5 research outputs found
Choice of Optimal Shift Parameter for the Intruder State Removal Techniques in Multireference Perturbation Theory
An extensive critical evaluation of intruder state removal
techniques
(aka shift techniques) applicable to multireference perturbation theory
(MRPT) shows that the magnitude of the shift parameter σ does
not influence the spectroscopic parameters of diatomics to a significant
degree, provided that the shift is chosen to be sufficiently large.
In such case, typical variation of spectroscopic parameters over a
wide range of shift parameters is smaller than 0.005 Ã… for equilibrium
distances, 30 cm<sup>–1</sup> for harmonic vibrational frequencies,
and 0.1 eV for dissociation energies. It is found that large values
of σ not only remove intruder states but they also bring the
MRPT energies and properties closer to experimental values. The presented
analysis allows us to determine optimal values of the shift parameters
to be used in conjunction with various versions of MRPT; these values
are recommended to replace the <i>ad hoc</i> values of σ
suggested in MRPT manuals in calculations for diatomics. Transferability
of the optimal shift parameters to larger molecular systems and to
other basis sets than aug-cc-pVTZ is anticipated but remains to be
formally established
Structural Insights into the Glycine Pair Motifs in Type III Collagen
Human type III collagen has been
suggested to play vital roles
in a series of pathophysiological conditions. Sequence analysis among
major fibril-forming collagens (types I, II, and III) revealed that
Gly-Gly pairs are a distinct sequence feature in type III collagen.
This motif occurs more than five times as often in type III compared
to type I and II collagens. We used an integrated computational modeling
and biophysical approach to analyze the glycine pair motifs to understand
how they govern the structure of type III collagen at the molecular
level. Triple helical peptides to model the regions of type III collagen
containing GG motifs were used to analyze structural and thermodynamic
effects of GG incorporation into the collagen sequence. We found that
when amino acids adjacent to a GG motif are charged, the collagen
adopts a more flexible, random conformation. The GG motif led to altered
hydrogen bond patterns and decreased global melting temperatures of
the triple helical peptides. The local entropic destabilization effect
of the glycine pair helps explain the difference in the flexibility
between types I and III collagen fibrils. This finding reveals potential
physiological roles of type III collagen in regulating the mechanical
properties of collagen fibrils and may enable the design of future
collagen-like materials with tunable mechanical properties
Carnosic Acid Prevents 6‑Hydroxydopamine-Induced Cell Death in SH-SY5Y Cells via Mediation of Glutathione Synthesis
Understanding the neuroprotective effects of the rosemary
phenolic
diterpene carnosic acid (CA) has attracted increasing attention. We
explored the mechanism by which CA modulates the neurotoxic effects
of 6-hydroxydopamine (6-OHDA) in SH-SY5Y cells. Cells were pretreated
with CA for 12 h followed by treatment with 100 μM 6-OHDA for
12 or 24 h. Cell viability determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolim
bromide (MTT) assay indicated that 0.1 to 1 μM CA dose-dependently
attenuated the cell death induced by 6-OHDA, whereas the effect of
3–5 μM CA was weaker. CA at 1 μM suppressed the
6-OHDA-induced nuclear condensation, reactive oxygen species generation,
and cleavage of caspase 3 and PARP. Immunoblots showed that the phosphorylation
of c-Jun NH<sub>2</sub>-terminal kinase (JNK) and p38 by 6-OHDA was
reduced in the presence of CA. Incubation of cells with CA resulted
in significant increases in the total glutathione (GSH) level and
the protein expression of the γ-glutamylcysteine ligase catalytic
subunit and modifier subunit. l-Buthionine-sulfoximine, an
inhibitor of GSH synthesis, attenuated the effect of CA on cell death
and apoptosis. Treatment with CA also led to an increase in nuclear
factor erythroid-2 related factor 2 (Nrf2) activation, antioxidant
response element (ARE)-luciferase reporter activity, and DNA binding
to the ARE. Silencing of Nrf2 expression alleviated the reversal of
p38 and JNK1/2 activation by CA. These results suggest that the attenuation
of 6-OHDA-induced apoptosis by CA is associated with the Nrf2-driven
synthesis of GSH, which in turn down-regulates the JNK and p38 signaling
pathways. The CA compound may be a promising candidate for neuroprotection
in Parkinson’s disease
Circular Dichroism Control of Tungsten Diselenide (WSe<sub>2</sub>) Atomic Layers with Plasmonic Metamolecules
Controlling
circularly polarized (CP) states of light is critical to the development
of functional devices for key and emerging applications such as display
technology and quantum communication, and the compact circular polarization-tunable
photon source is one critical element to realize the applications
in the chip-scale integrated system. The atomic layers of transition
metal dichalcogenides (TMDCs) exhibit intrinsic CP emissions and are
potential chiroptical materials for ultrathin CP photon sources. In
this work, we demonstrated CP photon sources of TMDCs with device
thicknesses approximately 50 nm. CP photoluminescence from the atomic
layers of tungsten diselenide (WSe<sub>2</sub>) was precisely controlled
with chiral metamolecules (MMs), and the optical chirality of WSe<sub>2</sub> was enhanced more than 4 times by integrating with the MMs.
Both the enhanced and reversed circular dichroisms had been achieved.
Through integrations of the novel gain material and plasmonic structure
which are both low-dimensional, a compact device capable of efficiently
manipulating emissions of CP photon was realized. These ultrathin
devices are suitable for important applications such as the optical
information technology and chip-scale biosensing
Plasmonic Carbon-Dot-Decorated Nanostructured Semiconductors for Efficient and Tunable Random Laser Action
Carbon
dots have emerged as popular materials in various research fields,
including biological and photovoltaic areas, while significant reports
are lacking related to their applications in laser devices, which
play a significant role in our daily life. In this work, we demonstrate
the first controllable random laser assisted by the surface plasmon
effect of carbon dots. Briefly, carbon dots derived from candle soot
are randomly deposited on the surface of gallium nitride (GaN) nanorods
to enhance the ultraviolet fluorescence of GaN and generate plasmonically
enhanced random laser action with coherent feedback. Furthermore,
potentially useful functionalities of tunable lasing threshold and
controllable optical modes are achieved by adjusting the numbers of
carbon dots, enabling applications in optical communication and identification
technologies. In addition to providing an efficient alternative for
plasmonically enhanced random laser devices with simple fabrication
and low cost, our work also paves a useful route for the application
of environmentally friendly carbon dots in optoelectronic devices