Voltammetric Behavior of Dopamine at ct-DNA Modified Carbon Fiber Microelectrode

A sub-micrometer thin-layer DNA modified carbon fiber microcylinder electrode was prepared by electrodeposition of ct-DNA at 1.5V (vs. Ag/AgCl). The voltammetric behavior of dopamine (3-hydroxytyramine) was investigated at the modified electrode. It was found that the modified electrode exhibits a highly electrocatalytic activity toward dopamine oxidation. Differential pulse voltammetry was used for determination of dopamine in pH 7.4 phosphate buffer solution. A linear response of the peak current versus the concentration was found in the range of 4×10^–6 to 10^–4molL^–1 at 10^–4molL^–1 AA (ascorbic acid) coexistence (R=0.9959) and the range of 6×10^–5 to 10^–3molL^–1 at 10^–3molL^–1 AA (R=0.9960). The presence of a high concentration of ascorbic acid did not interfere with the determination. The proposed method exhibited good recovery and reproducibility. This method can be applied to the detection of DA in real samples.     

Determination of Lead Using a New Chromogenic Reagent 2-(2-Sulfo-4-acetylphenylazo)-7-(2,4,6-trichlorophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic Acid

A novel chromogenic reagent, 2-(2-sulfo-4-acetylphenylazo)-7-(2,4,6-trichlorophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid 1, was prepared by diazo coupling of 4-acetylaniline-2-sulfonic acid and 2,4,6-trichloroaniline to chromotropic acid through –N=N– groups. Based on this reagent, a simple, sensitive and selective spectrophotometric method was developed for the determination of lead. In 0.20M phosphoric acid medium, lead reacts with 1 to form a 1:2 blue complex with an absorption maximum of 654nm. Beers law is obeyed in the range of 0–0.6mgL^–1 of lead. The apparent molar absorptivity is 1.25×10⁵Lmol^–1cm^–1. The detection limit and quantification limit were found to be 0.63µgL^–1 and 2.1µgL^–1, respectively. The relative standard deviation for eleven replicate measurements was of 2.6%. The interference of foreign ions was also investigated. All the other foreign ions studied did not interfere with lead determination except for Ca(II) and Ba(II). The interference caused by Ca(II) and Ba(II) can be eliminated by prior extraction of lead with potassium iodide-methylisobutylketone (KI-MIBK). The proposed method was applied to the determination of lead in certified samples with satisfactory results.     

Mechanism of the cooperative vibronic emission of1δg singlet oxygen in solutions

The mechanism for inducing the probability of the ¹_g-X³_g ^– transition in an oxygen molecule with the simultaneous excitation of a vibration state of the solvent has been considered. The intensification of the 0-0 band of this transition under the influence of the solvent is attributed to the induction of the electric dipole moment of the b¹_g ⁺- ¹_g (m_ba) transition during a collision between O₂ and solvent molecules. It has been shown that m_ba is strongly dependent on the intermolecular distance and, consequently, on the normal coordinate of the vibrations of the solvent (Q) at a given collision parameter. Calculation of the derivative m_ba/Q (with consideration of the strong spin-orbit coupling of the b¹_g ⁺ and X³_g ^– states) makes it possible to account for the intensity of the new luminescence band of¹_g singlet oxygen, which is shifted toward longer wavelengths relative to the 0-0 band of the ¹_g-X³_g ^– by the value of the vibrational quantum of the solvent.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 594–596, September–October, 1985.     

Calculation of lower electronic states of the GaO and InO molecules by the SCF-Xα scattered wave method

In the overlapping atomic spheres approximation of the SCF-X SW method in different variants (spin-restricted, spin-unrestricted, and quasirelativistic), we have calculated fragments of the potential curves for the electronic ground state (X ₂) and the lower excited states (1 ², 2 ², 2 ², 3 ²) of the GaO and InO molecules. We have calculated the spectroscopic constants (T_e, _e, _ex_e, B_e, _e, R_e, A_e) for the molecules in the indicated states, the matrix elements for electronic transitions from the electronic ground state to the excited states, the Franck-Condon factors for the transitions 3 ², 2 ², 2 ² 1 ², X ² (v, v 10). For the InO molecule, we discuss the effect of relativistic corrections on the calculated molecular constants.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 11–19, January–February, 1986.     

Heterobinuclear and heterotrinuclear transition-metal μ-allenyl complexes

Binuclear and trinuclear transition-metal -allenyl complexes—especially mixedmetal complexes—are reviewed. In recent years, a number of such compounds have been prepared by use of several synthetic methods. The most general of these methods, viz. reactions of metal propargyls and of the lower nuclearity metal allenyls with low-valent metal complexes such as metal carbonyls and platinum(0) compounds, are considered in some detail. The structures of the binuclear metal -¹,²- and -³,²-allenyl complexes and of the trinuclear metal ₃-¹,²,²-allenyl complexes—both triangular and open—are presented and compared. Trends in the¹H and¹³C NMR spectroscopic properties of these compounds are examined. Some aspects of reaction chemistry of the heteronuclear platinum-ruthenium -¹,²-allenyl complexes are presented.     

Estimation of inorganic phosphate in aqueous solutions of DNA: A modification of the Berenblum-Chain method

Some modifications of the stannous chloride reduction method for the estimation of inorganic phosphate reported by Berenblum-Chain are suggested. By this method, it is possible to measure 25 g l^–1 of phosphorus /P/ as inorganic phosphate in the presence of macromolecules like deoxyribonucleic acid /100 g ml^–1/, as compared to 200 g l^–1 of P by the original method. If a larger sample volume /30 ml/ is used, even 5 g l^–1 of P can be measured.     

Acid strength distributions in the Mo?Al?Si and the Ni?Mo?Al oxide systems determined by ammonia adsorption

Acid strength distributions of Mo–Al–Si and Ni–Mo–Al oxide systems have been found by means of a relationship that gives pK_a values from amounts of ammonia adsorption. Molybdenum is suggested to cause a homogenization in the acid strength distribution of alumina but a heterogenization in silicaalumina, whereas nickel is found to neutralize strong acid sites inherent to molybdenum.

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Mo–Al–Si Ni–Mo–Al , . , , .

     

Phase composition of a selective V2O5?Fe2O3 catalyst of methanol oxidation to formaldehyde

Redispersion of Re/SiO₂ catalysts during air-aging at ambient temperature has been confirmed by TEM analysis. The splitting of large primary crystallites (>10 nm) under the influence of the strain energy of the oxide layer formed on the Re surface has been proposed to explain the observed phenomenon.

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Re/SiO₂ . , Re(>10 nm), , .

     

Proanthocyanidin dimers fromSpiraea hypericifolia

Summary From the bark and roots ofSpiraea hypericifolia L. we have isolated and identified proanthocyanidins consisting of dimers of 3,3,4,5,7-pentahydroxyflavans: a dimer from the bark (B-1) with the 2R:3R configuration of the asymmetric centers of the top half of the molecule and 2R:3S of the bottom half and a dimer from the roots with the 2R:3R configurations of the asymmetric centers of both the top and bottom halves of the molecule.S. M. Kirov Kazakh State University, Alma-Ata. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 735–742, November–December, 1976.     

Observation of vibration-electronic exchange in gas-surface collisions

Intensity increase of exoelectronic emission in the interaction of vibrationally excited hydrogen beam (v1) with emitter surface (CaSO₄) has been found. The effect proves to be due to the transfer of vibrational energy from molecules to trapped electrons, i.e. to the v-e transition in gas-surface collisions.

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- (v1) (CaSO₄). , .. v-e- -.

     

XPS and chemisorption studies of the surface layer of Pd?Ag catalysts for CO oxidation

XPS and chemisorption studies of the surface composition of a Pd–Ag alloy (5% Pd) before and after its application in CO oxidation have been performed. It is shown that in a freshly prepared sample the bulk and surface layer compositions are the same. High-temperature treatment of the catalyst in the reaction medium leads to a thermodynamic equilibrium between surface and bulk.

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Pd–Ag Pd 5% CO . , . .

     

Determination of sucrose content of cariogenic diets by thermal analysis

The sucrose content of cariogenic diets was determined by thermal analysis. The thermal characteristics of various cariogenic diets were examined up to 700 °C. A linear correlation was found between the sucrose content of the sample and the mass loss in the range 180–240 °C.The values determined by thermogravimetry were compared with those obtained by photometry as reference values.

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Zusammenfassung Mittels Thermoanalyse wurde der Saccharosegehalt von Karies verursachenden Diäten bestimmt. Die thermischen Eigenschaften verschiedener kariogener Diäten wurden bis 700 °C untersucht. Zwischen Saccharosegehalt der Probe und Massenverlust bei 180–240 °C konnte ein linearer Zusammenhang festgestellt werden. Die thermogravimetrisch erhaltenen Werte wurden mit den durch Fotometrie erhaltenen Werten als Referenzwerte vergliche.

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. 700°. 180–240°. , , , .

     

Kinetics of oxidation of glycine by aqueous chlorine

The kinetics of oxidation of glycine with aqueous chlorine has been investigated. The reaction is first order with respect to both molecular chlorine and glycine and inverse first order with respect to H⁺. The effect of various factors on the initial rate has also been studied. The kinetic parameters have been calculated and a possible mechanism is proposed.

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. , H⁺. , . .

     

Phase equilibria in the V2O5-FeVMoO7 system

The progress of the reactions of water with brownmillerite (C₄AF⁺) and its mixtures with gypsum (C¯SH₂) and calcium sulphoaluminate (C₄A₃¯S) was investigated by means of calorimetric measurements in situ and X-ray diffractometry to determine the reaction heat and the conversion of the solid reactants as functions of time up to 50 h. The rapid reaction of C₄AF with water and the modifying effect of sulphates on the composition of the hydrated phases were confirmed. The presence of sulphates causes the induction period during the reactions of aluminium and iron-containing clinker phases with water. These phenomena are important technologically too, especially in cements with increased contents of C₄AF and of sulphate-yielding phases (C¯SH₂ and C₄A₃¯S).

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Zusammenfassung Der Verlauf der Hydratation von Brownmillerit Ca₄AF^* bzw. seinen Mischungen mit Gips (C¯SH₂) und Calcium-sulfat-aluminat (C₄A₃¯S) wurde durch kalorimetrische Messungen in situ und Röntgendiffraktometrie verfolgt, um die Abhängigkeit der Reaktionswärme und des Umsatzes der festen Reaktanden von der Zeit (bis 50 h) zu bestimmen. Die schnelle Reaktion von C₄AF mit Wasser und der modifizierende Effekt der Sulfate auf die Zusammensetzung der hydratisierten Phase wird bestätigt. Die Anwesenheit von Sulfat bewirkt eine Induktionsperiode bei der Reaktion von alumimum- und eisenhaltigen Klinkerphasen mit Wasser. Diese Erscheinungen sind von technischer Bedeutung, insbesondere für Zemente mit erhöhtem Gehalt an C₄AF und sulfatbildenden Phasen wie C¯SH₂ und C₄A₃¯S.

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(4 · l23 · Fe2O3) (4 · 3l23 · SO3) ( 50 ). . - . , , - .

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Dedicated to F. Hanic, D. Sc. on the occasion of his 60th birthday     

Kinetic parameters obtained from TG and DTG curves of acrylamide-maleic anhydride copolymers

The thermal behaviour of acrylamide-maleic anhydride copolymers was studied by thermogravimetric (TG and DTG) analysis. The obtained data permitted the calculation of activation energies and reaction orders of the decomposition steps by the Coats-Redfern and Freeman-Carroll methods.Thermal analysis shows four distinct peaks in the case of polyacrylamide and AAMA (71) copolymer and only three for AAMA (11) copolymer.In AA:MA (11) copolymers intermolecular imidization occurs only and thermal degradation is influenced more by the anhydride groups which are equal in number with the amide ones.

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Zusammenfassung Das thermische Verhalten von Acrylamid-Maleinsäureanhydrid-Kopolymeren wurde durch thermogravimetrische Analyse (TG und DTG) untersucht. Aus den erhaltenen Daten wurden die Aktivierungsenergien und Reaktionsordnungen der Zersetzungsschritte nach den Methoden von Coats-Redfern und Freeman-Carroll berechnet. Durch thermische Analyse können im Falle von Polyacrylamid und AAMA (71 (-Kopolymeren 4 Peaks und bei AA:MA (11) -Kopolymeren nur 3 Peaks unterschieden werden. Bei AAMA (1 1)-Kopolymeren verläuft nur eine intermolekulare Imidisierung und der thermische Abbau wird mehr durch die in gleicher Zahl wie die Amidgruppen vorliegenden Anhydridgruppen beeinflußt.

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T () — (). , - -, . : ( 71) , : 11 — . : 11 , , .

     

Four types of relaxation in chemical kinetics (linear case)

According to results obtained previously for the linear equations of chemical kinetics, the relation between the steady-state reaction rate and the relaxation time has been studied.

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, , .

     

Energy Transfer Electrogenerated Chemiluminescence for the Determination of Sulfite

A simple and novel electrogenerated chemiluminescence (ECL) method for the determination of sulfite has been developed based on the energy transfer ECL process. It was found that a weak ECL signal of sulfite was electrochemically generated on a platinum electrode in neutral aqueous solution. The signal was strongly enhanced by rhodamine B as an energy receptor and further enhanced by the neutral surfactant Tween 80. In 0.10M phosphate buffer solution (pH=7.5) containing 2.0×10^–6gmL^–1 rhodamine B and 0.4% (v/v) Tween 80, the ECL response to the concentration of sulfite at a potential of 0.82V was linear over a range of 1.0×10^–7gmL^–1 to 8.0×10^–6gmL^–1, and the detection limit was 5×10^–8gmL^–1. The relative standard deviation (n=11, 1.0×10^–6gmL^–1) was 3.8%. The proposed method has been successfully applied to the determination of sulfite in pharmaceutical injections and white sugar samples.     

Mechanism of carbon monoxide oxidation on nickel oxide and its solid solutions

On the basis of studying the isotope exchange of oxygen and the position of the Fermi level in the system MiO–Li_xNi_1–xO, an explanation is proposed for the compensation effect in the reaction of CO oxidation on nickel oxide and its solid solutions.

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NiO–Li_xNi_1–xO CO .