Synthesis, characterization and DNA binding of magnesium–ciprofloxacin (cfH) complex [Mg(cf)2]·2.5H2O

Interactions of the tested systems (title compound [Mg(cf)(2)] * 2.5H(2)O (1), ciprofloxacin (cfH) and ciprofloxacin in the mixture with MgCl(2)), with single and double stranded calf thymus DNA, poly[d(AT)] * poly[d(AT)] and poly[d(GC)] * poly[d(GC)] were studied by UV-spectrophotometric (melting curves) and fluorescence emission measurements. Pronounced quenching of ciprofloxacin's fluorescence intensity has been observed for all the tested compounds after titration with various GC containing DNA molecules. It seems probable that quenching originates in the electron transfer from guanine to the photo-excited fluoroquinolone. The UV-spectrophotometric results obtained for 1 are substantially different from the other solutions and the biggest differences were observed for GC containing DNAs. Solution of 1 provokes a large thermal destabilization of poly[d(GC)] * poly[d(GC)]. This process is irreversible which suggests that the species present in solution of 1 alone inhibit re-annealing by associating irreversibly with the single strands. We have realized that aqueous solutions of 1 are colloidal and we propose that colloidal particles are involved in specific binding to GC containing sequences, most probably in the major groove of DNA.

X-Ray crystallographic, NMR and antimicrobial activity studies of magnesium complexes of fluoroquinolones - racemic ofloxacin and its S-form, levofloxacin

The magnesium complexes of racemic ofloxacin (oflo) and its pure S-form levofloxacin (S-oflo) have been studied by X-ray crystallography and NMR spectroscopy. Two compounds, [Mg(R-oflo)(S-oflo)(H(2)O)(2)].2H(2)O (1) and [Mg(S-oflo)(2)(H(2)O)(2)].2H(2)O (2), respectively, have been prepared by hydrothermal reactions and their crystal structures have been determined. In both structures the anionic fluoroquinolone ligands are coordinated through the keto and carboxylate oxygens forming 1:2 Mg:oflo complexes. The two structures are practically identical except for the orientation of one of the oxazine methyl groups at the chiral center of 2 which was found in equatorial position, the other oxazine methyl groups in 1 and 2 being axial. This difference affects the stacking pattern of quinolone molecules in the cell. (1)H NMR chemical shift data and Mn(II) paramagnetic line broadening measurements on the free ofloxacin suggest that the coordination of the ligands in solution involves the keto and carboxylate oxygens. However, it is not possible to decide whether the complexes in aqueous solution have 1:1 or 1:2 stoichiometry. The methylated piperazine nitrogen does not interact with the metal ion. Magnesium-quinolone interaction is discussed in relation to the biological activity of quinolones. The antimicrobial activity of the complexes against various microorganisms was tested and it was established that their activity is similar to that of free quinolone drugs.

Mixed-valence Cu(II)/Cu(I) complex of quinolone ciprofloxacin isolated by a hydrothermal reaction in the presence of l-histidine: comparison of biological activities of various copper–ciprofloxacin compounds

A new quinolone-metal complex was prepared by a hydrothermal reaction in the presence of L-histidine that served as a reducing agent for a metal. The title compound [Cu(II)(cfH)(2)(Cu(I)Cl(2))(2)] (1) is a mixed-valence Cu(II)-Cu(I) complex, which contains two ciprofloxacin (cfH) molecules bonded to the central copper(II) atom and two almost planar [Cu(I)Cl(2)](-) moieties. Both metal centers are connected through two bridging atoms (chloride and quinolone oxygen). The electrochemical methods (differential-pulse polarography and cyclovoltammetric measurements) confirmed the presence of various copper-ciprofloxacin complex species in aqueous solution at low concentrations used in biological activity tests and also indicated that the equilibria in this system are very complex. The biological properties of the title compound and some previously isolated copper-ciprofloxacin complexes ([Cu(cfH)(2)Cl(2)].6H(2)O (2) and [CuCl(cfH)(phen)]Cl.2H(2)O (3)) (phen=1, 10-phenantroline) were determined and compared. The DNA gyrase inhibition tests and antibacterial activity tests have shown that the effect of copper complexes is comparable to that of free quinolone. Additionally, an interesting DNA cleavage activity of the title compound was also discovered.

A novel copper(II) complex with 1,10-phenanthroline and ciprofloxacin

The X-ray structure analysis of the title compound, chloro[1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(piperazin-4-ium-1-yl)-3-quinolinecarboxylate-kappa(2)O(3),O(4)](1,10-phenanthroline-kappa(2)N,N')copper chloride dihydrate, [CuCl(C(17)H(18)FN(3)O(3))(C(12)H(8)N(2))]Cl x 2H(2)O or [CuCl(cfH)(phen)]Cl x 2H(2)O, where cfH is 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(piperazin-4-ium-1-yl)-3-quinolinecarboxylate and phen is 1,10-phenanthroline, shows that the geometry around the Cu ion is a slightly distorted square pyramid. Two O atoms of the carbonyl and carboxyl groups of ciprofloxacin and two N atoms of 1,10-phenanthroline are coordinated to the metal centre in the equatorial plane, and a Cl(-) ion is coordinated at the apical position. Extensive intermolecular hydrogen bonding produces a supramolecular structure that consists of alternating six- and 12-membered rings.

Influence of copper(II) and magnesium(II) ions on the ciprofloxacin binding to DNA

The influence of magnesium(II) and copper(II) ions on the binding of ciprofloxacin to double stranded calf thymus DNA was studied by fluorescence emission spectroscopy, ultraviolet- and circular dichroism (CD) spectroscopy. The interaction of ciprofloxacin and copper(II) ions was followed by strong fluorescence quenching which was almost unaffected by the presence of DNA. On the other hand, only a slight decrease in fluorescence emission intensity, which was enhanced in the presence of DNA, was observed for ciprofloxacin interaction with magnesium(II) ions. Furthermore, magnesium(II) ions increase the thermal stability of the DNA, while, in the presence of ciprofloxacin, the degree of stabilisation is smaller. In contrast, copper(II) ions destabilise double helical DNA to heat, while ciprofloxacin slightly affects only the second transition of the biphasic melting curve of calf thymus DNA. Magnesium(II) ions at 25 degrees C induce conformational transitions of DNA at concentrations of 1.5 mM and 2.5 M, as monitored by CD. On the other hand copper(II) ions induce only one conformational transition, at a concentration of 12.7 microM. At higher concentrations of copper(II) ions (c>700 microM) DNA starts to precipitate. Significant changes in the CD spectra of DNA were observed after addition of ciprofloxacin to a solution containing DNA and copper(II) ions, but not to DNA and magnesium(II) ions. Based on our spectroscopic results, we propose that copper(II) ions are not directly involved into ciprofloxacin binding to DNA via phosphate groups as it has been suggested for magnesium(II) ions.

Characterization of ciprofloxacin binding to the linear single- and double-stranded DNA

The binding of ciprofloxacin to natural and synthetic polymeric DNAs was investigated at different solvent conditions using a combination of spectroscopic and hydrodynamic techniques. In 10 mM cacodylate buffer (pH 7.0) containing 108.6 mM Na(+), no sequence preferences in the interaction of ciprofloxacin with DNA was detected, while in 2 mM cacodylate buffer (pH 7.0) containing only 1.7 mM Na(+), a significant binding of ciprofloxacin to natural and synthetic linear double-stranded DNA was observed. At low ionic strength of solution, ciprofloxacin binding to DNA duplex containing alternating AT base pairs is accompanied by the largest enhancement in thermal stability (e.g. DeltaT(m) approximately 10 degrees C for poly[d(AT)].poly[d(AT)]), and the most pronounced red shift in the position of the maximum of the fluorescence emission spectrum (lambda(max)). Similar red shift in the position of lambda(max) is also observed for ciprofloxacin binding to dodecameric duplex containing five successive alternating AT base pairs in the row. On the other hand, ciprofloxacin binding to poly[d(GC)].poly[d(GC)], calf thymus DNA and dodecameric duplex containing a mixed sequence is accompanied by the largest fluorescence intensity quenching. Addition of NaCl does not completely displace ciprofloxacin bound to DNA, indicating the binding is not entirely electrostatic in origin. The intrinsic viscosity data suggest some degree of ciprofloxacin intercalation into duplex.