Tran Thi Thanh Van

Preliminary investigation of a highly sulfated galactofucan fraction isolated from the brown alga Sargassum polycystum

A fucoidan preparation was isolated from the brown alga Sargassum polycystum (Fucales, Sargassaceae). The preparation was fractionated by anion-exchange chromatography, and two highly sulfated fractions F3 and F4 were obtained. The fractions were quite similar in composition, but different in chemical structure. F4 was analyzed by chemical methods, including desulfation, methylation, Smith degradation, and partial acid hydrolysis with mass-spectrometric monitoring, as well as by NMR spectroscopy. Several 2D NMR procedures, including HMQC-TOCSY and HMQC-NOESY, were used to obtain reliable structural information from the complex spectra. Molecules of F4 were shown to contain a backbone built up mainly of 3-linked α-L-fucopyranose 4-sulfate residues, as in many other fucoidans, but rather short sequences of these residues are interspersed by single 2-linked α-D-galactopyranose residues also sulfated at position 4. This rather unusual structural feature should have a great influence on the conformation of the polymeric molecule and may be important for biological activity of the polysaccharide. Hence, F4 is an example of a new sulfated galactofucan isolated from the brown alga. According to the data obtained, the distribution of galactose residues along the polysaccharide backbone seems to be not strictly regular, but the definitive sequence of monomers in the polymeric molecules awaits additional investigation.

Anti-HIV activity of fucoidans from three brown seaweed species.

Fucoidans are sulfated polysaccharides derived from marine brown algae. In the current work the anti-HIV activity of three fucoidans, extracted from three brown seaweeds Sargassum mcclurei, Sargassum polycystum and Turbinara ornata and collected from Nha Trang bay, Vietnam was investigated. Fucoidans extracted from the three species displayed similar antiviral activities with a mean IC50 ranging from 0.33 to 0.7 μg/ml while displaying no cell toxicity. Our results showed that the anti-HIV activity of fucoidans is not primarily linked to the sulfate content and the appropriate position of sulfate groups in the fucoidan backbones was also not associated with the antiviral activity. Fucoidans inhibited HIV-1 infection when they were pre-incubated with the virus but not with the cells, and not after infection, blocking the early steps of HIV entry into target cells. These data contribute to a better understanding of the influence of fucoidans structural characteristics on their biological activity.

Structure and hypolipidaemic activity of fucoidan extracted from brown seaweed Sargassum henslowianum

The aim of this study is to elucidate the structure and investigate the hypolipidaemic activity of a fucoidan extracted from brown seaweed Sargassum henslowianum collected at Hai Van–Son Cha peninsula, Hue province, Vietnam by using tandem electrospray ionisation mass spectrometry. The results demonstrated that the fucoidan has α(1 → 3)-linked l-fucopyranose backbone and sulphate groups occupied mostly at C-2, C-4 and sometimes at C-3 position of fucose residues. The results of in vivo bioactivity examination revealed that the fucoidan in the dose of 100 mg/kgP/day by oral administration helped decrease cholesterol, triglyceride and LDL-cholesterol levels on obese mice.

On the theory of three types of polaritons (phonon, exciton and plasmon polaritons)

We have investigated the similarities and difference between three well-known types of polaritons: phonon polariton, exciton polariton and surface plasmon polariton. For first two types (phonon polariton and exciton polariton) the interaction between photon and media can be expressed via a longitudinal-transversal splitting (LT-splitting), while for third type of polariton (surface plasmon polariton) via the boundary condition. Considering an analogy of these three types of polaritons, an effective LT-splitting was introduced for surface plasmon polariton. We discuss a possible existence of an evanescent state in the band gap of polaritons. Finally, the Nambu broken symmetry theory and Anderson-Higgs mechanism are discussed for lower branch of these polaritons.

π-Plasmon model for carbon nano structures: Application to porphyrin

In traditional concept, the optical properties of semiconductors and semimetals near their fundamental optical band gaps are attributed to single excitations (such electron-hole pairs, excitons...). In our earlier article, we proposed the collective mechanism of π-plasmons for optical properties of low dimensional carbon nano structures. A simple way to calculate the peak positions of UV-vis absorption spectra was pointed out and gave a good agreement with experimental data. In this work we analyze different schemas to calculate the UV-vis absorption peaks. A new parameter k which characterizes the dependence of schema on geometry and number of carbon sites is defined. As an example, the case of porphyrin was investigated.

Thermodynamic Equivalent between Noninteracting Bose and Fermi Gas in Metallic Carbon Nanotubes

The equivalent between Bose and Fermi ideal gases is usually taken in high temperature limit only. Recently, there has been considerable interest in surprising thermodynamic “equivalences” between certain ideal Bose and spineless Fermi gas systems in lower temperature. In this work, we follow that idea to investigate the quasi onedimensional system of metallic carbon nanotubes. Due to the linear dispersion law, the non-interacting Bose and Fermi gases in metallic carbon nanotubes are equivalent. This equivalence could be applied to the gas systems of exciton photon (Bose particles) and electron hole (Fermi particles) in metallic carbon nanotubes.

Entanglement of a Scattered Single Photon and an Exciton

A single photon which is initially uncorrelated with an exciton will evolve to be entangled with the exciton on their continuous kinetic variables in the process of resonant scattering. We find the relations between the entanglement and their physical control parameters, which indicates that high entanglement can be reached by changing specific parameters of exciton.