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J Geriatr Cardiol ; 16(5): 429-430, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31217797
Angew Chem Int Ed Engl ; 56(20): 5603-5606, 2017 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-28398613


Aqua ligands can undergo rapid internal rotation about the M-O bond. For magnetic resonance contrast agents, this rotation results in diminished relaxivity. Herein, we show that an intramolecular hydrogen bond to the aqua ligand can reduce this internal rotation and increase relaxivity. Molecular modeling was used to design a series of four Gd complexes capable of forming an intramolecular H-bond to the coordinated water ligand, and these complexes had anomalously high relaxivities compared to similar complexes lacking a H-bond acceptor. Molecular dynamics simulations supported the formation of a stable intramolecular H-bond, while alternative hypotheses that could explain the higher relaxivity were systematically ruled out. Intramolecular H-bonding represents a useful strategy to limit internal water rotational motion and increase relaxivity of Gd complexes.

Meios de Contraste/química , Complexos de Coordenação/química , Gadolínio/química , Meios de Contraste/síntese química , Complexos de Coordenação/síntese química , Ligação de Hidrogênio , Ligantes , Modelos Moleculares , Conformação Molecular , Água/química
J Phys Condens Matter ; 27(37): 373002, 2015 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-26325114


In both research and industry, materials will be exposed to stresses, be it during fabrication, normal use, or mechanical failure. The response to external stress will have an important impact on properties, especially when atomic details govern the functionalities of the materials. This review aims at summarizing current research involving the responses of graphene and graphene materials to applied stress at the nanoscale, and to categorize them by stress-strain behavior. In particular, we consider the reversible functionalization of graphene and graphene materials by way of elastic deformation and strain engineering, the plastic deformation of graphene oxide and the emergence of such in normally brittle graphene, the formation of defects as a response to stress under high temperature annealing or irradiation conditions, and the properties that affect how, and mechanisms by which, pristine, defective, and polycrystalline graphene fail catastrophically during fracture. Overall we find that there is significant potential for the use of existing knowledge, especially that of strain engineering, as well as potential for additional research into the fracture mechanics of polycrystalline graphene and device functionalization by way of controllable plastic deformation of graphene.

Elasticidade , Grafite/química , Plásticos/química , Elétrons , Nanotecnologia , Estresse Mecânico
Nanotechnology ; 26(7): 075704, 2015 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-25627961


The knowledge on the influence of surface roughness and the electron-phonon (el-ph) interaction on electrical transport properties of nanoscale metal films is important from both fundamental and technological points of view. Here we report a study of the temperature dependent electron transport properties of nanoscale copper films by measuring temperature dependent electrical resistivity with thickness ranging from 4 to 500 nm. We show that the residual resistivity, which is temperature independent, can be described quantitatively using both measured vertical surface root-mean-square roughness and lateral correlation length in the nanoscale, with no adjustable parameter, by a recent quasi-classical model developed by Chatterjee and Meyerovich (2010 Phys. Rev. B 81 245409-10). We also demonstrate that the temperature dependent component of the resistivity can be described using the Bloch-Grüneisen equation with a thickness dependent el-ph coupling constant and a thickness dependent Debye temperature. We show that the increase of the el-ph coupling constant with the decrease of film thickness gives rise to an enhancement of the temperature dependent component of the resistivity.

J Chem Phys ; 136(13): 134507, 2012 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-22482572


We present an approach for calculating nonlinear spectroscopic observables, which overcomes the approximations inherent to current phenomenological models without requiring the computational cost of performing molecular dynamics simulations. The trajectory mapping method uses the semi-classical approximation to linear and nonlinear response functions, and calculates spectra from trajectories of the system's transition frequencies and transition dipole moments. It rests on identifying dynamical variables important to the problem, treating the dynamics of these variables stochastically, and then generating correlated trajectories of spectroscopic quantities by mapping from the dynamical variables. This approach allows one to describe non-Gaussian dynamics, correlated dynamics between variables of the system, and nonlinear relationships between spectroscopic variables of the system and the bath such as non-Condon effects. We illustrate the approach by applying it to three examples that are often not adequately treated by existing analytical models--the non-Condon effect in the nonlinear infrared spectra of water, non-Gaussian dynamics inherent to strongly hydrogen bonded systems, and chemical exchange processes in barrier crossing reactions. The methods described are generally applicable to nonlinear spectroscopy throughout the optical, infrared and terahertz regions.