title: Fluorescence spectra, fluorescence quantum yield and dissociation constant of sarafloxacin.
abstract: In this study, the fluorescence spectra of sarafloxacin (SAR) under different pH conditions were investigated to determine the structural changes due to protonation that result from change in pH. At pH < 1.02, SAR exists in the H3L2+form for which the maximum fluorescence emission wavelength was about 455 nm. At pH 1.87-4.94, SAR exists in the H2L+form in which H3L2+loses one proton in the nitrogen molecule at the 1-position in the quinoline ring. Fluorescence intensity was strong and steady and the maximum emission wavelength was 458 nm. At pH 7.14-9.30, the maximum emission wavelengths were gradually blue shifted to 430 nm with increase in pH, here SAR exists in the form of a bipolar ion HL in which H2L+loses a carboxyl group proton. At pH > 11.6, HL transforms into anionic L-in which HL loses one proton from the piperazine ring, leading to a decrease in fluorescence intensity, and the maximum emission wavelength was red shifted to approximately 466 nm. The two-step dissociation constant pKa for SAR was calculated, pKa1was 6.06 ± 0.37 and pKa2for SAR was 10.53 ± 0.19. In a pH 3.62 buffer solution with quinine sulfate as the reference, the fluorescence quantum yield of SAR at the maximum excitation wavelength of 276 nm was 0.09.
authors.affiliation: College of Chemistry and Environmental Science, Key Laboratory of Analytical Science and Technology of Hebei Province, Hebei University, Baoding, Hebei Province, People's Republic of China.
authors.forename: Tongtong
authors.initials: T
authors.lastname: Li
authors.affiliation: College of Chemistry and Environmental Science, Key Laboratory of Analytical Science and Technology of Hebei Province, Hebei University, Baoding, Hebei Province, People's Republic of China.
authors.forename: Baosheng
authors.initials: B
authors.lastname: Liu
authors.affiliation: College of Chemistry and Environmental Science, Key Laboratory of Analytical Science and Technology of Hebei Province, Hebei University, Baoding, Hebei Province, People's Republic of China.
authors.forename: Shaotong
authors.initials: S
authors.lastname: Duan
authors.affiliation: College of Chemistry and Environmental Science, Key Laboratory of Analytical Science and Technology of Hebei Province, Hebei University, Baoding, Hebei Province, People's Republic of China.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Cui
mesh_terms: D002939:Ciprofloxacin / Q000031:analogs & derivatives* / Q000737:chemistry; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D011522:Protons; D013050:Spectrometry, Fluorescence
chemical_list: D011522:Protons; D002939:Ciprofloxacin; C047224:sarafloxacin
keywords: dissociation constant; fluorescence quantum yield; fluorescence spectroscopy; sarafloxacin