HPLC-MS of anthraquinoids, flavonoids, and their degradation products in analysis of natural dyes in archeological objects

LC with MS detection was optimized for sensitive and selective analysis of main classes of natural dyes used in ancient times for dyeing textiles -- red anthraquinoids, yellow flavonoids, and known degradation products of flavonols -- hydroxybenzoic acids. Fragmentation patterns of both negative and positive molecular ions for the above mentioned compounds were investigated. Three acquisition modes of MS analysis: scanning, SIM, and multiple reaction monitoring (MRM) in both positive and negative ion modes were optimized and compared with each other and with the UV-Vis diode-array detection. Even though in the applied chromatographic system formic acid was used in the mobile phase, SIM in the negative ion mode was the most selective and sensitive detection for all the investigated compounds when both mixtures of standards and analysis of extracts from archeological samples were concerned, with one exception -- alizarin, for which MS detection in positive ion mode was more sensitive. Detection limits obtained with MS detection for all investigated compounds except quinizarin were lower than the ones obtained with the diode-array UV-Vis detection, making MS detection the most suitable tool for the analysis of natural dyes and their degradation products in extracts from archeological samples.     

Distance sets of well-distributed planar sets for polygonal norms

LetX be a two-dimensional normed space, and letBX be the unit ball inX. We discuss the question of how large the set of extremal points ofBX may be ifX contains a well-distributed set whose distance set Δ satisfies the estimate |Δ∩[0,N]|≤CN ^3/2-ε. We also give a necessary and sufficient condition for the existence of a well-distributed set with |Δ∩[0,N]|≤CN.     

The surface properties of iron catalyst for ammonia synthesis

The reduction process and the surface properties of industrial prereduced triply and doubly promoted iron catalyst for ammonia synthesis have been studied using thermogravimetry, thermal desorption of N₂ and X-ray diffraction. The properties of both catalysts have been discussed on the basis of the double layer model of iron catalyst. A concept of facet formation on the active surface of the catalysts has been proposed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Secondary structure elements in polylactic acid models

Geometry optimization results are reported on putative elements of secondary structure in decameric units of polylactic acid (PLA) analogous to those seen in protein structure—helical structures (α, π, 3₁₀) as well as a β-sheet—employing molecular mechanics, semiempirical, ab initio and density functional methods. The four possible structures of the deca-PLA are generally predicted, with all methods to be within ~15 kcal/mol of each other, with the more stable conformation varying depending on the method employed. The highest-level method employed here (M062x/6-311+G**) predicts that the α, π and 3₁₀ structures have very similar energies, with π slightly favored by values within the error limits of the method; this is in contrast with results obtained with less accurate semiempirical and empirical methods, which predict larger differences and other structures as favorites. Relative energies of poly-l and poly-d,l lactic acid structures indicate the former to be energetically-favored over the latter. Three types of weak interactions appear to dictate the relative stabilities of secondary structure elements in polylactic acid structures.     

Right Nuclei of Quasigroup Extensions

The aim of this article is the study of right nuclei of quasigroups with right unit element. We investigate an extension process in this category of quasigroups, which is defined by a slight modification of non-associative Schreier-type extensions of groups or loops. The main results of the article give characterizations of quasigroup extensions satisfying particular nuclear conditions. We apply these results for constructions of right nuclear quasigroup extensions with right inverse property.     

Diamino Acid Derivatives of Porphyrins Penetrate into Yeast Cells, Induce Photodamage, but Have No Mutagenic Effect

The yeast Saccharomyces cerevisiae was used as a model eukaryotic organism to study the uptake of diamino acid derivatives of porphyrins and their phototoxicity with particular emphasis on possible mutagenic effects. The water-soluble hematoporphyrin derivatives diarginate (HpD[Arg]₂) and 1-arginin di(N-amino acid)-protoporphyrinate used in this study are effective photosensitizers in tumor photodynamic therapy. Depending on the amino acid substituent, the porphyrin derivatives differ in their affinity for yeast cells. It is shown that HpD(Arg)₂ and PP(Met)₂ (Arg)₂ penetrate into the yeast cell and are metabolized. Both compounds sensitize yeast cells to photodamage but have no mutagenic effect on nuclear or mitochondrial genomes.     

An assisted solvolysis of 23-spirostanyl bromides and tosylates. A new rearrangement of spirostanes to the bisfuran systems

Steroidal sapogenins bearing a good leaving group at C23 undergo a completely stereospecific rearrangement under a variety of conditions via a mechanism involving neighboring-group participation by the acetal oxygen atom in the departure of the nucleofuge from C23. The reactions of equatorial (23S)-23-bromo- or (23S)-23-tosyloxyspirostanes with either the alpha (25R) or beta (25S) oriented 25-methyl group lead to the bisfuran products with inversion of configuration at C23. The reactions of the starting compounds with axial substituents (23R) at C23 require drastic conditions and result in the formation of the corresponding olefin accompanied by the rearranged product (in the case of the 25S isomer only).     

Analysis of drying oils used as binding media for objects of art by capillary electrophoresis with indirect UV and conductivity detection

Capillary electrophoresis (CE) was applied to analyse the long-chain fatty acid composition of vegetable oils, and their degradation products formed upon ageing when drying oils are used as binding media. The analytes were detected with contactless conductivity detection (CCD) and indirect UV absorption, both detectors positioned on-line at the separation capillary. The long-chain fatty acids were resolved in a background electrolyte (BGE) consisting of phosphate buffer (pH = 6.86, 15 mM) containing 4 mM sodium dodecylbenzensulfonate, 10 mM Brij 35, 2% (v/v) 1-octanol and 45% (v/v) acetonitrile. As in this system dicarboxylic analytes, the products of oxidative degradation of unsaturated fatty acids, cannot be determined, a suitable background electrolyte was developed by the aid of computer simulation program PeakMaster. It makes use of a 10 mM salicylic acid, 20 mM histidine buffer, pH 5.85, which combines buffering ability with the optical properties obligatory for indirect UV detection. This buffer avoids system eigenpeaks, which are often impairing the separation efficiency of the system. Separation of the dicarboxylic analytes was further improved by a counter-directed electroosmotic flow (EOF), obtained by dynamically coating the capillary wall with 0.2 mM cetyltrimethylammonium bromide. Long-chain fatty acids and their decomposition products could be determined in recent and aged samples of drying oils, respectively, and in samples taken from two paintings of the 19th century.     

Phase relations in subsolidus area of ZnO-V2O5-Fe2O3 system

Phase equilibria in subsolidus area in the ZnO-V₂O₅-Fe₂O₃ system have been investigated over the whole concentration range of the oxides. The components of this system form two compounds: Zn₂FeV₃O₁₁ and Zn₃Fe₄(VO₄)₆. A solidus area projection onto the component concentration triangle plane of the ZnO-V₂O₅-Fe₂O₃ system has been constructed using DTA and XRD methods. 11 subsidiary subsystems can be distinguished in this system. Melting temperatures of mixtures of solid phases coexisting at equilibrium in each of subsidiary subsystems were determined. This revised version was published online in July 2006 with corrections to the Cover Date.