BioPHYSICAL chemistry

et al. (2005) on the FMO complex, demonstrate the feasibility of apply-

ing 2D optical spectroscopy to complexbiological systems.

Research direction: single-molecule spectroscopy

Most spectroscopic measurements are performed on the order of 10^23 or

a larger number of molecules and so represent an average over the entire

ensemble. As a result, rare events cannot be identified from the aver-

age property. Also, a series of temporally distinguishable events, such as

binding of polymerase to DNA followed by attachment of an amino acid

and release, cannot be distinguished unless the process can be made to

start simultaneously for all molecules. With technical advances in instru-

mentation, individual molecules can be detected optically and their time

evolution can be measured (Nie & Zare 1997; Weiss 1999; Mollova 2003;

Peterman et al. 2004).

310 PART 2 QUANTUM MECHANICS AND SPECTROSCOPY

Exciton

1

2

3

4

7

5

6

E 7

6

5

5, 6

4

3

3, 7

2

2, 4

1

1

Transport

Figure 14.18The structure of the seven bacteriochlorophylls in the complex. Two pathways for
energy transfer are identified in the 2D experiments with the figure on the right showing the
relative energies of the seven pigments. Modified from Brixner et al. (2005).