Vera Kapetanović

Recent Developments in Electroanalytical Chemistry of Cephalosporins and Cefamycins

Cephalosporins (I, R4 = H) and cefamycins (I, R4 = OCH3) are antibiotics with a broad spectrum of antimicrobial and antibacterial properties. These compounds contain a β-lactam ring which is fused with a six-membered dihydrothiazine ring bearing substituents R1 and R2 in the side-chains at C-3 and C-7 (I)(Table I).

Spectrophotometric and polarographic investigation of the ofloxacin-Cu(II) complexes

By means of spectrophotometric methods it was found that ofloxacin reacts with copper(II) ions to form complexes with molar ratios of ofloxacin: Cu(II) of 1:1 at pH 4.00, 2:1 at pH 7.02 and 3:1 at pH 8.30. The stability constants of the complexes were determined. The formation of ofloxacin:Cu(II) 1:1 and 3:1 complexes was confirmed by a polarographic method and the corresponding overall stability constant was evaluated.

Two-step reduction of the O-methyloxime group in the antibiotic cefetamet

Abstract Most oximes as well as their N-alkyl and O-alkyl derivatives are electrochemically reduced in a single four-electron step to the amine. Some exceptions have been reported, where the reduction occurs in two two-electron steps. The reduction of the O-methyloxime grouping in the antibiotic cefetamet occurs at pH 5–9 in two steps, corresponding to a reduction to the imine and amine, respectively. It has been shown that the separation of the two two-electron processes is caused by differences in position and rate of establishment of acid–base equilibria resulting in protonations of the oxime and imino grouping.

Voltammetric methods for analytical determination of fleroxacin in Quinodis® tablets

The direct current (dc) and differential pulse (dp) polarographic reduction of fleroxacin was done in a wide pH range from 2.48 to 13.00. The appropriate buffer choice was made for its dp polarographic determination in a range from 1.845 to 16.926 microg /ml, at pH 8.50. The adsorptive properties of fleroxacin were investigated in order to achieve an increase in sensitivity and a possibility of fleroxacin determination by applying the adsorptive stripping voltammetric method. The adsorptive processes at the hanging mercury drop electrode were investigated in Britton-Robinson and borate buffers. Adsorptive preconcentration followed by differential-pulse cathodic stripping showed one wave at approximately - 1.1 V being the most sensitive for analytical determination of fleroxacin. Two linear ranges were obtained, the first one from 18.465 to 258.51 ng/ml, and the second one from 3.693 to 18.465 ng/ml.

Electrochemical study of cefetamet-Na and its polarographic determination.

Polarographic behavior of cephalosporin cefetamet-Na (Cef-Na) in aqueous solutions of pH ranging from 1.7 to 12.5 was investigated by applying direct current (dc) polarography, differential pulse polarography (dpp), alternating current (ac) polarography, cyclic voltammetry and electrolysis at constant potential. The characteristics of the corresponding electrode reaction are presented and discussed. The electrode reaction was found to be affected by strong adsorption, strongly and slightly pronounced in acidic and alkaline media, respectively. The methoxyimino group electroreduction was carried out and the mechanistic scheme was suggested. In addition, a sensitive dpp method was proposed for analytical determination of a very low concentrations of Cef-Na.

Study of acid-base equilibria of fleroxacin.

The acid-base equilibria of fleroxacin were studied by means of potentiometry and spectrophotometry. It was established that fleroxacin undergoes a complex acid-base equilibrium due to its zwitterionic nature and two proton-binding sites of similar acidity. The stoichiometric equilibrium constants were determined at 25 degrees C and constant ionic strength 0.1 M (NaCl). The acidity constants pK1 = 5.59 +/- 0.01 and pK2 = 8.08 +/- 0.04 were found by potentiometry, and pK1 = 5.61 +/- 0.03 and pK2 = 8.11 +/- 0.06 by spectrophotometry. The distribution diagram of the corresponding ionic species is given.

Potentiometric and spectrophotometric determination of the dissociation constants of cefetamet

SummaryThe dissociation constants of cefetamet-Na have been determined using potentiometric titrations and spectrophotometry. The investigations were carried on in water solutions at constant temperature and ionic strength, and at differentH0 andpH values. Potentiometric investigations were performed at three different temperatures and ionic strengths. The concentration dissociation constants and the corresponding thermodynamic dissociation constants were calculated by a computer program. The mixed dissociation constants (pK′) of cefetamet-Na have been determined spectrophotometrically in theH0 range from -5.80 to 0.00 and atpH values from 0.00 to 12.70 and are in good agreement with values achieved by graphical methods as well as with those obtained by potentiometric methods. Based on the determined values, the thermodynamic parameters (ΔG, ΔH, ΔS) were calculated atI=0.1M.ZusammenfassungDie Dissoziationskonstanten von Cefetamet-Na wurden mittels potentiometrischer Titrationen und auf spektrophotometrischem Weg bestimmt. Die Untersuchungen wurden in wäßriger Lösung bei konstanter Temperatur und Ionenstärke und verschiedenenH0- undpH-Werten durchgeführt. Potentiometrische Messungen wurden bei drei verschiedenen Temperaturen und Ionenstärken vorgenommen. Die stöchiometrische Dissozation und die entsprechenden thermodynamischen Dissoziationskonstanten wurden mit Hilfe eines Computerprogramms berechnet. Die gemischten Dissoziationskonstanten (pK′) wurden spektrophotometrisch imH0-Bereich von -5.80 bis 0.00 und impH-Bereich von 0.00 bis 12.70 bestimmt und stimmen sowohl mit Werten, die mit Hilfe der graphischen Methode erhalten wurden, als auch mit potentiometrisch bestimmten gut überein. Aus den ermittelten Werten der Dissoziationskonstanten wurden die thermodynamischen Parameter (ΔG, ΔH, ΔS) fürI=0.1M berechnet.

Simultaneous determination of cefotaxime and desacetylcefotaxime in real urine sample using voltammetric and high-performance liquid chromatographic methods

Two rapid, accurate and sensitive methods are developed and validated for the quantitative simultaneous determination of cefotaxime (CFX) and its active metabolite desacetylcefotaxime (DCFX) in urine. Based on the previous results which showed the four electron reduction of CFX at approximately -0.5 V, and the new findings that DCFX reduction occurred at more positive potential (-0.23 V), the new adsorptive stripping differential pulse voltammetric (AdSDPV) method was developed for determination of CFX in the presence of DCFX. Linear responses were observed over a wide concentration range (0.07-0.52 microg/ml for CFX and 0.22-1.3 microg/ml for DCFX) in urine. The second assay involves subsequent separation on a reversed-phase HPLC column, with ultraviolet detection at 262 nm. Retention times were 4.057 and 1.960 min for CFX and DCFX, respectively. Linear responses were observed over a wide range, 0.55-6.60 microg/ml for CFX and 1.10-11.00 microg/ml for DCFX, in urine. The statistical evaluation for both methods was examined by means of within-day repeatability (n=5) and day-to-day precision (n=3) and was found to be satisfactory with high accuracy and precision.

Adsorptive stripping voltammetric determination of cefetamet in human urine.

On the basis of previously established mechanism of cefetamet (CEF) reduction, two methods were suggested for CEF determination-differential pulse polarographic and differential pulse adsorptive stripping voltammetric method. Two pH values were chosen, 2.0 and 8.4, where the electrochemical process was defined as one four-electron and two two-electron processes, respectively. The methods were performed in Britton-Robinson (BR) buffer and the corresponding calibration graphs were constructed and statistical parameters were evaluated. Applying the AdSV method at pH 2.0 linearity was achieved from 2 x 10(-8) to 2 x 10(-7) M with limit detection and limit determination of 4 x 10(-9) and 1.4 x 10(-8) M, respectively. At pH 8.4, the linearity was obtained between 6 x 10(-8) and 6 x 10(-7) M, with limit detection and limit determination of 1.5 x 10(-8) and 5 x 10(-8) M, respectively. Since the AdSV method enabled lower concentrations of CEF to be determined, this method was tested for CEF determination in spiked urine samples, and DPP method was used as a comparative one.

Polarographic investigation of the Cu(II) complex with ampicillin

The complex of Cu(II) ion and ampicillin is investigated polarographically in aqueous medium, at pH = 6, an ionic strength μ = 0.2, and room temperature. The stoichiometric ratio of Cu(II) and ampicillin in the complex, and the stability constant, logK′ = 5.1, were determined by Linganes method.