Lifetime analysis

Wilms, C. D., Schmidt, H. and Eilers, J. (2006). Quantitative two-photon Ca2+ imaging via fluorescence lifetime analysis. Cell Calcium 40, 73-9. 

M.S. Zhao, M. Mladenovic, D.G. Truhlar, D.W. Schwenke, O. Sharafeddin, Y. Yan, D.J. Kouri, Spectroscopic analysis of transition state energy levels Bending-rotational spectrum and lifetime analysis of H3 quasibound states, J. Chem. Phys. 91 (1989) 5302. 

The formation of these ternary luminescent lanthanide complexes was the result of displacement of the two labile metal-bound water molecules, which was necessary because the energy transfer process between the antenna and the Ln(III) metal centre is distance-dependent. This ternary complex formation was confirmed by analysis of the emission lifetimes in the presence of DMABA and showed the water molecules were displaced by a change in the hydration state q from 2 to 0, with binding constants of log fCa = 5.0. The Eu(III) complexes were not modulated in either water or buffered solutions at pH 7.4. Lifetime analysis of these complexes showed that the metal-bound water molecules had not been displaced and that the ternary complex was not formed. Of greater significance, both Tb -27 and Tb -28 could selectively detect salicylic acid while aspirin was not detected in buffered solutions at pH 7.4, using the principle as discussed for DMABA where excitation of the binding antenna resulted in a luminescent emission upon coordination of salicylic acid to the complex. 

Figure 8.9 Time-resolved fluorescent lifetime analysis of Cy3 attached to double-stranded DNA (Iqbal et al., 2008b). Fluorescent decay curve for Cy3 attached to a 16 bp DNA duplex, showing the experimental data and the instrument response function (IRF), and the fit to three exponential functions (line). The decay curve was generated using time-correlated single-photon counting, after excitation by 200 fs pulses from a titanium sapphire laser at 4.7 MHz.

McGown and co-workers have recently described a new instrumental approach for FDCD measurements that is capable of individually resolving multiple chiral fluorophores in complex mixtures [31-33]. As has been pointed out [31], CD measurements, and consequently FDCD measurements provide information about the average chiral characteristics of the sample under study. By introducing lifetime resolution into the FDCD experiment, identical fluorophores residing in different chemical environments can be resolved by measuring the differences in their excited state lifetimes. As has been demonstrated, lifetime analysis is a very powerful tool for probing complex systems and the chemical characteristics which one can differentiate by such an approach can be extremely subtle. 

The positron group at WSU, Pullman, other than the authors, carried out the brunt of the data acquisition and analysis. Mihail P. Petkov was a fantastic asset during his time at WSU. His effort jump-started the progress. Cai-Lin Wang introduced us to the complexities of lifetime analysis in general and the maximum entropy method (MELT) in particular. 

A sharp peak at about 6 ns, occurs when backscattered positrons pass the grid and reach the CEMA and trigger timing pulses without the secondary electron time of flight. This 6 ns peak vanishes in statistical noise in the case of samples that cause longer lifetimes. In the lifetime analysis, the data in the 6 ns peak region are ignored in the present discussion. 

In the following the double peak shape will considered as two distinct lifetimes. However, they may simply represent lower and upper bounds of a broad single distribution. The lifetime analysis was performed on the full range of porogen loads. The results are shown in Figures. 20 and 21. 

Bimodal or not bimodal—critical comments Is the bimodal distribution as observed by beam based positron lifetime analysis (BPALS) real or a systematic effect of the data analysis To date the answer cannot be given with certainty. Arguments could be made why such a distribution is not observed by SAXS and is observed by BPALS in data shown here [62], and in work by Gidley et al.[46] Positrons are implanted at specific depths and only after measuring at different mean depth can one... 

Simulations have revealed a systematic tendency of the lifetime analysis technique to split broad distributions into two or possibly more narrow ones. The separation of the pore size distributions shown in Figure 7.19 is not as clear as for the smaller lifetime components. As an example the bimodal result shown in Figure 7.19 was used to create a noisy dataset. A second set was simulated from a lifetime distribution where the two pore size distributions were smeared into one broad component. Care was taken not to shift the mean lifetime and the intensity share of the distribution compared to the total was kept constant. The simulation input is shown in Figure 7.26. 

The analysis of the positron annihilation lifetime spectra is a very important aspect of using the PAL techniques to analyze polymers. Without proper data analysis interpretation of data might be misleading and important scientific information will be lost. In PAL studies of polymers the PAL spectrum can be analyzed in two ways (1) a finite lifetime analysis or (2) continuous lifetime analysis. In the finite lifetime analysis the PAL spectra is resolved into a finite number of negative exponentials decays. The experimental data y(t) is expressed as a convoluted expression (by a symbol ) of the instalment resolution function R(t) and a finite number (n) of negative exponentials ... 

In continuous lifetime analysis, a PAL spectrum is expressed in a continuous decay form [20] ... 

In practice the lifetime distributions are usually obtained using a computer program such as the MELT [21] or CONTIN [22, 23] programs. The reliablity of these programs for measurring the o-PS lifetime distribution in polymers was shown by Cao et al [24]. A detailed description of these methods of data analysis is presented in Chapter 4. The advantage of the continuous lifetime analysis is that one can obtain free volume hole distributions rather that the average values obtained in the finite analysis. 

P.G. Hipes and A. Kuppermann, Lifetime analysis of high-energy resonances in three-dimensional reactive scattering. Chem. Phys. Lett., 133 1-7, 1987. 

Russell MD, Gouterman M, van Zee JA, Excitation-emission-lifetime analysis of multicomponent systems. III. Platinum, palladium and rhodium porphyrins, Spectrochimia Acta, 1988, 44A, 873-882. 

FILDA Fluorescence Intensity Distribution and Lifetime Analysis. Uses... 

For lifetime analysis, collect the time duration between the appearance and disappearance of individual fluorescent spots on the membrane (Fig. 3b). 

Lifetime analysis has been successfully applied to the study of ligand-receptor complexes and downstream molecules including PTEN and PH domain-containing proteins (2-A). 

As shown in Fig. 4d, lifetime analysis can be applied to other signaling molecules including cAMP and PTEN. Because the lifetime of cARl-Halo-TMR reflects on the photobleaching times of TMR in living cells, the measurements of cARl-Halo-TMR provide a good control experiment for other molecules. 

In conclusion, the lifetime analysis of the experimental data of Drazer and Zanette provided important clues regarding the kinetics and mechanism of the desorption process. In particular, the knowledge of the fractal exponents of the adsorption isotherm and of the tail of the lifetime distribution was enough to elucidate the shape and structure of the activation energy barrier. We have also shown that the experimental data indicate that the adsorption rate and the adsorption activation energies are constant and only the desorption rate and desorption activation energy are random. The application of the method may involve detailed theoretical developments for different systems nevertheless we expect that the results are worth the effort. 

When using routine LT9.0, a partial improvement occurs by assuming that the o-Ps lifetime xs shows a distribution. The artifacts are removed more or less completely when the distribution in the e+ lifetime X2 is also taken into account. As mentioned, we have confirmed these conclusions by LT9.0 analysis of simulated spectra. The allowance of a distribution in x uncouples the t2 analyzed from T3, and the allowance of a distribution in X2 uncouples ri from t2. The reason that LT9.0 avoids artifacts also observed in continuous Melt and Contin analysis lies in reduction in the degree of freedom by assuming a number of different lifetime channels in LT9.0. Moreover, because the lifetime analysis is less sensitive to the particular shape of the distributions, the assumed lognormal k function usually seems to describe the real situation sufficiently well. These are the reasons that we prefer to use the routine LT9.0 for the analysis of positron lifetime spectra. 

Hydrogen-bond lifetime analysis revealed that HBs between the polar head groups of the micelle and the water molecules are much stronger than those between two water molecules in bulk water and thus exhibit much slower dynamics - almost 13 times slower than that of bulk water. This result indicates the presence of quasibound water molecules on the surface. 

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