Magic sized ZnS quantum dots as a highly sensitive and selective fluorescence sensor probe for Ag+ ions

A green and simple chemical synthesis of magic sized water soluble blue-emitting ZnS quantum dots (QDs) has been accomplished by reacting anhydrous Zn acetate, sodium sulfide and thiolactic acid (TLA) at room temperature in aqueous solution. Refluxing of this mixture in open air yielded ZnS clusters of about 3.5 nm in diameter showing very strong and narrow photoluminescence properties with long stability. Refluxing did not cause any noticeable size increment of the clusters. As a result, the QDs obtained after different refluxing conditions showed similar absorption and photoluminescence (PL) features. Use of TLA as a capping agent effectively yielded such stable and magic sized QDs. The as-synthesized and 0.5 h refluxed ZnS QDs were used as a fluorescence sensor for Ag(+) ions. It has been observed that after addition of Ag(+) ions of concentration 0.5-1 μM the strong fluorescence of ZnS QDs was almost quenched. The quenched fluorescence can be recovered by adding ethylenediamine to form a complex with Ag(+) ions. The other metal ions (K(+), Ca(2+), Au(3+), Cu(2+), Fe(3+), Mn(2+), Mg(2+), Co(2+)) showed little or no effect on the fluorescence of ZnS QDs when tested individually or as a mixture. In the presence of all these ions, Ag(+) responded well and therefore ZnS QDs reported in this work can be used as a Ag(+) ion fluorescence sensor.     

N-oxides in metal-containing multicomponent molecular complexes

Syntheses and structures of three-component rare cocrystals of 4-nitrobenzoic acid, aromatic N-oxides, and aqua complexes of manganese and zinc and their transformation to metal complexes as well as coordination polymers are presented.     

Oxidation of Cu(II) aminopolycarboxylates by carbonate radical: A flash photolysis study

Reactions of carbonate radical (Co₃ ⁻) generated by photolysis or by radiolysis of a carbonate solution, with Cu(II) complexes of aminopolycarboxylic acids viz., Cu(II)ethylenediamine tetraacetate [Cu^IIEDTA]²⁻ and Cu(II)-iminodiacetate [Cu^IIIDA] were studied at pH 10. 5 and ionic strength 0.2 mol·dm⁻³. Time-resolved spectroscopy and kinetics for the transients were studied using flash photolysis and stable products arising from the ligand degradation of the complex were ascertained by steady-state radiolysis experiments. From the kinetic data it is observed that CO₃ ⁻, radical reacts initially with Cu^II-complex to form a transient intermediate having maximum absorption at 335 nm and 430 nm. From the subsequent reactions of this intermediate it was assigned to be Cu^III. species. This Cu(III) species undergoes intermolecular electron transfer with the Cu^II-complex to give a radical intermediate which again slowly reacts with Cu^II-complex to give a long lived species containing Cu−C bond. This long lived species, however, slowly decomposed to give glyoxalic reaction between Cu^III-complex and a suitable donor, the one electron reduction potential for [Cu^IIIEDTA]¹⁻/[Cu^IIEDTA]²⁻ and [Cu^IIIIDA]⁺¹/Cu^IIIDA was determined.     

Phase separation of a binary fluid in the inertia-dominated regime

The phase separation kinetics of a binary fluid is studied analytically through an effective one-fluid model with a random force spectrum determined self-consistently: the rate of kinetic energy injection by the random force is consistent with the droplet coalescence rate. Our detailed results for the rates of energy dissipation and kinetic energy decay are consistent with previous numerical studies. We find that simple nontrivial scaling, if any, is associated with a new universality class where the velocity length scale follows .     

Commensurate-incommensurate transition and disordering in dilute graphite-bromine

Results of a x-ray scattering study of the inplane ordering in dilute graphite-bromine in the temperature range from 300 to 400K are presented. Evidence is obtained for a commensurate-incommensurate transition which is found to behave differently from those observed in the case of adsorbed monolayers. The bromine layers undergo continuous order-disorder transition from the incommensurate phase at 374K. Implications of this result and the large value of the measured exponent (β=0.32) are discussed.     

B and collider physics: Working group report

This report summarises the work done during WHEPP-6 (Institute of Mathematical Sciences, Chennai, India, Jan 3–15, 2000) in Working group on ‘B and collider physics’.     

Revisiting the ‘cis-effect’ in 1,2-difluoro derivatives of ethylene and diazene using ab initio multireference methods

The relative stabilities of cis- and trans- isomers of 1,2-difluoroethylene and 1,2-difluorodiazene have been studied via the state-specific multireference coupled cluster (SS-MRCC) method and its perturbative counterpart through the computation of the optimised structures and corresponding energies. Despite the existence of several cis-destabilising mechanisms, present calculations reveal the energetic preference of the cis- isomer (the cis-effect) for the systems considered here. Differences in structural parameters and vibrational frequencies among cis- and trans- isomers have been discussed. Very good agreement of our estimates has been found with the benchmark theoretical and experimental results. The SS-MRCC methods produce a smooth and consistent behaviour across the entire torsional surface for the cis–trans isomerisation indicating that the method has sufficient flexibility to model large changes in electronic structure that accompany chemical changes.     

Influence of Moringa oleifera on pharmacokinetic disposition of rifampicin using HPLC‐PDA method: a pre‐clinical study

The influence of active fraction isolated from pods of an indigenous plant, Moringa oleifera (MoAF) was studied on the pharmacokinetic profile of the orally administered frontline anti‐tuberculosis drug rifampicin (20 mg/kg b.w.) in Swiss albino mice. The antibiotic rifampicin alone and in combination with MoAF (0.1 mg/kg b.w.) was administered orally and heparanized blood samples were collected from the orbital plexus of mice for plasma separation at 0, 1, 2, 3, 4 and 5 h, post treatment. Plasma rifampicin concentration, pharmacokinetic parameters and drug metabolizing enzyme (cytochrome P‐450) activity were determined. The pharmacokinetic data revealed that MoAF‐treated animals had significantly increased rifampicin plasma concentration, C_max, K_el, t_½(a), t_½(el), K_a and AUC as well as inhibited rifampicin‐induced cytochrome P‐450 activity. In conclusion, the result of this study suggested that the bioavailability‐enhancing property of MoAF may help to lower the dosage level and shorten the treatment course of rifampicin. Copyright © 2010 John Wiley & Sons, Ltd.     

Nonlocal continuum electrostatic theory predicts surprisingly small energetic penalties for charge burial in proteins

We study the energetics of burying charges, ion pairs, and ionizable groups in a simple protein model using nonlocal continuum electrostatics. Our primary finding is that the nonlocal response leads to markedly reduced solvent screening, comparable to the use of application-specific protein dielectric constants. Employing the same parameters as used in other nonlocal studies, we find that for a sphere of radius 13.4 ? containing a single +1e charge, the nonlocal solvation free energy varies less than 18 kcal/mol as the charge moves from the surface to the center, whereas the difference in the local Poisson model is ～35 kcal/mol. Because an ion pair (salt bridge) generates a comparatively more rapidly varying Coulomb potential, energetics for salt bridges are even more significantly reduced in the nonlocal model. By varying the central parameter in nonlocal theory, which is an effective length scale associated with correlations between solvent molecules, nonlocal-model energetics can be varied from the standard local results to essentially zero; however, the existence of the reduction in charge-burial penalties is quite robust to variations in the protein dielectric constant and the correlation length. Finally, as a simple exploratory test of the implications of nonlocal response, we calculate glutamate pK(a) shifts and find that using standard protein parameters (ε(protein) = 2-4), nonlocal results match local-model predictions with much higher dielectric constants. Nonlocality may, therefore, be one factor in resolving discrepancies between measured protein dielectric constants and the model parameters often used to match titration experiments. Nonlocal models may hold significant promise to deepen our understanding of macromolecular electrostatics without substantially increasing computational complexity.