Cevdet Akbay

Antimicrobial Activity of Some Thiourea Derivatives and Their Nickel and Copper Complexes

Five thiourea derivative ligands and their Ni2+ and Cu2+ complexes have been synthesized. The compounds were screened for their in vitro anti-bacterial activity using Gram-positive bacteria (two different standard strains of Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Streptococcus pyogenes, Bacillus cereus) and Gram-negative bacteria (Esherichia coli, Pseudomonas aeruginosa, Enterobacter cloacae, Proteus vulgaris, Enterobacter aerogenes) and in vitro anti-yeast activity (Candida albicans, Candida krusei, Candida glabrata, Candida tropicalis, Candida parapsilosis). The minimum inhibitory concentration was determined for all ligands and their complexes. In vitro anti-yeast activity of both ligands and their metal complexes is greater than their in vitro anti-bacterial activity. The effect of the structure of the investigated compounds on the antimicrobial activity is discussed.

Electrokinetic chromatography of twelve monomethylbenz(a)anthracene isomers using a polymerized anionic surfactant

A method for the separation of twelve monomethyl‐substituted benz[a]anthracene isomers using poly‐(sodium undecylenic sulfate) (poly‐SUS) surfactant by means of electrokinetic capillary chromatography (EKC) is described. Several parameters such as concentration of acetonitrile (ACN), pH, as well as applied voltage were studied to optimize the EKC separation. ACN at a concentration of 35% v/v, 12.5 mM phosphate‐borate buffer, 30 kV with 0.5% w/v poly‐SUS at a pH of 9.5 provided a resolution of a mixture of nine out of twelve methylbenz[a]anthracene (MBA) isomers in 50 min. The results of this study suggest that molecular length of MBA rather than length‐to‐breath ratio plays an important role in the elution order of some isomers.

Cationic gemini surfactants as pseudostationary phases in micellar electrokinetic chromatography. Part I: Effect of head group

Two cationic gemini surfactants with pyrrolidinium or alkyl ammonium head groups with but-2-yne spacers, but with the same length hydrocarbon chain have been characterized with respect to their aggregation behaviors and separation power as pseudostationary phases (PSPs) for micellar electrokinetic chromatography (MEKC). They were compared with a commonly used PSP, sodium dodecylsulfate (SDS). The results suggest that the head groups of the surfactants have some effect on physicochemical properties such as critical micelle concentration (CMC), C(20), gamma(CMC), partial specific volume, methylene selectivity and mobilities of the surfactants. CMC values of G1, G2 and SDS in pure water were found to be 0.82, 0.71, and 8.08 mM, respectively; they were reduced to 0.21, 0.11, and 3.0 mM when measured in 10 mM phosphate buffer at pH 7.0. G1 (alphaCH2 = 2.74) and G2 (alphaCH2 = 2.48) provided the most and the least hydrophobic environment, respectively. According to their partial specific volumes, geminis were found to have more flexible structures as compared with sodium dodecylsulfate. The effects of the head group structure were also characterized with the linear solvation energy relationship (LSER) model, which was able to evaluate the role of solute size, polarity/polarizability, and hydrogen bonding on retention and selectivity. The cohesiveness, hydrogen bond acidic and basic character of the surfactant systems were found to have the most significant influence on selectivity and MEKC retention of the gemini surfactants. It should be noted that with their large positive coefficient a values, G1 and G2 were found to be stronger HB acceptors than anionic and most of the cationic surfactants studied in the literature.

Separation of monomethyl-benz[a]anthracene isomers using cyclodextrin-modified electrokinetic chromatography

Cyclodextrin-modified electrokinetic chromatography (CD-EKC) was investigated for the separation of 12 monomethylbenz[a]anthracene (MBA) isomers. Combined use of a polymeric surfactant, poly(sodium 10-undecenyl sulfate) (poly-SUS), with various types of neutral cyclodextrins (CDs) [beta-CD, gamma-CD, dimethyl-beta-CD (DM-beta-CD), trimethyl-beta-CD (TM-beta-CD) and hydroxypropyl-beta-CD (HP-beta-CD)] were successful in CD-EKC separation of the MBA isomers. Baseline resolution of 10 of the 12 isomers, except for 9-MBA and 2-MBA, was achieved with gamma-CD at pH 9.75. The beta-CD, gamma-CD, and beta-CD derivatives (DM-beta-CD, TM-beta-CD, HP-beta-CD) were found to have different resolution and selectivity. Additionally, the tR/t0 values of isomers were found to be dependent on the type and concentration of the CD additives. In general, tR/t0 values of MBA isomers decrease with an increase in the concentration of beta-CD derivatives, whereas the reversed was true when the concentrations of native beta-CD and gamma-CD were varied. The combination of 5 mM gamma-CD, 0.5% (w/v) poly-SUS, 35% (v/v) acetonitrile at a pH of 9.75 provided the best selectivity and resolution of the MBA isomers with a separation time of 110 min. However, the use of 30 mM DM-beta-CD under similar EKC conditions resulted in much faster separation (ca. 16 min) of 10 MBA isomers.

Binary mixed micelles of chiral sodium undecenyl leucinate and achiral sodium undecenyl sulfate: I. Characterization and application as pseudostationary phases in micellar electrokinetic chromatography

Sodium 10-undecenyl sulfate (SUS), sodium 10-undecenyl leucinate (SUL) and their five different mixed micelles at varied percent mole ratios were prepared. The critical micelle concentration (CMC), C(20), gamma(CMC), partial specific volume, methylene group selectivity, mobilities and elution window were determined using a variety of analytical techniques. These surfactant systems were then evaluated as novel pseudostationary phases in micellar electrokinetic chromatography (MEKC). As a commonly used pseudostationary phase in MEKC, sodium dodecyl sulfate (SDS) was also evaluated. The CMC values of SUS and SUL were found to be 26 and 16 mM, respectively, whereas the CMC of mixed surfactants was found to be very similar to that of SUL. The C(20) values decreased dramatically as the concentration of SUL is increased in the mixed micelle. An increase in SUL content gradually increased the methylene group selectivity making the binary mixed surfactants more hydrophobic. Linear solvation energy relationships (LSERs) and free energy of transfer studies were also applied to predict the selectivity differences between the surfactant systems. The cohesiveness and the hydrogen bond acidic character of the surfactant systems were found to have the most significant influence on selectivity and MEKC retention. The SUS and SDS showed the strongest while SUL showed the weakest hydrogen bond donating capacity. The basicity, interaction with n and pi-electrons of the solute and dipolarity/polarizability were the least significant factors in LSER model for the surfactant systems studied. Free energies of transfer of selected functional groups in each surfactant systems were also calculated and found to be in good agreement with the LSER data.

Characterization and application of molecular binary mixed molecular micelles of sodium 10-undecenyl sulfate and sodium N-undecenyl leucinate as pseudostationary phases in micellar electrokinetic chromatography.

Poly (sodium 10-undecenyl sulfate) (poly SUS), poly (sodium 10-undecenyl leucinate) (poly SUL), and their five molecular binary mixed micelles with varied SUS:SUL composition were prepared. The purity of these molecular micelles was confirmed by elemental analysis. Their partial specific volume, aggregation number, methylene selectivity, polarity, phase ratio, mobility, and elution window values were determined using a variety of analytical techniques. These molecular micelles were then evaluated as pseudostationary phases in micellar electrokinetic chromatography (MEKC) for separation of benzene derivatives with a wide range of chemical properties. Elemental analysis results reveal that the ratio of the two surfactants in the binary mixture does not change significantly during the polymerization process. Poly SUS was found to have the lowest partial specific volume and it increases gradually with an increase of SUL mole fraction. Poly SUL was found to provide the most hydrophobic environment for test solutes. Based on the retention results, the strength of interaction between the molecular micelles and the analytes was found to follow the following order: NHB>HBA>HBD. This order indicates that the hydrophobic interaction plays a major role in retention of benzene derivatives.

Study of chemical selectivity of molecular binary mixed micelles of sodium 10-undecenyl sulfate and sodium N-undecenyl leucinate using linear solvation energy relationships model.

Poly(sodium 10-undecenyl sulfate) (poly-SUS), poly(sodium N-undecenyl leucinate) (poly-SUL) and their five molecular binary mixed micelles with varied SUS:SUL composition were prepared and used as pseudostationary phases in micellar electrokinetic chromatography (MEKC). Linear solvation energy relationships (LSERs) model and free energy of transfer studies were used to characterize the retention behavior and the selectivity differences among the seven surfactant systems. System constant differences and regression models for varied benzene derivative compounds are used to establish the selectivity differences of the seven pseudostationary phases. The cavity formation and dispersion interaction (the v system constant) and the hydrogen-bonding acidity (the b system constant) of the surfactant systems were found to have the most significant influence on selectivity and MEKC retention. The molecular micelle with sulfate head group, poly-SUS, was found to be more hydrogen-bond acidic than the molecular micelle with leucinate head group, poly-SUL. The other system constants (a, s and e) have modest effect on the retention and selectivity of the benzene derivatives. The model intercept coefficients (c system constants), which are negative for all surfactant systems have unusually large values. The free energy changes of transfer for the functional groups studied have all negative values except phenol and benzyl alcohol. Selectivity differences between pseudostationary phases were also compared by plotting the log k values against each other and were found to agree well with LSER results.

Estimation of Octanol-Water Partition Coefficient Using Cationic GeminiSurfactants by Micellar Electrokinetic Chromatography

Micellar electrokinetic chromatography (MEKC) provides a simple and rapid approach for determining n-octanolwater partition coefficients (log Pow). A set of non-hydrogen bonding (NHB), hydrogen bond accepting (HBA) and hydrogen bond donating (HBD) benzene derivatives with known log Pow values was used as sample solutes. Two novel cationic gemini surfactants with different head groups were used as pseudostationary phases. Sodium dodecyl sulfate (SDS) was also used for comparison. Two approaches were applied for the determination of log Pow values: calibration curve and phase ratio. In calibration curve approach, the MEKC retention factors (log k) of six alkyl phenyl ketones were plotted against their literature log Pow values for constructing the calibration curve. Log Pow values of benzene derivatives were then determined from the slope and the y-intercept of the linear calibration line. In the phase ratio approach, total surfactant concentration, critical micelle concentration, partial specific molar volume and experimental log k values were utilized for estimation of the log Pow values. Both approaches provided comparable results for HBA solutes; however, the calibration curve approach and phase ratio approach were found to be more successful for NHB and HBD solutes, respectively. In general, gemini surfactants provided better estimated log Pow values for NHB and HBA solutes while SDS gave better values for HBD solutes.