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 H L form for which the maximum fluorescence emission wavelength was about 455 nm. At pH 1.87-4.94, SAR exists in the H L form in which H L 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 H L 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, pK was 6.06 ± 0.37 and pK for 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.

Rapid detection of sulfamethazine and ofloxacin residues in duck meat using synchronous fluorescence spectroscopy coupled with chemometric methods

“…But, it can be derivatized by a derivatizing agent like o-phthalaldehyde owing to its primary amine group, and its derivative has a fluorescence excitation peak at Δλ/λ exc of 150/292.5 nm ( Figure 1 A). On the other hand, OFL has excellent fluorescence properties because its molecule has a conjugate and rigid structure ( Li et al, 2017 ). It could be seen that OFL had fluorescence excitation peaks at Δλ/λ exc of 170/330 nm and 210/295 nm ( Figure 1 B).…”