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Alejo-Molina A.,Autonomous University of Mexico State | Hingerl K.,Johannes Kepler University | Hardhienata H.,Johannes Kepler University | Hardhienata H.,Bogor Agricultural University
Journal of the Optical Society of America B: Optical Physics | Year: 2015

We report a comprehensive study of the fourth rank tensor describing third harmonic generation (THG) and electric field induced second harmonic (EFISH) in centrosymmetric material from two different viewpoints: group theory and the simplified bond hyperpolarizability model (SBHM). We show that the fourth rank tensor related to THG and direct current EFISH can be reduced to two independent elements, whereas SBHM always gives only one, reproducing perfectly well EFISH experimental results in a metal oxide semiconductor. We argue that it is possible to reduce the fourth rank tensor describing EFISH to a third rank tensor and further deliver a classical explanation of EFISH regarding symmetry breaking, where the term containing r3 in the potential immediately leads to second harmonic generation. © 2015 Optical Society of America. Source


Martinez S.S.,Autonomous University of the State of Morelos | Uribe E.V.,Autonomous University of Mexico State
Ultrasonics Sonochemistry | Year: 2012

The degradation of azure B dye (C15H16ClN 3S; AB) has been studied by Fenton, sonolysis and sono-electroFenton processes employing ultrasound at 23 kHz and the electrogeneration of H 2O2 at the reticulated vitreous carbon electrode. It was found that the dye degradation followed apparent first-order kinetics in all the degradation processes tested. The rate constant was affected by both the pH of the solution and initial concentration of Fe2+, with the highest degradation obtained at pH between 2.6 and 3. The first-order rate constant decreased in the following order: sono-electroFenton > Fenton > sonolysis. The rate constant for AB degradation by sono-electroFenton is ∼10-fold that of sonolysis and ∼2-fold the one obtained by Fenton under silent conditions. The chemical oxygen demand was abated ∼68% and ∼85% by Fenton and sono-electroFenton respectively, achieving AB concentration removal over 90% with both processes. © 2011 Elsevier B.V. All rights reserved. Source


Mendez-Arroyo J.,Northwestern University | Barroso-Flores J.,Autonomous University of Mexico State | Lifschitz A.M.,Northwestern University | Sarjeant A.A.,Northwestern University | And 2 more authors.
Journal of the American Chemical Society | Year: 2014

A biomimetic, ion-regulated molecular receptor was synthesized via the Weak-Link Approach (WLA). This structure features both a calix[4]arene moiety which serves as a molecular recognition unit and an activity regulator composed of hemilabile phosphine alkyl thioether ligands (P,S) chelated to a Pt(II) center. The host-guest properties of the ion-regulated receptor were found to be highly dependent upon the coordination of the Pt(II) center, which is controlled through the reversible coordination of small molecule effectors. The environment at the regulatory site dictates the charge and the structural conformation of the entire assembly resulting in three accessible binding configurations: one closed, inactive state and two open, active states. One of the active states, the semiopen state, recognizes a neutral guest molecule, while the other, the fully open state, recognizes a cationic guest molecule. Job plots and 1H NMR spectroscopy titrations were used to study the formation of these inclusion complexes, the receptor binding modes, and the receptor binding affinities (Ka) in solution. Single crystal X-ray diffraction studies provided insight into the solid-state structures of the receptor when complexed with each guest molecule. The dipole moments and electrostatic potential maps of the structures were generated via DFT calculations at the B97D/LANL2DZ level of theory. finally, we describe the reversible capture and release of guests by switching the receptor between the closed and semiopen configurations via elemental anion and small molecule effectors. © 2014 American Chemical Society. Source


Zarabadi-Poor P.,University of Tehran | Badiei A.,University of Tehran | Yousefi A.A.,Iran Polymer And Petrochemical Institute | Barroso-Flores J.,Autonomous University of Mexico State
Journal of Physical Chemistry C | Year: 2013

The H-acid dye intermediate was successfully attached to the SBA-15 mesoporous silica surface in a two-step modification process. Synthesized materials were characterized using several techniques including Fourier transform infrared spectroscopy, N2 adsorption-desorption measurements, small-angle X-ray scattering, transmission electron microscopy, and thermogravimetric analysis. The fluorescent sensing properties were examined in the final product toward several metal ions and showed high selectivity for Hg2+. Computational studies were performed in order to obtain a detailed electronic description of the quenching mechanism of H-acid fluorescence by Hg2+ as well as studying the structure and bonding in the [H-acid]Hg2+ complex. © 2013 American Chemical Society. Source


Sanchez J.,Autonomous University of Mexico State | Holmgren J.,Gothenburg University
Indian Journal of Medical Research | Year: 2011

After De ́s pivotal demonstration in 1959 of a diarrhoeogenic exo-enterotoxin in cell-free culture filtrates from Vibrio cholerae (of classical biotype), much insight has been gained about cholera toxin (CT), which is arguably now the best known of all microbial toxins. The subunit structure and function of CT, its receptor (the GM1 ganglioside), and its effects on the cyclic AMP system and on intestinal secretion were defined in the 1970s, and the essential aspects of the genetic organization in the 1980s. Recent findings have generated additional perspectives. The 3D-crystal structure of CT has been established, the CT- encoding operon has been shown to be carried by a non-lytic bacteriophage, and in depth knowledge has been gained on how the bacterium controls CT gene expression in response to cell density and various environmental signals. The mode of entry into target cells and the intracellular transport of CT are becoming clearer. CT has become the prototype enterotoxin and a widely used tool for elucidating important aspects of cell biology and physiology, e.g., cell membrane receptors, the cyclic AMP system, G proteins, as well as normal and pathological ion transport mechanisms. In immunology, CT has emerged as a potent, widely used experimental adjuvant, and the strong oral-mucosal immunogenicity of the non-toxic B-subunit (CTB) has led to the use of CTB as a protective antigen together with killed vibrios in a widely licensed oral cholera vaccine. CTB has also been shown to promote immunological tolerance against certain types of mucosally co-administered antigens, preferably tissue antigens linked to the CTB molecule; this has stimulated research and development to use CTB in this context for treatment of autoimmune and allergic diseases. In summary, in the 50 years after De's discovery of CT, this molecule has emerged from being the cholera patient's "foe" to also becoming a highly useful scientist's "friend". Source

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