyclitol inhibitors of O‐GlcNAcase (OGA), the enzyme responsible for catalyzing removal of O‐GlcNAc from nucleocytoplasmic proteins. Structural details regarding the binding of these inhibitors to a bacterial homologue of OGA reveal the basis for potency. These compounds are orally available and permeate into rodent brain to increase O‐GlcNAc, and should prove useful tools for studying the role of OGA in health and disease.     

Stable Aqueous Dispersion of PEGylated Nanoparticles by Polyelectrolyte Complex Formation

Stable aqueous dispersions of nanoparticles were prepared by polyelectrolyte complex formation between well‐defined poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propane sodium sulfonate) and poly(ethylene glycol)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] diblock copolymers. Controlled synthesis of the copolymers was achieved by water‐based atom transfer radical polymerization (ATRP). The nanoparticles were characterized by a quite narrow and monomodal size distribution as evidenced by dynamic light scattering (DLS) and confirmed by atomic force microscopy (AFM) after solution casting and freeze‐drying.