A colloidal route for delamination of layered solids: Novel porous-clay nanocomposites

Under soft conditions, it is possible to cause the irreversible delamination of organoclays (long-chain alkylammonium cation-exchanged smectites, and vermiculite-layered silicate derivatives) via a sol-gel process that involves alkoxysilanes (e.g., tetraethoxysilane) and that finally gives silica-clay heteromaterials. These intermediate silica-organoclay nanocomposites facilitate the diffusion of the alkoxides which, in the presence of water, are hydrolyzed and subsequently polymerized. This process is a heterocoagulation that gives homogeneous gels in which the order in the layer stacking of clays is partially or completely lost, depending on the nature of the layered silicate. After calcination to eliminate the organic moiety, that is, the alkylammonium chains, the gel is irreversibly transformed into a silica-clay material in which the silicate layers are fully separated by the silica network generated by the alkoxide. The resulting solids are inorganic-inorganic nanocomposites which could be compared to polymer-clay nanocomposites, but in the present case the inorganic silica network is the continuous phase and the individual layers the corresponding disperse phase of the nanocomposite. These materials are solids of high specific surface area (> 400 m2 g-1), which exhibit micro- and mesoporosity, and also have properties inherent to both components, the pristine clay (e.g., a cation-exchange capacity) and the silica network (e.g., an ability to be functionalized).This work was partially supported by the CICYT, Spain (Projects: MAT2000-0096-P4-02, MAT2003-06003-C02-01, and BTE2003-05757-C02-02

A colloidal route for delamination of layered solids: Novel porous-clay nanocomposites

Under soft conditions, it is possible to cause the irreversible delamination of organoclays (long-chain alkylammonium cation-exchanged smectites, and vermiculite-layered silicate derivatives) via a sol-gel process that involves alkoxysilanes (e.g., tetraethoxysilane) and that finally gives silica-clay heteromaterials. These intermediate silica-organoclay nanocomposites facilitate the diffusion of the alkoxides which, in the presence of water, are hydrolyzed and subsequently polymerized. This process is a heterocoagulation that gives homogeneous gels in which the order in the layer stacking of clays is partially or completely lost, depending on the nature of the layered silicate. After calcination to eliminate the organic moiety, that is, the alkylammonium chains, the gel is irreversibly transformed into a silica-clay material in which the silicate layers are fully separated by the silica network generated by the alkoxide. The resulting solids are inorganic-inorganic nanocomposites which could be compared to polymer-clay nanocomposites, but in the present case the inorganic silica network is the continuous phase and the individual layers the corresponding disperse phase of the nanocomposite. These materials are solids of high specific surface area (> 400 m2 g-1), which exhibit micro- and mesoporosity, and also have properties inherent to both components, the pristine clay (e.g., a cation-exchange capacity) and the silica network (e.g., an ability to be functionalized).This work was partially supported by the CICYT, Spain (Projects: MAT2000-0096-P4-02, MAT2003-06003-C02-01, and BTE2003-05757-C02-02

Parvovirus B19 antibodies and correlates of infection in pregnant women attending an antenatal clinic in central Nigeria

Human parvovirus B19 infection is associated with spontaneous abortion, hydrops foetalis, intrauterine foetal death, erythema infectiosum (5th disease), aplastic crisis and acute symmetric polyarthropathy. However, data concerning Nigerian patients with B19 infection have not been published yet. The purpose of this study was to establish the prevalence of B19 IgG and IgM antibodies, including correlates of infection, among pregnant women attending an antenatal clinic in Nigeria. Subsequent to clearance from an ethical committee, blood samples were collected between August-November 2008 from 273 pregnant women between the ages of 15-40 years who have given their informed consent and completed self-administered questionnaires. Recombinant IgG and IgM enzyme linked immunosorbent assay kits (Demeditec Diagnostics, Germany) were used for the assays. Out of the 273 participants, 111 (40.7%) had either IgG or IgM antibodies. Out of these, 75 (27.5%) had IgG antibodies whereas 36 (13.2%) had IgM antibodies, and those aged 36-40 years had the highest prevalence of IgG antibodies. Significant determinants of infection (p < 0.05) included the receipt of a blood transfusion, occupation and the presence of a large number of children in the household. Our findings have important implications for transfusion and foeto-maternal health policy in Nigeria. Routine screening for B19 IgM antibodies and accompanying clinical management of positive cases should be made mandatory for all Nigerian blood donors and women of childbearing age