Fluorescence quenching of 2,2″ dimethyl-p-terphenyl by carbon tetrachloride in different solvents and temperatures

The fluorescence quenching of 2,2″-dimethyl-p-terphenyl (DMT) by carbon tetrachloride by steady state in different solvents, and by transient method in benzene has been carried out at room temperature. The Stern-Volmer (SV) plot has been found to be non-linear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex and sphere of action static quenching models. Using these models various rate parameters have been determined. The magnitudes of these parameters imply that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation in the SV plots is attributed to the static and dynamic quenching. Further, from the studies of temperature dependence of rate parameters and lifetime measurements, it could be explained that the positive deviation is due to the presence of a small static quenching component in the overall dynamic quenching. With the use of finite sink approximation model, it was possible to check whether these bimolecular reactions as diffusion limited and to estimate independently distance parameter R′ and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R′ and D with the values of the encounter distance R and the mutual diffusion coefficient D determined using the Edward's empirical relation and Stokes-Einstein relation.     

Design and synthesis of novel thiopheno-4-thiazolidinylindoles as potent antioxidant and antimicrobial agents

A novel and convenient synthesis of thiopheno-4-thiazolidinyl indole analogues is presented (IVa-IVi), with the aim of obtaining biologically active compounds. 3,5-disubstituted indol-2-carboxyhydrazides (Ia-If) were allowed to react with 3-acetyl-2,5-dichlorothiophene (II) to yield the corresponding 3,5-disubstituted indol-2-carbohydrazides (IIIa-IIIf). The pre-formed indolecarbohydrazides (IIIa-IIIf) were allowed to react with 2-mercaptoacetic acid or 2-mercaptopropanoic acid to produce thiopheno-4-thiazolidinylindoles (IVa-IVi). This reaction protocol affords a simple, eco-friendly, non-hazardous, easier preparation and high yields. The antioxidant (free radical scavenging, total antioxidant capacity and ferric-reducing antioxidant power) and antimicrobial activities of the synthesised compounds were evaluated. The structures and purity of the products were confirmed by their IR, ¹H NMR, ¹³C NMR and mass spectral and analytical data. Most of the compounds tested showed very significant scavenging, antioxidant and antimicrobial activities. Compounds containing electron donor group (CH₃) at the fifth position of indole exhibit an excellent ferric-reducing activity. The present study suggests that compounds IIIa-IIIb, IIIf, IVa-IVc, IVf-IVi, may serve as promising lead scaffolds for antioxidant and antimicrobial agents.