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We present the first solid-state NMR experiments developed using optimal control theory. Taking heteronuclear dipolar recoupling in magic-angle-spinning NMR as an example, it proves possible to significantly improve the efficiency of the experiments while introducing robustness toward instrumental imperfections such as radio frequency inhomogeneity. The improvements are demonstrated by numerical simulations as well as practical experiments on a 13Calpha,15N-labeled powder of glycine. The experiments demonstrate a gain of 53% in the efficiency for 15N to 13Calpha coherence transfer relative to the typically double-cross-polarization experiments.

Many applications of magnetic resonance are limited by rapid loss of spin coherence caused by large transverse relaxation rates. In NMR of large proteins, increased relaxation losses lead to poor sensitivity of experiments and increased measurement time. In this article, we develop broadband relaxation-optimized pulse sequences that approach fundamental limits of coherence transfer efficiency in the presence of very general relaxation mechanisms that include cross-correlated relaxation. These broadband transfer schemes use techniques of chemical shift refocusing (specific trajectory adapted refocusing echoes) that are tailored to specific trajectories of coupled spin evolution. We present simulations and experimental data indicating significant enhancement in the sensitivity of multidimensional NMR experiments of large molecules through these methods. The loss of signal because of spin relaxation (1) is a major problem in many practical applications of magnetic resonance. An important application is NMR spectroscopy of proteins (2, 3). Multidimensional coherence transfer experiments in protein NMR are characterized by large transverse relaxation rates. When these relaxation rates become comparable to the spin-spin couplings, the efficiency of coherence transfer is considerably reduced, leading to poor sensitivity and limiting the size of macromolecules that can be analyzed by NMR. Recent advances have made it possible to significantly extend the size limit of biological macromolecules amenable to study by liquidstate NMR (4-7). These techniques take advantage of the phenomenon of cross-correlation or interference between two different relaxation mechanisms (8-13). Until recently, it was not clear whether further improvements could be made and what the physical limit is for the coherence transfer efficiency between coupled spins in the presence of cross-correlated relaxation. In our recent work, using methods from optimal control theory, we derived fundamental limits on the efficiency of polarization transfer in the presence of general relaxation mechanisms (14-16). This work established that state-of-the-art experiments in NMR have the potential for significant improvement. We also provided relaxation-optimized pulse sequences that achieve the theoretical maximum transfer efficiency for a single spin pair. However, to apply these methods to practical NMR experiments, one needs to simultaneously address a family of coupled spin pairs with dispersion in their Larmor frequencies. In the limiting cases where cross-correlation rates are either much smaller or much larger than the spin-spin coupling, modifying the narrowband relaxation-optimized pulses into broadband transfer schemes is straightforward through conventional refocusing techniques. However, in experiments where both coupling and cross-correlation rates are comparable, the use of conventional refocusing methods for making relaxation-optimized sequences broadband significantly reduces the transfer efficiencies as these methods eliminate either the spin-spi...

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We have investigated the use of optimal control theory for the design of improved multiple-quantum excitation schemes for the popular multiple-quantum magic-angle spinning NMR experiment for quadrupolar nuclei with half-integer quadrupolar spin. The advantage of the new low-power experiments, termed OCFASTER, is demonstrated by sensitivity improvements approaching 50% for 87Rb in RbClO4 and RbNO3 as compared to FASTER and standard strong-pulse excitation schemes.

In conventional NMR, samples from works of art in sizes above those considered acceptable in the field of art conservation would have to be removed to place them into the bore of large superconducting magnets. The portable permanent-magnet-based systems, by contrast, can be used in situ to study works of art, in a noninvasive manner. One of these portable NMR systems, NMR-MOUSE(R), measures the information contained in one pixel in an NMR image from a region of about 1 cm(2), which can be as thin as 2-3 microm. With such a high depth resolution, profiles through the structures of art objects can be measured to characterize the materials, the artists' techniques, and the deterioration processes. A novel application of the technique to study a deterioration process and to follow up a conservation treatment is presented in which micrometer-thick oil stains on paper are differentiated and characterized. In this example, the spin-spin relaxation T (2) of the stain is correlated to the iodine number and to the degree of cross-linking of the oil, parameters that are crucial in choosing an appropriate conservation treatment to remove them. It is also shown that the variation of T (2) over the course of treatments with organic solvents can be used to monitor the progress of the conservation interventions. It is expected that unilateral NMR in combination with multivariate data analysis will fill a gap within the set of high-spatial-resolution techniques currently available for the noninvasive analysis of materials in works of art, where procedures to study the inorganic components are currently far more developed than those suitable for the study of the organic components.