Solid-State NMR Group

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Research Interests

1. Biological Materials

Spider dragline silk. Much of our work has focused on the dragline silk of the golden orb weaver (Nephila clavipes). This outstanding biomaterial has an energy to break greater than Kevlar, yet is synthesized from organic starting materials and is biodegradable. We use solid-state nuclear magnetic resonance to probe the conformation and dynamics of the various amino acid components of the silk protein.

Nephila calivipes (golden orb weaver). Dragline silk of the golden orb-weaving spider is synthesized in the major ampullate gland, at the top of the spider's abdomen. The prespun silk is believed to adopt a liquid crystalline form.

Resilin. Resilin is an extraordinary protein-based rubber made by many insects and other arthropods. We have investigated the protein structure of natural resilin (from dragonfly tendons) and synthetic resilin-based materials (using recombinant proteins). Better understanding of resilin's high elastic efficiency, high extensibility, and long fatigue lifetime will aid in incorporating these properties into synthetic materials in the future.

Hagfish Slime. When agitated, hagfish are able to release a specialized mixture of proteins which, upon contact with water, produce an enormous quantity of "slime". In addition to the slippery proteins commonly seen in mucous secretions, hagfish slime also contains fine fibres (slime threads) with interesting tensile properties. They are remarkably elastic but also tough under high strain, where the α-helical proteins take on a more extended β-sheet formation. By studying these materials, we hope to learn more about the biophysics of intermediate filaments in other areas of biology that are difficult to study, such as within cells.

Whelk Egg Capsules. Sea snails deposit their eggs in tough protective capsules specifically adapted to their anticipated wear and tear in the harsh marine environment. Busycon eggs are released in metre-long helical strands known as mermaid necklaces that link up to 160 capsules. These are buffeted about for months by breakers at velocities of up to 10 m/s along the seashores of the east coast of North America. Given the punishing environment, how the Busycon capsules shield the delicate embryos from damage is of fundamental interest. Recent investigations of the Busycon capsule wall have found it to consist of cross-plied sheets of protein fibres. with effective shock-absorbing tensile properties. The large and reversible extension of biopolymers in the Busycon egg capsule wall is strongly suggestive of an elastomer. Elastomeric proteins have an essential role in a variety of extracellular structural tissues and their long-range elastic properties are useful, for instance, as shock absorbers (for example, in hydrated dragline spider silks), for elastic energy storage capacity in jumping and flying insects and to ensure adequate elasticity in the integument and arteries of various organisms. Previous study supports the notion that high extensibility is due to a fully reversible alpha-helix to beta sheet structural transition on loading. We are currently using solid-state NMR to further our understanding of the structure and structural transition that occur on loading of this remarkable material.

Nanocrystalline Cellulose. We have been collaborating with Dr. Wadood Hamad at FP Innovations to study the phase structure of NCC. Our work suggests that NCC particles contain distributions of environments distinguished by their structures and crystalline perfection. Portions of the solid-state 13C NMR spectrum previously assigned as disordered/surface appear inaccessible to D2O exchange indicating that the NCC crystallites contain abundant disordered domains in the interiors.

2. Synthetic Materials

Solid polymer electrolytes. We have been working with collaborators in France and Washington state to study the diffusion of Li ions in solid-polymer electrolyte material candidates. A home-built gradient probe and driver capable of short, intense gradient pulses provides a unique ability to measure diffusion in samples having sub-ms T2 relaxation times.

Porous glass. We are collaborating with Mark MacLachlan's group from UBC chemistry to study a novel type of porous glass they have recently invented. This is a mesoporous (pore diameter is 2 - 50 nm) organosilica, and has the unique proerty that the pores have chirality--that is, they have a twist to them. The interference of light from this twist causes iridescence, as seen below. This material has many possible applications. Absorbed liquid crystals can allow it to act as a temperature-dependent sensor. Through NMR, we can study how the LC mesogens align within the pores. This material may also act as an enantioselective filter, allowing racemic mixtures to be seperated. With this goal in mind, we are characterizing the pore size through NMR with pulse-field gradient diffusion measurements and cryoporometry.

Two flakes of the chiral nematic organosilica showing the iridescence resulting from the interaction of the chiral pores with light. The scale bar is 18 mm. Image from Shopsowitz et al, JACS 134, 867 (2012).

3. NMR Methodology + Instrumentation

Earth's field NMR. We have developed a low-cost Earth's-field nuclear magnetic resonance spectrometer. This instrument is now being deployed in the PHYS 102 laboratory to introduce magnetic resonance imaging (MRI) to first-year science students. The system is capable of collecting simple two-dimensional MRI images in about 15 minutes.

Coil assembly of the Earth's-field NMR spectrometer. The outer coils provide controllable magnetic field gradients. Inside, two solenoids are used for polarizing nuclear spins and for exciting/detecting the NMR signals.

    bottle with a + shape inside

An image of a 500 ml water bottle with a plastic + shape inside, taken with this spectrometer.

Two-photon NMR+NQR. Nearly all NMR experiments employ oscillating or rotating magnetic fields having frequencies close to the natural resonant frequencies of the sample of interest. NMR signals however can also be observed following excitation at one-half (or other subharmonics) of the ordinary resonance frequency. Simultaneous excitation with two fields whose frequencies add or subtract to the resonance frequency is also possible. These styles of excitation offer some advantages, such as immunity from radio-frequency ring down dead-times, and the opportunity to simultaneously manipulate and observe NMR signals.

Two photon NMR

NMR signals acquired during excitation with two-photon excitation. The top row shows nutation signals with continuous irradiation. The second row shows a 90 degree pulse and subsequent evolution. The bottom row shows spin locking.

Orthogonalized Shimming. A new, automated method for optimizing the magnetic field gradients ("shimming") of nuclear magnetic resonance instruments has been developed. Modern NMR spectrometers incorporate as many as 50 independently adjustable field gradient coils to allow fine tuning of the magnet's homogeneity. Optimizing the currents in these coils can be a time-consuming and frustrating task because the gradients, as supplied by the hardware, are generally not mutually orthogonal. Our new method mathematically orthogonalizes the gradients allowing independent optimization in a fully automated manner.
Orthogonalized shimming

Fully automated shimming as for a brand-new probe. Left, solution NMR line-shape with all shim currents set to 0. Right, line-shape after orthogonalization and optimization of 24 shim gradients.

High resolution spectra in inhomogeneous fields. We have developed a method of collecting high-resolution NMR spectra in inhomogeneous magnetic fields, based upon the spatial encoding of a pseudorandom noise sequence. This technique can also be used to eliminate artifacts arising from radiation damping. Presently, the method has implemented and tested with field inhomogeneity in one dimension, but a full three dimensional version of the technique is planned.
Glucose in non-uniform field

NMR spectra showing degraded resolution (blue) of glucose in D2O. The spectra in red were acquired in the same non-uniform field with the noise encoding.