Kinetic study on the mechanism of inhibition of trypsin and trypsin-like enzymes by p-guanidinobenzoate ester

It was found that [4-(2-succinimidoethylthio)phenyl 4-guanidinobenzoate]methanesulfonate (E-3123) inhibits trypsin, thrombin and kallikrein, and its inhibitory activity is most potent toward trypsin. The interactions of these enzymes with E-3123 were studied mainly by using stopped-flow spectrophotometry. E-3123 behaved as a quasi-substrate of the enzymes and the inhibitory property was due to the efficient production of the stable acyl-enzyme. The acylation process with trypsin was exceedingly effective, and the resulting acyl-enzyme was the most stable among the three enzymes tested. This observation affords a rational basis for explaining the action of E-3123, which is a transient inhibitor most active toward trypsin.     

Determination of imipenem (N-formimidoyl thienamycin) in human plasma and urine by high-performance liquid chromatography, comparison with microbiological methodology and stability

High-performance liquid chromatographic (HPLC) methods using ultraviolet (UV) detection have been developed for the assay of the antibiotic imipenem (N-formimidoyl thienamycin) in human plasma and urine. A reversed-phase analytical column is employed in the plasma assay method and a cation-exchange column is used in the urine assay method. Both methods use borate buffer in the mobile phase. The method of preparation of human fluid samples for HPLC injection has been optimized with respect to the stability of imipenem in aqueous buffers, in morpholine buffer--ethylene glycol stabilizer, and in urine and plasma. Preparation of the samples before injection into the HPLC systems involves deproteination/filtration of the plasma/urine samples. The open lactam metabolite and the coadministered dehydropeptidase inhibitor, cilastatin sodium, do not interfere with the 313-nm detection of imipenem in either the plasma or the urine assay. Thienamycin, the precursor of imipenem and an impurity in imipenem formulations, is separated from the drug using both of these methods. Concentrations generated from the HPLC analysis of plasma and urine samples from two healthy volunteers compare favorably with results using a microbiological assay method. Correlation of the two methods gives r greater than or equal to 0.990 for both fluids.     

Total synthesis of thienamycin analogs. II Synthesis of 2-alkyl and 2-aryl thienamycin nuclei

A new general synthesis leading to 2-alkyl and 2-aryl-1-carba-2-penem-3-carboxylic acids involves the preparation of a key thiolester intermediate 3. This is reacted with Me₂CuLi or (C₆H₅)₂MgCuX to give the corresponding methyl or phenyl ketone which undergoes a Wittig reaction to give the desired penems, which can be deblocked photolytically or by hydrogenolysis to give acids with good antibacterial activity.     

Kinetic determination of carminic acid by its inhibition of lanthanide-sensitized luminescence

 The stopped-flow mixing technique was used to develop a simple and fast kinetic method for the determination of carminic acid based on its inhibitory effect on the fluorescence intensity of the europium(III)- diphacinone-ammonia system in the presence of Triton X-100. Analytical data can be obtained within 10 s after the reactants are mixed, which minimizes manipulation and enables the ready application of the proposed method to routine analyses for carminic acid in orange soft drinks. The dynamic range of the calibration graph was 0.5–15 μg ml^-1 and the relative standard deviation less than 4%. The analytical recoveries obtained by applying the method directly to the analysis of samples ranged from 90.0 to 111.8%. Received : 11 November 1995/Revised: 2 February 1996/Accepted: 6 February 1996     

Kinetic study on the system of FeOCl and pyridine

The layer compound FeOCl absorbs pyridine molecules into its interlayer regions. The kinetics of this intercalation were investigated in the temperature region from room temperature to 130°C. The reaction products had different compositions, $\text{FeOCl(pyridine)}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ and $\text{FeOCl(pyridine)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$, in the temperature regions below and above 60°C, respectively. Reaction mechanisms were explained by nucleation and diffusion processes. The nucleation processes followed different rate equations in the respective temperature regions, the first-order rate law at lower temperatures, and the two-dimensional Avrami-Erofeev equation at higher temperatures. The diffusion processes were well described by two-dimensional Jander's diffusion equation. Activation energies of all processes were about 10 kcal/mole.     

A study on the inhibition of cellulolytic activities by lignin

It is well known that cellulolytic enzymes hardly attack lignocellulose. Hitherto knowledge, however, has not yet fully elucidated the mechanisms of the inhibition; whether it depends on a steric hindrance or protein-binding inhibition. For the purpose of acceleration of enzymatic digestion of lignocellulose biomass, the study was carried out using partially purified cellulase of Meicelase and milled wood lignin from soft or hard wood. Milled wood lignin was prepared from soft wood,Picea jezoensis, or from hard wood,Quercus serrata, by the method of Björkman. Lignin was dissolved in methyl cellosolve, since the solvent has little effect on cellulolytic activities, and enzymic activities were followed with partially purified Meicelase. The results show that cellobiose activities of enzymes fromTrichoderma viride are markedly depressed by both lignin of soft and hard wood, and the former lignin inhibits the reaction stronger than the latter. Lignins show no inhibition in the reaction with CMC and debris of filter paper. Liberation of glucose from filter paper by the enzyme in the presence of lignin is also depressed, and addition of cellobiase instead of lignin in the above enzyme reaction shows the delay of time for breakdown of filter paper. This phenomenon indicates that lignin inhibits enzymic decomposition of cellobiose in the degradation pathway of cellulose and accumulated cellobiose gives a feedback function to digestion of fibers of paper.     

Kinetic study of dipivaloylmethane by ozawa method

The lanthanidic complexes of general formula Ln(C₁₁H₁₉O₂)₃ were synthesized and characterized by elementary analysis, infrared absorption espectroscopy, thermogravimetry (TG) and differential scanning calorimetry (DSC). The reaction of thermal decomposition of complexes has been studied by non-isothermal and isothermal TG. The thermal decomposition reaction of complexes began in the solid phase for Tb(thd)₃, Tm(thd)₃ and Yb(thd)₃ and in the liquid phase for Er(thd)₃ and Lu(thd)₃, as it was observed by TG/DTG/DSC superimposed curves. The kinetic model that best adjusted the experimental isothermal thermogravimetric data was the R1 model. Through the Ozawa method it was possible to find coherent results in the kinetic parameters and according to the activation energy the following stability order was obtained: Tb(thd)₃>Lu(thd)₃>Yb(thd)₃>Tm(thd)₃>Er(thd)₃ This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetic study of Pt-cytostatics reactions by HPLC

HPLC with DAD (diode array detector) was applied as rapid method for the analytical control of the purity and stability of carboplatin and oxocarboplatin as effective cytostatics of 2nd generation. The stability of carboplatin has been measured in some infusion media (sodium chloride, glucose, sodium citrate) and compared to the cisplatin (cytostatic of 1st generation) stability. In addition ligand-exchange reactions between cisplatin and carboplatin have been studied together with the influence of temperature, pH and the concentrations of reactants. A method was developed for the analysis of clinical samples using solid-phase extraction as a preseparation and preconcentration step. The detection limits were 5 g/ml serum for cisplatin, 0.16 g/ml for carboplatin and 0.23 g/ml for oxo-carboplatin.Dedicated to Professor J. F. K. Huber on the occasion of his 65th birthday     

Kinetic determination of hexacyanoferrates by their inhibition of an oscillating chemical reaction

A method for the kinetic determination of traces of hexacyanoferrate based on an oscillating chemical reaction is presented. In a Belousov-Zhabotinskii reaction system, by using a bromide ion-selective electrode, the amplitude decrease of the potentiometric oscillation is linearly proportional to the concentration of Fe(CN)^3?₆ [or Fe(CN)^4?₆] in the range 7 × 10^?8?5 × 10^?6 M. The relative standard deviation for 1 × 10^?6 M Fe(CN)^3?₆ is 2.7% (n = 6). Cyclic voltammetry was applied to study the mechanism of the proposed system. The procedure was utilized to determine hexacyanoferrates in silver plating and photographic solutions.     

Kinetic study of the oxidation of thioacids by pyridinium fluorochromate

Summary Kinetics of oxidation of thioglycollic, thiolactic and thiolmalic acids by pyridinium fluorochromate (PFC) to the corresponding disulphides have been studied using a stopped-flow technique. The reaction is first order with respect to PFC; Michaelis-Menten type kinetics were observed with respect to the thioacid. The formation constants for the thioacid-PFC complexes and the rates of their decomposition at different temperatures have been evaluated. Thermodynamic parameters for complex formation and the activation parameters for their decomposition have also been calculated. The oxidation was studied in nineteen different organic solvents; analysis of the solvent effect indicated that both cation-and anion-solvating powers of the solvents play important roles. A suitable mechanism has been proposed.     

Kinetic study of the oxidation of alcohols by cetyltrimethylammonium permanganate

Kinetics of the oxidation of 2-propanol, 1-butanol, 2-butanol and 1-pentanol by cetyltrimethylammonium permangenate oxidant have been investigated. The reactions are autocatalytic, colloidal manganese dioxide as one of the reaction products has been identified as the auto-catalyst.

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2-, 1-, 2- 1- . . , , .

     

Kinetic study of the oxidation of isobutyraldehyde by aqueous chlorine

The kinetics of oxidation of isobutyraldehyde with aqueous chlorine has been investigated in 11.6 vol. % aqueous acetic acid. The reaction is first order with respect to both substrate and chlorine. Molecular chlorine is the principal oxidant. The influence of various factors, e.g. ionic strength, inorganic salts, D₂O and temperature on the initial rate has been studied. The activation parameters have been calculated and a possible mechanism is suggested.

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11,6% . , . . ( , , D₂O) . .

     

Kinetic spectrofluorimetric determination of trace ascorbic acid based on its inhibition on the oxidation of pyronine Y by nitrite

A highly sensitive spectrofluorimetric method is proposed for the determination of trace amount of ascorbic acid using a new indication. The method is based on the inhibition of ascorbic acid on the oxidation of pyronine Y (PRY) by nitrite. The detection limit for ascorbic acid is 0.012 microg ml(-1), the linear range of the determination is 0.02-0.36 microg ml(-1). Analytical parameters, such as reagent concentration, pH, reaction temperature and time, were optimized. The relative standard deviations of eleven replication determinations of 0.12 and 0.24 microg ml(-1) ascorbic acid were 1.4 and 0.72%, respectively. This method has been used to determine ascorbic acid in pharmaceuticals, vegetables, fruits and soft drink with satisfactory results.     

Kinetic study of transmembrane electron transport by the hinkle process

Trans-membrane redox reactions mediated by t-amylferrocene (one-electron carrier) were studied kinetically in a liposome system separating two redox pairs (ferricyanide/ferrocyanide and dehydroascorbate/ascorbate). In order to eliminate the membrane potential generated, which suppressed the rate of the reaction, the rate was measured in the presence of carbonylcyanide m-chlorophenylhydrazone. The reaction rate was independent of concentrations of ascorbate and dehydroascorbate. Ferricyanide also had virtually no effect on the rate, but addition of ferrocyanide decreased it. The results were analysed on the basis of rate equations derived from the possible reaction mechanism, and it was concluded that the rate-determining step of the trans-membrane redox reaction was the process of diffusion of the mediator in the membrane.     

聚醚桥连二异羟肟酸配合物催化羧酸酯水解的动力学研究

研究羧酸酯和磷酸酯的水解在环境和生物应用等方面具有越来越重要的意义。为实现对环境友好、高经济效益的生产过程,许多研究者致力于研发反应条件温和、催化效率高和高度专一性的催化剂。因而,仿酶研究倍受人们的关注,其中,水解金属酶是被研究得较为广泛的一类。我们曾报道过异羟肟酸过渡金属配合物仿生催化氧化性能和二氧亲合性能。本文我们将4种聚醚桥连二异羟肟酸过渡金属铜（Ⅱ）、锌（Ⅱ）、钴（Ⅱ）和锰（Ⅱ）配合物（见图1）作为仿水解酶模型,在底物浓度高于催化剂浓度10倍以上的条件下,研究了配合物在缓冲溶液中催化α-吡啶甲酸对硝基苯酯（PNPP）的水解反应的机理,并建立了相应的动力学数学模型;考查了配合物中心金属离子、溶液酸度和反应温度等对催化PNPP水解反应性能的影响。     

Two-photon excited fluorescence of nitrogen-vacancy centers in proton-irradiated type Ib diamond

Two-photon fluorescence spectroscopy of negatively charged nitrogen-vacancy [(N-V)-] centers in type Ib diamond single crystals have been studied with a picosecond (7.5 ps) mode-locked Nd:YVO(4) laser operating at 1064 nm. The (N-V)- centers were produced by radiation damage of diamond using a 3 MeV proton beam, followed by thermal annealing at 800 degrees C. Prior to the irradiation treatment, infrared spectroscopy of the C-N vibrational modes at 1344 cm(-1) suggested a nitrogen content of 109 +/- 10 ppm. Irradiation and annealing of the specimen led to the emergence of a new absorption band peaking at approximately 560 nm. From a measurement of the integrated absorption intensity of the sharp zero-phonon line (637 nm) at liquid nitrogen temperature, we determined a (N-V)- density of (4.5 +/- 1.1) x 10(18) centers/cm3 (or 25 +/- 6 ppm) for the substrate irradiated at a dose of 1 x 1016) H(+)/cm(2). Such a high defect density allowed us to observe two-photon excited fluorescence and measure the corresponding fluorescence decay time. No significant difference in the spectral feature and fluorescence lifetime was observed between one-photon and two-photon excitations. Assuming that the fluorescence quantum yields are the same for both processes, a two-photon absorption cross section of sigma(TPA) = (0.45 +/- 0.23) x 10(-50) cm(4).s/photon at 1064 nm was determined for the (N-V)- center based on its one-photon absorption cross section of sigma(OPA) = (3.1 +/- 0.8) x 10(-17) cm2 at 532 nm. The material is highly photostable and shows no sign of photobleaching even under continuous two-photon excitation at a peak power density of 3 GW/cm(2) for 5 min.     

Kinetic study on crystal growth in gels by radioisotopic labelling

The paper deals with a kinetic study of crystal growth in gelatin and agar gels, using a technique based on radioactive tracers.²⁰⁴TlCl,²⁰⁴TlBr,²⁰⁴TlI,⁶⁰CoC₂O₄ and⁶⁰CoH₄C₄O₆ crystals in gels have been obtained. The global kinetic process of appearance of crystals has been found to be made up of two distinct stages: diffusion of the ions in the gel and crystallization, having different rate constants.     

Kinetic study of wood chips decomposition by TGA

Pyrolysis of a wood chips mixture and main wood compounds such as hemicellulose, cellulose and lignin was investigated by thermogravimetry. The investigation was carried out in inert nitrogen atmosphere with temperatures ranging from 20°C to 900°C for four heating rates: 2 K min⁻¹, 5 K min⁻¹, 10 K min⁻¹, and 15 K min⁻¹. Hemicellulose, cellulose, and lignin were used as the main compounds of biomass. TGA and DTG temperature dependencies were evaluated. Decomposition processes proceed in three main stages: water evaporation, and active and passive pyrolysis. The decomposition of hemicellulose and cellulose takes place in the temperature range of 200–380°C and 250–380°C, while lignin decomposition seems to be ranging from 180°C up to 900°C. The isoconversional method was used to determine kinetic parameters such as activation energy and pre-exponential factor mainly in the stage of active pyrolysis and partially in the passive stage. It was found that, at the end of the decomposition process, the value of activation energy decreases. Reaction order does not have a significant influence on the process because of the high value of the pre-exponential factor. Obtained kinetic parameters were used to calculate simulated decompositions at different heating rates. Experimental data compared with the simulation ones were in good accordance at all heating rates. From the pyrolysis of hemicellulose, cellulose, and lignin it is clear that the decomposition process of wood is dependent on the composition and concentration of the main compounds.     

Kinetic and mechanistic study of the reduction of 2,6-dichlorophenol indophenol by dithionites

The reaction of 2,6-dichlorophenolindophenol (DCPI) and dithionites is studied kinetically by applying the stopped-flow technique. Reaction rate constants are given for the pH range 1.30–6.80. The reaction was found to follow first-order kinetics with respect to each of the reactants. For pH 3.97, 5.10 and 6.80, the second-order reaction rate constant was determined by applying four different technique. Mean values of k = 172±5, 200±2 and 276±4 l mol^?1s^?1 are given for pH 3.97, 5.10 and 6.80, respectively. A mechanism is proposed for the reaction, which suggests partial reactions of all possible species of DCPI and dithionites at any pH. An equation for the calculation of k at any pH is derived, which gives k as a function of [H⁺], the partial reaction rate constants and the dissociation constants of DCPI and H₂S₂O₄. Values of reaction rate constants of all possible partial reactions are also presented.