Haixia Li

Effects of pH and polarity on the excited states of norfloxacin and its 4’- N -acetyl derivative：a steady-state and time-resolved study

The properties of norfloxacin (NFX) and its 4′-N-acetyl derivative (ANFX) are investigated in different pH aqueous solutions and H2O-CH3CN mixed solutions, to determine the effects of pH and polarity on their ground and excited states. The triplet states of NFX and ANFX are affected more by pH than by polarity. The pH dependence of the NFX and ANFX triplet states is likely due to the different quantum yields of different protonated forms. Steady-state fluorescence, time-resolved fluorescence, and laser flash photolysis experiments at different pH values provide clear evidence of the involvement of different intramolecular charge-transfer pathways in the singlet states of NFX and ANFX. The different electron-donating capacities of 1-N, 1′-N, and 4′-N under different conditions determine the major pathway.

Ciprofloxacin Photosensitized Oxidation of 2'-Deoxyguanosine-5'-Monophosphate in Neutral Aqueous Solution

Laser flash photolysis studies have been carried out to investigate the reactions of ciprofloxacin (CPX) with 2′‐deoxyguanosine‐5′‐monophosphate (dGMP), N, N, N′, N′‐tetramethyl‐p‐phenylenediamine (TMPD) and ferulic acid (FCA) in neutral aqueous solutions, respectively. CPX triplet state (3CPX*) can be quenched by TMPD, FCA and dGMP, with rate constants of 1.8 × 109, 1.5 × 109 and 5.8 × 107 dm3 mol−1 s−1, respectively. TMPD radical cation (TMPD·+) and FCA radical cation (FCA·+) were observed directly. The formation rate of CPX radical anion (CPX·−) was determined to be 1.5 × 109 dm3 mol−1 s−1. Redox reaction of dGMP was investigated through competing reactions using TMPD and FCA as probe. The triplet energy of CPX was determined to be 262 kJ mol−1. Electron transfer from TMPD, FCA and dGMP to 3CPX* was proposed.

Photochemical properties and phototoxicity of Pazufloxacin: a stable and transient study.

Photochemical properties and phototoxicity of Pazufloxacin (PAX) were systematically investigated in aqueous solutions using UV-Vis, fluorescence, laser flash photolysis, pulse radiolysis and SDS-PAGE gel electrophoresis techniques. PAX triplet-state ((3)PAX(*)) absorption spectra (λ(max)=570 nm) was determined. (3)PAX(*) was quenched by PAX and O(2), with rate constants of 6.9×10(8) and 3.2×10(8) dm(3) mol(-1) s(-1), respectively. The pK(a) values (5.7 and 8.6) for the protonation equilibrium were determined by UV-Vis and fluorescence techniques. The PAX triplet energy (E(T)=260.3 kJ/mol) was obtained using energy transfer method. The reaction of electron transfer from tryptophan (TrpH) and dGMP to (3)PAX(*) was found with rate constants of 8.8×10(7) and 8.7×10(6) dm(3) mol(-1) s(-1), respectively. The rate constants for reactions of ()OH, SO(4)(-) and hydrated electron with PAX were found to be 5.8×10(8), 2.1×10(9) and 9×10(9)d m(3) mol(-1) s(-1), respectively. Based on the results obtained, a rational scheme for dGMP, TrpH and lysozyme photodamage induced by PAX was proposed.

Pulse radiolysis study on gatifloxacin — A fluoroquinolone antibiotic

The reactions between gatifloxacin (GFX) and various one-electron oxidants, such as ·OH, N3·, Br2·−, and SO4·−, have been studied by pulse radiolysis techniques. The GFX radical anion formed in the reaction of GFX with eaq− could either be protonated or deprotonated, and the absorption of GFX radical anion was located at 390 nm. The transient species produced by the reaction of GFX with ·OH radical shows a broad band in the 380–600 nm region with a shoulder, while the oxidation by N3·, SO4·−, and Br2·− results in an absorption band with λmax = 370 nm. At neutral condition (pH 7), the rate constants of GFX reacting with ·OH, N3·, Br2·−, SO4·− and eaq− are estimated to be 1.0 × 1010, 3.1 × 109, 2.8 × 109, 3.0 × 109, and 1.8 × 1010 dm3 mol−1 s−1, respectively. From the pH dependence on the formation of electron adducts and on the rate constant of GFX with eaq−, the pKa of GFX radical anion is estimated to be 5.5 and 9.3.

Photosensitive damage of lysozyme caused by pazufloxacin and the protective effect of ferulic acid

Laser flash photolysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) experiments were carried out to study the photosensitive damage induced by pazufloxacin (PAX) and the protection of lysozyme (Lyso) by ferulic acid (FCA), an active antioxidant. Transient absorption spectra revealed electron transfer from Lyso and FCA to 3PAX*, with respective bimolecular reaction rate constants of 6.3×107 and 1.4×1010 dm3/(mol s). A pulse radiolysis study was also performed to investigate the formation of Lyso radical cations. Results showed that FCA effectively inhibits the cross-linking of protein induced by fluoroquinolones. Finally, a mechanism of the protective effect of FCA on Lyso was proposed.

Photosensitized oxidation of tryptophan and tyrosine by aromatic ketones: A laser flash photolysis study

Photochemical processes of benzophenone (BP) and xanthone (XT) with tryptophan (TrpH) and tyrosine (TyrOH) were studied using the laser flash photolysis technique. It has been observed that the triplet state of BP and XT reacted with TrpH and TyrOH by hydrogen transfer with the formation of BP and XT ketyl radicals and oxidized radicals of Trp· and TyrO·. The related rate constants of these reactions were determined in this paper. The free energy changes (ΔG) of these reactions suggested that the proposed hydrogen transfer mechanism was thermodynamically feasible. These results provide theoretical foundation for further studying structural effects on the photochemical behaviors of proteins with triplet state BP and XT.

Spectroscopy of several drugs in the terahertz region

We use terahertz time-domain spectroscopy (THz-TDS) to measure the absorption spectra of six drugs, atenolol, furosemide, tropicamide, lobeline hydrochloride, propranolol hydrochloride, and promethazine hydrochloride, in the frequency range of 0.3 THz to 2.0 THz. Furosemide, tropicamide, and promethazine hydrochloride show distinct absorption features, whereas atenolol, lobeline hydrochloride, and propranolol hydrochloride exhibit no obvious absorption peaks. The use of THz-TDS makes it possible to rapidly distinguish the drugs with characteristic absorption peaks. Our results demonstrate that THz-TDS is highly sensitive to the structure and spatial arrangement of molecules. As a result, THz-TDS will have potential exploitation in pharmaceutical fields.