Peter Bukovec

Crystal structure of ciprofloxacin hexahydrate and its characterization

Ciprofloxacin hexahydrate has been prepared and its crystal structure has been determined by X-ray crystallography. The molecule is in the zwitterionic form in solid state, the carboxylic proton being present at terminal piperazine nitrogen atom (N(74)) which is in contrast to the previously reported structures of quinolones. Water molecules are involved in a very complicated hydrogen bonding network. Different other techniques (IR, Raman spectroscopy, thermal and elemental analysis) were used to characterize the title compound and to compare its properties with similar compounds.

Antibacterial tests of Bismuth(III)–Quinolone (Ciprofloxacin, cf) compounds against Helicobacter pylori and some other bacteria. Crystal structure of (cfH2)2[Bi2Cl10]·4H2O

The antibacterial tests of two bismuth(III)-ciprofloxacin (cf) compounds against Helicobacter pylori (H. pylori) and some other bacteria were performed. The results have shown that the activity of both compounds is comparable to that of ciprofloxacin hydrochloride. The crystal structure of (cfH2)2[Bi2Cl10].4H2O (cfH2 = doubly protonated molecule of cf) is presented and discussed. The compound was isolated from acidic medium where quinolone is protonated and thus no bonding between quinolone and bismuth was observed. The bismuth(III) ions are coordinated by chloride ions forming dinuclear [Bi2Cl10]4- anions. The charge of this ion is compensated with protonated quinolone molecules (ionic interactions).

Comparison of the thermal stability of ciprofloxacin and its compounds

Abstract The thermal behaviour of ciprofloxacin, its hydrochloride and two copper (II) compounds of ciprofloxacin was studied by thermogravimetry (TG), differential scanning calorimetry (DSC), evolved gas analysis (EGA) and IR spectroscopy. In all the compounds studied, profound differences in the carboxylic v (CO) absorption were found after heating, which can be explained by the rearrangement of the hydrogen bonds.

Polymorphism and stability of norfloxacin, (1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinil)-3-quinolinocarboxylic acid

Norfloxacin was studied by thermal methods (TG and DSC), X-ray powder diffraction, and by FT-IR, UV-VIS and NMR spectroscopy. The drug substance can be prepared in two different crystalline forms and in amorphous state, depending on the experimental conditions of preparation. DSC examinations were carried out at various heating rates and by cycling the samples in the temperature range 50°–250°C. The unstable crystalline form undergoes two irreversible solid-solid phase transitions at 176.5° and 197.6°C. The polymorph melts in the temperature range 218.5°–220.0°C.ZusammenfassungNorfloxacin wurde mittels thermischer Methoden (TG und DSC), weiterhin mittels der Debye-Scherrer-Methode und FTIR-, UV-VIS-und NMR-Spektroskopie untersucht. Je nach den experimentellen Bedingungen bei der Herstellung kann die Wirkstoffsubstanz in zwei verschiedenen kristallinen und in einer amorphen Form hergestellt werden. Die DSC-Untersuchungen wurden bei zahlreichen Aufheizgeschwindigkeiten und durch abwechselnden Temperaturwechsel zwischen Raum- und Schmelztemperatur durchgeführt. Die unstabile kristalline Form unterliegt zwei irreversiblen Feststoff-Feststoff-Umwandlungen bei 176.5° und bei 195.6°C. Das polymorphe Material schmilzt im Temperaturbereich 218.5°–220.0°C.

Synthesis and structure of diaquadichlorobis {9-[(2-hydroxyethoxy)methyl]guanine} copper(II)

Abstract A compound with the title [Cu(C8H11N5O3)2(Cl)2(H2O)2] has been prepared from an aqueous solution of CuCl2 and 9-[(2-hydroxyethoxy)methyl]guanine, acyclovir. The crystal structure has been determined by x-ray diffraction. The compound crystallizes in the monoclinic space group C2/c with a = 19.416(2), b = 10.086(1), c = 13.524(2) A, β = 111.17(1)°, V = 2469.67 A3, Z = 4. Least-squares refinement of the structure based on 2775 observations led to an R factor of 0.038. The structure consists of distorted octahedral molecules with Cl ligands and H2O ligands in trans positions [Cu-Cl 2.883(1) and Cu-O(W) 1.983(2) A]. The 9-[(2-hydroxyethoxy)methyl]guanine is trans linked to Cu through N(7) [2.029(2) A]. The side chain is partially folded. A short intramolecular hydrogen bond between O(6) and O(Wl) [2.594 A] significantly lowers the carbonyl stretching frequency [1715 to 1657 cm−1] in the FT-IR spectrum.

Determination of trace elements and calcium in bone of the human iliac crest by atomic absorption spectrometry

A rapid and reliable analytical method for the determination of trace elements in human bone by atomic absorption spectrometry is reported. Calcium was determined to estimate the homogeneity of samples. Human bone from the iliac crest was obtained at autopsy of adult subjects. Before analysis samples were decomposed by microwave digestion and acid digestion in a Parr bomb. Zinc, rubidium, strontium, calcium and iron were determined by flame atomic absorption spectrometry (FAAS) and aluminium, copper and lead by electrothermal atomic absorption spectrometry (ETAAS) at optimum measurement conditions. The results for the two digestion procedures agreed for zinc, rubidium and calcium within +/-5%, for copper within +/-7% and for strontium, iron, aluminium and lead within +/-10%. The repeatability of measurement (R.S.D.) for determination of calcium and trace elements after microwave digestion and acid digestion in a Parr bomb was tested in one representative autopsy bone sample by six parallel determinations. It was found to be better than +/-5% either for microwave digested samples or samples digested in a Parr bomb, for all elements determined by FAAS and ETAAS techniques. The accuracy of the applied digestion procedures was checked by analysis of trace elements in NIST SRM 1486 Bone Meal reference material. Good agreement of the results with certified values was obtained for both digestion procedures. The microwave procedure developed for digestion of small amounts of sample was applied in trace elements analysis of bone biopsy samples from dialysis patients.

Environmentally safe sewage sludge disposal:The impact of liming on the behaviour of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn

Dewatered sewage sludge containing relatively high total concentrations of Cr (945 micrograms ml-1), Cu (523 micrograms ml-1), Ni (1186 micrograms ml-1) and Zn (2950 micrograms ml-1) was treated with quicklime and sawdust for sludge disinfection and post-stabilisation. The mobility of the heavy metals in the sludge samples was assessed by applying a modified five-step Tessier sequential extraction procedure. Water was added as a first step for estimation of the proportion of the easily soluble metal fractions. To check the precision of the analytical work the concentrations of heavy metals in steps 1-6 of the extraction procedure were summed and compared to the total metal concentrations. The mass balance agreed within +/- 3% for Cd, Cu, Cr, and Zn and within +/- 5% for Ni, Pb, Fe and Mn. Data from the partitioning study indicate that in the lime-treated sludge at a pH of 12 the mobility of Cu and Ni notably increased with the solubilisation of these metals from their organic and/or carbonate and Fe and Mn oxide and hydroxide fractions, respectively. Liming slightly decreased the proportion of other heavy metals in the easily soluble fractions while its impact on the partitioning between other sludge phases was almost insignificant. Due to the increased solubility of Ni and Cu as well as potential Cr oxidation at high pH, liming cannot be recommended for sludge disinfection. Addition of sawdust did not change the heavy metal partitioning.

Determination of high molecular mass Al species in serum and spent CAPD fluids of dialysis patients combining SEC and anion-exchange FPLC with ETAAS detection

Speciation of high molecular mass Al compounds (HMM-Al) in human serum is commonly performed by size-exclusion or ion-exchange chromatography. In general, size-exclusion chromatographic (SEC) columns are not able to completely separate transferrin from albumin. Fast protein liquid chromatography (FPLC), using an anion-exchange column, enables separation of transferrin from albumin. However, the possibility exists of coelution of LMM–Al species (e.g., citrate, phosphate) with HMM–Al species. In this case the concentration of HMM–Al species could be overestimated. It is therefore important to remove LMM–Al species before anion-exchange FPLC separation. For this purpose a novel analytical approach was developed for speciation of HMM–Al species in human serum by combination of SEC (Superdex 75 HR 10/30) and anion-exchange FPLC (Mono Q HR 5/5 anion-exchange FPLC) with UV detection at 278 nm. 1 cm3 of serum was injected onto the SEC column. Isocratic elution using 0.05 mol dm−3 TRIS-HCl + 0.03 mol dm−3 NaHCO3 was applied. It was experimentally proved that proteins were eluted in a 5 cm3 peak that was collected into a polyethylene cup. A 0.5 cm3 aliquot of the sample was then injected onto the anion-exchange FPLC column. The separation of serum proteins was obtained by applying linear gradient elution from 100% buffer A (0.05 mol dm−3 TRIS-HCl + 0.03 mol dm−3 NaHCO3) to 100% buffer B (A + 0.25 mol dm−3 NaCl). Well-resolved protein peaks were obtained. 0.25 cm3 fractions were collected during the chromatographic run and Al determined by ETAAS. It was experimentally proved that 90 ± 5% of Al in spiked serum from a dialysis patient was eluted under the transferrin peak which was identified, not only on the basis of the retention volume, but also by the SDS-PAGE electrophoresis. The same procedure may be applied for speciation of Al in spent CAPD fluids of dialysis patients if the concentration of Al is higher than10 ng cm−3. The proposed speciation procedure removes LMM–Al species and enables reliable determination of the concentration and composition of Al bound to proteins by anion-exchange FPLC-ETAAS.

Use of nitric acid in sample pretreatment for determination of trace elements in various biological samples by ETAAS

Trace elements in liquid biological samples may be determined by direct electrothermal atomic absorption spectrometry (ETAAS). In our previous work it was found that samples containing proteins or DNA may leak out of the graphite tube before the drying step, despite the addition of various modifiers. In order to keep the sample to the graphite tube, samples were diluted before analysis 1 + 1 with 32% v/v nitric acid, or 5 microl of 32% v/v nitric acid was added to the graphite tube before ETAAS determination. Applying the proposed procedure, the concentrations of lead in eluted fractions after gel chromatographic separation of human cerebellar nucleus dentatus supernatant and platinum in isolated DNA samples were determined. The use of nitric acid in sample pretreatment prevent sample leakage out of the graphite tube, provided for even drying and considerably reduced nonspecific absorption in lead determination. The repeatability of measurements was better than + 6%. The accuracy of the procedure was checked by spiking samples. The recoveries for both elements lay between 93--104%. Nitric acid was found to be a better modifier than TRITON X-100.

Chromium in soil layers and plants on closed landfill site after landfill leachate application

Landfill leachate (LL) usually contains low concentrations of heavy metals due to the anaerobic conditions in the methanogenic landfill body after degradation of easily degradable organic matter and the neutral pH of LL, which prevents mobilization and leaching of metals. Low average concentrations of metals were also confirmed in our extensive study on the rehabilitation of an old landfill site with vegetative landfill cover and LL recirculation after its treatment in constructed wetland. The only exception was chromium (Cr). Its concentrations in LL ranged between 0.10 and 2.75 mg/L, and were higher than the concentrations usually found in the literature. The objectives of the study were: (1) to understand why Cr is high in LL and (2) to understand the fate and transport of Cr in soil and vegetation of landfill cover due to known Cr toxicity to plants. The total concentration of Cr in LL, total and exchangeable concentrations of Cr in landfill soil cover and Cr content in the plant material were extensively monitored from May 2004 to September 2006. By obtained data on Cr concentration in different landfill constituents, supported with the data on the amount of loaded leachate, amount of precipitation and potential evapotranspiration (ETP) during the performance of the research, a detailed picture of time distribution and co-dependency of Cr is provided in this research. A highly positive correlation was found between concentrations of Cr and dissolved organic carbon (r=0.875) in LL, which indicates the co-transport of Cr and dissolved organic carbon through the system. Monitoring results showed that the substrate used in the experiment did not contribute to Cr accumulation in the landfill soil cover, resulting in percolation of a high proportion of Cr back into the waste layers and its circulation in the system. No negative effects on plant growth appeared during the monitoring period. Due to low uptake of Cr by plants (0.10-0.15 mg/kg in leaves and 0.05-0.07 mg/kg in stems of Salix purpurea), the estimated Cr offtake from LL by plants represented only a small proportion of the LL Cr mass load during the observation period, resulting in no dispersion of Cr into the environment through leaf drop.