DBSA mediated chemoselective synthesis of 2-substituted benzimidazoles in aqueous media

An efficient synthetic method has been developed for the facile synthesis of 2-substituted benzimidazoles in organized aqueous media in the presence of a surfactant (viz. DBSA) as catalyst and I₂ as co-catalyst. The method described has the advantages of operational simplicity, excellent yields, high chemoselectivity, and clean and green reaction profile.     

Room temperature solution studies of complexation between o-chloranil and a series of anilines by spectrophotometric method.

Electron donor-acceptor (EDA) complex formation between o-chloranil and a series of anilines has been studied in CCl4 medium. In all the cases, EDA complexes are formed instantaneously on mixing the donor and acceptor solutions. N,N-dimethylaniline and N,N-dimethyl-p-toluidine form stable EDA complexes with o-chloranil while the other complexes decay slowly into secondary products. The kinetics of all these reactions has been studied by UV-VIS absorption spectrophotometric method and the rate constants of the reactions and formation constants of the EDA complexes have been determined. The charge transfer (CT) transition energies of the complexes are found to change systematically with change in the number and position of the methyl groups in the donor molecules (methylanilines). From an analysis of this variation, the electron affinity of o-chloranil has been found to be 2.54 eV. A perturbational inductive effect Hückel parameter hMe has been found from this trend and the value obtained (-0.27) is very close to that (-0.3) obtained by Lepley (J. Am. Chem. Soc., 86 (1964) 2545) from a study of tetracyano ethylene (TCNE)-methylbenzene complexes.     

一个集值映射的不动点定理

得到了从度量空间X(不必是完备的)到X的非空有界子集族B(X)的集值映射的一些不动点,其结果推广了一些已有的结论.     

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.     

Self-Assembling Synthetic Oligopeptide-Based Gelators

Synthetic self-assembling oligopeptide gelators are an important class of compounds which form thermoreversible gels in various organic solvents as well as in aqueous medium. These gels are soft, viscoelastic materials which are envisaged for useful applications in biological and material sciences. The terminally protected self-assembling synthetic tripeptide Boc-Ala-Aib-β-Ala-OMe 1 (Aib: α-aminoisobutyric acid i.e. dimethyl glycine and β-Ala: β-Alanine) forms gels in various organic solvents, whereas its structural analog i.e. the peptide Boc-Ala-Gly-β-Ala-OMe 2 (another self-assembling synthetic tripeptide) fails to form gels under similar conditions and this issue has been addressed. The terminally protected tripeptide Boc-Ala-Val-Ala-OMe 3 has been found to form gels in different aromatic organic solvents. Several structural analogs of peptide 3 [using small structural changes either in protecting groups (at the N or C-terminal position) or in amino acid side chains] have been synthesized, characterized and studied for gelation to address the question how structural changes can regulate the gelation property. Results of the gelation studies indicate that some structural changes are useful to make new peptide gelators with some variations in gelation property and efficiency, while a few structural changes in the protecting groups are really detrimental, leading to abolition the gelation property. These gels are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-Transform Infrared (FT-IR) spectroscopy and ¹H NMR studies.