Layered-Expanded Mesostructured Silicas: Generalized Synthesis and Functionalization.

Mesostructured layered silicas have been prepared through a surfactant-assisted procedure using neutral alkylamines as templates and starting from atrane complexes as hydrolytic inorganic precursors. By adjusting the synthetic parameters, this kinetically controlled reproducible one-pot method allows for obtaining both pure and functionalized (inorganic or organically) lamellar silica frameworks. These are easily deconstructed and built up again, which provides a simple way for expanding the interlamellar space. The materials present high dispersibility, which results in stable colloidal suspensions.

Low-Cost Synthesis of Bimodal Mesoporous Silica-Based Materials by Pseudomorphic Transformation.

Nanoparticulate bimodal porous silica-based materials have been prepared through a surfactant-assisted procedure by using a simple template and starting from inexpensive sodium silicate as silicon source. Different procedural variables, such as pH or the nature and concentration of the surfactant, have been explored to optimize the preparative protocol, which allows, in turn, improved understanding of the formation process. The final bulk materials (called UVM-10 or M-UVM-10) are formed by pseudomorphic transformation of fresh silica-based xerogels under mild basic conditions. The UVM-10 architecture is constructed from small mesoporous nanoparticles, the aggregation of which generates a disordered secondary 3 D pore system (large-meso/macropores) defined by interparticle voids. Modulation of the intraparticle mesopore size is achieved by using surfactants with variable tail lengths, while maintaining the same head group. Textural porosity has been handled independently by hydrothermally modifying the particle size of the reactive silica-based xerogel. By simply adding metal alkoxides to the initial reaction mixture, the preparative protocol allows for functionalizing the silica walls by incorporating relatively high proportions of homogeneously dispersed heteroelements, such as Al and Ti.

Tetraethylorthosilicate as molecular precursor to the formation of amorphous silica networks. A DFT-SCRF study of the base catalyzed hydrolysis.

Quantum chemical calculations using density functional theory have been carried out to investigate two chemical pathways for the last step of the hydrolysis of tetraethylorthosilicate (TEOS) in basic catalyzed environment. The two models that are introduced in this study depend on the number of water molecules involved at the base catalyzed hydrolysis. Solution equilibrium geometries of the molecules involved in the transition states, reactants and product complexes of the two chemical pathways were fully optimized at B3LYP level of theory with the standard 6-31+G(d) basis set, modeling solvent effects using a polarizable continuum solvation model (PCM). Both models predict relative low activation energies. However, the model with two water molecules seems to be more adequate to describe the basic hydrolysis. A natural bond orbital (NBO) analysis seems to show that the proton transfer from water to ethoxy group would occur through a large hyperconjugative interaction, LP(O) → σ*(O-H), which is related to the nonbonding oxygen lone pair orbital from ethoxy group with the vicinal σ*(O-H) anti bonding orbital O-H of a water molecule.

[Risk factors associated with preeclampsia: case-control study]. / Factores de riesgo asociados con preeclampsia: estudio de casos y controles.

BACKGROUND: Preeclampsia is one of the most frequent and serious complication of pregnancy characterized by systemic perfusion reduction generated by vasospasm and activation of coagulation systems. OBJECTIVE: To evaluate the association between preeclampsia sociodemographics and obstetrics antecedents. MATERIAL AND METHOD: An unmatched case-control study was carried out in which all the clinical registries of patients with preeclampsia (cases: n = 196) assisted in the period 2003-2007 in the Hospital Civil of Culiacan, Sinaloa State of Mexico were analyzed. As controls the clinical registries of patients assisted during the same period were selected at random but that they didn't show up preeclampsia (n = 470). The association of preeclampsia with socioeconomic level, tobacco use, alcohol use, gynecologic and obstetric antecedents (sexual partners, pregnancies, deliveries and abortions number, prenatal control, contraceptive method) and previous pregnancy with preeclampsia were analyzed. RESULTS: There were not association between tobacco use (OR: 3.05; 95% CI: 0.81-11.48), beginning of sexual activity (p = 0.1509), number of sexual partners (OR: 1.23; 95% CI: 0.83-1.83; p = 0.3009) and sexual cohabitation less than 12 months (OR: 0.90; 95% CI: 0.63-1.27). The alcoholism (OR: 5.77; 95% CI: 1.48-22.53), socioeconomic level (p < 0.05), pregnancy previous with preeclampsia (RM:14.81; 95% CI: 1.77-123.85; p = 0.0006) were associated with preeclampsia. There were differences in the use of the contraceptive method between groups (p < 0.005). CONCLUSIONS: Preeclampsia was significantly associated with the alcoholism, low socioeconomic level and pregnancy previous with preeclampsia.

Biomimetic chitosan-mediated synthesis in heterogeneous phase of bulk and mesoporous silica nanoparticles.

Both bulk and mesoporous silica nanoparticles can be obtained in the form of granular aggregates using chitosan flakes as additive under very soft biomimetic reaction conditions.

[Social-economic and obstetric factors associated to premature rupture of membranes]. / Factores sociodemográficos y obstétricos asociados con rotura prematura de membranas.

BACKGROUND: The premature rupture of membranes is the delivery of amniotic liquid after 20 weeks of gestation and before the beginning of labour. OBJECTIVE: To evaluate the association between premature rupture of membranes and sociodemographics and obstetrics antecedents. MATERIAL AND METHODS: Unmatched case-control study carried out in patients from Hospital Civil de Culiacan, Sinaloa (Mexico), from January 2003 to December 2006. Risk factors frequency was compared in women with and without premature rupture of membranes (cases: 1,399; controls: 1,379). Most important variables were: socio-economic level, smoking, and gyneco-obstetric history (sexual partners, pregnancies, newborns, abortions, prenatal control and intergenesic interval). Odds ratio, crude and adjusted, and interval of confidence (IC 95%) were obtained by means of non-conditional logistic regression models. RESULTS: Prevalence of premature rupture of membranes was 8.9%. Socio-economic level was similar in both groups. Premature rupture of membranes was associated with smoking, beginning of sexual activity, and intergenesic interval. History of two or more cesarean sections was considered a protective factor of premature rupture of membranes. Number of sexual partners was marginally meaningful (p = 0.053). Preterm birth frequency was higher in cases group. Resolution of pregnancy was the same for both groups (p = 0.233). CONCLUSIONS: Premature rupture of membranes was significantly associated with smoking, beginning of sexual activiti, intergenesic interval and a preterm birth history. Two or more previous caesarean sections were considered as protective factor.

Nanoparticulated silicas with bimodal porosity: chemical control of the pore sizes.

Nanoparticulated bimodal porous silicas (NBSs) with pore systems structured at two length scales (meso- and large-meso-/macropores) have been prepared through a one-pot surfactant-assisted procedure by using a simple template agent and starting from silicon atrane complexes as hydrolytic inorganic precursors. The final bulk materials are constructed by an aggregation of pseudospherical mesoporous primary nanoparticles process, over the course of which the interparticle (textural) large pore system is generated. A fine-tuning of the procedural variables allows not only an adjustment of the processes of nucleation and growth of the primary nanoparticles but also a modulation of their subsequent aggregation. In this way, we achieve good control of the porosity of both the intra- and interparticle pore systems by managing independent variables. We analyze in particular the regulating role played by two physicochemical variables: the critical micelar concentration (cmc) of the surfactant and the dielectric constant of the reaction medium.

Mesosynthesis of ZnO-SiO(2) porous nanocomposites with low-defect ZnO nanometric domains.

Silica-based ZnO-MCM-41 mesoporous nanocomposites with high Zn content (5≤Si/Zn≤50) have been synthesized by a one-pot surfactant-assisted procedure from aqueous solution using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure-directing agent, and starting from molecular atrane complexes as inorganic hydrolytic precursors. This preparative technique allows optimization of the dispersion of the ZnO nanodomains in the silica walls. The mesoporous nature of the final materials is confirmed by x-ray diffraction (XRD), transmission electron microscopy (TEM) and N(2) adsorption-desorption isotherms. The ZnO-MCM-41 materials show unimodal pore size distributions without blocking of the pore system even for high Zn content. A careful optical spectroscopic study (using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and UV-visible spectroscopy) of these materials shows that, irrespective of the Si/Zn ratio, the Zn atoms are organized in well-dispersed, uniform low-defect ZnO nanodomains (radius about 1 nm) and are partially embedded within the silica walls.

Large monolithic silica-based macrocellular foams with trimodal pore system.

Silica-based materials with hierarchical pore systems at three different length scales (small mesopores-large mesopores-macropores) have been prepared through a nanotectonic approach by using mesoporous nanoparticles as building blocks; the resulting materials present a highly accessible foam-like architecture and can be prepared as large monoliths.

Silica-based powders and monoliths with bimodal pore systems.

Porous pure and doped silicas with pore sizes at two length scales (meso/macroporous) have been prepared and shaped both as powders and monoliths through a one-pot surfactant assisted procedure by using a simple template agent and starting from atrane complexes as inorganic precursors.