Jolanta Flieger

Synthesis, characterization and preliminary anticonvulsant evaluation of some 4-alkyl-1,2,4-triazoles.

Designed and synthesized 4-alkyl-1,2,4-triazole-3-thione derivatives showed significant anticonvulsant activity, determined in the maximal electroshock-induced seizure (MES) test. The chemical structure of all new compounds was confirmed by spectral methods ((1)H NMR, (13)C NMR, IR, MS). A sensitive and selective method was elaborated for the determination of the anticonvulsant compounds levels in mice brain tissue, based on HPLC with diode array detector (DAD). Chromatographic tests showed that lack of anticonvulsant effect of two derivatives (15, 16) with long alkyl chains at N-4 position of the 1,2,4-triazole ring was due to the inability to cross the blood-brain barrier (BBB).

Simultaneous Densitometric Determination of Rifampicin and Isoniazid by High-Performance Thin-Layer Chromatography

High-performance thin-layer chromatography (HPTLC) on silica gel 60 F254 TLC plates, with ethyl acetate-methanol-acetone-acetic acid, 5 + 2 + 2 + 1, as mobile phase, has been used for simultaneous determination of rifampicin and isoniazid. Quantitative analysis was accomplished by UV-visible densitometric scanning.

Usefulness of reversed-phase HPLC enriched with room temperature imidazolium based ionic liquids for lipophilicity determination of the newly synthesized analgesic active urea derivatives

Lipophilicity of several novel analgesic active 1-(1-arylimidazolidyn-2-ylidyn)-3-arylalkyl urea derivatives has been estimated by the use of chromatographic method. The investigated compounds were analyzed by reversed-phase high performance liquid chromatography (RP-HPLC) using mixtures of methanol or acetonitrile and water with addition of imidazolium based room temperature ionic liquids varying in an anion chaotropicity as the mobile phases. The relationships between log k values vs. concentration of organic solvent was used for determination of the log k(w) values by extrapolation technique. The partition coefficients (log P) values were calculated by means of the Pallas 3.1.1.2. and Spartan 10.0 softwares and further correlated with log k(w) measured experimentally in classical organic-aqueous eluent system and systems modified with ionic liquids addition. It was found that log k(w) values measured in eluent system modified with butyl-methyl imidazoilum chloride correlate the best with the logarithm of partition coefficient calculated by Pallas software (log P(calc.)). Furthermore, it was found that the examined compounds form H-bonding with imidazoilum cation of modifiers improving the chromatographic peak parameters (the symmetry factor, the theoretical plates number) especially when ionic liquids anion was more chaotropic. Amphiphilic ionic liquid possessing longer alkyl chain substituent (OMIM BF(4)) can be considered as a new cationic surfactant. Micellar conditions improved separation selectivity of chloro- and methoxy substituted derivatives.

Identification of ionic liquid components by RP-HPLC with diode array detector using chaotropic effect and perturbation technique.

Sodium hexafluorophosphate, perchlorate and tetrafluoroborate were applied as the ion-pair reagents in reversed-phase chromatography of several imidazolium-based ionic liquids. The optimization of the retention was performed by changing the kind of organic modifier (methanol, acetonitrile), concentration and the kind of the ion-pair reagents in the mobile phase and the column kind (Zorbax SB-C18, Zorbax SB-Phenyl, Zorbax SB-CN, Zorbax SB-NH2 and Supelcosil LC-F). The selectivity of the proposed chromatographic systems according to the cation kind was compared on the basis of the resolution of ionic liquid mixture. The perturbation method was applied to identify the anion kind. The formation of ion-associated complexes between promethazine as counter-cation and chaotropic anions controlling their retention was confirmed.

Ionic liquids as surfactants in micellar liquid chromatography.

This paper is devoted to application of ionic liquids as surfactants in LC of organic compounds, derivatives of 1,4-thiosemicarbazides. According to HPLC requirements the most advantageous conditions such as transparency for ultraviolet light, low CMC, additional inorganic salt additives, and appropriate organic solvent were established. The CMC was determined using conductivity measurements. Suitability of two different stationary phases: RP-C18 and cyanopropyl bonded phase was examined under micellar conditions. Chosen ionic liquid surfactant was compared to common traditional amphiphilic reagent - SDS. Elaborated on chromatographic micellar conditions were tested as a pilot technique for prediction of distribution coefficients of organic analytes in ionic liquid-based aqueous two-phase system.

Usefulness of chaotropic salt additive in RP‐HPLC of organic nonionized compounds

New synthesized 1,4-disubstituted thiosemicarbazide derivatives were analyzed in the RP system, modified with the addition of salts; chaotropic (sodium hexafluorophosphate - Na PF(6)), cosmotropic (sodium phosphate - NaH(2)PO(4)), and neutral (NaCl) on Zorbax XDB C18 column. The effect of the eluent composition on the analytes retention (k), system efficiency (N), peak symmetry (A(s)), and LOD values were all examined and compared to unmodified organic-aqueous mobile phase system. It was established that eluent modified with chaotropic salts addition was also the most advantageous according to other peak parameters such as the theoretical plates numbers and asymmetry factors. The lower LOD values were achieved in comparison to unmodified organic-aqueous eluent system. Compatibility of lipophilicity parameters calculated by the use of computer software with experimental ones measured by RP-HPLC was also the best for chaotropic modified mobile phase. To explain the observed phenomena, molecular modeling was performed for chosen representative compound in different environment representing examined mobile phase composition.

IONIC LIQUIDS AS MOBILE PHASE ADDITIVES IN REVERSED-PHASE HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

Ionic liquids are compounds of salt structure with melting point below 100°C and even 25°C known as room temperature ionic liquids. They have been widely investigated as new nonmolecular solvents exhibiting a wide range of changing properties, in many fields of analytical chemistry. This work reports on the use of 1-butyl-3-methylimidazolium of varying anion chaotropicity as a mobile phase additive for separation and chromatographic behavior studies of acidic, basic, and amphoteric compounds in reversed-phase liquid chromatography on two hydrophobic columns: Zorbax XDB-C18 and Zorbax SB-Phenyl. Satisfactory separations are achieved by the use of carefully optimized chromatographic systems modified with ionic liquids’ additives. The retention mechanism involving molecular interactions between analytes and additives and partitioning process between mobile phase and interphase created during equilibration process are discussed.

Analysis of new potential anticonvulsant compounds in mice brain tissue by SPE/HPLC/DAD

This paper describes a novel reversed-phase high performance liquid chromatography (RP-HPLC) with photo-diode array detection (DAD) method for the determination of three new derivatives of 4-alkyl-5-(3-chlorophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione with different antiepileptic activity in the brains of mice treated with the doses of 300mgkg(-1) of body weight. Samples were prepared by solid-phase extraction (SPE) method using BAKERBOND™ spe Octadecyl (C(18)) and analyzed by the use of an isocratic elution mode over an Zorbax Extend-C18 column (150mm×4.6mm I.D., 5-μm, Agilent Technologies). The mobile phase consisted of 80% methanol (for compound TP-315) and 85% acetonitrile (for compound TP-321) for 80% 2-propanol (for TP-323) at a flow rate of 1.0mLmin(-1) and 0.5mLmin(-1) in the last case. Gradient elution mode was also proposed for all examined analytes in mixture with common antiepileptic drugs: carbamazepine, phenobarbital and phenytoin in view of possible synergistic activity. Photodiode-array investigations of the peaks after degradation studies indicate the stability of the compounds under conditions proposed for sample preparation procedure. Linear coefficients of correlation (r(2)) were >0.995 for all analytes. The proposed strategy gives extraction yields higher than 95% with the intra- and inter-day relative standard deviation lower than 3% and 5%, respectively. This method was applied to the analysis of brain tissue of mice treated with investigated compounds. Obtained results enable to explain the differences in their pharmacological activity.

Usefulness of the chaotropic effect in sample preparation for chromatographic analysis of acidic xenobiotics in human plasma

In this study a new RP-HPLC with photo-diode array detection method for the determination of ibuprofen ((RS)-2-(4-isobutylphenyl)propionic acid) in human plasma samples was developed. Samples were prepared by SPE and analyzed by an isocratic elution mode over a C18 column using 80% methanol. A novel sample pretreatment method, based on the addition of ionic liquids possessing chaotropic ions to small human plasma sample (100 μL), was elaborated. 1-Butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4 ) were tested from the point of view of extraction yield. Quantification was based on calibration curve applying diclofenac as the internal standard. Owing to dilution of plasma sample by 2 mM aqueous solution of BMIM BF4 before SPE, appropriate sample purification and extraction yields higher than 95% with precision lower than 2% can be achieved. Linear coefficients of correlation (r(2)) were >0.99 in the range of 0.3-5 μg/mL ibuprofen concentration in plasma. The limit of quantification was 65 ng/mL and the detection limit for ibuprofen was 19.5 ng/mL.

Micropreparative Isolation of Cu(II) Complexes of Isoniazid and Ethambutol and Determination of their Structures

We report the chromatographic behavior of the antitubercular drugs isoniazid (INH), pyrazinamide (PYR), ethambutol (ETB), and p-aminosalicylic acid (PAS) in reversed-phase TLC with organic aqueous mobile phases modified with Cu(II) chloride. The spectra of the free ligands and complexes formed during chromatography were measured densitometrically by use of a scanner equipped with a diode-array detector and compared in the range 200-700 nm. The complexes of Cu(II) with isoniazid and ethambutol were isolated on a micropreparative scale. The structures of the INH-Cu and EMB-Cu complexes were analyzed by electron paramagnetic resonance (EPR) spectroscopy and illustrated graphically by molecular modeling using GaussView software.