Search

Some organic compounds form hydrates in eluents under the conditions of reversed-phase high-performance liquid chromatography (RP HPLC). For some of them, variation of water to the organic solvent ratio in an eluent may influence the ratio of hydrated and non-hydrated forms of analytes, X + nH2O ⇄ X·nH2O, which complicates the relations of their chromatographic retention. To reveal the formation of such hydrates, the recurrent approximation of their retention parameters is recommended, tR(C + ΔC) = atR(C) + b (*), where ΔC = const is the concentration increment of an organic modifier in an eluent, and a and b are coefficients calculated by the least-squares method. If an analyte exists in a hydrated or non-hydrated form only, the correlation coefficients (R) of equation (*) exceed 0.999. If the reversible formation of hydrates takes place within the concentration range Cmin to Cmax, it leads to distortion of linear dependence (*) and to deviations of some data points from regression lines (R < 0.999). One of the structural factors responsible for the reversible formation of hydrates is the presence of polar sulfonamide group –SO2NRR' in a molecule. To confirm this, a series of N-substituted p-toluenesulfonamides were synthesized and characterized. However, the nonlinearity of recurrences (*) is observed only for acetonitrile-containing eluents. [ABSTRACT FROM AUTHOR]

A single robust reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed and validated as per International Conference on Harmonization guidelines for the accurate quantification of curcuminoids in commercial turmeric products, Ayurvedic medicines, and nanovesicular systems. The proposed chromatographic method was found to be specific, linear (r2 ≥ 0.999), precise at intra- and inter-day levels (percentage relative standard deviation <2.0%), accurate (percentage recovery 99.14–102.29%), and robust. The limits of detection and quantification were found to be 7.40 and 24.70 ng mL−1for curcumin, 9.24 and 30.80 ng mL−1for demethoxycurcumin, and 6.48 and 21.61 ng mL−1for bisdemethoxycurcumin, respectively. Among different commercial turmeric products and Ayurvedic medicines tested, the contents of curcumin (3.54 ± 0.06–25.8 ± 0.08 mg g−1), demethoxycurcumin (1.28 ± 0.02–9.97 ± 0.03 mg g−1), and bisdemethoxycurcumin (0.50 ± 0.01–5.97 ± 0.01 mg g−1) varied significantly. The developed method was effectively applied to the determination of encapsulation efficiency of curcuminoids (ranged between 84.33 ± 3.50 and 96.59 ± 2.53%) in the nanovesicular systems. In conclusion, the reported method is suitable for the analysis of curcuminoids in a wide variety of turmeric products and used for the quality control of products that contain curcuminoids. [ABSTRACT FROM PUBLISHER]

This paper investigates correlations between the standard chromatographic parameter, log kw, obtained experimentally (classical thermodynamic) and obtained through the use of quantitative structure-retention relationships (QSRR) models (extrathermodynamic approach). QSRR models were created using descriptors from calculation chemistry, selected a priori on the basis of chemical intuition. Four modern analytical columns (packed with C18), often used in pharmaceutical analysis, were selected for the study. The simple extrathermodynamic model was demonstrated to be superior in terms of retention description with relation to rather complex models based on thermodynamic hermeneutics. However, all the QSRR equations derived are of limited predictive value as regards prediction of retention on the basis of the structure of the analyte. Nonetheless, they allow the differentiation of mechanism of separation operating on individual tested stationary phases. The descriptors, which are most significant in QSRR equations, appear to characterize better the net effect of interactions of the analytes with the stationary phases and the mobile phase containing acetonitrile as compared to the HPLC systems comprising methanol. These observations suggest that retention properties of new stationary phases studied in this work differ. [ABSTRACT FROM PUBLISHER]

The integration of physicochemical profiling screens such as Log P into natural products drug discovery programs is emerging as an approach to front-load drug-like properties of natural product libraries for high-throughput screening. In this study a fast-gradient HPLC method using a polystyrene-divinylbenzene PRP-1 column was developed to estimate the lipophilicity of marine natural products. An excellent correlation was found between the results of the experimental determined and the literature log P values for a diverse set of commercially available drugs using the PRP-1 column. The log P of a series of 24 marine natural products were evaluated using the new method and a good correlation was observed between the experimentally determined and software calculated log P values. Some discrepancies were observed between the measured value of log P and the software calculations of the natural products containing halogens atoms. The method is rapid, insensitive to impurities, and requires very little compound and is amenable for integration into a natural products drug discovery research program. [ABSTRACT FROM AUTHOR]

A simple isocratic reversed-phase high performance liquid chromatographic (HPLC) method was developed for the determination of 2-(4-isobutylphenyl) propionic acid and its major impurity 4-isobutylacetophenone in a gel formulation. The chromatographic separation was achieved with sodium phosphate buffer (pH 3.0) and methanol (40:60, v/v) as mobile phase, a ChromSpher C18 column (100 mm×3 mm and 5 µm), and UV detection at 220 nm. The analysis time was less than 10 min. The method was validated with respect to linearity, range, precision, accuracy, specificity, and robustness. The calibration curves showed good linearity over the concentration range of 0.10-80 µg/mL. The correlation coefficients were ≥0.9997 in each case. The RSD values for intra- and inter-day precision studies were less than 0.50%. The procedure described here is simple, selective, and is suitable for routine quality control analysis. [ABSTRACT FROM AUTHOR]

HPLC provides a user's friendly, rapid, and compound sparing methodology, which is successfully applied to determine drug lipophilicity. Under suitable chromatographic conditions isocratic and extrapolated retention factors correlate well with octanol-water partition or distribution coefficients. The present review provides an overview of the stationary and mobile phases, which are preferably used for lipophilicity assessment mainly in the case of basic compounds. Difficulties raised by the interference of silanophilic interactions in the partition mechanism, and the ways proposed to face this problem are discussed. Attention has been given to the extrapolation procedure and the standardization of conditions to obtain 1:1 correlation between extrapolated retention factors and logP or logD. Other chromatographic indices encoding information on the lipophilic behavior are briefly presented. A separate section refers to recent advances in IAM Chromatography, its similarities/dissimilarities with reversed phase HPLC and the octanol-water system, as well as its potential to mimic specific interactions with phospholipids. [ABSTRACT FROM AUTHOR]

A simple isocratic reversed-phase high performance liquid chromatographic (HPLC) method was developed for the determination of 2-(4-isobutylphenyl) propionic acid and its major impurity 4-isobutylacetophenone in a gel formulation. The chromatographic separation was achieved with sodium phosphate buffer (pH 3.0) and methanol (40:60, v/v) as mobile phase, a ChromSpher C18 column (100 mm×3 mm and 5 µm), and UV detection at 220 nm. The analysis time was less than 10 min. The method was validated with respect to linearity, range, precision, accuracy, specificity, and robustness. The calibration curves showed good linearity over the concentration range of 0.10-80 µg/mL. The correlation coefficients were ≥0.9997 in each case. The RSD values for intra- and inter-day precision studies were less than 0.50%. The procedure described here is simple, selective, and is suitable for routine quality control analysis. [ABSTRACT FROM AUTHOR]

A comparison of various presentation forms of retention parameters measured in multi‐step gradient elution regimes in reversed phase HPLC indicates that retention indices in the scale of n ‐alkyl phenyl ketones (so‐called Smith′s RI system) have the maximal reproducibility. However, the determination of these parameters for most hydrophilic compounds eluted before the first reference acetophenone (RI=800) implies their calculation by extrapolation, that can lead to the high irreproducibility of results, especially in regimes with initial isocratic stages followed by fast gradient elution. This fact explains the necessity of elaboration of a new calculation method based on the extrapolation of retention concentrations, which provides the appropriate interlaboratory coincidence of RI values at least within the range 600–800 i.u. Using this algorithm, retention indices for about 60 phenolic compounds have been determined, that permits us to identify them in complex mixtures of natural plant's extractive substances using HPLC without corresponding reference samples. [ABSTRACT FROM AUTHOR]

The collagen family is a diverse group of proteins distinguished by a native triple-helical structure. The collagen triple-helix is important for the integrity and workings of multiple connective tissues, including skin, bone, cartilage, tendon, and dentin. Most collagens assist in anchoring cells to the extracellular matrix and some function in cellular regulation. Multiple hereditary connective tissue diseases have been linked to collagen mutations. These mutations most often disrupt collagen folding. The very nature of the collagen family, one that is extensive, ubiquitous, abundant, well characterized, and responsible for various disease states, makes it a model protein family for intense proteomic studies. Proteomic analyses for triple-helical proteins may involve several different multidimensional approaches, such as two-dimensional liquid chromatography (2DLC), coupled liquid chromatography/capillary electrophoresis, and multidimensional protein identification technique (MudPIT) that couples 2DLC with mass spectrometry (MS). Following analysis, collagen and collagen-like proteins may be further characterized by expression of collagen and/or synthesis of triple-helical peptides (THPs) incorporating collagen sequences of interest. Collagen structure–function relationships have been well established by combined proteomic approaches. [ABSTRACT FROM AUTHOR]