Optimization of background electrolytes for capillary electrophoresis: II. Computer simulation and comparison with experiments

A mathematical and computational model described in the previous paper (Gas, B., Coufal, P., Jaros, M., Muzikár, J., Jelínek, L., J. Chromatogr. A 2001, 905, 269-279) is adapted, algorithmized, and a computer program PeakMaster having a status of freeware (http://natur.cuni.cz/ approximately gas) is introduced. The model enables optimization of background electrolyte (BGE) systems for capillary zone electrophoresis. The model allows putting to use uni- or di- or trivalent electrolytes and allows also for modeling highly acidic or alkaline BGEs. It takes into account the dependence of ionic mobilities and dissociation of weak electrolytes on the ionic strength. The model calculates the effective mobility of analytes and predicts parameters of the system that are experimentally available, such as the transfer ratio, which is a measure of the sensitivity in the indirect UV detection or the molar conductivity detection response, which expresses the sensitivity of the conductivity detection. Further, the model enables evaluation of a tendency of the analyte to undergo electromigration dispersion or peak broadening. The suitability of the model is verified by comparison of the predicted results with experiments, even under conditions that are far from ideal (under extreme pH and a high ionic strength).     

Concentration dependencies of NaCl salting of lysozyme by calorimetric methods

Concentration dependence of NaCl salting of lysozyme was investigated in the range of 0.5-9 mM lysozyme concentration in 0.1 M sodium acetate buffer, pH=4.25and the concentration of NaCl up to 0.1 M. Calorimetric experiments were performed with the use of a titration ITC Omega MicroCal calorimeter. It was found that the estimated number of bonding sites depended on the lysozyme concentration. For infinitely diluted lysozyme solution, the number of binding sites could be roughly estimated to ∼50. In the range of 2-9 mM protein concentration, the number of weakly binding (K=2.7±0.8 M⁻¹) sites on the protein surface was estimated to 35±7. McMillan and Mayer’s approach reduced to the third order virial coefficients demonstrates that besides the dominating effect of the protein—salt interaction (a₁₁) the coefficient describing the lysozyme aggregation upon salt addition (a₁₂) is statistically significant.     

Synthesis of alkylphenanthrenes from naphthylalkylidenemalonodinitriles. A route to 1-methyl-, 2-methyl-, and 1,2-dimethylphenanthrene

The study has been carried out to evaluate the feasibility of synthesis of 1-methyl-, 2-methyl-, 1,2-dimethyl-, and 1-ethyl-2-methylphenanthrene through the annulation of the naphthalene system with the exploitation of the dicyanovinyl moiety of 2-naphthylalkylidenemalonodinitriles as an active electrophile in cold solutions of concentrated sulfuric acid. 2-(2-Naphthyl)propanal (3), 1-(2-naphthyl)propan-2-one (9), 3-(2-naphthyl)butan-2-one (14), and 3-(2-naphthyl)pentan-2-one (19) had been condensed with malonodinitrile to afford 2-naphthylalkylidenemalonodinitriles which were then cyclised to give 4-amino-1-methylphenanthrene-3-carbonitrile (5), 4-amino-2-methylphenanthrene-3-carbonitrile (11), 4-amino-1,2-dimethylphenanthrene-3-carbonitrile (16), and 4-amino-1-ethyl-2-metylphenanthrene-3-carbonitrile (21). The nitrile function has been removed from the aminonitriles, with the exception of 21, through hydrolysis and decarboxylation in alkaline ethanolic solutions under elevated pressure (∼3 MPa) and temperature 220-230°C to give the respective 4-amino-methylphenanthrenes. Diazotisation of the phenanthreneamines and the reaction with hypophosphorus acid has lead to the methylphenanthrenes in moderate yields (50-52%).     

The comparative molecular surface analysis (COMSA)--a nongrid 3D QSAR method by a coupled neural network and PLS system: predicting pK(a) values of benzoic and alkanoic acids

A self-organizing neural network was used to design a novel method capable of the quantitative prediction of molecular properties. The method is based on the comparison of molecular surfaces performed by the coupled neural network and PLS system. Unlike CoMFA and related methods it does not compare the properties describing a discrete set of points but the average property values calculated for a certain area of the molecular surface. It has been found that the results of the PLS analysis of the series of the comparative matrices of the molecular electrostatic potential (MEP) are quite stable. Also the results only slightly depend on such parameters as the number of points sampled at the molecular surface (D) or a winning distance (MD) of the self-organizing neurons. The influence of these parameters for modeling the effects limited by steric and electronic effects was determined and the pK(a) values of the ortho-, meta-, and para- (o-, m-, p-) analogues of benzoic acid and selected alkanoic acids were predicted. We generally found that for the series analyzed CoMSA gave better models than CoMFA.     

Sets which are almost starshaped

A nonempty setS in a real topological linear spaceL is said to be quasi-starshaped if and only if there is some pointq in clS such that the subset of points ofS visible viaS fromq is everywhwere dense inS and contains intS, and the set of all such pointsq is called the quasi-kernel ofS and denoted by qkerS. It is proved that forS connected with slncS nonempty {conv Â_z:z slncS} qkerS, where slncS denotes the set of strong local nonconvexity points ofS and Â_z={s clS:z is clearly visible froms via S}. Familiar procedures generate then the Krasnosel'skii-type characterizations for the dimension of the quasi-kernel ofS. This contributes to an open problem.Jakub Oswald gewidmet     

Spatial structure and NMR spectra of strained [2.2.2]cyclophanes

The chemical shifts and coupling constants in the NMR spectra of the title compounds are influenced by their strain and the proximity of the aromatic rings. These parameters are studied by density functional theory (DFT) calculations for 1–4 and measured for 3 and 4. We find that, in spite of the strain, the calculations reproduce the experimental values satisfactorily. This finding is of special importance for novel hypothetical molecules like hexahydrosuperphane 5 for their future identification and in searches of hydrocarbons exhibiting unusual NMR parameters. Our results demonstrate the influence of strain on the parameters studied. Most proton and carbon chemical shifts for the molecules under study having nonplanar aromatic rings differ considerably from the corresponding values for the relatively unstrained trimethylbenzenes and ethylbenzene. In addition, the calculated values of the coupling constants through three bonds in most cases do not follow Karplus relation. Copyright © 2009 John Wiley & Sons, Ltd.