Photophysics and dynamics of a β-carboline analogue in room temperature ionic liquids

Room temperature ionic liquids are rapidly emerging as a new class of media that are ideally suited for various applications including carrying out chemical reactions. In the present article, we report the photophysics of a β-carboline analogue, namely, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in three room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO<SUB>4</SUB>]), 1-butyl-3-methylimidazolium octyl sulfate ([BMIM][C<SUB>8</SUB>SO<SUB>4</SUB>]) and 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MeSO<SUB>4</SUB>]). Out of these, [BMIM][C<SUB>8</SUB>SO<SUB>4</SUB>] is a typical RTIL that forms micellar aggregates above a critical micellar concentration (CMC). Steady state absorption, steady state and time resolved fluorescence techniques are used to probe the properties of these systems. The investigation reveals that the photophysics of AODIQ is modified significantly in the micelle-forming RTIL as compared to that in the other two. A comparative study with the fluorophore in [BMIM][C<SUB>8</SUB>SO<SUB>4</SUB>] and a conventional anionic surfactant of a similar hydrophobic chain length from the sodium-n-alkyl sulfate series, viz., sodium octyl sulfate (S<SUB>8</SUB>S), reveals that the fluorophore experiences a more constrained environment in the RTIL micelle as compared to the conventional anionic micelle

Polarity dependence of the radiative and nonradiative rates of flavone derivatives comprising structurally similar amino moieties: change in the nature of the emitting state

Photophysical behavior of several structurally related electron donor-acceptor flavone derivatives, which have been synthesized and characterized, has been studied as a function of the polarity of the media. Significant variation of the absorption and fluorescence response of the systems has been observed with change in the polarity of the medium. The results show an increase in the radiative rate constant and a decrease in the nonradiative rate constant of the systems with increase in the polarity of the media. This finding has been attributed to the change in the nature of the emitting state from a mixed n−π<SUP>∗</SUP> and π−π<SUP>∗</SUP> state to a dominant π−π<SUP>∗</SUP> state with increase in the polarity of the medium. The results of single-crystal diffraction studies and theoretical calculations based on density functional method support the idea of close proximity of the n−π<SUP>∗</SUP> and π−π<SUP>∗</SUP> states and the change in their relative contributions toward the emission process with the polarity of the medium. Laser flash photolysis studies show that the triplet state is not involved in the variation of the fluorescence response of the systems

Impact of silver sulfide on rheology and streaming electrification of mineral oil and mixed fluid

This study reports the effect of adding silver sulfide to mineral oil and mixed fluid on their static electrification and visco-elastic properties. The flow electrification studies indicate an increase in streaming current for higher silver sulfide concentration with the hysteresis pattern indicating a higher current during the decrement of disc velocity. The transition from loss modulus to storage modulus was visible in the mixed fluid compared to mineral oil. Further, the effect of silver sulfide has reduced the storage modulus with frequency sweep and temperature sweep testing on both mineral oil and mixed fluid

Studies of triton X-165-β-cyclodextrin interactions using both extrinsic and intrinsic fluorescence

The interaction of β-cyclodextrin with the non-ionic micelle-forming surfactant Triton X-165 (TX-165) has been studied using steady state fluorescence and fluorescence anisotropy techniques. Both extrinsic and intrinsic fluorescence have been exploited for the purpose. Phenosafranin (PSF), a cationic phenazinium dye, has been used as the extrinsic probe while fluorescence of TX-165 has served as the intrinsic one. PSF shows discernible interactions with both TX-165 and β-CD. The experimental results reveal that the extent of interaction of PSF with TX-165 is greater than with β-CD. However, addition of β-CD to a micellar solution of TX-165 containing PSF leads to a disruption of the micelles whereby the fluorophore is released from the micellar environment to the bulk aqueous phase. It has been substantiated that an inclusion complex is formed between the non-ionic surfactant and the cyclodextrin. A 1:1 stoichiometry of the TX-165-β-CD inclusion complex has been proposed. Such a complexation between TX-165 and β-CD results in an inhibition in the micellization process of TX-165 leading to an enhancement in the apparent CMC value. The inferences are drawn from a series of experiments, viz., binding studies, determination of micropolarity, heavy-ion quenching studies and steady state fluorescence anisotropy experiments monitoring both extrinsic and intrinsic fluorescences

Virulence Characteristics and Molecular Epidemiology of Enteroaggregative Escherichia coli Isolates from Hospitalized Diarrheal Patients in Kolkata, India

Enteroaggregative Escherichia coli (EAEC) is an important diarrheal enteropathogen defined by aggregative adherence to cultured epithelial cells. We have detected EAEC from 121 (6.6%) of 1,826 hospitalized patients admitted with diarrhea to the Infectious Diseases Hospital in Kolkata, India. Watery diarrhea was recorded significantly (P = 0.0142) more often in children. The majority of the EAEC isolates were not serotypeable (62%) and showed resistance to five or more antibiotics (76%). We studied different virulence genes and the molecular epidemiology of 121 EAEC isolates recovered from diarrheal patients. A PCR assay for detection of virulence genes, an assay for determination of clump formation in liquid culture, and a HeLa cell adherence assay were carried out to characterize the EAEC isolates. Investigations were also conducted to correlate the virulence gene profiles with diarrheal symptoms and molecular epidemiology by pulsed-field gel electrophoresis (PFGE). Two or more virulence genes were detected in 109 (90.1%) EAEC isolates. In the cluster analysis, some isolates with specific gene profiles and phenotypes formed a group or subcluster. This study highlights the comparative distributions of three fimbrial adhesins and other virulence genes among EAEC isolates. The diverse virulence gene and PFGE profiles, along with the existence of diverse serotypes and antibiograms, suggests that the EAEC isolates are genetically heterogeneous in Kolkata

Virological Characteristics of Acute Hepatitis B in Eastern India: Critical Differences with Chronic Infection.

Hepatitis B Virus (HBV) manifests high genetic variability and is classifiable into ten genotypes (A-J). HBV infection can lead to variable clinical outcomes, ranging from self-limiting acute hepatitis to active chronic hepatitis, cirrhosis and hepatocellular carcinoma. The present study characterizes HBV strains circulating among patients with acute (AHB) and chronic HBV infection (CHB). Among a total of 653 HBsAg positive cases, 40 manifested acute infection. After sequencing the surface(S), basal core promoter/pre-core(BCP/PC) and the X gene regions, phylogenetic tree was constructed using MEGA4 by neighbor-joining method. Statistical robustness was established with bootstrap analysis. Nucleotide diversity was determined by Shannon entropy per site using the Entropy program of the Los Alamos National Laboratories. Analyses of acute patients revealed that HBV/D2 is the major circulating sub-genotype and commonly associated with sexual promiscuity and the age group between15-30 years. Comparison of AHB and CHB patients revealed that HBeAg positivity, ALT levels and genotype D were significantly high in AHB, whereas CHB patients were predominantly male, had a high viral load, and were commonly associated with genotype C. The frequencies of mutations in the S, BCP/PC, and X gene were low in AHB as compared to CHB. Drug resistant mutations were not detectable in the polymerase gene of AHB. Average nucleotide diversity in AHB was considerably low as compared to CHB. Further, the highest average ΔH (average difference in entropy between chronic and acute infection) was observed in the BCP/PC region implying that this region was most vulnerable to mutations upon HBV persistence, especially in case of genotype C. Additionally, among all substitutions, the A1762T and G1764A BCP mutations were the strongest indicators of chronicity. In conclusion, the study exhibits a general portrait of HBV strains circulating among acute hepatitis B patients in Eastern India and their intricate differences with chronic patients which should be useful from the clinical point of view

Association of cytolethal distending toxin locus cdtB with enteropathogenic Escherichia coli isolated from patients with acute diarrhea in Calcutta, India

Among Escherichia coli strains isolated from stool specimens from patients with acute diarrhea, 1.4% were found to harbor cdtB by use of enrichment cytolethal distending toxin (CDT) PCR. These isolates were identified as being enteropathogenic E. coli (EPEC). In a retrospective study using a probe hybridization assay, 6 of 138 EPEC strains were found to harbor the cdtB locus. cdtB-positive isolates mostly belong to the O86a and O127a serogroups, with the former being associated with higher expression of CDT. Pulsed-field gel electrophoresis profiles showed that the EPEC strains harboring cdtB strains are genetically diverse

Frequencies of some principal mutations in the HBV genome compared in acute and chronic Hepatitis B patients.

<p>Figure depicts some signature mutations in the surface gene (S), basal core promoter/pre-core regions (BCP/PC) and X gene.</p

Analysis of the association of HBV sub-genotypes with biochemical parameters.

<p>Median (A) ALT (IU/liter) and (B) bilirubin (IU/liter) levels in patients vary with circulating HBV sub-genotypes. Only significant differences (p<0.05) have been marked in the figure.</p