Solvent-free synthesis of some new 2-（3,5-dimethoxy-4-methylphenyl）-5-aryl-1,3,4-oxadiazoles

An expeditious microwave-accelerated one-step synthesis of some new 2-（3,5-dimethoxy-4-methylphenyl）-5-aryl-1,3,4- oxadiazoles by reaction of 3,5-dimethoxy-4-methyl hydrazide with different carboxylic acids in presence of thionyl chloride under neat conditions,has been achieved.     

Microwave-accelerated synthesis of some 1-aroyl-3,5-dimethylpyrazoles

Rapid and highly efficient synthesis of some 1-aroyl-3,5-dimethylpyrazoles is achieved by the cyclocondensation of corresponding aroyl hydrazides with 2,4-pentanedione in the absence of solvent and catalyst, under microwave irradiation. The reaction proceeds rapidly and is completed within 40-70 s giving a series of 1-aroyl-3,5-dimethylpyrazoles derivatives in high yields. All of the compounds have been characterized by FTIR, ^1H NMR, and mass spectroscopy.     

Studies of inhibitor binding to the [4Fe-4S] cluster of quinolinate synthase

Stop for NadA! A [4Fe-4S] enzyme, NadA, catalyzes the formation of quinolinic acid in de?novo nicotinamide adenine dinucleotide (NAD) biosynthesis. A structural analogue of an intermediate, 4,5-dithiohydroxyphthalic acid (DTHPA), has an in?vivo NAD biosynthesis inhibiting activity in E. coli. The inhibitory effect can be explained by the coordination of DTHPA thiolate groups to a unique Fe site of the NadA [4Fe-4S] cluster.     

Sturm theory for the equation of vibrating beam

In this paper we develop an extension of the classical Sturm theory [C. Sturm, Sur une classe d'equations à derivée partielle, J. Math. Pures Appl. 1 (1836) 373-444], to study the oscillation properties for the eigenfunctions of some fourth-order two point boundary value problems on the interval [0,1]. We are mainly interested in the case when these problems have negative eigenvalues induced by the sign of the parameters in the boundary conditions. In particular, we give an asymptotic estimate of the number of zeros in (0,1) of the first eigenfunction in terms of the variation of parameters in the boundary conditions.