Physicochemical Characterization of an Exopolysaccharide Produced by Lipomyces sp. and Investigation of Rheological and Interfacial Behavior

The present study aimed to evaluate the rheological and interfacial behaviors of a novel microbial exopolysaccharide fermented by L. starkeyi (LSEP). The structure of LSEP was measured by LC-MS, 1H and 13C NMR spectra, and FT-IR. Results showed that the monosaccharide composition of LSEP was D-mannose (8.53%), D-glucose (79.25%), D-galactose (7.15%), and L-arabinose (5.07%); there existed the anomeric proton of α-configuration and the anomeric carbon of α- and β-configuration; there appeared the characteristic absorption peak of the phosphate ester bond. The molecular weight of LSEP was 401.8 kDa. The water holding capacity (WHC, 2.10 g/g) and oil holding capacity (OHC, 12.89 g/g) were also evaluated. The results of rheological properties showed that the aqueous solution of LSEP was a non-Newtonian fluid, exhibiting the shear-thinning characteristics. The adsorption of LSEP can reduce the interfacial tension (11.64 mN/m) well and form an elastic interface layer at the MCT–water interface. Such functional properties make LSEP a good candidate for use as thickener, gelling agent, and emulsifier to form long-term emulsions for food, pharmaceutical, and cosmetic products.

Structural and functional features of Rhodococcus ruber lipoarabinomannan

The genus Rhodococcus is part of the phylogenetic group nocardioform actinomycetes, which also includes the genus Mycobacterium. Members of this phylogenetic group have a characteristic cell envelope structure, which is dominated by various complex lipids. Among these, lipoglycans are of particular interest since mycobacterial lipoarabinomannans are important immunomodulatory molecules that are likely to be involved in the subsequent fate of mycobacterial bacilli once inside phagocytic cells. Rhodococcus ruber is a species closely related to an established opportunistic human pathogen, Rhodococcus equi. This paper reports the isolation and characterization of R. ruber lipoarabinomannan, designated as RruLAM. SDS-PAGE and gas chromatography analyses revealed that RruLAM was of an intermediate size between Mycobacterium tuberculosis lipoarabinomannan and lipomannan. Using a combination of chemical degradation and 1H, 13C-NMR experiments, the carbohydrate structure of RruLAM was unambiguously shown to be composed of a linear (α1→6)-Manp backbone substituted at some O-2 positions by a single t-α-Araf sugar unit. Integration of the anomeric proton signals provided an indication of the degree of branching as approximately 45 %. The RruLAM structure is much simpler than that established for M. tuberculosis lipoarabinomannan but is also different from that determined for the closely related species and opportunistic human pathogen, R. equi. RruLAM was unable to induce the production of TNF-α by either human or murine macrophage cell lines, suggesting that more sophisticated structures, such as phosphoinositol capping motifs, are required for such activity.

The application of double-quantum and spin echo nuclear magnetic resonance spectroscopy to the assignment of 1H chemical shifts of RNA oligomers

Specific assignment of the non-exchangeable base and ribose anomeric protons is difficult for oligoribonucleotides with a high pyrimidine content. Problems arise from the narrow range of pyrimidine H-6 chemical shifts and the overlap of pyrimidine H-5 resonances with the ribose anomeric proton signals. To solve these problems two multiple pulse methods were used which depend on the scalar coupling between H-6 and H-5. The first method was double-quantum nmr which established the connectivity between specific pyrimidine H-6 and H-5 resonances. A refocussing pulse was added to the end of the double-quantum pulse sequence to improve the identification of several H-6 and H-5 connectivities in a single experiment. The second procedure involved homonuclear decoupled spin echo nmr to remove H-5 signals selectively from the ribose anomeric proton region. These techniques are illustrated by the assignment of the spectra of the oligoribonucleotides UpUpC, UpUpU, GpCpUpC, and UpApGpCpUpU.

Isolation and Characterization of 1'-O-Abscisic Acid- β -D-Glucopyranoside From Vegetative Tomato Tissue

A new, polar metabolite of abscisic acid (ABA) has been isolated from an aqueous extract of tomato plants. The compound is acidic, soluble in butanol and slightly soluble in acidic ethyl acetate. It is a major constituent of the products formed from (�)-[2-14C]abscisic acid and it occurs naturally. The structure was determined by gas-liquid chromatography-mass spectrometry (g.l.c.-m.s.) and nuclear magnetic resonance (n.m.r.) spectrometry as the 1'-O-β-D-giucopyrairoside of abscisic acid (ABAGS). The glucosyl moiety was identified by g.l.c.-m.s. and a glucose oxidase test, the ABA by n.m.r. and g.l.c. Tests with α- and β-glucosidase proved inconclusive, but the signal of the anomeric proton in the �H n.m.r. spectrum showed the 8 Hz coupling of a β-glucoside. ABAGS can be methylated with redistilled diazomethane and, like the glucose ester of ABA (ABAGE), it is unstable in alkaline solutions.

1H nuclear magnetic resonance study of 2,2′-anhydro-O2-β-D-arabinosyluracil. Four- and five-bond coupling constants in the sugar moiety

A high resolution proton magnetic resonance spectrum for 2,2′-anhydro-O2-β-D-arabinosyluracil in aqueous solution at 80 °C is presented. The spectrum provides evidence for the presence of long-range four-bond (4J1′3′, 4J1′4′, 4J2′4′) and five-bond (5J1′5′, 5J1′5′′, 5J2′5′, 5J2′5′′) coupling interactions involving the furanose hydrogens. The 5J data represent the first reported evidence for the presence of coupling interactions involving the anomeric proton and exocyclic C5′ protons in a furanose system. The relative signs of the 4J and 5J couplings were determined by double resonance methods. The 4J and 5J interactions are discussed using crystallographic data and the theory of long-range couplings.