Bursting photosynthesis: designing ad-hoc fluorophores to complement the light harvesting capability of the photosynthet
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Bursting photosynthesis: designing ad-hoc fluorophores to complement the light harvesting capability of the photosynthetic reaction center Roberta Ragni1, Omar Hassan Omar2, Rocco Roberto Tangorra1, Francesco Milano3, Danilo Vona1, Alessandra Operamolla1, Simona La Gatta1, Angela Agostiano1, Massimo Trotta3* and Gianluca M. Farinola1* 1
Dipartimento di Chimica, Università degli Studi di Bari Aldo Moro. Via Orabona, 4, 70126 Bari, Italy. 2 Istituto di Chimica dei Composti Organometallici, Consiglio Nazionale delle Ricerche, Via Orabona, 4, 70126 Bari, Italy. 3 Istituto per i Processi Chimico Fisici, Consiglio Nazionale delle Ricerche, Via Orabona, 4, 70126 Bari, Italy. ABSTRACT The covalent functionalization of photosynthetic proteins with properly tailored organic molecular antennas represents a powerful approach to build a new generation of hybrid systems capable of exploiting solar energy. In this paper the strategy for the synthesis of the tailored aryleneethynylene organic fluorophore (AE) properly designed to act as light harvesting antenna is presented along with its successful bioconjugation to the photosynthetic reaction center RC from the bacterium Rhodobacter sphaeroides . INTRODUCTION The covalent binding of tailored organic molecules to enzymes, such as the photosynthetic proteins, represents a very intriguing research topic which opens the way to the development of new hybrid biomimetic systems capable of exploiting solar energy to drive chemical reactions or to produce electrical energy. [1] These hybrid systems are, therefore, promising materials for a new generation of artificial supramolecular machines with applications in various fields, including photocatalysis, photovoltaics and biosensing. In photosynthetic organisms, plants, algae and some bacteria, the photosynthetic apparatus very efficiently converts solar light in chemical and electrical energy used to drive their metabolism. Even the simplest molecular machinery, e.g. the one from purple photosynthetic bacterium Rhodobacter sphaeroides, is very complex and can be hardly manipulated and exploited for energy conversion outside the bacterium. Luckily the reaction center (RC), which is the bacterial photosynthetic core, (Figure 1A), is sturdier than the antenna proteins, and can be easily purified and handled, under rather routinely lab conditions, without loss of photochemical activity.[1]
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Figure 1. (A) Three-dimensional structure of the photosynthetic RC from the carotenoidless strain R26 of the bacterium Rhodobacter sphaeroides. The RC is a membrane-spanning protein composed of three subunits L, M, and H non-covalently allocating nine cofactors, shown not in scale on the right: two ubiquinone-10 molecules (on the bottom), one iron ion (black sphere), two bacteriopheophytins (in the center), and four bacteriochlorophylls, two of which forming a functional dimer (D, at the very top). For sake of clarity the cofactors hydrophobic chain is omitted. (B) Absorption spectrum of the RC with the main peaks at 280, 366, 390, 540, 600, 76
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