Biomedical subjects

Merike Vaher

Publications and source records attributed to Merike Vaher.

10 recordsLinked to original sources

PubMed2006

Characterization of the antioxidative activity of novel nontoxic neuropeptides by using capillary electrophoresis.

In the present study, we have monitored the oxidation process of novel nontoxic neuropeptides and determined its rate constants, which describe the antioxidative potential of the peptides. A capillary electrophoretic method was implemented which ensures the simultaneity of analysis of reactants and products in a short time of analysis. The rate constants of oxidation of the four novel peptides, 4-methoxy-L-tyrosinyl-gamma-L-glutamyl-L-cysteinyl-glycine (UPF1), D-serinyl-gamma-L-glutamyl-L-cysteinyl-glycine (UPF6), 4-methoxy-L-tyrosinyl-alpha-L-glutamyl-L-cysteinyl-glycine and D-serinyl-alpha-L-glutamyl-L-cysteinyl-glycine, designed by us, were compared with those of oxidation of glutathione (reduced glutathione) by using capillary electrophoresis. The second-order rate constants were similar for all peptides if the oxidation was carried out with hydrogen peroxide (k(II) = 0.208 - 0.236 x 10(3)/M.min). The rate constants were also determined for the mixtures of peptides. When the oxidation is caused by hydroxyl radical (OH*), the gamma-glutamate containing peptides (UPF1 and UPF6) exhibited two to four times higher antioxidative activity (k(II) = 4.428 and 2.152 x 10(3)/M.min, respectively). The results suggest that the antioxidative potential of the peptides studied is not determined by the formation of disulphide bridge alone.

Antioxidants↗

PubMed2006

Comparison of the stability of glutathione and related synthetic tetrapeptides by HPLC and capillary electrophoresis.

Glutathione and related peptides are interesting targets as protectors of biological systems against an oxidative injury. Two novel glutathione analogues, UPF1 and UPF15, have been designed and synthesised. As a result of different reactions taking place, the thiol-containing compounds oxidise to disulfides. In this study, the stability of UPF1, UPF15 and glutathione in various solutions was investigated by using HPLC and CE. The results showed that UPF1 and UPF15 are powerful hydroxyl radical scavengers and their dimerisation process velocity is higher than that of glutathione.

Chromatography, High Pressure Liquid↗

PubMed2005

Characterization of phenolic profiles of Northern European berries by capillary electrophoresis and determination of their antioxidant activity.

Berries are known to contain phenolic substances (i.e., flavonoids and phenolic acids), which comprise two large and heterogeneous groups of biologically active nonnutrients. This investigation evaluated the content and profile of the phenolic compounds present in six different berries found in Northern Europe. The latter included bilberry (Vaccinium myrtillus), cowberry (Vaccinium vitis-idaea), cranberry (Vaccinium oxycoccus), strawberry (Fragaria ananassa), black currant (Ribes nigrum), and red currant (Ribes rubrum). The study was focused on two areas. The first involved the extraction and analysis of berries for total phenolic content and determination of their antioxidant activity. The total phenolic level of berries was correlated with their antioxidant activity. Second, the berry extracts were analyzed by capillary electrophoresis to determine the content and profile of selected bioactive compounds. The analytes of interest included trans-resveratrol, cinnamic acid, ferulic acid, p-coumaric acid, quercetin, and morin.

Antioxidants↗

PubMed2005

Specific background electrolytes for nonaqueous capillary electrophoresis.

The use of organic solvents or mixture of solvents in capillary electrophoresis is gaining wider attention. The electroosmotic flow mobility of eight organic solvents (acetonitrile, acetone, dimethylformamide, dimetylsulphoxide, propylene carbonate, methanol, ethanol, n-propanol) and of mixtures of several solvents (methanol-acetonitrile, methanol-propylene carbonate, acetonitrile-propylene carbonate) has been studied. The influence of 1,3-alkylimidazolium salts in different solvents on the separation of different analytes has been investigated. Some of these salts have shown usefulness for matrix-assisted laser desorption ionization matrices and off-line analysis of electrophoresis fractions. It also appears that nonaqueous capillary electrophoresis with 1,3-alkylimidazolium salts as background electrolytes is suitable for separation small inorganic ions.

Electrolytes↗

PubMed2005

On-column capillary electrophoretic monitoring of rapid reaction kinetics for determination of the antioxidative potential of various bioactive phenols.

An on-column capillary electrophoretic procedure for the determination of the antioxidative potential of various bioactive phenols, found in plant, fruit, and vegetable extracts, is described. The assay is based on a rapid mixing of phenols or phenolic extracts before the capillary, followed by pressurized injection of the reaction mixture into the capillary. After incubation of the reaction mixture inside the capillary, high voltage is switched on and separation of reactants and products is performed. Using hydrogen peroxide as a stressor, the kinetics of the oxidation of various bioactive phenols was studied (rutin, chlorogenic acid, quercetin, caffeic acid, gallic acid, and combinations of these) and compared with the oxidation rate of L-ascorbic acid as a reference. The concept was demonstrated for the determination of the antioxidative potential of various polyphenol mixtures and of the methanol extract of the sea buckthorn (Hippophae rhamnoides L.). In most cases quercetin has the highest rate constant of oxidation among the tested phenolic compounds. However, in the mixture L-ascorbic acid/quercetin, the oxidation rate of L-ascorbic acid was enhanced and oxidation of quercetin was strongly inhibited compared with the other combinations of tested polyphenols.

Antioxidants↗

PubMed2004

Analysis of bioactive ingredients in the brown alga Fucus vesiculosus by capillary electrophoresis and neutron activation analysis.

Two different types of bioactive components of the seaweed Fucus vesiculosus were analysed: (1) polyphenols (phlorotannins) by capillary electrophoresis (CE) and (2) mineral part (including bioactive microelements) by neutron activation analysis (NAA). CE experiments were carried out using a UV detector (at 210 nm) and an uncoated silica capillary. The best separation was achieved at a voltage of 20 kV using borate or acetate buffer in a methanol/acetonitrile mixture as background electrolyte. The CE analysis data were confirmed by high-performance liquid chromatography (HPLC). Determination of mineral composition of algal biomass by NAA was performed on the basis of various nuclides; the best results (from 38 elements determined) were obtained for Mn, Fe, Zn, As, Br, Sr, I, Ba, Au and Hg.

Chromatography, High Pressure Liquid↗

PubMed2004

Stroboscopic sampling in comprehensive high-performance liquid chromatography-capillary electrophoresis via a pneumatic sampler.

A new approach is presented to solve the problem of a long separation time in the second dimension of comprehensive two-dimensional chromatography. The need for a rapid separation in the second column is overcome by repeating analysis of a sample many times. In each of these individual analysis cases the sample is injected into the first dimension column and after a delay a low amount of the effluent at the end of the first column is sampled to the second-dimensional column. The time interval between the samplings from the first column to the second column is constantly increased. Thus, the system enables a comprehensive analysis of the effluent emerging from the first into the second column. This approach, which we call stroboscopic sampling, is tested for coupling high-performance liquid chromatography (HPLC) to capillary electrophoresis (CE) by an interface which operates on the principle of transporting the effluent from the HPLC column to the capillary inlet by small pressure pulses (0.5 MPa). The performance of the interface for accomplishing the comprehensive HPLC-CE analysis was demonstrated for an on-line connection of a short ion-exchange column and an ion-exclusion column to the CE capillary.

Chromatography, High Pressure Liquid↗

PubMed2003

Separation of polyphenolic compounds extracted from plant matrices using capillary electrophoresis.

Phenolic compounds constitute a large group of secondary plant products whose chemical structure may range from quite simple compounds to highly polymerized substances. The polyphenols content have been investigated in the alcoholic extract of the fruits of three different plants: sweet gale, sea buckthorn, hiprose. The trans-resveratrol content we have studied in roots, stems, leaves and flowers of Japanese knotweed grown in Estonia. Plant material was pre-treated in two different ways: by infusing with methanol and by supercritical fluid extraction with carbon dioxide modified with different alcohols. The relationship between variables (pressure, temperature, modifier amount) and yields are examined. The capillary zone electrophoresis methods were developed for the separation of polyphenolic anti-oxidative compounds. Using both water based borate buffer and acetonitrile based non-aqueous media it was possible to get reliable separation of several polyphenolic compounds. Based on that there has been identified such as flavone, trans-resveratrol, catechin, chlorogenic acid, quercetin and myricetin in plant extracts. Changes in the relative concentrations of trans-resveratrol in different parts of the knotweed have been established.

Electrophoresis, Capillary↗

PubMed2003

Heteroconjugation-based capillary electrophoretic separation of phenolic compounds in acetonitrile and propylene carbonate.

A mixture of methyl- and hydroxy-substituted phenols was separated by capillary electrophoresis in pure acetonitrile and propylene carbonate. Interactions between undissociated phenolic compounds and the background electrolytes were investigated. In the present work, benzyltriethylammonium chloride, tetrabutylammonium acetate, and two room temperature-molten salts, 1-butyl-3-methyl imidazolium trifluoroacetate and 1-butyl-3-methyl imidazolium heptafluorobutanoate, were used as background electrolytes. The formation of a negative complex between background electrolyte anion and neutral phenolic compound was observed and the formation constant calculated. The formation constants for anion-analyte complexes were approximately the same in propylene carbonate and in acetonitrile. In both solvents the formation constants were the highest for acetate and the lowest for trifluoroacetate. The separation of analytes was slightly influenced by the nature of the solvent: in acetonitrile the resolution between peaks was higher for 1,3-dihydroxyphenol and 1,3,5-trihydroxyphenol, in propylene carbonate 3-methylphenol and phenol were better separated. It was demonstrated that traces of water influence the mobilities of anion-phenol complexes in propylene carbonate.

Acetonitriles↗

PubMed2002

Ionic liquids as electrolytes for nonaqueous capillary electrophoresis.

Acetonitrile is a well-suited medium for nonaqueous capillary electroseparations and enables extending the range of applications of capillary electrophoresis (CE) techniques to more hydrophobic species. In this study, the dialkylimidazolium-based low temperature melting organic salts know as "ionic liquids" (ILs) are used as electrolytes. At room temperature these liquids are miscible with acetonitrile which makes it easy to use them for adjustment of analyte mobility and separation. The anionic part as well as the concentration of an IL influence the general electrophoretic mobility of the buffer system. The separation of different analytes is achieved because they become charged in the presence of ILs in separation media. There is also a possibility for a complex formation between the solute and the electrolyte which alters the mobility of the solute. A selected application of separations of phenols and aromatic acids will be discussed.

Electrolytes↗