Elisabeth Scholander

Bromine oxidation of methyl α- and β-pyranosides of D-galactose, D-glucose, and D-mannose☆

Abstract Methyl α- and β-pyranosides of D -galactose, D -glucose, and D -mannose have been oxidized with bromine in aqueous solution at various pH values. The resulting keto glycosides were converted into their more-stable O -methyloxime derivatives which were characterized by spectroscopy and chromatography. Oxidation at a ring carbon atom where the hydrogen is axial is hindered by bulky substituents in syn ( i.e. , a 1,3) diaxial relationship. Thus, the aglycon group in the α anomers protects position 3, the axial HO-4 in galactopyranosides protects position 2, and the axial HO-2 in mannopyranosides protects position 4 from oxidation.

Analysis of bromine-oxidised dextran by 13C-n.m.r. spectroscopy

Abstract Dextran T 10, elaborated by Leuconostoc mesenteroides NRRL B-512, was oxidised with aqueous bromine at pH 7.0. The resulting oxodextran and its methoximated derivative were analysed by 13C-n.m.r. spectroscopy. The total amount of keto groups and their positions were established. Assignments of the 13C signals were made by referring to spectra of the corresponding methyl glucosiduloses and an oxodextran having most of the carbonyl groups at position 3 of the glycopyranosyl residues. In accordance with the mechanism for bromine oxidation of mono- and di-saccharides, the glucopyranosyl residues of dextran were oxidised mainly at C-2 and C-4. Over-oxidation resulted in a small proportion of acidic, ring-cleavage products.

Coupling of proteins and other amines to sepharose by bromine oxidation and reductive amination

Abstract Reactive carbonyl groups have been introduced into Sephadex and Sepharose gels by oxidation with aqueous bromine at pH 7. Proteins and other amines have been coupled in high yields to oxidized Sepharose gels by reductive amination. The reactions are carried out in aqueous solutions at pH 7 with sodium cyanoborohydride as a reducing agent. The biological activity of a tested immobilized enzyme (urokinase) is not altered. The effect of the oxidation-reduction procedure on the chromatographic properties of Sepharose gels in insignificant. The Sephadexes are much altered at high degrees of oxidation.

Bromine oxidation of 1,2-O-isopropylidene-α-d-Glucofuranose and sucrose

Abstract Sucrose and 1,2-O- isopropylidene-α- d -glucofuranose ( 1 ) were oxidised with bromine in aqueous solution at pH 7 and room temperature. The resulting keto derivatives were converted into their more-stable O -methyloximes, which were characterised by spectroscopic and chromatographic methods. Oxidation of 1 occurred at C-3 and C-5, with a preference for C-5. In the sucrose derivatives isolated after oxidation, those having a keto group in the glucopyranosyl moiety preponderated. The axial fructofuranosyl aglycon protects position 3 in the glucopyranosyl group and oxidation occurs only at C-2 and C-4. Small amounts of sucrose oxidised at C-3 in the fructofuranosyl moiety were also found.

Infrared characterization of complex sandwich structures: Heparin immobilized on polyethylene surfaces

Surface modification to provide, e.g., a biocompatible surface is an important molecular engineering method. As an example the FTIR-Attenuated Total Reflection (ATR) method has been applied to follow the different steps in the immobilization process of heparin on polyethylene (PE). This chemical multicomponent modification process is based on van der Waals and electrostatic interaction between alternating layers of cross-linked polyethylene imine and dextran sulfate, and finally covalent attachment of partly nitrous acid degraded heparin. Modified PE sheets were withdrawn and analyzed after each reaction step in the process. The overall spectral agreement between the ATR spectra and the spectra obtained from the pure substances used is good, except for slight changes in position and relative intensities of the sulfate and amino peaks. This observation indicates that the amino and sulfate groups are important (electrostatic) binding sites between the alternating polyethylene imine and dextran sulfate layers. The amount of covalently attached heparin was determined according to the “thin film model” by Harrick. The surface concentration, Γ, falls typically in the range of 2.4–2.7 μg/cm2, which is in good agreement with the result from a chemical analysis. The choice of peak areas used in the calculation of Γ is also discussed.