Amplified electrochemical detection of DNA through the aggregation of Au nanoparticles on electrodes and the incorporation of methylene blue into the DNA-crosslinked structure

The amplified electrochemical sensing of DNA is accomplished by the analyte-induced aggregation of nucleic acid-functionalized Au nanoparticles, deposition of the aggregates on a thiolated monolayer-functionalized electrode, and the voltammetric analysis of the redox-active methylene blue intercalated in the nucleic acid duplexes associated with the aggregates.     

Stereochemistry of rHint1 hydrolase assisted cleavage of P-N bond in nucleoside 5'-O-phosphoramidothioates

The Hint-1 hydrolase assisted cleavage of the P-N bond in adenosine-5'-O-[N-(tryptophanylamide)]phosphoramidothioate proceeds with retention of configuration at the phosphorus atom which is consistent with the formation of a covalent enzyme-substrate complex.     

Theoretical investigation of the EPR hyperfine coupling constants in amino derivatives

The HFCCs of the radical cations of a series of amines have been determined at different levels of approximation including the CISD, QCISD, and CCSD ab initio correlated methods and density functional theory approaches employing the B3LYP, PBE0, BHandHLYP, TPSS, and BLYP exchange-correlation functionals. Although quantitative differences with respect to experimental data have been noticed, these are mostly systematic within a given class of N and H atoms. As a consequence, these different levels of theory are reliable in most cases to account for the substituent and structure effects on the HFCCs of amines. Linear regression fits have then been performed to reach quantitative agreement between the theoretical and experimental values. This has finally been substantiated by considering the EPR signal of the recently synthesized radical cations of two derivatives of [10-(4-aminophenyl)-9-anthryl]aniline as well as in confirming a recent assignment of the EPR signal of n-propylamine.     

Synthesis of alpha-phosphorylated alpha,beta-unsaturated imines and their selective reduction to vinylogous and saturated alpha-aminophosphonates

An efficient synthesis of alpha,beta-unsaturated imines derived from alpha-aminophosphonates is achieved through aza-Wittig reaction of P-trimethyl phosphazenes with beta,gamma-unsaturated alpha-ketophosphonates. Selective 1,2-reduction of such 1-azadienes affords beta,gamma-unsaturated alpha-aminophosphonates, phosphorylated analogs of vinylglycines, which are hydrogenated to yield saturated alpha-aminophosphonate derivatives.     

Trifluoperazine causes a disturbance in glycerophospholipid monolayers containing phosphatidylserine (PS): effects of pH, acyl unsaturation, and proportion of PS

We have studied the interaction of trifluoperazine (TFP) with monolayers of various glycerophospholipids at 37 degrees C. TFP (1-10 microM) had little effect on surface pressure/molecular area isotherms in monolayers (on pure water) of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine but greatly increased the mean molecular area (mma) of dipalmitoylphosphatidylserine; the increment was greatest between 0 and 1 microM, and a further increase to 10 microM TFP gave only a slight increase in mma. With phosphatidylserine (PS)-containing stearoyl and varying acyls in the sn-1 and -2 positions, respectively, TFP increased the mma in a manner that depended on the number of double bonds and chain length. In mixtures of DPPC with two of these PS species the TFP-induced mma of the monolayers (on buffer, pH 7.4) increased linearly with the proportion of PS. Both PS and TFP have ionizable groups, and the TFP-induced mma increase had optima at pH 5.0 and 7.0. We conclude that the TFP-PS interaction is mainly, but not entirely, driven by electrostatic interactions between the TFP cation and PS headgroup anion, with an insertion of the phenothiazine moiety among the acyls in the monolayer that depends on the packing of the acyls.     

Synthesis and conformational analysis of novel trimeric maleimide cross-linking reagents

Nine homotrifunctional cross-linking reagents are presented. Their synthesis and chemical properties as well as their characterization by classical mechanical conformational searching techniques is reported. Mixed Low Mode and Monte Carlo searching techniques were used to exhaustively sample the OPLS2005/GBSA(water) potential energy surface of trisubstituted cyclohexane and benzene derivatives of C3 symmetry. Geometric structure, molecular length, and hydrogen-bonding patterns were analyzed. Nonaromatic compounds exhibited exclusively chair conformations at low energies, with a preference for axial or equatorial arms depending upon the presence of additional ring substituent Me groups. Increasing chain length often resulted in overall shorter molecular length due to additional chain flexibility. These results were consistent with one- and two-dimensional temperature-dependent NMR studies.     

Influence of bond fixation in benzo-annulated N-salicylideneanilines and their ortho-C(=O)X derivatives (X = CH3, NH2, OCH3) on tautomeric equilibria in solution

1H, 13C, and 15N NMR spectra show that an ortho-C(=O)X group present in the molecules of N-salicylideneanthranilamide (X = NH2), methyl N-salicylideneanthranilate (X = OCH3), N-salicylidene-o-aminoacetophenone (X = CH3), and their benzo analogues have only a minor effect on the tautomeric OH/NH-equilibrium in solution. Only two of three possible tautomers were detected. Lability of the absent form was proved by theoretical calculations. Calculated energies show that the enolimino form (OH) is less stable than the enaminone (NH) form only for dibenzo-annulated N-salicylideneanilines. The population of each species in the tautomeric mixture was found to be inversely proportional to its energy. Application of the geometry-based aromaticity index HOMA shows that the effectiveness of the pi-electron delocalization in different rings in the molecule depends mostly on the position of benzo-annulation. Both the NH...O and N...HO hydrogen bonds present in the NH and OH tautomers, respectively, increase the aromaticity of the quasirings H-O-C=C-C=N and O=C-C=C-N-H and decrease the aromatic character of the fused benzene ring. These results seem to be reliable when N-salicylideneanilines studied are compared with naphthalene and their benzo-annulated derivatives, i.e., phenanthrene, anthracene, and triphenylene. An analysis of the effectiveness of pi-electron delocalization confirms that in all cases studied, the OH form is more stable. Although the HOMA values and calculated energies are not a criterion that allows determination of the dominating tautomer, both of these parameters correctly show the effect of changes in the molecular topology on tautomeric preferences.     

Bismuth Film Electrodes for Adsorptive Stripping Voltammetric Determination of Sunset Yellow FCF in Soft Drinks

The bismuth film electrode was used to record well‐developed voltammograms of azo food coloring Sunset Yellow FCF (SY). The employed Bi(III)/HClO₄ plating solutions produced very adhesive and mechanically stable films that were applied in both stationary and flow conditions. The influence of the dimensions of the glassy carbon support, plating solution concentration and potential was discussed. The sensitivity of SWV was sufficient to obtain a linear calibration curve for low concentration levels of SY (below 0.1 mg/L; LOD=1 µg/L, linear range 4.4–87 µg/L). The measurements in a flow system were considered as a tool for the determination of relatively high concentrations (>1 mg/L; LOD=300 µg/L, linear range 300–8800 µg/L) of SY.     

Intermolecular Interactions in Systems Containing Bi(III) – ClO−4 – H2O – Selected Amino Acids in the Aspect of Catalysis of Bi(III) Electroreduction

The paper describes recent results of studies on the accelerating effect of sulfur‐containing protein amino acids and water activity on multistep Bi(III) ion electroreduction at mercury electrode. The catalytic effect of methionine (Mt), cystine (CY) and cysteine (CE) was analyzed based on kinetic and thermodynamic parameters, which correlated with water activity. Investigations of adsorption of those amino acids at the electrode/solution interface provided information for the analysis of the electrical double layer and its influence on the kinetics of the electrode process. The multistep Bi(III) electroreduction process is controlled by the kinetics of active complexes formation, which precedes transfer of consecutive electrons.     

Thermoanalytical,magnetic and structural investigation of Co(II) complexes with dipyridylamine and 2-hydroxyphenones

The simultaneous TG/DTG–DTA technique was used for three new cobalt(II) complexes with dipyridylamine (dpamH) and the anion of a 2-hydroxyphenone ligand (phenone), with the general formula [Co(dpamH)₂(phenone)]Br, in order to determine their thermal degradation in static air and dynamic nitrogen atmospheres, which was found to be a multi-step decomposition related to the release of the ligand molecules. The complexes were characterized by elemental analyses, FT-IR and UV–Vis spectroscopy, magnetic and conductivity measurements. All structures were determined by X-ray crystallography revealing octahedral coordination of cobalt(II) and monomeric nature of the compounds, [Co(dpamH)₂(2-OH-acetophenone)]Br (1), [Co(dpamH)₂(2-OH-propiophenone)]Br (2) and [Co(dpamH)₂(2-OH, 5-CH₃-acetophenone)]Br·EtOH (3). The variable temperature (76–303 K) magnetic susceptibility measurements showed a paramagnetic nature of the complexes, in accordance with their molecular structure.