We present a detailed analysis of the long-range (Forster-type) triplet-to-triplet energy transfer between the photoexcited triplet states of the zinc and magnesium protoporphyrin IX chromophores of Zn- and Mg-substituted hemoglobin. The observations of this rarely detected process are made in fluid solution and at ambient temperature by monitoring the time dependence of triplet-triplet absorption subsequent to flash excitation. This appears to be the first time that rate constants have been measured for Forster energy transfer (triplet) between chromophores at crystallographically known distances and orientations. To provide further reference data on chromophore-protein complexes, we have measured the triplet decay rates for zinc myoglobin (k1 = 70 ± 5 s-1) and magnesium myoglobin (k = 24 ± 1 s-1) and the bimolecular rate constant for quenching the zinc myoglobin triplet by 02 (k1 = 1.25 X 108 m-1 s-1) and by dithionite (kq = 2.4 X 106 m-1 s-1).
ASJC Scopus subject areas
- Colloid and Surface Chemistry