Construction And Application Of Artificial Photoenzyme

Photobiocatalysis is a frontier interdisciplinary subject of organic chemistry and chemical biology that integrating the merits of photochemistry and enzymes for driving organic transformations.However,naturally occurring photoenzymes are very limited and specific in terms of their type and catalytic repertoire.It is in general highly challenging to modify natural photoenzymes towards non-natural organic reactions.Therefore,the innovation of artificial enzymes containing non-natural catalytic centers to expand the scope of photobiocatalysis is of high significance.This thesis reviews the principles of photocatalysis,features of the known natural photoenzymes,the established approaches to construct artificial photobiocatalytic systems.On the BSAis of these background,we proposed our strategy of devising novel artificial photoenzyme by statistical covalent chemical modification of protein with small molecular photosensitizers.Human Serum Albumin(HSA)and thioxanthone(TXO)were taken as macromolecular scaffold and photosensitizer,respectively to synthesize the designed photoenzyme,which were characterized by absorption and Mass spectroscopies.The application of HSA-TXO as photoenzyme for organic synthesis and photo-decaging of prodrugs were preliminarily evaluated.We found this enzyme was highly effective for catalyzing selective aerobic oxidation of alkenes into carbonyl compounds without over-oxidation to carboxylic acids.Only 0.01% enzyme loading was required and the products were obtained in moderate to high yields(43% to 99%).For the photo-decaging reaction of 5-fluorouridine(5FU),it was found that both HSA-TXO and photocaged 5-FU exhibited certain degree of cytotoxicity at high concentration.Unfortunately,no significant photo-decaging effect was observed when using the highest concentration of both with no cytotoxicity.We then designed the dHSA-PEG-TXO pretein that can encapsulate caged-5FU in artifical photoenzyme,hoping to improve the efficiency of energy transfer between the photosensitizer and the substrate.However,experiments showed that although this strategy can reduce the cytotoxicity under non-illuminated conditions,it still can not achieve significant photo-decaging effect,and further modification and optimization are needed.In light of the wide application of TXO as catalyst in photochemical reaction,the HSA-TXO prepared in our study is expected to find more application in catalytic organic reactions.For its application for photo-decaging reaction,we need to modify the photosensitizer with more significant bathochromic shift or devising new photoenzymes and prodrugs with low cytotoxicity that allows using the drug at a higher concentration.Alternatively,one can integrate the photoenzyme with prodrug to devise nanoparticles to improve the efficiency of photo-decaging reaction in order to achieve high photo-decaging effect.