Synthesis of Thioglycosides from Propargyl Glycosides Exploiting Alkynophilic Gold Catalyst

Various thioglycosides were synthesized from stable propargyl glycosides using catalytic quantity of AuBr₃ and various thiol aglycons. The current protocol enables preparation of thioglycosides from propargyl glycosides in an efficient and simple manner. The reaction is fast, catalytic, and mild. Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Carbohydrate Chemistry to view the free supplemental file.     

A comparison of two methods on non-uniqueness for a class of two-point boundary value problems

We consider two methods that have been used in [1] to prove multiple non-negative solutions for nonlinear boundary value problems of the form-u′(x) =λf(u(x)) ; x ? (0,1)u(0) = 0 =u(1) ,namely (A) using a quadrature technique and (B) using sub-super solutions. In this short paper we compare these methods and give an interesting proof showing that (A) is often sharper than (B) for establishing non-uniqueness. However, we also point out the advantage of (B) over (A)     

Removal of heat of adsorption from adsorbent by forced convection

An analytical mathematical model is used to investigate the effectiveness of forced convection for removal of the heat of adsorption from an adsorbent mass undergoing a differential adsorption process in a flow system. An example of such a process is measurement of gas adsorption kinetics using a differential adsorption bed. Isothermal operation may not be achieved even when a high gas flow rate is used, particularly if the sorption kinetics is relatively fast. Very small changes in the adsorbent temperature can cause significant departure from the isothermal uptake behavior when the heat of adsorption is moderately large. A criterion for validity of isothermal data analysis is given.     

Properties of electropolymerised polypyrrole thin film on silver

This paper reports the properties of electropolymerised polypyrrole thin film on silver. The transmission, reflection, conductivity and dielectric behavior of polypyrrole coated silver has been studied in the 8-12 GHz frequency range of the electromagnetic spectrum. The polypyrrole thin film makes silver a better conductor for microwaves. The microwave conductivity is larger than the DC conductivity by many orders of magnitude. The real and imaginary part of dielectric constant increases in magnitude with increasing doping level and also it decreases in magnitude with increasing frequency.     

Pyridinium bromochromate: a new and efficient reagent for bromination of hydroxy aromatics

Pyridinium bromochromate (PBC) has been used as an efficient and selective nuclear brominating agent for bromination of various substituted hydroxy-acetophenones, aldehydes and phenols.     

Uniqueness of non-negative solutions for a semipositone problem with concave nonlinearity

We study a semilinear Dirichlet problem where the nonlinearlity is monotone, negative at zero (Semipositone), and concave. We assume that the outer boundary of the region is convex and show that for large values of a parameter there can be only one non-negative solution. We show that such a solution is positive in the region.     

Soluble aromatic polyamides modified by incorporation of 1,2,4-triazole and pentadecyl units into the backbone of polymer

Abstract

A new series of soluble aromatic polyamides was synthesized by low temperature solution polycondensation of novel aromatic diamine namely 3,5-bis-(4′-amino phenyl)-4-(4″-methoxy-2″-pentadecyl phenyl) 1,2,4-triazole (VII) with aromatic diacid chlorides, viz. isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC). The aromaticdiamine (VII) was characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C), and mass spectrometry. Copolyamides were also synthesized by employing various mole proportions of IPC and TPC with diamine (VII). Inherent viscosities of these polyamides were in the range of 0.50–0.65 dL/g in DMAc, indicating formation of moderate to high molecular weight of polyamides. These polyamides showed good solubility in polar aprotic solvents such as N,N-Dimethyl acetamide (DMAc), N-Methyl 2-pyrrolidone (NMP), N, N, Dimethyl formamide (DMF), and Dimethyl sulphoxide (DMSO), which may be due to incorporation of pendant methoxyphenyl moiety with pentadecyl units. The amorphous morphology of polyamides as evidenced by XRD. These polyamides had lower glass transition temperatures; as determined by DSC, compared to the T_g of conventional aromatic polyamides due to internal plasticization effect of long alkyl pentadecyl group. Polymers showed good thermal stability, with initial decomposition temperature above 300?°C.