6 research outputs found
Landing Proteins on Graphene Trampoline Preserves Their Gas-Phase Folding on the Surface
Molecule–surface
collisions are known to initiate dynamics
that lead to products inaccessible by thermal chemistry. These collision
dynamics, however, have mostly been examined on bulk surfaces, leaving
vast opportunities unexplored for molecular collisions on nanostructures,
especially on those that exhibit mechanical properties radically different
from those of their bulk counterparts. Probing energy-dependent dynamics
on nanostructures, particularly for large molecules, has been challenging
due to their fast time scales and high structural complexity. Here,
by examining the dynamics of a protein impinging on a freestanding,
single-atom-thick membrane, we discover molecule-on-trampoline dynamics that disperse the collision impact away from the incident
protein within a few picoseconds. As a result, our experiments and ab initio calculations show that cytochrome c retains its
gas-phase folded structure when it collides onto freestanding single-layer
graphene at low energies (∼20 meV/atom). The molecule-on-trampoline dynamics, expected to be operative on many freestanding atomic membranes,
enable reliable means to transfer gas-phase macromolecular structures
onto freestanding surfaces for their single-molecule imaging, complementing
many bioanalytical techniques
Landing Proteins on Graphene Trampoline Preserves Their Gas-Phase Folding on the Surface
Molecule–surface
collisions are known to initiate dynamics
that lead to products inaccessible by thermal chemistry. These collision
dynamics, however, have mostly been examined on bulk surfaces, leaving
vast opportunities unexplored for molecular collisions on nanostructures,
especially on those that exhibit mechanical properties radically different
from those of their bulk counterparts. Probing energy-dependent dynamics
on nanostructures, particularly for large molecules, has been challenging
due to their fast time scales and high structural complexity. Here,
by examining the dynamics of a protein impinging on a freestanding,
single-atom-thick membrane, we discover molecule-on-trampoline dynamics that disperse the collision impact away from the incident
protein within a few picoseconds. As a result, our experiments and ab initio calculations show that cytochrome c retains its
gas-phase folded structure when it collides onto freestanding single-layer
graphene at low energies (∼20 meV/atom). The molecule-on-trampoline dynamics, expected to be operative on many freestanding atomic membranes,
enable reliable means to transfer gas-phase macromolecular structures
onto freestanding surfaces for their single-molecule imaging, complementing
many bioanalytical techniques
Active Conformation Control of Unfolded Proteins by Hyperthermal Collision with a Metal Surface
The
physical and chemical properties of macromolecules like proteins
are strongly dependent on their conformation. The degrees of freedom
of their chemical bonds generate a huge conformational space, of which,
however, only a small fraction is accessible in thermal equilibrium.
Here we show that soft-landing electrospray ion beam deposition (ES-IBD)
of unfolded proteins allows to control their conformation. The dynamics
and result of the deposition process can be actively steered by selecting
the molecular ion beam’s charge state or tuning the incident
energy. Using these parameters, protein conformations ranging from
fully extended to completely compact can be prepared selectively on
a surface, as evidenced on the subnanometer/amino acid resolution
level by scanning tunneling microscopy (STM). Supported by molecular
dynamics (MD) simulations, our results demonstrate that the final
conformation on the surface is reached through a mechanical deformation
during the hyperthermal ion surface collision. Our experimental results
independently confirm the findings of ion mobility spectrometry (IMS)
studies of protein gas phase conformations. Moreover, we establish
a new route for the processing of macromolecular materials, with the
potential to reach conformations that would be inaccessible otherwise
Chemical Modification of Graphene via Hyperthermal Molecular Reaction
Chemical
functionalization of graphene is achieved by hyperthermal
reaction with azopyridine molecular ions. The one-step, room temperature
process takes place in high vacuum (10<sup>–7</sup> mbar) using
an electrospray ion beam deposition (ES-IBD) setup. For ion surface
collisions exceeding a threshold kinetic energy of 165 eV, molecular
cation beams of 4,4′-azobisÂ(pyridine) covalently attach to
chemical vapor deposited (CVD) graphene. A covalent functionalization
degree of 3% of the carbon atoms of graphene is reached after 3–5
h of ion exposure of 2 × 10<sup>14</sup> azopyridinium/cm<sup>2</sup> of which 50% bind covalently. This facile approach for the
controlled modification of graphene extends the scope of candidate
species that would not otherwise react via existing conventional methods
A Close Look at Proteins: Submolecular Resolution of Two- and Three-Dimensionally Folded Cytochrome c at Surfaces
Imaging of individual protein molecules at the single
amino acid
level has so far not been possible due to the incompatibility of proteins
with the vacuum environment necessary for high-resolution scanning
probe microscopy. Here we demonstrate electrospray ion beam deposition
of selectively folded and unfolded cytochrome c protein ions on atomically
defined solid surfaces in ultrahigh vacuum (10<sup>–10</sup> mbar) and achieve unprecedented resolution with scanning tunneling
microscopy. On the surface folded proteins are found to retain their
three-dimensional structure. Unfolded proteins are observed as extended
polymer strands displaying submolecular features with resolution at
the amino acid level. On weakly interacting surfaces, unfolded proteins
refold into flat, irregular patches composed of individual molecules.
This suggests the possibility of two-dimensionally confined folding
of peptides of an appropriate sequence into regular two-dimensional
structures as a new approach toward functional molecular surface coatings
The Quantum Magnetism of Individual Manganese-12-Acetate Molecular Magnets Anchored at Surfaces
The high intrinsic spin and long spin relaxation time
of manganese-12-acetate (Mn<sub>12</sub>) makes it an archetypical
single molecular magnet. While these characteristics have been measured
on bulk samples, questions remain whether the magnetic properties
replicate themselves in surface supported isolated molecules, a prerequisite
for any application. Here we demonstrate that electrospray ion beam
deposition facilitates grafting of intact Mn<sub>12</sub> molecules
on metal as well as ultrathin insulating surfaces enabling submolecular
resolution imaging by scanning tunneling microscopy. Using scanning
tunneling spectroscopy we detect spin excitations from the magnetic
ground state of the molecule at an ultrathin boron nitride decoupling
layer. Our results are supported by density functional theory based
calculations and establish that individual Mn<sub>12</sub> molecules
retain their intrinsic spin on a well chosen solid support