Toshihiko Hanai

Separation of polar compounds using carbon columns.

The objective of this review with 122 references is to provide structure and retention mechanisms of porous graphitic carbon by chromatographic analysis and computational chemical analysis of retention mechanisms. Synthesis methods of porous graphitic carbon are described. Applications for use as matrix for dynamic coating on porous graphitic carbon and direct separation of polar compounds on porous graphitic carbon demonstrated that the physical and chemical stability of graphitic carbons performed in both chromatography and extraction, especially for polar compounds, those are difficult on both silica-based and organic polymer-based packing materials. The disadvantage is difficult desorption of non-polar compounds adsorbed on the surface. The development of 3.5-microm particles improves the separation power of graphitic carbon columns with the high theoretical plate number.

Prediction of pKa values of phenolic and nitrogen-containing compounds by computational chemical analysis compared to those measured by liquid chromatography

The pKa values of 64 phenolic and 50 nitrogen-containing compounds were obtained by reversed-phase liquid chromatography and computational chemical calculation. The chromatographically obtained values of phenolic compounds were equal to pKa values from references and Hammetts equation, and those of nitrogen-containing compounds were lower than the reference values. It appeared difficult to calculate the properties of the ortho effect and nitro group by the computational calculation method. However, the calculation was simpler than selecting different constants of Hammetts equation for a variety of compounds.

Influence of glycosylation on the drug binding of human serum albumin

The influence of glycosylation on the drug binding of human serum albumin (HSA) was studied using HSA containing different amounts and degrees of glycosylated HSA. The drugs used were furosemide, naproxen, procaine, phenylbutazone, salicylic acid, sulphamethoxazole, tolbutamide and warfarin. The drug-HSA parameters (lognK) were measured by the ultrafiltration method, frontal analysis and a modified Hummel-Dreyer method. The modified Hummel-Dreyer method was the simplest method with high precision and required the smallest amounts of proteins. The lognK values were well correlated with the octanol-water partition coefficients; the correlation coefficients were over 0.95. The results suggested that hydrophobic interaction is the predominant force for the drug binding. The early stage of glycosylation of HSA did not significantly affect the drug-binding capacity. Generally, the binding affinity of HSA decreased, perhaps due to a conformational change or steric hindrance (except naproxen) when further glycosylation occurred.

Structure-retention correlation in liquid chromatography

The analysis of retention mechanisms and the prediction of retention time in liquid chromatography were examined by physico-chemical parameters. The basic parameters used for the calculation were the octanol—water partition coefficient (log P), the Van der Waals volume, the dissociation constant and Hammetts sigma constant. The log P values were calculated by Rekkers method and the Van der Waals volumes were calculated by Bondis method. The dissociation constants were calculated by the modified Hammetts equation. A method for the prediction of retention time in reversed-phase liquid chromatography is proposed and demonstrated from these calculated values and the retention was analysed by the measured enthalpy and proposed selectivity.

PREDICTION OF RETENTION FACTORS OF PHENOLIC AND NITROGEN-CONTAINING COMPOUNDS IN REVERSED-PHASE LIQUID CHROMATOGRAPHY BASED ON logP AND pKa OBTAINED BY COMPUTATIONAL CHEMICAL CALCULATION

The new logP values (NlogP) of phenolic and nitrogen-containing compounds based on the modified CAChe™ MOPAC calculation improved the correlation coefficient with measured logP values (MlogP) to 0.950 from 0.662 (n = 87). The best correlation coefficient was obtained between retention factors of their molecular form and NlogP values among NlogP, CAChe logP, MOPAC-BlogP, Rekker’s logP, Hansch’s logP, and MlogP. Correlation coefficients were 0.880 (n = 50) for phenolic compounds and 0.900 (n = 48) for nitrogen-containing compounds. The correlation coefficients between predicted and measured maximum retention factors were 0.883 (n = 50) for phenolic compounds and 0.891 (n = 48) for nitrogen-containing compounds. Addition of pka values predicted by partial charges of atoms calculated using CACheTM MOPAC to NlogP values could predict their retention factors in eluents at given pH. The correlation coefficient between predicted and measured retention factors of phenolic compounds at pH 8.49 was 0.927 (n = 20), and that of nitrogen-containing compounds at pH 4.0 was 0.833 (n = 45).

Chromatography of guanidino compounds.

Guanidino compounds involved in the urea and guanidine cycles have been found in serum of nephritic patients, and some guanidino compounds have been suspected to be uremic toxins. The simultaneous analysis of naturally occurring metabolites is important for diagnosis of diseases. In this review, liquid chromatographic analysis of natural metabolites of guanidino compounds are described. the information about arginine as a precursor of nitric oxide are included. The reports of pharmaceutical compounds having a guanidino group, peptides containing arginine and aminoglycosides are summarized in Table 1.

Development of Crude Drug Analysis by Liquid Chromatography, and UV and MS Spectrometers

Abstract The retention indeces of 42 standard compounds in naturally occurring drugs were studied in reversed-phase liquid chromatography. The effluent was monitores by a photodiode array detector and mass spectrometer. The spectra and the retention indeces were used for qualitative analysis of the crude extract components.

Liquid chromatography of guanidino compounds using a porous graphite carbon column and application to their analysis in serum

The retention mechanism of guanidino compounds on a porous graphitic carbon seemed to be mainly hydrophobic interaction, according to the retention factors in buffer solutions and the results of an analysis by computational chemical calculation using molecular mechanics (MM2). The baseline separation of ten guanidino compounds was achieved by the addition of a hydrophobic counterion. The retention mechanism may be dynamic ion-exchange. The stable system was applied to the analysis of guanidino compounds in serum from nephritic patients. The effluent was monitored by a post-column labeling detection method using ninhydrin. The detection limit of guanidino compounds was a few picomoles; however, that of creatinine was one hundredth of those of the other compounds. The reproducibilities of the peak height and area of the ten guanidino compounds using gradient elution were quite high, and the standard deviations were within a few percent (n=5), except for creatinine. The recovery of the compounds from serum was more than 90% (n=5). The reproducibility of retention times was within 1% (n=5).

Reversed-phase liquid chromatography on rigid vinyl alcohol copolymer gels

Abstract The selectivity and specificity of rigid vinyl alcohol copolymer gels in reversed-phase liquid chromatography were examined. The results were compared with those obtained on octadecyl-bonded silica gels. The selectivity for polyaromatic hydrocarbons was very weak compared with that of polystyrene gels but was stronger than that of octadecyl-bonded silica gels. The phenomenon was explained as the difference in the energy effects of the retention of some groups of compounds. The HETP of columns packed with the 9-μm gel was less than 0.02 mm.

Effect of enthalpy on retention in reversed-phase liquid chromatography

Abstract Retention in reversed-phase liquid chromatography has been found to be related to the Van der Waals volume, pi-energy and hydrogen-bonding energy effects. However, higher-molecular-weight compounds were retained more strongly than expected. In order to investigate this effect more fully, the retention times of phenols were measured on an octadecyl-bonded silica gel in acidic acetonitrile—water mixtures at different temperatures. The enthalpies of phenols were then calculated from their log k ′ values. The magnitude of the enthalpy effect increases with increasing molecular size, but the polarity of the molecule is the predominant factor in the enthalpy effect.