Investigation of particle-based and monolithic columns for cation exchange protein displacement chromatography using poly(diallyl-dimethylammonium chloride) as displacer

The overall topic of the investigation was the separation of basic proteins by cation exchange displacement chromatography. For this purpose two principal column morphologies were compared for the separation of ribonuclease A and alpha-chymotrypsinogen, two proteins found in the bovine pancreas. These were a column packed with porous particles (Macro-Prep S, 10 microm, 1000 A) and a monolithic column (UNO S1). Both columns are strong cation exchangers, carrying -SO3(-)-groups linked to a hydrophilic polymer support. Poly(diallyl-dimethylammonium chloride) (PDADMAC), a linear cationic polyelectrolyte composed of 100-200 quaternary pyrrolidinium rings, was used as displacer. The steric mass action (SMA) model and, in particular, the operating regime and dynamic affinity plots were used to aid method development. To date the SMA model has been applied primarily to simulate non-linear displacement chromatography of proteins using low molar mass displacers. Here, the model is applied to polyelectrolytes with a molar mass below 20000 g mol(-1), which corresponds to a degree of polymerization below 125 and an average contour length of less than 60 nm. The columns were characterized in terms of the adsorption isotherms (affinity, capacity) of the investigated proteins and the displacer.     

Systematic Errors in the Determination of Trace Metals,Part II. Memory Effects of Quartz Vessels Used for Sample Preparation in the Determination of Ultra-Trace Levels of Platinum

The influence of different cleaning procedures applied to quartz vessels used for sample preparation on the Pt contents in blank solutions was studied. The platinum concentration was determined by inductively coupled plasma mass spectrometry. The strong dependence of the memory effect of the quartz crucible on the previously stored Pt content of the sample was observed. It was shown that cleaning a quartz crucible previously used for Pt determinations with hot nitric acid was insufficient. When heating the vessels with a mixture of nitric, perchloric and hydrochloric acid, considerable amounts of Pt are released. In the case of new crucibles, the platinum contents in blanks were very low after cleaning with hot nitric acid.     

New imide 5-HT1A receptor ligands - modification of terminal fragment geometry

Two sets of new o-methoxyphenylpiperazine (MPP; series a) and 1,2,3,4-tetrahydroisoquinoline (THIQ; series b) derivatives, containing various imide moieties derived from NAN190, were synthesized and evaluated in vitro for their ability to bind to the serotonin 5-HT(1A) and 5-HT(2A) receptors. All new derivatives from series a demonstrated high 5-HT(1A) affinities, whereas THIQ analogues were much less active. With respect to 5-HT(2A) receptors, three MPP derivatives presented moderate activity but the rest of the investigated compounds were practically inactive. The influence of changes in terminus geometry on 5-HT(1A) receptor affinity was analyzed in regard to model compounds NAN190and MM199.     

The importance of both charge exchange and proton transfer in the analysis of polycyclic aromatic compounds using atmospheric pressure chemical ionization mass spectrometry

The response of atmospheric pressure chemical ionization (APCI) mass spectrometry to selected polycyclic aromatic compounds (PACs) was examined in a Micromass Quattro atmospheric pressure ion source as a function of both solvents and source gases. Typical PACs found in petroleum samples were represented by mixtures of naphthalene, fluorene, phenanthrene, pyrene, fluoranthene, chrysene, triphenylene, perylene, carbazole, dibenzothiophene, and 9-phenanthrol. A large range of different gases in the APCI source was studied, with emphasis on nitrogen, air, and carbon dioxide. Solvents used included water-acetonitrile, acetonitrile, dichloromethane, and hexanes. The signal responses were dependent on both the gases and solvents used, as was the ionization mechanism, as indicated by the degree of protonation with respect to the level of charge exchange. The combination of carbon dioxide in the nebulizer gas stream with nitrogen in the other streams gave a three- to fourfold better sensitivity than using nitrogen alone for both test mixtures and for complex samples.     

Analysis of Non-Selective Calcium-Channel Blockers by Reversed-Phase TLC

The selectivity of TLC separation of non-selective calcium-channel blockers prenylamine, lidoflazine, bepridil, and fendiline has been investigated silanized silica gel RP8 and RP18 plates. Optimization of retention and selectivity for these compounds was achieved by altering the pH and the concentration of organic modifier (methanol, ethanol, tetrahydrofuran, acetonitrile) in the aqueous mobile phases. The substances were separated in horizontal chambers and the drugs were detected by videoscanning and illumination of the plates at λ = 254 nm. On RP8 plates the best separation was achieved with 50% acetonitrile in pH 2.06 phosphate buffer as mobile phase. On RP18 the best separation was achieved with 50% ethanol in pH 2.06 phosphate buffer.

     

TheO,O′-dibenzoyl derivative of (R,R)-tartaric acid as a host compound for simple organic ethers

TheO, O-dibenzoyl derivative of (R, R)-tartaric acid shows a good inclusion ability for diethyl and di-n-propol ethers. The two crystalline inclusion compounds have 1:1 stoichiometry and reveal isomorphous structures. Hydrogen bonded host molecules form chains running along thez axis of the unit cell and guest molecules join to these chains by short O–H...O hydrogen bonds. Hydrogen bonding in the crystals is characterized by a C(7)D first-order network. The ether molecules are in a fully extended conformation. They are accommodated in channel-like voids running along thex axis. Atomic displacement parameters are significantly larger for diethyl ether than for the di-n-propyl ether molecule reflecting less dense packing for this inclusion compound.Supplementary Data: relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82195 (19 pages)     

Chiral building blocks: enantioselective syntheses of benzyloxymethyl phenyl propionic acids

The synthesis of (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methoxyphenyl)- propionic acid, (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methylphenyl)propionic acid and (2S)-2-benzyl-oxymethyl-3-(2,4-dimethylphenyl)propionic acid has been achieved by TiCl4 mediated alkylation of the corresponding (4R)-4-benzyl-3-[3-(2-fluoro-4-methoxyphenyl-, 2-fluoro-4-methylphenyl-, 2,4- dimethylphenyl-)propionyl]-2-oxazolidinones, followed by hydrolysis of the chiral auxiliary. The stereochemistry of the alkylation reaction was confirmed by an X-ray crystal structure of (4R)-4-benzyl-3-[(2S)-2-benzyloxymethyl-3-(2- fluoro-4-methylphenyl)propionyl]-2-oxazolidinone.     

Cyclisation at very high temperature. Thermal transformations of N-alkyl and N,N-dialkyl cinnamic amides into pyrrolidin-2-ones under FVT conditions

Novel cyclisations of N-alkyl and N,N-dialkyl cinnamic amides to the corresponding pyrrolidin-2-ones under the conditions of flash vacuum thermolysis, are described. It was found that this reaction proceeds at 950-1000 °C affording a mixture of isomeric pyrrolidin-2-ones in various yields. Two possible mechanisms are proposed for the process.     

Uniqueness in the inverse transmission scattering problem for periodic media

We study the problem of the scattering by a periodic, penetrable medium. We present certain uniqueness results and give the integral equation formulation of the transmission problem which is of Fredholm type and provides the existence and continuous dependence result. Next we investigate the question of the uniqueness for the inverse transmission problem, i.e. we concentrate on the amount of information that is necessary to completely determine the profile and constitutive parameters of the scattering grating. Copyright © 1999 John Wiley & Sons, Ltd.     

Decision Rules Derived from Optimal Decision Trees with Hypotheses

Conventional decision trees use queries each of which is based on one attribute. In this study, we also examine decision trees that handle additional queries based on hypotheses. This kind of query is similar to the equivalence queries considered in exact learning. Earlier, we designed dynamic programming algorithms for the computation of the minimum depth and the minimum number of internal nodes in decision trees that have hypotheses. Modification of these algorithms considered in the present paper permits us to build decision trees with hypotheses that are optimal relative to the depth or relative to the number of the internal nodes. We compare the length and coverage of decision rules extracted from optimal decision trees with hypotheses and decision rules extracted from optimal conventional decision trees to choose the ones that are preferable as a tool for the representation of information. To this end, we conduct computer experiments on various decision tables from the UCI Machine Learning Repository. In addition, we also consider decision tables for randomly generated Boolean functions. The collected results show that the decision rules derived from decision trees with hypotheses in many cases are better than the rules extracted from conventional decision trees.