172

Bioelectromagnetism

 

FIGURE 4.14 Time profles of the transient absorption observed at 690 nm and those observed at 510 nm with and

without magnetic feld, A(B = 0.2 T) and A(B = 0 T), respectively (Horiuchi et al., 2003). Te subtractions A(B =0.2

T) − A(B = 0 T) are superimposed. (a) Time profles were observed in the system of 0.18 mM ribofavin and 1 mM

indole. (b) Time profles observed in the system of 0.18 mM ribofavin and 1 mM tryptophan. (Reproduced with

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

(Miura et al., 2003). In this system, the magnetic feld efect of 0.25 T in the mixture of the favin mononu­

cleotide and Trp as a free amino acid was about 2% of the yield of the free radical formation (Miura et al.,

2003). In the ribofavin–hen egg white lysozyme system, the magnetic feld efect increased to 5%–7%.

Tese results are assumed to refect the slower difusion and higher collision probability in large protein

molecules (Miura et al., 2003). In the favin mononucleotide–hen egg white lysozyme system, the mag­

netic feld efect was up to 13% and decreased rapidly upon the addition of NaCl (Miura et al., 2003). Te

only diference between favin mononucleotide and ribofavin is a phosphoric acid group (Miura et al.,

2003). Coulombic interaction between the protein surface and the ionic phosphoric acid group at the side

chain of the favin mononucleotide molecule plays an important role in the dynamics of the radical pair

(Miura et al., 2003). Tese results suggest that the calculation of the radical pair dynamics containing

molecular dynamics and intermolecular interactions is an interesting subject in the investigation of the

chemical kinetics and magnetic spin efects in biological environments (Miura et al., 2003).

As for the methods for detecting the spin dynamics of radical pairs, the measurements of time-

resolved EPR or electron spin resonance are used in addition to the transient absorption measurements.