On the Role of Water as a Catalyst in Prebiotic Chemistry.

In this manuscript we provide computational support to the catalytic role of water in all kinds of pseudopericyclic reactions operating in the reductive acid cycle, as well as in other metabolic processes. Water catalysis is not limited to those reactions where simple translocation of hydrogen atoms occurs, such as those represented by NuH+E→Nu-EH general equation. Indeed, water catalysis is more general and extremely important in tautomerization reactions of the type HX-Y=Z→X=Y-ZH, which operate in the reductive citric acid cycle and metabolic processes. Moreover, the comprehensive theoretical study reported herein illustrates that these reactions appear to behave as authentic enzyme-catalyzed reactions showing Michaelis-Menten behavior, however with the abnormal singularity that the concentration of the catalytic "water clusters" of different length and nature must be taken as a huge number. Overall, the results presented are suggestive of the workability of the so-called "metabolism first" proposal in a hot water world, as water catalysis eliminates the dilution problem frequently associated to this proposal.

The role of proton shuttling mechanisms in solvent-free and catalyst-free acetalization reactions of imines.

Proton transfer is central to the understanding of chemical processes. More so in addition reactions of the type NuH + E → Nu-EH taking place under solvent-free and catalyst-free conditions. Herein we show that the addition of alcohols or amines (the NuH component) to imine derivatives (the E component), in 1 : 1 ratio, under solvent-free and catalyst-free conditions, are efficient methods to access N,O and N,N-acetal derivatives. In addition, computational studies reveal that they are catalyzed reactions involving two or even three NuH molecules operating in a cooperative manner as H-bonded NuH(NuH)nNuH associates (many body effects) in the transition state through a concerted proton shuttling mechanism (addition of alcohols) or stepwise proton shuttling mechanism (addition of amines), thereby facilitating the key proton transfer step.

Organocatalysis by Networks of Cooperative Hydrogen Bonds: Enantioselective Direct Mannich Addition to Preformed Arylideneureas.

The concept of noncovalent organocatalysis by means of networks of cooperative hydrogen bonds (NCHB organocatalysis) has been explored. Arylideneureas were chosen as ideal substrates because of their powerful donor-acceptor properties. We have examined their uncatalyzed, direct Mannich reaction with acetoacetates in comparison with that catalyzed by a number of salan derivatives capable of providing a network of cooperative hydrogen bonds. Catalyst D [(R,R)-N,N'-bis(salicyl)cyclohexane-1,2-diamine] was found to drive the above direct Mannich reaction in an enantioselective manner, thereby allowing the synthesis of several Biginelli dihydropyrimidinones with high enantioselectivity. DFT calculations (B3LYP-D-PCM/6-31+G*//B3LYP/6-31+G*) revealed that the NCHB organocatalyst lowers the energy barrier of the reaction. The NCHB organocatalysts appear to function as biomimetic catalysts.

[Ln(binolam)3]·(OTf)3, a new class of propeller-shaped lanthanide(III) salt complexes as enantioselective catalysts: structure, dynamics and mechanistic insight.

The ligand 3,3'-bis(diethylaminomethyl)-1,1'-bi-2-naphthol (binolam) contains an arrayed Brønsted acid-Brønsted base (BABB) system, which is responsible for the original shape of its lanthanide compounds. The solution structure of Pr, Nd and Yb compounds is solved by means of paramagnetic NMR spectroscopy and it is demonstrated that they are substantially isostructural, but with a completely new fold compared to the apparently similar heterobimetallic systems based on 1,1'-bis(2-naphthol) (binol) and alkali cations. The aromatic nuclei lie in a region equatorial with respect to the C(3) symmetry axis, whereas the alkylamine chain stretches almost parallel to C(3), above (and below) Ln(3+). This is also found in the crystal structure of the binolamo-scandium complex. A detailed study of the proton-exchange processes within the network of BABBs present in the complex is reported, which provides insight into the mechanism of the enantioselective Henry reaction promoted by these systems.

Enantioselective, organocatalytic Morita-Baylis-Hillman and Aza-Morita-Baylis-Hillman reactions: stereochemical issues.

Conscious of the importance that stereochemical issues may have on the design of efficient organocatalyts for both Morita-Baylis-Hillman and aza-Morita-Baylis-Hillman reaction we have analyzed them in this minireview. The so-called standard reactions involve "naked" enolates which therefore should lead to the syn adducts as the major products, irrespective of the E, Z stereochemistry of the enolate. Accordingly, provided the second step is rate determining step, the design of successful bifunctional or polyfunctional catalysts has to consider the geometrical requirements imposed by the transition structures of the second step of these reactions. On the other hand, MBH and aza-MBH reactions co-catalyzed by (S)-proline and a secondary or tertiary amine (co-catalyst) involve the aldol-type condensation of either a 3-amino-substituted enamine, dienamine, or both, depending on the cases. A Zimmerman-Traxler mechanism defines the stereochemical issues regarding these co-catalyzed condensations which parallel those of the well established (S)-proline catalyzed aldol-like reactions.

Lesiones producidas en la rodilla durante el enclavado endomedular retrógrado del fémur. Estudio experimental en rodillas cadavéricas / Knee injuries due to retrograde nailing in the femur. Experimental study in cadaveric knees

Introducción: El enclavado intramedular retrógrado es una alternativa en el tratamiento de las fracturas del fémur. Las probables lesiones articulares en la zona de ingreso no están del todo aclaradas. El objetivo de este trabajo es evaluar, en rodillas cadavéricas, las lesiones que se producen con este abordaje. Materiales y métodos: Se reprodujo el procedimiento quirúrgico para la colocación de un clavo endomedular retrógrado con un abordaje mínimamente invasivo en 12 rodillas cadavéricas. Luego se realizó su disección. Resultados: En cuatro rodillas (33 por ciento) se produjeron lesiones osteocondrales: tres en la zona de inserción delligamento cruzado anterior y una en el cóndilo interno. Conclusiones: Existe una alta posibilidad de producir lesiones iatrogénicas durante la colocación de un clavo retrógrado. La asistencia artroscópica podría reducir esa posibilidad.(AU)

Lesiones producidas en la rodilla durante el enclavado endomedular retrógrado del fémur. Estudio experimental en rodillas cadavéricas / Knee injuries due to retrograde nailing in the femur. Experimental study in cadaveric knees

Introducción: El enclavado intramedular retrógrado es una alternativa en el tratamiento de las fracturas del fémur. Las probables lesiones articulares en la zona de ingreso no están del todo aclaradas. El objetivo de este trabajo es evaluar, en rodillas cadavéricas, las lesiones que se producen con este abordaje. Materiales y métodos: Se reprodujo el procedimiento quirúrgico para la colocación de un clavo endomedular retrógrado con un abordaje mínimamente invasivo en 12 rodillas cadavéricas. Luego se realizó su disección. Resultados: En cuatro rodillas (33 por ciento) se produjeron lesiones osteocondrales: tres en la zona de inserción delligamento cruzado anterior y una en el cóndilo interno. Conclusiones: Existe una alta posibilidad de producir lesiones iatrogénicas durante la colocación de un clavo retrógrado. La asistencia artroscópica podría reducir esa posibilidad.

On the "gluing" effect of lithium: the lithium-driven assembly of circum-arranged, edge-fused cyclopentadienyl lithium compounds and aza analogues.

Predictions (DFT/B3LYP calculations) are that cyclopentadienyl lithium edge-fused to [n]circulenes in a circum-like manner should self-assemble as rod-like, nanometer long, supersandwich compounds (see figure). On the contrary, triazolyl lithium analogues prefer to dimerize thereby giving rise to shell-like dimers of variable curvatures.This study is aimed at exploring M. Etter's (T. W. Panunto, Z. Urbanczyk-Lipkowska, R. Jonhson, M. Etter, J. Am. Chem. Soc. 1987, 109, 7786-7797) bottom-up approach towards the design of organic-solid sate materials. Guided by the electrostatic paste ("gluing") effect of lithium, we examined the self-assembly modes of a series of cyclopentadienyl lithium edge-fused to benzene, as well as to [n]circulenes, arranged in a circum-like manner by means of DFT/B3 LYP calculations. We have also examined the self-assembly modes of the analogous triazolyl derivatives. Generally, well defined trends have been found. Thus, whereas cylcopentadienyl derivatives 1, 3 and 5 tend to aggregate as rod-like, nanometer-long, supersandwich compounds, the corresponding triazolyl analogues 2, 4 and 6 tend to dimerize thus giving rise to shell-like dimers of variable curvatures. In our view, M. Etter's bottom-up approach combined with high level calculations appears to have great potential for designing complex molecular architectures and nanostructures. Hopefully, these studies will spur the activity of synthetic and materials chemists.

Lanthanide (III) salt complexes: arrayed acid-base networks for enantioselective catalysis. The nitroaldol reaction upon aldehydes and trifluoromethylketones.

Shelf stable, chiral-at-metal, D(3) symmetric, 3:1 complexes of lanthanide (III) triflate salts are easily available by complexation with binolam (3,3'-diethylaminomethyl-2,2'-dihydroxy-1,1'-dinaphthalene) 1 or binolamo (3,3'-diethylaminooxymethyl-2,2'-dihydroxy-1,1'-dinaphthalene) 2 ligands. The resulting compounds 3Ln and 4Ln are isostructural, as demonstrated by their spectroscopic data, and possess an arrayed acid-base LABABB network. Complexes are kinetically labile, and in solution undergo hydrolysis by water. The lanthanum complex derived from binolam, i.e., (Delta,S,S,S)- (binolam)(3).la(OTf)(3)3La was found to be the most active catalyst in promoting direct nitroaldol reactions upon aldehydes and trifluoromethyl ketones, thereby giving rise to secondary nitroalcohols and tertiary alpha-trifluoromethyl-beta-nitroalcohols, respectively, with high ee in both cases. Enantiomerically enriched tertiary nitroalcohols were easily reduced to the corresponding aminoalcohols having a quaternary asymmetric carbon without loss of enantiomeric purity.

Reconstruccion de las partes blandas en la pierna: Complicaciones y su resolucion / Soft tissue reconstruction in the leg: Complications and solutions

Objetivo: El propósito de este trabajo es analizar la evolución, las complicaciones y las variables pronósticas en un grupo de pacientes que sufrieron fracturas graves de la pierna, a los cuales se les realizaron procedimientos de cirugía reconstructiva sobre las partes blandas. Materiales y métodos: En un período de 5 años, se incluyeron 21 pacientes con fracturas expuestas graves de la pierna. Se utilizaron el ISS, las clasificaciones AO y Gustilo, el MESS y el score de McPherson. Se evaluaron en forma retrospectiva los tiempos de consolidación y de curación de las partes blandas, el tiempo de internación, los procedimientos quirúrgicos y las complicaciones. Resultados: En su mayoría, la selección del procedimiento de partes blandas fue independiente de la clasificaciónde la lesión. Se realizaron 9 colgajos con dorsalancho, 5 musculares rotatorios de gemelos y 7 fasciocutáneos surales. De los colgajos de dorsal ancho, uno (11,1%) sufrió necrosis total y 2, necrosis parcial (22,2%). Los 6 restantes(66,7%) evolucionaron sin complicaciones.Uno (20%) de los colgajos rotatorios de gemelo sufrió necrosis completa. Los 4 (80%) restantes evolucionaron de manera favorable. De los 7 colgajos fasciocutáneos (surales), 6 (85,7%)evolucionaron sin problemas y sólo uno (14,3%) se necrosó. Se utilizaron 2 colgajos fasciocutáneos como rescate ante el fracaso de otro procedimiento, pero uno no tuvo buen resultado. Conclusiones: La tasa de complicaciones en la reconstrucción de las partes blandas en lesiones graves de la pierna es considerable, pero el abordaje multidisciplinario de estos pacientes y los protocolos de tratamiento facilitan su resolución.

Direct, catalytic enantioselective nitroaldol (Henry) reaction of trifluoromethyl ketones: an asymmetric entry to alpha-trifluoromethyl-substituted quaternary carbons.

Herein we describe the first direct, catalytic enantioselective nitroaldol (Henry) reaction of simple alpha-trifluoromethyl ketones with nitromethane using a chiral monometallic lanthanum(III) triflate salt complex, namely [(Delta,S,S,S)-Binolam]3.La(OTf)3, as enantioselective catalyst. The resulting alpha-trifluoromethyl tertiary nitroaldols were obtained in moderate to high yields (up to 93%) and enantioselectivities (up to 98% ee). These adducts are versatile chiral building blocks and may be reduced (NiCl2/NaBH4) to their beta-amino-alpha-trifluoromethyl tertiary alcohols without loss of enantiomeric purity.