Nuclear Dipolar Couplings Research Articles

Nuclear spin polarization and control in hexagonal boron nitride

Electron spins in van der Waals materials are playing a crucial role in recent advances in condensed-matter physics and spintronics. However, nuclear spins in van der Waals materials remain an unexplored quantum resource. Here we report optical polarization and coherent control of nuclear spins in a van der Waals material at room temperature. We use negatively charged boron vacancy ([Formula: see text]) spin defects in hexagonal boron nitride to polarize nearby nitrogen nuclear spins. We observe the Rabi frequency of nuclear spins at the excited-state level anti-crossing of [Formula: see text] defects to be 350 times larger than that of an isolated nucleus, and demonstrate fast coherent control of nuclear spins. Further, we detect strong electron-mediated nuclear-nuclear spin coupling that is five orders of magnitude larger than the direct nuclear-spin dipolar coupling, enabling multi-qubit operations. Our work opens new avenues for the manipulation of nuclear spins in van der Waals materials for quantum information science and technology.

Optically induced nuclear spin–spin couplings in GaAs manifested by spin echo decays under optical pumping

Optically induced nuclear spin–spin coupling in semiconductors is expected to serve for gate operations in nuclear-magnetic-resonance (NMR) quantum computations. However, not much is known about its characteristics. In this study, we investigate optically induced couplings in GaAs via double-resonance spin-echo decay experiments under optical pumping. The squared echo decay rate left( {1/T_2} right)^2 of 71Ga measured under various light powers revealed that optically induced couplings increase with increasing light power, and the sign of heteronuclear couplings between Ga–As pairs is opposite to that of dipolar couplings, which cancel each other out. Under higher light power, the optically induced “controllable” coupling is expected to eventually surpass the “uncontrollable” nuclear dipolar coupling, becoming dominant, which is preferable for the gate operation in NMR quantum computation.

Solid-state NMR and short-range order in crystalline oxides and silicates: a new tool in paramagnetic resonances.

Most applications of high-resolution NMR to questions of short-range order/disorder in inorganic materials have been made in systems where ions with unpaired electron spins are of negligible concentration, with structural information extracted primarily from chemical shifts, quadrupolar coupling parameters, and nuclear dipolar couplings. In some cases, however, the often-large additional resonance shifts caused by interactions between unpaired electron and nuclear spins can provide unique new structural information in materials with contents of paramagnetic cations ranging from hundreds of ppm to several per cent and even higher. In this brief review we focus on recent work on silicate, phosphate, and oxide materials with relatively low concentrations of paramagnetic ions, where spectral resolution can remain high enough to distinguish interactions between NMR-observed nuclides and one or more magnetic neighbors in different bonding configurations in the first, second, and even farther cation shells. We illustrate the types of information available, some of the limitations of this approach, and the great prospects for future experimental and theoretical work in this field. We give examples for the effects of paramagnetic transition metal, lanthanide, and actinide cation substitutions in simple oxides, pyrochlore, zircon, monazite, olivine, garnet, pyrochlores, and olivine structures.

Structural studies of proteins by paramagnetic solid-state NMR spectroscopy

Paramagnetism-based nuclear pseudocontact shifts and spin relaxation enhancements contain a wealth of information in solid-state NMR spectra about electron–nucleus distances on the ∼20Å length scale, far beyond that normally probed through measurements of nuclear dipolar couplings. Such data are especially vital in the context of structural studies of proteins and other biological molecules that suffer from a sparse number of experimentally-accessible atomic distances constraining their three-dimensional fold or intermolecular interactions. This perspective provides a brief overview of the recent developments and applications of paramagnetic magic-angle spinning NMR to biological systems, with primary focus on the investigations of metalloproteins and natively diamagnetic proteins modified with covalent paramagnetic tags.

Distinct solid and solution state self‐assembly pathways of RADA16‐I designer peptide

Solid state NMR measurements on selectively (13) C-labeled RADA16-I peptide (COCH3 -RADARADARADARADA-NH2 ) were used to obtain new molecular level information on the conversion of α-helices to β-sheets through self-assembly in the solid state with increasing temperature. Isotopic labeling at the A4 Cβ site enabled rapid detection of (13) C NMR signals. Heating to 344-363 K with simultaneous NMR detection allowed production of samples with systematic variation of α-helix and β-strand content. These samples were then probed at room temperature for intermolecular (13) C-(13) C nuclear dipolar couplings with the PITHIRDS-CT NMR experiment. The structural transition was also characterized by Fourier transform infrared spectroscopy and wide angle X-ray diffraction. Independence of PITHIRDS-CT decay shapes on overall α-helical and β-strand content infers that β-strands are not observed without association with β-sheets, indicating that β-sheets are formed at elevated temperatures on a timescale that is fast relative to the NMR experiment. PITHIRDS-CT NMR data were compared with results of similar measurements on RADA16-I nanofibers produced by self-assembly in aqueous salt solution. We report that β-sheets formed through self-assembly in the solid state have a structure that differs from those formed through self-assembly in the solution state. Specifically, solid state RADA16-I self-assembly produces in-register parallel β-sheets, whereas nanofibers are composed of stacked parallel β-sheets with registry shifts between adjacent β-strands in each β-sheet. These results provide evidence for environment-dependent self-assembly mechanisms for RADA16-I β-sheets as well as new constraints on solid state self-assembled structures, which must be avoided to maximize solution solubility and nanofiber yields.

Optical switching of nuclear spin–spin couplings in semiconductors

Two-qubit operation is an essential part of quantum computation. However, solid-state nuclear magnetic resonance quantum computing has not been able to fully implement this functionality, because it requires a switchable inter-qubit coupling that controls the time evolutions of entanglements. Nuclear dipolar coupling is beneficial in that it is present whenever nuclear–spin qubits are close to each other, while it complicates two-qubit operation because the qubits must remain decoupled to prevent unwanted couplings. Here we introduce optically controllable internuclear coupling in semiconductors. The coupling strength can be adjusted externally through light power and even allows on/off switching. This feature provides a simple way of switching inter-qubit couplings in semiconductor-based quantum computers. In addition, its long reach compared with nuclear dipolar couplings allows a variety of options for arranging qubits, as they need not be next to each other to secure couplings.

Orientational order in liquid crystals by combiningH2andC13nuclear magnetic resonance spectroscopy and density functional theory calculations

Structural and orientational order properties of the liquid crystal 4,4'-bis-heptyl-azoxybenzene (HAB) have been obtained in its nematic and smectic- A phases by simultaneously analyzing several observables extracted from 2H and 13C nuclear magnetic resonance (NMR) spectra, i.e., 2H quadrupolar, 2H-1H and 13C-2H dipolar couplings, as well as 13C chemical shift anisotropy. 13C experiments required the application of high-resolution solid-state NMR techniques like 1H high-power decoupling and cross polarization, as well as the independent determination of chemical shift tensors by means of density functional theory (DFT) calculations, here performed taking into account the effect of the anisotropic medium by the polarizable continuum model method. The approach, consisting in the simultaneous analysis of all the 2H and 13C experimental data to derive orientational order parameters, and in the use of geometrical parameters determined by DFT methods, allows more detailed and reliable results to be obtained with respect to the traditional approach based on the sole analysis of 2H experiments.

Enantiodiscrimination and extraction of short and long range homo- and hetero-nuclear residual dipolar couplings by a spin selective correlation experiment

A two dimensional correlation experiment for the measurement of short and long range homo- and hetero- nuclear residual dipolar couplings (RDCs) from the broad and featureless proton NMR spectra including 13C satellites is proposed. The method employs a single natural abundant 13C spin as a spy nucleus to probe all the coupled protons and permits the determination of RDCs of negligible strengths. The technique has been demonstrated for the study of organic chiral molecules aligned in chiral liquid crystal, where additional challenge is to unravel the overlapped spectrum of enantiomers. The significant advantage of the method is demonstrated in better chiral discrimination using homonuclear RDCs as additional parameters.

Structure Determination of a Flexible Cyclic Peptide Based on NMR and MD Simulation 3J‐Coupling

Molecular dynamics (MD) simulations, in which experimental values such as nuclear Overhauser effects (NOEs), dipolar couplings, (3)J-coupling constants or crystallographic structure factors are used to bias the values of specific molecular properties towards experimental ones, are often carried out to study the structure refinement of peptides and proteins. However, (3)J-coupling constants are usually not employed because of the multiplicity of torsional angle values (phi) corresponding to each (3)J-coupling constant value. Here, we apply the method of adaptively enforced restraining using a local-elevation (LE) biasing potential energy function in which a memory function penalizes conformations in case both the average <(3)J> and the current (3)J-values deviate from the experimental target value. Then, the molecule is forced to sample other parts of the conformational space, thereby being able to cross high energy barriers and to bring the simulated average <(3)J> close to the measured <(3)J> value. Herein, we show the applicability of this method in structure refinement of a cyclo-beta-tetrapeptide by enforcing the (3)J-value restraining with LE on twelve backbone torsional angles. The resulting structural ensemble satisfies the experimental (3)J-coupling data better than the NMR model structure derived using conventional single-structure refinement based on these data. Thus, application of local-elevation search MD simulation in combination with biasing towards (3)J-coupling makes it possible to use (3)J-couplings quantitatively in structure determination of peptides.

Simultaneous Determination of the Conformation and Relative Configuration of Archazolide A by Using Nuclear Overhauser Effects,J Couplings, and Residual Dipolar Couplings

Simultaneous Determination of the Conformation and Relative Configuration of Archazolide A by Using Nuclear Overhauser Effects,J Couplings, and Residual Dipolar Couplings

Dynamics of electron-nuclear and heteronuclear polarization transfers in optically oriented semi-insulating InP:Fe

Dynamics of the electron-nuclear and heteronuclear polarization-transfer processes in the optically oriented semi-insulating iron-doped indium phosphide were investigated through the characteristic time scales of the processes. (1) In the optical-nuclear-orientation process, we find that the buildup times for $^{31}\mathrm{P}$ and $^{115}\mathrm{In}$ nuclear polarizations are of the same order. From the analysis of the cross-relaxation process between photoexcited electrons and nuclei, it is concluded that electron-nuclear dipolar couplings are responsible for the polarization transfer in this case. This example shows that the nuclear-site dependence of the buildup time can be utilized to identify hyperfine couplings responsible for the process. (2) In the heteronuclear polarization-transfer (cross polarization) process between optically oriented $^{31}\mathrm{P}$ and $^{115}\mathrm{In}$, we find that the cross-relaxation time is rather short; it is an order of magnitude shorter than that expected for nuclear dipolar couplings when a magnetic field is applied parallel to the crystalline [100] axis. From the cross polarization spectral density analysis, it is concluded that a large $J$ coupling of the order of $2\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$ exists between these nuclei and that its angular dependence is not of a simple pseudodipolar type.

Restriction Endonuclease Inhibitor IPI* of Bacteriophage T4: A Novel Structure for a Dedicated Target

Phage T4 protects its DNA from the two-gene-encoded gmrS/gmrD ( glucose- modified hydroxymethylcytosine restriction endonuclease) CT of pathogenic Escherichia coli, CT596, by injecting several hundred copies of the 76-amino-acid-residue nuclease inhibitor, IPI*, into the infected host. Here, the three-dimensional solution structure of mature IPI* is reported as determined by nuclear magnetic resonance techniques using 1290 experimental nuclear Overhauser effect and dipolar coupling constraints (∼ 17 constraints per residue). Close examination of this oblate-shaped protein structure reveals a novel fold consisting of two small β-sheets (β1: B1 and B2; β2: B3–B5) flanked at the N- and C-termini by α-helices (H1 and H2). Such a fold is very compact in shape and allows ejection of IPI* through the narrow 30-Å portal and tail tube apertures of the virion without unfolding. Structural and dynamic measurements identify an exposed hydrophobic knob that is a putative gmrS/gmrD-binding site. A single gene from the uropathogenic E. coli UT189, which codes for a gmrS/gmrD-like UT fusion enzyme (with ∼ 90% identity to the heterodimeric CT enzyme), has evolved IPI* inhibitor immunity. Analysis of the gmrS/gmrD restriction endonuclease enzyme family and its IPI* family phage antagonists reveals an evolutionary pathway that has elaborated a surprisingly diverse and specifically fitted set of coevolving attack and defense structures.

Orientational ordering of linearn-alkanes in silicon nanotubes

Orientational ordering of short and intermediate -alkanes confined to silicon nanotubes has been studied using 1H NMR. The measured residual nuclear dipolar couplings characterizing the degree of molecular ordering were found to depend on the pore size and the molecular length in a complex way. It is inferred from the experimental results that the observed behavior is governed by concomitance of surface and intermolecular interactions as well as the effect of confinement.

Practical NMR relaxation for chemists

Preface. 1. How and Why Nuclei Relax. 1.1. Nucleus in the magnetic field. 1.2. Spin--lattice and spin--spin nuclear relaxation. 1.2.1. Macroscopic magnetization: relaxation times T1 and T2. 1.3. Molecular motions as reason of nuclear relaxation. 1.3.1. Correlation times and activation energies of Molecular Motions. 1.3.2. Isotropic and anisotropic molecular motions. 1.4. Bibliography for Chapter 1. 2. How to Measure the NMR Relaxation Times. 2.1. Exponential and non--exponential nuclear relaxation. 2.2. Measurements of spin--lattice relaxation times. 2.3. Measurements of selective and bi--selective T1 times. 2.4. Determinations of T1( and T2 times. 2.5. Preparation of samples for relaxation experiments. 2.6. Bibliography to Chapter 2. 3. Errors in Determinations of Relaxation Times. 3.1. Instrumental errors. 3.2. Incorrect parameters for T1, T2 measurements and T1, T2 calculations. 3.3 Coupled nuclear relaxation. 3.4. Chemical exchanges. 3.5. Bibliography to Chapter 3. 4. NMR Relaxation by Dipole--Dipole and Quadrupole Interactions. 4.1. The intramolecular dipole--dipole relaxation: homo-- and hetero--nuclear dipolar coupling and the spectral density function. 4.2. Haw to reveal the presence of the dipolar mechanisms. 4.2.1. NOE as a test for dipole--dipole nuclear relaxation. 4.2.2. Evaluations of the dipolar contributions from selective and non--selective T1 times. 4.3. Intermolecular dipole--dipole interactions. 4.4. Electric field gradients at quadrupolar nuclei. 4.5. Nuclear quadrupole coupling constant as a measure of the electric field gradient. 4.6. Quadrupole relaxation. 4.7. Bibliography to Chapter 4. 5. Relaxation by Chemical Shift Anisotropy, Spin--Rotation Relaxation, Scalar Relaxation of the Second Kind and Cross--Mechanisms. 5.1. Relaxation by chemical shift anisotropy. 5.2. Spin--rotation relaxation. 5.3. Interference mechanisms of nuclear relaxation. 5.4. The scalar relaxation of the second kind. 5.5 Bibliography to Chapter 5. 6. Nuclear Relaxation in Molecular Systems with Anisotropic Motions. 6.1. Spin--lattice nuclear relaxation in ellipsoid molecules: Temperature dependences of T1times. 6.2. How to reveal anisotropic molecular motions in solutions. 6.3. Nuclear relaxation in the presence of correlation time distributions. 6.4. Bibliography to Chapter 6. 7. 1H T1 Relaxation Diagnostics in Solutions. 7.1. Revealing weak intermolecular interactions by T1 time measurements in solutions. 7.2. T1 studies of exchanges in simple molecular systems. 7.3. Structural 1H T1 criterion. 7.4. Partially--relaxed NMR spectra. 7.5. Bibliography to Chapter 7. 8. Internuclear Distances from the 1H T1 Relaxation Measurements in Solutions. 8.1. X...H distances: metal -- hydride bond lengths. 8.1.1. How to determine metal--hydride bond lengths by standard 1H T1 measurements. 8.1.2. Metal--hydride bond lengths by 1H T1sel and 1H T1min times measurements. 8.2. Proton--proton distances by standard T1 measurements. 8.3. H--H distances from T1sel / T1bis measurements. 8.4. H--H distances in intermediates. 8.5. Analyzing the errors in 1H T1 determinations of internuclear distances. 8.6. Bibliography to Chapter 8. 9. Deuterium Quadrupole Coupling Constants from 2H T1 Relaxation Measurements in Solutions. 9.1. How to determine DQCC values. 9.2. DQCC values from the 2H T1 times measurements in solutions (fast motional regime). 9.3. DQCC values via 2H T1min measurements in solutions. 9.4. Errors in DQCC determinations. 9. 5. Bibliography to Chapter 9. 10. Spin--Lattice 1H and 2H Relaxation in Mobile Groups. 10.1. 1H T1 times and H--H distances in the presence of fast vibrations and librations. 10.2. 1H T1 times and H--H distances in the presence of fast rotational diffusion. 10.3. The spectral density function for high--amplitude librations. 10.4. 900--jumps in four--fold potential. 10. 5. Deuterium spin--lattice NMR relaxation in mobile molecular fragments. 10.6. Bibliography to Chapter 10. 11. Relaxation of Nuclei Other Than 1H and 2H) and Specific Relaxation Experiments. 11.1. Chemical shift anisotropies and nuclear quadrupole coupling constants from T1 times of heavy nuclei in solutions. 11.2. Multinuclear relaxation approaches to complexation, association and H--bonding. 11.3. Na relaxation in solutions of complex molecular systems. 11. 4. Character of molecular motions from 17O and 2H T1 relaxation in solutions. 11.5. 2D T1 and T1( NMR experiments. 11.6. Chemical exchanges in complex molecular systems from 15N nuclear relaxation in solutions. 11.7. R1/R2 method. 11.8. Cross--correlation relaxation rates and structure of complex molecular systems in solutions. 11.9. Variable -- field relaxation experiments. 11.10. Bibliography to Chapter 11. 12. Paramagnetic NMR Relaxation. 12.1. Theoretical basics of the paramagnetic relaxation enhancement. 12.2. Paramagnetic relaxation rate enhancements in the presence of chemical exchanges. 12.3. Structural applications of paramagnetic relaxation rate enhancements. 12.4. Kinetics of ligand exchanges via paramagnetic relaxation rate enhancements. 12.5. Longitudinal electron relaxation time in paramagnetic centers from variable--high field NMR experiments. Bibliography. Concluding Remarks. Index.

Decoherence of Nuclear Spin Quantum Memory in a Quantum Dot

Recently an ensemble of nuclear spins in a quantum dot have been proposed as a long-lived quantum memory. A quantum state of an electron spin in the dot can be faithfully transfered into nuclear spins through controlled hyperfine coupling. Here we study the decoherence of this memory due to nuclear spin dipolar coupling and inhomogeneous hyperfine interaction during the {\it storage} period. We calculated the maximum fidelity of writing, storing and reading operations. Our results show that nuclear spin dynamics can severely limits the performance of the proposed device for quantum information processing and storage based on nuclear spins.

NMR Studies of Guest Dynamics in Clathrate Hydrates: Spherical Tops SF6, SeF6 and CH4 in Structure II Hydrate

Spin−lattice relaxation time measurements, obtained between 2 and ∼150 K, are presented for 19F in two structure II clathrate hydrates, SF6·17D2O and SeF6·17D2O, as well as for 1H in a double structure II deuteriohydrate of methane and tetrahydrofuran-d8. The 19F results were analyzed in terms of three relaxation mechanisms related to the guest motions, including fluctuations in nuclear dipolar couplings and the anisotropic chemical shift, plus a contribution from spin rotation interactions above ∼50 K. For quantitative agreement, the incorporation of a distribution function into the relaxation equations is required to account for the proton disorder in the hydrate cages, in this case a normal distribution in activation energies. The dynamic parameters derived from relaxation measurements also account for the motional narrowing of the 19F spectra. This is the first instance where a single motional model has accounted for both spectral narrowing and relaxation times for guest dynamics in clathrate hydrates over a wide range of temperatures. The 1H relaxation times, measured for CH4 in the small cages of structure II, are generally consistent with the above model, except that, because of quantum symmetry effects, only intermolecular dipolar couplings appear to be effective in providing relaxation. Trends in activation energies for guest reorientation and the associated distributions, as well as previously published work, are discussed in terms of our understanding of guest dynamics in clathrate hydrates.

The effect of charged axial ligands on the EPR parameters in oxovanadium(IV) compounds: an unusual reduction of the Az (51V) values.

Two series of octahedral oxovanadium(IV) compounds, containing charged or neutral axial ligands, with the tetradentate amidate molecules Hcapca and H2capcah of the general formulae trans-[V(IV)OX(capca)]0/+ (where X = Cl- (1.CH2Cl2), SCN- (2), N3 (3), CH3COO- (4), PhCOO- (5), imidazole (6. CH3NO2), and eta-nBuNH2 (7)) and cis-[V(VI)OX(Hcapcah)]0/+ (where X = Cl- (8.0.5CH2Cl2), SCN (9), N3 (10.2CH3OH), and imidazole (11)), were synthesized and characterized by X-ray crystallography (1.CH3OH,8.CHCl3, 9.2CH3CN, 10.CH3CN and cis-[VO(imidazole)(Hcapcah)+) and continuous-wave electron paramagnetic resonance (cw EPR) spectroscopy. In addition to the synthesis, crystallographic and EPR studies, the optical, infrared and magnetic properties (room temperature) of these compounds are reported. Ab initio calculations were also carried out on compound 8 CHCl3 and revealed that this isomer is more stable than the trans isomer, in good agreement with the experimental data. The cw EPR studies of compounds 1-5, that is, the V(IV)O2+ species containing monoanionic axial ligands, revealed a novel phenomenon of the reduction of their A, components by about 10% relative to the N4 reference compounds ([V(IV)O-(imidazole)4]2+ and [V(IV)O(2,2-bipyridine)2]2+). In marked contrast, such a reduction is not observed in compounds 6. CH3NO2-11, which contain neutral axial ligands. Based on the spin-Hamiltonian formalism a theoretical explanation is put forward according to which the observed reduction of Az is due to a reduction of the electron - nuclear dipolar coupling (P). The present findings bear strong relevance to cw EPR studies of oxovanadium(IV) in vanadoproteins, V(IV)O2+-substituted proteins, and in V(IV)O2+ model compounds, since the hyperfine coupling constant, Az, has been extensively used as a benchmark for identification of equatorial-donor-atom sets in oxovanadium(IV) complexes.

Accurate and rapid docking of protein-protein complexes on the basis of intermolecular nuclear overhauser enhancement data and dipolar couplings by rigid body minimization.

A simple and rapid method is presented for solving the three-dimensional structures of protein-protein complexes in solution on the basis of experimental NMR restraints that provide the requisite translational (i.e., intermolecular nuclear Overhauser enhancement, NOE, data) and orientational (i.e., backbone (1)H-(15)N dipolar couplings and intermolecular NOEs) information. Providing high-resolution structures of the proteins in the unbound state are available and no significant backbone conformational changes occur upon complexation (which can readily be assessed by analysis of dipolar couplings measured on the complex), accurate and rapid docking of the two proteins can be achieved. The method, which is demonstrated for the 40-kDa complex of enzyme I and the histidine phosphocarrier protein, involves the application of rigid body minimization using a target function comprising only three terms, namely experimental NOE-derived intermolecular interproton distance and dipolar coupling restraints, and a simple intermolecular van der Waals repulsion potential. This approach promises to dramatically reduce the amount of time and effort required to solve the structures of protein-protein complexes by NMR, and to extend the capabilities of NMR to larger protein-protein complexes, possibly up to molecular masses of 100 kDa or more.

Lineshape Fitting of Deuterium Magic Angle Spinning Spectra of Paramagnetic Compounds in Slow and Fast Limit Motion Regimes

Deuterium solid-state NMR spectra of paramagnetic compounds can be used to study metal−ligand geometry, spin couplings, and conformational dynamics. We report spinning sideband intensity simulations of temperature-dependent deuterium magic angle spinning spectra of paramagnetic complexes based upon straightforward application of the Herzfeld−Berger type routines. We adopt a point dipole description of the anisotropic hyperfine interaction and utilize an isotropic g tensor. Despite these simplifications, we demonstrate that fine structure constants, including electron−nuclear dipolar coupling and mutual orientation of the dipolar and quadrupolar tensors, can be determined on the basis of the simulations within 0.5 A and 20°, respectively. These simulations have sufficient sensitivity to detect the electron−nuclear dipolar couplings as weak as 5 kHz, which corresponds to the distance between the metal and the deuteron(s) of 3 A for S = 1/2 or 6.5 A for S = 5/2.

Determination of solution structures of paramagnetic proteins by NMR.

Standard procedures for using nuclear Overhauser enhancements (NOE) between protons to generate structures for diamagnetic proteins in solution from NMR data may be supplemented by using dipolar shifts if the protein is paramagnetic. This is advantageous since the electron -nuclear dipolar coupling provides relatively long-range geometric information with respect to the paramagnetic centre which complements the short-range distance constraints NOEs. Several different strategies have been developed to date, but none of these attempts to combine data from NOEs and dipolar shifts in the initial stages of structure calculation or to determine three dimensional protein structures together with their magnetic properties. This work shows that the magnetic and atomic structures are highly correlated and that it is important to have additional constraints both to provide starting parameters for the magnetic properties and to improve the definition of the best fit. Useful parameters can be obtained for haem proteins from Fermi contact shifts; this approach is compared with a new method based on the analysis of dipolar shifts in haem methyl groups with respect to data from horse and tuna ferricytochromes c. The methods developed for using data from NOEs and dipolar shifts have been incorporated in a new computer program, PARADYANA, which is demonstrated in application to a model data set for the sequence of the haem octapeptide known as microperoxidase-8.