RESUMO
A joint experimental/theoretical study has been carried out on the putative MMA polymerization catalyzed by an yttrium isopropyloxide complex. Despite its high activity in lactone polymerization, this catalyst is found to be unreactive on methyl methacrylate (MMA) polymerization. This surprising result is rationalized using a computational approach at the DFT level. Indeed, the endothermicity of the initiation step explains this lack of reactivity. The theoretical proposal of yttrium amido complexes as catalysts allows overcoming this initiation problem.
Assuntos
Aminas/química , Compostos Organometálicos/química , Polimetil Metacrilato/síntese química , Teoria Quântica , Ítrio/química , Estrutura Molecular , Compostos Organometálicos/síntese química , Polimerização , Polimetil Metacrilato/químicaRESUMO
Conventional diagnostic magnetic resonance imaging (MRI) techniques have focused on improving the spatial resolution and image acquisition speed (whole-body MRI) or on new contrast agents. Most advances in MRI go beyond morphologic study to obtain functional and structural information in vivo about different physiological processes of tumor microenvironment, such as oxygenation levels, cellular proliferation, or tumor vascularization through MRI analysis of some characteristics: angiogenesis (perfusion MRI), metabolism (MRI spectroscopy), cellularity (diffusion-weighted MRI), lymph node function, or hypoxia [blood-oxygen-level-dependent (BOLD) MRI]. We discuss the contributions of different MRI techniques than must be integrated in oncologic patients to substantially advance tumor detection and characterization risk stratification, prognosis, predicting and monitoring response to treatment, and development of new drugs (AU)
