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Homework 9
1. CO2 fixation in photosynthesis can be approximated by CO2 + H2O -> (CH2O) + O2
(CH2O) represents 1/6 molecule of carbohydrate like glucose. The enthalpy change for
this endothermic reaction is H = 485kJ/mol of CO2 fixed. What are the minimum # of
photons that must be absorbed to fix 1 mol CO2 via photosynthesis? If the efficiency of
photosynthesis is 2%, how many are needed? (Use  = 680nm in photosynthesis for your
photon wavelength).
2. Think about UV-Vis, IR and the microwave part of the electromagnetic spectrum. In
For a spectrum, (Absorbance vs wavelength), in each region, give an example of an
absorbance peak for each of the three regions. Indicate what type of transition it
corresponds to. Give selection rules for each type of spectrum as well. What detectors
are used in each region. Why are there different detectors for each region?
3. Give a general description of fluorescence. What is the Franck-Condon Principle?
How does this affect the fluorescence.
4. What is fluorescence quenching? Name at least three ways that quenching can occur
and give a description of each of these.
5. What is FRET? What type of information about proteins can be determined from
FRET analysis?
6. Dansyl chloride, which absorbs maximally at 330nm and fluoresces maximally at 510
nm, can be used to label amino acids in fluorescence microscopy and FRET studies. The
variation of the fluorescence intensity of an aqueous solution of dansyl chloride with time
after excitation by a short laser pulse (with Io the initial fluorescence intensity) is
t/ns 5.0
If/Io 0.45
10.0
0.21
15.0
0.11
20.0
0.05
a) calculate the observed fluorescence lifetime of dansyl chloride in water.