4 research outputs found
Molecular Dynamics Simulation of Supercoiled DNA Rings
DNA supercoiling is a widespread
phenomenon in biology. Here we
introduce a coarse-grained DNA model and study supercoiled DNA rings
via a rigid body molecular dynamics simulation. Our model allows us
to investigate these structures in more detail than previously. The
simulations are performed on rings of one to six kilobase pairs length
and are compared to available experimental data and former simulation
studies. The current study provides new additional information about
some of the geometrical parameters of the supercoiled DNA rings. It
also shows how enforcing a supercoiled DNA ring to two-dimensional
space changes its geometrical parameters. Finally, our molecular dynamics
method allows us to observe some dynamical effects like the creation
and movement of supercoiled branches
Variation of Protein Corona Composition of Gold Nanoparticles Following Plasmonic Heating
It
is well recognized that the primary interaction of most biological
environments with nanoparticles (NPs) is strongly influenced by a
long-lived (“hard”) protein corona that surrounds the
NP and remains strongly adsorbed to its surface. The amount and composition
of associated proteins in the corona adsorbed onto the NPs is related
to several important factors, including the physicochemical properties
of the NPs and the composition of the protein solution. Here, for
the first time, it is shown that plasmonic heat induction (by laser
activation) leads to significant changes in the composition of the
hard protein corona adsorbed on low aspect ratio gold nanorods. Using
mass spectrometry, several proteins in the corona were identified
whose concentrations change most substantially as a result of photoinduced
(plasmonic) heating versus simple thermal heating. Molecular modeling
suggests that the origin of these changes in protein adsorption may
be the result of protein conformational changes in response to much
higher local temperatures that occur near the gold nanorods during
photoinduced, plasmonic heating. These results may define new applications
in vivo for NPs with hyperthermia capability and better define the
likely interactions of cells with NPs after plasmonic heating. Potential
changes in the protein corona following hyperthermia treatment may
influence the final biological fate of plasmonic NPs in clinical applications
and help elucidate safety considerations for hyperthermia applications
Bimodal Phonon Scattering in Graphene Grain Boundaries
Graphene has served as the model
2D system for over a decade, and the effects of grain boundaries (GBs)
on its electrical and mechanical properties are very well investigated.
However, no direct measurement of the correlation between thermal
transport and graphene GBs has been reported. Here, we report a simultaneous
comparison of thermal transport in supported single crystalline graphene
to thermal transport across an individual graphene GB. Our experiments
show that thermal conductance (per unit area) through an isolated
GB can be up to an order of magnitude lower than the theoretically
anticipated values. Our measurements are supported by Boltzmann transport
modeling which uncovers a new bimodal phonon scattering phenomenon
initiated by the GB structure. In this novel scattering mechanism,
boundary roughness scattering dominates the phonon transport in low-mismatch
GBs, while for higher mismatch angles there is an additional resistance
caused by the formation of a disordered region at the GB. Nonequilibrium
molecular dynamics simulations verify that the amount of disorder
in the GB region is the determining factor in impeding thermal transport
across GBs
Modeling and Analysis of Intercalant Effects on Circular DNA Conformation
The
large-scale conformation of DNA molecules plays a critical role in
many basic elements of cellular functionality and viability. By targeting
the structural properties of DNA, many cancer drugs, such as anthracyclines,
effectively inhibit tumor growth but can also produce dangerous side
effects. To enhance the development of innovative medications, rapid
screening of structural changes to DNA can provide important insight
into their mechanism of interaction. In this study, we report changes
to circular DNA conformation from intercalation with ethidium bromide
using all-atom molecular dynamics simulations and characterized experimentally
by translocation through a silicon nitride solid-state nanopore. Our
measurements reveal three distinct current blockade levels and a 6-fold
increase in translocation times for ethidium bromide-treated circular
DNA as compared to untreated circular DNA. We attribute these increases
to changes in the supercoiled configuration hypothesized to be branched
or looped structures formed in the circular DNA molecule. Further
evidence of the conformational changes is demonstrated by qualitative
atomic force microscopy analysis. These results expand the current
methodology for predicting and characterizing DNA tertiary structure
and advance nanopore technology as a platform for deciphering structural
changes of other important biomolecules