13 KB75 KB12 KB199820252000Nemec, MarjancaPečar, SlavkoSchara, Milan Valterštevilka:1letnik:478 stranistr. 39-46ISSN:1318-0207COBISSID:22021893URN:URN:NBN:SI:doc-JMRGYATZenSlovensko kemijsko društvoActa chimica slovenicaanalizna kemijakinetikanitroksidni radikaliredukcijasečna kislinaspektralna analizasuperoksidni radikaliThe involvement of uric acid in the scavenging of nitroxide radicals by ascorbate|The reaction kinetics, measured by electron paramagnetic resonance (EPR) was used to study the involvement of uric acid in the reactions of nitroxide radical (TEMPONE) scavenging by ascorbate (PBS, pH 7.4 and T=37 C). In absence of iron ions, the oxygen reoxidation of hydroxylamine was slow and the addition of uric acid not change the observed kinetics. On the other hand, in presence of iron ions the reoxidation starts to recover the nitroxide radical. This reaction rate is strongly enhanced by uric acid, In fact there are two hypotheses, the first ascribes more efficient iron complexes with uric acid, by which the reoxidation increases. Especially the competition between the phosphate and uric acid ligands might be important. However, uric acid could be directly involved in scavenging the hydroxyl radicals, and herewith influence the reaction rate. No scavenging activity of uric acid in UV irradiated aqueous solutions was found. The trapped adducts of hydroxyl andthe superoxide radicals sho the same concetration in presence and absence of uric acidRaziskali smo vpliv sečne kisline na kinetiko redukcije nitroksidnih radikalovz askorbatom. Uporabili smo metodo metodo elektroparamagnetne resomamce (EPR) in spinski označevalec TEMPON. Reakcije so potekale v PBS oziroma Tris-HCI pufru pri pH 7,4 in T=37 C. V odsotnosti železovih ionov je bila reoksidacija hidroksilamina počasna in dodatek sečne kisline ni povzročil sprememb hitrosti reakcije. V prisotnosti železovih ionov je reoksidacija hitrejša, prisotnost sečne kisline pa bistveno pospeši reoksidacijo hidroksilamina. Dejansko sta tu dve možnosti in sicer, da sečna kislina tvori železov kompleks, ki je bolj aktiven v smislu hitrosti redoks reakcije-reoksidacije kot železovi fosfati, oziroma da sečna kislina mimo tega posega v hitrost reakcije neposredno. Glede na poskus v Tris-HCI pufru, kjer pospeševalnega efekta sečne kisline ni, je prva hipoteza bolj verjetna. To potrjujeta tudi oba poskusa s spinskimi lovilci, kjer ni bilo opaziti vpliva sečne kisline na tvorbo kisikovih radikalov, z vzbujanjem tvorbe kisikovih radikalov s Fentonovo reakcijo, oziroma z obsevanjem z UV žarkiTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaSlovensko kemijsko društvo