Based on the current bottlenecks with SSNMR workflows and the gaps between commercial instrumentation and the needs of the community, we propose three highly synergistic and complementary efforts: (A) to make better, more efficient, reliable and rigorous use of spectrometers already in operation; (B) to build better spectrometer components, especially probes and the related spinning, temperature and RF interfacing; and (C) to make data collection more rigorous and reproducible and couple data collection most effectively to analysis procedures described in TR&D3. The explicit goals are to build the world’s best NMR spectrometers at NMRFAM and then to disseminate the technologies to other labs.
Aim 1. Spectrometer configuration and experimental optimizations: to ensure the best possible resolution and sensitivity of each experiment, whether setup by an expert or novice; to produce rigorous measurements over many weeks for series of samples and quantitative analyses; to reduce the amount of instrument time wasted on repeat or unnecessary calibrations; and ultimately to enable complete reproducibility in data collection both with a given spectrometer and probe, but also with other instruments and at facilities in the broader network. Benchmark sub-aims: (1) develop algorithms for automated shimming to 0.01 ppm in under an hour; (2) establish community standards for sensitivity and resolution at 600 to 900 MHz and MAS rates up to 60 kHz; (3) integrate B1 control (amplifier stabilization) into all NMRFAM systems; (4) develop SIMPLEX-based hierarchical optimization of pulse widths, CP conditions, decoupling, soft pulses, special parameters (“BioSolidsPack”).
Aim 2. Probe and spectrometer RF designs: to improve sensitivity especially for 1H and 13C detection, to reduce effects of sample dielectric on performance, to enhance B0 and B1 magnetic field homogeneity, to deliver compatibility with narrow bore 900 MHz and higher (1.1-1.2 GHz) magnets, to enable quadruple resonance for irradiation of 19F, 31P, or 2H simultaneously with 1H, 13C, and 15N, and to stabilize spectrometer performance for back-to-back comparison samples, quantitative series of measurements and long-term reproducibility and rigor. Benchmark sub-aims: (1) achieve 1.6 mm Phoenix NMR HF/X/Y triple resonance performance at 600 and 900 MHz narrow bore (NB) magnets based on 750 MHz wide bore specifications; (2) establish universal sensitivity standards for SSNMR and benchmark at 600, 750 and 900 MHz; (3) design and build quadruple resonance HCDN probes at 600 and 900 MHz; (4) design and build HPCN probes at 600 and 900 MHz; (5) integrate quadruple resonance with pulsed optical photoillumination (TR&D1, DBP1).
Aim 3. Monitoring and controlling long-term data acquisition: to reduce reliance of novice and intermediate users on expert advice during the course of experiments; to establish a set of quantitative decision-making milestones in the course of collecting complex multidimensional SSNMR spectra; to determine optimal end points for signal averaging; to detect when parameters require recalibration (and do so); and to detect deviations from specified performance automatically and localize required maintenance and repair to specific components on the spectrometer. Benchmark sub-aims: (1) develop protocols and specified “NMR scores” for commonly used multidimensional SSNMR experiments; (2) automate evaluation of polarization transfer efficiency and decoupling performance according to best practices (target scoring functions); (3) automatically and continuously monitor sensitivity of crosspeaks in region of interest as a function of signal averaging time (or mixing time or other selected parameters); (4) collect actual RF transmission data to enable retrospective troubleshooting of performance; (5) monitor time-dependent environmental parameters (temperature, RF output, MAS, VT) to identify correlations with NMR performance and identify required improvements; (6) design interfaces to feed data forward to ADAPT-NMR analysis procedures of TR&D3A.
We will target these developments first for Bruker Avance III (currently on 600 and 900 MHz NMRFAM spectrometers for SSNMR) and NEO (future 1.1 GHz and/or other Bruker purchases in 2021-2013), while further extending capabilities for Varian spectrometers being moved from Illinois (600 and 750 MHz InfinityPlus and VNMRS DirectDrive1/2). The majority of the current marketplace is Bruker and so the best means to reach the NMRFAM and broader user communities, but NMRFAM has historically supported spectrometers from all major vendors and will continue to do so moving forward. We envision that: (1) software and workflow technologies will in many cases be immediately used in other labs (Y1); (2) minor spectrometer hardware accessories will be disseminated starting Y2; (3) probe designs shared as published Y2-Y4; and (4) construction of new probes will ramp up Y3 and be in second generation designs by Y5. Towards the end of this funding cycle, we will decide whether to include probe fabrication as a major objective of the next cycle, and/or if a major effort is required to provide open source spectrometers to the NMR community.