Studies on the Efficiency of Iron Release from Fe(III)-EDTA and Fe(III)-Cit and the Suitability of These Compounds for Tetracycline Degradation.

Iron ions can be used to degrade tetracycline dispersed in nature. Studies of absorption and fluorescence spectra and quantum chemistry calculations showed that iron is more readily released from Fe(III)-citrate than from Fe(III)-EDTA, so Fe(III)-citrate (Fe(III)-Cit) is more suitable for tetracycline (TC) degradation. At 30 °C, a severe degradation of TC by Fe(III)-Cit occurred as early as after 3 days of incubation in the light, and after 5 days in the dark. In contrast, the degradation of TC by Fe(III)-EDTA proceeded very slowly in the dark. By the fifth day of incubation of TC with Fe(III)-Cit in darkness, the concentrations of the former compound dropped by 55% and 75%, at 20 °C and 30 °C, respectively. The decrease in tetracycline concentrations caused by Fe(III)-EDTA in darkness at the same temperatures was only 2% and 6%, respectively. Light increased the degradation rates of TC by Fe(III)-EDTA to 20% and 56% at 20 °C and 30 °C, respectively. The key role of the light in the degradation of tetracycline by Fe(III)-EDTA was thus demonstrated. The TC degradation reaction showed a second-order kinetics. The rate constants of Fe(III)-Cit-induced TC degradation at 20 °C and 30 °C in darkness were k = 4238 M-1day-1 and k = 11,330 M-1day-1, respectively, while for Fe(III)-EDTA were 55 M-1day-1 and 226 M-1day-1. In light, these constants were k = 15,440 M-1day-1 and k = 40,270 M-1day-1 for Fe(III)-Cit and k = 1012 M-1day-1 and 2050 M-1day-1 at 20 °C and 30 °C; respectively. A possible reason for the higher TC degradation rate caused by Fe(III)-Cit can be the result of its lower thermodynamical stability compared with Fe(III)-EDTA, which we confirmed with our quantum chemistry calculations. Two quantum chemistry calculations showed that the iron complex with EDTA is more stable (the free energy of the ensemble is 15.8 kcal/mol lower) than the iron complex with Cit; hence, Fe release from Fe(III)-EDTA is less effective.

Physiological and Biochemical Parameters of Common Duckweed Lemna minor after the Exposure to Tetracycline and the Recovery from This Stress.

In this study, the ability of Lemna minor L. to recover to normal growth, after being degraded in a tetracycline-containing medium, was extensively investigated. The plants were exposed to tetracycline (TC) at concentrations of 1, 2.5, and 10 mM. Subsequently, their physiological status was analysed against the following criteria: rate of plant growth; free radical accumulation; antioxidant enzyme activity; chlorophyll content; HSP70 protein content; cell membrane permeability, and mitochondrial activity. The study showed that duckweed can considerably recover from the damage caused by antibiotics, within a week of cessation of stress. Of the plant properties analysed, mitochondrial activity was the most sensitive to antibiotic-induced disturbances. After transferring the plants to a tetracycline-free medium, all plant parameters improved significantly, except for the mitochondrial activity in the plants grown on the medium containing the highest dose of tetracycline. In the plants treated with this antibiotic at the concentration of 10 mM, the proportion of dead mitochondria increased and was as high as 93% after one week from the beginning of the recovery phase, even after the transfer to the tetracycline-free medium.

Effect of Dimer Structure and Inhomogeneous Broadening of Energy Levels on the Action of Flavomononucleotide in Rigid Polyvinyl Alcohol Films.

The results of time-resolved fluorescence measurements of flavin mononucleotide (FMN) in rigid polyvinyl alcohol films (PVA) demonstrate that fluorescence intensity decays are strongly accelerated in the presence of fluorescent dimers and nonradiative energy transfer processes. The fluorescence decay originating both from H and J dimer states of FMN was experimentally observed for the first time. The mean fluorescence lifetimes for FMN dimers were obtained: τfl = 2.66 ns (at λexc = 445 nm) and τfl = 2.02 (at λexc = 487 nm) at λobs = 600 nm and T = 253 K from H and J state of dimers, respectively. We show that inhomogeneous orientational broadening of energy levels (IOBEL) affects the shape of the fluorescence decay and leads to the dependence of the average monomer fluorescence lifetime on excitation wavelength. IOBEL affected the nonradiative energy transfer and indicated that different flavin positioning in the protein pocket could (1) change the spectroscopic properties of flavins due to the existence of "blue" and "red" fluorescence centers, and (2) diminish the effectiveness of energy transfer between FMN molecules.

Cadmium ion-chlorophyll interaction - Examination of spectral properties and structure of the cadmium-chlorophyll complex and their relevance to photosynthesis inhibition.

Chlorophyll was shown to spontaneously form a complex with cadmium, which is incorporated at the central position of the chlorophyll molecule porphyrin ring, where it replaces magnesium. The rate of complex formation depended on the ratio of Cd2+ ions to chlorophyll concentration in the solution. In solutions with chlorophyll concentration of C = 1 × 10-5 M and Cd2+ concentrations of C = 1 × 10-5 M, C = 1 × 10-3 M and C = 9 × 10-3 M, Cd-Chl complex formation was completed after 200 h, 50 h and 33 h, respectively. The formation of Cd-Chl complex followed the second order over all substrates reaction order, first order over Cd2+ concentration and first over Chl concentration. The pseudo second order reaction rate constant k, when Cd2+ concentration was equal Chl concentration have been obtained as k = 1.510 ± 0.023 × 10-4 M-1min-1. Quantum chemistry computations showed that Cd-chlorophyll complex existed in two conformations in the methanol solution with cadmium ion placed either below or above the coordination plane. Two times smaller overlap integral of the Chl fluorescence spectrum with the Cd-Chl absorption spectrum IChl,Cd-Chl= 2.4223 × 10-13 cm3/M in comparison with the overlap integral of the Chl fluorescence spectrum with the Chl absorption spectrum IChl,Chl= 4.6210 × 10-13 cm3/M (twice lower probability of energy transfer Chl∗ → Cd-Chl than Chl∗ → Chl) and lower Förster critical distance for resonance energy transfer: RoChl→Cd-Chl= 46.773 Å, RoChl→Chl= 52.086 Å, indicated that in plants intoxicated with cadmium, taken up from the contaminated soil, the energy transfer between Chl and Cd-Chl in antennas will be disturbed, which may be one of the reasons for the inhibition of photosynthesis.

Investigation of chlorophyll degradation by tetracycline.

Antibiotics represent a novel type of environment pollutants which modify chlorophyll content in plants. Spectroscopic methods were employed to investigate the effect of tetracycline on chlorophyll degradation. Changes in absorbance and fluorescence demonstrated that tetracycline reaction with chlorophyll results in the formation of pheophytin, which was confirmed by new bands typical of pheophytin which appeared in the absorbance spectrum. The rate of pheophytin formation depended on ratio tetracycline to chlorophyll concentration in solution. In solutions with chlorophyll concentration of C = 1 × 10-5 M and tetracycline concentrations of C = 1 × 10-3 M and C = 1 × 10-2 M, pheophytin was formed after 28 h and 25 min, respectively. The obtained lifetime for pheophytin formed during chlorophyll reaction - with tetracycline hydrochloride was τ = 5.71 ±â€¯0.02 ns and its value coincides, within the error limits, with the value obtained for pure pheophytin purchased from ChromaDex. The experiment demonstrated two mechanisms of chlorophyll degradation to pheophytin by tetracycline hydrochloride, i.e. 1) loss of Mg2+ ions from the chlorophyll molecule as a result of the presence of H+ ions in solution (i.e. as a result of medium acidification), and 2) removal of Mg2+ ions directly from chlorophyll by tetracycline which binds Mg2+ ions from the chlorophyll. We demonstrated that magnesium occurring in low concentrations attached to a tetracycline molecule in the BCD ring, and that the second ion of Mg2+ may attach to the A ring of tetracycline at higher Mg2+ concentrations. Two fluorescence bands appeared which indicated such magnesium attachments indeed occurred.

Influence of light and Fe(III) ions on tetracycline degradation.

Tetracycline (TC) is an antibiotic produced on the largest scale in the world and used for the treatment of both humans and animals. Its removal from the circulation chain between the natural environment and animals is still a serious problem. Fe(III) ions can be used to break this chain. Fe(III) ions appear in water in spite of irradiation of Fe(III)-Cit complex and oxidation by oxygen present in water. Fe(III)-Cit was a reservoir of Fe(III) ions from which they were continuously released. Therefore, in this paper we studied an interaction between tetracycline (TC) and Fe(III) ions under fluorescent light at 20 °C and 30 °C in the water environment. This interaction leads to TC + Fe(III) coordinating complex formation. Changes caused by this process were monitored within 1860 min by measuring absorption and fluorescence spectra. The absorption spectra showed a charge-transfer stacking band(s) of oxidized and non-oxidized form of TC above 400 nm; in turn the fluorescence spectra revealed decay of initial bands and formation of the new ones. The initial, main fluorescence band at 16,660 cm-1 associated with the intramolecular proton transfer has gradually disappeared after Fe(III) ions binding to oxygen atoms in the BCD system rings of a TC molecule. Gaussian decomposition of all fluorescence spectra allowed extracting new bands, their evolution in time and calculating the rate of the first reaction step. Temperature rise of 10 °C caused more than a ten-fold increase in the first-order reaction rate.

Instability of chlorophyll in yellow lupin seedlings grown in soil contaminated with ciprofloxacin and tetracycline.

With increasing soil concentrations of ciprofloxacin and tetracycline a decrease of leaf chlorophyll content was observed. Tetracycline was more detrimental than ciprofloxacin. The chlorophyll content in plants growing for ten days on a tetracycline containing soil decreased by 68%. The decrease of chlorophyll concentration was even sharper in new leaves that formed after application of the antibiotic (up to 81% drop). The comparison of absorption spectra of commercial, reagent grade chlorophyll, alone and incubated with antibiotics, has shown that ciprofloxacin and tetracycline can react directly with chlorophyll and decrease its concentration by 47.7% and 48.5%, respectively. The changes in fluorescence spectra confirmed the formation of chlorophyll degradation product. The chlorophyll decay was a second order reaction and depended on antibiotic concentration and duration of exposure. Reaction rate constants differed with antibiotics and their soil concentrations. With increasing contents of antibiotics in soil the constant of chlorophyll degradation rate in lupin plants increased from k = 870 M-1day-1 for 3 mg ciprofloxacin to k = 2490 M-1day-1 for 90 mg ciprofloxacin, and in the case of tetracycline the reaction rate constant increased from k = 1330 M-1day-1 to k = 2910 M-1day-1. The sensitivity of chlorophyll to ciprofloxacin and tetracycline was confirmed by determining EC and TU indices.

Steady State and Time Resolved Fluorescence Studies of Azadioxatriangulenium (ADOTA) Fluorophore in Silica and PVA Thin Films.

A cationic azadioxatriangulenium (ADOTA) dye was entrapped in silica thin films obtained by the sol-gel process and in poly (vinyl) alcohol (PVA) thin films. Azadioxatriangulenium is a red emitting fluorophore with a long fluorescence lifetime of ~20 ns. The fluorescent properties of azadioxatriangulenium in silica thin films and PVA films were studied by means of steady-state and time resolved fluorescence techniques. We have found that the azadioxatriangulenium entrapped in silica thin film has a wider fluorescence lifetime distribution (Lorentzian distribution), lower fluorescence efficiencies, shorter lifetimes compared to Azadioxatriangulenium in a PVA film. The local environment of azadioxatriangulenium molecules in the silica thin film is rich with water and ethanol, which creates the possibility of forming excited state aggregates due to high concentration of dye within a small confined area. In contrast to the PVA matrices, the porous silica films allow restricted rotations of Azadioxatriangulenium molecules, which result in faster and complex fluorescence anisotropy decays suggesting energy migration among dye molecules.

Influence of diffusion on nonradiative energy transfer between FMN molecules in aqueous solutions.

Concentration dependence of photoluminescence quantum yield of FMN aqueous solutions (66mM potassium phosphate buffer, pH 7.0) is investigated over the concentration range from 6.31x10(-5) M to 1.8x10(-2) M at temperatures 298.2 and 323.9K. Experimental data are compared with those obtained theoretically based on two different models of excitation energy transfer and migration in the system of FMN monomers and dimers. The first model does not take the material diffusion into account [Acta Phys. Acad. Sci. Hung. 30 (1971) 145] and the second model is based on the second-order transfer rates which are diffusion dependent [Chem. Phys. Lett. 41 (1976) 139; J. Lumin. 27 (1982) 441]. The comparison shows that the process of material diffusion cannot be neglected in the solutions studied as the relative contribution of the diffusion accelerated nonradiative energy transfer to the total drop of the quantum yield can be even higher then 70%. It is also shown, that in order to obtain a good agreement of the experimental and theoretical data it is necessary to introduce into the theory an additional channel of deactivation for the excitation energy. It is proposed that this additional channel can be partial degradation of excitation energy during its migration between the monomers.

The effect of temperature on FMN absorption spectra in rigid poly(vinyl alcohol) matrices.

Electronic absorption spectra of flavomononucleotide (FMN) in poly(vinyl alcohol) films (PVA) were measured over the concentrations ranging from 6.9 x 10(-4) to 6.8 x 10(-1) M and temperatures from 263 to 338 K. The FMN absorption spectra measurements performed at room temperature have shown two ranges of different changes as a function of dye concentration. For concentrations c<10(-1) M (range I) the spectra exhibited regular changes showing an isosbestic point, which evidences the equilibrium between monomers and dimers. However, for range II (c>1.05 x 10(-1) M) the FMN absorption spectra occurred to be almost independent of concentration and they nearly overlapped with the dimer spectrum (within the error limit). Temperature measurements have shown that the FMN absorption spectra in PVA are stable over a wide temperature range. The mean distances between FMN molecules in PVA films are calculated. For maximal concentrations (from the range II), they are below 13.1 A, whereas the mean dimensions of FMN monomers and dimers are 15.8 and 21.1 A, respectively, which indicates that the orientation of dimers and monomers in the PVA film cannot be random at high concentrations. Molecules are partly ordered, adopting approximately parallel orientation, which is in agreement with the calculations of dimer structure by molecular modelling method (MMM).