RESUMO
UVB radiation is already known as initiator and promoter of carcinogenesis in skin. UVB is well absorbed in proteins and DNA leading to products such as cyclobutane pyrimidine dimers. In contrast, UVA radiation generates reactive oxygen species such as singlet oxygen, which can initiate a variety of cellular damages and cellular signalling. It was the goal to investigate whether and to which extent UVB radiation is additionally able to cause oxidative damages via singlet oxygen. Potential endogenous photosensitizers such as vitamin B molecules or unsaturated fatty acids were irradiated in solution using monochromatic UVB radiation at 308 nm. Singlet oxygen was directly detected and quantified by its luminescence at 1270 nm. All investigated endogenous photosensitizers showed clear singlet oxygen signals with a quantum yield ranging from 5 to 40%. UVB radiation altered the photosensitizer molecules during irradiation yielding a change of absorption in the entire ultraviolet spectrum (280-400 nm). UVB irradiation of endogenous photosensitizers produced singlet oxygen that in turn changes the absorption of those molecules. Being an important prerequisite, the changed absorption may either reduce or increase singlet oxygen production. An increase in singlet oxygen generation may initiate a vicious cycle that has the potential to amplify UVB- or UVA-mediated effects in skin cells.
Assuntos
Ácidos Graxos/efeitos da radiação , Oxigênio Singlete/química , Raios Ultravioleta , Vitaminas/efeitos da radiação , Ácido Araquidônico/química , Ácido Araquidônico/efeitos da radiação , Ácidos Graxos/química , Ácido Linoleico/química , Ácido Linoleico/efeitos da radiação , Medições Luminescentes , Niacina/química , Niacina/efeitos da radiação , Oxirredução , Fenalenos/química , Fenalenos/efeitos da radiação , Fotólise , Fármacos Fotossensibilizantes/química , Fármacos Fotossensibilizantes/efeitos da radiação , Porfirinas/química , Porfirinas/efeitos da radiação , Piridoxina/química , Riboflavina/química , Riboflavina/efeitos da radiação , Espectrofotometria Ultravioleta , Vitaminas/química , Ácido alfa-Linolênico/química , Ácido alfa-Linolênico/efeitos da radiaçãoRESUMO
The behaviour of imazapyr (2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid), a broad spectrum herbicide of the imidazolinone family, has been studied under UV radiation in the presence of metal salts. Complexation interactions between imazapyr and metal ions decreased imazapyr photolysis. A chemometric study compared the photodegradation of imazapyr in aqueous solutions in the presence of Na+, Ca2+ or Cu2+ and their concomitant anionic species (Cl-, NO3-) at various pesticide/metal ion molar ratios. The study showed the major role of metal ions in the degradation of imazapyr and its main photoproducts. The molecules were strongly stabilised on complexation with metal ions, leading to an increase in persistence of the pesticide.
Assuntos
Herbicidas/efeitos da radiação , Imidazóis/efeitos da radiação , Niacina/análogos & derivados , Resíduos de Praguicidas/efeitos da radiação , Sais , Cobre , Imidazóis/metabolismo , Niacina/metabolismo , Niacina/efeitos da radiação , Raios Ultravioleta , Poluentes Químicos da Água/efeitos da radiaçãoRESUMO
Numerous derivatives of nicotinic acid hydrazids are suitable for sensitive fluorescence determination of metal ions. The reaction proceeds upon ultraviolet illumination in the presence of an oxidizing agent and catalyst forming a fluorescent product. Therefore, the catalyst metal ion can be quantitatively determined by fluorescence methods. We have studied the reaction of nicotinic acid (di-pyridin-2-yl-methylene)-hydrazide (NADPMH), catalyzed by Mn(II)ion, and determined the optimal parameters of metal ion method.
