PINCER COMPLEXES OF PRECIOUS METALS

The synthesis and characterization of several new iridium(I) and iridium(III) carbonyl complexes supported by aminophosphinite pincer ligands is reported. A surprising diversity of reaction pathways were accessible upon treatment of Ir carbonyl complexes with salts of redox-inactive alkali, alkaline earth, and lanthanide metal cations. Iridium(III) hydridocarbonyl chloride complexes underwent either halide abstraction or halide substitution reactions, whereas iridium(I) carbonyl complexes underwent protonative oxidative addition reactions. When the nitrogen donor of the pincer ligand is an aza-crown ether macrocycle, cation–macrocycle interactions can be supported, leading to divergent reactivity in some cases. New iridium and rhodium complexes supported by aminophosphinite pincer-crown ether ligands were synthesized. Iridium-catalyzed hydroformylation of allylbenzene was explored. Catalytic amounts of LiOTf (OTf = trifluoromethanesulfonate) doubled the rate of hydrofunctionalization. The iridium pincer complexes were found to undergo remetallation pathways under the conditions of catalysis. This guided the design of a new, more active iridium catalyst supported by a pincer ligand with a methoxy substituent incorporated to prevent remetallation. Rhodium-catalyzed hydroformylation of 1-octene was explored as well. A systematic decrease in the n (linear) to iso (branched) aldehyde ratio was observed in the presence of increasingly bulky ammonium additives. However, catalyst stability studies showed that rhodium pincer complexes undergo decomposition under hydroformylation conditions and presumably simply act as pre-catalysts. The first mononuclear gold(III) PNP pincer complexes (PNP = bis(2- diisopropylphosphinophenyl)amide) are reported. The chloro complex [(PNP)Au(Cl)][OAcF] (OAcF = OCOCF3) was synthesized by microwave irradiation of a tetrachloroaurate salt and the neutral PNHP ligand. Dehalogenation with AgOAcF afforded the trifluoroacetate-bound complex [(PNP)Au(OAcF)][OAcF]. Electronic absorption spectroscopy and time-dependent density functional theory studies assigned the electronic transition that imbues the complexes with a deep royal blue color. The Au(III) trifluoroacetate complex is surprisingly stable, and no reactivity towards ethylene was observed, even under high pressures and at high temperatures. Density functional theory calculations suggest that the lack of reactivity is due to the high energy of the putative dicationic ethylene-bound intermediate invoked in a formal insertion reaction.Doctor of Philosoph

Propuesta para la sustituci?n del combustible Di?sel en los veh?culos de transporte de pasajeros

La presente tesis propone un cambio de la matriz energ?tica en el transporte urbano de pasajeros, que consume combustible di?sel y en su mayor?a de importaci?n, Para tal efecto hemos seleccionado a la empresa de Transportes Unidos el Chino S.A. (ETUCHISA) como caso estudio y l?nea base para realizar una transici?n energ?tica al Gas Natural y/o bater?as el?ctricas, para ello se plantea evaluar lo siguiente: - Rentabilidad econ?mica del combustible di?sel, - Evaluaci?n del impacto ambiental de las alternativas, - Evaluaci?n de la sostenibilidad social de las alternativas, - Seleccionar la alternativa que permita sustituir el combustible di?sel. De las evaluaciones a los buses de transporte urbano de pasajeros, realizadas en t?rminos privados y sociales, se determina que los primeros 5 a?os de operaci?n es rentable el uso del combustible di?sel, posteriormente, desde el a?o 5 al a?o 20, el uso de buses a Gas Natural es m?s rentable y finalmente, desde el a?o 20 en adelante, el uso de Bater?as el?ctricas es definitivamente m?s rentable que las otras dos alternativas de combustible. Finalmente, proponemos que las entidades gubernamentales MINEM, MINAM y MTC realicen coordinaciones y pol?ticas p?blicas integradas para que de esta manera se elabore el plan estrat?gico para la transici?n energ?tica planteada

Comportamiento epidemiológico de los factores de riesgo asociados a enfermedades crónicas no transmisibles en estudiantes universitarios

Describir el comportamiento epidemiológico de los factores de riesgo relacionados a enfermedades crónicas no transmisibles asociados a hipertrigliceridemia presentes en los estudiantes del primer año de la carrera de Médico y Cirujano de la Universidad de San Carlos de Guatemala. Estudio descriptivo transversal realizado en 1097 estudiantes, en los cuales se aplicó el cuestionario del método paso a paso para la vigilancia de factores de riesgo de enfermedades crónicas (STEPS) modificado. Se encontró 610 (56%) estudiantes sexo femenino, la media de edad fue de 19 años (±1.56); en relación a los factores de riesgo modificables: 219 (20%) consumen cigarrillo, 274 (25%) consumen alcohol nocivamente, 838 (76%) se alimentan de forma inadecuada, 887 (81%) no practica actividad física significativa; se identificó que 405 (37%) presentaron un índice cintura – cadera considerado de riesgo. En cuanto a los factores asociados a la presencia de hipertrigliceridemia: obesidad se identificó en 147 (13%) estudiantes (X2 de 104.98 y OR de 7), obesidad central en 204 (19%) (X2 de 55.74 y OR de 3), el sobrepeso en 330 (30%) (X2 de 53.4727 y OR de 3), presión arterial alta en 397 (36%) (X2 de 18.63 y OR de 2), y glucemia alterada en ayunas alta en 198 (18%) (X2 de 8.3 y OR de 2). La hipertrigliceridemia se presentó en 411 estudiantes (37%), siendo la edad más afectada la de 19 años. La mayoría de estudiantes estudiados es de sexo femenino. Existe una alta prevalencia de factores de riesgo modificables asociados a enfermedades crónicas no transmisibles, de estos se identificó que factores como obesidad, obesidad central, sobrepeso, presión arterial alta y glucemia alterada en ayunas alta tienen una significativa asociación al desarrollo de hipertrigliceridemia, con un aumento del riesgo de 7, 3, 3, 2 y 2, respectivamente

Surface Doping Quantum Dots with Chemically Active Native Ligands: Controlling Valence without Ligand Exchange

One remaining challenge in the field of colloidal semiconductor nanocrystal quantum dots is learning to control the degree of functionalization or valence per nanocrystal. Current quantum dot surface modification strategies rely heavily on ligand exchange, which consists of replacing the nanocrystal\u27s native ligands with carboxylate- or amine-terminated thiols, usually added in excess. Removing the nanocrystal\u27s native ligands can cause etching and introduce surface defects, thus affecting the nanocrystal\u27s optical properties. More importantly, ligand exchange methods fail to control the extent of surface modification or number of functional groups introduced per nanocrystal. Here, we report a fundamentally new surface ligand modification or doping approach aimed at controlling the degree of functionalization or valence per nanocrystal while retaining the nanocrystal\u27s original colloidal and photostability. We show that surface-doped quantum dots capped with chemically active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Specifically, vinyl and azide-terminated carboxylic acid ligands survive the high temperatures needed for nanocrystal synthesis. The ratio between chemically active and inactive-terminated ligands is maintained on the nanocrystal surface, allowing to control the extent of surface modification by straightforward organic reactions. Using a combination of optical and structural characterization tools, including IR and 2D NMR, we show that carboxylates bind in a bidentate chelate fashion, forming a single monolayer of ligands that are perpendicular to the nanocrystal surface. Moreover, we show that mixtures of ligands with similar chain lengths homogeneously distribute themselves on the nanocrystal surface. We expect this new surface doping approach will be widely applicable to other nanocrystal compositions and morphologies, as well as to many specific applications in biology and materials science

Posterior oblique technique for sacroiliac joint fusion leads to greater pain relief and similar improvement in function compared to the lateral technique: A retrospective, comparative study

Background: Management of chronic sacroiliac joint (SIJ) pain among patients who do not respond to nonsurgical treatment is increasingly turning toward minimally invasive SIJ fusion. There are different techniques available to perform this procedure, with the lateral technique being more commonly studied than the posterior oblique technique. This study examined the effects of these techniques on pain relief and functional improvement, both preoperatively and at a 12-month follow-up. Methods: This retrospective cohort study analyzed data from 45 patients who underwent SIJ fusion. Included patients were ≥50 years old, nonresponsive to conservative treatment. Subjects were divided into 2 cohorts based on the SIJ fusion technique. Primary outcomes were pain relief, measured by Visual Analog Scale (VAS), and functional improvement, determined by the Oswestry Disability Index (ODI); both were recorded and assessed at baseline, postoperative, and the change from pre- to postoperative. Additionally, data regarding patient demographics, previous lumbar fusion, operative time, and duration of hospital stay were collected and analyzed. Results: Baseline demographic and clinical variables exhibited no significant differences in distribution between groups. The posterior oblique cohort demonstrated a substantial reduction in operative time (over 50%) and duration of hospital stay compared to lateral cohort. Pain relief (postoperative VAS: lateral 3.5±1.7 vs. posterior oblique 2.4±1.5 [p=.02]) and functional improvement (postoperative ODI: lateral 29.6±7.3 vs. posterior oblique 21±5.7 [p≤.001]) were significantly better in the posterior oblique group. Pre- to postoperative improvement analysis indicated greater reduction in pain (VAS: lateral −4.4±1.9 vs. posterior oblique −6.1±1.5 [p=.002]) in the posterior oblique group. Conclusions: Compared to the lateral technique group, patients undergoing minimally invasive SIJ fusion through the posterior oblique technique experienced greater pain relief and demonstrated a trend toward better functional improvement, with shorter operative times and duration of hospital stay. The posterior oblique technique may be more efficient and beneficial to manage patients suffering from chronic SIJ pain through joint fusion

Surface Doping Quantum Dots with Chemically Active Native Ligands: Controlling Valence without Ligand Exchange

One remaining challenge in the field of colloidal semiconductor nanocrystal quantum dots is learning to control the degree of functionalization or "valence" per nanocrystal. Current quantum dot surface modification strategies rely heavily on ligand exchange, which consists of replacing the nanocrystal's native ligands with carboxylate- or amine-terminated thiols, usually added in excess. Removing the nanocrystal's native ligands can cause etching and introduce surface defects, thus affecting the nanocrystal's optical properties. More importantly, ligand exchange methods fail to control the extent of surface modification or number of functional groups introduced per nanocrystal. Here, we report a fundamentally new surface ligand modification or "doping" approach aimed at controlling the degree of functionalization or valence per nanocrystal while retaining the nanocrystal's original colloidal and photostability. We show that surface-doped quantum dots capped with chemically active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Specifically, vinyl and azide-terminated carboxylic acid ligands survive the high temperatures needed for nanocrystal synthesis. The ratio between chemically active and inactive-terminated ligands is maintained on the nanocrystal surface, allowing to control the extent of surface modification by straightforward organic reactions. Using a combination of optical and structural characterization tools, including IR and 2D NMR, we show that carboxylates bind in a bidentate chelate fashion, forming a single monolayer of ligands that are perpendicular to the nanocrystal surface. Moreover, we show that mixtures of ligands with similar chain lengths homogeneously distribute themselves on the nanocrystal surface. We expect this new surface doping approach will be widely applicable to other nanocrystal compositions and morphologies, as well as to many specific applications in biology and materials science.Reprinted (adapted) with permission from Chemistry of Materials 24 (2012): 4231, doi: 10.1021/cm3026957. Copyright 2012 American Chemical Society.</p

El Plan de Reconstrucción Nacional y la participación de las ONG

Evalúa el Plan de Reconstrucción Nacional (PRN), con relación a la participación de las Organizaciones no Gubernamentales (ONG). Detalla el marco general del PRN, el origen y destino de los fondos y el desarrollo de los programas que forman parte de ello, pasando a una exposición del papel de las ONG en la implementación del Plan, comparado con sus capacidades disponibles. Presenta conclusiones tanto sobre el Plan como sobre las ONG y recomienda mayor participación de éstas en aquel

Surface Doping Quantum Dots with Chemically Active Native Ligands: Controlling Valence without Ligand Exchange

One remaining challenge in the field of colloidal semiconductor nanocrystal quantum dots is learning to control the degree of functionalization or “valence” per nanocrystal. Current quantum dot surface modification strategies rely heavily on ligand exchange, which consists of replacing the nanocrystal’s native ligands with carboxylate- or amine-terminated thiols, usually added in excess. Removing the nanocrystal’s native ligands can cause etching and introduce surface defects, thus affecting the nanocrystal’s optical properties. More importantly, ligand exchange methods fail to control the extent of surface modification or number of functional groups introduced per nanocrystal. Here, we report a fundamentally new surface ligand modification or “doping” approach aimed at controlling the degree of functionalization or valence per nanocrystal while retaining the nanocrystal’s original colloidal and photostability. We show that surface-doped quantum dots capped with chemically active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Specifically, vinyl and azide-terminated carboxylic acid ligands survive the high temperatures needed for nanocrystal synthesis. The ratio between chemically active and inactive-terminated ligands is maintained on the nanocrystal surface, allowing to control the extent of surface modification by straightforward organic reactions. Using a combination of optical and structural characterization tools, including IR and 2D NMR, we show that carboxylates bind in a bidentate chelate fashion, forming a single monolayer of ligands that are perpendicular to the nanocrystal surface. Moreover, we show that mixtures of ligands with similar chain lengths homogeneously distribute themselves on the nanocrystal surface. We expect this new surface doping approach will be widely applicable to other nanocrystal compositions and morphologies, as well as to many specific applications in biology and materials science

Pronunciation of phonemes in relation to the degree of malocclusion and position of the incisal edges-lip vermilion border

"Introduction: Phonetics helps to establish an ideal incisal Edge position in relation to the vermilion border during phoneme articulation. Objective: To evaluate the relationship between the incisal edge of the anterior teeth and the vermilion border with the severity of the malocclusion and phonemes articulation of patients attending from January to February 2015 at the Orthodontics Service of Mexico Children’s Hospital «Dr. Federico Gomez"