Magic Angle Spinning Effects on Longitudinal NMR Relaxation: 15N in L-Histidine

Solid-state magnetic resonance is a unique technique that can reveal the dynamics of complex biological systems with atomic resolution. Longitudinal relaxation is a mechanism that returns longitudinal nuclear magnetization to its thermal equilibrium by incoherent processes. The measured longitudinal relaxation rate constant however represents the combination of both incoherent and coherent contributions to the change of nuclear magnetization. This work demonstrates the effect of magic angle spinning rate on the longitudinal relaxation rate constant in two model compounds: L-histidine hydrochloride monohydrate and glycine serving as proxies for isotopically-enriched biological materials. Most notably, it is demonstrated that the longitudinal 15N relaxation of the two nitrogen nuclei in the imidazole ring in histidine is reduced by almost three orders of magnitude at the condition of rotational resonance with the amine, while the amine relaxation rate constant is increased at these conditions. The observed phenomenon may have radical implications for the solid-state magnetic resonance in biophysics and materials, especially in the proper measurement of dynamics and as a selective serial transfer step in dynamic nuclear polarization

Wood lignocellulosic stabilizers : effect of their characteristics on stability and rheological properties of emulsions

Lignocellulosic materials from the forest industry have shown potential to be used as sustainable hydrocolloids to stabilize emulsions for many applications in life science and chemical industries. However, the effect of wood species and recovery method on the product’s properties and ability to stabilize emulsions of isolated lignocellulosic compounds is not well understood. Hemicelluloses, abundant lignocellulosic side stream, exhibit differences in their water solubility, anionic character, lignin content, and degree of acetylation. Here, we explored stability and rheological properties of model emulsions (5% hexadecane and 1% stabilizer, w/w) stabilized by different grades of sprucewood galactoglucomannan (GGM) and birchwood glucuronoxylan (GX) hemicelluloses. The results were compared to known soluble, insoluble, charged, and non-charged cellulosic stabilizers, namely methyl cellulose (MC), carboxymethyl cellulose (CMC), anionic- and nonionic-cellulose nanocrystals (aCNC and dCNC). The results showed that GX emulsions were highly stable compared to GGM emulsions, and that deacetylation and lignin removal markedly reduced emulsion stability of GGM. Carboxymethylation to increase anionic characters enhanced the emulsion stabilization capacity of GGM, but not that of GX. Investigating flow behaviors of emulsions indicated that hemicelluloses primarily stabilize emulsions by adsorption of insoluble particles, as their flow behaviors were similar to those of cellulose nanocrystals rather than those of soluble celluloses. Understanding the impact of the variations in composition and properties of hemicellulose stabilizers to stabilize emulsions allows tailoring of their recovery processes to obtain desirable hydrocolloids for different applications.Peer reviewe

Cohomology of bundles on homological Hopf manifold

We discuss the properties of complex manifolds having rational homology of $S^1 \times S^{2n-1}$ including those constructed by Hopf, Kodaira and Brieskorn-van de Ven. We extend certain previously known vanishing properties of cohomology of bundles on such manifolds.As an application we consider degeneration of Hodge-deRham spectral sequence in this non Kahler setting.Comment: To appear in Proceedings of 2007 conference on Several complex variables and Complex Geometry. Xiamen. Chin

Ag2PdP2O7

Disilver(I) palladium(II) diphosphate, Ag2PdP2O7, is isotypic with Na2PdP2O7. It consists of infinite diphosphato-pallad­ate(II) [Pd(P2O7)2/2]2− ribbons with the PdII ion in an almost square-planar coordination ( symmetry) and the P2O7 group exhibiting 2 symmetry. The [Pd(P2O7)2/2]2− ribbons are linked by distorted [AgO6] octa­hedra. 31P-MAS NMR studies on Ag2PdP2O7 are in accordance with one independent site for phospho­rus; its isotropic chemical shift δiso = 21.5 p.p.m. is similar to that of Pd2P2O7

Structural investigation of aluminium doped ZnO nanoparticles by solid-state NMR spectroscopy

The electrical conductivity of aluminium doped zinc oxide (AZO, ZnO:Al) materials depends on doping induced defects and grain structure. This study aims at relating macroscopic electrical conductivity of AZO nanoparticles with their atomic structure, which is non-trivial because the derived materials are heavily disordered and heterogeneous in nature. For this purpose we synthesized AZO nanoparticles with different doping levels and narrow size distribution by a microwave assisted polyol method followed by drying and a reductive treatment with forming gas. From these particles electrically conductive, optically transparent films were obtained by spin-coating. Characterization involved energy-dispersive X-ray analysis, wet chemical analysis, X-ray diffraction, electron microscopy and dynamic light scattering, which provided a basis for a detailed structural solid-state NMR study. A multinuclear (Al-27, C-13, H-1) spectroscopic investigation required a number of 1D MAS NMR and 2D MAS NMR techniques (T-1-measurements, Al-27-MQMAS, Al-27-H-1 2D-PRESTO-III heteronuclear correlation spectroscopy), which were corroborated by quantum chemical calculations with an embedded cluster method (EEIM) at the DFT level. From the combined data we conclude that only a small part of the provided Al is incorporated into the ZnO structure by substitution of Zn. The related Al-27 NMR signal undergoes a Knight shift when the material is subjected to a reductive treatment with forming gas. At higher (formal) doping levels Al forms insulating (Al, H and C containing) side-phases, which cover the surface of the ZnO:Al particles and increase the sheet resistivity of spin-coated material. Moreover, calculated Al-27 quadrupole coupling constants serve as a spectroscopic fingerprint by which previously suggested point-defects can be identified and in their great majority be ruled out

Reconstruction of Self-Sparse 2D NMR Spectra from Undersampled Data in the Indirect Dimension†

Reducing the acquisition time for two-dimensional nuclear magnetic resonance (2D NMR) spectra is important. One way to achieve this goal is reducing the acquired data. In this paper, within the framework of compressed sensing, we proposed to undersample the data in the indirect dimension for a type of self-sparse 2D NMR spectra, that is, only a few meaningful spectral peaks occupy partial locations, while the rest of locations have very small or even no peaks. The spectrum is reconstructed by enforcing its sparsity in an identity matrix domain with ℓp (p = 0.5) norm optimization algorithm. Both theoretical analysis and simulation results show that the proposed method can reduce the reconstruction errors compared with the wavelet-based ℓ1 norm optimization

Reduced TCA cycle rates at high hydrostatic pressure hinder hydrocarbon degradation and obligate oil degraders in natural, deep-sea microbial communities

Petroleum hydrocarbons reach the deep-sea following natural and anthropogenic factors. The process by which they enter deep-sea microbial food webs and impact the biogeochemical cycling of carbon and other elements is unclear. Hydrostatic pressure (HP) is a distinctive parameter of the deep sea, although rarely investigated. Whether HP alone affects the assembly and activity of oil-degrading communities remains to be resolved. Here we have demonstrated that hydrocarbon degradation in deep-sea microbial communities is lower at native HP (10 MPa, about 1000 m below sea surface level) than at ambient pressure. In long-term enrichments, increased HP selectively inhibited obligate hydrocarbon-degraders and downregulated the expression of beta-oxidation-related proteins (i.e., the main hydrocarbon-degradation pathway) resulting in low cell growth and CO2 production. Short-term experiments with HP-adapted synthetic communities confirmed this data, revealing a HP-dependent accumulation of citrate and dihydroxyacetone. Citrate accumulation suggests rates of aerobic oxidation of fatty acids in the TCA cycle were reduced. Dihydroxyacetone is connected to citrate through glycerol metabolism and glycolysis, both upregulated with increased HP. High degradation rates by obligate hydrocarbon-degraders may thus be unfavourable at increased HP, explaining their selective suppression. Through lab-scale cultivation, the present study is the first to highlight a link between impaired cell metabolism and microbial community assembly in hydrocarbon degradation at high HP. Overall, this data indicate that hydrocarbons fate differs substantially in surface waters as compared to deep-sea environments, with in situ low temperature and limited nutrients availability expected to further prolong hydrocarbons persistence at deep sea