Current limitations of solid-state NMR in carbohydrate and cell wall research.

High-resolution investigation of cell wall materials has emerged as an important application of biomolecular solid-state NMR (ssNMR). Multidimensional correlation experiments have become a standard method for obtaining sufficient spectral resolution to determine the polymorphic structure of carbohydrates and address biochemical questions regarding the supramolecular organization of cell walls. Using plant cellulose and matrix polysaccharides as examples, we will review how the multifaceted complexity of polysaccharide structure is impeding the resonance assignment process and assess the available biochemical and spectroscopic approaches that could circumvent this barrier. We will emphasize the ineffectiveness of the current methods in reconciling the ever-growing dataset and deriving structural information. We will evaluate the protocols for achieving efficient and homogeneous hyperpolarization across the cell wall material using magic-angle spinning dynamic nuclear polarization (MAS-DNP). Critical questions regarding the line-broadening effects of cell wall molecules at cryogenic temperature and by paramagnetic biradicals will be considered. Finally, the MAS-DNP method will be placed into a broader context with other structural characterization techniques, such as cryo-electron microscopy, to advance ssNMR research in carbohydrate and cell wall biomaterials.

Catalytic activity of Fe/ZrO2 nanoparticles for dimethyl sulfide oxidation.

A low-temperature vapor phase catalytic oxidation of dimethyl sulfide (DMS) with ozone over nano-sized Fe2O3-ZrO2 catalyst is carried out at temperatures of 50-200°C. Nanostructured Fe2O3-ZrO2 catalyst (FZN) is prepared by modified sol-gel method using citric acid as a chelating agent and conventional FZ catalyst is prepared with co-precipitation method. The catalysts are characterized using N2-BET surface area and pore size distributions, X-ray diffraction, TPR, TPD of DMS and NH3, SEM and TEM. The effects of operating temperature, ozone/DMS concentration and gas hourly space velocity (GHSV) on DMS removal efficiencies via catalytic ozonation are investigated. Relatively higher amount of ozone decomposition is observed on nanocatalyst compared to the co-precipitate catalyst from 50°C to 150°C. In contrast, at 200°C irrespective of the particle size, both catalysts performed similar activity. It clearly demonstrates that under ozone assisted catalytic oxidation over nanocatalyst offers the 100% of DMS conversion at lower temperature. The synthesized nanocatalyst and ozone are observed highly efficient for low temperature catalytic oxidation of DMS. The stability test shows that the nanocatalyst have relatively high activity and stability under the reaction conditions. A plausible reaction mechanism has been proposed for the oxidation of DMS based on the possible reaction products.

Rattling motion of alkali metal ions through the cavities of model compounds of graphyne and graphdiyne.

We study the passage of the alkali metal ions (Li(+), Na(+), and K(+)) through some conjugated carbon-based ring systems, starting from C12H6 and C24H12 (tribenzocyclyne; TBC), which serve as model compounds for graphyne to some of the higher analogues, C26H12, C28H12, and C30H12, the model systems for graphdiyne. The motion of the ions through cyclic carbon clusters, C12 and C14, is also investigated. The potential for the motion of the ions from one side of the ring to the other through the cavities of the molecules is a symmetric double well in most cases, while it is a rather flat potential in others, arising due to the free motion of the ions through the cavities. Electrostatic potential (ESP) analyses reveal that the ions bind to the ring systems at the most negative regions of ESP. The estimated energy barriers for the motion of Li(+) through C12H6 and C24H12 are 4.7 and 4.3 kcal mol(-1), respectively, and are comparable to the barrier for the classic case of umbrella-like inversion in ammonia. Transmission of Li(+) through C26H12, C28H12, C30H12, C12, and C14 rings is barrierless. We predict that the rattling motion of Li(+) through the model compounds of graphyne and graphdiyne should be experimentally observable. We also model the effectively one-dimensional motion of the ions through the rings using discrete variable representation (DVR) and calculate the energy levels of the complexes in the symmetric double well potentials. The molecular orbital analyses and the nuclear independent chemical shift (NICS) values for the rings suggest distinct trends based on the (4n + 2/4n) π electron count, leading us to propose two neutral complexes, (C12H6)Li2 and (C24H12)Li2, that are highly stable with binding energies of 400 and 356 kcal mol(-1), respectively.

Management of a severely resorbed mandibular ridge with the neutral zone technique.

The loose and unstable lower complete denture is one of the most common problems faced by denture patients. One of the methods used to solve this problem is the neutral zone technique. The neutral zone is the area where the displacing forces of the lips, cheeks, and tongue are in balance. It is in this zone that the natural dentitions lie and this is where the artificial teeth should be positioned. This area of minimal conflict may be located by using the neutral zone technique. The artificial teeth can then be set up in the correct positions.