36 research outputs found
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Photooxidative Generation of Dodecaborate-Based Weakly Coordinating Anions
Redox-active proanions of the type B_(12)(OCH_2Ar)_(12) [Ar = C_6F_5 (1), 4-CF_3C_6H_4 (2), 3,5-(CF_3)_2C_6H_3 (3)] are introduced in the context of an experimental and computational study of the visible-light-initiated polymerization of a family of styrenes. Neutral, air-stable proanions 1–3 were found to initiate styrene polymerization through single-electron oxidation under blue-light irradiation, resulting in polymers with number-average molecular weights (M_n) ranging from ∼6 to 100 kDa. Shorter polymer products were observed in the majority of experiments, except in the case of monomers containing 4-X (X = F, Cl, Br) substituents on the styrene monomer when polymerized in the presence of 1 in CH_2Cl_2. Only under these specific conditions are longer polymers (>100 kDa) observed, strongly supporting the formulation that reaction conditions significantly modulate the degree of ion pairing between the dodecaborate anion and cationic chain end. This also suggests that 1–3 behave as weakly coordinating anions (WCA) upon one-electron reduction because no incorporation of the cluster-based photoinitiators is observed in the polymeric products analyzed. Overall, this work is a conceptual realization of a single reagent that can serve as a strong photooxidant, subsequently forming a WCA
Coupling of SARS-CoV‑2 to Aβ Amyloid Fibrils
The COVID-19 infection
has been more problematic for individuals
with certain health predispositions. Coronaviruses could also interfere
with neural diseases if the viruses succeed in entering the brain.
Therefore, it might be of principal interest to examine a possible
coupling of coronaviruses and amyloid fibrils. Here, molecular dynamics
simulations were used to investigate direct coupling of SARS-CoV-2
and Aβ fibrils, which play a central role in neural diseases.
The simulations revealed several stable binding configurations and
their dynamics of Aβ42 fibrils attached to spike proteins of
the Omicron and Alpha variants of SARS-CoV-2
Enantioselective Molecular Transport in Multilayer Graphene Nanopores
Multilayer
superstructures based on stacked layered nanomaterials offer the possibility
to design three-dimensional (3D) nanopores with highly specific properties
analogous to protein channels. In a layer-by-layer design and stacking,
analogous to molecular printing, superstructures with lock-and-key
molecular nesting and transport characteristics could be prepared.
To examine this possibility, we use molecular dynamics simulations
to study electric field-driven transport of ions through stacked porous
graphene flakes. First, highly selective, tunable, and correlated
passage rates of monovalent atomic ions through these superstructures
are observed in dependence on the ion type, nanopore type, and relative
position and dynamics of neighboring porous flakes. Next, enantioselective
molecular transport of ionized l- and d-leucine
is observed in graphene stacks with helical nanopores. The outlined
approach provides a general scheme for synthesis of functional 3D
superstructures
Control Mechanisms of Photoisomerization in Protonated Schiff Bases
We
performed ab initio excited-state molecular dynamics simulations
of a gas-phase photoexcited protonated Schiff base (C<sub>1</sub>–N<sub>2</sub>C<sub>3</sub>–C<sub>4</sub>C<sub>5</sub>–C<sub>6</sub>) to search for control mechanisms of its photoisomerization.
The excited molecule twists by ∼90° around either the
N<sub>2</sub>C<sub>3</sub> bond or the C<sub>4</sub>C<sub>5</sub> bond
and relaxes to the ground electronic state through a conical intersection
with either a trans or cis outcome. We show that a large initial distortion
of several dihedral angles and a specific normal vibrational mode
combining pyramidalization and double-bond twisting can lead to a
preferential rotation of atoms around the C<sub>4</sub>C<sub>5</sub> bond. We also show that selective pretwisting of several dihedral
angles in the initial ground state thermal ensemble (by analogy to
a protein pocket) can significantly increase the fraction of photoreactive
(cis → trans) trajectories. We demonstrate that new ensembles
with higher degrees of control over the photoisomerization reaction
can be obtained by a computational directed evolution approach on
the ensembles of molecules with the pretwisted geometries
Control Mechanisms of Photoisomerization in Protonated Schiff Bases
We
performed ab initio excited-state molecular dynamics simulations
of a gas-phase photoexcited protonated Schiff base (C<sub>1</sub>–N<sub>2</sub>C<sub>3</sub>–C<sub>4</sub>C<sub>5</sub>–C<sub>6</sub>) to search for control mechanisms of its photoisomerization.
The excited molecule twists by ∼90° around either the
N<sub>2</sub>C<sub>3</sub> bond or the C<sub>4</sub>C<sub>5</sub> bond
and relaxes to the ground electronic state through a conical intersection
with either a trans or cis outcome. We show that a large initial distortion
of several dihedral angles and a specific normal vibrational mode
combining pyramidalization and double-bond twisting can lead to a
preferential rotation of atoms around the C<sub>4</sub>C<sub>5</sub> bond. We also show that selective pretwisting of several dihedral
angles in the initial ground state thermal ensemble (by analogy to
a protein pocket) can significantly increase the fraction of photoreactive
(cis → trans) trajectories. We demonstrate that new ensembles
with higher degrees of control over the photoisomerization reaction
can be obtained by a computational directed evolution approach on
the ensembles of molecules with the pretwisted geometries
Linker-Mediated Self-Assembly Dynamics of Charged Nanoparticles
Using <i>in situ</i> liquid
cell transmission electron
microscopy (TEM), we visualized a stepwise self-assembly of surfactant-coated
and hydrated gold nanoparticles (NPs) into linear chains or branched
networks. The NP binding is facilitated by linker molecules, ethylenediammonium,
which form hydrogen bonds with surfactant molecules of neighboring
NPs. The observed spacing between bound neighboring NPs, ∼15
Å, matches the combined length of two surfactants and one linker
molecule. Molecular dynamics simulations reveal that for lower concentrations
of linkers, NPs with charged surfactants cannot be fully neutralized
by strongly binding divalent linkers, so that NPs carry higher effective
charges and tend to form chains, due to poor screening. The highly
polar NP surfaces polarize and partly immobilize nearby water molecules,
which promotes NPs binding. The presented experimental and theoretical
approach allows for detail observation and explanation of self-assembly
processes in colloidal nanosystems
Linker-Mediated Self-Assembly Dynamics of Charged Nanoparticles
Using <i>in situ</i> liquid
cell transmission electron
microscopy (TEM), we visualized a stepwise self-assembly of surfactant-coated
and hydrated gold nanoparticles (NPs) into linear chains or branched
networks. The NP binding is facilitated by linker molecules, ethylenediammonium,
which form hydrogen bonds with surfactant molecules of neighboring
NPs. The observed spacing between bound neighboring NPs, ∼15
Å, matches the combined length of two surfactants and one linker
molecule. Molecular dynamics simulations reveal that for lower concentrations
of linkers, NPs with charged surfactants cannot be fully neutralized
by strongly binding divalent linkers, so that NPs carry higher effective
charges and tend to form chains, due to poor screening. The highly
polar NP surfaces polarize and partly immobilize nearby water molecules,
which promotes NPs binding. The presented experimental and theoretical
approach allows for detail observation and explanation of self-assembly
processes in colloidal nanosystems