MoS presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. The intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s (65-75 mV/dec), 3.2 s (65-85 mV/dec), and 0.1 s (120-160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7-10%, and the number of sulfur vacancies in high crystalline quality MoS is higher than that in low crystalline quality MoS, which may be related with the proximity of different local crystalline structures to the vacancies.

A magnetostructural correlation (conformational electron spin exchange modulation) within an isostructural series of biradical complexes is presented. X-ray crystal structures, variable-temperature electron paramagnetic resonance spectroscopy, zero-field splitting parameters, and variable-temperature magnetic susceptibility measurements were used to evaluate molecular conformation and electron spin exchange coupling in this series of molecules. Our combined results indicate that the ferromagnetic portion of the exchange couplings occurs via the cross-conjugated pi-systems, while the antiferromagnetic portion occurs through space and is equivalent to incipient bond formation. Thus, molecular conformation controls the relative amounts of ferro- and antiferromagnetic contributions to exchange coupling. In fact, the exchange parameter correlates with average semiquinone ring torsion angles via a Karplus-Conroy-type relation. Because of the natural connection between electron spin exchange coupling and electronic coupling related to electron transfer, we also correlate the exchange parameters in the biradical complexes to mixed valency in the corresponding quinone-semiquinone radical anions. Our results suggest that delocalization in the cross-conjugated, mixed-valent radical anions is proportional to the ferromagnetic contribution to the exchange coupling in the biradical oxidation states.

A novel universal linker (UnyLinker) molecule which has a conformationally rigid and chemically stable bridge head ring oxygen atom carrying a conventional 4,4′-dimethoxytrityl (DMT) and succinyl groups locked in a syn orientation has been developed to carry out oligonucleotide synthesis efficiently and smoothly. The geometry of the vicinal syn oxygen functionalized group allows fast and clean cleavage under standard aqueous ammonia deprotection conditions to afford high-quality oligonucleotides. No base modification is observed, based on the ion-pair HPLC−UV−MS (IP-HPLC−UV−MS) method with detection limit of <0.1%. A class of impurities formed by branching from the exocyclic amino group of nucleosides loaded onto a solid support has been eliminated by the use of this method. Examples demonstrating the versatile nature of this molecule are shown by syntheses of different chemistries such as 2′-deoxy, 2′-O-methyl, 2′-O-methoxyethyl, Lock nucleic acids (LNA), 2′-α-fluoro nucleic acids (FANA), conjugates such as 5′-phosphate monoester and biotin, and phosphate diester and phosphorothioate backbone modifications. This molecule was loaded onto several commercial solid supports and used in both gas-sparged and packed-bed automated DNA/RNA synthesizers. Large-scale syntheses (up to 700 mmol) of multiple phosphorothioate first- and second-generation antisense drugs on GE-Amersham’s OligoProcess synthesizer are demonstrated further, showing that this chemistry could be used for efficient synthesis of multiple oligonucleotide drugs using a single raw material, thereby eliminating a difficult to characterize nucleoside-loaded polymer matrix used as a starting material. A mechanism for deprotection and cleavage of the linker molecule to liberate the free oligonucleotide is proposed. Characterization of the cyclic byproduct formed during release of the oligonucleotide is presented. The exo-syn configuration of the dihydroxy structure of the UnyLinker molecule is conclusively established by X-ray crystallography studies. A novel method to remove the last traces of osmium used during the synthesis of the UnyLinker molecule to reach undetectable levels (<1 ppm) is also described.

Epitaxial thin films heterostructures of topological insulator candidate Sr3SnO (SSO) are grown on a cubic yttria-stabilized zirconia (c-YSZ)/Si (001) platform by pulsed laser deposition. X-ray and electron diffraction patterns confirm the epitaxial nature of the layers with cube-on-cube orientation relationship: (001)[100]SSO∥(001)[100]c-YSZ∥(001)[100]Si. The temperature dependent electrical resistivity shows semiconductor behavior with a transport mechanism following the variable-range-hopping model. The SSO films show room-temperature ferromagnetism with a high saturation magnetization, and a finite non-zero coercivity persisting up to room temperature. These results indicate that SSO is a potential dilute magnetic semiconductor, presumably obtained by controlled introduction of intrinsic defects.