A CRITICAL STUDY ON THE INTERACTIONS OF HESPERITIN WITH HUMAN HEMOGLOBIN: FLUORESCENCE SPECTROSCOPIC AND MOLECULAR MODELING APPROACH

Hesperitin, a ubiquitous bioactive flavonoid abundant in citrus fruits is known to possess antioxidant, anti-carcinogenic, hypolipidemic, vasoprotective and other important therapeutic properties. Here we have explored the interactions of hesperitin with normal human hemoglobin (HbA), using steady state and time resolved fluorescence spectroscopy, far UV circular dicroism (CD) spectroscopy, combined with molecular modeling computations. Specific interaction of the flavonoid with HbA is confirmed from flavonoid-induced static quenching which is evident from steady state fluorescence as well as lifetime data. Both temperature dependent fluorescence measurements and molecular docking studies reveal that apart from hydrogen bonding and van der Waals interactions, electrostatic interactions also play crucial role in hesperitin-HbA interactions. Furthermore, electrostatic surface potential calculations indicate that the hesperitin binding site in HbA is intensely positive due to the presence of several lysine and histidine residues.     

Thiol derivatives of arylnaphthylmethane as novel anti-osteoporotic agents

(Mercaptophenyl)naphthylmethane derivatives were synthesized as novel estrogen receptor binding ligands. [4-(Methylsulfonyl)phenyl](naphth-1-yl)ketone shows a very promising activity towards osteoporosis. Correspondence: Sangita, Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226001, India.     

Late stage modification of peptides via CH activation reactions

Recently developed strategies for late stage modification of peptides through CH activation, an arena of contemporary interest in chemical biology and drug discovery, are discussed. Through this tactic, non-polar amino acids in peptides have been selectively functionalized and CH activation enabled new CC and CX bond formations (arylation, alkynylation, fluorination, hydroxylation, azidation, etc.) are documented. Significant advances have been made in Pd or Au-catalyzed, racemization-free, tryptophan specific modifications of large peptides via CH arylation and alkynylation reactions without any protecting group requirement. Development of a new biaryl stapling technique for complex peptides, 18F radiofluorine introduction and diversity oriented post synthetic applications on bio-active cyclopeptides like valinomycin and aureobasidin are additional highlights which underscores the vast potential of late stage CH activation reactions in peptide based therapeutics research.     

Binding of the bioflavonoid robinetin with model membranes and hemoglobin: Inhibition of lipid peroxidation and protein glycosylation

Recent years have witnessed burgeoning interest in plant flavonoids as novel therapeutic drugs targeting cellular membranes and proteins. Motivated by this scenario, we explored the binding of robinetin (3,7,3′,4′,5′-pentahydroxyflavone, a bioflavonoid with remarkable ‘two color’ intrinsic fluorescence properties), with egg yolk phosphatidylcholine (EYPC) liposomes and normal human hemoglobin (HbA), using steady state and time resolved fluorescence spectroscopy. Distinctive fluorescence signatures obtained for robinetin indicate its partitioning (K_p = 8.65 × 10⁴) into the hydrophobic core of the membrane lipid bilayer. HbA–robinetin interaction was examined using both robinetin fluorescence and flavonoid-induced quenching of the protein tryptophan fluorescence. Specific interaction with HbA was confirmed from three lines of evidence: (a) bimolecular quenching constant K_q ? diffusion controlled limit; (b) closely matched values of Stern–Volmer quenching constant and binding constant; (c) τ₀/τ = 1 (where τ₀ and τ are the unquenched and quenched tryptophan fluorescence lifetimes, respectively). Absorption spectrophotometric assays reveal that robinetin inhibits EYPC membrane lipid peroxidation and HbA glycosylation with high efficiency.     

Development and validation of an LC-ESI-MS/MS method for simultaneous quantitation of olmesartan and pioglitazone in rat plasma and its pharmacokinetic application

A simple, high‐throughput and specific high‐performance liquid chromatography tandem mass spectrometry method has been developed and validated according to the FDA guidelines for simultaneous quantification of olmesartan and pioglitazone in rat plasma. The bioanalytical method consists of liquid–liquid extraction and quantitation by triple quadrupole mass spectrometry using electrospray ionization technique, operating in multiple reaction monitoring and positive ion modes. The compounds were eluted isocratically on a C₁₈ column with a mobile phase consisting of a mixture of methanol and water (containing 0.5% formic acid) in a ratio of 9:1. The response to olmesartan and pioglitazone was linear over the range 0.01–10 µg/mL. The validation results demonstrated that the method had satisfactory precision and accuracy across the calibration range. Intra‐ and inter‐day precisions ranged from 0.66 to 3.32 and from 0.94 to 2.93% (%CV), respectively. The accuracy determined at three quality control levels was within 91.27–107.28%. There was no evidence of instability of the analytes in rat plasma following the stability studies. The method proved highly reproducible and sensitive and was successfully applied in a pharmacokinetic study after single dose oral administration of olmesartan and pioglitazone to the rat. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of copper sulphide and copper nanoparticles with microemulsion method

The present work is focused on the synthesis of nanocopper and nanocopper sulphide metallic particles. The precise control of size and shape is best achievable with microemulsion technique, with in situ synthesis in microemulsion. The effect of most crucial operating parameter, water-to-surfactant molar ratio (w), on the product specification including size as well as size distribution and morphology were investigated. The variation of size was observed with variation in w for copper sulphide and copper. Product specifications were analyzed using transmission electron microscope imaging, dynamic light scattering with particle size analyzer and absorption spectra using UV-visible spectrophotometer. It was observed that bigger particles were achieved at higher water-to-surfactant ratio. From systematic study of effect of w on the size and size distribution of copper nanoparticles, the optimum value was chosen for preparation of in situ catalyst. As copper on alumina catalyst has wide catalytic applications of commercial importance, alumina was selected as support. A novel deposition method is developed successfully to deposit the copper nanoparticles from microemulsion on the support. Thus prepared catalyst was analyzed with UV-visible spectrophotometer and found to contain characteristic peak of copper at 655 nm, indicating proper copper deposition on support. XRD analysis of copper on alumina catalyst confirmed presence of metallic copper.     

DNA Encapsulation of Ten Silver Atoms Produces a Bright, Modulatable, Near Infrared-Emitting Cluster

Photostability, inherent fluorescence brightness, and optical modulation of fluorescence are key attributes distinguishing silver nanoclusters as fluorophores. DNA plays a central role both by protecting the clusters in aqueous environments and by directing their formation. Herein, we characterize a new near infrared-emitting cluster with excitation and emission maxima at 750 and 810 nm, respectively that is stabilized within C(3)AC(3)AC(3)TC(3)A. Following chromatographic resolution of the near infrared species, a stoichiometry of 10 Ag/oligonucleotide was determined. Combined with excellent photostability, the cluster's 30% fluorescence quantum yield and 180,000 M(-1)cm(-1) extinction coefficient give it a fluorescence brightness that significantly improves on that of the organic dye Cy7. Fluorescence correlation analysis shows an optically accessible dark state that can be directly depopulated with longer wavelength co-illumination. The coupled increase in total fluorescence demonstrates that enhanced sensitivity can be realized through Synchronously Amplified Fluorescence Image Recovery (SAFIRe), which further differentiates this new fluorophore.     

Onset of turbulence from the receptivity stage of fluid flows

The traditional viewpoint of fluid flow considers the transition to turbulence to occur by the secondary and nonlinear instability of wave packets, which have been created experimentally by localized harmonic excitation. The boundary layer has been shown theoretically to support spatiotemporal growing wave fronts by Sengupta, Rao, and Venkatasubbaiah [Phys. Rev. Lett. 96, 224504 (2006)] by a linear mechanism, which is shown here to grow continuously, causing the transition to turbulence. Here, we track spatiotemporal wave fronts to a nonlinear turbulent state by solving the full 2D Navier-Stokes equation, without any limiting assumptions. Thus, this is the only demonstration of deterministic disturbances evolving from a receptivity stage to the full turbulent flow. This is despite the prevalent competing conjectures of the event being three-dimensional and/or stochastic in nature.     

VEGFR-2 targeted cellular delivery of doxorubicin by gold nanoparticles for potential antiangiogenic therapy

We report a novel gold nanobioconjugate system that achieves targeted delivery of the small molecule drug doxorubicin to endothelial cells using anti-VEGFR-2 antibody conjugated gold nanoparticles (GNPs). The reported nanobioconjugate system combines the inherent ability of GNPs to undergo high levels of derivatization with the precision of antibody recognition of a cell surface antigen. Transmission electron microscopy (TEM) and surface-enhanced Raman spectroscopy (SERS) confirmed intracellular presence of the GNPs. Using a VEGFR-2 expressing cell line and a cell line that is negative for the receptor, in combination with competition assay we established the cell specific targeted delivery of the nanobioconjugate. The nanobioconjugate system described here may have potential drug delivery applications for antiangiogenic cancer therapy.