Electrogravimetric Real-Time and in Situ Michaelis-Menten Enzimatic Kinetics: Progress Curve of Acetylcholinesterase Hydrolysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Aerobic fitness level typical of elite athletes is not associated with even faster VO2 kinetics during cycling exercise

The aim of this study was to address the question if the VO2 kinetics is further improved as the aerobic training status increases from trained to elite level athletes. Maximal oxygen uptake (VO(2)max), work-rate associated to VO(2)max (IVO(2)max) and VO2 kinetics of moderate (Mod) and maximal exercise (Max) were determined in fifty-five subjects. Then, they were assigned into three groups: low (LF), intermediate (IF) and high (HF) aerobic fitness level. In average, the VO(2)max of LF, IF and HF groups were, respectively, 36.0 +/- 3.1, 51.1 +/- 4.5 and 68.1 +/- 3.9 ml . kg . min(-1) (p <= 0.05 among each other). VO2 kinetics mean response time of both exercise intensities were significantly faster (p <= 0.05) in HF (Mod, 27.5 +/- 5.5 s; Max, 32.6 +/- 8.3 s) and IF (Mod, 25.0 +/- 3.1 s; Max, 42.6 +/- 10.4 s) when compared to LF (Mod, 35.7 +/- 7.9 s; Max: 57.8 +/- 17.8 s). We can conclude that VO2 kinetics is improved as the fitness level is increased from low to intermediate but not further improved as the aerobic fitness level increases from intermediate to high.

Different inflammatory stimuli in the footpad of mice influence the kinetics of resident peritoneal cells

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Kinetics and mechanism of the forward and reverse reactions between N,N′-dimethyl-4,4′-bipyridinium and hexacyanoferrate(II)

The kinetics of the hexacyanoferrate(III)-N,N′-dimethyl-4,4′-bipyridinium radical (MV+) reaction was studied by a laser flash photolysis technique. The radical was generated, in the presence of Fe(CN)6 3-, by quenching the excited state *Ru(bpy)3 2+ with MV2+. The second-order rate constant for the Fe(CN)6 3--MV+ reaction is (7.6 ± 0.5) × 109 M-1 s-1 at 23°C and ionic strength 0.10 M. Comparison with the rate constants calculated for the diffusion-controlled reaction (4.7 × 109 M-1 s-1) and the activation-controlled reaction (5.2 × 1012 M-1 s-1, on the basis of self-exchange rate constants of 8.0 × 105 M-1 s-1 and 1.9 × 104 M-1 s-1 for the MV2+/+ and Fe(CN)6 3-/4- couples, respectively) leads to the conclusion that the Fe(CN)6 3--MV+ reaction is diffusion controlled. The rate constant for the Fe(CN)6-MV2+ reaction, calculated from the rate constant for the Fe(CN)6 3--MV+ reaction and the appropriate equilibrium constant, is 2.4 × 10-5 M-1 s-1 at 23°C and ionic strength 0.10 M. Microscopic reversibility considerations require that the Fe(CN)6 4--MV2+ reaction be controlled by the dissociation of the successor complex Fe(CN)6 3-|MV+. The thermal and optical electron transfers in the ion pair Fe(CN)6 4-|MV2+ and in related systems are analyzed and discussed. © 1982 American Chemical Society.

Kinetics of the reaction of alkylamines with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in organic solvents

The following sequence of substitution reactions was studied spectrophotometrically in organic solvents: RNH2 + TCNQ →-HCN 7-substituted TCNQ →-HCN +RNH2 7.7-disubstituted TCNQ where R = butyl, octyl, dodecyl, and hexadecyl. The production of 7-(alkylamino)-7,7,8-tricyanoquinodimethanes proceeds via the formation of the anion radical of TCNQ (TCNQ-·) whose rate of appearance was found to be a function of the chain length of R, reaching a maximum for octylamine. The formation of TCNQ-· was sensitive to the solvent polarity and electron-donor power and was associated with a small enthalpy and a highly negative entropy of activation. Above a certain [C8H17NH2] the rate of disappearance of TCNQ-· was independent of the amine concentration, and the reaction had a much higher enthalpy and entropy of activation. The occurrence of tautomerism precluded an investigation of the conversion of 7-(octylamino)-7,8,8-tricyanoquinodimethane into 7,7-bis(octylamino)-8,8-dicyanoquinodimethane. A study of the reaction of octylamine with 7-morpholino-7,8,8-tricyanoquinodimethane (which does not exist in tautomeric forms) showed that the second substitution step proceeds with the same mechanism as the first one. The only difference between the two compounds (TCNQ and its monosubstituted morpholino derivative) is one of reactivity. © 1985 American Chemical Society.

Kinetics, electrochemistry and resonance raman spectra of the (2-mercaptopyridine) (edta)ruthenium(III) complex

The chemistry of the pentadentate edta complexes of ruthenium(III) and (II) with 2-mercaptopyridine (HSpy) has been investigated based on spectroscopic, kinetic and electrochemical techniques. The reaction of [Ru(III)(edta)H2O]- with HSpy proceeds with a specific rate of 1.05 × 104 M-1 S -1 (25°C, I = 0.10 M, acetate buffer), forming a red complex (λmax = 550 nm) which undergoes a relaxation process as a function of pH, with an apparent pKa = 4.35 and kobs = 0.31 S -1. The second reaction depends on the concentration of HSpy and leads to a stable green product (λmax = 630 mn). A pronounced enhancement has been observed in the Raman spectra of the complexes, particularly in the region of the metal-ligand vibrations. The electronic and resonance Raman spectra are consistent with the coordination of HSpy via the sulfur atom in the red complex, and with a chelate binding in the green species. © 1987.

Kinetics of the polarization reversal process in a non-constant applied electric field and the generalized superposition principle

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Non-isothermal study of the devitrification kinetics of fluoroindate glasses

The understanding of the kinetics of devitrification of a glass is important for anticipating its stability in a particular purpose, such as fiber-drawing processes. The crystallization kinetics of (BaF2)16(ZnF2)20(SrF 2)20(NaF)2 (GaF3)5(InF3)36(GdF 3)1 glass prepared by quenching were studied by differential scanning calorimetry (DSC). Avrami's exponent (n) obtained by a non-isothermal method was 4.3 for a solid and 2.4 for a powdered sample. According to the classical interpretation of n, these magnitudes correspond to an interface-controlled crystal growth and a diffusion-controlled crystal growth, respectively. The activation energies for crystallization (E) was 62 ± 1 kJ/mol for solid glass and 245 ± 2 kJ/mol for powdered glass. These results are discussed in terms of glass particle size. © 2000 Elsevier Science B.V. All rights reserved.

Non isothermal study of the devitrification kinetics of fluoroindate glasses

The kinetics of crystallization in an indium fluoride-based glass was studied by a non-isothermal method using differential scanning calorimetry. The experiments led to an Avrami's exponent of 4.6 for solid glass and 2.2 for a powdered sample. The apparent activation energy for crystallization was found to be 130 kJ/mol for solid glass and 354 kJ/mol for the powder. These results express the profound effect of glass particle size on those kinetic parameters, as different crystallization mechanisms take place during sample heating.

Effects of temperature and of the addition of accelerating and retarding agents on the kinetics of hydration of tricalcium silicate

The formation of calcium silicate hydrates (C-S-H) during the hydration of tricalcium silicate (C3S) in pure water and in water solutions containing 1% CaCl2 (accelerator) and 0.01% saccharose (retarder) was studied by small-angle X-ray scattering (SAXS). SAXS measurements were performed under isothermal conditions within the temperature range 25 °C T < 52 °C. The experimental results indicate that the time variation of the mass fraction of the C-S-H product phase, α(f), can be fitted, under all conditions of paste setting, by Avrami equation, α(t) = 1 -exp(-(kt)′), k being a rate parameter and n an exponent depending on the characteristics of the transformation. The parameter n is approximately equal to 2 for hydration of C^S in pure water. Depending on temperature, n varies from 2 to 2.65 for hydration in the presence of CaC^ and saccharose. The value n = 2 is theoretically expected for lateral growth of thin C-S-H plates of constant thickness. The time dependence of SAXS intensity indicates that the transformed phase (C-S-H) consists of colloidal particles in early stages of hydration, evolving by two-dimensional growth toward a disordered lamellar structure composed of very thin plates. The activation energy ΔE for the growth of C-S-H phase was determined from the time dependence of X-ray scattering intensity. These data were obtained by in situ measurements at different temperatures of hydration. The values of ΔE are 37.7, 49.4, and 44.3 kJ/mol for hydration in pure water and in water solutions containing CaCl2 and saccharose, respectively. © 2000 American Chemical Society.

Kinetics of spermatogenesis in the Mongolian gerbil (Meriones unguiculatus)

The Mongolian gerbil (Meriones unguiculatus) is a small rodent native to the arid regions of Mongolia and Northeastern China. The present study provides descriptions of both the cellular associations of the seminiferous-epithelium cycle and relative frequencies of stages in the gerbil. Based on the development of the acrosomic system and the nuclear morphology changes using the PAS-H staining technique, the transformation of spermatids into spermatozoa was divided into 15 steps. The first 12 steps were used to identify 12 stages or cellular associations and the other three steps were spread among the first six stages of the cycle of the seminiferous epithelium. The relative frequencies found for stages I through XII were: 13.15; 8.06; 8.98; 6.48; 5.37; 6.71; 7.36; 7.45; 7.27; 5.83; 11.53 and 11.81, respectively. Stage I had the highest frequency while stage V proved the lowest frequency among the XII stages. The pattern of spermatogenesis is similar to those of rodents used as laboratory animals. The present description is the first for this rodent and provides the foundation for a variety of future studies of the testis in this animal. © 2002 Elsevier Science Ltd. All rights reserved.