We developed a ReaxFF force field
for Fe/Cr/O/S, which is parametrized
against data from quantum mechanical (QM) calculations. Using this
force field, we studied the Cr-oxide catalyzed oxidation reaction
of butane at 1600 K. Our simulation results demonstrate that the active
oxygen species on the oxide surface play an important role in the
conversion of butane. Dehydrogenation of butane, which is found to
be catalyzed by oxygen species on the oxide surface, initiates the
reaction and generates butane radicals and surface OH groups. The
radical intermediates are associated with the oxygen atoms to form
C–O bonds or make double bonds when neighboring carbon atoms
are dehydrogenated, forming light alkenes. On the clean Cr-oxide,
the major oxidation product is CH2O. The presence of iron
pyrite (FeS2), a common inorganic component in coal-derived
fuels and a major slagging component, on Cr-oxide accelerates the
complete oxidation of butane forming CO2 and CO. Surface
reconstruction by iron pyrite is probably responsible for the change
of the catalytic behavior. Reoxidation of the reduced oxide surface
can occur through removal of surface H2O and adsorption
of gaseous molecular oxygen at the vacancy sites on the clean Cr-oxide.
On the other hand, on the modified Cr-oxide, it is found that a considerable
amount of SOH molecules are released from the surface. These results
can provide the detailed mechanisms for the catalytic oxidation of
alkane and product distributions in Cr-oxide catalyst and give, for
the first time, atomistic-scale insight in the complex surface chemistry
of these catalysts under realistic operating conditions.
The Raman spectra of Si nanocrystals are studied as a function of nanocrystal diameter using pseudopotential density functional theory and the Placzek approximation. Our calculations reproduce the redshift and broadening of the optical Raman peak with decreasing nanocrystal size, and calculated peak frequencies show good agreement with experimental values. We also find that a surface induced softening of vibrational modes is largely responsible for the Raman redshift, with relaxation of momentum conservation playing only a minor role.
Materials exhibiting
higher mobilities than conventional organic
semiconducting materials such as fullerenes and fused thiophenes are
in high demand for applications in printed electronics. To discover
new molecules in the heteroacene family that might show improved charge
mobility, a massive theoretical screen of hole conducting properties
of molecules was performed by using a cloud-computing environment.
Over 7 000 000 structures of fused furans, thiophenes
and selenophenes were generated and 250 000 structures were
randomly selected to perform density functional theory (DFT) calculations
of hole reorganization energies. The lowest hole reorganization energy
calculated was 0.0548 eV for a fused thioacene having 8 aromatics
rings. Hole mobilities of compounds with the lowest 130 reorganization
energy were further processed by applying combined DFT and molecular
dynamics (MD) methods. The highest mobility calculated was 1.02 and
9.65 cm2/(V s) based on percolation and disorder theory,
respectively, for compounds containing selenium atoms with 8 aromatic
rings. These values are about 20 times higher than those for dinaphthothienothiophene
(DNTT).
An astute modification of the plectin-1-targeting peptide KTLLPTP by introducing a C-terminal cysteine preceded by a tyrosine residue imparted a reducing property to the peptide. This novel property is then exploited to fabricate gold nanoparticles (GNP) via an in situ reduction of gold (III) chloride in a one-pot, green synthesis. The modified peptide KTLLPTPYC also acts as a template to generate highly monodispersed, spherical GNPs with a narrow size distribution and improved stability. Plectin-1 is known to be aberrantly expressed in the surface of pancreatic ductal adenocarcinoma (PDAC) cells while showing cytoplasmic expression in normal cells. The synthesized GNPs are thus in situ surface modified with the peptides via the cysteine residue leaving the N-terminal KTLLPTP sequence free for targeting plectin 1. The visual molecular dynamics based simulations support the experimental observations like particle size, gemcitabine conjugation and architecture of the peptide-grafted nanoassembly. Additionally, GNPs conjugated to gemcitabine demonstrate significantly higher cytotoxicity in vitro in two established PDAC cell lines (AsPC-1 and PANC-1) and an admirable in vivo antitumor efficacy in a PANC-1 orthotopic xenograft model through selective uptake in PDAC tumor tissues. Altogether, this strategy represents a unique method for the fabrication of a GNP based targeted drug delivery platform using a multifaceted peptide that acts as reducing agent, template for GNP synthesis and targeting agent to display remarkable selectivity towards PDAC.
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