We subsequently examined the relationship between the
structure of the reaction intermediates and the dimers generated
by the photochemical reaction in solution. Fig. 3(a) shows the
transient absorption spectra obtained from the lysozyme. The
component that absorbs in the range of 350–600 nm in this
spectrum has been reported to be a reaction intermediate of the
Trp62 residue [20,21]. while the absorption from 600 to 700 nm is
attributed to solvated electrons. Scheme 1(a) shows the initial
stage of the photochemical reaction of the lysozyme. In this
process, the lysozyme absorbs light and generates an excited state
consisting of Trp residues. An excited triplet state is subsequently
generated through intersystem crossing (ISC), which in turn
produces the Trp residue radicals that serve as reaction intermediates.
Transient absorption experiments reported in a previous
study showed that these protein radicals can decay via both firstorder
and second-order reaction mechanisms [14]. The secondorder
decay mechanism involves the combination of protein
radicals, as shown in Scheme 1(b). One such dimer generated in
this process is Trp62–Trp62 and the structure of this dimer is
presented in Scheme 1(c).