2 research outputs found
Computational and Experimental Investigation of the Structure of Peptide Monolayers on Gold Nanoparticles
The
self-assembly and self-organization of small molecules on the
surface of nanoparticles constitute a potential route toward the preparation
of advanced proteinlike nanosystems. However, their structural characterization,
critical to the design of bionanomaterials with well-defined biophysical
and biochemical properties, remains highly challenging. Here, a computational
model for peptide-capped gold nanoparticles (GNPs) is developed using
experimentally characterized Cys-Ala-Leu-Asn-Asn (CALNN)- and Cys-Phe-Gly-Ala-Ile-Leu-Ser-Ser
(CFGAILSS)-capped GNPs as a benchmark. The structure of CALNN and
CFGAILSS monolayers is investigated using both structural biology
techniques and molecular dynamics simulations. The calculations reproduce
the experimentally observed dependence of the monolayer secondary
structure on the peptide capping density and on the nanoparticle size,
thus giving us confidence in the model. Furthermore, the computational
results reveal a number of new features of peptide-capped monolayers,
including the importance of sulfur movement for the formation of secondary
structure motifs, the presence of water close to the gold surface
even in tightly packed peptide monolayers, and the existence of extended
2D parallel β-sheet domains in CFGAILSS monolayers. The model
developed here provides a predictive tool that may assist in the design
of further bionanomaterials
Effect of Base Oil Polarity on the Functional Mechanism of a Viscosity Modifier: Unraveling the Conundrum of Coil Expansion Model
Viscosity
improvement property of a lubricant additive
is commonly
attributed to polymer coil expansion with increasing temperature,
although only some polymer chemistries show conformance to this conceptual
mechanism. Herein, we show that the polarity of base oil governs whether
this mechanism underlies the action of a viscosity modifier (VM) by
combining experimental and computational studies. Poly(butyl methacrylate)
(PBMA) dissolved in diethylene glycol diethyl ether (DGDE) or a mixture
of DGDE (polar solvent) and squalane (SQ, nonpolar solvent) was used
as a model lubricant oil system. Specific viscosity of the polymer
solutions measured over a wide range of additive concentrations and
temperatures revealed that thickening efficiency of the VM decreased
with decreasing base oil polarity. While the VM counteracted temperature-induced
thinning of the low polarity base oil, in the polar solvent, the polymer
did not enhance the solution viscosity at higher temperatures. Aiming
to unravel the molecular mechanism underlying viscosity improvement
at elevated temperatures in the different solvent systems, the polymer
conformation and size in the dispersing oil were determined by combining
solution viscosity, small-angle X-ray scattering measurements, and
coarse-grained molecular dynamics simulations. Collectively, the experimental
and simulation results show that the coil-swelling model underpins
viscosity improvement of the polymer solution in DGDE, and the viscosity
of PBMA in DGDE/SQ solution increased with temperature due to polymer
association in solution. However, the thermoresponsive behavior of
the polymer is more pronounced in the mixed solvent system due to
their higher propensity to aggregate at elevated temperatures