title: pH effect on the photochemistry of 4-methylcoumarin phosphate esters: caged-phosphate case study.
abstract: There are numerous reports of coumarin ester derivatives, in particular phosphate esters, as photocleavable cages in biological systems. Despite the comprehensive analysis of the photocleavage mechanism, studies of 4-methylcoumarin caged phosphates and/or nucleotides were always performed at constant pH. In this work, we present the study of the pH effect on the photochemistry of (7-diethylaminocoumarin-4-yl)methyl phosphate (DEACM-P). Fluorescence and photocleavage quantum yields, as well as the fluorescence decay times were measured as a function of the pH. It was found that the pH produces significant changes in the overall photochemical quantum yield of DEACM-P, and the observed changes are complementary to those obtained from the fluorescence quantum yield. Deprotonation of DEACM-HPO(4)(-) to yield DEACM-PO(4)(2-), produces a decrease in the photochemical quantum yield (from 0.0045 to 0.0003) and an increase in the fluorescence quantum yield (from 0.072 to 0.092). Moreover, from the analysis of the decay times, we have also found that hydroxyl ion is not only relevant, but it is mechanistically involved in the photoreaction of DEACM-HPO(4)(-).
authors.affiliation: REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: André Vidal
authors.initials: AV
authors.lastname: Pinheiro
authors.forename: A Jorge
authors.initials: AJ
authors.lastname: Parola
authors.forename: Pedro V
authors.initials: PV
authors.lastname: Baptista
authors.forename: J C
authors.initials: JC
authors.lastname: Lima
mesh_terms: D003374:Coumarins / Q000737:chemistry*; D004952:Esters / Q000737:chemistry*; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D010710:Phosphates / Q000737:chemistry*; D010777:Photochemistry; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
chemical_list: C556999:(7-diethylaminocoumarin-4-yl)methyl phosphate; D003374:Coumarins; D004952:Esters; D010710:Phosphates