[PDF] Synthesis And Photochemistry Of Photosynthetic Model Systems eBook

Author : Kul Bhushan
Publisher :
Page : 105 pages
File Size : 34,38 MB
Release : 2012
Category : Photochemistry
ISBN :

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Most of the sunlight powering natural photosynthesis is absorbed by antenna arrays that transfer, and regulate the delivery of excitation energy to reaction centers in the chloroplast where photosynthesis takes place. Under intense sunlight the plants and certain organisms cannot fully utilize all of the sunlight received by antennas and excess redox species are formed which could potentially harm them. To prevent this, excess energy is dissipated by antennas before it reaches to the reaction centers to initiate electron transfer needed in the next steps of photosynthesis. This phenomenon is called non-photochemical quenching (NPQ). The mechanism of NPQ is not fully understood, but the process is believed to be initiated by a drop in the pH in thylakoid lumen in cells. This causes changes in otherwise nonresponsive energy acceptors which accept the excess energy, preventing oversensitization of the reaction center. To mimic this phenomenon and get insight into the mechanism of NPQ, a novel pH sensitive dye 3'6'-indolinorhodamine was designed and synthesized which in a neutral solution stays in a closed (colorless) form and does not absorb light while at low pH it opens (colored) and absorbs light. The absorption of the dye overlaps porphyrin emission, thus making energy transfer from the porphyrin to the dye thermodynamically possible. Several self-regulating molecular model systems were designed and synthesized consisting of this dye and zinc porphyrins organized on a hexaphenylbenzene framework to functionally mimic the role of the antenna in NPQ. When a dye-zinc porphyrin dyad is dissolved in an organic solvent, the zinc porphyrin antenna absorbs and emits light by normal photophysical processes. Time resolved fluorescence experiments using the single-photon-timing method with excitation at 425 nm and emission at 600 nm yielded a lifetime of 2.09 ns for the porphyrin first excited singlet state. When acetic acid is added to the solution of the dyad, the pH sensitive dye opens and quenches the zinc porphyrin emission decreasing the lifetime of the porphyrin first excited singlet state to 23 ps, and converting the excitation energy to heat. Under similar experimental conditions in a neutral solution, a model hexad containing the dye and five zinc porphyrins organized on a hexaphenylbenzene core decays exponentially with a time constant of 2.1 ns, which is essentially the same lifetime as observed for related monomeric zinc porphyrins. When a solution of the hexad is acidified, the dye opens and quenches all porphyrin first excited singlet states to

Author : Angelo Albini
Publisher : Royal Society of Chemistry
Page : 398 pages
File Size : 10,67 MB
Release : 2016-10-03
Category : Science
ISBN : 1782626956

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Providing critical reviews of recent advances in photochemistry including organic and computational aspects, the latest volume in the Series reflects the current interests in this area. It also includes a series of highlights on molecular devices, global artificial photosynthesis, silicon nanoparticles, solar energy conversion, organic heterogeneous photocatalysis and photochemistry in surface-water environments. Volume 44 of the annual Specialist Periodical Reports: Photochemistry is essential reading for anyone wishing to keep up with the literature on photochemistry and its applications.

Author : Roderick K. Clayton
Publisher : Cambridge University Press
Page : 300 pages
File Size : 41,4 MB
Release : 1980
Category : Medical
ISBN : 9780521294430

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Life on earth depends on the photosynthetic use of solar energy by plants, and efforts to develop alternative sources of energy include a major thrust toward the use of photosynthesis to yield fuels. The study of photosynthesis is an especially convincing way of bringing together the disciplines of physics, chemistry, and biology and can be a valuable element in the teaching of biophysics and biochemistry. This book provides the only detailed modern treatment of the subject in a concise form. Part I outlines the historical development of the subject, emphasizing the chemical nature of photosynthesis and the roles of chlorophylls and other pigments. Part II reviews our present knowledge of the structure and components of photosynthetic tissues in relation to their function. Part III deals with the photo-chemistry of photosynthesis and with the patterns of chemical events, principally electron and proton transfer, that follow the photo-chemistry. Part IV treats the relationships of electron and proton transport to ATP formation, and the metabolic patterns of carbon assimilation. An epilogue exposes major areas of confusion and ignorance and indicates potentially fruitful directions of research, including the development of photosynthetic systems for solar energy conversion. Throughout the book, there are frequent digressions into those aspects of optics and molecular physics relevant to the subject matter. Suitable for upper undergraduate and graduate course use, this book is also sufficiently detailed to give professional scientists a perspective of the subject at the level of contemporary research.