Redox reactions of 3'-azido-3'-deoxythymidine (AZT) and interaction of its OH-derived radical with bilirubin and riboflavin: A pulse radiolysis study

Using the technique of pulse radiolysis, redox studies of 3-azido-3-deoxythymidine (azidothymidine or AZT) with hydrated electron and hydroxyl radicals, generated in phosphate-buffered aqueous medium, are reported. The hydrated electron reacts with AZT (k = 1.9 × 10¹⁰ dm³ mol^-1 s^-1) to generate transients with absorption maxima at 300 and 340 nm. The hydroxyl radical adds to AZT to generate transients with absorption maxima at 310 and 365 nm, with formation rate constant of 9.0 × 10⁹ dm³ mol^-1 s^-1 as observed at 310 and 365 nm. The secondary radical 6-hydroxy-5-yl-azidothymidine, formed in the reaction of AZT with hydroxyl radical, reacts with bilirubin to give a transient of bilirubin with bimolecular rate constant of 1.8 × 10⁸ dm³ mol^-1 s^-1. In the reaction of hydroxyl radical with AZT/riboflavin pair, an ^. H atom transfer from riboflavin to the 6-hydroxy-5-yl-azidothymidine is observed. Reactions of OH-derived radicals of thymine with bilirubin and riboflavin are similar to that of AZT. Possible mechanisms are proposed for the observed reactions.     

Reaction between [Ru3(CO)10(μ-dppm)] (dppm = Ph2PCH2PPh2) and Te2(C6H4OEt-4)2: X-ray crystal structure of [Ru2(CO)6{μ-C6H4PPh(CH2)PPh}]

Treatment of [Ru₃(CO)₁₀(-dppm)] (1) with the ditelluride Te₂(C₆H₄OEt-4)₂ in refluxing toluene afforded the new aryltellurol bridged complex [Ru₂(CO)₄(-TeC₆H₄OEt-4)₂ (-dppm)] (2) together with three known complexes [Ru₄(CO)₈(-CO)(₄-Te)₂(-dppm)] (3), [Ru₂(CO)₆{-CH₂PPh(C₆H₄)PPh}] (4), and [Ru₂(CO)₆{-C₆H₄PPh(CH₂)PPh}] (5). All the four complexes were characterized by spectroscopic methods, including an X-ray structure determination for 5. Complex 5 crystallizes in the monoclinic space group P2₁/c with a = 13.650(2), b = 9.995(2), c = 18.929(3) Å, = 97.49(2)°, V = 2560.4(8) ų, and Z = 4. In this complex the two ruthenium atoms are bridged by the phosphino-phosphide ligand C₆H₄PPh(CH₂)PPh which is attached to one Ru by the C₆H₄ group and a P atom while to the other Ru by both the two P atoms. Both the ruthenium atoms show distorted octahedral geometry. The Ru—Ru bond length is 2.8719(7) Å.     

Global dynamics of Chua Corsage Memristor circuit family: fixed-point loci,Hopf bifurcation,and coexisting dynamic attractors

Nonlinear Dynamics - This paper presents an in-depth and rigorous mathematical analysis of a family of nonlinear dynamical circuits whose only nonlinear component is a Chua Corsage Memristor (CCM)...     

Generalized Rabi oscillations in a three-level metastable system under periodic and quasiperiodic perturbations

The quantum dynamics of prototypical three-level metastable system under external perturbations, both time-independent and time-dependent, are studied numerically as well as analytically. The regular Rabi oscillations generated in the system under a monochromatic perturbation are shown to develop additional features when the system has a metastable state. The autocorrelation function of ψ(t) reveals nondecaying, almost quasiperiodic, behavior in such systems. The Rabi oscillations turn more complex when a bichromatic perturbation with two incommensurate frequencies is allowed to interact with the three-level system, irrespective of the presence or absence of a metastable state. A rapid decay in the autocorrelation function of the wavefunction [ψ(t)] is observed in such cases. © 1996 Wiley & Sons, Inc.     

Remarks on some zero-sum theorems

In the present paper, we give a new proof of a weighted generalization of a result of Gao in a particular case. We also give new methods for determining the weighted Davenport constant and another similar constant for some particular weights.     

Uncertainty modeling of carbon nanotube terahertz oscillators

Significant uncertainties have been reported in the material properties of carbon nanotubes. In this paper, a probabilistic approach to take account of these uncertainties is proposed. The probability density function of the natural frequencies is derived in closed-form. The new results are compared with high-fidelity stochastic finite element simulations.     

Limits on gravitational-wave emission from selected pulsars using LIGO data

We place direct upper limits on the amplitude of gravitational waves from 28 isolated radio pulsars by a coherent multidetector analysis of the data collected during the second science run of the LIGO interferometric detectors. These are the first direct upper limits for 26 of the 28 pulsars. We use coordinated radio observations for the first time to build radio-guided phase templates for the expected gravitational-wave signals. The unprecedented sensitivity of the detectors allows us to set strain upper limits as low as a few times 10(-24). These strain limits translate into limits on the equatorial ellipticities of the pulsars, which are smaller than 10(-5) for the four closest pulsars.     

Chain‐extended,hydroxyterminated‐polybutadiene‐based polyurethaneureas: Synthesis,reaction kinetics,and properties

Hydroxyterminated‐polybutadiene‐based prepolyurethanes were prepared with two different catalysts, dibutyltindilaurate (DBTDL) and triethylamine (TEA); chain extension of the prepolyurethanes followed with two different aromatic diamines, oxydianiline and 4,4′‐diaminodiphenylsulfone, in various concentrations. The prepolyurethane synthesis followed second‐order kinetics, with the DBTDL catalyst showing better efficiency for urethane formation than TEA. TEA‐catalyzed synthesis suffered from the self‐association of isocyanates as a major side reaction, following second‐order kinetics with respect to isocyanate concentration. Although there was a gradual increase in the intrinsic viscosity during prepolyurethane synthesis in the presence of DBTDL, the intrinsic viscosity remained almost constant with the progress of the reaction in the presence of TEA. The tensile properties of prepolyurethane and polyurethaneureas synthesized in DBTDL‐catalyzed reactions were higher than the properties of those synthesized in TEA‐catalyzed reactions. The variation of the tensile strength with the diamine concentration was correlated with the crosslink density and sol fraction. The solubility of the hard segment of polyurethaneurea in the reaction medium appeared to be important in influencing the tensile properties. The effects of the diamine concentration (chain extender) on the diffusion coefficient and activation energy of diffusion of toluene in polyurethaneureas were studied. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2978–2992, 2001     

Isomeric Effects on Structures and Properties of Polyaminophenols Synthesized in Basic Medium

The oxidative chemical polymerizations of three isomers of aminophenol, ortho, meta, and para (PoAP, PmAP, PpAP) were performed in aqueous NaOH using ammonium persulfate (APS) as oxidant. Solubility tests for the synthesized polymers were performed in various solvents and it was found that all three polymers are soluble in DMSO and DMF. PpAP is soluble in aqueous strong acid, as well as in base, but PoAP is soluble in acid, whereas PmAP is soluble in base. The difference in their solubility is due to their structural difference, which can be supported by the proposed mechanisms of polymerizations. The film casting from the DMF or DMSO solution of PoAP and PpAP is difficult due to the presence of quinone impurity while casting of PmAP film from DMSO solution is possible. The intrinsic viscosities of the polymers were determined from the DMSO solution. The polymers were characterized by UV-VIS, FTIR and¹H-NMR spectroscopy and elemental analyses. From structural analysis, it is found that PoAP and PpAP do not contain π -electron conjugation due to ether linkage in the backbone chain. So, PoAP and PpAP do not show any conductivity like sulfuric acid doped PmAP.