Preparation of amino-zirconia bonded phases and their evaluation in hydrophilic interaction chromatography of carbohydrates with pulsed amperometric detection

A series of non-porous, microspherical zirconia-based stationary phases with surface bound amine functionality have been introduced and evaluated in hydrophilic interaction chromatography (HILIC) of underivatized, neutral carbohydrates and anion exchange chromatography of nucleotides using pulsed amperometric detection and ultraviolet detection, respectively. Three aminopropyl alkoxysilane compounds were used in the surface modification of the non-porous zirconia support, namely 3-aminopropyltrimethoxysilane (monoamine), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (diamine), and trimethoxysilylpropyldiethylenetriamine (triamine). Due to the relatively low specific surface area of the non-porous zirconia support used in this study (ca. 7.3 m²/g), zirconia with surface coating of the triamine type yielded the best results as far as the separations of chitooligosaccharides and maltooligosaccharides are concerned. Since a non-porous zirconia could be readily modified with amine functionality via Zr? O? Si bonds, it is expected that all the three aminopropyl alkoxysilane compounds would yield satisfactory results with porous zirconia microparticles because of their much higher specific surface areas. Although the non-porous zirconia exhibited some limitations, the present study has demonstrated that microspherical zirconia particles are suitable supports for the production of polar sorbents for HILIC of carbohydrates. Another surface modification, which involved the activation of the zirconia surface with aldehyde groups followed by reductive amination with tetraethylenepentamine, was also evaluated. Although this chemistry would in principle yield sorbents with higher concentration in amine groups, the conversion of the majority of the primary amine groups of the tetraethyle-nepetamine molecules to secondary amine functions in the course of the reductive amination reaction have provided a stationary phase that did not afford satisfactory resolution for carbohydrates. However, this same stationary phase behaved as a weak anion exchanger and allowed the high resolution separation of nucleoside-5′-mono-, -di-, and triphosphates. Overall, the results obtained with zirconia-based hydrophilic sorbents paralleled those obtained on amino-silica bonded phases.     

Thermodynamics of transfer processes, 1. Solubility of hydrophilic solutes in dioxane-water mixtures

Summary The solubility profiles of oxalic and malonic acid in various dioxane-water mixtures are reported. These values are analyzed in terms of dipole moment and solubility parameter using theHildebrand treatment for regular solutions. The effect of temperature upon the solubility values was investigated and thus the thermodynamic parameters of the solutions were derived. The thermodynamic transfer functions of oxalic and malonic acid from water to aquo-dioxane mixtures were also calculated and analyzed in terms of solute-solvent interactions.

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Thermodynamik von Transferprozessen, 1. Mitt. Löslichkeit hydrophiler Verbindungen in Dioxan-Wasser-Mischungen

Zusammenfassung Das Löslichkeitsverhalten von Oxalsäure und Malonsäure in verschiedenen Dioxan-Wasser-Mischungen wurde untersucht. Die erhaltenen Werte werden im Hinblick auf Dipolmoment und Löslichkeitsparameter unter Verwendung derHildebrandschen Beziehung für reguläre Lösungen diskutiert. Aus der Temperaturabhängigkeit der Löslichkeit wurden die thermodynamischen Parameter der Lösungen abgeleitet. Die thermodynamischen Transferfunktionen für Oxalsäure und Malonsäure zwischen Wasser und Wasser-Dioxan-Mischungen wurden ebenfalls berechnet und werden im Zusammenhang mit Wechselwirkungen zwischen Lösungsmittel und gelöster Substanz diskutiert.

     

Capillary electrochromatography with monolithic-silica columns. II. Preparation of amphiphilic silica monoliths having surface-bound cationic octadecyl moieties and their chromatographic characterization and application to the separation of proteins and other neutral and charged species

Three different synthetic routes have been introduced and evaluated for the preparation of amphiphilic silica-based monoliths possessing surface-bound octadecyl ligands and positively charged groups. The amphiphilic silica monoliths (designated as cationic C18-monoliths) have been designed for use in reversed-phase capillary electrochromatography (RP-CEC) with hydro-organic mobile phases. These amphiphilic stationary phases yielded anodic electroosmotic flow (EOF) over a wide range of mobile phase pH. The magnitude of EOF remained constant up to pH 4.0 and then decreased at pH > 4.0 due to the ionization of silanol groups and the subsequent decrease in the net positive surface charge density of the amphiphilic monoliths. The cationic C18-monoliths exhibited reversed-phase chromatography (RPC) behavior toward non-polar solutes (e.g., alkyl benzenes), which parallels that observed with octadecyl-silica (ODS) monoliths. On the other hand, the amphiphilic stationary phases exhibited both non-polar and polar interactions toward slightly polar solutes such as anilines and PTH-amino acids. CEC retention factor k* and velocity factor k*e, which reflects the contribution of the electrophoretic mobility, were evaluated for charged solutes such as anilines and proteins.     

Structure of trihydrated rare-earth acid diphosphates LnHP2O7·3H2O (Ln=La, Er)

In trihydrated lanthanum acid-diphosphates LnHP₂O₇·3H₂O, prepared from acid LnCl₃ and Na₄P₂O₇ solutions (pH=1), two crystal forms were obtained. Layered structures of two representative members of this family have been determined by single-crystal X-ray diffraction (XRD) technique. In the case of orthorhombic LaHP₂O₇·3H₂O (type I), lanthanum cations are ninefold coordinated and diphosphate groups adopt a staggered (alternated) configuration. In the case of triclinic ErHP₂O₇·3H₂O (type II), erbium cations are eightfold coordinated and diphosphate groups adopt an eclipsed configuration. In agreement with Infrared (IR) spectroscopic data, a bended configuration for diphosphate groups has been deduced. In both structures, one-dimensional chains of edge-sharing rare-earth polyhedra are linked together by diphosphate groups to form the phosphate layers. In both diphosphates, PO₄ and HPO₄ environments have been identified by ³¹P MAS-NMR technique. In the two compounds, OH groups of HPO₄ tetrahedra point out of diphosphate planes interacting with adjacent layers. In La-diphosphate, the interaction between HPO₄ groups and water molecules of adjacent layers is favored; however, in Er-diphosphate, the interaction between phosphate acid groups of contiguous layers is produced. Based on structural information deduced, differences detected in IR and NMR spectra of two disphosphates are discussed.     

Electrochemical urea biosensor based on Proteus mirabilis urease immobilized over polyaniline PANi-Glassy carbon electrode

In this study, a novel, sensitive electrochemical enzyme-based biosensor for urea detection was presented. This biosensor combines a three-electrode system consisting of a classic Glassy Carbon Electrode (GCE) as the working electrode, a platinum counter electrode, and Ag/AgCl as the reference electrode. To construct this urea platform, a GCE was modified with a polyaniline (PANi) film. Then, bacterial urease from Proteus mirabilis was immobilized on the modified GCE (P_m-Urease-PANi-GCE). For the characterization of surface modification, Cyclic Voltammetry (CV) and Scanning Electron Microscope (SEM) were applied, while the Square Wave Voltammetry (SWV) technique was performed for urea detection. The main analytical characteristics of the P_m-Urease-PANi-GCE biosensor showed a good linear range from 0.1 to 10 mM of urea, a limit of detection (LOD) of 0.1 mM, a Michaelis-Menten K_m of 0.23 mM, and a sensitivity value 46 μA/mM/cm². This biosensor allows the detection of urea in solutions, and it could be improved for further medical, environmental, or engineering applications.     

Neutral octadecyl monolith for reversed phase capillary electrochromatography of a wide range of solutes

A neutral octadecyl monolithic (ODM) column for RP capillary electrochromatography (RP-CEC) has been developed. The ODM column was prepared by the in situ polymerization of octadecyl acrylate (ODA) as the monomer and trimethylolpropanetrimethacrylate (TRIM) as the crosslinker, in a ternary porogenic solvent containing cyclohexanol, ethylene glycol, and water. The ODM column exhibited cathodal EOF over a wide range of pH and ACN concentration in the mobile phase despite the fact that it was devoid of any fixed charges. It is believed that the EOF is due to the adsorption of ions from the mobile phase onto the surface of the monolith thus imparting to the neutral ODM column the zeta potential necessary to support the EOF required for mass transport across the monolithic column. Furthermore, the adsorption of mobile phase ions to the neutral monolith modulated solute retention and affected the separation selectivity. The wide applications of the neutral ODM column were demonstrated by its ability to separate a wide range of small and large solutes, both neutral and charged. While the separation of the neutral solutes was based on RP retention mechanism, the charged solutes were separated on the basis of their electrophoretic mobility and hydrophobic interaction with the C18 ligands of the stationary phase. As a typical result, the neutral monolithic column was able to separate peptides quite rapidly with a separation efficiency of nearly 200,000 plates/m, and this efficiency was exploited in tryptic peptide mapping of standard proteins, e. g., lysozyme and cytochrome C, by isocratic elution.     

Capillary electrophoresis of some free fatty acids using partially aqueous electrolyte systems and indirect UV detection. Application to the analysis of oleic and linoleic acids in peanut breeding lines

This study has shown for the first time the suitability of CE with a partially aqueous electrolyte system for the analysis of free fatty acids (FFAs) in small portions of single peanut seeds. The partially aqueous electrolyte system consisted of 40 mM Tris, 2.5 mM adenosine-5'-monophosphate (AMP) and 7 mM alpha-CD in (N-methylformamide) NMF/dioxane/water (5:3:2 by volume) mixture, pH 8-9. While AMP served as the background UV absorber for indirect UV detection of the FFAs, the alpha-CD functioned as the selectivity modulator by affecting the relative effective electrophoretic mobilities of the various FFAs due to their differential association with alpha-CD. This CE method allowed the screening of peanut seeds for their content of oleic and linoleic acids, which is essential in breeding of peanuts of high-oleic acid content. The extraction method of FFAs from peanut seeds is very reproducible with a high recovery approaching quantitative yield (approximately 97% recovery).     

Effect of shear rate on aggregate size and morphology investigated under turbulent conditions in stirred tank

Aggregation and breakage of aggregates produced from fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tank. Detailed investigation of the initial kinetics showed that the collision efficiency, alpha, depends on the shear rate according to alpha proportional to G(-b), with a power law exponent, b, equal to 0.18. After steady state was reached the dynamic response of the system on a change in stirring speed and solid volume fraction was investigated. It was found that the steady-state values of two measured moments of the cluster mass distribution (CMD) are fully reversible upon a change in stirring speed. This indicates that although the moments of CMD at steady-state depend on the applied shear rate, the aggregate structure is independent of the shear rate in the given range of stirring speeds. This was proved by independent measurement of the fractal dimension, d(f), using image analysis which provided a d(f) equal to 2.62 +/- 0.18 independent of applied stirring speed. The critical aggregate size, below which breakage is negligible, determined by dilution experiments was consequently used to evaluate the aggregate cohesive force holding the aggregate together, which was found to be independent of the aggregate size and equal to 6.2 +/- 1.0 nN.     

Spectrophotometric and atomic absorption determination of ramipril, enalapril maleate and fosinopril through ternary complex formation with molybdenum (V)-thiocyanate (Mo(V)-SCN)

Three different sensitive and accurate spectroscopic procedures were developed for the determination of three angiotensin-converting enzyme inhibitors, namely, ramipril, enalapril maleate and fosinopril. The first two spectrophotometric (extractive and non-extractive) procedures were based on ternary complex formation with molybdenum(V) thiocyanate. The formed complex can be determined by extraction with chloroform measured at lambdamax 517 nm Beer's law was obeyed in the concentration range from (10--90 microg ml(-1)) for ramipril and fosinopril and (4--36 microg ml(-1)) for enalapril maleate with molar absorptivity 1.2x10(4), 2x10(4) and 3.4x10(4) l mol(-1) cm(-1), respectively, or by direct measurement after addition of benzalkonium chloride as surfactant and measuring the formed ternary complex at lambdamax 545 nm with a linear relationship in the concentration range from (8-7-2 microg ml(-1)), (3--27 microg ml(-1)) and (8--72 microg ml(-1)) for ramipril, enalapril maleate and fosinopril with molar absorptivity 1.5x10(4), 5x10(4) and 2.1x10(4) l mol(-1) cm(-1), respectively. The third procedure is atomic absorption measurement through the quantitative determination of molybdenum content of the complex. These methods hold their accuracy and precision well when applied to the determination of ramipril, enalapril maleate and fosinopril in their dosage forms.     

Studies toward a marine toxin immunogen: enantioselective synthesis of the spirocyclic imine of (-)-gymnodimine

[reaction: see text] An enantioselective Diels-Alder reaction catalyzed by an Evans' copper-bis(oxazoline) complex was utilized to construct a highly functionalized spirolactam, a key intermediate in our projected total synthesis of the marine toxin, gymnodimine. Additional transformations, including a mild N-tosyl group deprotection, afforded a keto spirocyclic imine moiety, the proposed pharmacophore of gymnodimine. Thus, the prepared ketone is a potentially useful intermediate for conjugation to provide an immunogen for eventual monitoring of gymnodimine and congeners.