Tetrakis(trimethylsilyl)silane as a standard compound for fast spinning Solid-State NMR experiments.

The development of magic angle spinning (MAS) at rates ranging from 30 kHz to greater than 100 kHz has substantially advanced solid-state nuclear magnetic resonance (SSNMR) spectroscopy H-detection methods. The small rotors required for such MAS rates have a limited sample volume and low C-detection sensitivity, rendering the traditional set of standard compounds for SSNMR insufficient or highly inconvenient for shimming and magic-angle calibration. Additionally, the reproducibility of magic angle setting, chemical shift referencing, and probe position can be especially critical for SSNMR experiments at high fields.

Low power supercycled TPPM decoupling.

Improving the spectral sensitivity and resolution of biological solids is one of the long-standing problems in nuclear magnetic resonance (NMR) spectroscopy. In this report, we introduce low-power supercycled variants of two-pulse phase-modulated (TPPM) sequence for heteronuclear decoupling. The utility of the sequence is shown by improvements in the transverse relaxation time of observed nuclei (with H decoupling) with its application to different samples (uniformly C, N, H-labeled GB1 back-exchanged with 25% HO and 75% DO, uniformly C, N, H-labeled human derived Asyn fibril back-exchanged with 100% HO and uniformly C, N -labeled human derived Asyn fibril) at fast MAS using low radiofrequency (RF) fields.

Automatic fitting of multiple-field solid-state NMR spectra.

The NMR lineshapes produced by half-integer quadrupolar nuclei are sensitive to 11 distinct fit parameters per inequivalent site. To date, automatic fitting routines have failed to replace manual parameter insertion and evaluation due to the importance of local minima and the need for fitting multiple-field magic-angle spinning (MAS) and static spectra simultaneously. Herein we introduce a new tool, AMES-Fit (Automatic Multiple Experiment Simulation and Fitting), to automatically find the global best-fit simulation parameters for a series of multiple-field NMR lineshapes.

Zirconium-Catalyzed C-H Alumination of Polyolefins, Paraffins, and Methane.

C-H/Et-Al exchange in zirconium-catalyzed reactions of saturated hydrocarbons and AlEt affords versatile organoaluminum compounds and ethane. The grafting of commercially available Zr(OBu) on silica/alumina gives monopodal ≡SiO-Zr(OBu) surface pre-catalyst sites that are activated in situ by ligand exchange with AlEt. The catalytic C-H alumination of dodecane at 150 °C followed by quenching in air affords -dodecanol as the major product, revealing selectivity for methyl group activation.

Determining the Three-Dimensional Structures of Silica-Supported Metal Complexes from the Ground Up.

The immobilization of molecularly precise metal complexes to substrates, such as silica, provides an attractive platform for the design of active sites in heterogeneous catalysts. Specific steric and electronic variations of the ligand environment enable the development of structure-activity relationships and the knowledge-driven design of catalysts. At present, however, the three-dimensional environment of the precatalyst, much less the active site, is generally not known for heterogeneous single-site catalysts.

Synthesis-enabled exploration of chiral and polar multivalent quaternary sulfides.

An innovative method of synthesis is reported for the large and diverse (RE)(TM) (Tt)S (RE = rare-earth, TM = transition metals, Tt = Si, Ge, and Sn) family of compounds (∼1000 members, ∼325 contain Si), crystallizing in the noncentrosymmetric, chiral, and polar 6 space group. Traditional synthesis of such phases involves the annealing of elements or binary sulfides at elevated temperatures. The atomic mixing of refractory components technique, presented here, allows the synthesis of known members and vastly expands the family to nearly the entire transition metal block, including 3d, 4d, and 5d TMs with oxidation states ranging from 1+ to 4+.

Third time's the charm: intricate non-centrosymmetric polymorphism in SiP ( = La and Ce) induced by distortions of phosphorus square layers.

Complex polymorphic relationships in the LnSiP3 (Ln = La and Ce) family of compounds are reported. An innovative synthetic method was developed to overcome differences in the reactivities of the rare-earth metal and refractory silicon with phosphorus. Reactions of atomically mixed Ln + Si with P allowed for selective control over the reaction outcomes resulting in targeted isolation of three new polymorphs of LaSiP3 and two polymorphs of CeSiP3.

Phase-sensitive γ-encoded recoupling of heteronuclear dipolar interactions and H chemical shift anisotropy.

γ-encoded recoupling sequences are known to produce strong amplitude modulations that lead to sharp doublets when Fourier transformed. These doublets depend very little on the recoupled tensor asymmetry and thus enable for the straightforward determination of dynamic order parameters. It can, however, be difficult to measure small anisotropies, or small order parameters, using such sequences; the resonances from the doublet may overlap with each other, or with the zero-frequency glitch.