----------------------------TEXT FILE-------------------------------------------------------------- * Title: Genetic algorithms and solid state NMR pulse sequences * Authors: Matthias Bechmann Department of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstr. 69, A-4040 Linz, Austria +43 (0)732 2468 1786 matthias.bechmann@jku.at Angelika Sebald, Department of Chemistry, University of York, Heslington, YO10 5DD York, UK +44 (0)1904 324539 angelika.sebald@york.ac.uk John Clark, Department of Computer Science, University of York, Deramore Lane, YO10 5GH York, UK +44 (0)1904 325354 john.clark@cs.york.ac.uk * Corresponding Author: Matthias Bechmann * Abstract of paper: The use of genetic algorithms for the optimisation of magic angle spinning NMR pulse sequences is discussed. The discussion uses as an example the optimisation of the C7 dipolar recoupling pulse sequence, aiming to achieve improved efficiency for spin systems characterised by large chemical shielding anisotropies and/or small dipolar coupling interactions. The optimised pulse sequence is found to be robust over a wide range of parameters, requires only minimal a priori knowledge of the spin system for experimental implementations with buildup rates being solely determined by the magnitude of the dipolar coupling interaction, but is found to be less broadbanded than the original C7 pulse sequence. The optimised pulse sequence breaks the synchronicity between r.f. pulses and sample spinning. * List of criteria (claimed to be) met: (A) (B) (C) (D) (E) (F) (F) (G) * Statement why above stated criteria are met: Nowadays, solid-state NMR plays a crucially important role in structural characterisation of crystalline and non-crystalline materials. In particular, so-called recoupling magic angle spinning (MAS) NMR experiments are prominent as these give access to accurate internuclear distances in a model-free manner. Most of these experiments are developed using an approximative description of the quantum-mechanical spin dynamics called average Hamiltonian theory (AHT) [1] . As a fundamental consequence of this approximation the r.f. pulses and sample rotation (MAS) of the experiment are to be kept synchronised. Another theoretical approach used in this field is Floquet theory [2] This approach does not impose this synchronisation restriction in general, but is exceedingly difficult to operate if this simplification is omitted. In consequence, all MAS NMR pulse sequences designed to date within this approximative framework have in common that, when faced with 'real world' samples / spin systems, they often tend to fail or only work with rather limited efficiency. In this work our genetic-algorithm (GA) did point the way to experiments that are non-rotor synchronised. Non-rotor synchronised experiments have been completely absent from the repertoire of NMR so far. Our work enables the exploitation of a very large range of completely new (tailor-made) MAS NMR experiments for structural characterisation. (A) non-rotorsynchronous multipulse experiments have been non-existent in solid-state NMR and the specific effects of non-rotorsynchronicity have not been exploited and researched so far. (B) our new experiment carries traits of formerly published experiments POST-C7 [3] and C7 [4] which were developed using AHT. However, our experiment offers much improved experimental performance. (C) the results have been published in a peer-reviewed scientific journal (Journal of Magnetic Resonance), publicly available. (D) our results greatly enhance the operational range of solid-state NMR experiments and provide pointers for the future development of new theoretical methods. (E) the suppression of chemical shielding anisotropy has not been better in any other experiment under these experimental conditions. (F) the seminal papers POST-C7 [3] and C7 [4] were immensely influential on the development and success of solid-state NMR over the past two decades. (G) measuring internuclear distances without chemical shielding interference is a long standing issue in solid-state NMR. Our initial results only partially solve the problem because NMR experiments typically require multiple performance criteria to be met at once; however, our GA holds all necessary requirements for extending our research to include multi-objective performance criteria optimisations in the next step. Most likely, the concept of non-synchrounicity can be applied to all types of NMR experiments, opening a completely new school of thought how NMR experiments should best be conducted. References [1] Waugh, J. S. (2007). Average Hamiltonian Theory. In: (Ed.), Encyclopedia of Magnetic Resonance, John Wiley & Sons, Ltd. [2] Leskes, M.; Madhu, P. and Vega, S. (2010). Floquet theory in solid-state nuclear magnetic resonance, Progress in Nuclear Magnetic Resonance Spectroscopy 57 : 345-380. [3] Hohwy, M.; Jakobsen, H. J.; Edén, M.; Levitt, M. H. and Nielsen, N. C. (1998). Broadband dipolar recoupling in the nuclear magnetic resonance of rotating solids: A compensated C7 pulse sequence, The Journal of Chemical Physics 108 : 2686-2694. [4] Lee, Y. K.; Kurur, N. D.; Helmle, M.; Johannessen, O. G.; Nielsen, N. C. and Levitt, M. H. (1995). Efficient dipolar recoupling in the NMR of rotating solids. A sevenfold symmetric radiofrequency pulse sequence, Chemical Physics Letters 242 : 304 - 309. * Full citation of paper: peer-reviewed publication in: Bechmann, M.; Clark, J. & Sebald, A. Genetic algorithms and solid state NMR pulse sequences, Journal of Magnetic Resonance , 2013, 228, 66-75 open access via: Bechmann, M.; Clark, J. & Sebald, A. Genetic algorithms and solid state NMR pulse sequences, arxiv:submit/0729482 * Statement of price money distribution: "any prize money, if any, is to be divided equally among the co-authors" * Statement why best: the method of GA did not only provide better than human-developed experiments but also pointed towards new theoretical work by humans and GA.