Abstract

The pH-related characteristics of 4-thiothymidine and its stability during prolonged exposure, at room temperature, to a neon lamp emitting in the 400-700 nm wavelength range were investigated by different spectroscopic techniques (UV-Vis, FTIR-ATR, H-1-NMR) and by ElectroSpray Ionization Mass Spectrometry (ESI-MS). The evaluation of the nucleoside photostability was performed as a control, with the perspective of studying its reactivity under the same conditions but in the presence of visible light-absorbing photosensitizers, able to generate reactive oxygen species. The comparison between UV-Vis spectra recorded at different pH values in the 7-12 range suggested the presence of an equilibrium related to the deprotonation of the N-3-H group of 4-thiothymidine, with a pK(a) estimated to be close to 9. Some effects of the deprotonation occurring at alkaline pH were observed also in FTIR-ATR spectra, the main feature being the appearance of a band related to C=N stretching, interpreted with the assumption of a partial double bond character by C-2-N-3, N-3-C-4 and C-2-O- bonds, as a consequence of negative charge delocalization on the pyrimidine ring. As for photostability, UV-Vis, FTIR-ATR and NMR measurements suggested the generation of thymidine as a by-product but only after a prolonged (48 hours) irradiation time, whereas no significant alteration occurred in a shorter time range (1-2 hours), i.e. the one that will be considered in future studies involving the presence of photosensitizers. The nucleoside stability up to 2 hours of irradiation was confirmed by ESI-MS analyses; furthermore, on the other hand, the latter indicated the presence of three additional by-products, besides thymidine, after 48 hours of irradiation. In particular, an hydroxylated form of 4-thiothymidine and two dimeric species, characterized by S-S and S-O covalent bridges between two 4-thiothymidine and a 4-thiothymidine and a thymidine molecule, respectively, were detected.

Autore Pugliese

• Fini Paola

Tutti gli autori

• Rizzi V.; Losito I.; Ventrella A.; Fini P.; Agostiano A.; Longobardi F.; Cosma P.

Titolo volume/Rivista

RSC advances

Anno di pubblicazione

2014

ISSN

2046-2069

ISBN

Non Disponibile

Numero di citazioni Wos

Nessuna citazione

Ultimo Aggiornamento Citazioni

Non Disponibile

Numero di citazioni Scopus

Non Disponibile

Ultimo Aggiornamento Citazioni

Non Disponibile

Settori ERC

Non Disponibile

Codici ASJC

Non Disponibile