Investigation of DNA Pesticide Interactions by Sensitive Electrochemiluminescence Method

A solid-state [Ru(bpy)₂(dppz)]²⁺ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a: 2′,3′-c]phenazine) electrochemiluminescence (ECL) biosensor for studying the binding interactions between pesticides of heterocyclic polycyclic aromatic hydrocarbon (heteroPAH) and natural double-stranded DNA (ds-DNA) was constructed. Layer-by-layer films of negatively charged natural ds-DNA and polycationic poly (diallyldimethylammonium chloride) (PDDA) were assembled on the surface of a glassy carbon electrode (GCE). The complex of [Ru(bpy)₂(dppz)]²⁺ was used as a probe. Tripropylamine (TPA) was used as an electron donor to chemically amplify the ECL intensity of the probe. If the xenobiotic molecules compete with the probe for the same site on the DNA film, it would displace the probe from the DNA to decrease the ECL signal. The interactions of DNA with three pesticide molecules, quinalphos, quinclorac and carbendazim, were studied. From the displacement curve, the values of binding constant K _b of three pesticides to DNA is determined, which is in the range of 0.5 × 10⁴ to 2.3 × 10⁴ M^?1.     

Analytical Study of a Picrate Ion Selective Membrane Electrode Using Chloride as Reference Anion

Abstract

A series of anion selective electrodes of the liquid membrane type have been examined with respect to selectivity characteristics. The resulting selectivity data are examined in terms of theory of liquid membrane electrodes and correlations are made with extraction constants.     

Potentiometric studies of the interaction of amine-bridged dinuclear palladium(II) complex with nitrogen bases

Complexes formed by interaction of trans-diamminepalladium(II) chloride (Pd^II) with 1,6-hexanediamine (HDA) and nitrogen bases (B) (imidazole derivatives or methylamine) are investigated at 25°C and 0.1?mol?L^?1 NaNO₃ ionic strength using potentiometric measurements. The stability constants of all possible mononuclear and binuclear complexes were determined. The concentration distribution diagram of the binuclear Pd^II-HDA-Im derivative reveals the complexes predominating in the physiological pH range; the reaction of the binuclear Pd^II-HDA-Pd^II with imidazole derivatives is quite feasible.     

Assessment of aptamer-steroid binding using stacking-enhanced capillary electrophoresis

The binding affinity of 17β-estradiol with an immobilized DNA aptamer was measured using capillary electrophoresis. Estradiol captured by the immobilized DNA was injected into the separation capillary using pH-mediated sample stacking. Stacked 17β-estradiol was then separated using micellar electrokinetic capillary chromatography and detected with UV-visible absorbance. Standard addition was used to quantify the concentration of estradiol bound to the aptamer. Following incubation with immobilized DNA, analysis of free and bound estradiol yielded a dissociation constant of 70 ± 10 μM. The method was also used to screen binding affinity of the aptamer for estrone and testosterone. This study demonstrates the effectiveness of capillary electrophoresis to assess the binding affinity of DNA aptamers.     

Mechanism for the reaction of 2-naphthol with N-methyl-N-phenyl-hydrazine suggested by the density functional theory investigations

For the first time the computed mechanisms for the novel reaction of 2-naphthol with N-methyl-N-phenylhydrazine, leading to 1-amino-2-naphthol (Tang et al., J Am Chem Soc 2008, 130, 5840), have been investigated using the density functional theory. Four distinct possible pathways were evaluated: two amination mechanisms with the attack of NH(2) group respectively at the α-position C1 and β-position C3 atoms of 2-naphthol (pathways 1 and 2) as well as two rearrangement processes with displacement of the phenolic hydroxyl group followed by the benzidine-like rearrangement at the α-position C1 and β-position C3 atoms of 2-naphthol, respectively (pathways 3 and 4). Solvent effect has been tested based on the optimized geometries of the stationary points in solution at the B3LYP/PCM/6-31+G(d,p) level of theory with an averaged dielectric constant of binary solvent. Single-point energies of the optimized structures have been calculated using three hybrid density functionals, B3LYP, MPW3LYP, and B3PW91 with the 6-311++G(3df,2p) basis set. Our computed results clearly manifest that pathway 1 (α-amination) has the highest possibility to occur, with the Gibbs free energies being lower by 6 to 20 kcal/mol compared with the other three pathways, which leads to 1-amino-2-naphthol and N-methylaniline as products. It is in excellent agreement with the experimental observation.     

Temperature dependence of the rate constant of ionic analogs of H + H2 → H2 + H reaction by quantum instanton method

Rate constant ratios k(T)/k(1,500K) for two symmetrical reactions H^? + H₂ → H₂ + H^? and H⁺ + H₂ → H₂ + H⁺ are reported. Direct method based on quantum instanton approximation for evaluation of the temperature dependence of the quantum‐mechanical reaction rate constant is used. Implementation of the theory involves thermodynamic integration and path integral Monte Carlo method. Results of anionic case shows resemblance to neutral case, whereas cationic case is significantly different and below 1,000K rate constant shows strong deviation form linearity of Arrhenius plot due to high activation barrier. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

The influence of hydrophobic amino acid side groups on the acidity of the aromatic imidazole ring of histidine: A theoretical study

In this study we have calculated the acidity constant (pKa) of imidazole ring in Histidine‐Hydrophobic amino acid dipeptides using the quantum chemistry and continuum solvation methods. Density functional theory calculations with the large basis sets are used to determine the Gibbs free energy of deprotonate in the gas and liquid phases. Based on our results ΔG_S values are located between ?69.38 and ?18.82 kcal mol^?1 which are related to His⁺–Gly and His forms, respectively. pKa of the dipeptides in the aqueous phase was obtained from the calculated gas‐phase and solvation free energies through a thermodynamic cycle and the solvation model chemistry of Martin Karplus et al. Solvation effects are treated using a self‐consistent reaction field formalism involving polarized continuum models. According to our calculations pKa values are between 5.50 and 8.19 that are belong to His⁺–ILe and His⁺–Ala forms, respectively. Natural bond orbital analysis of dipeptides reveals that the electron delocalization in imidazole ring is the most effective factor in determination of acidity order for these compounds. Structural analysis confirmed that the orientation of carbonyl group with respect to imidazole ring is an effective factor in imidazole ring stability. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

POLAROGRAPHY IN n-BUTYL PHOSPHATE

Abstract

Direct polarographic measurements in n-butyl phosphate have shown that solvents of very low dielectric constant can be utilized to gather quantitative analytical data. Solutions containing cadmium in the millimolar range in 0.10M lithium perchlorate have been analyzed.     

逐步增加Ⅱ型截尾下指数分布恒加试验的统计分析

本文对逐步增加Ⅱ型截尾下指数分布场合恒定应力加速寿命试验进行了统计分析,得到参数的最大似然估计存在唯一的充要条件。最后通过模拟例子表明最大似然估计是有效的。     

Bifurcations of limit circles and center conditions for a class of non-analytic cubic Z 2 polynomial differential systems

In this paper, bifurcations of limit cycles at three fine focuses for a class of Z ₂-equivariant non-analytic cubic planar differential systems are studied. By a transformation, we first transform nonanalytic systems into analytic systems. Then sufficient and necessary conditions for critical points of the systems being centers are obtained. The fact that there exist 12 small amplitude limit cycles created from the critical points is also proved. Henceforth we give a lower bound of cyclicity of Z ₂-equivariant non-analytic cubic differential systems.