| Abstract | Fenolni spojevi se sve više istražuju radi mnogobrojnih bioloških učinaka među kojima se ističe antioksidativni učinak. Za praćenje antioksidativnog učinka često se koristi metoda s DPPH• radikalom. U ovom diplomskom radu određene su konstante brzine reakcija fenolnih kiselina: p-kumarinske kiseline, ferulične kiseline, vanilinske kiseline, vanilina i flavonoida kvercetina s DPPH• u dioksanu te smjesi otapala dioksan-voda (0,99:0,01 v/v i 0,95:0,05 v/v). Određeni su kinetički izotopni efekti reakcija navedenih fenolnih spojeva i DPPH• u smjesi otapala dioksan-voda (0,99:0,01 v/v i 0,95:0,05 v/v). Dobiveni kinetički izotopni efekti, za sve spojeve osim vanilina, upućuje na reakcijski mehanizam HAT (hydrogen atom transfer) ili PCET (proton-coupled electron transfer), što podrazumijeva da u stupnju koji određuje brzinu reakcije dolazi i do prijelaza protona i do prijelaza elektrona. U slučaju vanilina dobiven je inverzni KIE koji upućuje na drugačiji i složeniji mehanizam reakcije. U literaturi nisu pronađeni podatci o kinetičkim izotopnim efektima navedenih reakcija. Dobiveni rezultati doprinose razumijevanju kinetike i mehanizma reakcija fenolnih spojeva i radikala, s čime je povezan jedan dio antioksidativne aktivnosti ovih spojeva. |
| Abstract (english) | Phenolic compounds are increasingly being researched for their numerous biological effects, among which the antioxidant effect stands out. To monitor the antioxidant potential, the DPPH• free radical scavenging method is often used. In this thesis, the reaction rate constants of phenolic acids: p-coumaric acid, ferulic acid, vanillic acid, vanillin and the flavonoid quercetin with DPPH• in dioxane and solvent mixture dioxane-water (0,99:0,01 v/v and 0,95:0,05 v/v) were examined. The kinetic isotopic effects for the mentioned phenolic compounds and DPPH• reaction in the solvent mixture dioxane-water (0,99:0,01 v/v and 0,95:0,05 v/v) were determined. The obtained kinetic isotope effects, for all compounds except vanillin, refer to the reaction mechanism HAT (hydrogen atom transfer) or PCET (proton-coupled electron transfer), which implies that in the rate-determining step of the reaction, both proton and electron transitions occur. In the case of vanillin, an inverse KIE was obtained, which points to a different and more complex reaction mechanism. No data on the kinetic isotope effects for the mentioned reactions were found in the literature. The obtained results contribute to the understanding of the kinetics and mechanism of reactions of phenolic compounds with radicals, with which a part of the antioxidant activity of these compounds is associated. |
