1463is facilitated by increasing quencher concentration. The decrease of the second-order rates with increasing global concentration [Q], is a particularity of the restricted reaction space.6 An increase in [Q] means a decrease in the available free sites per quencher. Thus, even though the quenching species becomes more abundant, facilitating fmt-order kinetics, the probability for a single quencher to reach the fluorophore decreases, making second-order kinetics slower. The k's do not always decrease with increasing [Q], Thus for pyrene in mPG vesicles, which provide a less restrictive lipidic core, it has been found that both K's and k's increase with [Q]. However, in that case, the increase in the K's is faster. Notice also, that for DPH in the DPPGLcYPG mixture in Table I1 and pyrene in DPPG in Table I11 kl increases with [Q]. We attribute this last result to the high efficiency of the reaction at short times and high quencher concentrations, due to quasi-static quenching. Failure to repeat this same result with the pair pyrene-12-DSME in DPFG in Table I11 is most probably due to the limited accuracy of the data obtained with this last system. Notice that both first-order and second-order rates are 1 order of magnitude higher for all data obtained with DPH than for those obtained with pyrene. This difference in reaction efficiency goes along with the time scales of survival of the two excited species. In other words, the reaction is faster for the fast-decaying DPH. Of course, this behavior is expected when a substantial quenching occurs within the same concentration ranges. Notice the large difference between the reaction rates at short times (KI) and at long times (KJ. This is due to the relatively low f values observed in this work (cf. Figure 1). The average R is, generally, higher in L~P G than in DPPG vesicles. Apparently, this is due to the higher fluidity of the LCYPG lipidic core. Notice, finally, the extensive increase of K1 with [Q] in the vesicles of the DPPG-mPG mixture (Table I) and of DPPG (Table 11). This is consistent with our above assertion of quasi-static quenching, in particular in these systems.The above discussion shows that the information on reaction rates obtained through eqs 1 and 2 provides an extensive knowledge of the behavior of the reactants in microheterogeneous environments.An additional final remark concerns the behavior under variable temperatures. Previous measurements with pyrene excimers have shown that an increase in temperature increases the calculated fvalues? However, no variation infwas detected with DPH. We attribute this result to the time scale of the DPH data, which is too short to allow any detectable temperature effect. ConclusionThe fluorescence decay of DPH embedded in small unilamellar vesicles of DPPG, L~P G , or a mixture of these two phospholipids (80% DPPG, 20% LCXPG) has been studied in the presence of varying concentration of 12-DSME used as fluorescence quencher. The vesicle concentration was held constant. The results have been compared with sim...
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.