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"Molecular Structure"
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Atomic and molecular structure
Learn about the atom, what it is, the people responsible for helping us understand it, and how it affects us in the world today.
Book
Boosting triplet self-trapped exciton emission in Te(IV)-doped Cs2SnCl6 perovskite variants
Perovskite variants have attracted wide interest because of the lead-free nature and strong self-trapped exciton (STE) emission. Divalent Sn(II) in CsSnX
3
perovskites is easily oxidized to tetravalent Sn(IV), and the resulted Cs
2
SnCl
6
vacancy-ordered perovskite variant exhibits poor photoluminescence property although it has a direct band gap. Controllable doping is an effective strategy to regulate the optical properties of Cs
2
SnX
6
. Herein, combining the first principles calculation and spectral analysis, we attempted to understand the luminescence mechanism of Te
4+
-doped Cs
2
SnCl
6
lead-free perovskite variants. The chemical potential and defect formation energy are calculated to confirm theoretically the feasible substitutability of tetravalent Te
4+
ions in Cs
2
SnCl
6
lattices for the Sn-site. Through analysis of the absorption, emission/excitation, and time-resolved photoluminescence (PL) spectroscopy, the intense green-yellow emission in Te
4+
:Cs
2
SnCl
6
was considered to originate from the triplet Te(IV) ion
3
P
1
→
1
S
0
STE recombination. Temperature-dependent PL spectra demonstrated the strong electron-phonon coupling that inducing an evident lattice distortion to produce STEs. We further calculated the electronic band structure and molecular orbital levels to reveal the underlying photophysical process. These results will shed light on the doping modulated luminescence properties in stable lead-free Cs
2
MX
6
vacancy-ordered perovskite variants and be helpful to understand the optical properties and physical processes of doped perovskite variants.
Journal Article
Molecular Asymmetry and Optical Cycling: Laser Cooling Asymmetric Top Molecules
We present a practical roadmap to achieve optical cycling and laser cooling of asymmetric top molecules (ATMs). Our theoretical analysis describes how reduced molecular symmetry, as compared to diatomic and symmetric nonlinear molecules, plays a role in photon scattering. We present methods to circumvent limitations on rapid photon cycling in these systems. We calculate vibrational branching ratios for a diverse set of asymmetric top molecules and find that many species within a broad class of molecules can be effectively cooled with a manageable number of lasers. We also describe methods to achieve rotationally closed optical cycles in ATMs. Despite significant structural complexity, laser cooling can be made effective by using extensions of the current techniques for linear molecules. Potential scientific impacts of laser-cooled ATMs span frontiers in controlled chemistry, quantum simulation, and searches for physics beyond the Standard Model.
Journal Article
Molecules
\"Molecules may be minuscule, but life wouldn't exist without them! This approachable look at an important chemistry topic takes young scientists on a tour of the world at the atomic level. They'll learn how atoms combine to form molecules and about some familiar and vital molecules, such as carbon dioxide. Thought-provoking fact boxes offer even more interesting information, while useful diagrams help learners visualize the amazing processes of nature\"-- Provided by publisher.
Book
Crystal Structure of a Lipid G Protein—Coupled Receptor
The lyso-phospholipid sphingosine 1-phosphate modulates lymphocyte trafficking, endothelial development and integrity, heart rate, and vascular tone and maturation by activating G protein—coupled sphingosine 1-phosphate receptors. Here, we present the crystal structure of the sphingosine 1-phosphate receptor 1 fused to T4-lysozyme (S1P₁-T4L) in complex with an antagonist sphingolipid mimic. Extracellular access to the binding pocket is occluded by the amino terminus and extracellular loops of the receptor. Access is gained by ligands entering laterally between helices I and VII within the transmembrane region of the receptor. This structure, along with mutagenesis, agonist structure-activity relationship data, and modeling, provides a detailed view of the molecular recognition and requirement for hydrophobic volume that activates S1P₁, resulting in the modulation of immune and stremal cell responses.
Journal Article
Evidence for Interstitial Carbon in Nitrogenase FeMo Cofactor
The identity of the interstitial light atom in the center of the FeMo cofactor of nitrogenase has been enigmatic since its discovery. Atomic-resolution x-ray diffraction data and an electron spin echo envelope modulation (ESEEM) analysis now provide direct evidence that the ligand is a carbon species.
Journal Article
Structural Basis for Allosteric Regulation of GPCRs by Sodium Ions
Pharmacological responses of G protein-coupled receptors (GPCRs) can be fine-tuned by allosteric modulators. Structural studies of such effects have been limited due to the medium resolution of GPCR structures. We reengineered the human A 2A adenosine receptor by replacing its third intracellular loop with apocytochrome b⁵⁶² RIL and solved the structure at 1.8 angstrom resolution. The high-resolution structure allowed us to identify 57 ordered water molecules inside the receptor comprising three major clusters. The central cluster harbors a putative sodium ion bound to the highly conserved aspartate residue Asp 2.50 . Additionally, two cholesterols stabilize the conformation of helix VI, and one of 23 ordered lipids intercalates inside the ligand-binding pocket. These high-resolution details shed light on the potential role of structured water molecules, sodium ions, and lipids/cholesterol in GPCR stabilization and function.
Journal Article