De novo design of proteins housing excitonically coupled chlorophyll special pairs

Natural photosystems couple light harvesting to charge separation using a ‘special pair’ of chlorophyll molecules that accepts excitation energy from the antenna and initiates an electron-transfer cascade. To investigate the photophysics of special pairs independently of the complexities of native photosynthetic proteins, and as a first step toward creating synthetic photosystems for new energy conversion technologies, we designed C2-symmetric proteins that hold two chlorophyll molecules in closely juxtaposed arrangements. X-ray crystallography confirmed that one designed protein binds two chlorophylls in the same orientation as native special pairs, whereas a second designed protein positions them in a previously unseen geometry. Spectroscopy revealed that the chlorophylls are excitonically coupled, and fluorescence lifetime imaging demonstrated energy transfer. The cryo-electron microscopy structure of a designed 24-chlorophyll octahedral nanocage with a special pair on each edge closely matched the design model. The results suggest that the de novo design of artificial photosynthetic systems is within reach of current computational methods

Oxidative conversion of benzoic and o-chlorobenzoic acid hydrazides to their corresponding acids by thallium(III) : A mechanistic study

79-82The reactions between thallium(III)  and benzoic ac id and 0-chlorobenzoic acid hydrazides have been studied in a mixture of perchloric and hydrochloric acid medium. The reaction involves formation of complex between the reactants, which decompose in the subsequent step to give products. The reaction proceeds by direct two electron transfer without intervention of free radicals. Increase in [H+] and [Clˉ] decreases the rate of the reaction. The increase in the ionic strength does not affect the rate of the reaction while decrease in the relative permitivity increases the same. The effect of temperature on the reaction has been studied between 25 to 45oC and the activation parameters were determined for the slow step of the reaction