BioPHYSICAL chemistry

14.10Since the photon carries a spin of 1, the angular momentum of the

electron must change by 1 to conserve momentum.

14.11 Only the stimulated process has an incident photon required for

the transition.

14.12 The stimulated process has two identical photons output for every

transition, leading to amplification, but for a spontaneous process

there is no coordination of the light.

14.13The fluorescent spectrum is always red, shifted relative to the absorp-

tion spectrum.

14.14 The factors that give rise to line width in biological samples are the

interactions between the pigment and the protein surroundings, a

distribution of pigment conformations, and vibrational states.

14.15 (a)

(b)

(c)

14.16kobs=knonradiati 9 e+kradiati 9 e→knonradiati 9 e=kobs−kradiati 9 e

=1ns−^1 −0.1 ns−^1 =0.9 ns−^1

14.17

14.18The chlorosomes contain pigments that can funnel light energy into

the reaction center. The efficiency of the chlorosomes allows the

organisms to live under very low light intensity if necessary.

14.19 An off-diagonal peak shows that the pigments associated with the

two absorption bands on the diagonal are coupled together.

14.20The single-molecule measurements allow direct measurement of the

individual spectral properties as well as of the individual reaction rates.

14.21 The bulk rates represent an average whereas the single-molecule

measurements probe the individual rates.

14.22Excitation of Cy3 results in energy transfer only in state c. With time,

fluorescence is observed from Cy3 or Cy5, depending on which state

is present at that time. The duration of any peak width corresponds

to the time that the junction is in that state. Notice that the fluores-

cence from Cy5 jumps up when the fluorescence from Cy3 drops.

10

10

10

4

81

81

−

−

= − + →

s

s k

k

nonradiati e

nonr

9

aadiati e 9 =

1012 s−^1

Quantum yield==

k

k

radiati e k

obser ed

9 radia

9

tti e

kknonradiati e radiati e

9

99 +

Ef ciency

Å

Å

1

()

()(

=

+

=

+

r

rrDA

0

6

0

66

6

6

10

10 200

10

64 10

1

(^664)
6
Å) = ×^6 =
Ef ciency

Å

Å

1

()

()

=

+

=

+

r

rrDA

0

6

0

66

6

6

10

10 (()

.

10

6 05

Å

=

Ef ciency

Å

Å

1

()

()

=

+

=

+

r

rrDA

0

6

0

66

6

6

10

10 (()1

6 1

Å

≈

474 ANSWERS TO PROBLEMS

9781405124362_5_end.qxd 4/29/08 9:17 Page 474