Potential role of formaldehyde in the mechanism of action of ascorbigens on the basis of BioArena studies

The effect of ascorbigen and 1′‐methylascorbigen as a model compound pair was studied on the phytopathogenic bacterium Pseudomonas savastanoi pv. phaseolicola in the BioArena experimental system after overpressured layer chromatography. Results showed a characteristic, strong antibacterial effect of 1′‐methylascorbigen and weak effect of ascorbigen present on the adsorbent layer as chromatographic spot. Addition of formaldehyde capture compounds (l ‐arginine, glutathione, dimedone) partially or totally reduced the antibacterial effect of 1′‐methylascorbigen and ascorbigen. On adding Cu(II) ions—which mobilize and coordinate formaldehyde—to the culture medium, the antibacterial effect of both compounds became stronger. It is supposed that the weak antibacterial effect of ascorbigen may have originated from the 1′‐methylascorbigen formed in situ on the adsorbent layer by partial enzymatic methylation of ascorbigen. Copyright © 2008 John Wiley & Sons, Ltd.     

Critical evaluation of experimental conditions influencing the surface-enhanced Raman spectroscopic (SERS) detection of substances separated by layer liquid chromatographic techniques

Summary Surface-enhanced Raman spectra (SERS) ofp-dimethylaminobenzylidenerhodanine have been recorded on silica gel 60 F₂₅₄ and Si60 F₂₅₄ Raman TLC plates. Spectra were enhanced by use of a silver sol prepared according to the modified Lee-Meisel procedure. The standard deviations of the intensities and the band ratios for the seven most intense peaks were calculated for 30 parallel measurements. Although the Raman plate gives more reproducible results, several experimental difficulties are encountered in the development of chromatograms. SERS detection of ascorbigen and 1′-methylascorbigen was performed after chromatography on silica gel 60 F₂₅₄ TLC and HPTLC plates and on Si60 F₂₅₄ Raman TLC plates. Traditional development was used for the silica gel 60 F₂₅₄ TLC plates and Si60 F₂₅₄ Raman plates, and the personal OPLC technique for the silica gel 60 F₂₅₄ HPTLC plates. It was found that the SERS spectrum gave information about the indole ring only. Because bonding of the analyte to the stationary phase results in a change in molecular conformation-in contrast with the behaviour of rhodanine-the type of the plateused and the development procedure employed can significantly influence the quality of the SERS spectrum. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary September 1–3, 1999     

Use of Reversed-Phase High-Performance Liquid Chromatography in QSAR Analysis of 2,4-Dihydroxythiobenzanilide Analogues

Abstract

Thiobenzanilides are found to show strong biological activity as antimicrobial, antimycotic, and tuberculostatic agents. In addition, they are relatively weakly toxic to higher organisms.

A large set of new (N-phenyl-)-2,4-dihydroxybenzenecarbothioamide derivatives was obtained. Preliminary studies showed high microbiological action of some of them. In the process of chromatographic analysis, several different chromatographic parameters were obtained. In case of RP-HPLC, these parameters correspond to hydrophobicity of the solute. Obtained chromatographic parameters exhibited moderate correlation with calculated log P parameter.

Linear dependence of bacteriostatic or fungostatic activity on lipophilicity was observed. The degree of correlation of different parameters was compared. The lipophilicity of analysed tioamides was the most important factor responsible for fungostatic and bacteriostatic activity. In comparison to methanol eluent system, chromatographic parameters obtained in acetonitrile system were better correlated with bioactivity. Conversely with the calculated log P values, the experimentally derived parameters exhibited significant higher correlation to fungostatic activity determined on dermatophytes. While in case of other tested microorganisms log P was comparably or sometimes slightly better correlated.     

Determination of indole-type phytonutrients in cruciferous vegetables

Abstract

Consumption of cruciferous vegetables has been associated with a low risk of developing cancer. Indole-type phytonutrients, derived from enzymatic hydrolysis of glucobrassicin, exhibit cancer-preventive properties and occur in all vegetables of the Brassicaceae family. A LC-Q-TOF-MS methodology was developed and applied in extracts from seven cruciferous vegetables allowing the rapid determination of indole-3-carbinol, indole-3-carbaldehyde, ascorbigen, indole-3-acetic acid and indole-3-acetonitrile. The novel method described herein, was validated and is characterized by low detection limits and excellent linearity. The simultaneous determination of indole-type phytonutrients in turnip and radish was performed for the first time.     

Synthesis of 1-N-(β-D-Glucopyranosyl)- and 1-N-(1-Deoxy-2,3,4,5,6-penta-O-acetyl-D-galactit-1-yl)ascorbigens

The 1-N-carbohydrate-containing ascorbigens 1-N-(-D-glucopyranosyl)ascorbigen and 1-N-(1-deoxy-2,3,4,5,6-penta-O-acetyl-D-galactit-1-yl)ascorbigen were synthesized.     

Ethylenediamine-Derived Chromatographic Ligand to Separate BSA,Lysozyme, and RNase A

Chromatography has become an essential tool for the purification of proteins, since most purification schemes involve some forms of this methodology. Recently, using chromatographic matrices prepared from symmetrical aminosquarylium cyanine dyes immobilized on Sepharose via a central alkylamino residue, we were able to isolate lysozyme, α-chymotrypsin and trypsin from a mixture. Following this, we envisioned that the immobilization of an asymmetric squarylium dye bearing an N-carboxyethyl group in one of its ending nuclei, on ethylenediamine-activated Sepharose, through EDC/NHS amidation coupling, could enhance the ligand’s mobility and improve the interactions with the target proteins. The prepared support was found to separate an artificial mixture of BSA, lysozyme, and RNase A. Unexpectedly, the support prepared in the absence of the dye exhibited a separation performance similar to that of the dyed support, contrary to that observed in all previous studies using cyanine dyes as ligands for affinity chromatography, which prompted us to try to determine the structural molecular constitution of the matrix surface. A synthetic route to the final chromatographic support could be devised, which is believed to consist in the cyclization of two nearby ethylenediamine units, involving the inclusion of a succinimide-derived residue between them and the EDC-mediated Lossen rearrangement of an intermediary hydroxamic acid.

     

Kinetic Study on the Isomerization of Perindopril by HPLC

The isomerization of perindopril has been investigated using dynamics chromatography and an unified equation introduced by Trapp that was based on stochastic and theoretical plate models to determine the energies. The isomerization rate constants and Gibbs activation energies of isomerization are directly calculated from chromatographic peak parameters, i.e., retention times of the inter-converting species, peak width at half height, and relative plateau height. From the rate constant \( k_{1}^{ue} (T) \), measured at variable temperatures, the kinetic eyring activation parameters ΔG ^#, ΔH ^# and ΔS ^# of isomerization of perindopril were obtained. By variation of the flow rate of the mobile phase, the expected independence of the isomerization barrier from the chromatographic time scale was demonstrated for the first time. The relationships between peak shape and chromatographic conditions, such as flow rate, temperature, pH, organic modifier, and β-cyclodextrin, such as an additive, were investigated. In addition, an NMR investigation on perindopril was described.

     

Liquid chromatographic enrichment ofN-acetylmethionine from casein hydrolysates for stable-isotope-ratio analysis of sulfur

Summary A chromatographic method has been developed for enrichment of methionine-bound sulfur in casein, for stable-isotope analysis. Casein is precipitated from milk samples and cleaved by acid hydrolysis in 6m hydrochloric acid at 95 °C. The amino acids released are converted into theirN-acetyl derivatives by addition of acetic acid anhydride. After lyophilization,N-acetylmethionine is separated from the accompanying components on octadecylsilica by use of a gradient prepared from 0.02m formic acid and methanol. The fractions containingN-acetylmethionine are pooled and freeze dried. Procedures for hydrolysis and derivatization were optimized to furnish the highest yields. The influence of the abundance ratio on the chromatographic separation is shown and discussed. From 1.0 g casein 16.5 mgN-acetylmethionine were isolated.     

Synthesis of thioridazine-VLA-4 antagonist hybrids using N-propargyl northioridazine enantiomers

Abstract

Herein, we report the synthesis of thioridazine-VLA-4 hybrid epimers. These hybrid molecules were obtained by means of a click reaction involving N-propargyl northioridazine enantiomers and an azide containing VLA-4 antagonist. A synthesis of northioridazine enantiomers from racemic thioridazine was developed and the absolute stereochemistry was confirmed by X-ray crystallography. Access to N-substituted thioridazine analogs may reveal that this phenothiazine core has therapeutic potential in other disease avenues.     

A strategy for chromatographic and structural analysis of monosaccharide species from glycoproteins

A general strategy for the chromatographic and structural analysis of the monosaccharide species fucose (Fuc), N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), galactose (Gal), glucose (Glc), mannose (Man), N-acetylneuraminic acid (NANA) present in glycoproteins is described. Qualitative and quantitative aspects for the separation of these glycoprotein monosaccharides (monosaccharide species) using ligand-exchange chromatography (LEC) and high pH anion-exchange chromatography (HPAEC) in combination with pulsed-amperometric detection (PAD), refractive index (RI) and ultraviolet (UV) monitoring are discussed in detail. The conditions for the acidic hydrolysis of glycoproteins and for the liquid chromatographic analyses of glycoprotein monosaccharides using HPAEC and LEC technique were optimised. Furthermore, the characterisation of glycoproteins according to their purity and molecular mass connected with a comparison to biomolecules that are not glycosylated or whose extent of glycosylation is low was carried out by means of matrix-assisted laser-desorption ionisation mass spectrometry (MALDI-MS). The identification of glycoprotein monosaccharides using an on-line coupling liquid chromatography mass spectrometry (LC-MS/MS) was performed by means of their characteristic quasi molecule ions such as (M + NH₄)⁺ and (2M + NH₄)⁺. The different chromatographic and structural methods used in combination with each other were applied to characterise and determine the monosaccharide species of fetuin and a membrane glycoprotein fraction.     

Optimization and Validation of an LC Method for the Determination of Cefdinir in Dosage Form and Human Urine

A simple and reliable liquid chromatographic method has been developed and validated for the determination of cefdinir in human urine and capsule samples. A chromatographic separation was achieved on a C₁₈ column using a mobile phase consisting of potassium dihydrogen phosphate (10 mM, pH 4.5)–acetonitrile (90:10, v/v). Quantitation was achieved with UV detection at 285 nm, based on peak area with linear calibration curve at a concentration range of 0.7–39 µg mL⁻¹. This method was successfully applied for the establishment of an urinary excretion pattern after oral dose.

     

An automatic peak finding method for LC‐MS data using Gaussian second derivative filtering

A highly automated procedure for localising and characterising peaks in the chromatographic time domain of LC‐MS data has been developed. The work was initiated by an identified need to facilitate the detection and tracking of chromatographic peaks during method development for the analysis of impurities in pharmaceutical products. The algorithm is mainly based on a digital filter for which the settings are automatically adapted to the data set under study. The procedure was evaluated for synthetic data sets with various S/N levels, peak widths and baseline properties. It was found that even for the worst case tested with S/N=10 and a high variability in the baseline, 94% of the simulated analytical peaks could be detected without producing any false‐positive identifications. Furthermore, the number of correctly estimated peak heights and peak widths falling within a 10% error of the true values were 94 and 91%, respectively. For experimental data sets, peak height, and width estimations were more difficult, but the processed reconstructions showed an excellent agreement with the analytical signals of the raw data, and also a clearly improved visualisation in total ion‐ and base‐peak chromatograms.     

Differences in reactivity of N-acetyl- and N,N-diacetylsialyl chlorides caused by their different supramolecular organization in solutions

O-Sialylation of a substituted indolin-3-one under phase-transfer catalysis conditions, which does not occur when N-acetylsialyl chloride is used, proceeds with N,N-diacetylsialyl chloride as the glycosyl donor. A study using dynamic light scattering of solutions of both sialyl chlorides under conditions close to the conditions used for glycosylation showed a difference in the correlation radii of light scattering particles in such solutions. This suggests that the introduction of an additional N-acetyl group into the sialyl chloride significantly alters the structure of the supramers of glycosyl donor, which apparently have an increased accessibility of individual molecules for the attack by a nucleophile, which increases its reactivity.

     

Three gemini cationic surfactants as biodegradable corrosion inhibitors for carbon steel in HCl solution

Three gemini cationic surfactants with different hydrophobic spacer chain lengths were synthesized and characterized. The inhibition effect of N,N′-bis(2-hydroxyethyl)-N,N′-dimethyl-N,N′-bis(2-(tetradecanoyloxy)ethyl)ethane-1,2-diaminium bromide (G-2); N,N′-bis(2-hydroxyethyl)-N,N′-dimethyl-N,N′-bis(2-(tetradecanoyloxy)ethyl) hexane-1,6-diaminium bromide (G-6); and N,N′-bis(2-hydroxyethyl)-N,N′-dimethyl-N,N′-bis (2-(tetradecanoyloxy) ethyl) dodecane-1,12-diaminium bromide (G-12) on the corrosion of carbon steel in 1.0 M HCl solution at 25–60 °C was studied by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results show that the synthesized inhibitors are effective inhibitors even at very low concentration, and the adsorption on the carbon steel surface obeys the Langmuir adsorption isotherm. Potentiodynamic polarization curves reveal that the synthesized inhibitors behave as a mixed-type inhibitor. Adsorption of used inhibitors led to a reduction in the double layer capacitance and an increase in the charge transfer resistance. Thermodynamic parameters have been obtained by adsorption theory. Surface activity and corrosion inhibition relationship were discussed. The biodegradability of the synthesized surfactants showed their readily biodegradation in the open environment and were considered as environmentally friendly corrosion inhibitors.

     

Thermochemical study of the trans- and cis-isomeric forms of 4-(4-methoxystyryl)pyridine N-oxide

The trans and cis form of 4-(4-methoxystyryl)pyridine N-oxide were studied. The spectral characteristics of cis-4-(4-methoxystyryl)pyridine N-oxide were determined in acetonitrile. The melting and thermal decomposition processes of the trans and cisforms of 4-(4-methoxystyryl)pyridine N-oxide were studied by thermochemical methods. It was establish that the thermal decomposition of 4-(4-methoxystyryl)pyridine N-oxide begins with the cleavage of the bond between the pyridine and benzene rings.

     

Validated Chiral LC Method for the Enantiomeric Separation of Palonosetron Hydrochloride

A new and accurate chiral liquid chromatographic method has been developed for the separation of palonosetron hydrochloride (PALO) and its (R,R)-enantiomer in bulk drug samples with an elution time of about 20 min. The chromatographic separation was carried out by normal phase chromatography using an immobilized cellulose based chiral stationary phase (Chiralpak-IC) with a mobile phase composed of n-hexane:ethanol:1,4 dioxane:trifluoroacetic acid:diethylamine (65:30:5:0.3:0.3, v/v) pumped at a flow rate of 1.0 mL min⁻¹. The resolution (R _s ) between the enantiomers was found to be greater than 3.0 and interestingly the (R,R)-enantiomer was eluted prior to the (S,S)-enantiomer (PALO) in the developed method. Mobile phase additives, trifluoroacetic acid and diethylamine played a key role in achieving chromatographic resolution between the enantiomers and also in enhancing chromatographic efficiency. The limit of detection (LOD) and limit of quantification (LOQ) of the (R,R)-enantiomer were found to be 0.03 and 0.1 μg respectively for 10 μL injection volume. The developed method shows excellent linearity (r ² > 0.999) over a range of LOQ to 0.3% for the (R,R)-enantiomer. The percentage recovery of the (R,R)-enantiomer in bulk drug samples ranged from 97.2 to 102.3 revealing good sensitivity of the developed method. Robustness studies were also carried out on the developed method.

     

Chromatographic Fingerprint Analysis of the Flowers of Abelmoschus manihot Using HPLC with Photodiode Array Detection

Abstract

A simple and valid chromatographic fingerprint analysis method was developed using high‐performance liquid chromatography‐photodiode array detection for the quality analysis of the flowers of Abelmoschus manihot. For the first time, the feasibility and advantages of employing chromatographic fingerprint were investigated and demonstrated for the evaluation of the flowers of A. manihot by systematically comparing chromatograms with professional analytical software recommended by State Food and Drug Administration. Our results revealed that the chromatographic fingerprint combining similarity evaluation could be used efficiently for the identification and quality assessment of raw herbs of the flowers of A. manihot from different sources.     

Modeling the retention mechanism for high‐performance liquid chromatography with a chiral ligand mobile phase and enantioseparation of mandelic acid derivatives

The chromatographic retention mechanism describing relationship between retention factor and concentration of Cu²⁺(l ‐phenylalanine)₂ using chiral ligand mobile phase was investigated and eight mandelic acid derivatives were enantioseparated by chiral ligand exchange chromatography. The relationship between retention factor and concentration of the Cu²⁺(l ‐phenylalanine)₂ complex was proven to be in conformity with chromatographic retention mechanism in which chiral discrimination occurred both in mobile and stationary phase. Different copper(II) salts, chiral ligands, organic modifier, pH of aqueous phase, and conventional temperature on retention behavior were optimized. Eight racemates were successfully enantioseparated on a common reversed‐phase column with an optimized mobile phase composed of 6 mmol/L of l ‐phenylalanine or N,N‐dimethyl‐l ‐phenylalanine and 3 mmol/Lof copper(II) acetate or copper(II) sulfate aqueous solution and methanol.     

Anionic ring-opening polymerization of several N-substituted diphenimides

Five N-substituted diphenimides were prepared from the corresponding N-substituted amic acids. Attempts to polymerize the prepared seven-membered ring imides were partially successful. N-phenyldiphenimide was relatively the best monomer that polymerized anionically using n-butyl lithium or sodium metal as the initiater. The other N-substituted imides were sluggish in anionic polymerization. The resistance of the seven-membered ring imides toward ring-opening polymerization was attributed to the stability of the rings caused by the two phenylene groups adjacent to the carbonyls. © 1993 John Wiley & Sons, Inc.     

An X-ray Photoelectron Spectroscopic Study of the Poly-N-vinylpyrrolidone Desorption from the Surface of a Granulated Carbon Sorbent

The surface of a carbon sorbent modified with poly-N-vinylpyrrolidone was studied by X-ray photoelectron spectroscopy (XPS). The modification involves polymerization of N-vinylpyrrolidone on the carbon sorbent surface to form poly-N-vinylpyrrolidone. The elemental composition of the carbon sorbent surface before and after modification was determined by XPS. The electronic state of atoms of the identified elements on the surface was evaluated. The contact of the modified carbon sorbent with normal saline simulating the biological medium leads to partial removal (desorption) of the polymer from the granulated sample.