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G Gübitz

Publications and source records attributed to G Gübitz.

At least 19 recordsLinked to original sources
PubMed2002

Chiral separation of beta-methyl-amino acids by ligand exchange using capillary electrophoresis and HPLC.

This paper deals with the chiral separation of optical isomers of beta-methyl-amino acids by CE and HPLC using the principle of ligand-exchange. Capillary zone electrophoresis was carried out using Cu(II) complexes of L-4-hydroxyproline (L-4-Hypro), N-(2-hydroxypropyl)-L-4-hydroxyproline (HP-L-4-Hypro) and N-(2-hydroxyoctyl)-L-4-hydroxyproline (HO-L-4-Hypro) as chiral selectors, added to the electrolyte. The HPLC separations were performed on a chiral stationary ligand-exchange chromatography phase containing L-4-Hypro chemically bonded to silica gel. With both techniques nearly all compounds investigated are baseline resolved using different background electrolytes and mobile phases, respectively.

Amino Acids↗
PubMed2002

Production of laccase by a newly isolated strain of Trametes modesta.

The effects of the carbon and nitrogen sources, initial pH and incubation temperature on laccase production by Trametes modesta were evaluated using the one-factor-at-a-time method. The final optimisation was done using a central composite design resulting in a four-fold increase of the laccase activity to 178 nkat ml(-1). Response-surface analysis showed that 7.34 g l(-1) wheat bran, 0.87 g l(-1) glucose, 2.9 g l(-1) yeast extract, 0.25 g l(-1) ammonium chloride, an initial pH of 6.95 and an incubation temperature of 30.26 degrees C were the optimal conditions for laccase production. Laccase produced by T. modesta was fully active at pH 4 and at 50 degrees C. The laccase was very stable at pH 4.5 and at 40 degrees C but half-lives decreased to 120 and 125 min at higher temperature (60 degrees C) and lower pH (pH 3).

Biotechnology↗
PubMed2001

Chiral ligand-exchange capillary electrophoresis.

This review summarizes the application of capillary electrophoresis and capillary electrochromatography for the chiral separation of various substance classes using the principle of ligand exchange. The application of this principle to various substance classes is reported.

Chromatography↗
PubMed2001

Enantioselective high-performance liquid chromatography of therapeutically relevant aminoalcohols as their fluorescent 1-naphthyl isocyanate derivatives.

A method for determining the enantiomers of 10 therapeutically relevant aminoalcohols using HPLC and precolumn derivatization was developed. Naphthyl isocyanate reacted with racemic aminoalcohols to form urea derivatives which were separated isocratically on a cellulose tris(3,5-dimethylphenylcarbamate) coated silica gel column, and detected fluorometrically in the lower ng mL(-1) range. The effluents can also be monitored at lower sensitivity, using an ultraviolet detector operated at 220 nm.

Amino Alcohols↗
PubMed2000

Hydrolysis of isolated coffee mannan and coffee extract by mannanases of Sclerotium rolfsii.

Different mannanase preparations obtained from the filamentous fungus Sclerotium rolfsii were used for the hydrolysis of coffee mannan, thus reducing significantly the viscosity of coffee extracts. Mannan is the main polysaccharide component of these extracts and is responsible for their high viscosity, which negatively affects the technological processing of instant coffee. Coffee mannan was isolated from green defatted Arabica beans by delignification, acid wash and subsequent alkali extraction with a yield of 12.8%. Additionally, coffee extract polysaccharides were separated by alcohol precipitation and were found to form nearly half of the coffee extract dry weight. These isolated mannans as well as the mannan in the coffee extract were efficiently hydrolysed by the S. rolfsii mannanase, which resulted in significant viscosity reductions. Concurrently, the reducing sugar content increased continuously due to the release of various mannooligosaccharides including mannotetraose, mannotriose, and mannobiose. Both a partially purified, immobilised and a soluble, crude mannanase preparation were successfully employed for the degradation of coffee mannan.

Basidiomycota↗
PubMed2000

Application of ligand-exchange capillary electrophoresis to the chiral separation of alpha-hydroxy acids and beta-blockers.

The application of the principle of ligand-exchange capillary electrophoresis to two substance classes is described. As chiral selector N-(2-hydroxyoctyl)-L-4-hydroxyproline-copper(II) complex was used. This principle was applied to the chiral separation of alpha-hydroxy acids and drugs containing amino alcohol structure such as beta-blockers. The enantioselectivity was found to be strongly dependent on pH corresponding to the optimal conditions for complex formation for each structure class.

Adrenergic beta-Antagonists↗
PubMed2000

HPLC enantiomeric resolution of novel aromatase inhibitors on cellulose- and amylose-based chiral stationary phases under reversed phase mode.

The chiral resolution of seven aromatase inhibitors (four triazole derivatives (Ia, Ib, Ic, and Id) and three tetrazole derivatives (IIa, IIb, and IIc)) was achieved on Chiralcel OJ-R [cellulose tris (4-methyl benzoate)], Chiralcel OD-RH [cellulose tris (3,5-dimethylphenyl carbamate)], and Chiralpak AD-RH [amylose tris (3,5-dimethylphenyl carbamate)] chiral stationary phases. The mobile phases used were A: 2-PrOH-MeCN (90:10, v/v); B: 2-PrOH-MeCN (50:50, v/v); C: MeCN-H(2)O (50:50, v/v); D: MeCN-H(2)O (80:20, v/v); and E: MeCN-H(2)O (95:05, v/v). The flow rate was 0.5 mL/min for all the mobile phases. The resolution capability of these chiral stationary phases were in the order Chiralpak AD-RH > Chiralcel OD-RH > Chiralcel OJ-R. The values of alpha and Rs of the resolved enantiomers of the aromatase inhibitors varied from 1.02-5.63 and 1. 12-6.72, respectively.

Amylose↗
PubMed2000

Chiral separation of amino acids by ligand-exchange capillary electrochromatography using continuous beds.

A chiral ligand-exchange phase for capillary electrochromatography based on continuous bed technology was developed. The chiral stationary phase is prepared by a one-step in situ copolymerization procedure using methacrylamide, piperazine diacrylamide, vinylsulfonic acid and N-(2-hydroxy-3-allyloxypropyl)-L-4-hydroxyproline. These chiral continuous beds are inexpensive and easy to prepare. They also have several advantages over silica-based packed capillaries. Since the bed is covalently attached to the capillary wall, no frit is required. The applicability of this new approach to the chiral separation of underivatized amino acids is demonstrated.

Amino Acids↗
PubMed2000

Recent progress in chiral separation principles in capillary electrophoresis.

This review summarizes recent developments in the field of chiral separations by electromigration techniques including capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE), isotachophoresis (ITP), electrokinetic chromatography (EKC), and capillary electrochromatography (CEC). This overview focuses on the development of new chiral selectors and the introduction of new techniques rather than applications of already established selectors and methods. The mechanisms of the different chiral separation principles are discussed.

Animals↗
PubMed2000

Chiral separation by capillary electrochromatography.

The state of art in chiral capillary electrochromatography is reviewed. Chiral separations by capillary electrochromatography were carried out using capillaries packed with chiral stationary phases or achiral stationary phases in combination with a chiral selector added to the mobile phase. Furthermore, the use of open tubular capillaries containing the chiral selector coated to the capillary wall was also reported. Among other separation principles moleculary imprinted polymers represent a challenging approach for chiral capillary electrochromatography. A recent trend is the use of polymeric continuous beds with a chiral selector incorporated.

Chromatography, High Pressure Liquid↗
PubMed1999

Chiral separation of sympathomimetics by ligand exchange capillary electrophoresis.

A rapid and simple approach to the chiral separation of sympathomimetic drugs with amino alcohol structure by ligand exchange capillary electrophoresis is described. An N-(2-hydroxyoctyl)-L-4-hydroxyproline/copper(II) complex is used as chiral selector. Thirteen sympathomimetics were resolved, nine with baseline resolution. The influence of pH and composition of the electrolyte on resolution was investigated. The optimal pH for complexation of these amino alcohols was found to be 12.

Electrophoresis, Capillary↗
PubMed1998

Stereoselective interaction of drug enantiomers with human serum transferrin in capillary zone electrophoresis (II).

Further studies on chiral resolution of drugs with different chemical structures by capillary zone electrophoresis using iron-free human serum transferrin are described. The substances passed a highly concentrated pseudo-stationary protein zone applied in a coated capillary and the possible chiral separation of the optical isomers was followed. Eighteen drugs with different structures were screened, and the enantiomers of clofedanol, buphenine, acebutolol and chlorphenamine were resolved. Several, but not all drugs, showed longer migration times while passing the protein zone, indicating an interaction with transferrin, although chiral resolution was not observed in all cases. The observations provided further information about the properties of the surface interaction sites of transferrin.

Electrophoresis, Capillary↗
PubMed1998

Chiral separation of alpha-amino acids by ligand-exchange capillary electrophoresis using N-(2-hydroxy-octyl)-L-4-hydroxyproline as a selector.

The direct chiral resolution of underivatized alpha-amino acids by capillary zone electrophoresis (CZE) based on the principle of ligand exchange is described. An N-(2-hydroxyoctyl)-L-4-hydroxyproline/Cu(II) complex was used as a chiral selector. Besides amino acids containing aromatic residues, the basic amino acid histidine was resolved. Baseline separations were obtained for all amino acids investigated. The influence of selector concentration, electrolyte composition and pH on the resolution was investigated. It was found that there is a correlation between pI of the amino acids and the optimal pH.

Amino Acids↗
PubMed1998

Efficient production of mannan-degrading enzymes by the basidiomycete Sclerotium rolfsii.

Sclerotium rolfsii CBS 191.62 was cultivated on a number of carbon (C) sources, including mono- and disaccharides, as well as on polysaccharides, to study the formation of different mannan-degrading enzyme activities. Highest levels of mannanase activity were obtained when alpha-cellulose-based media were used for growth, but formation of mannanase could not be enhanced by employing galactomannan as the only carbon source. Although both xylanase and cellulase formation was almost completely repressed when S. rolfsii was grown on more readily metabolizable carbohydrates, including glucose or mannose, considerable amounts of mannanase activity were secreted under these growth conditions. Enhanced mannanase production only commenced when glucose was depleted in the medium. The maximal mannanase activity of 240 IU/mL obtained in a laboratory fermentation is remarkable. Mannanase activity formed under these derepressed conditions could be mainly attributed to one major, acidic mannanase isoenzyme with a pI value of 2.75.

Basidiomycota↗
PubMed1998

Development of solid-phase chemiluminescence immunoassays for digoxin comparing flow injection and sequential injection techniques.

The development of a competitive solid-phase immunoassay for digoxin making use of the acridinium chemiluminescence system is described. Two different instrumental approaches are compared. One is based on a continuous flow system using a peristaltic flow injection analysis pump; the other uses a new sequential injection technique. In both systems a flow cell, consisting of transparent PTFE tubing packed with immobilized antibodies, acts as an immunoreactor. The entire assay, including both the immunoreaction and the chemiluminescence reaction, takes place in this immunoreactor cell. Compared with the flow injection technique, the sequential injection mode showed higher precision, ranging from 2.16 to 5.5% RSD depending on concentration. The total assay time, including regeneration, is less than 8 min with the sequential injection technique. The detection limit for both techniques is in the low femtomole range.

Cardiotonic Agents↗
PubMed1996

Chiral resolution of the dansyl derivative of 2-methyltaurine by capillary electrophoresis.

A cyclodextrin-modified micellar capillary electrophoretic method was developed for the chiral separation of 2-methyltaurine. The racemic mixture was separated after derivatization with dansyl chloride. The enantiomeric separation of the dansyl derivative was done using electrolyte solutions containing beta-cyclodextrin (beta-CD) or different ratios of beta- and gamma-CD. The mixture of beta- and gamma-CD optimally resolved the compound studied.

Cyclodextrins↗