Vietnam Journal of Chemistry

This work presented the results of the study on synthesis and characterization of nanosilica from rice husk ash (RHA). Nanosilica was obtained by calcination of HCl treated RHA at 700 oC for 2 h. X-ray diffraction (XRD) pattern showed only one peak at 2q ~22o confirming the amorphous structure of nanosilica. The chemical composition assessed by energy dispersive X-ray spectroscopy (EDX) showed that the obtained nanosilica was of high purity. TEM image measured by transmission electron microscopy (TEM) revealed that the obtained nanosilica was in spherical morphology with the average diameter of about 45.5±7.2 nm. The particle size distribution of nanosilica determined by dynamic laser scattering (DLS) was of Gaussian mode. The FTIR spectrum indicated the presence of silanol and siloxane groups in nanosilica. Thus, the synthesized nanosilica can be used for application in different fields. Keywords. Rice husk ash, nanosilica, amorphous.

The hydrothermal method was used for preparation porous hydroxyapatite (HA) ceramic from coral scaffold, in two ways: synthesized directly from coral skeleton and synthesized from CaO, which was product of coral thermal decomposition. The obtained samples were characterized by techniques including X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The analytical results confirmed that HA ceramic was formed by the indirect synthesis from fresh obtained CaO from coral aragonite. Determined reaction conditions were at 180oC and 14 atm pressure for 36 hours.

Four flavone glycosides were isolated from the leaves of Antidesma ghaesembilla. They were elucidated to be vitexin, orientin, isovitexin, and homoorientin by 1D- and 2D-NMR and in comparison with literature data. These compounds have been reported from the genus Antidesma for the first time.

β-Sitosterol, stigmasterol, cardamomin (1), chalconaringenin 2′-O-methyl ether (2), alpinetin (3), and naringenin 5-O-methyl ether (4) were isolated from the MeOH extract of Alpinia conchigera Griff. (Zingiberaceae). Their structures were determined on the basis of spectroscopic analyses. The antimicrobial and free radical scavenging activities of the isolates 1-4 were evaluated in correlation with those of the soluble fractions.Key words: Alpinia conchigera; Zingiberaceae; chalcone; flavanone; antimicrobial activity; free radical scavenging activity.

Graft polymerization of acrylic acid (AA) onto tapioca starch was carried out using ceric ammonium nitrate (CAN) as initiator in aqueous nitric acid medium. The kinetics of the graft polymerization of AA onto starch was studied by gravimetric method. The following rate expression (rate of graft polymerization) Rg = k. [AA]1.02 [CAN]0.478 [Starch]0.543 was obtained and a suitable mechanism was suggested. The overall activation energy was found to be 41.33kJ/mol within the temperature range of 30 - 40oC.

The first chemical investigation on Vietnamese medicinal plant Psychotria reevesii Wall. (Rubiaceae) led to the isolation and structural determination of β-sitosterol and stigmasterol as a mixture, 1-octacosene, and asperglaucide from n-hexane- and CHCl3-soluble fractions of MeOH extract from the aerial parts of P. reevesii. Phytochemical screening based on color reactions, HPLC analysis, and NMR spectroscopy revealed the concentration of condensed tannins in EtOAc- and n-BuOH soluble fractions. The high accumulation of tannins may be responsible for the antibacterial activities of the polar fractions against Staphylococcus aureus, Pseudomonas aeruginosa, Shigella sonnei, and Shigella flexneri. However, they did not exhibit any inhibitory effect against Escherichia coli, Candida albicans, and Candida stellatoides.Keywords: Psychotria reevesii; Rubiaceae; asperglaucide; antibacterial activity; antifungal activity.

From the roots of Codonopsis pilosula (Franch) Nannf (Campanulaceae) five triterpenoids: taraxerol, taraxeryl acetate, 14-a-taraxeran-3-one and D:B-friedoolean-5-ene-3-b-ol as well as a-spinasterone were isolated. Their structures have been identified by MS, 1H-, 13C-NMR spectroscopy and comparison with reported data.

Chemical investigation of Celastrus hindsii Benth. growing in Quang Binh province, Vietnam led to the isolation and structural elucidation of clionasterol, D:A-friedo-oleanane-3,21-dione, lup-20(29)-ene-3b-ol and lup-12-ene-3b-ol. Their structures were determined on the basis of MS, NMR spectra and comparison with reported data.

From the ethyl acetate extract of the rhizomes from Belamcanda chinensis (Iridaceae) five compounds irisflorentin (1), tectorigenin (2), iristectorigenin A (3), irigenin (4), and acetovanillone(5) were isolated. Their structures were elucidated by spectroscopic methods. This is first report of 5 from B. chinensis. Keywords: Belamcanda chinensis, Iridaceae, acetovanillone.

From the fruits of Silybum marianum (L.) Gaertn. cultivated in the North of Vietnam, (±)2,6-bis(4′-hydroxy-3′-methoxy-phenyl)-3,7-dioxabicyclo[3.3.0]octane (pinoresinol) (1) and 3,4′,5,7-tetrahydroxy-3′-methoxyflavanone (2) were isolated. Their structures were elucidated by analyses of the NMR and mass spectra in comparison with the reported data. This is the first report of both 1 and 2 from Silybum species.