Preparation and characterization of terdentate [C,N,N] acetophenone and acetylpyridine hydrazone platinacycles: a DFT insight into the reaction mechanism.

The reaction of N-ortho-chlorophenyl-substituted acetylpyridine hydrazones (a and d) with K2[PtCl4] (n-butanol/water, 100 °C) gave mononuclear complexes 1a and 1d with the ligands as [N,N] bidentate. In contrast, the reaction of N-phenyl or N-meta-chlorophenyl hydrazones (b and c, respectively) under analogous reaction conditions gave the cycloplatinated species 2b and 2c with the ligand as [C,N,N] terdentate. The treatment of the mononuclear complexes 1a and 1d with NaOAc (n-butanol, 100 °C) gave the corresponding cycloplatinated complexes 2a and 2d. Acetophenone hydrazone platinacycle 2e was prepared in a similar fashion and its reaction with tertiary mono- and triphosphines gave mono- or trinuclear species depending on the reaction conditions. The X-ray crystal structures of some of these complexes showed interesting π-π slipped stacking interactions between metallacyclic rings which, according to NCI analyses, showed an aromatic character. With an aim to rationalize the different reactivities shown by acetylpyridine hydrazones and the precise role of the acetate anion, the energy profiles for the three main steps of cycloplatination (iminoplatinum complex formation, chelation and cyclometallation) have been determined by using the DFT (M06) methods. Calculations indicate that the cycloplatination of 1b proceeds via electrophilic substitution, involving the direct replacement of the chloride anion at the Pt(ii) centre with the N-phenyl moiety as the rate-determining step, to give an agostic intermediate 5b+ that, subsequently, leads to the elimination of a proton as hydrogen chloride. When present as an "external" base, acetate enters the coordination sphere around the Pt(ii) centre and facilitates hydrazone N-H deprotonation and electrophilic C-H activation through a dissociative route, leading to a Wheland-type σ-complex intermediate 9ac.

Self-assembly of dinuclear Pd(ii)/Pt(ii) metallacyclic receptors incorporating N-heterocyclic carbene complexes as corners.

We report herein the self-assembly of a series of new square and rectangular-shaped dinuclear M2L2 metallacycles (M = Pd(ii)/Pt(ii)), receptors self-assembled in water from four different N-monoalkyl-4,4'-bipyridinium derivatives as ligands and square-planar Pd(ii) and Pt(ii) metal centers having the chelating N-heterocyclic carbene 1,1'-di(methyl)-3,3'-methylene-4-diimidazolin-2,2'-diylidene. The concentration-dependent Pd2L2 metallacycles were successfully obtained and characterized by means of NMR experiments in aqueous media. Due to the strong trans effect exerted by the carbene ligands, the synthesis of the Pt2L2 receptors was achieved as well by self-assembly of the components at room temperature in a few hours, in clear contraposition to the harsh reaction conditions usually required for the labilization of other kinetically inert Pt(ii)-N(pyridine) bonds. X-ray diffraction studies of suitable single crystals of two of the obtained receptors offered additional information on the structure of the obtained supramolecules, whose ability as receptors has been explored by the preparation and study of the corresponding inclusion complexes in water with 1,5-dihydroxynaphthalene as the model substrate.

Representación radiológica de la fuerza de gravedad en la columna lumbar / Radiographic screening of the gravity strenght in the lumbar spine

Se examinaron 14 especímenes de columna lumbar, de los cuales seis se obtuvieron de la fosa común, semidesecados, y ocho del Servicio Médico Forense y del Instituto Politécnio Nacional, provistos de su sistema ligamentario, con el objeto de analizar la dirección de las fuerzas de gravedad por medio de la orientación de sus travéculas. Los especímenes semidesecados, sin ligamentos, se trataron con solución de cal en agua al 25%, desecación solar y cortes con segueta de acero. Los especímenes frescos, conservados en formol se analizaron con tomógrafo hipocicloidal. Los resultados mostraron cierta diferencia intrínseca en la traveculación entre las cinco vértebras lumbares, pero en general se encontró que la fuerza de gravedad es absorvida en 70 a 80%por el cuerpo vertebral. El sistema ligamentario sufre fuerzas antagónicas a la compresión. El pedículo se considera una zona resistente que trasmite cargas de compresión o de tensión a las láminas y facetas articulares. La pars articularis en cambio sufre un conjunto de fuerzas compresivas y tensionales, y estructuralmente es una zona de menor resistencia que se encuentra sometida a cargas de cizallamiento, y como consecuencia, a riesgo de rotura.

Tratamiento conservador en fracturas de columna lumbar. Seguimiento de dos años / Conservative treatment of lumbar spine fractures. Two years follow-up

Se considera que en las fracturas de columna vertebral cuando presentan signos radiológicos aparentes de estabilidad pero con conservación de los pars articularis y un mínimo de un tercio del muro posterior, es posible la reparación y remodelación ósea con tratamiento conservador. Se revisaron 32 pacientes con fractura de columna lumbar y sin daño neurológico, tratados mediante reducción y aplicación de corsé de yeso en mesa de Putti bajo anestesia. El corsé tipo Taylor se usó por 10 a 12 semanas. Se logró reducción en el 90%de los pacientes. En todos se obtuvo consolidación. A dos años de la fractura se reprodujo xifosis de 15 grados en 27 de los pacientes.