Evaluation of N-bromosuccinimide as a new analytical reagent for the spectrophotometric determination of fluoroquinolone antibiotics

Analytical studies were carried out, for the first time, to evaluate the use of N-bromosuccinimide (NBS) as an analytical reagent for the spectrophotometric determination of eleven therapeutically important fluoroquinolone antibiotics (FQA). The procedures involved the reaction of the FQA with NBS and subsequent measurement of the excess NBS by its reaction with p-phenylenediamine (PDA) to give a violet colored product that was measured at 530 nm. Different variables affecting the reaction (concentration of NBS, concentration of PDA, pH of reaction medium, reaction time, and the diluting solvents) were carefully studied and optimized. The molar ratio and mechanism of the reaction between each of the studied FQA with NBS were proposed using UV-vis, IR, and NMR techniques. Under the optimum reaction conditions, the analytical method was developed and validated. Beer's law was obeyed in the general concentration range of 3-25 microg/ml. The assay limits of detection and quantitation were 0.33-1.29 and 1.10-4.31 microg/ml, respectively. The precision of the method was satisfactory; the values of relative standard deviations did not exceed 2%. The proposed method was successfully applied to the analysis of the investigated FQA in their pure and pharmaceutical dosage forms without interference from the common excipients (label claim values were 99.85-100.17+/-0.13-0.59%). Interference from ascorbic acid, that is co-formulated as a stabilizer for the ampoule form, was avoided by its pre-oxidation with potassium bromate before applying the analytical procedure. The results obtained by the proposed method were comparable with those obtained by the official and reported methods.     

Structure of two new compounds of fluoroquinolone antibiotics with mineral acids

New compounds of sparfloxacin (C₁₉H₂₂F₂N₄O₃, SfH) and levofloxacin (C₁₈H₂₀FN₃O₄, LevoH) with mineral acids, namely, sparfloxacinium bromide (SfH · HBr, I) and levofloxacindium diperchlorate (LevoH · 2HClO₄, II), have been synthesized and characterized by X-ray diffraction. Crystallographic data are a = 7.7151(7) Å, b = 26.109(3) Å, с = 10.008(1) Å, β = 103.556(1)°, V = 1959.7(3) ų, space group P2₁/n, Z = 4 for I and a = 9.727(6) Å, b = 20.440(12) Å, с = 12.286(7) Å, β = 104.327(8)°, V = 2367(2)ų, space group P2₁, Z = 4 for II. The structures of these compounds are stabilized by intra- and intermolecular hydrogen bonds and π–π interaction between SfH₂⁺ or LevoH₃²⁺ ions.     

Dichlorosilane-dimethyl ether aggregation: a new motif in halosilane adduct formation

The crystal structures of (H(3)C)(2)O, H(2)SiCl(2) and an adduct of these were determined by low-temperature X-ray crystallography on crystals grown in situ at low temperatures on a diffractometer. The adduct of (H(3)C)(2)O and H(2)SiCl(2) has the composition [(H(3)C)(2)O.H(2)SiCl(2)](2) and contains a four-membered Si(2)O(2) ring, with the Cl atoms pointing to the outside and the Si-H functions pointing to the inner side of the ring. The Si(2)O(2) ring has two longer and two shorter SiO bonds and thus deviates from a square. Quantum chemical calculations give a geometry for [(H(3)C)(2)O.H(2)SiCl(2)](2) which has D(2h) symmetry and allow to obtain an estimate for the adduct formation energies, which are -13.4 kJ mol(-1) for the formation of the mono adduct [(H(3)C)(2)O + H(2)SiCl(2)-->(H(3)C)(2)O.H(2)SiCl(2)], -14.4 kJ mol(-1) for the dimerization of two mono adducts [(H(3)C)(2)O.H(2)SiCl(2)-->[(H(3)C)(2)O.H(2)SiCl(2)](2)] and -41.2 kJ mol(-1) for the reaction 2 (H(3)C)(2)O + 2 H(2)SiCl(2)-->[(H(3)C)(2)O.H(2)SiCl(2)](2). The results are used to rationalize the strongly reduced reactivity of H(2)SiCl(2) towards nucleophilic substitution reactions in (H(3)C)(2)O at low temperatures.     

Organometallic derivatives of penicillins and cephalosporins a new class of semi-synthetic antibiotics

Novel semi-synthetic derivatives of penicillin and cephalosporin have been prepared in which the conventional phenyl or heteroaromatic group has been replaced by a ferrocene moiety, and in which the metal atom is in close proximity to the β-lactam ring of the antibiotic; several of the compounds exhibit high antibiotic activity and others are potent β-lactamase inhibitors.     

Delivery platform for hydrophobic drugs: prodrug approach combined with self-assembled multilayers

We report the design of a platform for the delivery of hydrophobic drugs via a macromolecular prodrug approach combined with LbL-assembled polyelectrolyte multilayers. A hyaluronan ester prodrug of the chemotherapeutic drug paclitaxel has been synthesized. Conjugation of the drug to hyaluronan through a labile succinate ester did not inhibit its activity. Using quartz crystal microbalance, atomic force microscopy, and UV spectroscopy, we have shown that the presence of the hydrophobic paclitaxel moieties does not prohibit the layer-by-layer construction of the multilayers. Release of the drug from the paclitaxel-loaded multilayers upon hydrolysis of the ester linkage resulted in a drastic cell death. Application of this delivery platform to substrates such as colloids, biomedical implants, or vascular tissues may lead to new therapeutic strategies.     

Atomic absorption spectroscopic, conductometric and colorimetric methods for determination of fluoroquinolone antibiotics using ammonium reineckate ion-pair complex formation

Three accurate, rapid and simple atomic absorption spectrometric, conductometric and colorimetric methods were developed for the determination of norfloxacin (NRF), ciprofloxacin (CIP), ofloxacin (OFL) and enrofloxacin (ENF). The proposed methods depend upon the reaction of ammonium reineckate with the studied drugs to form stable precipitate of ion-pair complexes, which was dissolved in acetone. The pink coloured complexes were determined either by AAS or colorimetrically at lambdmax 525 nm directly using the dissolved complex. Using conductometric titration, the studied drugs could be evaluated in 50% (v/v) acetone in the range 5.0-65, 4.0-48, 5.0-56 and 6.0-72 microg ml-1 of NRF, CPF, OFL and ENF, respectively. The optimizations of various experimental conditions were described. The results obtained showed good recoveries of 99.15 +/- 1.15, 99.30 +/- 1.40, 99.60 +/- 1.50, and 99.00 +/- 1.25% with relative standard deviations of 0.81, 1.06, 0.97, and 0.69% for NRF, CPF, OFL, and ENF, respectively. Applications of the proposed methods to representative pharmaceutical formulations are successfully presented.     

Comparison of solid-phase sorbents for the determination of fluoroquinolone antibiotics in wastewater

Three different SPE sorbents (weak cation exchange, mixed cation exchange, and hydrophobic-lipophilic balance polymers) were compared in terms of recovery, precision, and the effect of matrix components on analyte response for the determination of fluoroquinolones antibiotics. The influence of ethylenediaminetetraacetic acid disodium salt (Na2-EDTA) was as well tested. Two of the sorbents, hydrophilic-lipophilic balance (HLB) and weak cation exchange (WCX), turned out to be suitable for ultratrace analysis. HLB sorbent showed higher capacity for analyte trapping and better precision while weak cation exchange sorbent had a superior performance in terms of selectivity. In complex samples, the higher capacity of HLB was outweighed by the higher selectivity of WCX when considering the LODs of the methods.     

Enthalpies of formation of organic free radicals of alcohol and ether derivatives

Numerical values of the enthalpies of formation of oxygen-containing organic radicals of alcohol and ether derivatives (Δ_f H°) were analyzed. For seven out of 25 compounds the corresponding Δ_f H° values were determined more accurately. For 35 radicals, the Δ_f H° values were determined for the first time based on the published values of bond dissociation energies in molecules and on the corresponding enthalpies of their formation. Based on the analysis of the Δ_f H° values for 60 radicals studied, a structure—property (enthalpy of formation) correlation was established, described in the framework of the group additivity scheme. The parameters for calculations of Δ_f H° values for the title radicals were recommended.     

Determination of fluoroquinolone antibacterials as N-acyl derivatives

Summary A simple and quantitative method for the preparation and high performance liquid chromatography (HPLC) of N-acylated fluoroquinolones has been developed. The acylation procedure was performed with four different acid anhydrides and found to be applicable to several fluoroquinolones. The acylated derivatives were chromatographed directly on a Nucleosil C₁₈ column without the necessity of further sample manipulation. Detector response for the N-acetyl derivatives of norfloxacin, ciprofloxacin, sarafloxacin, and temafloxacin was linear to at least 50 g/mL. The retention behavior of the N-acyl derivatives can be predicted by the length of the carbon chain of the amide.     

Reactivity of imidazolidin-4-one derivatives of primaquine: implications for prodrug design

In contrast to peptide-based imidazolidin-4-ones, those synthesized from N-(α-aminoacyl) derivatives of the antimalarial drug, primaquine and ketones are unexpectedly stable in pH 7.4 at 37 °C. The kinetics of hydrolysis of primaquine-based imidazolidin-4-ones were investigated in the pH range 0.3-13.5 at 60 °C. The hydrolysis to the parent α-aminoacylprimaquine is characterized by sigmoidal-shaped pH-rate profiles, reflecting the spontaneous decomposition of both unionized and protonated (at N-1) forms of the imidazolidin-4-one. The kinetically determined pK_a values are ca. 3.6-4.0, i.e., 4 pK_a units lower than those of amino acid amides, thus implying that hydrolysis of imidazolidin-4-ones at pH 7.4 involves the unionized form. Reactivity of this form decreases with the steric crowding of the amino acid α-substituent. In contrast, the rate constant for the spontaneous decomposition of the unionized form increases sharply for imidazolidin-4-ones derived from cyclic ketones, an observation that can be explained by the I-strain (internal strain) effect. These results are consistent with a mechanism of hydrolysis involving an S_N1-type unimolecular cleavage of the imidazolidin-4-one C2-N3 bond with departure of an amide-leaving group. The mechanism for the decomposition of the protonated imidazolidin-4-one is likely to involve an amide-carbonyl oxygen protonated species, followed by the C2-N3 bond scission, as supported by computational studies. The results herein presented suggest that imidazolidin-4-ones derived from simple N-alkyl α-aminoamides are too stable and therefore, may be useful as slow drug release prodrugs.     

Cation complexation behavior of pyrene- and anthracene-appended new crown ether derivatives

Pyrene- and anthracene-appended new crown ether derivatives have been synthesized by Schiff's base reaction, and cation complexation behavior was investigated by fluorescence spectroscopy measurements. Based on photo-induced electron transfer and intramolecular charge transfer mechanism, the host molecules emit stronger fluorescence in the presence of various cations Na(+), K(+), Rb(+), Cs(+) and NH(4)(+) since the complexation between guest cations and crown ether compounds inhibit partial electron transfer from the nitrogen atom to the chromophores and subsequently fluorescence is enhanced. The binding constants were estimated from the plots of the fraction of binding sites filled for crown ether compound as a function of free-ion concentration. Results show that 15-crown-5 derivatives exhibit higher binding ability with sodium cations while 18-crown-6 derivatives had higher affinity for potassium cations, which is consistent with the hole-size relationship of the crown ethers. Ammonium ion complexation caused largest fluorescence enhancement. It is understood that ammonium ion cannot only complex with crown ether, but also interact directly with the lone pair electrons of nitrogen atom in C=N bond so that electron transfer from the nitrogen atom to chromophores is further inhibited.     

Mild and nonracemizing conditions for Ullmann-type diaryl ether formation between aryl iodides and tyrosine derivatives

CuI/N,N-dimethylglycine-catalyzed coupling reaction of L-tyrosine derivatives and L-phenylalanine-derived iodides in the presence of Cs2CO3 works at 90 degrees C to provide the corresponding diaryl ether. Partial racemization occurs when N-Boc- and N-Cbz-protected aromatic amino esters are used, while N-trityl- and N,N-dibenzyl-protected aromatic amino esters give rise to coupling products without loss of optical purity. Little racemization is also observed in cases of N-Boc- and N-Cbz-protected aromatic amino acids as substrates. But their reaction yields are moderate. On the basis of these studies, shorter protocols for assembling (S,S)-isodityrosine and K-13 are developed.     

新型磁性分子印迹聚合物的制备及其在氟喹诺酮类抗生素检测中的应用

建立了磁性分子印迹聚合物固相萃取与高效液相色谱联用同时检测环境水中4种氟喹诺酮类抗生素的研究方法。分别利用扫描电子显微镜、透射电子显微镜、X-射线衍射、傅里叶红外光谱、振动样品磁强计对合成的磁性分子印迹聚合物进行表征,对影响吸附实验的参数（包括吸附剂用量、吸附和解析时间、洗脱液种类、样品pH值）进行了考察和优化。在最佳的实验条件下,4种氟喹诺酮类抗生素的方法检出限为4.1~21.3 μg/L,方法定量限为13.7~71.0 μg/L,样品加标回收率为70.6%~103.6%。该方法快速、灵敏,能够满足环境水样中氟喹诺酮类抗生素的残留检测要求。     

Development of a capillary zone electrophoresis-electrospray ionisation tandem mass spectrometry method for the analysis of fluoroquinolone antibiotics

The applicability of a capillary zone electrophoresis–electrospray ionisation tandem mass spectrometric (CZE–ESI-MS–MS) method for the separation of nine fluoroquinolones was investigated. Method optimisation involved systematic trouble-shooting starting with the type and duration of capillary pre-washing and conditioning, the choice of both the CE run buffer, MS sheath liquid, CE run potential, ESI spray voltage, sheath gas flow-rate, MS capillary voltage and CE capillary and MS capillary temperatures. Another extremely important factor was found to be the degree to which the CE capillary protrudes into the ESI chamber as well as whether or not sheath gas and spray voltage are employed during the CE injection or not. The importance of the latter has, to our knowledge, not been addressed elsewhere. Nine fluoroquinolones have been separated and detected in a single run by this technique.     

Simultaneous separation of five fluoroquinolone antibiotics by capillary zone electrophoresis

A chiral separation method for glycidol enantiomers determination by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry was developed. Two chiral stationary phases, amylose tris-(3,5-dimethylphenylcarbamate) (Chiralpak AD-H) and (S)-indoline-2-carboxylic acid and (R)-1-(α-naphthyl) ethylamine (SUMICHIRAL OA-4900) have been investigated. The effects of the mobile phase composition, elution program and column temperature were also studied. Under the best conditions: Chiralpak AD-H column, mobile phase composition n-hexane:ethanol (70:30, v/v), flow rate of 0.8 mL/min and 40 °C column temperature, a good resolution (Rs = 1.6) for both enantiomers has been achieved with an analysis time of 16 min. The method was found to be linear in the range from 100 to 500 ppm for both glycidol enantiomers with a good determination coefficient (r² higher than 0.99) and good precision. Limits of detection of 31 and 50 ppm for (R)-(+)-glycidol and (S)-(−)-glycidol, respectively, were obtained. The method was applied to the determination of the enantiomeric excess and yield obtained in a asymmetric epoxidation process of allyl alcohol with a chiral titanium-tartrate complex as catalyst.     

Polymethacrylate microparticles covalently functionalized with an ionic liquid for solid-phase extraction of fluoroquinolone antibiotics

Microparticles were synthesized by suspension copolymerization of the synthetic ionic liquid (IL) 1-allyl-3-methyl-imidazolium bromide with ethylene glycol dimethacrylate. The particles have a regular spherical shape and an average diameter of 65 ± 24 μm. Their affinity for the fluoroquinolone antibiotics ofloxacin (OFL), lomefloxacin (LOM) and ciprofloxacin (CIP) is much higher than that of the blank polymer (not containing an IL), of polymers using methacrylic acid as functional monomer, of hydrophilic-lipophilic balanced sorbents, and of C₁₈ sorbents. The microparticles were applied to the solid-phase extraction and rapid preconcentration of the fluoroquinolones from urine which then were quantified by HPLC. The calibration plot covers the 0.05 to 20 μg mL⁻¹ concentration range, and the average recoveries at three spiking levels range from 93.6 to 103.7 %, with RSD of ≤5.7 %. The method was successfully applied to the determination of fluoroquinolones in spiked urine.

Microparticles covalently functionalized with an ionic liquid ([Amim][Br]) were synthesized by suspension copolymerization and show higher affinity for fluoroquinolones than other sorbents. The microparticles were used as a sorbent for solid-phase extraction and preconcentration of three fluoroquinolones from urine.

     

Water-compatible molecularly imprinted polymer for the selective recognition of fluoroquinolone antibiotics in biological samples

A novel water-compatible molecularly imprinted polymer (MIP), prepared with enrofloxacin (ENR) as the template, has been optimised for the selective extraction of fluoroquinolone antibiotics in aqueous media. The results of a morphological characterisation and selectivity tests of the polymer material for ENR and related derivatives are reported. High affinity for the piperazine-based fluoroquinolones marbofloxacin, ciprofloxacin, norfloxacin and ofloxacin was observed, whereas no retention was found for nonrelated antibiotics. Various parameters affecting the extraction efficiency of the polymer have been optimised to achieve selective extraction of the antibiotics from real samples and to reduce nonspecific interactions. These findings resulted in a MISPE/HPLC-FLD method allowing direct extraction of the analytes from aqueous samples with a selective wash using just 50% (v/v) organic solvent. The method showed excellent recoveries and precision when buffered urine samples fortified at five concentration levels (25–250 ng mL⁻¹ each) of marbofloxacin, ciprofloxacin, norfloxacin, enrofloxacin and sarafloxacin were tested (53–88%, RSD 1–10%, n = 3). Moreover, the biological matrix of the aqueous samples did not influence the preconcentration efficiency of the fluoroquinolones on the MIP cartridges; no significant differences were observed between the recovery rates of the antibiotics in buffer and urine samples. The detection limits of the whole process range between 1.9 and 34 ng mL^–1 when 5-mL urine samples are processed. The developed method has been successfully applied to preconcentration of norfloxacin in urine samples of a medicated patient, demonstrating the ability of the novel MIP for selective extraction of fluoroquinolones in urine samples.     

Spectroscopic properties of fluoroquinolone antibiotics in water-methanol and water-acetonitrile mixed solvents

The fluorescence properties of ofloxacin (OFL), norfloxacin (NOR) and flumequine (FLU) were studied in H2O-CH3OH and H2O-CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. The emission spectra of OFL and NOR were very sensitive to the composition of the solvents. In the Lippert-Mataga analysis of the steady-state fluorescence data of OFL and NOR, clear reverse solvatochromism was exhibited in both mixed solvents. This observation can be explained by the twisted excited-state intramolecular charge transfer, which is accelerated by water. Theoretical treatments further support these results. The radiative and nonradiative rate constants were analyzed as a function of solvent dipolarity-polarizability (pi*) and hydrogen-bond donor acidity (alpha). These results were well consistent with the suggested mechanism of the excited-state chemical process of OFL and NOR, which depended upon the solvent-solute interactions such as bulk dielectric effects and specific hydrogen-bonding interactions. However, the influence of dielectric effects was more significant. The solvent structures of H2O-CH3CN and the preferential solvation by water were also examined. The emission spectra of FLU do not exhibit any characteristic responses to the properties of the environment.