Self-quenching time

Composition and Self-Quenching Times for Phosphorus Containing CO Polymers... 

Figure 2. Self-quenching time vs. atmospheric oxygen content for terpolymer...

Figure 5. Percent oxygen in atmosphere for 1- and 5-sec self-quenching time as a function of TGA residue at 500°C...

The fluorescence decay time, calculated for the 400 nm emission of TIN in PMMA films, decreases from 1.3 0.2 ns to 0.20 0.02 ns as the concentration of TIN is increased from 0.07 mole% to 1.1 mole% respectively. This is further evidence that the TIN molecules are involved in a concentration-dependent, self-quenching... 

Table 3. Life times of triplet states (3x), rate constants of self quenching (3k, ), of quenching with monomers (3k ) and of quenching with diphenyliodonium hydrogensulfate (3kJ,)...

Although this experiment is the simpler way to ascertain the pH-sensitivity of the liposomes, similar experiments can be conducted with encapsulated drugs. The same procedure can be used if the drug is fluorescent, and self-quenched when encapsulated (e.g., doxorubicin). However, in the case of nonfluorescent compounds, the drug released must be separated from the liposome by SEC or dialysis at each time-point and then assayed by the appropriate analytical method. 

Frequently, the reactant M itself acts as a quencher of its excited molecules M, M + M —> 2M. It is difficult to determine self-quenching accurately from the dependence of the quantum yield on the concentration cM, because the absorbance by M increases as its concentration is raised. However, the effect is readily measured by time-resolved methods. Replacing the index q by M in Equation 3.39 and replacing t° by l/ obs(cM 0) one obtains Equation 3.40. The observed decay rate constant of the excited molecule M, k(thfcM) =1/rM, increases linearly with the concentration of M. The slope kM is the rate constant of self-quenching and the intercept kobfcM > 0) is the decay rate constant of M at infinite dilution.229... 

Figure 4. Observed absorbance change at 409 nm vs. time following pulse radiolysis of 2 fiM a5Ru (His48)HHMb(Fe ==0) in N20-saturated, 40 mM sodium phosphate, 12 mM sodium formate, pH 7.0,1 — 0.1 M, 25.2 V, path length 2.0 cm. The concentration of C02 generated in the pulse was 0.37 pM, and the observed A 409 -23 mM cm is only 25% of that expected for HHMb(Fe ==0) reduction due to competition from C02 self-quenching and scavengers. The solid curve shows the fit of the experimental points to first-order kinetics. (Reproduced from reference 26. Copyright 1994 American Chemical Society.)...

Finally, C(t>= 1) quenching rate was measured for SOj. As in the case of self-quenching, a huge value was obtained (over 30 times larger than gas kinetic), in line with the assumption of a different mechanism for this state. 

Miranda et al. studied the excited-state behavior of chiral drugs bound to BSA and HSA. Inclusion of carprofen 101 (Scheme 1.22) in HSA significantly lengthened the triplet-state lifetime of 101 as a result of more rigid surroundings and the suppression of self-quenching of 101. The complexation of enantiomeric 101 with HSA caused a significant difference in triplet lifetime, and the lifetime of (5)-101-HSA complex is 4 times shorter than that of (/ )-101-HSA complex. Irradiation of 101 alone in aqueous buffer solution led to a polymerization of 101. However, dechlorinated carprofen 102 was... 

---