Auteur(s) : Mahandrimanana ANDRIANAINARIVELO (auteur)
par SiO2–ZrO2 and SiO2–TiO2 mixed oxides with various metal contents have been prepared by a non-hydrolytic sol–gel route involving the condensation between chloride and isopropoxide functions at 110 °C. Well condensed, monolithic gels were obtained in one step, without the use of additives. The Si/M ratio of the oxide may be controlled easily by the composition of the starting mixture. The Si/Zr oxides remained amorphous after calcination for 5 h at 600 °C; IR and 29Si NMR spectroscopy showed a large amount of Si–O–Zr bonds, indicating a homogeneous distribution of the components on the atomic scale. The crystallization of tetragonal zirconia took place at higher temperature; the transformation of tetragonal to monoclinic zirconia was strongly retarded and did not take place after 2 h at 1300 °C. The crystallization of zircon (for a sample containing 50 mol% Zr) started at 1500°C and was completed after 20 h at 1500°C. IR spectroscopy indicated the presence of a limited number of Si–O–Ti bonds in all the Si/Ti oxides after calcination for 5 h at 500 °C. The sample within the stable glass region (5 mol% Ti) appeared perfectly homogeneous: it crystallized at 900 °C as single-phase cristobalite oxide, with Ti4+ ions substituting Si4+ ions at random. On the other hand, the precipitation of anatase was observed for the Si/Ti oxides with a high Ti content (20–50 mol% Ti), which are outside the stable glass region. The transformation of anatase to rutile was not observed even after 2 h at 1300 °C.Auteur(s) : Mahandrimanana ANDRIANAINARIVELO (auteur)
par The efficiency of the nonhydrolytic sol−gel process based on the condensation between metal chlorides and metal alkoxides has been studied in the preparation of aluminum titanate gels. Solutions of aluminum and titanium precursors in the ratio Al/Ti = 2 gave gels with the same metal ratio. The structural evolution of the samples is unusual; they directly crystallize at T > 600 °C into metastable pseudo-brookite β-Al2TiO5 and are reluctant to decompose into stable TiO2 (rutile) and α-Al2O3 at 1150 °C. This behavior must be connected to the high homogeneity of the samples originating from the nonhydrolytic sol−gel process.Auteur(s) : Mahandrimanana ANDRIANAINARIVELO (auteur)
par The effectiveness of a non-hydrolytic sol–gel process for the preparation of bicomponent oxides has been studied in the 1:1 system TiO2–ZrO2 . Elemental analysis by energy dispersive X-ray analysis (EDXA) and by inductively coupled plasma (ICP) showed the same Ti:Zr ratio for the amorphous oxide and crystalline ZrTiO4 which corresponds to that of the initial solution. The direct crystallization of ZrTiO4 below 700 °C without the intermediate formation of TiO2 or ZrO2 indicates that the non-hydrolytic sol–gel process gives rise to the formation of homogeneous zirconium titanate gels.Auteur(s) : Mahandrimanana ANDRIANAINARIVELO (auteur)
par The effectiveness of nonhydrolytic Sol-Gel process to the synthesis of homogeneous bicomponent gels has been studied in the case of aluminium titanate and zirconium titanate. The direct crystallization of Al2TiO5 and ZrTiO4 at low temperature without the intermediate formation of TiO2 or Al2O3 in the former case and TiO2 or ZrO2 in the latter indicates that homogeneous bicomponent gels have been formed by this route.Auteur(s) : Maonja Finaritra Sitrakiniavo RAKOTONDRAMANGA (auteur) , Rivoarison RANDRIANASOLO (auteur principal) , Andrianambinina Andriamarolahy RAZAKARIVONY (auteur)
par New cardenolide glycoside 1 and steroid glycoside 2, named respectively corotoxigenin-3-O-β- digitalopyranosyl-(1–4)-O-β-digitoxopyanoside and 5∆-pregnene-3β,16α,20(S)-diol 20-O-[β-Ddigitalopyranosyl (1→2)-β-D-glucopyranoside], have been isolated from the leaves of Alafia sp. (Apocynaceae). Compound 2 was isolated for the first time in its natural state, together with the known compounds digitoxin, corotoxigenin, and β-sitosteryl-3-O-β-D-glycopyranoside. The structures of compounds 1 and 2 were elucidated through spectroscopic techniques and chemical methods.Auteur(s) : Andrianambinina Andriamarolahy RAZAKARIVONY (auteur principal) , Maonja Finaritra Sitrakiniavo RAKOTONDRAMANGA (co-auteur)
par A new gentisic acid derivative named micronyc acid (1) and a new 1,4-benzoquinone derivative named micronone (2) have been isolated from the root of Micronychia tsiramiramy together with the known compounds gallic acid (3), methyl gallate (4), moronic acid (5), masticadienolic acid (6), and masticadienediol (7). The structures of 1 and 2 were established using MS and NMR. Compound 1 was tested for antiplasmodial activity in vitro against the chloroquine-resistant strain Plasmodium falciparum W2 and displayed moderate antiplasmodial activity in vitro with an IC50 value of 25.6 μm. Compounds 1 and its acetyl derivative 1a were also tested for their cytotoxicity against the human cervix carcinoma cell line KB-3-1 and still showed moderate activity.Auteur(s) : Mahandrimanana ANDRIANAINARIVELO (auteur)
par Abstract The objective of this study to show that TiO2 can be attached to the external surface of clays. Two types of clay, white and green clay, have been used because those raw materials are very abundant in Madagascar. The composite material is useful to eliminate pathogenic microorganism and decompose organic compounds in polluted water, for example. The BET (Brunauer, Elmett and Teller) analysis is the best method to evaluate the capacity of the composite to catalyze the reaction of decomposition. The BET analysis of specific area are 60.71 m2/g for white clay (micropore surface 9.63 m2/g and outer surface 51.08 m2/g with pore size 151.46 Å, an A° = 1millionth of a millimeter) and 249.52 m2/g for green clay (micropore area 20.51 m2/g and outer surface 229.01 m2/g with pore size 49.96 Å). The size of the micropores is less than 17 Å. When TiO2-clays are treated at 600°C, the specific area of white clay increases, it becomes 94.07 m2/g while pore size decreases (81.39 Å). For green clay, the specific area is about the same (247.61 m2/g) and pore size doesn’t change (49.97 Å). Keywords: Clay, TiO2, Specific surface, Nanotechnology, Composite material