Biomedical subjects

Gerald Gübitz

Publications and source records attributed to Gerald Gübitz.

24 records · Page 2Linked to original sources

PubMed2003

Chiral resolution of diastereomeric di- and tripeptides on a teicoplanin aglycone phase by capillary electrochromatography.

The chiral separation ability of a capillary packed with teicoplanin aglycone as a chiral stationary phase was investigated. This stationary phase was used successfully for chiral resolution of both diastereomeric dipeptides and tripeptides possessing one or two chiral centers. The composition of the mobile phase was shown to be crucial for separation. The use of reversed-phase mode was clearly superior to the polar-organic mode. The nature of the organic modifier was found to have a marked influence on separation. After optimizing conditions, all diasteromeric dipeptides and tripeptides investigated were baseline-resolved, however, it was not possible to find a uniform mobile phase showing optimal results for all peptides investigated.

Chromatography↗

PubMed2003

Role of the charge in continuous beds in the chiral separation of hydroxy acids by ligand-exchange capillary electrochromatography.

This paper deals with the chiral separation of hydroxy acids using diallyl-dimethylammonium chloride as a positive charge-providing agent in the continuous bed. The chiral continuous bed was prepared by in situ copolymerization of monomers, including an L-4-hydroxyproline derivative as a chiral selector. This phase was applied to the chiral separation of hydroxy monocarboxylic acids and hydroxy dicarboxylic acids, respectively. The influence of both the selector concentration and the charge-providing agent on retention and separation was investigated.

Chromatography, Ion Exchange↗

PubMed2002

Influence of structure and chirality of the selector on the chiral recognition of amino acids using ligand-exchange capillary electrophoresis.

The dependence of the chiral recognition ability and enantiomer migration order on the structure, substitution pattern and chirality of chiral selectors used in ligand-exchange capillary electrophoresis is investigated. As chiral selectors different N-alkyl derivatives of proline and hydroxyproline as their copper(II) complexes are used. The influence of the position and conformation of the hydroxy group in the hydroxyproline derivatives and of the structure and chirality of the side chain on enantioselectivity is investigated. Furthermore, the effect of surfactants such as sodium dodecyl sulfate and cetyl trimethyl ammonium bromide on resolution and enantiomer migration order is studied. The investigations were carried out with three aromatic amino acids as model compounds.

Amino Acids↗

PubMedDate not supplied

Development of enantioselective chemiluminescence flow- and sequential-injection immunoassays for alpha-amino acids.

The development of an enantioselective flow-through chemiluminescence immunosensor for amino acids is described. The approach is based on a competitive assay using enantioselective antibodies. Two different instrumental approaches, a flow-injection (FIA) and a sequential-injection system (SIA), are used. Compared to the flow-injection technique, the sequential injection-mode showed better repeatability. Both systems use an immunoreactor consisting of a flow cell packed with immobilized haptens. The haptens (4-amino-L- or D-phenylalanine) are immobilized onto a hydroxysuccinimide-activated polymer (Affi-prep 10) via a tyramine spacer. Stereoselective antibodies, raised against 4-amino-L- or D-phenylalanine, are labeled with an acridinium ester. Stereoselective inhibition of binding of the acridinum-labeled antibodies to the immobilized hapten by amino acids takes place. Chiral recognition was observed not only for the hapten molecule but also for a series of different amino acids. One assay cycle including regeneration takes 6:30 min in the FIA mode and 4:40 min in the SIA mode. Using D-phenylalanine as a sample, the detection limit was found to be 6.13 pmol/ml (1.01 ng/ml) for the flow-injection immunoassay (FIIA) and 1.76 pmol/ml (0.29 ng/ml ) for the sequential-injection immunoassay (SIIA) which can be lowered to 0.22 pmol/ml (0.036 ng/ml) or 0.064 pmol/ml (0.01 ng/ml) by using a stopped flow system. The intra-assay repeatability was found to be about 5% RSD and the inter-assay repeatability below 6% (within 3 days).

Acridines↗

PubMedDate not supplied

Chiral separation of thiazide diuretics by HPLC on Chiralcel OD-RH, Chiralcel OJ-R and Chirobiotic-T phases.

This contribution deals with comparative studies on the chiral separation of thiazide diuretics using cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD-RH), cellulose tris(4-methylbenzoate) (Chiralcel OJ-R) and teicoplanin (Chirobiotic T) phases. All columns showed good chiral recognition ability for this class of compounds. Out of seven compounds investigated, six were resolved with baseline resolution with at least one of the three columns.

Benzoates↗

PubMedDate not supplied

Chiral separation of bioactive cyclic Mannich ketones by HPLC and CE using cellulose derivatives and cyclodextrins as chiral selectors.

The chiral separation of cyclic Mannich ketones of potential pharmaceutical interest is investigated using HPLC and CE. These Mannich ketones show a marked antibacterial and antifungal activity. In HPLC, stationary phases containing cellulose derivatives or beta-cyclodextrin were used and in CE different cyclodextrins, such as beta-CD, gamma-CD, carboxymethyl-beta-CD and succinyl-beta-CD were added to the background electrolyte as chiral selectors.

Biological Assay↗