M Mail Roethke, Stephani x X tn course: Physical Biochen x C When free in soluti
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M Mail Roethke, Stephani x X tn course: Physical Biochen x C When free in solution (ie X C D www.chegg.c mework-help/Physical-Chemistry-5th edition chapter 11-problem-VP solution-9/80136056065 E Chegg Study TEXTBOOK SOLUTIONS EXPERT Q&A; E Chapter 11, Problem 7P Bookmark Show all steps: a ON When free in solution e., not bound to opsin), both al-trans and cis retinal have absorption maxima of about 370-380 nm. a. How many electrons can be counted in the conjugated pi-system? b. Using 370 nm and the D particle in a box model, estimate the effective chain length of the retinal chromophore. c. For color vision, the absorption max irnum of 11 retinal is about 560 nm when incorporate by a Schiff-base linkage into the red photoreceptor protein. What would the effective chain length be in this case? Comparing your answers in (b) and (c evaluate the plausibility that the length of the conjugated chain could be the cause of these differences. d. When bound to opsin, the cis retinal Schiff-base linkage has an absorption of about 500 nm, while the opsin-bound al-trans retinal absorbs at about 540 nm. Assuming the length of the box cannot be invoked to ex plain these absorbances, how else might we modify the particle in a box model to ex plain these differences considering that the retinal chromophore is now located in a specialized pocket in the interior of the protein? al-rans-retinal a 9 I N Ask me any 1/11/20Explanation / Answer
For the given conjugated system,
a. The number of pi-electrons in the system is 12 electrons
b. effective chain length L would be,
L = sq.rt.(n^2.h^2/8mE)
= sq.rt.(6.626 x 10^-34 x 370 x 10^-9/8 x 9.1 x 10^-31 x 3 x 10^8)
= 3.35 x 10^-10 m
m = mass of electron
E = hc/lmax
lmax = 370 nm
h = planck's constant
c. when lmax = 560 nm
effective chain length L would be,
L = sq.rt.(6.626 x 10^-34 x 560 x 10^-9/8 x 9.1 x 10^-31 x 3 x 10^8)
= 4.12 x 10^-10 m
So the chain length goes up in case of c. when compared to b.
d. When opsin is bound to trans-retinal, the effective conjugation in the structure for opsin goes up, while reducing the conjugation slightly for trans-retinal and thus would increase the effective chain length. This decrease is enhanced in case when opsin is bound to 11-cis retinal schiff reagent.
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