4 research outputs found
Modeling Copper Binding to the Amyloid‑β Peptide at Different pH: Toward a Molecular Mechanism for Cu Reduction
Oxidative stress, including the production of reactive
oxygen species
(ROS), has been reported to be a key event in the etiology of Alzheimer’s
disease (AD). Cu has been found in high concentrations in amyloid
plaques, a hallmark of AD, where it is bound to the main constituent
amyloid-β (Aβ) peptide. Whereas it has been proposed that
Cu-Aβ complexes catalyze the production of ROS via redox-cycling
between the CuÂ(I) and CuÂ(II) state, the redox chemistry of Cu-Aβ
and the precise mechanism of redox reactions are still unclear. Because
experiments indicate different coordination environments for CuÂ(II)
and CuÂ(I), it is expected that the electron is not transferred between
Cu-Aβ and reactants in a straightforward manner but involves
structural rearrangement. In this work the structures indicated by
experimental data are modeled at the level of modern density-functional
theory approximations. Possible pathways for CuÂ(II) reduction in different
coordination sites are investigated by means of first-principles molecular
dynamics simulations in the water solvent and at room temperature.
The models of the ligand reorganization around Cu allow the proposal
of a preferential mechanism for Cu-Aβ complex reduction at physiological
pH. Models reveal that for efficient reduction the deprotonated amide
N in the Ala 2-Glu 3 peptide bond has to be protonated and that interactions
in the second coordination sphere make important contributions to
the reductive pathway, in particular the interaction between COO<sup>–</sup> and NH<sub>2</sub> groups of Asp 1. The proposed mechanism
is an important step forward to a clear understanding of the redox
chemistry of Cu-Aβ, a difficult task for spectroscopic approaches
as the Cu-peptide interactions are weak and dynamical in nature
Tailoring Bimetallic Alloy Surface Properties by Kinetic Control of Self-Diffusion Processes at the Nanoscale
Achieving control of the nanoscale structure of binary
alloys is
of paramount importance for the design of novel materials with specific
properties, leading to, for example, improved reaction rates and selectivity
in catalysis, tailored magnetic behavior in electronics, and controlled
growth of nanostructured materials such as graphene. By means of a
combined experimental and theoretical approach, we show that the complex
self-diffusion mechanisms determining these key properties can be
mostly defined by kinetic rather than energetic effects. We explain
how in the Ni–Cu system nanoscale control of self-diffusion
and segregation processes close to the surface can be achieved by
finely tuning the relative concentration of the alloy constituents.
This allows tailoring the material functionality and provides a clear
explanation of previously observed effects involved, for example,
in the growth of graphene films and in the catalytic reduction of
carbon dioxide
Steering the Chemistry of Carbon Oxides on a NiCu Catalyst
In the perspective of a sustainable
energy economy, CO<sub>2</sub> reduction is attracting increasing
attention as a key step toward the synthesis of fuels and valuable
chemicals. A possible strategy to develop novel conversion catalysts
consists in mimicking reaction centers available in nature, such as
those in enzymes in which Fe, Ni, and Cu play a major role as active
metals. In this respect, NiCu shows peculiar activity for both water-gas
shift and methanol synthesis reactions. The identification of useful
descriptors to engineer and tune the reactivity of a surface in the
desired way is one of the main objectives of the science of catalysis,
with evident applicative interest, as in this case. To this purpose,
a crucial issue is the determination of the relevant active sites
and rate-limiting steps. We show here that this approach can be exploited
to design and tailor the catalytic activity and selectivity of a NiCu
surface
Chemistry of the Methylamine Termination at a Gold Surface: From Autorecognition to Condensation
13The self-assembly of the naphthylmethylamine molecules (NMA) on the Au(111) surface is investigated by a combined experimental and theoretical approach. Three well-defined phases are observed upon different thermal treatments at the monolayer stage. The role played by the methylamine termination is evidenced in both the molecule–molecule and molecule–substrate interactions. The autorecognition process of the amino groups is identified as the driving factor for the formation of a complex hydrogen bonding scheme in small molecular clusters, possibly acting also as a precursor of a denitrogenation condensation process induced by thermal annealing.reservedmixedDri, Carlo; Fronzoni, Giovanna; Balducci, Gabriele; Furlan, Sara; Stener, Mauro; Feng, Zhijing; Comelli, Giovanni; Castellarin-Cudia, Carla; Cvetko, Dean; Kladnik, Gregor; Verdini, Alberto; Floreano, Luca; Cossaro, AlbanoDri, Carlo; Fronzoni, Giovanna; Balducci, Gabriele; Furlan, Sara; Stener, Mauro; Feng, Zhijing; Comelli, Giovanni; Castellarin Cudia, Carla; Cvetko, Dean; Kladnik, Gregor; Verdini, Alberto; Floreano, Luca; Cossaro, Alban