Chemistry Exam: Fluorescence Decay Rates and Proton NMR Spectra, Exams of Chemistry

Download Chemistry Exam: Fluorescence Decay Rates and Proton NMR Spectra and more Exams Chemistry in PDF only on Docsity! Chemistry 471 Half Exam 8 12/14/05 Page 1 of 2 Name:____________________________ (Please print clearly on all pages) 1. The decay of fluorescence of dansyl is measured by exciting the fluorescence with a very fast light pulse and then measuring the dansy fluorescence over time. A plot of the natural log of the fluorescence in- tensity versus time is plotted at right. a) What is the rate constant for the decay of the dansyl fluorescence? b) What is the fluorescence lifetime of dansyl? c) The fluorescence quantum efficiency for dansyl under the same conditions as in a) is 0.7. What is the intrinsic radiative fluorescence decay rate constant kf for dansyl? d) It has been determined separately that when dansyl is 2 nm away from the 11-cis-retial chromophore in rhodopsin, the efficiency of Förster energy transfer from dansyl to retinal is 50%. Suppose rhodopsin is covalently labeled with dansyl, and the fluorescence lifetime of this bound dansyl is found to be 6 nsec. What is the distance between the dansyl label and the retinal chromophore in rhodopsin? 6 6.5 7 7.5 8 8.5 9 9.5 0 5 10 15 20 time (nsec) ln (in te ns ity )