Biomimetic Sol–Gel Synthesis of TiO₂ and SiO₂ Nanostructures

We report the heptapeptide-mediated biomineralization of titanium dioxide nanoparticles from titanium alkoxides. We evaluated the influence of pH on the biomineralized products and found that nanostructured TiO₂ was formed in the absence of external ions (water only) at pH ∼ 6.5. Several variants (mutants) of the peptides with different properties (i.e., different charges, isoelectric points (p<i>I</i>s), and sequences) were designed and tested in biomineralization experiments. Acid-catalyzed experiments were run using the H1 (HKKPSKS) peptide at room temperature, which produced anatase nanoparticles (∼5 nm in size) for the first time via a heptapeptide and sol–gel approach. In addition, the peptide H1 was used to synthesize SiO₂ nanoparticles. The influence of the pH and the added ions were monitored: at higher pH levels (8–9), SiO₂ nanoparticles (20–30 nm in size) were obtained. In addition, whereas borate and Tris ions allowed the formation of colloidal systems, phosphate ions were unable to produce sols. The results presented here demonstrate that biomineralization depends on the sequence and charge of the peptide, and ions in solution can optimize the formation of nanostructures

Using the M13 Phage as a Biotemplate to Create Mesoporous Structures Decorated with Gold and Platinum Nanoparticles

By taking advantage of the physical and chemical properties of the M13 bacteriophage, we have used this virus to synthesize mesoporous silica structures. Major coat protein p8 was chemically modified by attaching thiol groups. As we show, the resulting thiolated phage can be used as a biotemplate able to direct the formation of mesoporous silica materials. Simultaneously, this thiol functionality acts as an anchor for binding metal ions, such as Au³⁺ and Pt⁴⁺, forming reactive M13–metal ionic complexes which evolve into metal nanoparticles (NPs) trapped in the mesoporous network. Interestingly, Au³⁺ ions are reduced to Au⁰ NPs by the protein residues without requiring an external reducing agent. Likewise, silica mesostructures decorated with Au and Pt NPs are prepared in a one-pot synthesis and characterized using different techniques. The obtained results allow us to propose a mechanism of formation. In addition, gold-containing mesoporous structures are tested for the reduction of 4-nitrophenol (4-NP) and methylene blue (MB) in the presence of NaBH₄. Although all of the gold-containing catalysts exhibit catalytic activity, those obtained with thiolated phages present a better performance than that obtained with M13 alone. This behavior is ascribed to the position of the Au NPs, which are partially embedded in the wall of the final mesostructures

Influencia de la urbanización en el cambio de la vegetación colindante del corredor Pachuca-Tizayuca (2000-2014)

Las áreas urbanas ejercen presión sobre la vegetación colindante a estas. Se ha demostrado que la diferencia en los índices de vegetación (DIV) es un buen indicador de su deterioro; aunque se relaciona con la presión urbana, no se ha establecido una metodología que cuantifique su impacto. Esta estrategia se aplicó en los principales municipios del Valle de Pachuca-Tizayuca, en donde la urbanización registra mayores crecimientos. Se obtuvo la clasificación supervisada en los años 2000 y 2014, mediante sistemas de información geográfica e imágenes Landsat (confiabilidad > 80 %). Se determinó el cambio de uso de suelo (NU) a urbano (U) con los cocientes U/NU y se compararon con DIV entre ambos años; se usaron los índices NDVI, MSAVI, SAVI y TSAVI; además de los AGEB rurales, como unidades geográficas de análisis. Posteriormente, se generó un archivo raster de distancias de cada pixel al borde de las zonas urbanas más cercanas (DU). La correlación lineal de DU se determina con el DIV a partir de la regresión espacial bivariada en IDRISI-Taiga. Las AGEB con creciente urbanización se identifican por los valores mayores del cociente U/NU y se observa que los DIV presentan mayores valores. Se demuestra que DU tiene más correlación con DIV en las AGEB con asentamientos humanos intermedios en expansión (R2 de 0.1 a 0.33). Se demuestra que la correlación espacial DIV vs. DU es una buena estrategia metodológica para estimar el impacto de presión urbana sobre la vegetación colindante a los asentamientos humanos

Water-Soluble Palladium(II) Complexes with Sulfonated N‑Heterocyclic Carbenes in Suzuki Cross-Coupling and Hydrodehalogenation Reactions

Water-soluble Pd­(II) complexes of general formula Na_<i>x</i>[(NHC)­PdCl₂L] (L = Cl^– (<b>1</b>), PPh₃ (<b>2</b>), PPh₂(C₆H₄-<i>m</i>-SO₃Na) (<b>3</b>), and 4-Mepy (<b>4</b>)), where NHC is a dianionic sulfonated and sterically hindered N-heterocyclic carbene, have been prepared. The new complexes are active catalysts for the Suzuki–Miyaura cross-coupling of aryl chlorides and boronic acids in mixtures of isopropyl alcohol/water or, in the case of water-soluble aryl chlorides, in pure water. The trichloride complex <b>1</b>, the crystal structure of which is reported, catalyzes the coupling of inactivated and sterically hindered substrates under mild conditions (60 °C, 0.1 mol % Pd). The corresponding biphenyls are obtained in almost quantitative yields, except in the case of some of the most hindered aryl chlorides, for which small amounts of arene are also formed by a competitive hydrodehalogenation process

Water-Soluble Palladium(II) Complexes with Sulfonated N‑Heterocyclic Carbenes in Suzuki Cross-Coupling and Hydrodehalogenation Reactions

Water-soluble Pd­(II) complexes of general formula Na_<i>x</i>[(NHC)­PdCl₂L] (L = Cl^– (<b>1</b>), PPh₃ (<b>2</b>), PPh₂(C₆H₄-<i>m</i>-SO₃Na) (<b>3</b>), and 4-Mepy (<b>4</b>)), where NHC is a dianionic sulfonated and sterically hindered N-heterocyclic carbene, have been prepared. The new complexes are active catalysts for the Suzuki–Miyaura cross-coupling of aryl chlorides and boronic acids in mixtures of isopropyl alcohol/water or, in the case of water-soluble aryl chlorides, in pure water. The trichloride complex <b>1</b>, the crystal structure of which is reported, catalyzes the coupling of inactivated and sterically hindered substrates under mild conditions (60 °C, 0.1 mol % Pd). The corresponding biphenyls are obtained in almost quantitative yields, except in the case of some of the most hindered aryl chlorides, for which small amounts of arene are also formed by a competitive hydrodehalogenation process