Binding of methacycline to human serum albumin at subdomain IIA using multispectroscopic and molecular modeling methods.

This study was designed to examine the interaction of methacyline (METC) with human serum albumin (HSA) by multispectroscopy and a molecular modeling method under simulative physiological conditions. The quenching mechanism was suggested to be static quenching based on fluorescence and ultraviolet-visible (UV-Vis) spectroscopy. According to the Vant' Hoff equation, the values of enthalpy (∆H) and entropy change (∆S) were calculated to be -95.29 kJ/mol and -218.13 J/mol/K, indicating that the main driving force of the interaction between HSA and METC were hydrogen bonds and van der Waals's forces. By performing displacement measurements, the specific binding of METC in the vicinity of Sudlow's site I of HSA was clarified. An apparent distance of 3.05 nm between Trp214 and METC was obtained via the fluorescence resonance energy transfer (FRET) method. Furthermore, the binding details between METC and HSA were further confirmed by molecular docking studies, which revealed that METC was bound at subdomain IIA through multiple interactions, such as hydrophobic effect, polar forces, hydrogen bonding, etc. The results of three-dimensional fluorescence and Fourier transform infrared (FTIR) spectroscopy showed that METC caused conformational and some microenvironmental changes in HSA and reduced the α-helix significantly in the range of 52.3-40.4% in HSA secondary structure. Moreover, the coexistence of metal ions such as Ca(2+), Al(3+), Fe(3+), Zn(2+), Cu(2+), Cr(3+) and Cd(2+) can decrease the binding constants of METC-HSA.

Optical properties of metacycline, oxytetracycline and chlortetracycline europium complexes in the presence of hydrogen peroxide.

Tetracycline possesses a great tendency to form complexes with a number of chemical species, particularly with Eu3+ ions. In this work we investigate the europium optical properties of three tetracyclines europium complexes: Metacycline (MTc), Oxytetracycline (OTc), and Chlortetracycline (CTc), in the presence and absence of hydrogen peroxide (HP). The results show that the emission band of EuOTc have enhancement in the presence of hydrogen peroxide. A calibration curve was shown for this complex with the best molar ratio obtained.

[Studies and application of fluorescence of metacycline enhanced by synergetic effect of beta-cyclodextrin and DBS].

The fluorescence of metacycline enhanced by the synergetic effect of beta-cyclodextrin with anion surfactant sodium dodecylbenzene sulfonate (DBS) was studied. It was found that the fluorescence intensity of metacycline was greatly enhanced in the system of beta-CD-DBS. Based on this a new sensitive method for the determination of metacycline was established. The experiments indicated that MTC-beta-CD-DBS can form 1 : 1 : 1 ternary inclusion complex with apparent stability constant of 1 294 L2 x mol(-2), respectively. The fluorescence intensity was linearly related to the metacycline concentration in the range of 1.7 x 10(-7) to 8.8 x 10(-5) mol x L(-1) with a correlation coefficient of 0.996 6. The detection limit was 7.4 x 10(-9) mol x L(-1) this method was satisfactorily applied to the determination of metacycline in pharmaceutical preparations. The recovery was within the range of 95% to 106%.

[Determination of metacycline in mixture sample by synchronous-derivative fluorimetry].

A new synchronous-derivative fluorimetric method for the determination of metacycline (MTC) in the presence of oxytetracycline (OTC) is proposed. The degradation products of MTC in 0.1 mol x L(-1) NaOH are strongly fluorescent. The addition of cetyltrimethylammonium bromide (CTMAB) enhances the fluorescence intensity 2-fold. The synchronous fluorescence spectra of MTC and OTC degradation products do not interfere with each other under the condition that deltalambda = 100 nm. MTC can be determined in the presence of OTC in the range of OTC+MTC ratio of 1+116-1+1. The recoveries of MTC in the mixture sample are in the range of 94%-102%.

Determination of tetracyclines residues in honey using high-performance liquid chromatography with potassium permanganate-sodium sulfite-beta-cyclodextrin chemiluminescence detection.

A novel method was developed for the simultaneous determination of tetracycline antibiotic (TCA) residues such as oxytetracycline (OTC), tetracycline (TC), and metacycline (MTC) by high-performance liquid chromatography (HPLC) coupled with chemiluminescence (CL) detection. The procedure was based on the chemiluminescent enhancement by TCAs of the potassium permanganate-sodium sulfite-beta-cyclodextrin system in a phosphoric acid medium. The separation was carried out with an isocratic elution using a mixture of acetonitrile and 0.001 M phosphoric acid. For the three TCAs, the detection limits at a signal-to-noise of 3 ranged from 0.9 to 5.0 ng/ml. The relative standard deviations for the determination of TCAs ranged from 3.1 to 7.4% within a day (n=11) and ranged from 2.2 to 8.6% in 3 days (n=9), respectively. The method was successfully applied to the determination of TCA residues in honey samples. The possible mechanism of the CL reaction was also discussed.

Lysozyme-enhanced europium(III)-metacycline luminescence and its application to the determination of metacycline.

A new spectrofluorometric method is described for the determination of metacycline (MC), based on modified enzyme-amplified lanthanide luminescence. Under the optimum conditions, Eu3+-MC forms a ternary complex with lysozyme in close proximity. Then lysozyme can remarkably enhance the characteristic fluorescence intensity of Eu3+ at 612 nm in metacycline-Eu3+ binary complex. The enhanced fluorescence intensity is in proportion to the concentration of MC. The limit of detection is 1.6 x 10(-8) mol L(-1), with a linear range from 6.2 x 10(-6) to 1.7 x 10(-5) mol L(-1). Interferences of other coexisting substances were studied. The developed method was successfully applied to the determination of MC in serum and urine samples. The mechanism of fluorescence enhancement was also studied.

In vitro release of tetracyclines in presence of H2-receptor antagonists.

There are a number of drug interactions reported for tetracyclines with many other drugs. In present study in vitro release of five different tetracyclines i.e., tetracycline, demeclocycline, oxytetracycline, methacycline and doxycycline in presence of cimetidine and ranitidine has been studied by USP XX dissolution method. The release of almost all tetracyclines was depressed in presence of cimetidine and ranitidine while in some cases the value were greatly increased due to the formation of charge transfer complexes of the antibiotic with H2-receptor antagonists, which gave absorbance at same wavelengths but with much higher molar absorptivity. An attempt was made to elucidate the mechanism of this effect.

The extra-weak chemiluminescence generated during oxidation of some tetracycline antibiotics. 1. Autoxidation.

Chemiluminescence (CL) appearing during autoxidation of tetracycline (TC) antibiotics has been studied. The CL spectrum consists of four emission bands with maxima at 520, 585, 640 and 700 nm. The bands at 585, 640 and 700 nm are similar to those observed for singlet molecular oxygen (1O2). The effect of 1O2 quenchers and free radical reaction inhibitors on the light emission is also reported. The data support the concept that, during the autoxidation of TCs, cytotoxic oxygen species such as HO., O2.-, H2O2 and 1O2 are formed.