Magic angle spinning (MAS) NMR linewidths in the presence of solid-state dynamics

In solid-state NMR, the magic angle spinning (MAS) technique fails to suppress anisotropic spin interactions fully if reorientational dynamics are present, resulting in a decay of the rotational-echo train in the time-domain signal. We show that a simple analytical model can be used to quantify this linebroadening effect as a function of the MAS frequency, reorientational rate constant, and magnitude of the inhomogeneous anisotropic broadening. We compare this model with other theoretical approaches and with exact computer simulations, and show how it may be used to estimate rate constants from experimental NMR data

Can We Reduce Prolonged Sitting? Feasibility of a Tactile Vibration Prompt To Initiate Movement

Please refer to the pdf version of the abstract located adjacent to the title

Preparation of highly and generally enriched mammalian tissues for solid state NMR.

An appreciable level of isotope labelling is essential for future NMR structure elucidation of mammalian biomaterials, which are either poorly expressed, or unexpressable, using micro-organisms. We present a detailed protocol for high level (13)C enrichment even in slow turnover murine biomaterials (fur keratin), using a customized diet supplemented with commercial labelled algal hydrolysate and formulated as a gel to minimize wastage, which female mice consumed during pregnancy and lactation. This procedure produced approximately eightfold higher fur keratin labelling in pups, exposed in utero and throughout life to label, than in adults exposed for the same period, showing both the effectiveness, and necessity, of this approach.The authors would like to acknowledge funding from the Biotechnology and Biological Sciences Research Council for DGR and RR; Engineering and Physical Sciences Research Council for WYC and VWCW; National Institute of Health Research for RAB.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s10858-015-9977-

Proline provides site-specific flexibility for in vivo collagen.

Fibrillar collagens have mechanical and biological roles, providing tissues with both tensile strength and cell binding sites which allow molecular interactions with cell-surface receptors such as integrins. A key question is: how do collagens allow tissue flexibility whilst maintaining well-defined ligand binding sites? Here we show that proline residues in collagen glycine-proline-hydroxyproline (Gly-Pro-Hyp) triplets provide local conformational flexibility, which in turn confers well-defined, low energy molecular compression-extension and bending, by employing two-dimensional 13C-13C correlation NMR spectroscopy on 13C-labelled intact ex vivo bone and in vitro osteoblast extracellular matrix. We also find that the positions of Gly-Pro-Hyp triplets are highly conserved between animal species, and are spatially clustered in the currently-accepted model of molecular ordering in collagen type I fibrils. We propose that the Gly-Pro-Hyp triplets in fibrillar collagens provide fibril "expansion joints" to maintain molecular ordering within the fibril, thereby preserving the structural integrity of ligand binding sites.BBSRC, EPSRC, Raymond and Beverly Sackler Fund for Physics of Medicine, Wellcome Trust, ER

Direct Observation of Proton-Neutron Short-Range Correlation Dominance in Heavy Nuclei

We measured the triple coincidence A(e,e′n p) and A(e,e′ p p) reactions on carbon, aluminum, iron, and lead targets at Q2 \u3e1.5  (GeV/c)2, xB \u3e 1.1 and missing momentum \u3e400  MeV/c. This was the first direct measurement of both proton-proton (pp) and neutron-proton (np) short-range correlated (SRC) pair knockout from heavy asymmetric nuclei. For all measured nuclei, the average proton-proton (pp) to neutron-proton (np) reduced cross-section ratio is about 6%, in agreement with previous indirect measurements. Correcting for single-charge exchange effects decreased the SRC pairs ratio to ∼3%, which is lower than previous results. Comparisons to theoretical generalized contact formalism (GCF) cross-section calculations show good agreement using both phenomenological and chiral nucleon-nucleon potentials, favoring a lower pp to np pair ratio. The ability of the GCF calculation to describe the experimental data using either phenomenological or chiral potentials suggests possible reduction of scale and scheme dependence in cross-section ratios. Our results also support the high-resolution description of high-momentum states being predominantly due to nucleons in SRC pairs