Rate measurements discrimination effects

The transport processes and biological response involved in quinone-stimulated human epithelial cells were further studied by Rotenberg and Mirkin. They demonstrated that quinone-based mediators rapidly cross the cell wall to electrochemically react in the intracellular lumen. These events are reported to occur on a microsecond timescale. The apparent electron transfer rates measured for nonmetastatic and metastatic cells demonstrate the modulation effects of protein kinase Ca. Such studies establish the potential for SECM to evolve in an analytical tool capable of discriminating between cancerous and healthy cells. As such, the judicious choice of redox mediator couple will be key in achieving the desired electrochemical contrast. ... 

CCSD(T) refers to a sophisticated coupled-clusters calculation ) derives activation free energies of 26.3712 kcal/mol, 26.3700 kcal/mol, 26.3674 kcal/mol and 26.3643 kcal/mol for reactions involving Sr, Sr, Sr and Sr, respectively. Normalizing to the rate constant for the Sr reaction the Sr, Sr and Sr reactions are 0.203%, 0.643% and 1.172% slower, respectively. To determine the effect that the KIE will have on the observed isotope distribution pattern requires propagation of the KIE through to extent-of-reaction. This last step will depend on pressure conditions in the individual reaction cell. One can see that the KIE can impart a mass discrimination effect on measured isotope distribution patterns. This effect will be alleviated when the extent of reaction approaches 1 (i.e. 100% complete). 

The main mechanistic difficulty involves Ce(IV) sulphate and V(V), which attack ketones at rates less than those of enolisation. The kinetics and relative oxidation rates are of little assistance in discriminating between attack on keto and enol forms. However, the solvent isotope effects in these oxidations are in strict accord with the measured acidity-dependences if attack had occurred on the enol then the change of solvent should have enhanced the expected koiolf HiO l y a factor of 2.5, because is favoured to such an extent in D2O as compared with H2O. No such enhancement is found and attack is, therefore, on the keto... 

The terminology describing the action of antioxidants is unfortunately not clear. Terms such as antioxidant power , antioxidant effectiveness , antioxidant ability , antioxidant activity , and antioxidant capacity are often used interchangeably and without discrimination. Here we use the term antioxidant activity as meaning a measure of the rate of antioxidant action, and the term antioxidant capacity as meaning a measure of the extent of antioxidant action, i.e. the amount of radicals or intermediates and products produced during oxidation that are quenched by a given antioxidant. Thus antioxidant activity is related to the kinetics of the antioxidant action and antioxidant capacity to the stoichiometry. 

Neurobehavioral effects, measured in various discrimination reversal and operant learning tests, were observed in lead exposed rats. PbB levels in rats as low as 15-20 pg/dL were associated with slower learning and higher rates of inappropriate responses (Cory-Slechta et al. 1985 Jadhav and Areola 1997). Neurobehavioral alterations were also reported in young rats that had been exposed to lead via maternal milk, but that at the time of testing had PbB levels below the detection limit (Cory-Slechta et al. 1992). 

Neuroimaging techniques assessing cerebral blood flow (CBF] and cerebral metabolic rate provide powerful windows onto the effects of ECT. Nobler et al. [1994] assessed cortical CBE using the planar xenon-133 inhalation technique in 54 patients. The patients were studied just before and 50 minutes after the sixth ECT treatment. At this acute time point, unilateral ECT led to postictal reductions of CBF in the stimulated hemisphere, whereas bilateral ECT led to symmetric anterior frontal CBE reductions. Regardless of electrode placement and stimulus intensity, patients who went on to respond to a course of ECT manifested anterior frontal CBE reductions in this acute postictal period, whereas nonresponders failed to show CBF reductions. Such frontal CBF reductions may reflect functional neural inhibition and may index anticonvulsant properties of ECT. A predictive discriminant function analysis revealed that the CBF changes were sufficiently robust to correctly classify both responders (68% accuracy] and nonresponders (85% accuracy]. More powerful measures of CBF and/or cerebral metabolic rate, as can be obtained with positron-emission tomography, may provide even more sensitive markers of optimal ECT administration. 

Effects of solvent mixtures can be seen in biochemical systems. Ligand binding to myoglobin in aqueous solution involves two kinetic components, one extramolecular and one intramolecular, which have been interpreted in terms of two sequential kinetic barriers. In mixed solvents and subzero temperatures, the outer barrier increases and the inner barrier splits into several components, giving rise to fast intramolecular recombination. Measurements of the corresponding solvent structural relaxation rates by frequency resolved calorimetry allows the discrimination between solvent composition and viscosity-related effects. The inner barrier and its coupling to structural relaxation appear to be independent of viscosity but change with solvent composition (Kleinert et al., 1998). 

Early warning indicator Rapid identification of potential effects. Use when endpoint is slow to respond or has delayed effect minimal time lag in response to stressor and rapid response rate low signal to noise ratio of the measure and low discrimination screening tool and false positives acceptable. 

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