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Ferocenoilne nukleobaze su osjetljive na svjetlost kada su otopljene u organskim otapalima, kao što je DMSO. Svjetlost inducira reakciju eliminacije ciklopentadiena, razgradnju ferocenskog dijela molekule i formiranje slobodne nukleobaze. Reakcija je proučena na primjeru derivata N9-ferocenoil-(6-benziloksi)purina i N1-ferocenoil-5-fluorouracila. Kompleksi željeza koji također nastaju kao produkti usporavaju reakciju. Otapalo (DMSO) djeluje kao reaktant i sudjeluje u nukleofilnom napadu na središnji atom željeza.. Red fotokemijske reakcije ovisi o molarnom apsorpcijskom (ekstinkcijskom) koeficijentu i uvjetima reakcije. Kada je reakcija pokrenuta crvenom lampom (λ = 645 nm) opaža se pseudo-prvi red, a kada je pokrenuta plavom lampom (λ = 405 nm) opaža se pseudo-nulti red. N,N-difenil-1-ferocenakarboksamid također je osjetljiv na svjetlost, ali se mehanizam reakcije razlikuje od fotorazgradnje ferocenoilnih-nukleobaza. Ukoliko se ferocenska jezgra zamijeni benzenskom, nastali benzoil-purinski derivati (N7-4-fluorobenzoil-purin)nisu osjetljivi na djelovanje svjetlosnog zračenja. Ferrocenoyl-substituted nucleobases are light-sensitive when dissolved in organic solvents, i.e. DMSO. Light induces an elimination reaction which results in degradation of ferrocene moiety, loss of cyclopentadiene ring and release of free nucleobase. N9-ferrocenoyl-(6-benzyloxi)purine and N1-ferrocenoyl-5-fluorouracyl were used in the study of this photochemical reaction. The formation od ring-deligated iron complexes during the reaction decreases the reaction rate. DMSO is also a reactant which assists in gradual displacement of the five-membered cyclopentadiene ring. Reaction conditions and molar absorption (extinction) coefficients of ferrocene conjugates affect the reaction order. Pseudo-first order kinetics occurs when the red lamp (λ = 645 nm) is used to trigger the reaction. When the blue lamp (λ = 405 nm) is used, it changes to pseudo-zero order. N,N-diphenyl-1-ferrocene carboxamide is also light-sensitive, but the reaction mechanism differs from the mechanism observed for ferrocenoyl-nucleobases. Different acyl-ferrocenes react in different manner in this photochemical reaction. When the ferrocene moiety is replaced by a benzene ring, like in N7-4-fluorobenzoyl-purine, the obtained compound is not light-sensitive. |
