Pyrene-main chain

Inhibition of main-chain scission by pyrene, p-terphenyl and benzene has been reported by Gardner and Epstein [412] and also attributed to energy transfer from polymer to additive. This protective effect of benzene has been confirmed by Wall and Brown [333] and by the present author. Energy transfer was also suggested by Wundrich [413, 414] to explain the decrease in main-chain scission yield observed in the presence of many aromatics. The protection increases with the size of the... 

The bimolecular quenching rate constants, of pyrene fluorescence in various systems are presented in Table II. The values of with the quenchers such as oxygen, nitromethane, and sodium iodide in PA-I8K2 polymer-micellar solutions are much smaller than in water or in homogeneous nonpolar solvents (viz. heptane) and even smaller than in SDS micellar solutions. The data suggest that the penetration of the selected quenchers to the pyrene hosted in the polymer micelle is inhibited by the main chain of the host polymer micelle. This restrictive effect is larger than in simple micellar systems, and it results from the more rigid environment of pyrene in polymer micellar systems. 

Often, experimental studies of lipid systems are based on spectroscopic approaches, which in turn frequently employ probes for enhancement of sensitivity and resolution. For example, in NMR, hydrogen atoms of lipids are replaced with deuterium, and in fluorescence spectroscopy and imaging, native lipid molecules are replaced with lipids in which one of the hydrocarbon chains is linked covalently to a fluorescent marker such as pyrene or diphenylhexatriene. Fluorescent markers allow one to follow numerous cellular processes in real time, such as intracellular trafficking of molecules and formation of domains within a biomembrane, see Fig. 3. The downside is that the probes tend to perturb their environment and affect the thermodynamic state of the system. Experiments have shown, for example, that probes may change the main transition temperature of a lipid membrane, and that the dynamics of probes may deviate considerably from the dynamics of corresponding native molecules (see discussion in Reference 27). Therefore, we wish to pose several questions. What is the range of perturbations induced by the probe How significant are these perturbations actually ... 

The main focus of this study is to utilize excimer formation between pyrene groups attached to PEG chain ends as a molecular probe of intermolecular complex formation. The change upon complexation was monitored by UV-vlsible absorption, excitation, and fluorescence spectroscopies as well as by fluorescence lifetime measurements. 

Enhancement of pyrene fluorescence was reported for the /5-CD-13 complex, owing to the addition of tert-butylamine or n-propylamine for amine concentration lower than 0.1 M. The addition of amines also caused a marked decrease in R from 1.42 for 13 in the presence of 10 M / -CD to 0.75 for the solution in which 10 M / -CD, 13, and 0.1 M amine were present simultaneously [128]. Further increase of the amine concentration led to fluorescence quenching and to an increase of R. The authors inferred that at low amine concentration pyrene is included in a low-polarity environment NMR measurements indicated that the aliphatic chain of the amine was included in the cavity of the cyclodextrin together with pyrene. At high concentrations, amines (mainly tert-butyl-) compete with pyrene for inclusion in the cavity. 

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