| Small metallopeptides with ruthenium chromophore have been designed as probes to investigate the dynamics of peptide-protein complex. The four negatively-charged metallopeptides synthesized are: (1) [Ru(bpy)2(phen-am)-Cys-(Glu) 5-Gly]3- (RuCE5G); (2) [Ru(bpy) 2(phen)-Cys-(Glu)5-Gly]3- (RuCE 5G-short); (3) [Ru(phen)2[Ru(phen) 2(DMphen-am)-Cys-(Glu)5-Gly]3- (DMPRuCE 5G) where bpy = 2,2'-bipyridine, phen-am = 5-acetoamido-1,10-phenanthroline, phen = 1,10-phenanthroline, DMphen = 4,7-dimethyl-1,10-phenanthroline. Photoinduced electron-transfer (ET) occurs between these metallopeptides, and ferricytochrome c (Cyt c). In the presence of Cyt c, the triplet state lifetime of the ruthenium metallopeptide is shortened and the emission decays via biexponential kinetics, which indicates the existence of two excited-state populations of ruthenium peptides. The faster decay component displays concentration-independent kinetics demonstrating the presence of a preformed peptide-protein complex that undergoes intra-complex electron-transfer. The slower decay component displays concentration-dependent kinetics that saturate at high concentrations of Cyt c, which indicates the existence of an excited-state encounter complex. The magnitude of both kobsET and kobsET ' decrease with increasing solvent viscosity, and the behaviors can be fit to the expression kobsET ∝ eta-alpha. The electron-transfer processes occurring in both the preformed and encounter complexes are therefore gated by a ratelimiting configurational changes of the complexes. Different values of kobsET and kobsET ' and viscosity dependence behaviors of the preformed and encounter complexes suggest that the encounter complex and the preformed complex are configurationally different and exhibit different rate limiting gating processes.; The more extended and rodlike conformation of RuCE5G-short due to the shorter and more rigid linker between the Ru chromophore and peptide backbone yields higher binding affinity and different motion dynamics: higher mobility of the preformed complex.; Metallopeptides, (bisPhenRuCE5G and DMPRuCE5G) with different redox potentials but similar conformations with those of RuCE 5G give different driving forces of the excited-state ET reaction. The reorganization energy (lambda) and donor-acceptor separation (r ) of the preformed complex between metallopeptides with the longer acetoamido linker between the Ru chromophore and peptide backbone and Cyt c are determined to be 1.25 eV and 16.4 A by measuring the actual ET rates of these three metallopeptides at their most stable configurations. These values are comparable with those of some protein-protein systems reported previously. |
