Mechanistic Aspects of Alloxan Diabetogenic Activity: A Key Role of Keto−Enol Inversion of Dialuric Acid on Ionization

The inversion of the keto-enol stability order of dialuric acid on ionization was calculated and verified experimentally. The radical cations in both forms were characterized. The spectrum of the keto form was observed upon direct ionization of dialuric acid under matrix conditions, whereas the enol form was formed upon a sequential electron-proton-proton attachment to alloxan under acidic aqueous condition. Facilitation of the one-electron oxidation of dialuric acid upon its enolization can result in a more effective formation of superoxide radical anion in the process of its auto-oxidation. This process is discussed in reference to the alloxan diabetogenic action. Both neutral keto and enol forms are energetically close, and under favorable conditions, the auto-oxidation of dialuric acid could involve participation of the enol form.

Induction of 3'-O-beta-D-ribofuranosyl adenosine during compatible, but not during incompatible, interactions of Arabidopsis thaliana or Lycopersicon esculentum with Pseudomonas syringae pathovar tomato

All hitherto identified aromatic compounds accumulating in leaves of Arabidopsis thaliana (L.) Heynh. upon infection with virulent or avirulent strains of Pseudomonas syringae pathovar tomato ( Pst) were indolic metabolites. We now report the strong accumulation of a novel type of natural product, 3'-O-beta-D-ribofuranosyl adenosine (3'RA), exclusively during compatible interactions. In contrast to the various indolic metabolites, 3'RA was undetectable in incompatible interactions of A. thaliana leaves with an avirulent Pst strain, as well as in uninfected control leaves. A similar, strong induction of 3'RA was observed in compatible but, again, not in incompatible interactions of Pst with its natural host, Lycopersicon esculentum. The strength of the effect and its confinement to compatible interactions suggests that it may be applicable as a diagnostic tool.

Profiling of flavonoid conjugates in Lupinus albus and Lupinus angustifolius responding to biotic and abiotic stimuli

Qualitative and quantitative composition of flavonoid and isoflavonoid glycosides as well as free aglycones in lupin seedlings (roots and aerial parts) grown under different light conditions or responding to infection with Pleiochaeta setosa, a fungus causing brown leaf spot, were monitored by liquid chromatography with UV and/or mass spectrometric detection. Both physical and biotic factors affected flavonoid and isoflavonoid levels in lupin tissues. Fungal infection evoked significant increase in the amounts of genistein, 2'-hydroxygenistein, and their prenylated derivatives that are thought to function as lupin phytoalexins. Effect on quantitative changes of glycosylated flavonoids and isoflavonoids in the roots and aerial parts was less significant. Moreover, different light conditions applied during seedling growth caused relative changes of flavonoid and isoflavonoid conjugates composition, especially in the leaves of white lupin plants. The chemical structures of flavonoid and isoflavonoid conjugates present in Lupinus angustifolius were elucidated. In addition to genistein and 2'-hydroxygenistein glycosides, flavonol conjugates were identified in leaves, while the composition of root isoflavonoids was similar to that of L. albus reported earlier.

Synthetic vascular prostheses

Polyethyleneterephthalate (PET), and to a lesser extent Teflon have become the major synthetic grafting material. Unlike nylon, Ivalon, and Vinyon-N which lose their tensile strength after implantation, PET and Teflon remain essentially unchanged even after long periods. TRICOMED S.A. produces the family of the knitted vascular implants Dallon made from PET fibres including: Dallon, Dallon H, Tricogel. Both Dallon and Dallon H are manufactured in a form of double (external and internal) velour surface using multifilament yarn and having optimal graft design (a variety of sizes and lengths). The velour surface gives the surface a velvety, plush texture, which improves tissue in--growth. Moreover, Dallon H is a unique vascular prostheses showing the increase in the blood susceptibility that is useful for 4 times less blood demand during preclotting as compared with standard prosthesis. Tricogel graft is made of thin-wall prostheses sealed with the porcine gelatin that provides intraoperative tightness (without preclotting) and the optimal healing process. Hydrophilic behavior of the graft is observed as an instant moistening of the surface with patient's blood and as sweating. The blood stream does not dissolve nor washes away the gelatin but causes the gelatin film to swell, which makes a better tightness. The work will describe the properties of manmade vascular grafts as well as their applications in the vascular surgery.

The complexity of oxidative cross-linking of phenylpropanoids - evidence from an in vitro model system

The development of an in vitro model system to study the process of dimerization of hydroxycinnamic acids is reported. Model compounds ferulic acid (FA) or methyl ferulate were reacted with H2O2 in the presence of horseradish peroxidase (HRP) or peroxidases from Lupinus albus L. apoplastic fluids. Following solid-phase extraction, the reaction products were analysed using gas chromatography-mass spectrometry. Major analytical and biochemical parameters of model reactions were determined and optimized. Six ferulic dimers were identified and quantified. With the use of this model system we found methyl ferulate to be a better substrate for lupin and horseradish peroxidases than FA. Use of various peroxidases did not influence the qualitative composition of reaction products although it affected the rate of substrate utilization and the quantitative output of reactions. Various isoforms of lupin apoplastic peroxidases revealed differentiated specificity towards hydroxycinnamic acids or their methyl esters. The potential of isoflavonoids (major phenolic components in white lupin cell walls) to influence peroxidase-catalysed formation of ferulic dehydrodimers was also tested. Genistein (5,7,4'-trihydroxyisoflavone) and genistin (genistein-7-O-β-glucoside) did not affect the qualitative composition of the reaction products. However, genistein inhibited the rate of ferulic substrate oxidation, while genistin showed the opposite effect, stimulating both utilization of ferulic substrate by HRP and subsequent polymerization and / or degradation of dehydrodimers formed. To our knowledge, this is the first indirect evidence that isoflavonoids might play a regulatory role in the oxidative formation of intermolecular cross-links in cell walls.

Electron-transfer-induced tautomerization in methylindanones: electronic control of the tunneling rate for enolization

The radical cations generated from 4-methyl- and 4,7-dimethylindanone, as well as their deuterated isotopomers, isolated in Argon matrices, were found to undergo enolization to the corresponding enol radical cations at rates that differ by orders of magnitude. It is shown by quantum chemical calculations that the effect of the remote methyl group in the 4-position is of purely electronic nature in that it stabilizes the unreactive pi-radical relative to the reactive sigma-radical state of the 7-methylindanone radical cation. The observed kinetic behavior of the two compounds can be reproduced satisfactorily on the basis of calculated height and width of the thermal barrier for enolization, using the Bell model for quantum mechanical tunneling. High-level calculations on the methylacrolein radical cation show that barriers for enolization in radical cations are overestimated by B3LYP/6-31G.

Profiling changes in metabolism of isoflavonoids and their conjugates in Lupinus albus treated with biotic elicitor

Liquid chromatography with ultraviolet and mass spectrometric detection was applied to monitor changes in profiles of isoflavonoid glycosides and free isoflavonoid aglycones in Lupinus albus L. Four isoflavonoid aglycones, fourteen isoflavonoid glycosides, four flavonol glycosides and flavone glycoside were identified in lupin tissue after LC/ESI/MS analyses. An elicitor preparation from purified yeast cell wall was used to inject the shoots of 3-week old seedlings or to infiltrate the cut lupin leaves. Qualitative and quantitative changes of isoflavonoids were measured at different time points after elicitation. In elicited lupin seedlings increased amounts of prenylated isoflavone aglycones were identified. The concentrations of glycosidic conjugates of isoflavones present in plant tissue were less affected.

Application of mass spectrometry to structural identification of flavonoid monoglycosides isolated from shoot of lupin (Lupinus luteus L.)

Flavonoid glycosides constitute important group of plant secondary metabolites. This class of natural products play significant role in different physiological processes. A new methodological approach where mass spectrometric techniques are applied to structural studies of this class of compounds is presented. Four flavonoid O-monoglycosides and one C-monoglycoside were isolated from green parts of lupin (Lupinus luteus L.). Several different mass spectrometric techniques were applied to structural elucidation of isolated compounds. Desorption ionization mass spectrometry was used for registration of mass spectra of intact and derivatized (permethylated) flavonoid glycosides. In some cases electron impact mass spectra of permethylated compounds were also recorded. Methylated samples after methanolysis and further derivatization of free hydroxyl groups (methylation or acetylation) were analyzed with gas chromatography-mass spectrometry. Combined information drawn from the registered mass spectra enabled us to define molecular mass, structure of aglycones and sugars, and positions of glycosidic bonds on the aglycon. Structures of four flavonoid monoglycosides were elucidated as follows: genistein 7-O-glucoside (1), genistein 4'-O-glucoside (2), 2'-hydroxygenistein 7-O-glucoside (3), and apigenin or genistein 8-C-glycoside (5). For the fourth O-glycoside (4) only molecular mass and masses of the aglycone and sugar were estimated.

Application of mass spectrometry to structural identification of flavonoid monoglycosides isolated from shoot of lupin (Lupinus luteus L.)

Flavonoid glycosides constitute important group of plant secondary metabolites. This class of natural products play significant role in different physiological processes. A new methodological approach where mass spectrometric techniques are applied to structural studies of this class of compounds is presented. Four flavonoid O-monoglycosides and one C-monoglycoside were isolated from green parts of lupin (Lupinus luteus L.). Several different mass spectrometric techniques were applied to structural elucidation of isolated compounds. Desorption ionization mass spectrometry was used for registration of mass spectra of intact and derivatized (permethylated) flavonoid glycosides. In some cases electron impact mass spectra of permethylated compounds were also recorded. Methylated samples after methanolysis and further derivatization of free hydroxyl groups (methylation or acetylation) were analyzed with gas chromatography-mass spectrometry. Combined information drawn from the registered mass spectra enabled us to define molecular mass, structure of aglycones and sugars, and positions of glycosidic bonds on the aglycon. Structures of four flavonoid monoglycosides were elucidated as follows: genistein 7-O-glucoside (1), genistein 4'-O-glucoside (2), 2'-hydroxygenistein 7-O-glucoside (3), and apigenin or genistein 8-C-glycoside (5). For the fourth O-glycoside (4) only molecular mass and masses of the aglycone and sugar were estimated.