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The past decade has demonstrated increasing interests in using optimal control based methods within coherent quantum controllable systems. The versatility of such methods has been demonstrated with particular elegance within nuclear magnetic resonance (NMR) where natural separation between coherent and dissipative spin dynamics processes has enabled coherent quantum control over long periods of time to shape the experiment to almost ideal adoption to the spin system and external manipulations. This has led to new design principles as well as powerful new experimental methods within magnetic resonance imaging, liquid-state and solid-state NMR spectroscopy. For this development to continue and expand, it is crucially important to constantly improve the underlying numerical algorithms to provide numerical solutions which are optimally compatible with implementation on current instrumentation and at same time are numerically stable and offer fast monotonic convergence toward the target. Addressing such aims, we here present a smoothing monotonically convergent algorithm for pulse sequence design in magnetic resonance which with improved optimization stability lead to smooth pulse sequence easier to implement experimentally and potentially understand within the analytical framework of modern NMR spectroscopy. [ABSTRACT FROM AUTHOR]

We present design of novel low-power homonuclear dipolar recoupling experiments for magic-angle-spinning solid-state NMR studies of proteins. The pulse sequences are developed by combining principles of symmetry-based dipolar recoupling and optimal control-based pulse sequence design. The scaffold of the pulse sequences is formed by known CN-type recoupling sequences, while the intrinsic sequence elements are designed using optimal control. This procedure allows for the development of high-performance pulse sequences demanding significantly weaker rf fields than previous symmetry-based pulse sequences while compensating for rf inhomogeneity and providing excitation over relevant ranges of chemical shifts for biological applications. The new recoupling experiments, referred to as optimal control CN (OCCN), are demonstrated numerically and experimentally by two-dimensional (2D) 13C–13C and three-dimensional (3D) 15N–13C–13C chemical shift correlation experiments on uniformly 13C, 15N-labeled ubiquitin. Exploiting the double-quantum, band-selective dipolar recoupling properties of the OCCN experiments, we demonstrate significant sensitivity enhancement for 2D and 3D correlation spectra showing exclusively one- or two-bond correlations. [ABSTRACT FROM AUTHOR]

Optimal control theory has recently been introduced to nuclear magnetic resonance (NMR) spectroscopy as a means to systematically design and optimize pulse sequences for liquid- and solid-state applications. This has so far primarily involved numerical optimization using gradient-based methods, which allow for the optimization of a large number of pulse sequence parameters in a concerted way to maximize the efficiency of transfer between given spin states or shape the nuclear spin Hamiltonian to a particular form, both within a given period of time. Using such tools, a variety of new pulse sequences with improved performance have been developed, and the NMR spin engineers have been challenged to consider alternative routes for analytical experiment design to meet similar performance. In addition, it has lead to increasing demands to the numerical procedures used in the optimization process in terms of computational speed and fast convergence. With the latter aspect in mind, here we introduce an alternative approach to numerical experiment design based on the Krotov formulation of optimal control theory. For practical reasons, the overall radio frequency power delivered to the sample should be minimized to facilitate experimental implementation and avoid excessive sample heating. The presented algorithm makes explicit use of this requirement and iteratively solves the stationary conditions making sure that the maximum of the objective is reached. It is shown that this method is faster per iteration and takes different paths within a control space than gradient-based methods. In the present work, the Krotov approach is demonstrated by the optimization of NMR and dynamic nuclear polarization experiments for various spin systems and using different constraints with respect to radio frequency and microwave power consumption. [ABSTRACT FROM AUTHOR]

The efficiency of dipole-dipole coupling driven coherence transfer experiments in solid-state nuclear magnetic resonance (NMR) spectroscopy of powder samples is limited by dispersion of the orientation of the internuclear vectors relative to the external magnetic field. Here we introduce general design principles and resulting pulse sequences that approach full polarization transfer efficiency for all crystallite orientations in a powder in magic-angle-spinning experiments. The methods compensate for the defocusing of coherence due to orientation dependent dipolar coupling interactions and inhomogeneous radio-frequency fields. The compensation scheme is very simple to implement as a scaffold (comb) of compensating pulses in which the pulse sequence to be improved may be inserted. The degree of compensation can be adjusted and should be balanced as a compromise between efficiency and length of the overall pulse sequence. We show by numerical and experimental data that the presented compensation protocol significantly improves the efficiency of known dipolar recoupling solid-state NMR experiments. [ABSTRACT FROM AUTHOR]

Composite spin-state-selective rotations are introduced. They are devised to remedy the following problem: When determining scalar plus residual dipolar couplings by conventional NMR experiments in partially aligned molecules, a considerable variation in the effective coupling constant often entails systematic errors compromising the accuracy of the measurements. The concept of composite pulses is extended in order to design spin-state-selective composite rotations (S[sup 3]CR) robust to variation in effective coupling constants. With the S[sup 3]CR approach the broadband performance of spin-state-selective excitation improves significantly as is demonstrated both numerically and experimentally. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The fact that membrane proteins are notoriously difficult to analyse using standard protocols for atomic-resolution structure determination methods have motivated adaptation of these techniques to membrane protein studies as well as development of new technologies. With this motivation, liquid-state nuclear magnetic resonance (NMR) has recently been used with success for studies of peptides and membrane proteins in detergent micelles, and solid-state NMR has undergone a tremendous evolution towards characterization of membrane proteins in native membrane and oriented phospholipid bilayers. In this mini-review, we describe some of the technological challenges behind these efforts and provide examples on their use in membrane biology. [ABSTRACT FROM AUTHOR]

Abstract: A computer program for fast and accurate numerical simulation of solid-state NMR experiments is described. The program is designed to emulate a NMR spectrometer by letting the user specify high-level NMR concepts such as spin systems, nuclear spin interactions, RF irradiation, free precession, phase cycling, coherence-order filtering, and implicit/explicit acquisition. These elements are implemented using the Tel scripting language to ensure a minimum of programming overhead and direct interpretation without the need for compilation, while maintaining the flexibility of a full-featured programming language. Basicly, there are no intrinsic limitations to the number of spins, types of interactions, sample conditions (static or spinning, powders, uniaxially oriented molecules, single crystals, or solutions), and the complexity or number of spectral dimensions for the pulse sequence. The applicability ranges from simple ID experiments to advanced multiple-pulse and multiple-dimensional experiments, series of simulations, parameter scans, complex data manipulation/visualization, and iterative fitting of simulated to experimental spectra. A major effort has been devoted to optimizing the computation speed using state-of-the-art algorithms for the time-consuming parts of the calculations implemented in the core of the program using the C programming language. Modification and maintenance of the program are facilitated by releasing the program as open source software (General Public License) currently at http://nmr.imsb.au.dk. The general features of the program are demonstrated by numerical simulations of various aspects for REDOR, rotational resonance, DRAMA, DRAWS, HORROR, C7, TEDOR, POST-C7, CW decoupling, TPPM, F-SLG, SLF, SEMA-CP, PISEMA, RFDR, QCPMG-MAS, and MQ-MAS experiments. [Copyright &y& Elsevier]

Abstract: A new experiment, clean HMBC, is introduced for suppression of strong-coupling induced artifacts in HMBC spectra. The culprits of these artifacts are an inherent shortcoming of low-pass J filters in the presence of strong coupling and the 1H π pulse in the middle of the evolution period aimed at suppressing evolution under heteronuclear J couplings and 1H chemical shifts. A π pulse causes coherence transfer in strongly coupled spin systems and, as is well known in e.g., homonuclear J spectra, this leads to peaks that would not be there in the absence of strong coupling. Similar artifacts occur in HMBC spectra, but they have apparently been overlooked, presumably because they have been assigned to inefficiency of low-pass J filters or not noticed because of a coarse digital resolution in the spectra. Clean HMBC is the HMBC technique of choice for molecules notorious for strong coupling among protons, such as carbohydrates, and the new technique is demonstrated on D-mannose. Finally, a fundamental difference between HMBC and H2BC explains why strong-coupling artifacts are much less of a problem in the latter type of spectra. [Copyright &y& Elsevier]

Abstract: A novel procedure for reconstruction of 2D separated-local-field (SLF) NMR spectra from projections of 1D NMR data is presented. The technique, dubbed SLF projection reconstruction from one-dimensional spectra (SLF-PRODI), is particularly useful for uniaxially oriented membrane protein samples and represents a fast and robust alternative to the popular PISEMA experiment which correlates 1H–15N dipole–dipole couplings with 15N chemical shifts. The different 1D projections in the SLF-PRODI experiment are obtained from 1D spectra recorded under influence of homonuclear decoupling sequences with different scaling factors for the heteronuclear dipolar couplings. We demonstrate experimentally and numerically that as few as 2–4 1D projections will normally be sufficient to reconstruct a 2D SLF-PRODI spectrum with a quality resembling typical PISEMA spectra, leading to significant reduction of the acquisition time. [Copyright &y& Elsevier]

Abstract: We present a historical recollection on the development of the software package SIMPSON (SIMulation Package for SOlid-state Nmr). This covers a brief description of the underlying ideas and events leading to creation of SIMPSON and numerous auxiliary programs as well as comments on its impact on the development and application of solid-state NMR in research laboratories world-wide. [Copyright &y& Elsevier]

We present the use of 2H magic-angle spinning (MAS) NMR on methyl-deuterated α-amino isobutyric acid (Aib) as a new method to obtain fast and accurate structural constraints on peptaibols in membrane-bound environments. Using nonoriented vesicle-reconstituted samples we avoid the delicate preparation of oriented samples, and the use of MAS ensures high sensitivity and thereby very fast acquisition of experimental spectra. Furthermore, given the high content (~40%) of Aib in peptaibols and the fact that the amino acid Aib may be synthesized from cheap starting materials, even in the case of 2H, or 13C, or 15N labeling, this method is ideally suited for studies of the membrane-bound conformation of peptaibols. [ABSTRACT FROM AUTHOR]

Abstract: Novel low-power pulse sequences for homonuclear dipolar recoupling in biological solid-state NMR spectroscopy are presented. The pulse sequences are developed numerically using the Simpson simulation program in combination with optimal control procedures. The quality criteria for the experiment optimizations are the achievement of the highest possible sensitivity for powder samples under typical experimental inhomogeneous radio-frequency (rf) field conditions, while keeping the rf field strength sufficiently low to prevent undesirable sample heating in biological applications. The new dipolar recoupling methods are demonstrated numerically and experimentally by double-quantum filtration magic-angle spinning NMR experiments for which sensitivity gains approaching a factor of 2 is observed. [Copyright &y& Elsevier]

The article demonstrates a new method that may significantly improve the resolution in solid-state nuclear magnetic resonance of oriented membrane proteins by anisotropic differential linebroadening. It demonstrates that significant improvement in the resolution of spectra for inhomogeneously disordered oriented samples may be obtained by recording spectra with homonuclear proton decoupling instead of conventional heteronuclear proton decoupling.