Influence Of Organic Modifier Research Articles

Enantioseparation, recognition mechanisms and binding of xanthones on human serum albumin by liquid chromatography.

Aim: To develop a method for enantioseparation of several chiral derivatives of xanthones (CDXs) by LC using a human serum albumin-chiral stationary phase (HSA-CSP) and screening CDX-HSA affinity. Additionally, recognition mechanisms were investigated. Materials & methods: The influence of organic modifier, buffer type, pH and ionic strength of mobile phase, and temperature were explored. The affinity was determined by measuring the retention times and further calculation of bound percentage. Chiral recognition mechanisms were investigated by docking. Results: Enantioselectivity and resolution values ranged from 1.40 to 9.16 and 1.51 to 4.97. Bound percentages ranged from 79.02 to 99.99%. Conclusion: LC systematic study and binding affinity of CDXs on HSA-CSP are presented here for the first time, expanding the applications of HSA-CSP for this class of compounds.

Influence of organic modifier and separation modes for lipophilicity assessment of drugs using thin layer chromatography indices

Lipophilicity constitutes one of the most important physicochemical properties in the design and development of drug molecules. In the present work thin layer chromatography (TLC) has been utilized to evaluate lipophilicity of 11 representative drugs, which included six proton pump inhibitors (omeprazole, pantoprazole, rabeprazole, lansoprazole, ilaprazole, and tenatoprazole), an anti-vertigo drug, betahistine, nonsteroidal anti-inflammatory drug, ibuprofen, anti-malarial drug, atovaquone, an anti-HIV agent, atazanavir and a hormonal drug, calcitriol. Normal as well as reversed-phase separation modes were evaluated to study the effect of different organic modifiers for the estimation of lipophilicity. The quantitative descriptor of lipophilicity, the partition coefficient (logP) was estimated by suitably optimizing the solvent systems for both the modes. The best mobile phase pairs for NPTLC and RPTLC were toluene-acetonitrile and water-methanol respectively. Principal component analysis, hierarchical cluster analysis, as well as non-parametric methods like sum of ranking differences and generalized pair wise correlation revealed the dominant pattern in the data. The results obtained from both the separation modes were comparable and were in good agreement with the computational data for all the drugs.

Influence of organic modifiers on RP-TLC determination of lipophilicity of some polydentate Schiff bases

The lipophilic character of polydentate Schiff bases was investigated by reversed-phase thin-layer chromatography. In order to determine retention parameter as a measure of the lipophilicity of the tested compounds, three different binary solvent systems, composed of water and organic modifier (methanol, acetonitrile, and tetrahydrofuran), were used. Lipophilicity parameters together with 2D molecular descriptors were subjected to the multivariate statistical analysis. Principal component analysis was employed to reveal the most influential factors governing the lipophilicity of the investigated compounds. Finally, the influence of organic modifier on determination of lipophilicity parameters was discussed.

Analysis of degradation products of esfenvalerate by SBSE/HPLC-UV/DAD using fractional factorial design

A simple procedure based on stir bar sorptive extraction and high-performance liquid chromatography-ultraviolet/photodiode array detection (SBSE/LC-UV/PAD) to determine intermediates and by-products of esfenvalerate is described. The influence of organic modifier, ionic strength, extraction time, temperature and pH were simultaneously evaluated by using a factorial experimental design. The utilization of different organic solvents and desorption times were also investigated to establish the optimal conditions for SBSE liquid desorption. Among the ten different peaks (intermediates and by-products) detected after degradation of esfenvalerate, eight (including 3-phenoxybenzoic acid and 3-phenoxybenzaldehyde) were successfully extracted by SBSE under the optimized conditions.

Teresa Cecchi: Ion-pair chromatography and related techniques

Teresa Cecchi: Ion-pair chromatography and related techniques

Development and validation of indirect RP-HPLC method for enantiomeric purity determination of d-cycloserine drug substance

A new chiral purity method was developed for d-cycloserine (d-cys) by reverse phase HPLC and validated. Chiral derivatizing reagents, viz., o-phthalaldehyde and N-acetyl-l-cysteine were utilized in this method. The resultant diastereomers were resolved using Zorbax SB Phenyl HPLC column under isocratic elution. A mobile phase of 95:05 (v/v), 20mM Na2HPO4 (pH 7), and acetonitrile, respectively, was used with the flow rate of 1.0mL/min and UV detection at 335nm. The method development with different chiral stationary phases and chiral derivatization reagents were also investigated. The stability of diastereomer derivative and influence of organic modifier and pH of the mobile phase were studied and optimized. The stability-indicating capability of the method was established by performing stress studies under acidic, basic, oxidation, light, humidity and thermal conditions. The detection and quantitation limit of l-cycloserine (l-cys) were 0.015 and 0.05% (w/w), respectively. A linear range from 0.05 to 0.30% (w/w) was obtained with the coefficient of determination (r2) 0.998. The recovery obtained for l-cys was between 92.9 and 100.2%. This method was applied successfully in pharmaceutical analysis to determine the content of l-cys in d-cys bulk drug.

Confocal Raman Microscopy of the Interfacial Regions of Liquid Chromatographic Stationary-Phase Materials

The influence of organic modifiers on the structure of reversed-phase liquid chromatographic (RPLC) stationary phases has been a topic of considerable investigation. Retention of organic modifiers in the stationary phase has previously been determined by chromatographic measurements, and the polarity and heterogeneity of the resulting solvation environment has been studied using solvatochromic, fluorescent, and spin probes. In the present work, the composition and solvation environment of a stationary phase is investigated using confocal Raman microscopy, which allows the in situ examination of the solvation environment within individual chromatographic stationary phase particles without the use of probe molecules. The accumulation of organic modifiers in the stationary phase can be quantified, and the environment of the modifier in the stationary phase can be determined. Specifically, we have investigated the interactions of acetonitrile with C(18)-functionalized silica particles using confocal Raman microscopy, which enables the sampling of small (approximately 1 fL) volumes within individual 10 microm particles. Bare chromatographic silica was also studied in order to investigate the interactions of acetonitrile with surface silanols. The nitrile-stretching (nu(CN)) frequency of acetonitrile responds sensitively to the dipolarity of its local microenvironment. The populations of solution-phase and interfacial acetonitrile are thus spectroscopically distinguishable. Scattering from nu(CN) shows contributions from three different environments within a single RPLC chromatographic particle: acetonitrile in the interparticle mobile phase, C(18)-chain associated acetonitrile, and acetonitrile that is interacting with residual surface silanols. Data are presented quantifying these populations and characterizing their environments within single stationary phase particles.

Thermal degradation kinetics of epoxy/organically modified montmorillonite nanocomposites

AbstractNanocomposites based on a commercial epoxy resin and organically modified montmorillonites (OMMTs), containing 5 and 10 phr OMMT, were prepared and characterized. Poly(oxypropylene) diamine (Jeffamine D400) and octadecylamine were used as organic modifiers. Another poly(oxypropylene) diamine (Jeffamine D230) was used as a curing agent. The thermal degradation kinetics of the neat resin system and nanocomposites were investigated by thermogravimetric analysis. The dispersion of silicate layers within the crosslinked epoxy matrix was verified by transmission electron microscopy. The activation energy of degradation for the investigated systems was determined by the isoconversional Kissinger–Akahira–Sunose method. The thermal behavior of the neat resin systems and nanocomposites was modeled with an empirical kinetic model. The influence of organic modifiers and the OMMT loading on the thermal stability of the nanocomposites was discussed. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008

Influence of organic modifiers on morphology and crystallization of poly(ϵ‐caprolactone)/synthetic clay intercalated nanocomposites

Abstractε‐caprolactone was polymerized in the presence of neat montmorillonite or organomontmorillonites to obtain a variety of poly(ε‐caprolactone) (PCL)‐based systems loaded with 10 wt % of the silicates. The materials were thoroughly investigated by different X‐ray scattering techniques to determine factors affecting structure of the systems. For one of the nanocomposites it was found that varying the temperature in the range corresponding to crystallization of PCL causes reversible changes in the interlayer distance of the organoclay. Extensive experimental and literature studies on this phenomenon provided clues indicating that this effect might be a result of two‐dimensional ordering of PCL chains inside the galleries of the silicate. Small angle X‐ray scattering and wide angle X‐ray scattering investigation of filaments oriented above melting point of PCL revealed that polymer lamellae were oriented perpendicularly to particles of unmodified silicate, while in PCL/organoclay systems they were found parallel to clay tactoids. Calorimetric and microscopic studies shown that clay particles are effective nucleating agents. In the nanocomposites, PCL crystallized 20‐fold faster than in the neat polymer. The crystallization rate in nanocomposites was also significantly higher than in microcomposite. Further research provided an insight how the presence of the filler affects crystalline fraction and spherulitic structure of the polymer matrix in the investigated systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2350–2367, 2007

Influence of organic modification on mechanical properties of melt processed intercalated poly(methyl methacrylate)–organoclay nanocomposites

AbstractThe influence of organic modifiers on intercalation extent, structure, thermal and mechanical properties of poly(methyl methacrylate) (PMMA)–clay nanocomposites were studied. Two different organic modifiers with varying hydrophobicity (single tallow versus ditallow) were investigated. The nanocomposites were prepared from melt processing method and characterized using wide angle X‐ray diffraction, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), and tensile tests. Mechanical properties such as tensile modulus (E), break stress (σbrk), and % break strain (εbrk) were determined for nanocomposites at various clay loadings. Extent of PMMA intercalation is sufficient and in the range 9–15 Å depending on organoclay and filler loading. Overall thermal stability of nanocomposites increases by 16–30°C. The enhancement in Tg of nanocomposite is merely by 2–4°C. With increase in clay loading, tensile modulus increases linearly while % break strain decreases. Break stress is found to increase till 4 wt % and further decreases at higher clay loadings. The overall improvement in thermal and mechanical properties was higher for the organoclay containing organic modifier with lower hydrophobicity and single tallow amine chemical structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Investigation into the influence of organic modifiers and ultradispersed hybrid fillers on the structure and properties of glass-ceramic coatings prepared by the sol-gel method

Glass-ceramic coatings on nickel and its alloys are produced from organic-inorganic hybrids by the sol-gel method. The coatings are applied using sol-gel systems composed of tetraethoxysilane (inorganic dopant), as well as of finely dispersed oxide and ultradispersed hybrid fillers. Acrylic and methacrylic acid derivatives are taken as organic modifiers. Oligocarbonate dimethacrylate-substituted tetranuclear titanium oxide clusters are used as the ultradispersed hybrid filler. The influence of the organic modifiers and ultradispersed hybrid fillers on the physicochemical processes occurring in the sol-gel systems and on the electrical parameters of the coatings are experimentally studied, and the data obtained are analyzed.

Direct Optical Resolution of Chiral Pesticides by High Performance Liquid Chromatography on Cellulose tris‐3,5‐Dimethylphenyl Carbamate Stationary Phase Under Reversed Phase Conditions

The direct optical resolution of five chiral pesticides on a cellulose tris‐3,5‐dimethylphenyl carbamate stationary phase (Chiralcel OD, 250 × 4.6 mm) under reversed‐phase conditions is described. The influence of organic modifiers, pH, and temperature was investigated. The two mobile phases used were water/methanol and water/acetonitrile. Of five chiral pesticides investigated, the three pesticides were observed to obtain the base separation under the suitable conditions and the other two were observed to be partially resolved. The values of α (1.04–6.65) and R s (0.63–13.16) have been reported.

Separation of Basic Drugs Using Pressurized Capillary Electrochromatography

AbstractA novel pressurized capillary electrochromatography (PCEC) was developed to separate basic drugs on strong cation exchange (SCX) column. The separation result by using PCEC was better than that by using micro‐HPLC. The effects of electrical field and pressure on plate height and resolution were investigated. Influence of organic modifier, ionic strength and pH value of buffer on retention behavior were evaluated, and the separation mechanism was also discussed.

Synthesis of 2-cyanoethyl-modified MCM-48 stable to surfactant removal by solvent extraction: Influence of organic modifier, base and surfactant

A 2-cyanoethyl grafted MCM-48 mesoporous silicate, which was stable to surfactant removal by solvent extraction, was synthesised by co-condensation of 2-cyanoethyltriethoxysilane and tetraethyl orthosilicate in basic conditions using cetyltrimethylammonium bromide as surfactant. The presence of the organic group was verified by infrared analysis. Additional studies confirmed that the concentration of sodium hydroxide used for this synthesis influenced the mesopore properties. MCM-41 and MCM-48 were formed using a narrow range of base concentrations while preparations outside this range gave disordered materials with reduced porosity. Materials synthesised using various quantities of cetyltrimethylammonium bromide showed that MCM-48 was formed over a range of surfactant concentrations although the order varied considerably. The mesopore phase was further adjusted by altering the concentration of 2-cyanoethyltriethoxysilane modifier. Preparations using 0–10 and 20 mol% organic modifier (of total silica) produced MCM-48 and MCM-41, respectively, while greater modifier concentrations gave disordered materials with significantly diminished porosity characteristics.

SYNTHESIS AND EVALUATION OF A NOVEL C8 ESTER-BONDED STATIONARY PHASE FOR REVERSED-PHASE HPLC

ABSTRACT A novel ester-bonded packing for reversed-phase HPLC (RP-HPLC) was synthesized by reacting octanoic acid with β-(3,4-epoxycyclohexyl) ethyltrimethoxy silane; then, the intermediate product was coupled onto porous silica. Characterization of the prepared packing was carried out with elemental analysis, solid-state 13C NMR, and Fourier transform infrared (FT-IR) analysis. The chromatographic properties of the novel ester-bonded phase have been investigated in RP-HPLC with acidic, basic, and neutral analytes as probes. The influence of organic modifier and pH of mobile phase and the hydrolytic stability of the packing were also studied. Results showed that the new stationary phase has excellent chromatographic properties in RP-HPLC and can resist hydrolysis between pH=2.5~7.5.

New derivative of β-cyclodextrin as chiral selectors for the capillary electrophoretic separation of chiral drugs

The uncharged β-cyclodextrin (β-CD) derivative mono-3- O-phenylcarbamoyl-β-CD was successfully used as chiral selector in capillary zone electrophoresis. Several chiral drugs such as propafenone and verapamil enantiomers belonging to different classes of compounds of pharmaceutical interest were resolved. The chiral resolution (Rs) was strongly influenced by the concentrations of the cyclodextrin derivative, the background electrolyte, and the pH of the background electrolyte. The influence of organic modifier was also studied. Under the conditions of 40 mmol/l borate buffer at pH 9.18 containing 2.5 mmol/l mono-3-phenylcarbamoyl-β-CD, baseline separation (Rs=3.88 for verapamil, Rs=3.32 for propafenone) of the enantiomers can be achieved.

Theoretical Migration Model for Micellar Capillary Electrophoresis and Its Application to the Separation of Anionic Metal Complexes of HEDTC and CDTA

A mathematical model relating the effective mobility of an analyte in micellar capillary electrophoresis (MCE) to the concentration of surfactant and organic modifier in the background electrolyte (BGE) was derived. Effective mobility is expressed in terms of the electrophoretic mobility of the analyte, the partition coefficient of the analyte into the micelle, and the influence of organic modifier on these two factors. The performance of the model was evaluated using Cd(II), Pb(II), Co(II), Ni(II), Bi(III), Cu(II), and Hg(II) complexes of bis(2-hydroxyethyl)dithiocarbamate, all of which carry a partial negative charge, and Cd(II), Pb(II), Co(II), Ni(II), Bi(III), Cu(II), Hg(II), Fe(III), Ag(I), Tl(I), and Mn(II) complexes of trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, all of which are anionic having charges in the range -1 to -3. These analytes were separated in borate BGEs containing 10-50 mM sodium dodecyl sulfate and 0-20% (v/v) methanol. Nonlinear regression was used to derive parameters for the model from experimental data and these parameters were used to predict effective mobilities of the analytes. Predicted values of effective mobilties agreed with experimental values to within 3.1%. Values of parameters from the model equation are used to explain changes in separation selectivity observed at different BGE compositions and the model equation is shown to be applicable to computer-assisted optimization of the BGE composition, in MCE using a limited number of experiments.

Capillary zone electrophoretic separation of biogenic amines: influence of organic modifier

The influence of organic modifier on the separation of six biogenic amines in capillary zone electrophoresis was investigated using ammonium acetate as a background electrolyte. The electrophoretic mobility of each biogenic amine at a given pH decreases to a different extent on addition of organic modifier which may lead to alteration of the migration order. The results indicate that addition of acetonitrile (30%, v/v) or methanol (40%, v/v) to ammonium acetate buffer (100 m M) at pH 7.5 effects the resolution of co-migrating biogenic amines. Complete separation of six biogenic amines was achieved in short times using a 44 cm×50 μm I.D. fused-silica capillary at 10 kV. Methanol is relatively less effective than acetonitrile as an organic modifier to separate these biogenic amines.

Influence of organic modifier and temperature on the enantiomeric separation of γ-lactams by HPLC

A high-performance liquid chromatographic method is reported for the resolution of the enantiomers of a series of fused γ-lactams (2,7-diaza-3-oxo[3.3.0]octan-6-ones) with probable anti-HIV and anticancer activity. Resolution was achieved on a Chiralcel® OD column, cellulose tris-(3,5-dimethylphenyl carbamate) adsorbed on macroporous silica gel; mixtures ofn-hexane and isopropyl alcohol in different proportions were used as the mobile phase. The analysis was studied at different temperatures.

Development of an isocratic high-performance liquid chromatographic method for monitoring of ciprofloxacin photodegradation

Abstract An isocratic reversed-phase ion-pair high-performance liquid chromatographic method was developed for monitoring the photodegradation of ciprofloxacin in aqueous solutions. Changes in the chromatographic behaviour of ciprofloxacin and its degradation products under the influence of organic modifiers, anionic and cationic ion-pair reagents and pH were investigated. Baseline separation was achieved with use of an eluent of acetonitrile-phosphoric acid (20 mM, pH 2.3) containing 2.5 mM 1-heptanesulphonic acid sodium salt. The method was applied to the quantification of ciprofloxcin in irradiated solutions. The calibration graphs were linear from 5 to 150 μg/ml (r > 0.9999). Within the same range, the accuracy was 99–102% of the expected values. The intra-assay repeatability of the peak areas and retention times was good (R.S.D. ⩽ 039%). Likewise the intra-day reproducibility of the method was good: R.S.D. values (n = 6) were ⩽ 2.3% and 1.8% for the lowest and highest concentrations, respectively. The inter-day precision gave a mean R.S.D. of 2.4% for peak areas and R.S.D. of 3.3% for retention times during a working period of three months.