Investigating ligand-receptor interactions at bilayer surface using electronic absorption spectroscopy and fluorescence resonance energy transfer

We investigate interactions between receptors and ligands at bilayer surface of polydiacetylene (PDA) liposomal nanoparticles using changes in electronic absorption spectroscopy and fluorescence resonance energy transfer (FRET). We study the effect of mode of linkage (covalent versus noncovalent) between the receptor and liposome bilayer. We also examine the effect of size-dependent interactions between liposome and analyte through electronic absorption and FRET responses. Glucose (receptor) molecules were either covalently or noncovalently attached at the bilayer of nanoparticles, and they provided selectivity for molecular interactions between glucose and glycoprotein ligands of E. coli. These interactions induced stress on conjugated PDA chain which resulted in changes (blue to red) in the absorption spectrum of PDA. The changes in electronic absorbance also led to changes in FRET efficiency between conjugated PDA chains (acceptor) and fluorophores (Sulphorhodamine-101) (donor) attached to the bilayer surface. Interestingly, we did not find significant differences in UV-vis and FRET responses for covalently and noncovalently bound glucose to liposomes following their interactions with E. coli. We attributed these results to close proximity of glucose receptor molecules to the liposome bilayer surface such that induced stress were similar in both the cases. We also found that PDA emission from direct excitation mechanism was ～2-10 times larger than that of the FRET-based response. These differences in emission signals were attributed to three major reasons: nonspecific interactions between E. coli and liposomes, size differences between analyte and liposomes, and a much higher PDA concentration with respect to sulforhodamine (SR-101). We have proposed a model to explain our experimental observations. Our fundamental studies reported here will help in enhancing our knowledge regarding interactions involved between soft particles at molecular levels.     

Isotope dependence of the lifetime of the vibration of oxygen in silicon

By simply changing the isotopes of the Si atoms that neighbor an oxygen Oi atom in crystalline silicon, the measured decay rate tau of the asymmetric-stretch vibration (nu3=1136 cm-1) of oxygen (Oi) in silicon changes by a factor of approximately 2.5. These data establish that nu3 decays by creating one nu1 symmetric-stretch, local-vibrational mode of the Si-Oi-Si structure. If the residual energy (nu3-nu1) is less than the maximum frequency num of the host lattice, as for 28Si-16O-28Si in natural silicon, then it is emitted as one lattice mode, and tau depends on the density of one-phonon states at nu3-nu1. If (nu3-nu1)>num, as for 16O in single-isotope 30Si silicon, two lattice modes are created in addition to nu1, increasing tau. Prediction of tau for a particular defect clearly requires a detailed knowledge of that defect.     

A study of\bar np annihilations between 0.5 and 0.8 GeV/c

A study of \(\bar np\) annihilations with \(\bar n\) momentum between 0.5 and 0.8 GeV/c is presented. The search fors-channel resonances in \(\bar np\) annihilations reveal possibly two narrow structures in the odd pions final state. Inclusiveρ ⁰ andf ⁰ cross sections in \(\bar np\) annihilations have been estimated to be 9.0±0.6 mb and 3.4±0.6 mb respectively. Longitudinal and transverse momentum distributions for inclusiveρ ⁰ production have been presented. A study of resonance production in exclusive final state revealsρ ⁰ production to be dominant in the odd pion final states andρ ⁺,ω ⁰ productions are most important for the even pion final states. Theπ ⁺ π ^? effective mass spectra in the backward and the forward directions in the \(\bar np\) c.m. system have been examined for a possible ?-ω interference effect.     

Hydrogen bond cooperativity in dimers of hydroxamic acids

Molecular orbital calculations are performed on various dimeric forms of four tautomers each of thioformohydroxamic acid and formohydroxamic acid. The analysis of stabilization energies associated with the dimerization and their correlation to proton affinities and deprotonation enthalpies of different potential sites present in the molecules indicate that the highest stabilization results when the most basic, site of the molecule acts as hydrogen bond acceptor but combination of the most acidic and the most basic site does not result in the largest stabilization when dimerization occurs. The presence of hydrogen bond cooperativity is indicated and the reasons for the observed cooperativity are explored in this study. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Discrepancy between different estimates of the hydrodynamic diameter of polymer-coated iron oxide nanoparticles in solution

We have synthesized iron oxide nanoparticles coated with a monolayer of dextran, with molecular weights of the polymer between 5 and 670 kDa. Transmission electron microscopy images confirm that the hard core has a crystalline diameter of approximately 12 nm. The hydrodynamic diameters of these coated nanoparticles in solution measured using dynamical light scattering and estimated from magnetic susceptibility studies vary from near 90 nm for the lightest polymer to 140 nm for the heaviest polymer. Conversely, fluorescence correlation spectroscopy measurements yield a diameter of approximately 55 nm for the 15?C20 kDa dextran coated nanoparticles, which is consistent with the expected value estimated from the sum of the hard-core diameter and monolayer dextran coating. We discuss the implications of this discrepancy for applications involving polymer-coated magnetic nanoparticles.     

Alumina Supported Synthesis of β-Lactams Using Microwave

N(4-hydroxycyclohexyl)-3-mercapto/cyano-4-arylazetidine-2-one were synthesised from N-(4-hydroxycyclohexyl)-arylaldimine by reacting with ethyl α-mercapto/α-cyanoacetate on basic alumina under microwaves, wherein not only the reaction time has been brought down from hours to minutes in comparison to conventional heating but also with improved yield.     

Renewable dehydrogenase-based interfaces for bioelectronic applications

Bioelectronic interfaces that establish electrical communication between redox enzymes and electrodes have potential applications as biosensors, biocatalytic reactors, and biological fuel cells. However, these interfaces contain labile components, including enzymes and cofactors, which have limited lifetimes and must be replaced periodically to allow long-term operation. Current methods to fabricate bioelectronic interfaces do not allow facile replacement of these components, thus limiting the useful lifetime of the interfaces. In this paper we describe a versatile new fabrication approach that binds the enzymes and cofactors using reversible ionic interactions. This approach allows the interface to be removed via a simple pH change and then replaced to fully regenerate the biocatalytic activity. The positively charged polyelectrolyte poly(ethylenimine) was used to ionically bond a dehydrogenase enzyme and its cofactor to a gold electrode that was functionalized with 3-mercaptopropionic acid and the electron mediator toluidine blue O. By reducing the pH, the surface-bound 3-mercaptopropionic acid was protonated, disrupting the ionic bonds and releasing the enzyme-modified polyelectrolyte. After neutralization, fresh enzyme and cofactor were bound, regenerating the bioelectronic interface. Cyclic voltammetry, chronoamperometry, constant potential amperometry, electrochemical impedance spectroscopy, and Fourier transform infrared spectroscopy analyses were used to characterize the bioelectronic interfaces. For the two enzymes tested (secondary alcohol dehydrogenase and sorbitol dehydrogenase) and their respective cofactors (beta-nicotinamide adenine dinucleotide phosphate and beta-nicotinamide adenine dinucleotide), the reconstituted interface exhibited a surface coverage, an electron-transfer coefficient, and a turnover rate similar to those of the original interface.     

Synthesis and Biological Activity of Mercaptobenzoxazole Based Thiazolidinones and Their Arylidenes

Arylidenes of thiazolidines with mercaptobenzoxazole, namely[(aryl‐4‐oxo‐1,3‐thiazolidin)‐hydrazinoacetyl‐mercaptobenxazole]; (5‐arylidene)‐2‐aryl‐4‐oxo‐1,3‐thiazoliden hydrazinoacetyl‐mercaptobenxazole were synthesized. Their chemical structures have been confirmed by ¹H NMR, IR, mass spectra and also by microanalytical data. Antimicrobial evaluation was done by agar dilution method against three pathogenic bacteria viz. Bacillus subtilis, Escherichia coli and Klebsiella pneumoniae and three pathogenic fungi viz. Aspergillus niger, Candida albicans and Fusarium oxysporum. Among new derivatives evaluated, the chloro derivatives exhibited higher potency as compared to the standard drugs streptomycin (for bacteria) and griseofulvin (for fungi) against the tested organisms.     

The triphenylmethyl (trityl) group and its uses in nucleotide chemistry

The triphenylmethyl (trityl) group can be removed from 5′-trityl 2′-deoxynucleosides (and their N-acyl derivatives) under aprotic neutral conditions without causing any side reactions. An efficient method for tritylation of N-acyl 2′-deoxynucleosides is described. Potential use of such derivatives for stepwise synthesis of deoxyoligonucleotides is discussed.