The rapid electronic state dynamics that occur prior to charge separation in the photosynthetic reaction center of Rhodobacter sphaeroides R-26 have been investigated by """"""""two-color"""""""" wavelength-resolved pump-probe and anisotropy measurements. A narrow band (40 fs duration transform limited) pump pulse is used to selectively excite reaction center pigments the accessory bacteriochlorophyll (B), the upper excitonic state of the special pair (Py+), or the lower excitonic state of the special pair (Py-). Population dynamics are then measured with a 12 fs duration probe pulse across the entire Qy absorption spectral region as a function of time. wavelength, and polarization. Excitation of either Py- or B results in the formation of a distinct optical band at 825 nm exhibiting polarization characteristics consistent with those expected for Py+, the band appears instantaneously upon excitation of Py- with a negative anisotropy and appears somewhat delayed after excitation o f B. The dynamics observed following direct excitation of the Py+ absorption band suggests that internal conversion between the excitonic states of P is rapid, occurring with a 65 fs time constant. Excitation of the accessory BChl (i.e., populating the excited state, B*) provides a detailed answer for the mechanism of energy transfer within the bacterial reaction center. The process proceeds via a two-step mechanism, flowing sequentially from B* to Py+ to Py- with time constants of 120 and 65 fs, respectively. These results, in conjunction with a range of the transient transmission spectra, suggest that the initially excited state of the zeroth order chromophores, i.e., B* and Py-, is delocalized at the earliest times, consistent with a supermolecular picture of the reaction center.

National Institute of Health (NIH)
National Center for Research Resources (NCRR)
Biotechnology Resource Grants (P41)
Project #
Application #
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Pennsylvania
United States
Zip Code
Sheth, Rahul A; Arellano, Ronald S; Uppot, Raul N et al. (2015) Prospective trial with optical molecular imaging for percutaneous interventions in focal hepatic lesions. Radiology 274:917-26
Roussakis, Emmanuel; Spencer, Joel A; Lin, Charles P et al. (2014) Two-photon antenna-core oxygen probe with enhanced performance. Anal Chem 86:5937-45
Courter, Joel R; Abdo, Mohannad; Brown, Stephen P et al. (2014) The design and synthesis of alanine-rich ?-helical peptides constrained by an S,S-tetrazine photochemical trigger: a fragment union approach. J Org Chem 79:759-68
Chuntonov, Lev; Ma, Jianqiang (2013) Quantum process tomography quantifies coherence transfer dynamics in vibrational exciton. J Phys Chem B 117:13631-8
Culik, Robert M; Annavarapu, Srinivas; Nanda, Vikas et al. (2013) Using D-Amino Acids to Delineate the Mechanism of Protein Folding: Application to Trp-cage. Chem Phys 422:
Kuroda, Daniel G; Bauman, Joseph D; Challa, J Reddy et al. (2013) Snapshot of the equilibrium dynamics of a drug bound to HIV-1 reverse transcriptase. Nat Chem 5:174-81
Lam, A R; Moran, S D; Preketes, N K et al. (2013) Study of the ?D-crystallin protein using two-dimensional infrared (2DIR) spectroscopy: experiment and simulation. J Phys Chem B 117:15436-43
Kuroda, Daniel G; Singh, Prabhat K; Hochstrasser, Robin M (2013) Differential hydration of tricyanomethanide observed by time resolved vibrational spectroscopy. J Phys Chem B 117:4354-64
Singh, Prabhat K; Kuroda, Daniel G; Hochstrasser, Robin M (2013) An ion's perspective on the molecular motions of nanoconfined water: a two-dimensional infrared spectroscopy study. J Phys Chem B 117:9775-84
Goldberg, Jacob M; Speight, Lee C; Fegley, Mark W et al. (2012) Minimalist probes for studying protein dynamics: thioamide quenching of selectively excitable fluorescent amino acids. J Am Chem Soc 134:6088-91

Showing the most recent 10 out of 128 publications