Quenched emission

Measiuements of the emission anisotropy A as a function of added collisional quencher are made with the steady fluorescence intensity, which integrates the different weighted fluorescence lifetimes. Quenching emission anisotropy plot of 1 /A vs I (Fig. 5.14) yields for A(o) a value of 0.246 and 0.243 for [L-Met2] DREK and DREK, respectively. These values, lower than that (0.278) measured at - 45 °C for tyrosine at 280 nm (Lakowicz and Maliwal, 1983), indicate that tyrosine residue in both peptides display residual motion independent of the global rotation of the peptide. It is possible to measure the relative importance of the mean residual motions of the tyrosine residues ... 

Table 9.6. Rotational correlation time ( )p of Mb obtained according to the classical Perrin plot, to the quenching emission anisotropy and to the theoretical equation.

The emission spectrum of the quenched residues can be calculated by taking the difference between the unquenched and quenched emission qiectra. This difference spectrum gure 8.13, right) shows that the quenched residues display an emission maximum at 348 nnu The... 

Figure 16.27. Fluorescence emission spectra of apoazurin Ade from Akaligents denitrificans in the absence (top curve) and presence (bottom curve) of 0.4SA/ Kl. The dashed curve is the difference spectrum and is due to the easily quenched emission (presumably from Tip>H8). The buffer was O.OSAf sodium acetate, pH 5.0. Revised from Ref. 79.

Figure 15 illustrates the active and prohibited PeT mechanisms in terms of frontier molecular orbitals. PeT blocks the usual relaxation pathway of excited fluorophore and quenches emission. If PeT-donor orbital... 

The fluorescence decay curves of all glass samples [excluding Gl, G6, G7, and G12, which show weak or quenching emissions) are measured hy monitoring the emissions of Tm at 1,470 nm and of Dy at 1,330 nm, while the lifetimes obtained from the first-order exponential fits are summarized in Table 6.2. Figure 6.11 compares the decay curves of the Tm single-doped sample [G8] and the Dy -Tm codoped sample [G9] where the lifetimes of Tm emission as a function of Dy2S3 content are shown in the inset. 

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