Reversed-Phase Pressurized Planar Electrochromatography and Planar Chromatography of Acetylsalicylic Acid,Caffeine, and Acetaminophen

JPC – Journal of Planar Chromatography – Modern TLC - We have investigated the use of pressurized planar electrochromatography (PPEC) and planar chromatography (TLC) for reversed-phase...     

Radical Stability Directs Electron Capture and Transfer Dissociation of β‐Amino Acids in Peptides

We report on the characteristics of the radical‐ion‐driven dissociation of a diverse array of β‐amino acids incorporated into α‐peptides, as probed by tandem electron‐capture and electron‐transfer dissociation (ECD/ETD) mass spectrometry. The reported results demonstrate a stronger ECD/ETD dependence on the nature of the amino acid side chain for β‐amino acids than for their α‐form counterparts. In particular, only aromatic (e.g., β‐Phe), and to a substantially lower extent, carbonyl‐containing (e.g., β‐Glu and β‐Gln) amino acid side chains, lead to N? C_β bond cleavage in the corresponding β‐amino acids. We conclude that radical stabilization must be provided by the side chain to enable the radical‐driven fragmentation from the nearby backbone carbonyl carbon to proceed. In contrast with the cleavage of backbones derived from α‐amino acids, ECD of peptides composed mainly of β‐amino acids reveals a shift in cleavage priority from the N? C_β to the C_α? C bond. The incorporation of CH₂ groups into the peptide backbone may thus drastically influence the backbone charge solvation preference. The characteristics of radical‐driven β‐amino acid dissociation described herein are of particular importance to methods development, applications in peptide sequencing, and peptide and protein modification (e.g., deamidation and isomerization) analysis in life science research.     

Anti-adhesive activities of flavan-3-ols and proanthocyanidins in the interaction of group A-streptococci and human epithelial cells

Bacterial adhesion to epithelial cells is a key step in infections, allowing subsequent colonization, invasion and internalization of pathogens into tissues. Anti-adhesive agents are therefore potential prophylactic tools against bacterial infections. The range of anti-adhesive compounds is largely confined to carbohydrate analogues. Tannins are generously recognized as potent antimicrobials, but little data exist on their anti-adherence potency. Using a model for mucosal pathogenesis with labeled group A-streptococci (GAS) and human laryngeal HEp-2 cells, a series of flavan-3-ols (epicatechin, epigallocatechin, epigallocatechin-3-O-gallate) and highly purified and chemically characterized proanthocyanidin samples including procyanidins based on epicatechin, catechin or 'mixed' constituent flavanyl units, prodelphinidins made up of (epi)gallocatechin monomeric unts as well as oligomers possessing A-type units in their molecules was evaluated for anti-adhesive effects. Reduced microbial adherence was observed exclusively for prodelphinidins, suggesting that pyrogallol-type elements, i.e., (epi)gallocatechin units are important structural features. This is the first report on structure-activity relationships regarding the anti-adhesive potency of proanthocyanidins. In addition, the structures of the first chemically defined proanthocyanidins from Pelargonium sidoides are disclosed.     

Reversed-phase high-performance liquid chromatography determination of selected phenolic acids in propolis concentrates in terms of standardization for drug manufacturing purposes

A reversed-phase high-performance liquid chromatography method with gradient elution was developed for the determination of the caffeic, p-coumaric, and ferulic acids in propolis concentrates. Solid-phase extraction on an RP18 column was applied for preliminary purification, and chromatographic separation was performed on 100 RP18e Lichrospher column of particle size 5 microm. The mobile phase was obtained by mixing in appropriate ratios 0.03 mM NaH2PO4, acidified with H3PO4 up to pH = 3.0, with acetonitrile to obtain a gradient in the elution process. Spectrophotometric detection was conducted at 320 nm. Under the established conditions, the method featured high sensitivity, good precision, and comparability of results, as proven by method validation and statistical analysis of the obtained results. The limits of detection were 0.315, 0.325, and 0.695 microg/mL for caffeic, p-coumaric, and ferulic acids, respectively. The corresponding recovery values were 98.14, 101.05, and 99.42% and the linearity ranges from 1.31 to 99.18 microg/mL, 1.52 to 119.16 microg/mL, and 2.42 to 184.14 microg/mL. The precision of the method was expresed by relative standard deviation values that did not exceed 3%. It was also shown that the propolis concentrates under examination had similar antibacterial activity against Staphylococcus aureus ranging from 119.8 to 124.3 microg/mL, contrary to model mixtures that showed no antibacterial activity.     

Hamiltonian path saturated graphs with small size

A graph G is said to be hamiltonian path saturated (HPS for short), if G has no hamiltonian path but any addition of a new edge in G creates a hamiltonian path in G. It is known that an HPS graph of order n has size at most and, for n?6, the only HPS graph of order n and size is K_n-1∪K₁. Denote by sat(n,HP) the minimum size of an HPS graph of order n. We prove that sat(n,HP)?⌊(3n-1)/2⌋-2. Using some properties of Isaacs’ snarks we give, for every n?54, an HPS graph G_n of order n and size ⌊(3n-1)/2⌋. This proves sat(n,HP)?⌊(3n-1)/2⌋ for n?54. We also consider m-path cover saturated graphs and P_m-saturated graphs with small size.     

Theorems for generalized Favard-Kantorovich and Favard-Durrmeyer operators in exponential function spaces

We consider the Kantorovich and the Durrmeyer type modifications of the generalized Favard operators and we prove some direct approximation theorems for functions f such that w _σ f ∈ L _p (R), where 1 ≤ p ≤ ∞ and w _σ (x) = exp(−σx ²), σ > 0.     

On reactions of spirostane sapogenins with benzeneseleninic anhydride

Direct dehydrogenation of spirostane sapogenins with benzeneseleninic anhydride/iodoxybenzene afforded the Δ²² derivatives in low yields. The reactions catalyzed by BF₃/Et₂O produced the 23-oxo-sapogenins in addition to their 22-oxo-23-spiro-isomers. The reactions of sapogenins with benzeneseleninic anhydride carried out in the presence of TiCl₄ afforded products chlorinated at C23.     

Adsorption of urea on a polycrystalline copper electrode

The adsorption of urea on a polycrystalline copper electrode from 0.01 M NaClO₄ solution has been studied by impedance spectroscopy and radiometric method. The dependence of the surface concentration of urea on the electrode potential and the bulk concentration was determined. From radiometric data, it follows that the adsorption of urea on the copper electrode takes place in the entire range of studied potentials where no faradaic processes occur. In this range, the process of adsorption is practically reversible with respect to the potential and the bulk concentration of urea. The experimental data were described by the Langmuir and the virial isotherms and the Gibbs energy of adsorption were calculated. The data of the urea adsorption on different electrodes have been compared and the role of the kind of the metal on the adsorption process was discussed.     

Modeling toxicity by using supervised kohonen neural networks

Counterprogation neural network is shown to be a powerful and suitable tool for the investigation of toxicity. This study mined a data set of 568 chemicals. Two hundred eighty-two objects were used as the training set and 286 as the test set. The final model developed presents high performances on the data set R(2) = 0.83 (R(2) = 0.97 on the training set, R(2) = 0.59 on the test set). This technique distinguishes itself also for the ability to give to the expert two-dimensional maps suitable for the study of the distribution/clustering of the data and the identification of outliers.