Sorbitol-Based Glass Matrices Enable Dynamic Nuclear Polarization beyond 200 K.

In magic angle spinning dynamic nuclear polarization (MAS-DNP) experiments, paramagnetic species are often dispersed in rigid glass-forming matrices such as glycerol/water mixtures, but their modest glass-transition temperature () restricts the viable temperature range for MAS-DNP. To expand applications of DNP at higher temperatures, new matrices and physical insights are required. Here we demonstrate that sorbitol, ≈ 267 K, advantageously replaces glycerol, ≈ 190 K, to carry out DNP at higher temperature while maintaining an identical C NMR spectrum footprint and thus minimizing spectral overlap.

MAS-DNP enables NMR studies of insect wings.

NMR is a valuable tool for studying insects. Solid-state NMR has been used to obtain the chemical composition and gain insight into the sclerotization process of exoskeletons. There is typically little difficulty in obtaining sufficient sample quantity for exoskeletons.

Psychoactive plant- and mushroom-associated alkaloids from two behavior modifying cicada pathogens.

Entomopathogenic fungi routinely kill their hosts before releasing infectious spores, but a few species keep insects alive while sporulating, which enhances dispersal. Transcriptomics- and metabolomics-based studies of entomopathogens with post-mortem dissemination from their parasitized hosts have unraveled infection processes and host responses. However, the mechanisms underlying active spore transmission by Entomophthoralean fungi in living insects remain elusive.

RF field strength control and an envelope detector.

A brief description of a radio-frequency (RF) field strength controller is presented along with an experiment to test the long-term RF field strength stability of a nuclear magnetic resonance (NMR) spectrometer. Active control of RF field strengths may be necessary for quantitative measurements of NMR parameters, especially when experiments require days to run. An envelope detector, easily incorporated in any spectrometer, is also presented.

Description of an rf field-strength controller for solid-state NMR experiments.

Some MAS NMR experiments are sensitive to fluctuations or drifts in rf field strengths. We examine the simple H-C CPMAS experiment and show that the C signal intensities vary over time due to drifts in rf field strengths. The causes of the drifts in rf field strengths are studied.

Solid-State NMR Study of the Cicada Wing.

Wings of flying insects are part of the cuticle which forms the exoskeleton. The primary molecular components of cuticle are protein, chitin, and lipid. How these components interact with one another to form the exoskeleton is not completely understood.

Determining the relative orientation between the chemical shift anisotropy and heteronuclear dipolar tensors in static solids by SEDOR NMR.

The measurement of the dipolar interaction between two spins provides the distance between nuclei. A better structural picture emerges when the distance is combined with the orientation of the internuclear vector in the principal axis system of the chemical shift anisotropy tensor. The SEDOR experiment is used on a static sample of alanine to show that the orientation of the vector connecting the nitrogen and carboxylate carbon nuclei can be accurately determined in the CSA PAS of the C carboxylate spin.

Adding a lens Improves spinning speed characterization.

Highly stable sample rotation is important in many solid-state NMR experiments. Whether the necessary stability is achieved is not always clear. Typically only an average frequency over some time interval (often relatively long and unknown) is available from the spinning speed controller readout, which is not representative of the short-term variations of instantaneous rotation frequency.

Tripeptides on Gold Nanoparticles: Structural Differences between Two Reverse Sequences as Determined by Solid-State NMR and DFT Calculations.

The reverse-sequence peptides CysAlaAla and AlaAlaCys may attach to gold nanoparticles through the thiol group, and they differ primarily by whether the charged amino or the carboxylate group is proximal to the sulfur. Alanine residues in these peptides are not expected to interact significantly with the gold surface and serve to place a large separation between the amino and carboxylate groups. Solid-state NMR experiments and DFT calculations were performed to explore the structural differences between CysAlaAla on gold nanoparticles and AlaAlaCys on gold nanoparticles.

Optical lever for monitoring of the magic angle.

Setting the magic angle and accurately maintaining it over a full range of experimental conditions can be a frustrating experience. We present a simple optical device for immediate indication of the stator angle, free of mechanical uncertainties present in typical adjustment mechanisms.

(1)H MAS NMR study of cysteine-coated gold nanoparticles.

(1)H MAS NMR experiments were performed on gold nanoparticles coated with l-cysteine. The experiments show that l-cysteine molecules are zwitterions and support a structural model of cysteine forming two layers. The inner layer is composed of cysteine molecules chemisorbed to the gold surface via the sulfur atom.

Recollections of REDOR.

Rotational-echo, double-resonance NMR (REDOR) is an experiment designed to measure heteronuclear dipolar couplings in solids and is most often used to obtain structural details in solids. A brief history of its inception and development is presented.

Using heat to control the sample spinning speed in MAS NMR.

A new approach using temperature to control the spinning speed of a sample rotor in magic-angle spinning NMR is presented. Instead of an electro-mechanical valve that regulates the flow of drive gas to control the spinning speed in traditional MAS NMR systems, we use a small heater wire located directly in the stator. The sample spinning speed is controlled very accurately with a surprisingly low heating power of 1 W.

Oxygen-17 appears only in protein in water-stressed soybean leaves labeled by (17)O2.

We have used a rotational-echo adiabatic-passage double-resonance (13)C{(17)O} solid-state NMR experiment to prove that the glycine produced in the oxygenase reaction of ribulose bisphosphate carboxylase-oxygenase is incorporated exclusively into protein (or protein precursors) of intact, water-stressed soybean leaves exposed to (13)CO(2) and (17)O(2). The water stress increased stomatal resistance and decreased gas exchange so that the Calvin cycle in the leaf chloroplasts was no more than 35% (13)C isotopically enriched. Labeled O(2) levels were sufficient, however, to increase the (17)O isotopic concentration of oxygenase products 20-fold over the natural-abundance level of 0.

Structural analysis of the Gly-rich region in spider dragline silk using stable-isotope labeled sequential model peptides and solid-state NMR.

The local structure of the Gly rich region in synthetic model peptides of spider dragline silk was analyzed with solid-state NMR and no dominant secondary structure was revealed.

A frequency-selective REDOR experiment for an SI2 spin system.

A frequency-selective REDOR experiment is described for SI2 spin systems. The experiment causes the net dipolar dephasing of the S spin to evolve only under the influence of one of the I spins. The experiment is based on a single pair of appropriately phased 90 degrees I-spin pulses, and the I spin causing the S-spin dipolar dephasing is determined by the relative phases between the two 90 degrees pulses.

Dipolar recoupling of I = 1/2, S = 3/2 spin pairs with SEDOR for static and spinning samples.

Spin-echo, double-resonance (SEDOR) dipolar recoupling experiments are illustrated on an I = 1/2, S = 3/2 spin system for static and spinning samples. An (15)N-(23)Na spin system is used to show that the simple pulse sequence is very effective in causing (15)N dipolar dephasing using either a (23)Na pi/2 recoupling pulse or a long radio-frequency (r.f.

High field 17O solid-state NMR study of alanine tripeptides.

(17)O chemical shifts of Ala-Ala-Ala, with parallel and anti-parallel beta-sheet structures, are observed using a 930-MHz high-resolution solid-state NMR spectrometer. Ala-Ala-Ala serves as a model sheet-forming peptide because it can be easily prepared as either a parallel or an anti-parallel beta-sheet structure. Spectral differences between the two samples are observed which arise from molecular packing differences between the two sheet structures.

Internuclear (31)P-(51)V distance measurements in polyoxoanionic solids using rotational echo adiabatic passage double resonance NMR spectroscopy.

We report the first results establishing rotational echo adiabatic passage double resonance (REAPDOR) experiments for distance measurements between a spin-1/2 (31P) and spin-7/2 (51V) pair in a series of vanadium-substituted polyoxoanionic solids from the Keggin and Wells-Dawson families. We have quantitatively measured 31P-51V distances in monovanadium substituted K4PVW11O40, 1-K7P2VW17O62, and 4-K7P2VW17O62. Numerical simulations of the experimental data yield very good agreement with the averaged P-W/P-V distances determined from the X-ray diffraction measurements in the same or related compounds.

Lignin biosynthesis in transgenic Norway spruce plants harboring an antisense construct for cinnamoyl CoA reductase (CCR).

An attractive objective in tree breeding is to reduce the content of lignin or alter its composition, in order to facilitate delignification in pulping. This has been achieved in transgenic angiosperm tree species. In this study we show for the first time that changes in lignin content and composition can be achieved in a conifer by taking a transgenic approach.

A simple, inexpensive, and precise magic angle spinning speed controller.

Certain magic-angle spinning heteronuclear dipolar recoupling experiments using rotor-synchronized pulse trains require very precise control of the sample-spinning rate. An inexpensive spinning speed controller for use in magic-angle solid-state NMR experiments is described which can control the spinning rate to within +/- 0.2 Hz.

Determining dihedral angles and local structure in silk peptide by 13C-2H REDOR.

13C-2H REDOR NMR experiments were performed on 30-residue (AlaGly)15 silk I mimics of Bombyx mori silk fibroin to gain structural details about the elusive structure of the silk I conformation. 13C,2H-labeling strategies are illustrated for measuring individual dihedral angles in peptides and for determining local structure by REDOR. A major turn of type II character is found in the region Gly(14)-Ala(17).

Internuclear distance determination of S = 1, I = 1/2 spin pairs using REAPDOR NMR.

A universal function is proposed to describe REAPDOR dephasing curves of an observed spin-1/2 nucleus dipole-recoupled to a spin-1 quadrupolar nucleus ((2)H or (14)N). Previous work had shown that, in contrast to REDOR, the shape of the dephasing curve depends on a large number of parameters including the quadrupolar coupling constant and asymmetry parameter, the sample rotation speed, the RF amplitude, and the relative orientations of the quadrupole tensor and the internuclear vector. Here we demonstrate by numerical simulations that the actual dispersion of REAPDOR dephasing curves is quite small, provided the rotation speed and the RF amplitude applied to the quadrupolar nucleus satisfy an adiabaticity condition.