Simulation of chromatography of phenolic compounds with a computational chemical method

Quantitative Explanation of Basic Compound Retention Mechanisms in Reversed-Phase Mode Liquid Chromatography

The quantitative analysis of the chromatographic behavior of basic compounds measured with pentyl-, hexenyl-, and octyl-bonded silica gels were analyzed in silico employing model phases. The main retention force was the van der Waals (VW) interaction, and the main desorption force was an electrostatic (ES) interaction. The contribution of hydrogen bonding (HB) was weak compared to that for acidic compounds. The quantitative explanation was achieved utilizing the calculated VW, HB, and ES energy values obtained from a molecular mechanics program. The electron localization was observed at the molecular interaction-site calculated MOPAC program. This fundamental approach was like that of explaining chemical reactions. The difference was electron localization in chromatography or electron transfer in a chemical reaction.

Fundamental Properties of Packing Materials for Liquid Chromatography

The high performance of chemically-modified silica gel packing materials is based on the utilization of pure silica gels. Earlier silica gels used to be made from inorganic silica; however, nowadays, silica gels are made from organic silanes. The surface smoothness and lack of trace metals of new silica gels permits easy surface modifications (chemical reactions) and improves the reproducibility and stability. Sharpening peak symmetry is based on developing better surface modification methods (silylation). Typical examples can be found in the chromatography of amitriptyline for silanol testing and that of quinizarin for trace metal testing. These test compounds were selected and demonstrated sensitive results in the measurement of trace amounts of either silanol or trace metals. Here, we demonstrate the three-dimensional model chemical structures of bonded-phase silica gels with surface electron density for easy understanding of the molecular interaction sites with analytes. Furthermore, a quantitative explanation of hydrophilic and hydrophobic liquid chromatographies was provided. The synthesis methods of superficially porous silica gels and their modified products were introduced.

Effect of germination on composition profiling and antioxidant activity of the polysaccharide-protein conjugate in black soybean [Glycinemax (L.) Merr.]

Black soybeans are commonly consumed as health foods and used in traditional Chinese medicine, but they are rarely cultivated as edible sprouts. During germination, the composition of seeds undergoes distinct changes that cause variations in bioactivities. In this study, the water-soluble black soybean polysaccharide (BSPS) was isolated from sprouts harvested at two-day intervals during the first week of seedling growth. The chromatographic profiles of the BSPS in ungerminated seeds showed fraction 1 (F1, about 64kDa) and fraction 2 (F2, <1kDa) that degraded during germination. The polysaccharide in F1 fraction of ungerminated seeds was covalently associated with the protein and mainly contained arabinose, galactose, glucose, and galacturonic acid at various levels during germination. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) scavenging activities and the reducing power of F1 were highest on the seventh day of germination. The phenolic and flavonoid content significantly increased after the fifth day of germination, suggesting that these ingredients also contributed to the antioxidant activities. During long-term germination, the polysaccharide-protein conjugate in the F1 fraction with enhanced antioxidant activities is regarded as a potential natural antioxidant for the development of functional foods.

Memory-efficient fully coupled filtering approach for observational model building

Generally, training neural networks with the global extended Kalman filter (GEKF) technique exhibits excellent performance at the expense of a large increase in computational costs which can become prohibitive even for networks of moderate size. This drawback was previously addressed by heuristically decoupling some of the weights of the networks. Inevitably, ad hoc decoupling leads to a degradation in the quality (accuracy) of the resultant neural networks. In this paper, we present an algorithm that emulates the accuracy of GEKF, but avoids the construction of the state covariance matrix-the source of the computational bottleneck in GEKF. In the proposed algorithm, all the synaptic weights remain connected while the amount of computer memory required is similar to (or cheaper than) the memory requirements in the decoupling schemes. We also point out that the new method can be extended to derivative-free nonlinear Kalman filters, such as the unscented Kalman filter and ensemble Kalman filters.

Models and objective functions for the optimisation of selectivity in reversed-phase liquid chromatography

Interpretive methodologies are the most efficient tools for finding the optimal conditions in chromatography. These methodologies are supported by models or algorithms able to infer the system behaviour upon changes in the experimental factors. Once the models are built with data obtained from sets of carefully designed experiments, molecular modelling or other approaches, they can be applied to predict the performance of new conditions. The different elements involved in these methodologies, for both isocratic and gradient elution, are given. Special attention is devoted to the description of retention, owing to its major impact on the prediction of chromatographic resolution. Several models considering the main factors affecting retention (i.e. organic modifiers, pH and temperature), and procedures that enhance the predictions, are presented. Both the existence of skewed peaks and the effect of elution conditions on peak profiles are considered. Finally, the assessment of resolution, as well as other secondary aims that affect the practical suitability of the optimal conditions, is discussed.

Chromatography in silica, quantitative analysis of retention mechanisms of benzoic acid derivatives

A quantitative analysis of the retention of benzoic acid derivatives in reversed-phase liquid chromatography was achieved using a molecular mechanics calculation in the CAChe program. Interaction energy values were calculated for both molecular and ionic forms. The predicted retention factors of partially ionized acids obtained using a combination of dissociation constants well correlated with the values measured by reversed-phase liquid chromatography with pH-controlled eluents. The molecular interaction energy value was calculated by subtracting the energy value of the complex from the sum of energy values of a model-phase and an analyte.

Chromatography in silico, basic concept in reversed-phase liquid chromatography

Basic phenomena in reversed-phase liquid chromatography have been quantitatively analyzed using a computational chemical calculation. Pyridine interacted with an ionized silica surface under neutral conditions. Alkyl-chain length affected the contact surface area with an analyte. Steric hindrance was demonstrated using a model graphitic carbon phase and unsaturated alkenes. Quantitative structure-retention relationships in reversed-phase liquid chromatography were demonstrated for phenolic compounds and acidic and basic drugs. The correlations between predicted and measured retention factors were satisfactory. Dissociation constants were derived from the atom partial charge and used to predict retention factors of partially ionized compounds.