Time-resolved fluorescence quenching (TRFQ) measurements will be performed on systems of micelles and vesicles which are models of lipid biomembranes and find applicatins in drug delivery and as biochemical reaction medial TRFQ yields information on the size distribution of micelles, the statistical distribution of additives and the dynamics of bimolecular collision rates between additives on the micelles. The goals are (1) perform TRFQ experiments on specific systems; (2) apply the combined techniques of TRFQ and electron paramagnetic resonance (EPR) on identical systems and arrive at a mutually consistent interpretation of data from both experiments; and thus show that the use of complementary techniques, greatly improves the quality of information; (4) apply the method to the study of phospholipid micelles and vesicles. The long term goal is to contribute to (1) the elucidation of biomembrane structure, (2) the understanding of the fundamentals of self-organization; (3) a synergetic multidisciplinary research with colleagues in the Chemistry and Biology departments. In TRFQ, pyrene will function as the fluorescence probe and a nitroxide free radical as the quencher (also a paramagnetic molecule). In interpreting experimental data, it is usually assumed that additives distribute randomly among the micelles. During the award period experiments will be conducted on some well studied systems, like SDS, LiDS, and CTAC in the presence of additives. In the TRFQ method the real time decay on the pyrene fluorescence is measured. The decay time is shortened (quenched) by the quenchers as a result of collisions with the probe. The quenching rate constant depends on the collision frequency between probe and quencher in or at the micelles, which in turn depends on themicelle size. A framework is available that relates the overall decay characteristics and the quenching rate constant to the average size and size disperson of micelles. In the complementary EPR experiments to be carried out by Prof. Bales at CSUN,on the same systems, spin relaxation time of nitroxide free radicals will be measured. Bimolecular collisions shorten the relatation time and the collision frequency depends on the micelle size. The extracted micelle sizes and distribution rely on assumptions of the statistical distribution of all additives on the micelles. The statistical distribution of the additives will be adjusted to conform to data from both experiments. The two techniques used together on the same system will thus give an accurate and reliable determination of the sizes of micelles and of the distribution of the additives.
| Monahan, Amanda J; Starz-Gaiano, Michelle (2016) Apontic regulates somatic stem cell numbers in Drosophila testes. BMC Dev Biol 16:5 |
