Excited-state dynamics of structurally characterized [ReI(CO)3(phen)(HisX)]+ (X=83,109) Pseudomonas aeruginosa azurins in aqueous solution

The triplet metal-to-ligand charge transfer ((MLCT)-M-3) dynamics of two structurally characterized Re-1(CO)(3)(phen)(HisX)-modified (phen = 1,10-phenanthroline; X = 83, 109) Pseudomonas aeruginosa azurins have been investigated by picosecond time-resolved infrared (TRIR) spectroscopy in aqueous (D2O) solution. The (MLCT)-M-3 relaxation dynamics exhibited by the two Re-1-azurins are very different from those of the sensitizer [Re-1(CO)(3)(phen)(im)](+) (im = imidazole). Whereas the Re-1(CO)(3) intramolecular vibrational relaxation in Re-1(CO)(3)(phen)(HisX)Az (4 ps) is similar to that of [Re-1(CO)(3)(phen)(im)](+) (2 ps), the medium relaxation is much slower (similar to 250 vs 9.5 ps); the 250-ps relaxation is attributable to reorientation of D2O molecules as well as structural reorganization of the rhenium chromophore and nearby polar amino acids in each of the modified proteins.