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Quantum Compass of Migratory Birds

FIGURE 4.13 Te magnetic feld efects on the transient absorption spectra observed in the ribofavin-indole

system (Horiuchi et al., 2003). (a) Time-resolved transient absorption spectra in an SDS micellar solution of ribo­

favin and indole. Te concentration of SDS was 50 mM. Other conditions of the experiment are given in the text.

(b) Time-resolved action spectra of the magnetic feld efect obtained by subtraction. (Reproduced with permission

from Horiuchi et al., 2003, Copyright 2003, Springer Nature.)

ribofavin-tryptophan (Trp) system (Figure 4.14b) apparently showed that the efciency of the geminate

recombination is much higher in the ribofavin-indole system. Additionally, the diference in the sub­

traction of the time profles is important. In the ribofavin-indole system, the subtraction curve reaches

its maximum at t = 0.8 µs and slightly decays within a few microseconds (Figure 4.14a). Tis decay of

the magnetic feld efect is rationalized by recombination of radical pair via spin relaxation from the T+1

and T−1 states to the S-T0 mixed spin states. Terefore, this type of slow decay observed in the subtracted

curve should be observed in cases where the escaping rate constant of the radical pair, kesc, is comparable

to the rate constant of the electron spin relaxation, krlx. In contrast, such features have not been observed

in the ribofavin-Trp system (Figure 4.14b). Tus, the magnetic feld efect on the ribofavin-indole sys­

tem was twice as large as that of ribofavin and Trp (Horiuchi et al., 2003). Tis result showed the difer­

ence in the dynamics of radicals in micelles (Horiuchi et al., 2003). Te escape rate of the cation radicals

generated from Trp was much faster than that generated from indole (Horiuchi et al., 2003). Horiuchi

et al. (2003) tentatively concluded that the diference in the magnetic feld efect is due to a large difer­

ence in the escape rate of cation radicals generated from indole derivatives.

As an example of another artifcial system, the magnetic feld efects of the system in the mixture of

the hen egg white lysozyme (Trp-containing protein) and the favin mononucleotide have been reported