Two Coulomb waves theory for direct excitation

A theoretical model of Dewangan, in which the total scattering wave function is approximated by a distorted wave containing two Coulomb wave functions, is discussed and its relation with the Brauner-Briggs-Klar model for ionization is examined. An important feature of the theory is that it includes a second Born amplitude naturally and in addition, contains, albeit approximately, both real and imaginary parts of all higher order Born terms. The theory is applied to study the 1s→2s excitation of hydrogen by electrons in the energy range 54.4 to 400eV. The differential and integral cross sections predicted by the theory are compared with the results of other theories and experimental data at 54.4eV and a good agreement is found.     

Cyanine dyes as protectors of K562 cells from photosensitized cell damage

Several cyanine dyes were found to protect K562 leukemia cells against toxicity mediated by cis-di(4-sulfonatophenyl)diphenylporphine (TPPS2) and light. Most cyanine dyes derived from dimethylindole were better photoprotectors than cyanine dyes with other structures. This correlated with the fact that cyanine dyes derived from dimethylindole were predominately monomeric at millimolar concentrations within K562 cells, while other cyanine dyes formed aggregates. For cyanine dyes that are derived from dimethylindole and have absorption band wavelengths greater than 700 nm, fluorescence-energy transfer from TPPS2 to the cyanine dye was the most important mechanism for photoprotection. There was no spectroscopic evidence for complex formation between the cyanine dyes and TPPS2. The dimethylindole derivative, 1,1',3,3,3',3'-hexamethylindodicarbocyanine, was an excellent photoprotector, but a poor quencher of TPPS2 fluorescence and a relatively poor singlet-oxygen quencher. This cyanine dye may act by quenching excited triplet TPPS2. Singlet-oxygen quenching may contribute to the photoprotection provided by cyanine dyes not derived from dimethylindole. Differences in the subcellular distribution of the various cyanine dyes studied may have contributed to the different apparent mechanisms of photoprotection.     

Renewable sol-gel carbon ceramic electrodes modified with a Ru-complex for the amperometric detection of l-cysteine and glutathione

A renewable three-dimensional chemically modified carbon ceramic electrode containing Ru [(tpy)(bpy)Cl] PF₆ was constructed by sol-gel technique. It exhibits an excellent electro-catalytic activity for oxidation of l-cysteine and glutathione at pH range 2-8. Cyclic voltammetry was employed to characterize the electrochemical behavior of the chemically modified electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for l-cysteine and glutathione by hydrodynamic amperometry. Optimum pH value for detection is 2 for both l-cysteine and glutathione. The catalytic rate constants for l-cysteine and glutathione were determined, which were about 2.1×10³ and 2.5×10³ M⁻¹ s⁻¹, respectively. Under the optimized condition the calibration curves are linear in the concentration range 5-685 and 5-700 μM for l-cysteine and glutathione determination, respectively. The detection limit (S/N=3) and sensitivity is 1 μM, 5 nA/μM for l-cysteine and 1 μM, 7.8 nA/μM for glutathione. The relative standard deviation (RSD) for the amperogram's currents with five injections of l-cysteine or glutathione at concentration range of linear calibration is <1.5%. The advantages of this amperometric detector are: high sensitivity, good catalytic effect, short response time (t<3 s), remarkable long-term stability, simplicity of preparation and reproducibility of surface fouling (RSD for six successive polishing is 3.31%). This sensor can be used as a chromatographic detector for analysis of l-cysteine and glutathione.     

Renewable-surface sol-gel derived carbon ceramic electrode fabricated by [Ru(bpy)(tpy)Cl]PF6 and its application as an amperometric sensor for sulfide and sulfur oxoanions

A highly sensitive and fast responding sensor for the determination of thiosulfate, sulfite, sulfide and dithionite is described. It consists of a chemically modified carbon ceramic composite electrode (CCE) containing [Ru(bpy)(tpy)Cl]PF6 complex that was constructed by the sol-gel technique. A reversible redox couple of Ru(II)/Ru(III) was observed as a solute in acetonitrile solution and as a component of carbon based conducting composite electrode. Electrochemical behavior and stability of modified CCE were investigated by cyclic voltametry, the apparent electron transfer rate constant (kappa(S)) and transfer coefficient (a) were determined by cyclic voltametry which were about 28 s(-1) and 0.43 respectively. Electrocatalytic oxidation of S(2-), SO3(2-), S2O4(2-) and S2O3(2-) were effective at the modified electrode at significantly reduced overpotentials and in the pH range 1-11. Optimum pH values for amperometric detection of thiosulfate, dithionite, sulfide and sulfite are 7, 9, 2 and 2. Under the optimized conditions the calibration curves are linear in the concentration ranges 1-500, 3-80, 2-90 and 1-100 microM for S2O3(2-), SO3(2-), S2- and S2O4(2-) determination. The detection limit (signal to noise is 3) and sensitivity are 0.5 and 12, 2.8 and 6, 1.6 and 8, and 0.65 microM and 80 nA microM(-1) for thiosulfate, sulfite, sulfide and dithionite detection. The modified carbon ceramic electrode doped with Ru-complex shows good reproducibility, a short response time (t < 2 s), remarkable long term stability (> 6 month) and especially good surface renewability by simple mechanical polishing (RSD for eight successive polishing is 2%). The advantages of this sulfur compound amperometric detector based on ruthenium doped CCE are high sensitivity, inherent stability at a broader pH range, excellent catalytic activity, less expense and simplicity of preparation in comparison with recently published papers. This sensor can be used as a chromatographic detector for analysis of sulfur derivatives.     

A selective modified carbon paste electrode for determination of cyanide using tetra-3,4-pyridinoporphyrazinatocobalt(II)

A chemically modified carbon paste electrode with 3,4-tetra pyridinoporphirazinatocobalt(II) (Co(3,4 tppa) was applied to the determination of free cyanide ion. The electrode has a linear range between 1.5 × 10⁻⁵ M and 1.0 × 10⁻² M with a Nernstian slope of 60 ± 1.5 mV/decade and its detection limit is 9 × 10⁻⁶ M. The response time of electrode is 5 min. The proposed electrode was applied successfully for the determination of cyanide in commercially available spring water. Some anions, such as SCN⁻, I⁻, Cl⁻, Br⁻ and oxalate that are usually serious interfering species for most of cyanide selective electrodes, did not have any interfering effect for this proposed electrode.     

An accurate expression for radial distribution function of the Lennard-Jones fluid

A simple and accurate expression for radial distribution function (RDF) of the Lennard-Jones fluid is presented. The expression explicitly states the RDF as a continuous function of reduced interparticle distance, temperature, and density. It satisfies the limiting conditions of zero density and infinite distance imposed by statistical thermodynamics. The distance dependence of this expression is expressed by an equation which contains 11 adjustable parameters. These parameters are fitted to 353 RDF data, obtained by molecular dynamics calculations, and then expressed as functions of reduced distance, temperature and density. This expression, having a total of 65 constants, reproduces the RDF data with an average root-mean-squared deviation of 0.0152 for the range of state variables of 0.5  T^*  5.1 and 0.35  ρ^*  1.1 (T^*=kT/ε and ρ^* = ρσ³ are reduced temperature and density, respectively). The expression predicts the pressure and the internal energy of the Lennard-Jones fluid with an uncertainty that is comparable to that obtained directly from the molecular dynamics simulations.     

Aluminium(III)-selective electrode based on a newly synthesized tetradentate Schiff base

A PVC membrane electrode for aluminium ion based on bis(5-phenyl azo salicylaldehyde) 2,3-naphthalene diimine (5PHAZOSALNPHN) as an ion carrier was developed. The electrode exhibits a Nernstian slope of 19.3+/-0.8 mV per decade and a linear range of 5.0x10(-6)-1.0x10(-2) M for Al(NO(3))(3). The limit of detection is 2.5x10(-6) M. It has a fast response time of about 10 s and can be used for at least 10 weeks without observing any deviation. The proposed membrane sensor revealed good selectivity for Al(3+) over a wide variety of other metal ions and could be used in pH range of 2.9-5.0. It was used as an indicator electrode in potentiometric titration of aluminium ion.     

Chromium(III) ion-selective electrode based on 4-dimethylaminoazobenzene

A PVC-based membrane of 4-dimethylaminoazobenzene reveals a Nernstian potentiometric response (with slope of 19.5+/-0.6 mV/decade and a correlation coefficient of 0.999) for Cr(III) over a wide concentration range (1.66 x 10(-6)-1.0 x10(-2) mol dm(-3)). The potential of this electrode is independent of pH in the range of 3.0-5.5. It has a fast response time of about 10 s and was used for a period of 3 months with good reproducibility. The detection limits of this membrane electrode was 8 x 10(-7) M. the proposed electrode has been used as an indicator electrode in the potentiometric titration of Cr(III) with EDTA. This sensor exhibits a very good selectivities for Cr(III) over a wide variety of metal ions.     

SINGLET-OXYGEN GENERATION AT GAS-LIQUID INTERFACES: A SIGNIFICANT ARTIFACT IN THE MEASUREMENT OF SINGLET-OXYGEN YIELDS FROM OZONE-BIOMOLECULE REACTIONS

Abstract— Several ozone-biomolecule reactions have previously been shown to generate singlet oxygen in high yields. For some of these orone-biomolecule reactions, we now show that the apparent singlet-oxygen yields determined from measurements of 1270 nm chemiluminescence were artifactually elevated by production of gas-phase singlet oxygen. The gas-phase singlet oxygen results from the reaction of gas-phase ozone with biomolecules near the surface of the solution. Through the use of a flow system that excludes air from the reaction chamber, accurate singlet-oxygen yields can be obtained. The revised singlet-oxygen yields (mol ¹O₂ per mol O₃) for the reactions of ozone with cysteine, reduced glutathione, NADH, NADPH, human albumin, methionine, uric acid and oxidized glutathione are 0.23 ± 0.02, 0.26 ± 0.02, 0.48 ± 0.04, 0.41 ± 0.01, 0.53 ± 0.06, 1.11 ± 0.04, 0.73 ± 0.05 and 0.75 ± 0.01, respectively. These revised singlet-oxygen yields are still substantial.     

Carbon nanotube composite coated platinum electrode for detection of Cr(III) in real samples

This paper demonstrates the application of composite multi-walled carbon nanotube (MWNT) polyvinylchloride (MWNT-PVC) based on 1,5-diphenylcarbazide as chromium ionophore in potentiometric measurement. The sensor shows a good Nernstian slope of 19.52 ± 0.40 mV/decade in a wide linear range concentration of 6.3 × 10⁻⁸ to 1.0 × 10⁻² M for Cr(NO₃)₃. The detection limit of this electrode was found to be 3.2 × 10⁻⁸ M of Cr(NO₃)₃ and is applicable in a pH range of 3.0-6.8. It has a short response time of about 10 s. This chromium electrode has a good selectivity over 16 various metal ions. The practical analytical utility of this electrode was demonstrated by measurement of Cr(III) in drinking water and mineral water samples without any serious preliminary pre-treatment and chromium in multivitamin.