On the absolute absorption cross-section of SF5CF3

The absolute absorption cross-sections of a recently discovered atmospheric gas, SF₅CF₃, have been measured at He I (21.22 eV) and Ne I (16.64 and 16.82 eV) photon energies using a VUV discharge lamp and a double ion chamber method. Absorption cross-sections of (9.52 ± 0.95) × 10⁻¹⁷ cm² (He I) and (8.79 ± 0.88) × 10⁻¹⁷ cm² (Ne I) were obtained and compared with data from other studies. The consequences for the cross-section at the hydrogen Lyman- energy (10.20 eV) are discussed.     

S2 → S0 fluorescence in an aromatic thioketone, xanthione

In addition to the red phosphorescence (T₁(³ A₂n, π^*) → S₀) xanthione exhibits in solution an emission with a maximum at ≈ 23 000 cm⁻¹ and φ_f(298°) = 5 × 10⁻³. It is shown that this emission is fluorescence from the second excited singlet state (S₂ (¹A₁ π, π^*) → S₀).     

Voltammetric study of the interaction of ciprofloxacin-copper with nucleic acids and the determination of nucleic acids

The behavior of the ciprofloxacin (CPFX) complex with copper, Cu(II)L₂, at a mercury electrode has been investigated in borax–boric acid buffer. The adsorption phenomena were observed by linear sweep voltammetry. The mechanism of the electrode reaction was found to be reduction of Cu(II)L₂ adsorbed on the surface of the electrode by an irreversible charge transfer to metal amalgam, Cu(0)(Hg). In the presence of DNA, the formation of the electrochemically non-active complexes Cu(II)L₂–DNA results in the decrease of the equilibrium concentration of Cu(II)L₂ and its peak current. Under the optimum conditions, the decrease of the peak current is proportional to DNA concentration. The linear ranges are 6.67×10⁻⁸ to 1.20×10⁻⁵ g ml⁻¹ for calf thymus DNA (ctDNA), 3.30×10⁻⁸ to 2.33×10⁻⁶ g ml⁻¹ for fish sperm DNA (fsDNA) and 1.0×10⁻⁸ to 1.2×10⁻⁶ g ml⁻¹ for yeast RNA. The detection limits are 5.00×10⁻⁹, 3.00×10⁻⁹ and 2.50×10⁻⁹ g ml⁻¹, respectively. This method exhibits good recovery and high sensitivity.     

An ionic liquid-type carbon paste electrode for electrochemical investigation and determination of calcium dobesilate

An ionic liquid-type carbon paste electrode (IL-CPE) had been fabricated by replacing non-conductive organic binders with a conductive room temperature ionic liquid, 1-pentyl-3-methylimidazolium hexafluorophosphate (PMIMPF₆). The electrochemical responses of calcium dobesilate were investigated at the IL-CPE and the traditional carbon paste electrode (T-CPE) in 0.05 mol L⁻¹ H₂SO₄, respectively. The results showed the superiority of IL-CPE to T-CPE in terms of provision of higher sensitivity, faster electron transfer and better reversibility. A novel method for determination of calcium dobesilate was proposed. The oxidation peak current was rectilinear with calcium dobesilate concentration in the range of 8.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹, with a detection limit of 4.0 × 10⁻⁷ mol L⁻¹(S/N = 3) by differential pulse voltammetry. The proposed method was applied to directly determine calcium dobesilate in capsule and urine samples.     

Dynamics of electronic polarization in molecular crystals

Dynamics of electronic polarization in the vicinity of charge carriers in molecular crystals is for the first time investigated here in connection with the carrier transport and intramolecular vibronic polarization. According to standard picture it has been assumed that the electronic polarization relaxation time is extremely short, as estimated from the relation τ_c = τ_d1 ≈ h/E_exc, where E_exc is the energy of the first single exciton state. In the case of anthracene (Ac) crystals, the value of τ_e is about 2 × 10⁻¹⁶ s, i.e. by several orders of magnitude shorter than a typical hopping (residence) time of charge carriers τ_h = 10⁻¹⁴ -10⁻¹³ s. It is argued that typical time of full reconstruction of the electronic polarization after individual carrier hops equals, in the slow carrier regime, approximately to t_d2 ≈ h/ΔE_exc is the width of the lowest singlet-exciton band. In Ac, this means t_d2 ≈ 0.73 × 10⁻¹⁴ s. Physical implications of this relatively high value of t_d2 in connection with carrier transport and molecular (vibronic) polarization are discussed.     

Collisional quenching of electronically excited germanium atoms, Ge[4p(S0)], by small molecules investigated by time-resolved atomic resonance absorption spectroscopy

The collisional quenching of electronically excited germanium atoms, Ge[4p²(¹S₀)], 2.029 eV above the 4p²(³P₀) ground state, has been investigated by time-resolved atomic resonance absorption spectroscopy in the ultraviolet at λ = 274.04 nm [4d(¹P₁⁰) ← 4p²(¹S₀)]. In contrast to previous investigations using the ‘single-shot mode’ at high energy, Ge(¹S₀) has been generated by the repetitive pulsed irradiation of Ge(CH₃)₄ in the presence of excess helium gas and added gases in a slow flow system, kinetically equivalent to a static system. This technique was originally developed for the study of Ge[4p²(¹D₂)] which had eluded direct quantitative kinetic study until recently. Absolute second-order rate constants obtained using signal averaging techniques from data capture of total digitised atomic decay profiles are reported for the removal of Ge(¹S₀) with the following gases (k_R in cm³ molecule⁻¹ s⁻¹, 300 K): Xe, 7.1 ± 0.4 × 10⁻¹³; N₂, 4.7 ± 0.6 × 10⁻¹²; O₂, 3.6 ± 0.9 × 10⁻¹¹; NO, 1.5 ± 0.3 × 10⁻¹¹; CO, 3.4 ± 0.5 × 10⁻¹²; N₂O, 4.5 ± 0.5 × 10⁻¹²; CO₂, 1.1 ± 0.3 × 10⁻¹¹; CH₄, 1.7 ± 0.2 × 10⁻¹¹; CF₄, 4.8 ± 0.3 × 10⁻¹²; SF₆, 9.5 ± 1.0 × 10⁻¹³; C₂H₄, 3.3 ± 0.1 × 10⁻¹⁰; C₂H₂, 2.9 ± 0.2 × 10⁻¹⁰; Ge(CH₃)₄, 5.4 ± 0.2 × 10⁻¹¹. The results are compared with previous data for Ge(¹S₀) derived in the single-shot mode where there is general agreement though with some exceptions which are discussed. The present data are also compared with analogous quenching rate data for the collisional removal of the lower lying Ge[4p²(¹D₂)] state (0.883 eV), also characterized by signal averaging methods similar to that described here.     

Voltammetric determination of glucose based on reduction of copper(II)–glucose complex at lanthanum hydroxide nanowire modified carbon paste electrodes

A novel voltammetric method for the determination of β-d-glucose (GO) is proposed based on the reduction of Cu(II) ion in Cu(II)(NH₃)₄²⁺–GO complex at lanthanum(III) hydroxide nanowires (LNWs) modified carbon paste electrode (LNWs/CPE). In 0.1 mol L⁻¹ NH₃·H₂O–NH₄Cl (pH 9.8) buffer containing 5.0 × 10⁻⁵ mol L⁻¹ Cu(II) ion, the sensitive reduction peak of Cu(II)(NH₃)₄²⁺–GO complex was observed at −0.17 V (versus, SCE), which was mainly ascribed to both the increase of efficient electrode surface and the selective coordination of La(III) in LNW to GO. The increment of peak current obtained by deducting the reduction peak current of the Cu(II) ion from that of the Cu(II)(NH₃)₄²⁺–GO complex was rectilinear with GO concentration in the range of 8.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹, with a detection limit of 3.5 × 10⁻⁷ mol L⁻¹. A 500-fold of sucrose and amylam, 100-fold of ascorbic acid, 120-fold of uric acid as well as gluconic acid did not interfere with 1.0 × 10⁻⁵ mol L⁻¹ GO determination.     

Electrocatalytic response of norepinephrine at a thiolactic acid self-assembled gold electrode

The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to catalyze the electrochemical response of norepinephrine (NE) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant (k_s) is 5.11×10⁻³ cm s⁻¹ at the self-assembled electrode. The electrode reaction is a pseudo-reversible process. The peak current and the concentration of NE are a linear relationship in the range of 4.0×10⁻⁵–2.0×10⁻³ mol l⁻¹. The detection limit is 2.0×10⁻⁶ mol l⁻¹. By ac impedance spectroscopy the apparent electron transfer rate constant (k_app) of Fe(CN)³⁻/Fe(CN)⁴⁻ at the TLA/Au electrode was obtained as 2.5×10⁻⁵ cm s⁻¹.     

Pulse radiolysis study of reactions of alkyl and alkylperoxy radicals originating from methyl tert-butyl ether in the gas phase

UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF₆ by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σ_R = (2.6 ± 0.4) × 10⁻¹⁸ cm² molecule⁻¹ and σ_RO2 = (4.1 ± 0.6) × 10⁻¹⁸ cm² molecule⁻¹ (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO₂ are (9.1 ± 1.5) × 10⁻¹³, (4.3 ± 1.6) × 10⁻¹² and (1.2 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule.     

Kinetic processes of Hg6s6p(P1) in xenon

The principal route for decay of Hg 6s6p(³P₁) in xenon is shown to be bimolecular deactivation to the mercury ground state, with rate coefficient 9.1 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹; relaxation to the ³P₀ state plays a negligible role. The equilibrium constant of the reaction Hg(³P₁) + Xe HgXe(A ³O⁺), has been recorded as 1.73 × 10⁻²⁰ cm³ molecule⁻¹ at 293 K.     

Time-resolved vibrational cemiluminescence: Rate constants for the reaction F + HC1 → HF + Cl and for the relaxtion of HF(v = 3) by HCl, CO2, N2O, CO, N2 and O2

The reaction: F + HCl→ HF (v 3) + Cl (1), has been initiated by photolysing F₂ using the fourth-harmonic output at 266 nm from a repetitively pulsed Nd: YAG laser By analysing the time-dependence of the HF(3,0) vibrational chemiluminescence, rate constants have been determined at (296 ± 5) K for reaction (1), k₁ = (7.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, and for the relaxation of HF(v = 3) by HCl, CO₂, N₂O, CO, N₂ and O₂: k_HCl = (1.18 ±0.14) × 10⁻¹¹ k_CO2 = (1.04 ± 0. 13) × 10⁻¹², k_N2O = (1.41 ± 0.13) × 10⁻¹¹ k_CO = (2.9 ± 0.3) × (10⁻¹², k_N2 = (7.1 ± 0.6) × 10⁻¹⁴ and k_O2 = (1.9 ± 0.6) × 10⁻¹⁴ cm³molecule⁻¹s⁻¹.     

Synthesis, structure and non-linear optical property of a copper(II) thiocyanate three-dimensional supramolecular compound

A novel copper(II) thiocyanate complex [Cu(im)₂(NCS)₂] 1 (im=imidazole) has been prepared and characterized by spectroscopic analysis and crystallographic method. This supramolecular compound exhibits a three-dimensional solid state structure constituted by N–HS hydrogen bonds and π–π stacking interactions. The compound in DMF solutions has a very strong third-order non-linear optical (NLO) behavior with absorption coefficient and refractive index ₂=1.18×10⁻¹¹ mw⁻¹, n₂=−9.00×10⁻¹⁶ m²w⁻¹, respectively, and third-order NLO susceptibility χ⁽³⁾ of 7.00×10⁻¹⁰ esu.     

Threonine-FX dosimeter for food irradiation

A detailed study for the spectrophotometric readout method for L-threonine powder, [CH₃CH(OH)CH(NH₂)COOH], was done. In this method, 400 mg unirradiated/irradiated L-threonine powder was dissolved in 10 ml of a solution which contains 3×10⁻⁴ mol dm⁻³ ferrous ammonium sulphate and 1.7×10⁻⁴ mol dm⁻³ xylenol orange (XO) in aerated aqueous 0.17 mol dm⁻³ sulphuric acid (FX). The peroxy radicals produced from irradiated threonine oxidize ferrous ions and XO forms a complex with ferric ions as well as controls the chain length of ferrous ion oxidation. The plot of absorbance at 556 nm against dose is linear in the dose range 20–400 Gy and doses down to about 1 Gy can be measured using 10-cm path cells. Response of the dosimeter is independent of irradiation temperature above 20. A dose of 50 Gy–10 kGy can be measured dissolving 50 mg threonine powder in 10 ml of a solution which contains 3×10⁻⁴ mol dm⁻³ ferrous ammonium sulphate and 1.3×10⁻⁴ mol dm⁻³ XO in aerated aqueous 0.06 mol dm⁻³ sulphuric acid (FX). The plot of absorbance at 552 nm against dose is non-linear. However dosimeter shows linear dose response up to 1000 Gy. Irradiated threonine powder is stable for about 3 months. The reproducibility of the method is better than ±2%. This dosimeter is very useful as transfer dosimeter for food irradiation programme.     

Anodic characterization of mercury microelectrodes for determinations of anions in real samples

The anodization of mercury microelectrodes was investigated in synthetic samples containing several strong and weak electrolytes at different concentrations. In particular, the effects on mercury anodization due to the presence of NaOH, HClO₄, NaCl, NaI, NaF, Na₂SO₄, NaHCO₃, Na₂CO₃, tartaric and citric acids, were studied in solutions containing either each species or mixtures of them, and without addition of supporting electrolyte. Some of the electrode processes studied led to linear calibration plots e.g. 1 × 10⁻⁵ − 1 × 10⁻⁴M Cl⁻, 1 × 10⁻⁶ − 1 × 10⁻⁵M I⁻, 5 × 10⁻⁴ − 3 × 10⁻³M SO₄²⁻, 5 × 10⁻⁴ − 2 × 10⁻²M HCO₃⁻, with typical correlation coefficients of 0.998–0.999. The anodization of mercury microelectrodes was also investigated directly in wine, rain, tap and mineral water, without pretreatment and without addition of supporting electrolyte. In the real samples only the ions Cl⁻ and HCO₃⁻ could be quantified, and the values found were in agreement, within 3–5%, with the reference values obtained by using Italian standard methods for food.     

Simultaneous derivative spectrophotometric determination of thorium and uranium in a micellar medium

Derivative photometric methods for trace analysis of Th(IV) and UO₂(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO₂(II) complexes at their λ_max, 614.5 nm and 637.0 nm are, 1.19 × 10⁴ 1/mol/cm and 1.12 × 10⁴ 1/mol/cm and 1.95 × 10⁻² μg/cm² and 2.13 × 10⁻² μg/cm² μg/cm², respectively. Calibration graph is linear over the range 9.28 × 10⁻²−18.56 μg/ml of Th(IV) and 9.52 × 10⁻²−19.04 μg/ml of UO₂(II). Though presence of Th(IV) and UO₂(II) causes interference in each others determination, 9.28 × 10⁻¹−9.28 μg/ml Th(IV) and 9.52 × 10⁻¹−9.52 μg/ml UO₂(II) when present together, can be simultaneously determined using derivative spectra.     

Square wave adsorptive stripping voltammetric determination of famotidine in urine

Electrochemical studies of famotidine were carried out using voltammetric techniques: cyclic voltammetry, linear sweep and square wave adsorptive stripping voltammetry. The dependence of the current on pH, buffer concentration, nature of the buffer, and scan rate was investigated. The best results for the determination of famotidine were obtained in MOPS buffer solution at pH 6.7. This electroanalytical procedure enabled to determine famotidine in the concentration range 1 × 10⁻⁹–4 × 10⁻⁸ mol L⁻¹ by linear sweep adsorptive stripping voltammetry (LS AdSV) and 5 × 10⁻¹⁰–6 × 10⁻⁸ mol L⁻¹ by square wave adsorptive stripping voltammetry (SW AdSV). Repeatability, precision and accuracy of the developed methods were checked. The detection and quantification limits were found to be 1.8 × 10⁻¹⁰ and 6.2 × 10⁻¹⁰ mol L⁻¹ for LS AdSV and 4.9 × 10⁻¹¹ and 1.6 × 10⁻¹⁰ mol L⁻¹ for SW AdSV, respectively. The method was applied for the determination of famotidine in urine.     

Enhancement effect of sodium dodecyl benzene sulfonate (SDBS) and its application into voltammetric determination of telmisartan

A sensitive and rapid electrochemical method was developed for the determination of telmisartan based on the enhancement effect of sodium dodecyl benzene sulfonate (SDBS). In 0.1 mol L⁻¹ HClO₄ and in the presence of 7.5 × 10⁻⁵ mol L⁻¹ SDBS, a well-defined and sensitive oxidation peak was observed for telmisartan at the acetylene black (AB) paste electrode. However, the oxidation peak is poor-shaped and the peak current is very low in the absence of SDBS, suggesting that SDBS shows obvious enhancement effect for the determination of telmisartan. After all the experimental parameters were optimized, a sensitive and simple electrochemical method was developed for determining telmisartan. The oxidation peak current is proportional to the concentration of telmisartan over the range from 2.5 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹. The detection limit is 7.5 × 10⁻⁸ mol L⁻¹ after 2 min of accumulation. This new voltammetric method was successfully used to detect telmisartan in drugs.     

Amphiphile bilayer films from DPPC: bilayer lipid membranes and Newton black films

Amphiphile bilayer films are obtained from 1,2 dipalmitoyl-glycero-3-phosphocholine (DPPC): bilayer lipid membranes (BLM) and Newton black films (NBF), through thinning of the respective thin liquid films, thus allowing for a very precise determination of the moment of their formation. Stability (or rupture) and formation of BLM and NBF are considered from a unified point of view with the microscopic theory of Kashchiev–Exerowa [J. Colloid Interface Sci., 77 (1980) 501–511], based on the formation of nanoscopic holes in them. BLM and NBF are obtained and studied with the microinterferometric method of Scheludko–Exerowa in its contemporary version. The equivalent thickness of both BLM (in benzene solution between two water phases with 0.1 M NaCl) and NBF in aqueous DPPC solution (in the presence of 0.1 M NaCl) is determined as being h_w = 7.0 nm for BLM and h_w = 7.8 nm for NBF. By means of the dependences: BLM lifetime versus DPPC concentration and probability for BLM formation versus DPPC concentration, it is established that there exist metastable BLM and stable NBF. The good fit between the experimental results of τ(C) dependence and theory in the case of BLM allow to determine the three constants: pre-exponential factor A = 1.5 × 10⁻³ s, related to the process kinetics; constant B = 20.2 ± 0.2, related to the specific hole energy γ = 1.7 × 10⁻¹¹ J/m and the equilibrium concentration C_e = 6 × 10⁻⁴ ± 7.2 × 10⁻⁶ m/l. The specific hole linear energy γ = 1.7 × 10⁻¹¹ J/m determined as well as the binding energy Q between first neighbor molecules in the bilayers Q = 1.48 × 10⁻¹⁹ J (36 kT) are lower than the ones determined for DPPC foam bilayer in gel state γ = 9.1 × 10⁻¹¹ J/m and Q = 55 kT. This means that interaction is weaker in the case of BLM. The critical concentration C_c at which bilayer formation starts is: for BLM C_c = 30 μg/ml and for NBF C_c = 70 μg/ml. This concentration characterizes quantitatively the formation of the amphiphile bilayer and is a very useful parameter that can be used for various purposes.     

Rate coefficients for the reactions of cyclohexadienyl (c-C6H7) radicals with O2 and NO at room temperature

Rate coefficients for the reactions of cyclohexadienyl (c-C₆H₇) radicals with O₂ and NO were measured at 296 ± 2 K. The c-C₆H₇ radicals were detected selectively by laser-induced fluorescence. The rate coefficient for the reaction of c-C₆H₇ with O₂, (4.4 ± 0.5) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, was independent of the bath-gas (He) pressure (13–80 Torr). In the reaction of c-C₆H₇ with NO, thermal equilibrium among c-C₆H₇, NO, and C₆H₇NO was observed. The forward and reverse reactions were in the falloff region, and the equilibrium constant was (1.5 ± 0.6) × 10⁻¹⁵ cm³ molecule⁻¹.     

Kinetics and mechanisms of the redox reaction of hexaaquotitanium(III) and the ethylenediamine tetraacetato titanium(III) complex by aqueous solutions of bromine

At 25°C, I = 1.0 M (CF₃SO₃⁻Li⁺+CF₃SO₃H), [H⁺] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H₂O), ₆³⁺ by bromine was found to be: −d/[Br₂]T/dt=kK/[Br₂][Ti^III]/[H⁺]+K+kK/[Br₃⁻][Ti^III]/[H⁺+K, where k = 9.2 × 10⁻³ M ⁻¹ s ⁻¹ and K = 4.5 × 10⁻³ M. At [H⁺] = 1.0 M, [Br⁻] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br⁻] increases.

The pH-dependence of the oxidation of Ti^III-edta by bromine is interpreted in terms of the change in identity of the Ti^III-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k₀^edta)² weighting into an equation of the form: k₀^edta =k₁+k₂K₁[H⁺]⁻¹+k₃K₁K₂[H⁺]^−2/1+K₁[H⁺[H⁺⁻¹+K₁K₂[H⁺]⁻², with K₁ and K₂ fixed as earlier determined at 9.55 × 10⁻³ and 2.29 × 10⁻⁹ M, respectively, for the oxidation of bromine. k₁=k₂=(3.1±0.32)×10³M⁻¹s⁻¹ k₃=(2.3±0.45)×10⁶N⁻¹s⁻¹.

It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br₂^.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for Ti^III-edta+Ti^IV-edta is estimated at 32 M⁻¹ s⁻¹.