Adsorption Kinetics and Binding Studies of Protein Quantum Dots Interaction: A Spectroscopic Approach

Protein Quantum dots interaction is crucial to investigate for better understanding of the biological interactions of QDs. Here in, the model protein Bovine serum albumin (BSA) was used to evaluate the process of protein QDs interaction and adsorption on QDs surface. The modified Stern-Volmer quenching constant (K_a), number of binding sites (n) at different temperatures (298 308 and 318 K?±?1) and corresponding thermodynamic parameters (ΔG?<?0, ΔH?<?0, and ΔS?>?0) were calculated. The quenching constant (K_s) and number of binding sites (n) is found to be inversely proportional to temperature. It signified that static quenching mechanism is dominant over dynamic quenching. The standard free energy change (ΔG?<?0) implies that the binding process is spontaneous, while the enthalpy change (ΔH?<?0) suggest that the binding of QDs to BSA is an enthalpy-driven process. The standard entropy change (ΔS?>?0) suggest that hydrophobic force played a pivotal role in the interaction process. The adsorption process were assessed and evaluated by pseudofirst-order, pseudosecond-order kinetic model, and intraparticle diffusion model.     

Chemo- and regioselective cyclohydrocarbonylation of alpha-keto alkynes catalyzed by a zwitterionic rhodium complex and triphenyl phosphite

alpha-Keto alkynes react with CO and H(2) in the presence of catalytic quantities of the zwitterionic rhodium complex (eta(6)-C(6)H(5)BPh(3))(-)Rh(+)(1,5-COD) and triphenyl phosphite affording either the 2-, 2(3H)-, or 2(5H)-furanones in 61-93% yields. The cyclohydrocarbonylation is readily accomplished using substrates containing alkyl, aryl, vinyl, and alkoxy groups at the acetylenic terminal, as well as a variety of primary, secondary, and tertiary alkyl, aryl, and heteroaryl groups connected to the ketone functionality. Structural and electronic properties present in the starting materials mediate the chemo- and regioselectivity of the reaction.     

The chemical nature of the 2'-substituent in the pentose-sugar dictates the pseudoaromatic character of the nucleobase (pKa) in DNA/RNA

We here show that the pKa (error limit: 0.01 to 0.03 pKa unit) of a nucleobase in a nucleotide can be modulated by the chemical nature of the 2'-substituent at the sugar moiety. This has been evidenced by the measurement of nucleobase pKa in 47 different model nucleoside 3',5'-bis- and 3'-mono-ethylphosphates. The fact that the electronic character of each of the 2'-substituents (Fig. 1) alters the chemical shift of the H2' sugar proton, and also alters the pKa of the nucleobase in the nucleotides has been evidenced by a correlation plot of pKa of N3 of pyrimidine (T/C/U) or pKa of N7 of 9-guaninyl with the corresponding deltaH2' chemical shifts at the neutral pH, which shows linear correlation with high Pearson's correlation coefficients (R = 0.85-0.97). That this modulation of the pKa of the nucleobase by a 2'-substituent is a through-bond as well as through-space effect has been proven by ab initio determined pKa estimation. Interestingly, experimental pKas of nucleobases from NMR titration and the calculated pKas (by ab initio calculations utilizing closed shell HF 6-31G** basis set) are linearly correlated with R = 0.98. It has also been observed that the difference of ground and protonated/de-protonated HOMO orbital energies (DeltaHOMO, a.u.) for the nucleobases (A/G/C/T/U) are well correlated with their pK(a)s in different 2'-substituted 3',5'-bis-ethylphosphate analogs suggesting that only the orbital energy of HOMO can be successfully used to predict the modulation of the chemical reactivity of the nucleobase by the 2'-substituent. It has also been demonstrated that pKa values of nucleobases in 3',5'-bis-ethylphosphates (Table 1) are well correlated with the change in dipole moment for the respective nucleobases after protonation or de-protonation. This work thus unambiguously shows that alteration of the thermodynamic stability (Tm) of the donor-acceptor complexes [ref. 20], as found with various 2'-modified duplexes in the antisense, siRNA or in triplexes by many workers in the field, is a result of alteration of the pseudoaromatic character of the nucleobases engineered by alteration of the chemical nature of the 2'-substitution.     

Biogenic Nanoparticle-Mediated Augmentation of Seed Germination,Growth, and Antioxidant Level of Eruca sativa Mill. Varieties

A study was undertaken to examine the influence of biogenic nanoparticles synthesized from Tridax procumbens on different parameters of seed germination, seedling growth, and various biochemical parameters in four Eruca sativa varieties having low percentage of germination. Seeds were treated with different concentrations (30 and 40 ppm) of biogenic nanoparticles, of which 30 ppm was found to be the most effective and was therefore used for subsequent studies. Initially, the effect of biogenic nanoparticles on germination percentage, speed of germination, coefficient of germination, mean germination time, shoot and root length, fresh and dry matter, and vigor index was studied. From the experiments performed and the results obtained, it was evident that the treatment with biogenic nanoparticles decreased the electrolyte leakage and level of malondialdehyde as compared to control. The treatment with biogenic nanoparticles enhanced the levels of proline and ascorbic acid and stimulated the antioxidant enzyme activities resulting in the reduced level of reactive oxygen species. These activities were found to be variety-dependent. The possible involvement of biogenic nanoparticles in the production of new pores in seed coat during their penetration, resulting in the influx of the nutrients inside the seed, is suggested. This accelerated seed germination is followed by rapid seedling growth. The present findings indicated that biogenic nanoparticles promote seed germination in E. sativa by overcoming the detrimental effects of reactive oxygen species (ROS) and improving the antioxidative defense system which finally result in increased seedling growth.     

Cross-linked polyvinylpyrrolidone nanoparticles: a potential carrier for hydrophilic drugs

Injectable hydrogel polymeric nanoparticles of polyvinylpyrrolidone cross-linked with N,N'-methylene bis-acrylamide and encapsulating water-soluble macromolecules such as FITC-dextran (FITC-Dx) have been prepared in the aqueous cores of reverse micellar droplets. These particles are 100 nm and below in diameter with a narrow size distribution. When dispersed in aqueous buffer these particles appear to be transparent and give an optically clear solution. Lyophilized powder of these nanoparticles is redispersable in aqueous buffer without any change in the size and morphology of the particles. The efficiency of FITC-Dx entrapment by these nanoparticles is high (>70%) and depends on the amount of cross-linking agent present in the polymeric material. The release of the entrapped molecules from these nanoparticles depends on the degree of cross-linking of the polymer, particle size, pH of the medium, and extent of loading, as well as temperature.     

International Guidelines for Bioanalytical Method Validation: A Comparison and Discussion on Current Scenario

US FDA released guidelines for bioanalytical method validation in 2001 and it became the basis for guidelines such as ANVISA and EMA. Even though there is a general agreement between these guidelines in terms of evaluation of validation parameters, significant diversity exists with respect to methodology employed. Present review compares and summarizes the regulatory guidelines issued by US FDA, ANVISA and EMA for bioanalytical method validation. This review also discusses evaluation of certain validation parameters such as matrix effect, incurred sample reanalysis, various stability aspects, effect of anticoagulant counter ions, specificity in the presence of concomitant medications, and identification of pharmacokinetic repeats wherein specific guidance and general consensus amongst scientific community does not exist.     

Synthesis and characterization of ABA‐type amphiphilic tri‐block copolymers through anionic polymerization using end functionalized poly(ethylene oxide) oligomers

ABA‐type amphiphilic tri‐block copolymers were successfully synthesized from poly(ethylene oxide) derivatives through anionic polymerization. When poly(styrene) anions were reacted with telechelic bromine‐terminated poly(ethylene oxide) ( 1 ) in 2:1 mole ratio, poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers were formed. Similarly, stable telechelic carbanion‐terminated poly(ethylene oxide), prepared from 1,1‐diphenylethylene‐terminated poly (ethylene oxide) ( 2 ) and sec‐BuLi, was also used to polymerize styrene and methyl methacrylate separately, as a result, poly (styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) and poly (methyl methacrylate)‐b‐poly(ethylene oxide)‐b‐poly(methyl methacrylate) tri‐block copolymers were formed respectively. All these tri‐block copolymers and poly(ethylene oxide) derivatives, 1 and 2 , were characterized by spectroscopic, calorimetric, and chromatographic techniques. Theoretical molecular weights of the tri‐block copolymers were found to be similar to the experimental molecular weights, and narrow polydispersity index was observed for all the tri‐block copolymers. Differential scanning calorimetric studies confirmed the presence of glass transition temperatures of poly(ethylene oxide), poly(styrene), and poly(methyl methacrylate) blocks in the tri‐block copolymers. Poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers, prepared from polystyryl anion and 1 , were successfully used to prepare micelles, and according to the transmission electron microscopy and dynamic light scattering results, the micelles were spherical in shape with mean average diameter of 106 ± 5 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Aza-Michael Addition of Amines to α,β-Unsaturated Compounds Using Molecular Iodine as Catalyst

Aza-Michael adducts are obtained in very good yields by the conjugate addition of aliphatic amines to α,β-unsaturated compounds using molecular iodine as catalyst in dichloromethane at room temperature. Aromatic amines were found to be reactive under reflux in toluene.     

Green Synthesis of Tetraalkylammonium Tribromide using Cerium(IV) Ammonium Nitrate (CAN) as Oxidant

Cerium(IV) ammonium nitrate (CAN) mediates oxidation of tetraalkylammonium bromide to tetraalkylammonium tribromide in greener reaction conditions using water as solvent. The procedure is simple, convenient, and environmentally benign for the synthesis of tetraalkylammonium tribromide with great yields.     

An Insight into the Mechanism of Holamine- and Funtumine-Induced Cell Death in Cancer Cells

Holamine and funtumine, steroidal alkaloids with strong and diverse pharmacological activities are commonly found in the Apocynaceae family of Holarrhena. The selective anti-proliferative and cell cycle arrest effects of holamine and funtumine on cancer cells have been previously reported. The present study evaluated the anti-proliferative mechanism of action of these two steroidal alkaloids on cancer cell lines (HT-29, MCF-7 and HeLa) by exploring the mitochondrial depolarization effects, reactive oxygen species (ROS) induction, apoptosis, F-actin perturbation, and inhibition of topoisomerase-I. The apoptosis-inducing effects of the compounds were studied by flow cytometry using the APOPercentage^TM dye and Caspase-3/7 Glo assay kit. The two compounds showed a significantly greater cytotoxicity in cancer cells compared to non-cancer (normal) fibroblasts. The observed antiproliferative effects of the two alkaloids presumably are facilitated through the stimulation of apoptosis. The apoptotic effect was elicited through the modulation of mitochondrial function, elevated ROS production, and caspase-3/7 activation. Both compounds also induced F-actin disorganization and inhibited topoisomerase-I activity. Although holamine and funtumine appear to have translational potential for the development of novel anticancer agents, further mechanistic and molecular studies are recommended to fully understand their anticancer effects.