Chemical Shift Tensors Research Articles

Intermolecular Interactions in Crystalline Theobromine as Reflected in Electron Deformation Density and (13)C NMR Chemical Shift Tensors.

An understanding of the role of intermolecular interactions in crystal formation is essential to control the generation of diverse crystalline forms which is an important concern for pharmaceutical industry. Very recently, we reported a new approach to interpret the relationships between intermolecular hydrogen bonding, redistribution of electron density in the system, and NMR chemical shifts (Babinský et al. J. Phys. Chem. A, 2013, 117, 497). Here, we employ this approach to characterize a full set of crystal interactions in a sample of anhydrous theobromine as reflected in (13)C NMR chemical shift tensors (CSTs). The important intermolecular contacts are identified by comparing the DFT-calculated NMR CSTs for an isolated theobromine molecule and for clusters composed of several molecules as selected from the available X-ray diffraction data. Furthermore, electron deformation density (EDD) and shielding deformation density (SDD) in the proximity of the nuclei involved in the proposed interactions are calculated and visualized. In addition to the recently reported observations for hydrogen bonding, we focus here particularly on the stacking interactions. Although the principal relations between the EDD and CST for hydrogen bonding (HB) and stacking interactions are similar, the real-space consequences are rather different. Whereas the C-H···X hydrogen bonding influences predominantly and significantly the in-plane principal component of the (13)C CST perpendicular to the HB path and the C═O···H hydrogen bonding modulates both in-plane components of the carbonyl (13)C CST, the stacking modulates the out-of-plane electron density resulting in weak deshielding (2-8 ppm) of both in-plane principal components of the CST and weak shielding (∼ 5 ppm) of the out-of-plane component. The hydrogen-bonding and stacking interactions may add to or subtract from one another to produce total values observed experimentally. On the example of theobromine, we demonstrate the power of this approach to identify and classify the intermolecular forces that govern the packing motifs in crystals and modulate the NMR CSTs.

Advanced Solid-State NMR Approaches for Structure Determination of Membrane Proteins and Amyloid Fibrils

Solid-state NMR (SSNMR) spectroscopy has become an important technique for studying the biophysics and structure biology of proteins. This technique is especially useful for insoluble membrane proteins and amyloid fibrils, which are essential for biological functions and are associated with human diseases. In the past few years, as major contributors to the rapidly advancing discipline of biological SSNMR, we have developed a family of methods for high-resolution structure determination of microcrystalline, fibrous, and membrane proteins. Key developments include order-of-magnitude improvements in sensitivity, resolution, instrument stability, and sample longevity under data collection conditions. These technical advances now enable us to apply new types of 3D and 4D experiments to collect atomic-resolution structural restraints in a site-resolved manner, such as vector angles, chemical shift tensors, and internuclear distances, throughout large proteins. In this Account, we present the technological advances in SSNMR approaches towards protein structure determination. We also describe the application of those methods for large membrane proteins and amyloid fibrils. Particularly, the SSNMR measurements of an integral membrane protein DsbB support the formation of a charge-transfer complex between DsbB and ubiquinone during the disulfide bond transfer pathways. The high-resolution structure of the DsbA-DsbB complex demonstrates that the joint calculation of X-ray and SSNMR restraints for membrane proteins with low-resolution crystal structure is generally applicable. The SSNMR investigations of α-synuclein fibrils from both wild type and familial mutants reveal that the structured regions of α-synuclein fibrils include the early-onset Parkinson's disease mutation sites. These results pave the way to understanding the mechanism of fibrillation in Parkinson's disease.

Chlorosilanes and 3,5‐Dimethylpyrazole: Multinuclear Complexes, Acetonitrile Insertion and 29 Si NMR Chemical‐Shift Anisotropy Studies

The multinuclear silicon complexes [{H2ClSi(μ-pz*)2}2SiH2] (1) and [Cl2Si(μ-pzRR)2SiCl2] (2, R = Me; 3, R = Ph) were formed by the reaction of dichlorosilane (for 1) or hexachlorodisilane with 1-trimethylsilyl-3,5-dimethylpyrazole (for 1 and 2) and the 3,5-diphenyl analogue (for 3). The reaction of trichlorosilane with 3,5-dimethylpyrazole (Hpz*) in MeCN resulted in the formation of two MeCN insertion products of 2 (4, 5). From different samples of synthesis products of this work a preferred hydrolysis product was obtained: [{(μ-pz*)2SiH}3–μ3-O]+Cl– (6). The structural and electronic features of the compounds synthesised in this work were analysed with single-crystal X-ray diffraction and 29Si cross-polarisation (CP)/magic-angle spinning (MAS) NMR spectroscopy combined with quantum chemical computations to investigate their 29Si chemical-shift anisotropy principal tensor components.

The diethyl dithiophosphate complex of tetraphenylantimony(V) and its solvated form, [Sb(C6H5)4{S2P(OC2H5)2}] · 1/2 C6H6: Synthesis, crystal structure, and 13C, 31P CP/MAS NMR study. an example of monodentate coordination of dithio ligands

The O,O′-diethyl dithiophosphate complex of tetraphenylantimony(V) [Sb(C6H5)4{S2P(OC2H5)2}] (I) and its benzene-solvated form I · 1/2C6H6 (II) were synthesized and studied by high-resolution solid-state 13C and 31P NMR (MAS NMR). The diethyl dithiophosphate (Dtph) groups in I and II were quantitatively characterized by the 31P chemical shift anisotropy (δaniso), the asymmetry parameter (η), and the principal values of chemical shift tensors (δxx, δyy, δzz). The calculation of the anisotropy parameters included construction of χ2 statistic diagrams from full 31P MAS NMR spectra. In both complexes, the Dtph groups were found to have mainly axially symmetric 31P chemical shift tensors (for δzz < δxx ≈ δyy) with similar anisotropy parameters (δaniso and η), which is due to their identical S-monodentate function. According to X-ray diffraction data, II has a trigonal bipyramidal (TBP) molecular structure with Smonodentate coordination of Dtph in the TBP axial position and outer-sphere position of the benzene molecule. The desorption of the outer-sphere benzene solvent molecules from structure II, which was noted in MAS NMR experiment, passes through the formation of three intermediate solvated forms with benzene content n < 1/2.

Multidimensional magic angle spinning NMR spectroscopy for site-resolved measurement of proton chemical shift anisotropy in biological solids.

The proton chemical shift (CS) tensor is a sensitive probe of structure and hydrogen bonding. Highly accurate quantum-chemical protocols exist for computation of (1)H magnetic shieldings in the various contexts, making proton chemical shifts potentially a powerful predictor of structural and electronic properties. However, (1)H CS tensors are not yet widely used in protein structure calculation due to scarcity of experimental data. While isotropic proton shifts can be readily measured in proteins even in the solid state, determination of the (1)H chemical shift anisotropy (CSA) tensors remains challenging, particularly in molecules containing multiple proton sites. We present a method for site-resolved measurement of amide proton CSAs in fully protonated solids under magic angle spinning. The approach consists of three concomitant 3D experiments yielding spectra determined by either mainly (1)H CSA, mainly (1)H–(15)N dipolar, or combined (1)H CSA and (1)H–(15)N dipolar interactions. The anisotropic interactions are recoupled using RN-sequences of appropriate symmetry, such as R12(1)(4), and (15)N/(13)C isotropic CS dimensions are introduced via a short selective (1)H–(15)N cross-polarization step. Accurate (1)H chemical shift tensor parameters are extracted by simultaneous fit of the lineshapes recorded in the three spectra. An application of this method is presented for an 89-residue protein, U-(13)C,(15)N-CAP-Gly domain of dynactin. The CSA parameters determined from the triple fits correlate with the hydrogen-bonding distances, and the trends are in excellent agreement with the prior solution NMR results. This approach is generally suited for recording proton CSA parameters in various biological and organic systems, including protein assemblies and nucleic acids.

Observation of a Continuous Random Network Structure in GexSe100–x Glasses: Results from High-Resolution 77Se MATPASS/CPMG NMR Spectroscopy

The coordination environments of Se atoms in binary Ge(x)Se(100-x) glasses with 5 ≤ x ≤ 30 are investigated using a novel, two-dimensional (77)Se nuclear magnetic resonance (NMR) spectroscopic technique. The high-resolution isotropic (77)Se NMR spectra allow for the identification of up to four distinct Se sites in these glasses. The chemical shift tensor parameters for these sites offer unique insights into their local site symmetries and nearest- and next-nearest-neighbor coordination environments. The structural results, when taken together, provide direct evidence in favor of the existence of a randomly connected network of GeSe(4) tetrahedra and Se-Se chain fragments in these glasses.

Interpretation of Crystal Effects on NMR Chemical Shift Tensors: Electron and Shielding Deformation Densities

The relationship between the NMR observables and the supramolecular structure of any system is not straightforward. In this work we examine the influence of the crystal packing for three purine derivatives (hypoxanthine, theobromine, and 6-(2-methoxy)benzylaminopurine) on the principal components of the NMR chemical shift tensors (CSTs). We employ density functional calculations to obtain various molecular properties (the ground-state electron density, the magnitudes and orientations of the components of NMR chemical shift tensor, and the spatial distribution of the isotropic magnetic shielding) for the isolated molecules and for the molecules embedded in supramolecular clusters modeling the crystal environment and evaluate their differences. The concept has enabled us to rationalize the effect of the crystal packing on the NMR CSTs in terms of the redistribution of the ground-state electron density induced by intermolecular interactions in the solid state.

A multinuclear solid state NMR, density functional theory and X-Ray diffraction study of hydrogen bonding in Group I hydrogen dibenzoates

An NMR crystallographic approach incorporating multinuclear solid state NMR (SSNMR), X-ray structure determinations and density functional theory (DFT) are used to characterise the H bonding arrangements in benzoic acid (BZA) and the corresponding Group I alkali metal hydrogen dibenzoates (HD) systems. Since the XRD data often cannot precisely confirm the proton position within the hydrogen bond, the relationship between the experimental SSNMR parameters and the ability of gauge included plane augmented wave (GIPAW) DFT to predict them becomes a powerful constraint that can assist with further structure refinement. Both the 1H and 13C MAS NMR methods provide primary descriptions of the H bonding via accurate measurements of the 1H and 13C isotropic chemical shifts, and the individual 13C chemical shift tensor elements; these are unequivocally corroborated by DFT calculations, which together accurately describe the trend of the H bonding strength as the size of the monovalent cation changes. In addition, 17O MAS and DOR NMR form a powerful combination to characterise the O environments, with the DOR technique providing highly resolved 17O NMR data which helps verify unequivocally the number of inequivalent O positions for the conventional 17O MAS NMR to process. Further multinuclear MAS and static NMR studies involving the quadrupolar 7Li, 39K, 87Rb and 133Cs nuclei, and the associated DFT calculations, provide trends and a corroboration of the H bond geometry which assist in the understanding of these arrangements. Even though the crystallographic H positions in each H bonding arrangement reported from the single crystal X-ray studies are prone to uncertainty, the good corroboration between the measured and DFT calculated chemical shift and quadrupole tensor parameters for the Group I alkali species suggest that these reported H positions are reliable.

Study of the thermal processes in molecular crystals of peptides by means of NMR crystallography

1D and 2D Very Fast Magic Angle Spinning (VF MAS) NMR experiments with sample rotation up to 55 kHz were applied to study both the dihydrate form of Tyr–(D)Ala–Phe–Gly (N-terminal sequence of opioid peptide dermorphin) and the anhydrous form, which was obtained by thermal treatment. Employing both homo-nuclear (1H–1H BABA, 13C–13C SHANGHAI) and hetero-nuclear 2D correlations (1H–13C and 1H–15N) with inverse detection, it was shown that removing water from the crystal lattice of this tetrapeptide does not destroy its subtle pseudo-cyclic structure, and its supramolecular array is preserved. The GIPAW method was employed to compute the geometry of the peptides and calculate the 13C σii principal elements of the NMR shielding tensor parameters and 1H isotropic NMR shifts. The theoretical values of 13C σii were compared with the experimental 13C δii chemical shift tensor values obtained by a 2D PASS experiment. The correlations 13C σii versus δii and 1H σiso versus δiso were used to evaluate the quality of the computational approach. With the new set of coordinates obtained by the GIPAW method, the crystal and molecular structure of the dehydrated Tyr–(D)Ala–Phe–Gly peptide that was obtained by thermal treatment was constructed. Methodology used in this project combining NMR measurements, analysis of X-ray powder diffraction data and advanced quantum mechanical calculations is known as NMR crystallography.

95Mo Solid-State Nuclear Magnetic Resonance Spectroscopy and Quantum Simulations: Synergetic Tools for the Study of Molybdenum Cluster Materials

The ability of (95)Mo solid-state nuclear magnetic resonance (SSNMR) spectroscopy to probe the atomic and electronic structures of inorganic molybdenum cluster materials has been demonstrated for the first time. Six cluster compounds were studied: MoBr(2), Cs(2)Mo(6)Br(14), (Bu(4)N)(2)Mo(6)Br(14), each containing the octahedral Mo(6)Br(14)(2-) cluster unit, and MoS(2)Cl(3), Mo(3)S(7)Cl(4), and MoSCl that contain metallic dimers, trimers, and tetramers, respectively. To overcome inherent difficulties due to the low sensitivity of (95)Mo SSNMR, both high-magnetic-field spectrometers and the quadrupolar Carr-Purcell Meiboom-Gill sensitivity enhancement pulse sequence under magic-angle-spinning conditions, combined with a hyperbolic-secant pulse were used. Experimental measurements as well as characterization of the (95)Mo electric field gradient and chemical shift tensors have been performed with the help of quantum-chemical calculations under periodic boundary conditions using the projector augmented-wave and the gauge-including projector augmented-wave methods, respectively. A large (95)Mo chemical shift range is measured, ∼3150 ppm, and the isotropic chemical shift of the Mo atoms is clearly correlated to their formal oxidation degree in the various clusters. Furthermore, a direct relation is evidenced between the molybdenum quadrupolar coupling constant and the bond lengths with its surrounding ligands. Our results demonstrate the efficiency of the combined use of quantum-chemical calculations and (95)Mo SSNMR experiments to study inorganic molybdenum cluster compounds.

NMR Crystallography Comparative Studies of Chiral (1R,2S,3R,5R)-3-Amino-6,6-dimethylbicyclo[3.1.1]heptan-2-ol and Its p-Toluenesulfonamide Derivative

The crystal structure of (1R,2S,3R,5R)-3-amino-6,6-dimethyl-2-hydroxybicyclo[3.1.1]heptane 1 was determined and it is presented in reference to the structure of (1R,2S,3R,5R)-3-(p-tosylamino)-6,6-dimethyl-2-hydroxybicyclo[3.1.1]heptane 2. 1H and 13C chemical shifts parameters for both structures and for whole unit cells were calculated by using the GIPAW (gauge including projector augmented waves) method. Theoretically calculated chemical shift tensor parameters were verified by 13C CP MAS, 2D PASS, and 13C–1H FSLG HETCOR results to obtain a full structural assignment for 13C and 1H resonances in the solid-state. PISEMA MAS experiment was performed to determine the molecular dynamics of aminoalcohol 1. The comparison of two structures, obtained after all-atom positions optimization after the GIPAW calculations, revealed small conformational differences consistent with the single-crystal X-ray diffaction results.

On the magnetic behavior of spherical aromatic compounds. Insights from the closo-[B12H12]2− cluster through chemical shift tensor maps

We employ density functional methods in order to gain a deeper understanding into the magnetic behavior of the archetypal closo-[B12H12]2− cluster revealing the axis dependence of the spherical aromaticity phenomena through the graphical representation of the induced magnetic field. The analysis of the different components of the through-the-space chemical shift tensor (δij, i,j=x,y,z), given by the anisotropic shielding surface (δaniso) introduced here, allows to recognize anisotropic zones arising from the spherical aromatic behavior in conjunction to the expected isotropic region observed as a sphere of radius 0.6Å confined at the center of the icosahedral cage.

Structural disorder and the effects of aging in a phosphate glass: Results from two-dimensional 31P PASS NMR spectroscopy

The nature of the short-range structural disorder and its dependence on the fictive temperature are investigated in a phosphate glass of composition 60ZnO·40P2O5 using 31P two-dimensional phase adjusted spinning sidebands nuclear magnetic resonance (2D PASS NMR) spectroscopy. The 2D PASS experiment is shown to be a robust method for determining the correlations between the 31P isotropic shift and chemical shift tensor parameters and their distributions in this glass that allows for a remarkably detailed quantification of structural disorder. The spectra in the isotropic dimension indicate a Q-species disproportionation reaction in this glass of the type 2Q1=Q2+Q0 that is driven to the right hand side with increasing fictive temperature. Such a reaction can be a source of configurational entropy as well as a mechanism of Q-species exchange associated with viscous flow in the supercooled liquid. In the anisotropic dimension, the 31P chemical shift anisotropy (CSA) parameters and their distributions are quantified for the constituent Q-species and are found to be sensitive to the thermal history of the glass. Specifically, the span and the asymmetry parameter of the 31P chemical shift tensor decrease with lowering of the fictive temperature implying a concomitant increase in the P site symmetry resulting from the structural relaxation of the network.

Constant time tensor correlation experiments by non-gamma-encoded recoupling pulse sequences

Constant-time tensor correlation under magic-angle spinning conditions is an important technique in solid-state nuclear magnetic resonance spectroscopy for the measurements of backbone or side-chain torsion angles of polypeptides and proteins. We introduce a general method for the design of constant-time tensor correlation experiments under magic-angle spinning. Our method requires that the amplitude of the average Hamiltonian must depend on all the three Euler angles bringing the principal axis system to the rotor-fixed frame, which is commonly referred to as non-gamma encoding. We abbreviate this novel approach as COrrelation of Non-Gamma-Encoded Experiment (CONGEE), which exploits the orientation-dependence of non-gamma-encoded sequences with respect to the magic-angle rotation axis. By manipulating the relative orientation of the average Hamiltonians created by two non-gamma-encoded sequences, one can obtain a modulation of the detected signal, from which the structural information can be extracted when the tensor orientations relative to the molecular frame are known. CONGEE has a prominent feature that the number of rf pulses and the total pulse sequence duration can be maintained to be constant so that for torsion angle determination the effects of systematic errors owing to the experimental imperfections and/or T(2) effects could be minimized. As a proof of concept, we illustrate the utility of CONGEE in the correlation between the C' chemical shift tensor and the C(α)-H(α) dipolar tensor for the backbone psi angle determination. In addition to a detailed theoretical analysis, numerical simulations and experiments measured for [U-(13)C, (15)N]-L-alanine and N-acetyl-[U-(13)C, (15)N]-D,L-valine are used to validate our approach at a spinning frequency of 20 kHz.

Linking 31P Magnetic Shielding Tensors to Crystal Structures: Experimental and Theoretical Studies on Metal(II) Aminotris(methylenephosphonates)

The (31)P chemical shift tensor of the phosphonate group [RC-PO(2)(OH)](-) is investigated with respect to its principal axis values and its orientation in a local coordinate system (LCS) defined from the P atom and the directly coordinated atoms. For this purpose, six crystalline metal aminotris(methylenephosphonates), MAMP·xH(2)O with M = Zn, Mg, Ca, Sr, Ba, and (2Na) and x = 3, 3, 4.5, 0, 0, and 1.5, respectively, were synthesized and identified by diffraction methods. The crystal structure of water-free BaAMP is described here for the first time. The principal components of the (31)P shift tensor were determined from powders by magic-angle-spinning NMR. Peak assignments and orientations of the chemical shift tensors were established by quantum-chemical calculations from first principles using the extended embedded ion method. Structure optimizations of the H-atom positions were necessary to obtain the chemical shift tensors reliably. We show that the (31)P tensor orientation can be predicted within certain error limits from a well-chosen LCS, which reflects the pseudosymmetry of the phosphonate environment.

Protonation state of E71 in KcsA and its role for channel collapse and inactivation

The prototypical prokaryotic potassium channel KcsA alters its pore depending on the ambient potassium; at high potassium, it exists in a conductive form, and at low potassium, it collapses into a nonconductive structure with reduced ion occupancy. We present solid-state NMR studies of KcsA in which we test the hypothesis that an important channel-inactivation process, known as C-type inactivation, proceeds via a state similar to this collapsed state. We test this using an inactivation-resistant mutant E71A, and show that E71A is unable to collapse its pore at both low potassium and low pH, suggesting that the collapsed state is structurally similar to the inactivated state. We also show that E71A has a disordered selectivity filter. Using site-specific K(+) titrations, we detect a local change at E71 that is coupled to channel collapse at low K(+). To gain more insight into this change, we site specifically measure the chemical shift tensors of the side-chain carboxyls of E71 and its hydrogen bond partner D80, and use the tensors to assign protonation states to E71 and D80 at high K(+) and neutral pH. Our measurements show that E71 is protonated at pH 7.5 and must have an unusually perturbed pK(a) (> 7.5) suggesting that the change at E71 is a structural rearrangement rather than a protonation event. The results offer new mechanistic insights into why the widely used mutant KcsA-E71A does not inactivate and establish the ambient K(+) level as a means to populate the inactivated state of KcsA in a controlled way.

Chemical shift tensor determination using magnetically oriented microcrystal array (MOMA): 13C solid-state CP NMR without MAS

Chemical shift tensors for the carboxyl and methyl carbons of l-alanine crystals were determined using a magnetically oriented microcrystal array (MOMA) prepared from a microcrystalline powder sample of l-alanine. A MOMA is a single-crystal-like composite in which microcrystals are aligned three-dimensionally in a matrix resin. The single-crystal rotation method was applied to the MOMA to determine the principal values and axes of the chemical shift tensors. The result showed good agreement with the literature data for the single crystal of l-alanine. This demonstrates that the present technique is a powerful tool for determining the chemical shift tensor of a crystal from a microcrystal powder sample.

Ab initio studies of single-wall carbon nanotube for drug delivery of (N- acetyl-L-cysteinato-O, S) diphenyl tin (IV) anticancer drug

Carbon nanotubes (CNT) have emerged as a new alternative and efficient tool for transporting and translocating therapeutic molecules. CNT can be attached to drugs, and used to deliver their cargos to cells and organs. In this work, the interaction behavior of the anticancer drug Sn(C6H5)2(N-acetyl-L-cysteinate) that is called (N-acetyl-Lcysteinato-O,S) diphenyl tin (IV) when binding single-walled carbon nanotubes was studied based on the Quantum chemicalab initio calculations by using the HF/ (LanL2DZ+STO-3G) and HF/ (LanL2DZ+6-31G) levels in both gas phase and solution. Thermodynamical analysis (large negative values of the ΔG and high positive values of ΔS) confirmed the structural stability of the Sn(C6H5)2(N-acetyl-L-cysteinato-O,S) – CNT in both gas phase and in solution. Also, The thermodynamic analysis show that Sn(C6H5)2(N-acetyl-L-cysteinato-O,S) – CNT has maximum stability in methanol at 313K. Moreover, nuclear magnetic resonance (NMR) parameters such as chemical shift tensor (δ), total atomic charge and asymmetry parameter (η) have been calculated using the Gauge Independent Atomic Orbital (GIAO) method, results being compared with CGST data. From the NMR calculations, it can be seen that the NMR parameters (δ, η) at the sites of nitrogen and oxygen are significantly influenced by intermolecular hydrogen- bonding interactions but the quantity at the site of S-27 is influenced by nonspecific solute-solvent interaction such as polarisability/polarity. Key words: Sn(C6H5)2(N-acetyl-L-cysteinate), ab initio, single wall carbon nanotubes(SWCNT), drug delivery.

Magnetic Response Properties of Coinage Metal Macrocyles. Insights into the Induced Magnetic Field through the Analysis of [Cu5(Mes)5], [Ag4(Mes)4], and [Au5(Mes)5] (Mes = 2,4,6-Me3C6H2)

The complexity of the magnetic response of coinage metal macrocycles supporting closed-shell d10–d10 interaction has been studied through the analysis of [Cu5(Mes)5], [Ag4(Mes)4], and [Au5(Mes)5] (Mes = 2,4,6-Me3C6H2) by means of relativistic DFT methods. Our effort relies on the description of the overall shielding tensor (δ) surrounding the molecular space in terms of its components (δij, i, j = x, y, z) by using chemical shift tensor maps to unravel the magnetic complexity of such molecular arrays. Additionally, the diamagnetic, paramagnetic, and spin–orbit contributions to the through the space chemical shift tensor are depicted for the first time in order to gain more insight into the variation of the magnetic response according to the atomic number (Z) of the metallic core involved. Our results show a strong axis-dependent (orientation-dependent) behavior of the coinage macrocycles indicating that the magneto-responsive properties increase according to Z with the core electrons mainly contributing t...

Survey of the magnetic behavior of [TTF] and [TTF2]2+ from shielding tensor maps

The overall magnetic response of tetrathiafulvalene (TTF) and its dimer dication, namely [TTF2]2+, is investigated using the representation of short- and long-range behavior through shielding tensor maps. In the dimeric dication an enhancing of the response is characterized due to the intermolecular π–π interaction and slightly bonding situation. Additionally, we use the ellipsoidal representation of the shielding tensor at the nucleus (σ) as a useful tool to understand the orientation of the anisotropy (skew parameter) derived from the chemical shift tensor components in the principal-axis-system (PAS) representation. From the anisotropy of the magnetic response in the space can be observed the gain in aromaticity upon oxidation of TTF.