Rapid lifetime determination

Ballew, R. M. and Demas, J. N. (1989). An error analysis of the rapid lifetime determination method for the evaluation of single exponential decays. Anal. Chem. 61, 30-3. 

Fig. 15 Fluorescence imaging of citrate in a microtiter plate via the EuTc probe by rapid lifetime determination (in false colors). The concentration of EuTc is 50 pmol I. 1 throughout citrate concentrations (from left to right) are 0, 0.16, 0.4, 1.0, 1.6, 4.0, 10.0, 16.0, 20., 40.0, 60.0 and 80.0 pmol L-1...

Fig. 19 Rapid lifetime determination imaging of the activity of glucose oxidase. Gray-scale image of the activity of glucose oxidase (left) and resulting calibration curve (right). Experiments were performed in triplicate (rows). The wells in the images contained, from 1 to 12, glucose oxidase activities of 0 (blank), 135, 54.1, 27.1, 13.5, 5.4, 2.7, 1.35, 0.54, 0.27, 0.14, and 0.05 mU ml. 1 respectively, 100 jiL of a 0.2 mmol L-1 EuTc solution, and 15 jiL of a 277.2 mmol I. 1 glucose solution. The total volume was made up to 200 xL with MOPS buffer...

In a first step, intermediate species form rapidly upon mixing the lanthanide ion with EUdota. Both excited state luminescence lifetime determinations for the Eum complex (Chang et al., 2001) and molecular mechanics calculations are consistent with a structure in which the lanthanide ion is coordinated to four carboxylate groups, well away from the nitrogen atoms of the macrocycle, two of which are protonated. This intermediate may react with a hydroxide group to form monoprotonated neutral species in a rapid equilibrium. 

Insufficient testing is one of the major causes of method failure. The amount of data needed to publish a new procedure in a peer-reviewed journal and the procedural detail supplied therein are often insufficient to allow a different user to validate a method rapidly. The developer should evaluate if the method will work using chemicals, reagents, solid-phase extraction columns, analytical columns, and equipment from various vendors. Separate lots of specific supplies within a vendor should be evaluated to determine if lot-to-lot variation significantly impacts method performance. Sufficient numbers of samples should be assayed to estimate the lifetime of the analytical column and to determine the effects of long-term use on the equipment. 

The interaction between the receptor and the G-protein is transient and rapidly reversible. This is indicated, for example, by the fact that a single light-activated rhodopsin molecule may activate 500 to 1000 transducin molecules during its 1 to 3 sec lifetime. Hence, the interaction should, in the endpoint, be governed by the normal laws of chemical interaction and expressible in terms of association and dissociation rate constants and binding affinity. The question then arises as to whether the affinity of different receptors for different G-proteins varies. That is, is there specificity in receptor-G-protein coupling, and, if so, what determines this ... 

Therefore, the sequence of reactions illustrated in Fig. 1 catalytically (the anthraquinone is regenerated) injects a radical cation into a DNA oligonucleotide that does not simultaneously contain a radical anion. As a result, the lifetime of this radical cation is determined by its relatively slow bimolecular reaction with H20 (or some other diffusible reagent such as 02- ) and not by a rapid intramolecular charge annihilation reaction. This provides sufficient time for the long distance migration of the radical cation in DNA to occur. 

The reactions of the bare sodium ion with all neutrals were determined to proceed via a three-body association mechanism and the rate constants measured cover a large range from a slow association reaction with NH3 to a near-collision rate with CH3OC2H4OCH3 (DMOE). The lifetimes of the intermediate complexes obtained using parameterized trajectory results and the experimental rates compare fairly well with predictions based on RRKM theory. The calculations also accounted for the large isotope effect observed for the more rapid clustering of ND3 than NH3 to Na+. 

Some of these measures are part of larger, semistructured interviews administered by the therapist. The most commonly used assessments in this category are a family of instruments developed mainly in the Veterans Administration (VA) hospital system. The first instrument in this family is known as the Addiction Severity Index (ASI McLellan et al., 1985). The ASI assesses for a wide variety of biographical data, so it has the advantage of potentially being used as part of an intake interview. The ASI asks about consequences in a wide variety of life domains, and determines recent and lifetime patterns of drug and alcohol use. The ASI also detects recent and lifetime occurrence of problems in these different life domains (e.g., work). Each domain can be scored for the severity of the problems based upon the responses of the client and the clinical judgment of the interviewer. The ASI can be administered by computer to provide for rapid interpretation of answers. 

The formation and subsequent redissociation of an NO intermediate of finite lifetime is consistent with the observed rapid incorporation251 of lsO into NOa by exchange with ieO atoms. The value of the elementary rate coefficient k35 (Table 18) was determined by Herron and Klein251 from the rate of incorporation of 180 assuming that only (35) and (—35) were responsible for the exchange. 

Because excited triplet states decay more slowly than excited singlet states, it is much easier to determine the excited triplet-state lifetime 3t than H. Phosphorescence emission from a degassed sample at low temperature (77K) lasts for longer than 1ms and may even be several seconds. The molecules in the sample are irradiated with a short ( 1 ps) flash and the decay of the phosphorescence signal is monitored using an oscilloscope. Any accompanying fluorescence signal will decay too rapidly to be observed. The excited triplet-state lifetime is obtained as the time taken for the emission intensity to fall to 1/e of its initial value. 

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