A sulfated galactofucan from the brown alga Hormophysa cuneiformis (Fucales, Sargassaceae).

The brown alga Hormophysa cuneiformis collected from the coastal waters of Vietnam was used to isolate a mixture of sulfated polysaccharides FHC, which was fractionated further by anion-exchange chromatography on DEAE-Sephacel. The main fraction F3 eluted with 1.5 M NaCl contained essentially l-fucose, d-galactose and sulfate and has very complex NMR spectra. Desulfation to obtain F3deS followed by Smith degradation to obtain F3deS-Sm was used to simplify the structure of F3, and all these preparations were characterized by methylation analysis and NMR spectra. A linear (1 → 3)-linked backbone built up of α-l-fucopyranose residues was identified as the main structural motif of molecules. Some fucose residues attached to position 4 of its 3-linked neighbor were found as branches. Galactose residues having both α- and ß-configurations were found mostly at the periphery of molecules. They are present as (1 → 6)-linked disaccharide of two ß-d-Galp attached to position 4 of the backbone or as single α-d-Galp attached to the same position. Sulfate groups in F3 may probably occupy any positions of the molecule. F3 acts as anticoagulant and is about half as active as the standard low-molecular mass heparin (enoxaparin). FHC was practically inactive in cytotoxicity test against six human cancer cell lines.

Structure, conformation in aqueous solution and antimicrobial activity of ulvan extracted from green seaweed Ulva reticulata.

The aim of this study is to elucidate the structure and investigate the antimicrobial activity of an ulvan obtained by water extraction from green seaweed Ulva reticulata collected at Nha Trang sea of Vietnam by using IR, NMR, SEC-MALLS and SAXS methods. The ulvan is composed of rhamnose, galactose, xylose, manose and glucose (mole ratio Rha: Gal: Xyl: Man: Glu = 1:0.12:0.1:0.06:0.03), uronic acid (22.5%) and sulphate groups (17.6%). Chemically structural determination showed that the ulvan mainly composed of disaccharide [→4)ß-D-GlcA(1→4)α-L-Rha3S-(1→]. The results from SAXS indicated that ulvan under study has a rod-like bulky chain conformation. Ulvan from U. reticulata showed high antimicrobial activity, with inhibition zone diameter of 20 mm against Enterobacter cloace and 18 mm against Escherichia coli.

Sulfated polysaccharides of the Vietnamese brown alga Sargassum aquifolium (Fucales, Sargassaceae).

A fucoidan preparation named FSA was isolated from the brown alga Sargassum aquifolium collected from the coastal waters of Vietnam. l-Fucose, d-galactose, d-mannose, d-glucuronic acid, d-xylose, and sulfate were found to be the main constituents of FSA. The preparation was fractionated by anion-exchange chromatography on DEAE-Sephacel eluted stepwise with 0.5, 1.0, 1.5, and 2.0 M NaCl to give four fractions differing in monosaccharide composition and degree of sulfation. Their NMR spectra were too complex to be completely interpreted. Fractions 1.0 M and 1.5 M were analyzed by methylation before and after desulfation. In addition, desulfated 1.0 M was fractionated by anion-exchange chromatography into six fractions according to the uronic acid content. They were characterized by methylation and NMR spectral data, and three structurally different polysaccharides were identified. One of them has a core of alternating 2-linked α-d-Manp and 4-linked ß-d-GlcpA residues, about a half of the former bearing single α-l-Fucp or ß-d-Xylp at position 3. The second polymer is a (1 â†’ 3)-ß-d-glucopyranuronan partially substituted with single ß-d-Xylp or single α-l-Fucp at position 4. The third polysaccharide is a xylo(fuco)galactan having a linear core of alternating 4-linked α-d-Gal and 3-linked ß-d-Gal residues. The latter bear single ß-d-Xylp or a short chain of 4-linked ß-d-Xyl, 6-linked ß-d-Gal, and variously linked α-l-Fuc. In FSA, these polysaccharides are sulfated at different positions and devoid of regularity. Fractions of FSA possess anticoagulant, cytotoxic, and antitumor activities, which increase with the degree of sulfation. The most sulfated fraction 2.0 M that contains mainly a sulfated fucogalactan, is about half as active as anticoagulant as the standard low-molecular mass heparin (enoxaparin).

Structure and cytotoxic activity of ulvan extracted from green seaweed Ulva lactuca.

The structure of an ulvan obtained by water extraction from green seaweed Ulva lactuca was elucidated by using IR, NMR, SEC-MALL and ESIMS methods. The ulvan was also evaluated for its cytotoxic effects on three human cancer cell lines. The results showed that the ulvan was composed of rhamnose, galactose, xylose, manose, glucose (with a mole ratio of Rha: Gal: Xyl: Man: Glu equal to 1: 0.03: 0.07: 0.01: 0.06), uronic acid (21.5%) and sulfate content (18.9%) with a molecular weight of 347000. This ulvan mainly consists of disaccharide [→4)-ß-d-GlcA-(1→4)-α-l-Rha3S-(1→] and other minor disaccharide ß-GlcA-(1→2)-α-Xyl and ß-GlcA-(→2)-α-Rha. The ulvan showed a significant cytotoxic activity against hepatocellular carcinoma (IC50 29.67±2.87µg/ml), human breast cancer (IC50 25.09±1.36µg/ml), and cervical cancer (IC50 36.33±3.84µg/ml).

Speciation of arsenic in environmental samples of the Nha Trang Harbor, Vietnam, using HPLC coupled HG-AAS.

A coupled high performance liquid chromatography-hydride generation-atomic absorption spectroscopy system was used to determine the speciation of arsenic in samples from the Nha Trang Harbor, Vietnam. Concentrations of arsenic in seawater, pore water, suspended solid, and sediment were 4.12-9.81 µg/L, 13.10-24.32 µg/L, 1.87-6.42 µg/g, and 3.37-9.06 µg/g, respectively. Extraction using H(3)PO(4) + NH(2)OH·HCl and ultrasonic digestion was optimized to yield a 76-85% of total arsenic. Arsenic (III) was the most abundant species in suspended solids and sediments whereas arsenic (V) represented for 30-50% of arsenic (III) concentration. Monomethylarsonic acid and dimethylarsinic acid species were undetectable.