ABSTRACT
Calcium titanate (CaTiO(3), perovskite) has been used to determine its apatite nucleation ability and propose a possible nucleation initial step. Measurements of calcium leaching from the calcium titanate surface and phosphate adsorption experiments were carried out separately by using commercial calcium titanate suspensions at room temperature. Adsorption behaviour determined by zeta potential measurements shows that phosphate is strongly adsorbed on the calcium titanate surface. It was found that the higher the pH, the higher the Ca present on the calcium titanate surface, but phosphate adsorption followed this trend only up to pH 7.4. Results suggest that phosphate ions are not adsorbed only on Ca sites but also on TiO(2) groups sites of the surface, formed after calcium leaching from the surface. When both ions are simultaneously added in a modified simulated body fluid containing calcium titanate, at 37 degrees C, apatite growth occurs on its surface after 1 week of immersion.
Subject(s)
Apatites/chemistry , Calcium Compounds/chemistry , Oxides/chemistry , Titanium/chemistry , Adsorption , Body Fluids/chemistry , Calcium/chemistry , Electrochemistry , Hydrogen-Ion Concentration , Materials Testing , Microscopy, Electron, Transmission , Phosphates/chemistry , Spectroscopy, Fourier Transform Infrared , Surface PropertiesABSTRACT
The prevalence of antibodies against the repeat epitope of the circumsporozoite protein (cs) of the standard (PV210) and variant (PVK247) strain of Plasmodium vivax was determined by ELISA in 1170 sera from individual residents of seven localities of the Region Huasteca of San Luis Potosi, Mexico. The capture antigens were the synthetic peptides DDAAD and (ANGAGNQPG) that correspond to the repeats of the PV210 and PVK247 cs proteins, respectively. Of the analyzed serum samples, 34.1% (400/1170) were positive with one or both of these antigens. Of the sera, 18.2% (214/1170) reacted with the DDAAD peptide and 6.6% (78/1170) were positive with the variant synthetic peptide. Additionally, 9.2% (108/1170) of the samples reacted with both peptides. A sample of 10% of positive sera for the variant cs repeat (18/78) was tested with the cs repeat peptide of P. malariae/P. brasilianum (NAAG); almost all of them (16/18, 89%) being positive. These results confirm that the transmission of the variant strain of P. vivax is a common phenomenon in endemic regions in Latin America, as well as in other tropical regions of the world. These findings may have implications for the development of aP. vivax vaccine since that based on the standard cs repeat only would not be universally protective.
