An analysis of avidin, biotin and their interaction at attomole levels by voltammetric and chromatographic techniques

The electroanalytical determination of avidin in solution, in a carbon paste, and in a transgenic maize extract was performed in acidic medium at a carbon paste electrode (CPE). The oxidative voltammetric signal resulting from the presence of tyrosine and tryptophan in avidin was observed using square-wave voltammetry. The process could be used to determine avidin concentrations up to 3 fM (100 amol in 3 l drop) in solution, 700 fM (174 fmol in 250 l solution) in an avidin-modified electrode, and 174 nM in a maize seed extract. In the case of the avidin-modified CPE, several parameters were studied in order to optimize the measurements, such as electrode accumulation time, composition of the avidin-modified CPE, and the elution time of avidin. In addition, the avidin-modified electrode was used to detect biotin in solution (the detection limit was 7.6 pmol in a 6 l drop) and to detect biotin in a pharmaceutical drug after various solvent extraction procedures. Comparable studies for the detection of biotin were developed using HPLC with diode array detection (HPLC-DAD) and flow injection analysis with electrochemical detection, which allowed biotin to be detected at levels as low as 614 pM and 6.6 nM, respectively. The effects of applied potential, acetonitrile content, and flow rate of the mobile phase on the FIA-ED signal were also studied.     

Volumetric determination of Pt(IV) in the presence of Ir,Pd, and Rh with ferrous ammonium sulfate in alkaline mannitol medium

A potentiometric reductimetric method for the determination of platinum (Pt(IV)Pt(II)) with a standard Fe(II) solution in an alkaline medium of mannitol is described. The method, the error of which does not exceed 2%, can be used in the presence of palladium, iridium, and rhodium.     

Nitrogen Adsorption Study of MCM-41 Molecular Sieves Synthesized Using Hydrothermal Restructuring

Nitrogen desorption scanning hysteresis loops (DSHLs) for large-pore MCM-41 silicas (pore diameter from 4.0 to 6.5 nm) are reported for the first time. DSHLs for MCM-41 were compared with those of conventional mesoporous silicas and no appreciable differences were found, although hysteresis loops and DSHLs for the latter were usually broader. Since desorption behavior of conventional porous silicas is appreciably influenced by pore connectivity, the observed similarity in hysteresis behavior suggests single-pore blocking effects for MCM-41 due to variation of pore diameter along its nonintersecting channels. It was also shown that the steepness of nitrogen desorption branches at relative pressures close to 0.4 often results from proximity of the lower pressure limit of adsorption-desorption irreversibility and consequently it is not justified to consider it as an indication of narrow pore size distribution. Thus, application of desorption data in calculations of pore size distributions may be grossly misleading.     

The use of liquid scintillation spectrometry for the determination of radionuclidic purity of 90Y from a radiochemical 90Y/90Srgenerator

Summary An extraction technique for the separation of ⁹⁰Sr from a high excess of⁹⁰Y has been developed. This procedure can be used for the determination of trace amounts of⁹⁰Sr in⁹⁰Y prepared by a radiochemical⁹⁰Y/⁹⁰Sr generator by liquid scintillation.     

The multiphase kinetics of phosphate uptake by plant roots

The multiphase character of phosphate uptake kinetics was stated in the experiments with intact maize roots depending on different phosphorus concentration in the external solution /from 0.0001 to 50 mM P/. The single phases are characterized by different K_m and V_max values as well as by transition points /T/. The separate phases of the multiphase isotherm of phosphates uptake are distinguished by transition points. T determines the critical concentration of phosphorus as a function of active membrane transport system /i.e. T_1–2=0.39 mM; T_2–3=1.96 mM; T_3–4=10 mM; T_4–5=33 mM/.     

Ein weiterer Beitrag zum Scandiumdicarbidproblem

Zusammenfassung Die bei 1850, 2000 bzw. 2300°C durch die Reduktion von Scandiumoxid mittels Kohlenstoff in dem der Scandiumdicarbidbildung entsprechenden Molverhältnis hergestellten Produkte wurden mit Wasser zersetzt und mit Hilfe der gleichzeitigen gaschromatographischen und massenspektrometrischen Analyse untersucht. Aus den Ergebnissen geht hervor, daß bei der Scandiumdicarbidbildung gleichzeitig ein weiteres Scandiumcarbid, höchstwahrscheinlich ein Sesquicarbid, entsteht.

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Scandium(III) dicarbide problem. Further experimental results

Products obtained by the reduction of Sc₂O₃ with carbon at 1850, 2000 and 2300°C, resp., in the molar ratio corresponding to the scandium dicarbide were hydrolysed with water. Gaseous reaction products were analysed using gas chromatography combined with mass spectrometry. Results show, that during dicarbide formation another scandium carbide, probably sesquicarbide, is also formed.

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Herrn Prof. Dr.H. Nowotny gewidmet.

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7. Mitt.: Coll. Czech. Chem. Commun., im Druck.     

The complexation efficiency

Studies have shown that cyclodextrins form both inclusion and non-inclusion complexes and that several different types of complexes can coexist in aqueous solutions. In addition, both cyclodextrins and cyclodextrin complexes are known to form aggregates and it is thought that these aggregates are able to solubilize drugs through micellar-type mechanism. Thus, stability constants determined from phase-solubility profiles are rarely true stability constants for of some specific drug/cyclodextrin complexes. A more precise method for evaluation of the solubilizing effects of cyclodextrins is to determine their complexation efficiency (CE). CE can be determined by measuring the solubility of a given drug at 2–3 cyclodextrin concentrations in pure water or a medium constituting the pharmaceutical formulation such as parenteral solution or aqueous eye drop formulation. Based on the CE value the drug:cyclodextrin ratio in the complexation medium can be determined as well as the increase in the formulation bulk in a solid dosage form. Determination of CE is a simple method for quick evaluating the solubilizing effects of different cyclodextrins and/or the effects of excipients on the solubilization. Here we report the CE of 43 different drugs with mainly 2-hydroxypropyl-β-cyclodextrin but also with randomly methylated β-cyclodextrin as well as few other cyclodextrins. Calculation of CE, drug:cyclodextrin molar ratio and the increase in the formulation bulk is discussed, as well as the influence of the intrinsic solubility and drug lipophilicity on the CE.     

Core-valence correlation potentials based on density functional theory. Applications to valence-electron-only calculations on Na and K diatomics

The core-valence correlation potential has been derived for Na and K employing atomic calculations which make use of the density functional formula worked out by Lee, Yang and Parr based on Colle-Salvetti approach. The numerical potential is fitted with a small number of Gaussians leading to a very simple expression for an one-electron corevalence correlation operator? _cv . The core-valence correlation corrections can be computed by applying? _cv on a quite general class of wavefunctions. Applications of the? _cv operator within the framework of valence-electron-only calculations using effective Hamiltonians are presented for Na and K atoms, for Na₂, K₂, NaK and their cations. Almost all the corrections calculated for the physical properties due to the core-valence correlation lead to results which are in good agreement with those obtained from much more sophisticated treatments and experimental data.     

Compact multipolar representation of the electrostatic potential for flexible molecules

A new method for generating a compact multipolar representation of the electrostatic potential (EP) for flexible molecules is presented. The method is based on a constrained minimization of the difference between the quantum mechanical and the classical EP. The fitting procedure used adopts the least absolute shrinkage and selection operator technique [R. Tibshirani, J. Roy. Stat. Soc. B 58, 267 (1996)] which can be seen as penalized ordinary least squares. The penalty function optimized for the particular molecule of interest effectively removes redundant multipoles. It is shown that the use of multiple conformations is crucial for the predictive ability of the EP model for flexible molecules. The multipole local coordinate systems are chosen in a way that best reflects the key conformational changes. It was demonstrated that such an approach improves the predictive ability of EP models. It also allows to exploit equivalence of atoms in the calculation of multipoles components. In the case of polar flexible molecules, the augmentation of the EP model based on charges by higher multipoles decreases the relative root mean square error by a factor of 1.5-5. The corresponding effect of enlargement of the set of multipoles was significantly reduced.     

Affinity chromatography of porcine pepsin A using quinolin-8-ol as ligand

Stationary phase containing quinolin-8-ol immobilized on macroporous methacrylate support for the affinity chromatography of porcine pepsin A is described. Optimized chromatographic conditions for separation of porcine pepsin A on this stationary phase were found investigating the influence of pH, concentration, ionic strength and chemical composition of the used mobile phases. The stationary phase shows a good reproducibility of chromatographic analyses (relative standard deviation, +/-2%), a high recovery (ca. 93%) and a satisfactory capacity (13 mg pepsin A/1 mL stationary phase) for porcine pepsin A. The obtained findings confirm the applicability of affinity chromatography on the stationary phase with immobilized quinolin-8-ol to the isolation and determination of porcine pepsin A.