Nature Communications - DFT calculations and theory do not support enantiospecificity in NMR J-coupling constants

Falcon Space is working to make the dream of advanced propulsion a reality through innovative experiments and UAP Reverse-Engineering.

It was recently reported that boron monoxide (BO) is formed through the cross-linking of B4O2 structural building units. Multiple theoretical phases agree with this description. Using pycnometry, mult...

Dynamic nuclear polarization surface-enhanced nuclear magnetic resonance (NMR) spectroscopy has enabled the determination of the three-dimensional configuration of surface sites, in particular supported metal complexes of relevance to single-site heterogeneous catalysis. These approaches have chiefly leveraged the application of NMR double-resonance experiments that either reveal the complex conformation via point-to-point intramolecular distances between spin-labeled atoms or the complex-surface orientation via distances between the spins and the surface plane. Either method typically requires expensive isotope labeling and each reports on different structural features. The application of an experiment that simultaneously reveals both types of distances with chemical resolution would be ideal. In this article, we describe an 17O{1H} pseudo-3D correlation experiment that achieves this goal. Specifically, Si–O–Si and Si–O–M oxygens are well-resolved by 17O NMR; therefore, distances can be simultaneously measured radially, between Si–17O–M and the 1H’s of the ligands, and vertically to the Si–17O–Si linkages of the silica support. We demonstrate the experiment using supported yttrium and zirconium complexes. Good agreement is obtained when comparing the experimental results to theoretical predictions from density functional theory calculations, highlighting the reliability of this relatively simple experiment.

Block copolymers of polyethylene (PE) and polyvinyl chloride (PVC) have remained elusive materials despite PE and PVC being the first and third most produced polymers globally, respectfully. The closest material is chlorinated polyethylene (CPE), which is commonly used as a compatibilizer and is synthesized by functionalizing PE. However, there does not exist a synthetic pathway either from monomers or via the functionalization of PE to yield a polymer that has a controlled chlorine amount and primary structure along the polymer chain. Herein, we report a series of novel block copolymers of PVC and PE, synthesized through selective hydrodechlorination of PVC. Contrary to CPE, the full range of chlorination can be obtained, and the block number can be altered. Interfacial adhesion studies reveal samples with competitive compatibilization of PVC/polyolefin elastomer (POE) blends. This method shows that postpolymerization modification can be a strategic top-down synthesis to achieve high-performance polymers that cannot be synthesized via conventional polymerization pathways.

Surface grafted organozirconium-catalyzes C–H/Et–Al exchange reactions, involving saturated hydrocarbons and AlEt3, to afford organoaluminum compounds and ethane. The Zr(OtBu)3@SiO2-Al2O3-700 (1) cat....

The rotation frequencies of amido ligands are highly sensitive to the electronic structure of d0 transition metal complexes and have been used to study ligand donor properties. While attempting to study the donor properties of silanolate ligands in a silica-supported Cr complex, we observed highly restricted motions due to the added steric hindrance from the support, with only approximately half of the amides rotating on a 50 ms time scale. Surprisingly, when the same species is grafted into narrow 2.2 nm pores, all amido ligands are able to rotate. Density functional theory calculations suggest that confinement may limit the possible coordination sites and the configuration of the formed surface species, potentially enabling the formation of conformationally homogeneous surface site populations.

The Department of Chemistry at the University of Virginia (UVA) invites applications for a Postdoctoral Research Associate to work in the laboratory of Prof. Amrit Venkatesh. The postdoc will engage i...

Single atom, low valent transition metals are important for heterogeneous catalysis but are challenging to generate and stabilize in a well-defined manner. Herein, we explored the functionalization of...

This mini-review summarizes the evolving debate regarding the origins of the absorptive features seen in the dynamic nuclear polarization (DNP) spectra of certain monoradicals when they are irradiated at their electron Larmor frequency. This feature has drawn attention due to its reverse scaling with respect to the magnetic field strength and potential for high-field DNP. Two competing hypotheses have been introduced to explain the DNP feature based on (1) the Overhauser effect and low-temperature molecular dynamics and (2) radical clustering and a thermal mixing mechanism. Since the original discovery, a large number of experimental observations have been made in attempts to understand and ultimately leverage the mechanism. We summarize these observations and provide critical assessments of how the competing hypotheses approach them.

Position Title: Postdoctoral Research Associate - Ames National Laboratory Appointment Type: Post Doc/Trainee Job Description: Summary of Duties and Responsibilities: Would you like to work for a Nati...

Confinement effects in stereoselective catalysis have been the topic of prolonged inquiry. Results have been largely mixed, with confinement having been reported to both enhance and degrade selectivity. Our ability to understand the surface’s impact on catalytic mechanisms, and thus selectivity, has been severely hindered by the low level of details commonly seen in the structures of supported metal complexes. Recent developments in sensitivity-enhanced NMR are revealing not only the molecular structure of surface sites but also their configuration, orientation, and proximities to neighboring molecules. In studying [Rh(cyclooctadiene)((S)-(−)-2-aminomethyl-1-ethyl-pyrrolidine)]CF3SO3 noncovalently immobilized to silica, an enantioselective hydrogenation catalyst, we observed a strong preference for a particular orientation of the complex relative to the support surface. We discuss how preferential adsorption may help reduce the number of competing reaction pathways and, in turn, have outsized effects on selectivity.

1H-detected magic-angle spinning (MAS) NMR experiments have revolutionized the NMR studies of biological and inorganic solids by providing unparalleled sensitivity and resolution. Despite these gains,...