Noriyuki Watanabe

Enantiomeric resolution of amino acids by high-performance ligand-exchange chromatography using histidine-bonded silica gel

The preparation of histidine-bonded silica gel is described. The formation of an amide bond between aminopropyl silica gel and Boc-Histidine (imTos) and cleavages of the protecting groups were characterized by IR spectroscopy. This histidine-bonded silica gel was able to resolve enantiomers of many amino acids, irrespective of the type of amino acids. In addition, d,l-mandelic acid was well resolved.

Amperometric detection of reducing carbohydrates in high-performance liquid chromatography using an amino-bonded column and acetonitrile-water as the eluent.

Amperometric detection of reducing carbohydrates using copper bis(phenanthroline) as the mediator in the post-column reaction was applied to the partition mode of high-performance liquid chromatography using an amino-bonded column with acetonitrile-water as the eluent. The proposed method appears to be the most sensitive means of detection in the partition separation of carbohydrates. Glucose can be determined at levels down to 5 pmol (1 ng injection). Excellent selectivity was demonstrated in examples of chromatograms obtained with fruit juices and human urine.

Amperometric detection of muramic acid in high-performance liquid chromatography with a post-column reaction.

Highly sensitive detection of muramic acid has been developed by using an amperiometric detector in high-performance liquid chromatography. The reducing ability of muramic acid was coupled with the redox reaction of bis(1,10-phenanthroline)copper(II), CBP, as mediator. CBP, reduced by muramic acid in a post-column reaction, was reoxidized with the amperometric detector, resulting in a highly sensitive and selective detection. A doublet peak was obtained, due to the alpha- and beta-anomers of muramic acid. This was merged into a single peak by adding phosphoric acid to the sample solution. Addition of phosphoric acid to serum, spiked with muramic acid, also clarified the chromatogram. The detection limit was 0.05 ppm (4 pmol of muramic acid injected) in serum samples.

13C-NMR study of 1-alkenes adsorbed on silica-gel and Ag-silica-gel

ZusammenfassungFür an Silicagel und Ag-Silicagel adsorbierte 1-Alkene (1-Penten, 1-Hexen, 1-Hepten, 1-Octen) wurden die 13C-Spektren und die T1-Werte gemessen. Die C1-Kohlenstoffe von Alkenen an Ag-Silicagel wiesen gro\e Shifts im oberen Feld auf (9,8–12,8 ppm), die C2-Kohlenstoffe dagegen nur geringe (0,8–1,4 ppm). Die Adsorption führte unabhÄngig von der Art der Adsorbentien zu einer Verringerung der T1-Werte der 1-Alkene. Die T1-Werte der doppelt gebundenen Kohlenstoffe, mit 1-Alken an der OberflÄche des Ag-Silicagels, verringerten sich von 10 s im flüssigen Zustand zu 0,1 s im adsorbierten Zustand. Mit zunehmender Entfernung von der Adsorptionsstelle nahmen die T1-Werte zu. Aus diesen Ergebnissen wurde geschlossen, da\ 1-Alkene auf Ag-Silicagel einen π-Komplex mit den Silberionen der OberflÄche bilden. Nach lÄngerer Zeit wurde 1-Penten an Silicagel zu trans-2-Penten isomerisiert.Summary13C-NMR spectra and T1 of 1-alkenes (1-pentene, 1-hexene, 1-heptene and 1-octene) adsorbed on silica-gel and Ag-silica-gel were measured. The C1-carbons of alkenes on Ag-silica-gel showed large upper field shifts (9.8–12.8 ppm); C2-carbons gave small upper field shifts (0.8–1.4 ppm). The adsorption led to a diminution of T1 for 1-alkenes irrespective of adsorbents.T1 of the double-bond carbons, with 1-alkene attached to the surface of Ag-silica-gel, were reduced from 10 s in liquid state to 0.1 s in adsorbed state. The increase of the distance from the adsorption site increased the T1 values. From these results, it is concluded that 1-alkene on Ag-silicagel formed a π-complex with surface Ag ions. Isomerization from 1-pentene to trans-2-pentene occurred on silica-gel after a prolonged period.