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Periodic Report Summary 1 - ODMR-CHEM (Optically detected magnetic resonance for ultra-sensitive chemical analysis, imaging and process monitoring)

Introduction
Nuclear magnetic resonance (NMR) is well-recognized across the chemical, physical, engineering and biomedical sciences as a technique for noninvasive, nondestructive chemical analysis of matter. NMR opens avenues in molecular structure elucidation, pharmaceutical screening, petrochemicals discovery and processing, materials science and imaging of objects.

In project ODMR-CHEM we proposed ultralow-field optical detection to increase the applicability of NMR for chemical process monitoring “on the plant” or “in the field”. Ultralow-field NMR avoids some features of conventional NMR instrumentation which has limited the extent of these activities to date, principally the high cost (>500,000 EUR for a commercial 14 tesla superconducting magnet and spectrometer console, and the need for several hundred liters of liquid helium in supply), high maintenance and non-portability. The use of nonconventional, but rapidly maturing atomic magnetometer technology was proposed to make sensitive, high resolution NMR feasible in situations where cryogenics are unavailable and dramatically reducing cost, size, and maintenance of the apparatus. We also proposed to utilize the ultralow-field NMR approach for the investigation of chemical behavior in materials that are of high importance in chemical processes but are challenging to study via NMR in high magnetic field due to the large gradients in magnetic-susceptibility (catalysts with paramagnetic sites, emulsions, porous materials with paramagnetic impurities).

Principal objectives:
Outgoing phase (01 October 2014 to 30 September 2016, WORK PACKAGES 1 AND 2)
• Enhance the knowledge of the fellow across diverse fields in scientific research, including low-field NMR and MRI, laser spectroscopy and optics (ultralow-field NMR instrumentation based on alkali-metal-vapor magnetometer technology), signal processing, organic reactions, fluid rheology and microfluidics.
• Develop and construct a sensitive ultralow-field NMR system suitable for portable use in online, or "on the plant", chemical process monitoring. To be used for experiments during the return phase of the project. Research work focuses on understanding the limits of the hardware and signal processing methods in relation to the systems of interest in chemical process technology.
• Develop high-resolution chemical signature identification through ultra-high (millihertz) measurement of spin-spin couplings at zero field. Develop methods that yield NMR signals for a specific functional group and which may be used to monitor chemical processes.
• Develop optically detected NMR towards chemical characterization, imaging and optimization of the technology with respect to sensitivity, data acquisition time, spectral resolution and data quality.

Return phase (ongoing since 01 October 2016, WORK PACKAGE 3)
• Relocate the instrument for ultralow-field NMR to the host institution.
• Apply the methods developed during the outgoing phase as tools for chemical reaction optimization and process quality control. Case study 1: investigate how one can best image flow reactor profiles (e.g. pipe cross section or distance along a line) by examining trade-offs between spatial and temporal resolution. Case study 2: monitor the rheological behavior of fluids inside porous materials versus their chemical activity.
• Advance the fellow towards a position of professional maturity and independence through academic achievement including research output and student supervision

Description of work performed and results since the beginning of the project
The first 24 months were spent working under guidance of Prof. Alexander Pines and Prof. Dmitry Budker in the departments of Chemistry and Physics of the University of California Berkeley in the USA. The fellow acquired competences in operating an alkali-vapor magnetometer. The heart of this magnetometer is a glass chamber containing vaporized rubidium-87. The spin states of atomic metal are well defined and very sensitive to magnetic and electric fields so they may be easily set, adjusted and read out by lasers. In this case, the magnetization of the NMR sample is detected via its perturbation on the optical rotation of polarized near-infrared light through the rubidium.

The results and data achieved so far generally indicate that the objectives for the outgoing phase have successfully kept to the proposed project plan. Beyond acquiring competence in the research subject, the fellow has developed methodology to enhance the range of NMR experiments in ultralow field including: the decoupling of heteronuclear spin-spin coupling interactions (submitted paper to J. Chem. Phys Lett., 2nd author); the implementation of conventional high-field pulse sequences (published paper in J. Magn. Reson. (year 2016, 1st author); the use of extremely low power, highly selective pulses (published paper in J. Phys. Chem. A, 2016, 2nd author) for spin control.

During the outgoing phase, ultralow-field NMR experiments were performed to assess the limitations for NMR and MRI characterization of chemically reactive systems. It is now within the experimental capability to study diffusion and relaxation in liquid-only systems on the order of 0.1 to 1.0 mL in volume. Additionally, some “model” liquid-solid systems were studied including high-voidage porous materials immersed in water or paraffins. These experiments are to be continued after the move to the return host institution, with extension to two and three-dimensional imaging of liquids in the samples.

The fellow has successfully built a working spectrometer for ultralow-field NMR that is research-grade in sensitivity, and is portable. This was assembled mostly using commercial components that were purchased using approximately 60% of the research expenses provided by the fellowship. Some parts were fabricated by the fellow in the machine shop of the host department, either because of their specialized design, or as ultralow-cost alternatives to commercial apparatus. The instrument was completed before the end of the outgoing phase and used for simple “test” experiments to benchmark performance. An invited manuscript of the instrument is in preparation (Rev. Sci. Instrum. 1st author).

In addition to the planned work, some highly productive collaborations were initiated during the project with partners who were unforeseen in the proposal stage – one paper submitted (1st author, Sakellariou group, Saclay France), another in progress (1st author, Vigneron group, UC San Francisco USA). During the period of March-September 2016 the fellow supervised two European master students who came to Berkeley for 6 months. Each of these projects is being prepared as a research paper.

The original project proposal mentioned the use of diamond nitrogen-vacancy sensors for magnetic resonance detection with ultrahigh spatial resolution, to be applied in the imaging of microfluidic channels. This research plan was not pursued due to a lack of available and suitable instrumentation at the outgoing phase institution. Instead effort was focused upon alkali vapor magnetometers.

Expected final results and potential impact
The return host group (Magnetic Resonance Research Center, Cambridge University) has spent the past 5-8 years developing low-field MR methods as one of its main objectives, motivated by applying compressed sensing tools to open up new opportunities for low field measurements. The return phase of ODMR-CHEM will focus on adapting the optical magnetometry techniques to interrogate the chemical behavior of specific systems (WORK PACKAGE 3). Using the ultralow-field NMR instrument developed so far, the expectation is to obtain data on the transport of liquids in multi-phase materials, including liquids inside pores, gels and emulsions, and correlate these with activity. These data will help with the design of more efficient chemical processes.

It is expected that the return phase of the project will lead to collaborative work with the existing industrial partners of the host (including Shell and Johnson Matthey) in the fields of catalysis and reaction monitoring. Academic collaborations established during the outgoing phase (with groups in France, Germany and the USA) should continue. There is opportunity to mature the research and add to the security to this field by employing at least 2 PhD students at the return institution, thus also strengthening academic sector and the profile of this research in the European network. Four publications are presently near submission to peer-reviewed international journals. At least two further publications are planned to disseminate the results gathered during the return phase of the project.

Reported by

THE CHANCELLOR, MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom

Subjects

Life Sciences
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