Gamma-radiation effects on the reduction of hematite to iron in the graphite-iron(III) oxide system

The effects of⁶⁰Co-gamma radiation and of various sample composition on the reduction of hematite to iron in the graphite-iron(III) oxide system in air were studied using isothermal and dynamic TG techniques. Kinetic analysis of isothermal data were performed according to various theoretical models of heterogeneous reactions and the results showed that the three-dimensional phase boundary model gives the best fit of data. Analysis of dynamic TG data were made using Ozawa integral method, Coats-Redfern method and a composite method based on the modified Coats and redfern equation. The activation parameters were calculated and the results of the different methods were compared and discussed.Radiation apparently did not introduce a change in the reaction model or mechanism. However, there is a decrease in activation energy and frequency factor upon irradiation and a decrease in the half-life time of the reaction which is remarkable at the higher temperatures and higher doses.

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Zusammenfassung Mittels isothermer und dynamischer TG wurde im Graphit-Eisen(III)oxidsystem in Luft der Einfluß von⁶⁰Co-Gammastrahlung und von verschiedenen Probenzusammensetzungen auf die Reduktion von Hämatit zu Eisen untersucht. Entsprechend verschiedener theoretischer Modelle heterogener Reaktionen wurde eine kinetische Analyse der isothermen Daten durchgeführt und die Ergebnisse zeigten, daß das dreidimensionale Phasengrenzenmodell die beste Übereinstimmung liefert. Die Analyse der dynamischen TG-Daten wurde mittels der Integralmethode von Ozawa, der Coats-Redfem-Methode und einer zusammengesetzten Methode auf der Grundlage der modifizierten Coats und Redfern Gleichung durchgeführt. Die Aktivierungsparameter wurden berechnet und die Ergebnisse der verschiedenen Methoden miteinander verglichen und diskutiert.Strahlung scheint keine Änderung des Reaktionsmodelles oder des Mechanismus hervorzurufen. Durch Bestrahlung gibt es aber ein Absinken der Aktivierungsenergie und des Frequenzfaktors sowie ein Absinken der Halbwertszeit der Reaktion, was bei höheren Temperaturen und höherer Dosis bemerkenswert groß ist.

     

The kinetics of reaction of 4-nitrophenylnitromethane with N’-Propyl-N,N-dipropylbenzimidamide in aprotic solvents. a steric effect on tunneling

Thermodynamic and kinetic parameters have been established for the reaction between the carbon acid, 4-nitrophenylnitromethane, (4-NPNM), and the base N’-n-propyl-N,N-di-n-propylbenzimidamide, (N’PDPBA), in mesitylene and in chlorobenzene. In some cases deuteron transfer from 4-(D₂)NPNM to the base has also been studied. In addition, some results for the proton transfer reaction in tetrahydrofuran have been collected. Spectrophotometric methods have been employed to monitor the ion-pair product, which is solvatochromic. In general the solvent dependence of the parameters is as expected, but there is some indication of specific solvation. The kinetic isotope effects of 11 and 8 in mesitylene and chlorobenzene, respectively, are larger than those predicted classically. However, as is discussed the n-propyl group on the secondary nitrogen of the base may serve to reduce the extent of tunneling compared to that in an unsubstituted analogue by a steric effect.     

Multilayer effects in liquid adsorption chromatography with mixed mobile phases

This paper describes the theory of liquid adsorption chromatography (LSC) with mixed mobile phase, involving formation of multilayer surface phases. An equation describing the dependence of the capacity ratio upon the mobile phase composition is derived and theoretical curves illustrating the same dependence are calculated accordingly by assuming different thicknesses of the surface phase.     

Linear free energy relationship of the energy of the CTTS transition of Halide ions with the solvatochromic parameter α

A linear free energy relationship was found betweenv _max, the energy of the absorption maximum of chloride, bromide, or iodide ion in various solvents, and the solvatochromic parameter which is a measure of the hydrogen bond donor ability of the solvent. The relationships are: for chloride,v _max=6.99+50.16 kK; for bromide,v _max=5.52+45.20 kK; for iodide,v _max=5.02+40.33 kK. The correlation ofv _max for iodide ion with gave a larger correlation coefficient and smaller standard deviation than a correlation with the E _T (30) parameter of Dimroth. From the values ofv _max for iodide ion and the solvated electron in liquid ammonia at 25°C, these correlations indicate a preliminary value of 0.00 for the parameter of liquid ammonia. This had not been reported before and is lower than expected from a general knowledge of the physical and chemical properties of liquid ammonia but is consistent with a more detailed consideration and recent gas phase measurements of hydrogen bond donor strength.     

Thermodynamics of Dipeptides in Water. Influence of the hydrophobic forces of the side-chains on the dissociation processes for some series of dipeptides

A calorimetric study has been carried out on the dissociation processes in water of both the free α-amino group belonging to the amino terminal residue and the free α-carboxyl groups belonging to the carboxyl terminal residue for a series having phenylalanine as the first common term. These thermodynamic quantities have been compared with those of the proton dissociation processes related to the same groups of the corresponding singleα-amino acids. The dissociation process values of this series have also been considered in connection with those obtained from others series of dipeptides previously studied, in an effort to compare the alkyl groups and benzene ring hydrophobic effects on the salvation processes of the zwitterions, undissociated molecules and ionic forms. This revised version was published online in August 2006 with corrections to the Cover Date.     

静电和疏水效应对TGEV主蛋白酶二聚体稳定性的影响

从TGEV 3CL蛋白酶二聚体结构出发,研究了TGEV 3CL蛋白酶二聚体单体之间的静电和疏水相互作用.蛋白质的静电相互作用通过有限差分方法求解Poisson-Boltzmann方程得到,疏水相互作用通过分析溶剂可及性表面模型得到.考察了不同pH值对TGEV 3CL蛋白酶二聚体静电和疏水相互作用的影响,在pH值为5.5～8.5时,二聚体静电相互作用能、静电去溶剂化能和疏水自由能都较小,表明在该条件下静电和疏水相互作用有利于二聚体的稳定存在,这符合实验结晶所需条件.pH值对静电去溶剂化能的影响大于疏水自由能,表明静电作用是造成强酸或强碱条件下二聚体不能稳定存在的主要原因.     

SYNTHESIS OF CONDUCTIVE POLYANILINE VIA OXIDATION BY MnO2

A unique process of chemical oxidation polymerization of aniline using manganese dioxide (MnO2) as the oxidizing agent in an aqueous medium is described. The reaction between aniline and MnO2 follows a mechanism by which the organic monomer is oxidized while the metal oxide undergoes reductive dissolution. The effects of the amount of oxidizing agent and aniline, pH and temperature of the reactive system, type of acid on the yield and conductivity of polyaniline are discussed. The resulting polyaniline was characterized by [R and UV-Vis spectrometry. Polyaniline with a conductivity of 12.5 S/cm was obtained using 0.033 tool of aniline oxidized by 0.023 tool MnO2 in the presence of 100 mL of 2.7 mol/L HCI at 25℃ for 4 h.     

Selection of a Representative Matrix for Calibration in Multianalyte Determination of Pesticides in Vegetables by Liquid Chromatography-Electrospray Tandem Mass Spectrometry

An analytical method for determining residues of twenty pesticides by liquid chromatography (LC) coupled to electrospray ionisation (ESI) tandem mass spectrometry (MS-MS) in eight commodities, cucumber, tomato, pepper, green bean, eggplant, zucchini, melon and watermelon, has been developed and validated. On one hand, calibration curves prepared in solvent were compared with calibration curves prepared in a blank matrix extract of each target matrix. On the other hand, calibration curves and recoveries for each commodity were compared. Cucumber was selected as potential reference matrix for the target vegetables.     

Temperature selectivity effects in reversed-phase liquid chromatography due to conformation differences between helical and non-helical peptides

In order to characterize the effect of temperature on the retention behaviour and selectivity of separation of polypeptides and proteins in reversed-phase high-performance liquid chromatography (RP-HPLC), the chromatographic properties of four series of peptides, with different peptide conformations, have been studied as a function of temperature (5-80 degrees C). The secondary structure of model peptides was based on either the amphipathic alpha-helical peptide sequence Ac-EAEKAAKEX(D/L)EKAAKEAEK-amide, (position X being in the centre of the hydrophobic face of the alpha-helix), or the random coil peptide sequence Ac-X(D/L)LGAKGAGVG-amide, where position X is substituted by the 19 L- or D-amino acids and glycine. We have shown that the helical peptide analogues exhibited a greater effect of varying temperature on elution behaviour compared to the random coil peptide analogues, due to the unfolding of alpha-helical structure with the increase of temperature during RP-HPLC. In addition, temperature generally produced different effects on the separations of peptides with different L- or D-amino acid substitutions within the groups of helical or non-helical peptides. The results demonstrate that variations in temperature can be used to effect significant changes in selectivity among the peptide analogues despite their very high degree of sequence homology. Our results also suggest that a temperature-based approach to RP-HPLC can be used to distinguish varying amino acid substitutions at the same site of the peptide sequence. We believe that the peptide mixtures presented here provide a good model for studying temperature effects on selectivity due to conformational differences of peptides, both for the rational development of peptide separation optimization protocols and a probe to distinguish between peptide conformations.     

New insight into solvent effects on the formal HOO. + HOO. reaction

The 2,2'-azobis(isobutyronitrile)(AIBN)-induced autoxidation of gamma-terpinene (TH) at 50 degrees C produces p-cymene and hydrogen peroxide in a radical-chain reaction having HOO* as one of the chain-carrying radicals. The kinetics of this reaction in cyclohexane and tert-butyl alcohol show that chain termination involves the formal HOO. + HOO. self-reaction over a wide range of gamma-terpinene, AIBN, and O2 concentrations. However, in acetonitrile this termination process is accompanied by termination via the cross-reaction of the terpinenyl radical, T., with the HOO. radical under conditions of relatively high [TH] (140-1000 mM) and low [O2] (2.0-5.5 mM). This is because the formal HOO. + HOO. reaction is comparatively slow in acetonitrile (2k approximately 8 x 10(7) M(-1) s(-1)), whereas, this reaction is almost diffusion-controlled in tert-butyl alcohol and cyclohexane, 2k approximately 6.5 x 10(8) and 1.3 x 10(9) M(-1) s(-1), respectively. Three mechanisms for the bimolecular self-reaction of HOO. radicals are considered: 1) a head-to-tail hydrogen-atom transfer from one radical to the other, 2) a head-to-head reaction to form an intermediate tetroxide, and 3) an electron-transfer between HOO. and its conjugate base, the superoxide radical anion, O2-.. The rate constant for reaction by mechanism (1) is shown to be dependent on the hydrogen bond (HB) accepting ability of the solvent; that by mechanism (2) is shown to be too slow for this process to be of any importance; and that by mechanism (3) is dependent on the pH of the solvent and its ability to support ionization. Mechanism (3) was found to be the main termination process in tert-butyl alcohol and acetonitrile. In the gas phase, the rate constant for the HOO. + HOO. reaction (mechanism (1)) is about 1.8 x 10(9) M(-1) s(-1) but in water at pH< or =2 where the ionization of HOO. is completely suppressed, this rate constant is only 8.6 x 10(5) M(-1) s(-1). The very large retarding effect of water on this reaction has not previously been explained. We find that it can be quantitatively accounted for by using Abraham's HB acceptor parameter, beta(2)(H), for water of 0.38 and an estimated HB donor parameter, alpha(2)(H), for HOO. of about 0.87. These Abraham parameters allow us to predict a rate constant for the HOO. + HOO. reaction in water at 25 degrees C of 1.2 x 10(6) M(-1) s(-1) in excellent agreement with experiment.