Synthesis and physico-chemical studies on transition metal complexes of symmetric bis-Schiff base ligands

Transition Metal Chemistry - A new series of symmetric bis-Schiff bases derived from 1,2-diaminoethane with bis-salicylaldehyde (H2L1) and/or bis-o-hydroxyacetophenone (H2L2) have been prepared....     

Ketenes in polymer-assisted synthesis

Since its inception, ketene chemistry has developed into a unique and well-established source of useful transformations for conventional synthetic organic chemistry. It is, therefore, not surprising that soon after their movement from the realm of peptide and peptoid libraries to that of small molecules, combinatorial chemists have sought the benefits of ketene chemistry to satisfy their own synthetic needs. The ability of these versatile molecules to undergo reactions with nucleophiles, and to participate in cycloadditions and cyclocondensations, has been utilized for the preparation of diverse heterocyclic compounds, and has added to the advantages of polymer-assisted synthesis for rapid purification. Different types of ketenes and different methods for their generation have been involved, which illustrates the potential diversity of the chemistry. There is now a better grasp of the effect of the fragility of these sometimes transient molecules on the reactions involving solid supports, and this augurs well for the application of some of the more recent developments in ketene chemistry to the generation of small-molecule libraries.     

Improvement of sample preparation in the chemical sampling of gold ore deposits

A procedure used in the chemical sampling of gold ore deposits for assessing the representative mass of samples and analytical weighed portions is improved. It is shown that the coefficient K used to assess the representative sample mass and characterizing the nonuniformity of the gold distribution in the gold ore sample can go beyond the limits established by the regulations of the Ministry of Natural Resources of the Russian Federation.     

Probabilistic Formulation of the Emergency Service Location Problem

The problem of locating emergency service facilities is studied under the assumption that the locations of incidents (accidents, fires, or customers) are random variables. The probability distribution for rectilinear travel time between a new facility location and the random location of the incident P _i is developed for the case of P _i being uniformly distributed over a rectangular region. The location problem is considered in a discrete space. A deterministic formulation is obtained and recognized to be a set cover problem. Probabilistic variation of the central facility location problem is also presented.An example and some computational experience are provided to emphasize the impact of the probabilistic formulation on the location decision.     

Resolution of the enantiomers of oxamniquine by capillary electrophoresis and high-performance liquid chromatography with cyclodextrins and heparin as chiral selectors

The methods of separation of the enantiomers of the chiral drug oxamniquine are compared, between HPLC with either cyclodextrins and their related derivatives as chiral selectors in the mobile phase or immobilisedin a chiral stationary phase (as Cyclobond I and II) and between capillary zone electrophoresis (CZE) where the cyclodextrins are added to the buffer solution. The HPLC experiments, which included structured method optimisation were largely unsuccessful in resolving the enantiomers, with the exception of when a Chiral-AGP protein stationary phase was introduced into the programme. However although this chiral stationary phase provided baseline resolution of the enantiomers the stability of the method was suspect to small changes in the pH (0.2 units). In contrast the CZE method developed for both cyclodextrins and their derivatives gave good resolution of the enantiomers and method stability (R.S.D. <1%, N = 10 on precision). The basis of the interaction mechanism between selector and selectand was shown as a 1:2 relationship of cyclodextrin to analyte by NMR. In addition the polysaccharide, heparin was investigated as a chiral additive and excellent resolution of the oxaminiquine was achieved with 3 mM heparin in 50 mM sodium dihydrogenphosphate (pH 3.0) as buffer in CZE, which also gave a stable procedure. This method allowed the detection of each of the enantiomers in the presence of the other down to 0.23% (m/m). The overall composition of the heparin material from different sources can however be slightly variable and this can result in small differences in resolution capability.     

Non-local matrix generalizations ofW-algebras

There is a standard way to define two symplectic (hamiltonian) structures, the first and second Gelfand-Dikii brackets, on the space of ordinarym ^th-order linear differential opeatorsL=–d ^m +U ₁ d ^m–1+U ₂ d ^m–2+...+U _m . In this paper, I consider in detail the case where theU _k aren×n-matrix-valued functions, with particular emphasis on the (more interesting) second Gelfand-Dikii bracket. Of particular interest is the reduction to the symplectic submanifoldU ₁=0. This reduction gives rise to matrix generalizations of (the classical version of) thenon-linear W _m -algebras, calledV _{n, m} -algebras. The non-commutativity of the matrices leads tonon-local terms in theseV _{n, m} -algebra.s I show that these algebras contain a conformal Virasoro subalgebra and that combinationsW _k of theU _k can be formed that aren×n-matrices of conformally primary fields of spink, in analogy with the scalar casen=1. In general however, theV _{m, n} -algebras have a much richer structure than theW _m -algebras as can be seen on the examples of thenon-linear andnon-local Poisson brackets {(U _2)ab(), (U _2)cd()}, {(U _2)ab(), (W _3)cd()} and {(W _3)ab(), (W _3)cd()} which I work out explicitly for allm andn. A matrix Miura transformations is derived, mapping these complicated (second Gelfand-Dikii) brackets of theU _k to a set of much simpler Poisson brackets, providing the analogoue of the free-field representation of theW _m -algebras.     

Simple proofs of the Cauchy-Schwartz inequality and the negative discriminant property in archimedean almost <Emphasis Type="Italic">f</Emphasis>-algebras

The paper presents simple proofs of the Cauchy-Schwartz inequality and the negative discriminant property in archimedean almost f-algebras^[5], based on a sequence approximation.      

Amino Acid Derivatives, VII [1]: Synthesis and Antiviral Evaluation of α-Amino Acid Esters Bearing an Indazole Side Chain

A series of peptide and dipeptide derivatives conjugated with an indazole residue were synthesized. The new compounds were evaluated in vitro for cytotoxicity against Hepatitis-A virus (HAV-27), Herpes Simplex virus-1 (HSV-1), and Hepatitis-B virus (HBV) and showed moderate to high activity.     

Amino Acid Derivatives, V [1]: Synthesis and Antiviral Evaluation of α-Amino Acid Esters Bearing an α-d -Mannofuranoside Side Chain

d-Mannose was treated with dry acetone in the presence of conc. H₂SO₄ to afford 2,3:5,6-di-O-isopropylidene-α-d-mannofuranoside. Treating the latter with ethyl chloroacetate gave carboethoxymethyl 2,3:5,6-di-O-isopropylidene-α-d-mannofuranoside, which was hydrolyzed with N₂H₄ · H₂O to afford the acid hydrazide derivative. Treating of the acid hydrazide with acylated amino acides, via the azide-coupling method afforded the corresponding O-glycopeptides. Reaction of the glycopeptide methyl esters with N₂H₄ · H₂O afforded the corresponding hydrazides, which were coupled with the amino acid methyl esters to afford the dipeptides. Deprotection was carried out by using 70% AcOH. The prepared O-glycopeptides were tested for antiviral activity against hepatitis B virus and showed moderate activities.     

Rheological properties of carboxymethyl cellulose (CMC) solutions

In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure–properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.