Methane and carbon dioxide are known greenhouse gases, and the conversion of these two C1-building blocks into useful fuels and chemicals is a subject of great importance. By solid-state NMR spectroscopy, we found that methane and carbon dioxide can be co-converted on a zinc-modified H-ZSM-5 zeolite (denoted as Zn/H-ZSM-5) to form acetic acid at a low temperature range of 523-773 K. Solid-state (13)C and (1)H MAS NMR investigation indicates that the unique nature of the bifunctional Zn/H-ZSM-5 catalyst is responsible for this highly selective transformation. The zinc sites efficiently activate CH4 to form zinc methyl species (-Zn-CH3), the Zn-C bond of which is further subject to the CO2 insertion to produce surface acetate species (-Zn-OOCCH3). Moreover, the Brønsted acid sites play an important role for the final formation of acetic acid by the proton transfer to the surface acetate species. The results disclosed herein may offer the new possibility for the efficient activation and selective transformation of methane at low temperatures through the co-conversion strategy. Also, the mechanistic understanding of this process will help to the rational design of robust catalytic systems for the practical conversion of greenhouse gases into useful chemicals.

Thiols can engage favorably with aromatic rings in S–H/π interactions, within abiological systems and within proteins. However, the underlying bases for S–H/π interactions are not well understood. The crystal structure of Boc-L-4-thiolphenylalanine tert-butyl ester revealed crystal organization centered on the interaction of the thiol S–H with the aromatic ring of an adjacent molecule, with a through-space Hthiol...Caromatic distance of 2.71 Å, below the 2.90 Å sum of the van der Waals radii of H and C. The nature of this interaction was further examined by DFT calculations, IR spectroscopy, solid-state NMR spectroscopy, and analysis of the Cambridge Structural Database. The S–H/π interaction was found to be driven significantly by favorable molecular orbital interactions, between an aromatic π donor orbital and the S–H σ* acceptor orbital (a π→σ* interaction). For comparison, a structural analysis of O–H/π interactions and of cation/π interactions of alkali metal cations with aromatic rings was conducted. Na+ and K+ exhibit a significant preference for the centroid of the aromatic ring and distances near the sum of the van der Waals and ionic radii, as expected for predominantly electrostatic interactions. Li+ deviates substantially from Na+ and K+. The S–H/π interaction differs from classical cation/π interactions by the preferential alignment of the S–H σ* toward the ring carbons and an aromatic π orbital rather than toward the aromatic centroid. These results describe a potentially broadly applicable approach to understanding the interactions of weakly polar bonds with π systems.

The principal values of the 13 C chemical shift tensors were measured for coronene and corannulene, both at room temperature and at approximately 100 K. At room temperature the molecules are moving, resulting in a motionally averaged powder pattern. A comparison of the principal values between the room temperature motionally averaged pattern and the low-temperature static pattern provides experimental information about the orientation of the principal axis system of the shift tensor for the bridgehead carbons in these molecules. For corannulene, the orientation of δ 33 component was determined to lie at an angle of 13°from the rotation axis (the 5-fold symmetry axis of the molecule) for the inner bridgehead carbons and at an angle 26°from this same rotation axis for the outer bridgehead carbons. These orientations are in good agreement with the angles necessary to place the δ 33 component along the p orbitals involved in π-bonding at these carbons. In the case of coronene, the differences between the principal values at the two temperatures indicate there is an angle of 14°between the axis of rotation and the δ 33 component for both the inner and outer bridgehead carbons. This indicates that the motion is not constrained to simple in-plane rotation, but must also have an out-of-plane component. Quantum chemical calculations of the shielding tensors were also completed using both experimental and optimized molecular geometries. The results of the calculations are in good agreement with the experimental findings.

The analysis of heavy-metal solids with NMR spectroscopy provides a means of investigating the electronic environment through the dependence of the chemical shift on structure. We have investigated the relation of the 207Pb NMR isotropic chemical shift, span, and skew of a series of solid Pb(II) compounds to lattice parameters. Complementary relativistic spin-orbit density functional calculations on clusters such as PbI64- that model the local environment in the dihalides show a dependence of NMR properties on the local structure in good agreement with experimental results.

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Solid-state (13)C, (19)F, and (15)N magic angle spinning NMR studies of Form I of atorvastatin calcium are reported, including chemical shift tensors of all resolvable carbon sites and fluorine sites. The complete (13)C and (19)F chemical shift assignments are given based on an extensive analysis of (13)C-(1)H HETCOR and (13)C-(19)F HETCOR results. The solid-state NMR data indicate that the asymmetric unit of this material contains two atorvastatin molecules. A possible structure of Form I of atorvastatin calcium (ATC-I), derived from solid-state NMR data and density functional theory calculations of various structures, is proposed for this important active pharmaceutical ingredient (API).

The proton spin-lattice relaxation times and proton chemical shifts for the hydroxyl and methyl protons in methanol were measured at liquid and supercritical densities using capillary high-pressure NMR spectroscopy. The pressure range for the proton nuclear relaxation measurements was between 50 and 3500 bar over a temperature range of 298-573 K. The proton chemical shifts of methanol were investigated for a pressure range of 50-3500 bar and a temperature range of 298-773 K. Attempts were made to separate the contributions of the dipolar and spin-rotation interactions to the spin-relaxation processes at each thermodynamic condition over methanol densities ranging from liquid to supercritical fluid. An average number of hydrogen bonds per molecule in methanol and the apparent activation energy of the methyl group internal rotation have been extracted from the experimental relaxation data. The extracted quantities show a moderate pressure dependence in addition to temperature effects, which suggest that molecular packing effects on hydrogen-bonded methanol are important at higher pressures. A comparison between methanol and water at similar thermodynamic conditions was also made to obtain new insight into these two important supercritical solvents.

The selectively direct conversion of methane to methanol on Cu-exchanged zeolites has attracted a lot of interest because of the abundant availability of methane. A detailed reaction mechanism of the transformation of methane to methanol aimed to improve the catalyst design has been long expected. On the basis of EPR and solid-state NMR studies, we demonstrate that CH4 activates on the [Cu2O]2+ core of the Cu/Na–ZSM-5 zeolite, producing a ·CH3 radical and an ·OH radical. The generated methanol molecule, which formed from the combination of ·CH3 and the ·OH radicals, adsorbs on the Cu+ species and forms the copper methoxy species (−Cu–O–CH3) and the −Al–OH group. Through the process of hydration, the copper methoxy species and the adsorbed methanol transform into free methanol. We expect that our mechanistic understanding of the methane to methanol process could pave the way for catalyst design.