An investigation of slow charge separation in a tyrosine M210 to tryptophan mutant of the Rhodobacter sphaeroides reaction center by femtosecond mid-infrared spectroscopy.

Energy and electron transfer in a tyrosine M210 to tryptophan (YM210W) mutant of the Rhodobacter sphaeroides reaction center (RC) were investigated through time-resolved visible pump/mid-infrared (mid-IR) probe spectroscopy at room temperature, with the aim to further characterize the primary charge separated states in the RC. This mutant is known to display slow and multi-exponential charge separation, and was used in earlier work to prove the existence of an alternative route for charge separation starting from the accessory bacteriochlorophyll in the active branch, B(L). The mutant RCs were excited at 860 nm (direct excitation of the primary donor (P) BChls (P(L)/P(M))), 600 nm (unselective excitation), 805 nm (direct excitation of both accessory bacteriochlorophyll cofactors B(L) and B(M)) and 795 nm (direct excitation of B(L)).

Identification of the first steps in charge separation in bacterial photosynthetic reaction centers of Rhodobacter sphaeroides by ultrafast mid-infrared spectroscopy: electron transfer and protein dynamics.

Time-resolved visible pump/mid-infrared (mid-IR) probe spectroscopy in the region between 1600 and 1800 cm(-1) was used to investigate electron transfer, radical pair relaxation, and protein relaxation at room temperature in the Rhodobacter sphaeroides reaction center (RC). Wild-type RCs both with and without the quinone electron acceptor Q(A), were excited at 600 nm (nonselective excitation), 800 nm (direct excitation of the monomeric bacteriochlorophyll (BChl) cofactors), and 860 nm (direct excitation of the dimer of primary donor (P) BChls (P(L)/P(M))). The region between 1600 and 1800 cm(-1) encompasses absorption changes associated with carbonyl (C=O) stretch vibrational modes of the cofactors and protein.

Charge separation and energy transfer in the photosystem II core complex studied by femtosecond midinfrared spectroscopy.

The core of photosystem II (PSII) of green plants contains the reaction center (RC) proteins D1D2-cytb559 and two core antennas CP43 and CP47. We have used time-resolved visible pump/midinfrared probe spectroscopy in the region between 1600 and 1800 cm(-1) to study the energy transfer and charge separation events within PSII cores. The absorption difference spectra in the region of the keto and ester chlorophyll modes show spectral evolution with time constants of 3 ps, 27 ps, 200 ps, and 2 ns.

Electron transfer in the reaction center of the Rb. sphaeroides R-26 studied by transient absorption.

Electron transfer at the reaction center of the purple photosynthetic bacterium Rb. sphaeroides R-26 was measured at room temperature by the time-resolved transient absorption spectroscopy technique with 200 fs temporal resolution. The absorbance changes characteristic of the excited state of the primary donor and extending over the whole spectral range investigated from 350 nm up to 720 nm appeared after excitation with a laser pulse of about 100 fs duration at 800 nm.

Initial electron donor and acceptor in isolated Photosystem II reaction centers identified with femtosecond mid-IR spectroscopy.

Despite the apparent similarity between the plant Photosystem II reaction center (RC) and its purple bacterial counterpart, we show in this work that the mechanism of charge separation is very different for the two photosynthetic RCs. By using femtosecond visible-pump-mid-infrared probe spectroscopy in the region of the chlorophyll ester and keto modes, between 1,775 and 1,585 cm(-1), with 150-fs time resolution, we show that the reduction of pheophytin occurs on a 0.6- to 0.