Light-Induced Nanosecond Relaxation Dynamics of Rhenium-Labeled Pseudomonas aeruginosa Azurins

Abstract

Time-resolved phosphorescence spectra of Re(CO) 3 (dmp) + and Re(CO) 3 (phen) + chromophores (dmp = 4,7-dimethyl-1,10-phenanthroline, phen = 1,10-phenanthroline) bound to surface histidines (H83, H124, H126) of Pseudomonas aeruginosa azurin mutants exhibit dynamic band maxima shifts to lower wavenumbers following 3-exponential kinetics with 1-5 and 20-100 ns major phases, and a 1.1-2.5 s minor (5-16%) phase. Observation of slow relaxation components was made possible by using an organometallic Re chromophore as a probe whose long phosphorescence lifetime extends the observation window up to ~3 s. Integrated emission-band areas also decay with 2-or 3-exponential kinetics; the faster decay phase(s) are relaxation-related, whereas the slowest one (360-680 ns (dmp); 90-140 ns (phen)) arises mainly from population decay. As a result of shifting bands, the emission intensity decay kinetics depend on the detection wavelength. Detailed kinetics analyses and comparisons with bandshift dynamics are needed to disentangle relaxation and population decay kinetics if they occur on comparable timescales. The dynamic phosphorescence Stokes shift in Re-azurins is caused by relaxation motions of the solvent, the protein and solvated amino acid side chains at the Re

Nonadiabatic excited-state dynamics of ReCl(CO)3(bpy) in two different solvents

“…Changes of oscillator strength in the course of excited-state relaxation likely is a general effect that can extend to pico- and nanosecond time domains in slow-relaxing complex media such as ionic liquids or proteins. 82–84 Results of our nonadiabatic simulations also qualitatively match femtosecond evolution of Raman features observed in Rebpy FSRS spectra, 75 that are now attributable to the initial restructuring during the “slow” ISC phase.…”

Tryptophan to Tryptophan Hole Hopping in an Azurin Construct

“…This barrier leads to an adiabatic reaction rate of ν N × 1.2 × 10 –3 s –1 , where ν N is the effective frequency of motion along the reaction coordinate. Dynamic phosphorescence and infrared absorption Stokes shift studies of various Re-labeled azurins revealed multiexponential solvation and protein relaxation dynamics ranging from picoseconds to tens of nanoseconds (plus a low-amplitude μs component). , Although not all these motions need to be coupled to ET, ν N can be safely estimated to be less than (100 ps) −1 , predicting ET to be slower than 83 ns, contrary to experiment (ca. 8 ns, likely faster for ″ in ″-CS1).…”

“…(For example, with H ab = 40 meV and λ = 800 meV, the Landau–Zener parameter 2πγ = π 3/2 < H ab 2 >/ h ν eff √(λ k B T ) equals 1 for ν eff = 1.5 × 10 13 s –1 (66 fs) –1 . Protein and solvent motions in Re-labeled azurins are orders of magnitude slower, , affording 2πγ ≫ 1, ensuring adiabaticity. , )…”

“…(For example, with H ab = 40 meV and λ = 800 meV, the Landau−Zener parameter 2πγ = π 3/2 <H ab 2 >/ hν eff √(λk B T) equals 1 for ν eff = 1.5 × 10 13 s −1 (66 fs) −1 . Protein and solvent motions in Re-labeled azurins are orders of magnitude slower, 31,32 affording 2πγ ≫ 1, ensuring adiabaticity. 33,34 ) Environmental (protein, solvent) dynamics, which affect W124 •+ ← W122 ET, were analyzed in terms of the temporal evolution of electrostatic potentials generated by surrounding atoms at scaled van der Waals surfaces of the two indoles (depicted in Figure S8, details in the Supporting Information, S10 and S11).…”

Solvent-Dependent Excited-State Evolution of Prodan Dyes

“…Slower phosphorescence than IR dynamic shifts also was observed for organometallic probes covalently appended to proteins. 46,49 ■ CONCLUSIONS Near-UV excitation of Prodan and Badan dyes in nonpolar (hexane) as well as polar (MeOH, glycerol) solvents produces an S 1 excited state of a ππ* character. In polar/H-bonding, the optically prepared S 1 (ππ*) state undergoes a solvent-driven intramolecular electron-density redistribution from NMe 2 to the CO group accompanied by lowering the S 1 excited-state energy.…”