Lifetime, determination

Fluorescence Studies. Fluorescence spectra of films on glass plates were obtained with a Perkin-Elmer MPF-3 spectro-fluorimeter. A previously-described phase fluorimeter was utilized for fluorescence lifetime determinations. 

The time-domain IRF can be comparatively broad and skewed functions. The IRF needs to be taken into account in the data acquisition procedure and analyses to minimize systematic errors in the lifetime determination, in particular if the lifetimes are short. 

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. 

Seybold, P. G., Gouterman, M. and Callis, J. (1969). Calorimetric, photometric and lifetime determinations of fluorescence yields of fluorescein dyes. Photochem. Photobiol. 9, 229-242. 

The rate at which this happens determines a radiative lifetime determined by... 

The recoilless nuclear resonance absorption of y-radiation (Mossbauer effect) has been verified for more than 40 elements, but only some 15 of them are suitable for practical applications [33, 34]. The limiting factors are the lifetime and the energy of the nuclear excited state involved in the Mossbauer transition. The lifetime determines the spectral line width, which should not exceed the hyperfine interaction energies to be observed. The transition energy of the y-quanta determines the recoil energy and thus the resonance effect [34]. 57Fe is by far the most suited and thus the most widely studied Mossbauer-active nuclide, and 57Fe Mossbauer spectroscopy has become a standard technique for the characterisation of SCO compounds of iron. 

Fig. 6.13. Data obtained by the phase-modulation technique with a Fluorolog tau-3 instrument (Jobin Yvon-Spex) operating with a xenon lamp and a Pockel s cell. Note that because the fluorescence decay is a single exponential, a single appropriate modulation frequency suffices for the lifetime determination. The broad set of frequencies permits control of the proper tuning of the...

Another method for lifetime determination uses the level-crossing technique 12 t) which measures the natural linewidth (and with it the lifetime) from the change of the spatial fluorescence intensity distri-... 

Logarithmic plots of the fluorescence decays for the lowest excited singlet state of H2TPP, H2OEP, and their deuterium analogues were described by single exponential forms. Fluorescence lifetimes of all compounds were obtained by deconvolution and fluorescence quantum yields were determined relative to rhodamine 640 in ethanol (32). Triplet quantum yields (0r) were determined relative to benzophenone in benzene by using the transient absorption (33). Quantum yields and lifetimes determined are summarized in "Table II". 

The possibility to carry out conformational studies of peptides at low concentrations and in the presence of complex biological systems represents a major advantage of fluorescence spectroscopy over other techniques. Fluorescence quantum yield or lifetime determinations, anisotropy measurements and singlet-singlet resonance energy transfer experiments can be used to study the interaction of peptides with lipid micelles, membranes, proteins, or receptors. These fluorescence techniques can be used to determine binding parameters and to elucidate conformational aspects of the interaction of the peptide with a particular macro-molecular system. The limited scope of this chapter does not permit a comprehensive review of the numerous studies of this kind that have been carried and only a few general aspects are briefly discussed here. Fluorescence studies of peptide interactions with macromolecular systems published prior to 1984 have been reviewed. 

The various methods for the measurement of t/, the actual lifetime, can be classified as steady state and nonsteady state methods. In the steady state methods are included lifetime determinations from fluorescence quenching data and depolarization studies, the theoretical aspect of which have already been discussed in Sections 6.4 and 4.10, respectively. 

Lifetime determinations have demonstrated that the position of the nitrogen atom has a strong influence on the stability of these intermediates. Thus, 2-aza-2,4-cyclopentadienone has a lifetime around 2 s, whereas the 3-isomer lifetime is 11 s, similar to that of the carbocyclic counterpart. These values seem to depend on the high reactivity of the Af-acylimine group contained in 2-aza-2,4-cyclopentadienone. 

Fig. 2 Data acquisition for time-domain FLIM. FI fluorescence intensity, h gated image no 1,12 gated image no 2. Left Excitation pulse of the light source and synchronized timegated detection with a CCD camera. Right Lifetime determination by two subsequent time-gates according to Eq. 2...

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...

Southern pine, Douglas-fir, and yellow poplar stakes were impregnated with phenolic resin and cured (impreg) or impregnated with phenolic resin, compressed, and cured (compreg). Separate samples were treated with urea-formaldehyde and cured. These samples were placed in the ground and their average lifetime determined. The results are shown in Table I (18). 

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