Transient Epr and Absorbance Changes in Photosynthetic Bacteria

Multiplicity of Electron Transport Reactions in Bacterial Photosynthesis

“…In contrast to these reported differences in the kinetics of absorbance changes of Pa and at 433 nm., the kinetics of the absorbance decay at 433 nm. is the same as that of the light-induced ESR signal of P,' (Ruby et al 1964; Loach & Sekura, 1967). The characteristics of this pigment appear to indicate its close relation to the primary reaction; the observations of Smith & Baltscheffsky (1956) suggest that the light-induced transient could be due to the reduced form of the pigment.…”

“…The rate constant for the formation of this signal at constant BChl concentration is proportional to light intensity over a thousand-fold range of light intensities, indicating that a primary photochemical reaction may be involved (Bolton, Cost & Frenkel, 1968). The kinetics of the dark decay of this signal parallel those of the reappearance of the far-red peak of Pa after it had been photobleached (Ruby, Kuntz & Calvin, 1964;Loach & Sekura, 1967); also the quantum yield for the formation of the free radical and for the bleaching of P870 are close to unity (Bolton et al 1969; Walsh, I 969) (Table I). These measurements strongly suggest that this light-induced free radical must be produced by the BChl species bleached in the light.…”

“…; its decay at room temperature is rapid, but the kinetics are not identical with the reversal of bleaching of Pa (Ke & Ngo, 1967). Other workers ; Vredenberg & Duysens, 1964;Ruby et al 1964) also have observed differences in the decay kinetics of the 430 nm. transient and the reversal of the light-induced bleaching of Pa.…”

“…The reappearance in the dark of the far-red absorption band of Pa following its photobleaching parallels the decay of the ESRL signal. This decay follows biphasic kinetics in Rhodospirillum rubrum cells and chromatophores (Ruby et al 1964;Loach & Sekura, 1967), as well as in Chromatium chromatophores (Schleyer, 1968). The question thus arises, does this decay pattern represent two different reactions or is it an artifact?…”

Combining Molecular Spintronics with Electron Paramagnetic Resonance: The Path Towards Single-Molecule Pulsed Spin Spectroscopy

“…Transient, which is the opposite of persistent, generally denotes processes that involve non-steady state and produce a decaying signal. The term "transient EPR" denotes EPR experiments, where the interesting properties are induced with light [176][177][178]. The typical transient EPR scheme is depicted in Fig.…”