pectins and sodium-borohydride

A new method was developed by flow-injection hydride-generation atomic absorption spectrometry (FI-HG-AAS) for direct determination of bismuth in bismuth pectin, which is mostly composed of pectin and bismuth and serves as one of pharmaceuticals for protecting stomach mucous membrane. The influences of some experimental parameters of this method, such as the acidity of sample solution, the reductant of KBH4 and NaOH that served as the stabilizer of KBH4, were studied and these parameters were optimized. Bismuth was detected directly with the linear range of 0.00-44.00 ng.mL-1. The equation of working curve was A = 0.012 + 0.017c (c:ng.mL-1), r = 0.9995, the detection limit was 0.095 ng.mL-1 (3 sigma), and the recovery was 97.3%-103.3%. The method proposed has been used in the analysis of practical sample for bismuth with 96.6%-100.1% founded and 2.1% of RSD. Experiments showed that this method was simple, rapid, accurate and suitable for the assay of bismuth in bismuth pectin.

Topics: Bismuth; Borohydrides; Flow Injection Analysis; Pectins; Sensitivity and Specificity; Spectrophotometry, Atomic

Rhamnogalacturonan II (RG-II) is a structurally complex pectic mega-oligosaccharide that is released enzymatically from the primary cell wall of higher plants. It contains roughly 30 monosaccharide units (MW approximately 5 kDa) including very unusual residues such as Kdo, Dha, aceric acid and apiose. Previous studies have demonstrated that these monomers are arranged into four structurally well-defined oligosaccharide side chains (A-D), linked to a homogalacturonan mainchain, but the specific attachment sites of these branches on the pectic backbone have not yet been elucidated. In the present work, fairly complete assignments of the 750 MHz 1H NMR spectra and partial assignments of the 13C NMR spectra of the sodium-borohydride-reduced RG-II monomer were obtained for a 5 mM sample isolated from red wine. On the whole, these data corroborate the primary structures of the sidechains previously established by methylation analysis, partial hydrolysis and FAB-MS spectrometry but some heterogeneity has been demonstrated (partial substitution at B5, B6, and A5). The preferred orientations of the majority of the sidechain glycosidic linkages in the RG-II monomer have been determined from the sequential nOe data and the solution structure is generally in good agreement with the stable conformers previously obtained by molecular modeling (MM3) of the disaccharide and sidechain oligosaccharide building blocks. All of a two-residue, a three-residue, and a four-residue segment of the backbone have been tentatively identified from long range interactions between sidechain protons as well as in the mainchain. Taking into account the length of the 9-mer galacturonan mainchain described in prior work, these building blocks constitute almost the complete structure of RG-II (Scheme 2).

Topics: Borohydrides; Carbohydrate Sequence; Carbon Isotopes; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Oxidation-Reduction; Pectins; Pentoses; Protons; Solutions; Spectrometry, Mass, Fast Atom Bombardment; Sugar Acids; Wine

An octasaccharide was released from sycamore cell wall rhamnogalacturonan-II (RG-II) by selective acid hydrolysis of the glycosidic linkages of apiosyl residues and purified to homogeneity by gel-permeation and high-performance anion-exchange chromatographies. The octasaccharide 1 contains a terminal nonreducing beta-L-arabinofuranosyl residue linked to position 2 of the alpha-L-rhamnopyranosyl residue of the aceric acid-containing heptasaccharide 2 that had been previously isolated from RG-II [M.W. Spellman et al. Carbohydr. Res., 122 (1983) 131-153]. Heptasaccharide 2 and octasaccharide 1 were found to be mono- or di-O-acetylated. The O-acetyl groups were located, by ESMSMS, on the terminal nonreducing 2-O-methyl-alpha-L-fucosyl residue and/or on the 2-linked beta-L-aceryl acid residue. Octasaccharide 1 and heptasaccharide 2 have the following structures: [structure: see text]

Topics: Borohydrides; Carbohydrate Conformation; Carbohydrate Sequence; Chromatography, Gel; Chromatography, Ion Exchange; Hydrolysis; Mass Spectrometry; Molecular Sequence Data; Oligosaccharides; Pectins; Sugar Alcohols