Determination of the lipophilicity (logPo/w) of organic compounds by microemulsion liquid chromatography

Binding studies of synthetic cathinones to human serum albumin by high-performance affinity chromatography

The binding affinity to human serum albumin (HSA) of a series of fourteen synthetic cathinones, new psychoactive substances widely abused, was investigated by high-performance affinity chromatography (HPAC). Zonal elution experiments were conducted to measure the retention times of each synthetic cathinone on an HSA column, which enabled the calculation of the percentage of the drug bound. For some synthetic cathinones, enantioselectivity on HSA was found. To gather information on the HSA binding sites and better understand the chiral recognition mechanisms, enantioresolution of selected cathinones was carried out at a milligram scale through liquid chromatography (LC) with carbamate polysaccharide-based columns. This work was followed by zonal displacement chromatography using known competitors with specific binding sites on HSA, namely (S)-ibuprofen and warfarin. Competition was observed between the tested drugs and both competitors (except for pentedrone with warfarin), which is consistent with an allosteric competition involving a non-cooperative binding mechanism.

A periodic table for liquid chromatography separation modes

The increasing trend for non-expert users to undertake analytical measurements using an expanding range of chromatographic approaches can lead to the use of unsuitable separation methods and the generation of poor-quality data. Technical Brief AMCTB No. 107 introduced liquid chromatography and guidance on selection of the appropriate separation modality. This publication aims to provide a quick and easy to use educational tool for optimizing the mode of liquid chromatographic separation. It will be of value to both expert and non-expert users across the natural, life and physical sciences.

Fatty acids-based microemulsion liquid chromatographic determination of multiple caffeoylquinic acid isomers and caffeic acid in honeysuckle sample

A green and efficient microemulsion liquid chromatographic (MELC) method using fatty acid as co-surfactant and electrochemical detection was established and validated for the determination of four caffeoylquinic acid isomers and caffeic acid in honeysuckle samples. The influences of each individual component within the isocratic oil-in-water (O/W) microemulsion mobile phase were systematically investigated, such as the type and concentration of co-surfactant, concentration of sodium dodecyl sulphate (SDS), organic modifier addition, type and concentration of oil phase, pH and detection voltage. Results indicated that excellent resolution was achieved using 3.0% w/v of propionic acid, 0.5% w/v of ethyl acetate, 1.0% w/v of SDS, 5% w/v acetonitrile, 90.5% v/v of water and 25 mM sodium dihydrogen phosphate at pH = 3 as microemulsion mobile phase and 0.8 V as the optimal voltage value. Under the optimal condition, analytical performance of developed method was evaluated. The detection limits were below 17.3 ng/mL and intra-day and inter-day precisions by relative standard deviations (RSD%) were between 0.5% and 3.6%. Satisfactory recovery (in the range of 83.8-109.1%) with good repeatability lower than 4.7% (n = 3) was obtained. Therefore, the developed O/W MELC method was rapid, precise and accurate for simultaneous determination of neochlorogenic acid, chlorogenic acid, isochlorogenic acid A and isochlorogenic acid C in honeysuckle samples, with contents of 2.6, 28.7, 18.1 and 5.2 mg/g, respectively.

Modulation of retention and selectivity in oil-in-water microemulsion liquid chromatography: A review

Microemulsions (MEs) are stable, isotropically clear solutions consisting of an oil and water stabilized by a surfactant and a co-surfactant. Oil-in-water microemuslion liquid chromatography (MELC) is a relatively new chromatographic mode, which uses an O/W ME as mobile phase. Retention, selectivity and efficiency can be modified by changing the concentration of the ME components and the ratio between the aqueous and oil phases. This work makes a critical survey on the information found in the literature about the mobile phase compositions that lead to the creation of successful O/W ME mobile phases, as well as the effect of pH for ionizable compounds and temperature. The viability of performing the analyses using isocratic and gradient elution is also considered. The complexity of the composition of a successful ME, and the fact that the different factors interact each other, may require many manipulations during method development to achieve an acceptable separation for complex mixtures. This is the reason of the proposal from several authors of a standard ME as starting point when developing a method for a new separation with no previous reports. Based on these initial conditions, the interest of several authors in applying computer-assisted approaches to optimize the composition of ME mobile phases, and reduce significantly the time and reagent consumption for method development, is described. Some practical tips are given to prepare stable ME mobile phases that yield reproducible results.

Consensus-based comparison of chromatographic and computationally estimated lipophilicity of benzothiepino[3,2-c]pyridine derivatives as potential antifungal drugs

Lipophilicity is one of the essential properties influencing drug absorption, excretion and metabolism. It is used for screening viable drug candidates. Chromatographic behavior of thiepino[3,2-c:6,7-c']dipyridine and 16 benzothiepino[3,2-c]pyridine derivatives as potential antifungal drugs was studied using thin-layer chromatography under typical reversed-phase conditions and two microemulsion chromatographic systems. Seventeen chromatographic and nine in silico lipophilicity measures were estimated. They were compared by classical multivariate approaches: principal component analysis, hierarchical cluster analysis, and ranked and grouped by the non-parametric method-Sum of ranking differences. Two computational and two chromatographic descriptors from the typical reversed-phase conditions using acetone/water mixtures emerged as the best candidates for lipophilicity estimation. The principal component scores related to typical reversed-phase conditions using dioxane/water were ranked as statistically insignificant (the worst). Microemulsion systems were positioned in between, performing worse than in silico estimates. Thiepine derivatives were ranked and grouped by sum of ranking differences, fusing multiple lipophilicity measures. In multicriteria maximization ranking, the compound substituted by phenyl group at position 8 was selected as the most lipophilic one. It is also the most active against Candida albicans. The ranking confirmed that introduction of phenyl core is essential for increasing the lipophilicity of the studied compounds.

Multivariate assessment of lipophilicity scales-computational and reversed phase thin-layer chromatographic indices

Needs for fast, yet reliable means of assessing the lipophilicities of diverse compounds resulted in the development of various in silico and chromatographic approaches that are faster, cheaper, and greener compared to the traditional shake-flask method. However, at present no accepted "standard" approach exists for their comparison and selection of the most appropriate one(s). This is of utmost importance when it comes to the development of new lipophilicity indices, or the assessment of the lipophilicity of newly synthesized compounds. In this study, 50 well-known, diverse compounds of significant pharmaceutical and environmental importance have been selected and examined. Octanol-water partition coefficients have been measured with the shake-flask method for most of them. Their retentions have been studied in typical reversed thin-layer chromatographic systems, involving the most frequently employed stationary phases (octadecyl- and cyano-modified silica), and acetonitrile and methanol as mobile phase constituents. Twelve computationally estimated logP-s and twenty chromatographic indices together with the shake-flask octanol-water partition coefficient have been investigated with classical chemometric approaches-such as principal component analysis (PCA), hierarchical cluster analysis (HCA), Pearson's and Spearman's correlation matrices, as well as novel non-parametric methods: sum of ranking differences (SRD) and generalized pairwise correlation method (GPCM). Novel SRD and GPCM methods have been introduced based on the Comparisons with One VAriable (lipophilicity metric) at a Time (COVAT). For the visualization of COVAT results, a heatmap format was introduced. Analysis of variance (ANOVA) was applied to reveal the dominant factors between computational logPs and various chromatographic measures. In consensus-based comparisons, the shake-flask method performed the best, closely followed by computational estimates, while the chromatographic estimates often overlap with in silico assessments, mostly with methods involving octadecyl-modified silica stationary phases. The ones that employ cyano-modified silica perform generally worse. The introduction of alternative coloring schemes for the covariance matrices and SRD/GPCM heatmaps enables the discovery of intrinsic relationships among lipophilicity scales and the selection of best/worst measures. Closest to the recommended logKOW values are ClogP and the first principal component scores obtained on octadecyl-silica stationary phase in combination with methanol-water mobile phase, while the usage of slopes derived from Soczewinski-Matyisik equation should be avoided.

Towards better understanding of lipophilicity: assessment of in silico and chromatographic logP measures for pharmaceutically important compounds by nonparametric rankings

Lipophilicity is one of the most frequently used physicochemical properties that affects compound solubility, determines its passive transport through biological membranes, influences biodistribution, metabolism and pharmacokinetics. We compared, ranked and grouped chromatographic lipophilicity indices and computationally estimated logP-s by sensitive and robust non-parametric approaches: sum of ranking differences (SRD) and generalized pairwise correlation method (GPCM). Chromatographic indices of fourteen neurotoxins and twenty one 1,2,4-triazole compounds have been derived from typical reversed-phase thin-layer chromatography and micellar chromatography. They were compared with in silico estimated logP-s. Under typical reversed-phase conditions, octadecyl-, octyl-, and cyanopropyl-modified silica have clear advantage over ethyl-, aminopropyl-, and diol-modified beds, i.e., the preferable choice of the stationary phase follows this order: octadecyl>octyl>cyanopropyl>ethyl>octadecylwettable>aminopropyl>diol. Many of these indices outperform the majority of computationally estimated logP-s. Clear distinction can be made based on cross-validation and statistical tests. Oppositely, micellar chromatography may not be successfully used for the lipophilicity assessment, since retention parameters obtained from the typical reversed-phase conditions outperform the parameters obtained by micellar chromatography. Both ranking approaches, SRD and GPCM, although based on different background, provide highly similar variable ordering and grouping leading to the same, above mentioned conclusions. However, GPCM results in more degeneracy, i.e., in some cases it cannot distinguish the lipophilicity parameters whereas SRD and its cross-validated version can. On the other hand GPCM produces a more characteristic grouping. Both methods can be successfully used for selection of the most and least appropriate lipophilicity measures.