Chemical Shift Tensors Research Articles

QUEST—QUadrupolar Exact SofTware: A fast graphical program for the exact simulation of NMR and NQR spectra for quadrupolar nuclei

We present a new program for the exact simulation of solid-state NMR spectra of quadrupolar nuclei in stationary powdered samples which employs diagonalization of the combined Zeeman-quadrupolar Hamiltonian. The program, which we call QUEST (QUadrupolar Exact SofTware), can simulate NMR spectra over the full regime of Larmor and quadrupolar frequency ratios, which encompasses scenarios ranging from high-field NMR to nuclear quadrupole resonance (NQR, where the Larmor frequency is zero) and does not make use of approximations when treating the quadrupolar interaction. With the use of the fast powder averaging scheme of Alderman, Solum, and Grant [51], exact NMR spectral simulations are only marginally slower than the second-order perturbation theory counterpart. The program, which uses a graphical user interface, also incorporates chemical shift anisotropy and non-coincident chemical shift and quadrupolar tensor frames. The program is validated against newly-acquired experimental data through several examples including: the low-field 79/81Br NMR spectra of CaBr2, the 14N overtone NMR spectrum of glycine, the 187Re NQR spectra of Re2(CO)10, and lastly the 127I overtone NQR spectrum of SrI2, which, to the best of our knowledge, represents the first direct acquisition of an overtone NQR spectrum for a powdered sample.

Solid‐state 11B and 13C NMR, IR, and X‐ray crystallographic characterization of selected arylboronic acids and their catechol cyclic esters

Nine arylboronic acids, seven arylboronic catechol cyclic esters, and two trimeric arylboronic anhydrides (boroxines) are investigated using (11)B solid-state NMR spectroscopy at three different magnetic field strengths (9.4, 11.7, and 21.1 T). Through the analysis of spectra of static and magic-angle spinning samples, the (11)B electric field gradient and chemical shift tensors are determined. The effects of relaxation anisotropy and nutation field strength on the (11)B NMR line shapes are investigated. Infrared spectroscopy was also used to help identify peaks in the NMR spectra as being due to the anhydride form in some of the arylboronic acid samples. Seven new X-ray crystallographic structures are reported. Calculations of the (11)B NMR parameters are performed using cluster model and periodic gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) approaches, and the results are compared with the experimental values. Carbon-13 solid-state NMR experiments and spectral simulations are applied to determine the chemical shifts of the ipso carbons of the samples. One bond indirect (13)C-(11)B spin-spin (J) coupling constants are also measured experimentally and compared with calculated values. The (11)B/(10)B isotope effect on the (13)C chemical shift of the ipso carbons of arylboronic acids and their catechol esters, as well as residual dipolar coupling, is discussed. Overall, this combined X-ray, NMR, IR, and computational study provides valuable new insights into the relationship between NMR parameters and the structure of boronic acids and esters.

A Combined Solid‐State NMR and X‐ray Crystallography Study of the Bromide Ion Environments in Triphenylphosphonium Bromides

Multinuclear ((31)P and (79/81)Br), multifield (9.4, 11.75, and 21.1 T) solid-state nuclear magnetic resonance experiments are performed for seven phosphonium bromides bearing the triphenylphosphonium cation, a molecular scaffold found in many applications in chemistry. This is undertaken to fully characterise their bromine electric field gradient (EFG) tensors, as well as the chemical shift (CS) tensors of both the halogen and the phosphorus nuclei, providing a rare and novel insight into the local electronic environments surrounding them. New crystal structures, obtained from single-crystal X-ray diffraction, are reported for six compounds to aid in the interpretation of the NMR data. Among them is a new structure of BrPPh(4), because the previously reported one was inconsistent with our magnetic resonance data, thereby demonstrating how NMR data of non-standard nuclei can correct or improve X-ray diffraction data. Our results indicate that, despite sizable quadrupolar interactions, (79/81)Br magnetic resonance spectroscopy is a powerful characterisation tool that allows for the differentiation between chemically similar bromine sites, as shown through the range in the characteristic NMR parameters. (35/37)Cl solid-state NMR data, obtained for an analogous phosphonium chloride sample, provide insight into the relationship between unit cell volume, nuclear quadrupolar coupling constants, and Sternheimer antishielding factors. The experimental findings are complemented by gauge-including projector-augmented wave (GIPAW) DFT calculations, which substantiate our experimentally determined strong dependence of the largest component of the bromine CS tensor, δ(11), on the shortest Br-P distance in the crystal structure, a finding that has possible application in the field of NMR crystallography. This trend is explained in terms of Ramsey's theory on paramagnetic shielding. Overall, this work demonstrates how careful NMR studies of underexploited exotic nuclides, such as (79/81)Br, can afford insights into structure and bonding environments in the solid state.

Solid-State NMR Studies of Form I of Atorvastatin Calcium

Solid-state (13)C, (19)F, and (15)N magic angle spinning NMR studies of Form I of atorvastatin calcium are reported, including chemical shift tensors of all resolvable carbon sites and fluorine sites. The complete (13)C and (19)F chemical shift assignments are given based on an extensive analysis of (13)C-(1)H HETCOR and (13)C-(19)F HETCOR results. The solid-state NMR data indicate that the asymmetric unit of this material contains two atorvastatin molecules. A possible structure of Form I of atorvastatin calcium (ATC-I), derived from solid-state NMR data and density functional theory calculations of various structures, is proposed for this important active pharmaceutical ingredient (API).

Computed and Experimental Chemical Shift Parameters for Rigid and Flexible YAF Peptides in the Solid State

DFT methods were employed to compute the (13)C NMR chemical shift tensor (CST) parameters for crystals of YAF peptides (Tyr-Ala-Phe) with different stereochemistry for the Ala residue. Tyr-D-Ala-Phe 1 crystallizes in the C2 space group while Tyr-L-Ala-Phe crystallizes in either the P2(1)2(1)2 space group (2a) or the P6(5) space group (2b). PISEMA MAS measurements for samples with a natural abundance of (1)H and (13)C nuclei and (2)H QUADECHO experiments for samples with deuterium labeled aromatic rings were used to analyze the geometry and time scale of the molecular motion. At ambient temperature, the tyrosine ring of sample 1 is rigid and the phenylalanine ring undergoes a π-jump, both rings in sample 2a are static, and both rings in sample 2b undergo a fast regime exchange. The theoretical values of the CST were obtained for isolated molecules (IM) and clusters employing the ONIOM approach. The experimental (13)C δ(ii) parameters for all of the samples were measured via a 2D PASS sequence. Significant scatter of the computed versus the experimental (13)C CST parameters was observed for 1 and 2b, while the observed correlation was very good for 2a. In this report, we show that the quality of the (13)C σ(ii)/(13)C δ(ii) correlations, when properly interpreted, can be a source of important information about local molecular motions.

Weak Halogen Bonding in Solid Haloanilinium Halides Probed Directly via Chlorine-35, Bromine-81, and Iodine-127 NMR Spectroscopy

A series of monohaloanilinium halides exhibiting weak halogen bonding (XB) has been prepared and characterized by 35Cl, 81Br, and 127I solid-state nuclear magnetic resonance (SSNMR) spectroscopy in magnetic fields of up to 21.1 T. The quadrupolar and chemical shift (CS) tensor parameters for halide ions (Cl–, Br–, I–) which act as electron density donors in the halogen bonds of these compounds are measured to provide insight into the possible relationship between halogen bonding and NMR observables. The NMR data for certain series of related compounds are strongly indicative of when such compounds pack in the same space group, thus providing practical structural information. Careful interpretation of the NMR data in the context of novel and previously available X-ray crystallographic data, and new gauge-including projector-augmented-wave density functional theory (GIPAW DFT) calculations has revealed several notable trends. When a series of related compounds pack in the same space group, it has been possible to interpret trends in the NMR data in terms of the strength of the halogen bond. For example, in isostructural series, the halide quadrupolar coupling constant was found to increase as the halogen bond weakens. In the case of a series of haloanilinium bromides, the 81Br isotropic chemical shift and CS tensor span both decrease as the bromide–halogen XB is weakened. These trends were reproduced using both GIPAW DFT and cluster-model calculations of the bromide ion magnetic shielding tensor. Such trends are particularly exciting given the well-known role that NMR has played historically in the characterization of hydrogen bonding.

Multinuclear Solid-State Nuclear Magnetic Resonance and Density Functional Theory Characterization of Interaction Tensors in Taurine

A variety of experimental solid-state nuclear magnetic resonance (NMR) techniques has been used to characterize each of the elements in 2-aminoethane sulfonic acid (taurine). A combination of (15)N cross-polarization magic angle spinning (CPMAS), (14)N ultrawideline, and (14)N overtone experiments enabled a determination of the relative orientation of the nitrogen electric field gradient and chemical shift tensors. (17)O spectra recorded from an isotopically enriched taurine sample at multiple magnetic fields allowed the three nonequivalent oxygen sites to be distinguished, and NMR parameters calculated from a neutron diffraction structure using density functional theory allowed the assignment of the (17)O parameters to the correct crystallographic sites. This is the first time that a complete set of (17)O NMR tensors are reported for a sulfonate group. In combination with (1)H and (13)C MAS spectra, as well as a previously reported (33)S NMR study, this provides a very broad set of NMR data for this relatively simple organic molecule, making it a potentially useful structure on which to test DFT calculation methods (particularly for the quadrupolar nuclei (14)N, (17)O, and (33)S) or NMR crystallography approaches.

Disentanglement of Heterogeneous Solid-State NMR Parameter Measurements in Model Membranes

Solid-state NMR is ideal for studying membranes and membrane-associated proteins and peptides that are difficult or impossible to study by other means. Disorder and heterogeneity that are typical of these types of samples, however, makes analysis of the resulting challenging. Examples include (a) heterogeneous distributions of 31P chemical shift tensor parameters that report on phospholipid headgroup disorder; and (b) distributions of internuclear distances measured by rotational-echo double-resonance (REDOR), for example, of heteronuclear pairs within membrane-associated peptides. A method that uses an adaptation of Boltzmann statistics maximum entropy for a model-free approach to analysis of this type of troublesome data provides the means to characterize the distributions of such heterogeneous systems.In the case of REDOR data, the method can reveal multiple distances with relatively few data points, which is of particular benefit in application to biological systems where signal lifetimes are limited by relaxation. This has been recently extended to include spin systems for which the observe nucleus is dipolar coupled to two or three dephasing nuclei. The method reverses the practice where preconceived internuclear distance models are slowly optimised to better “fit” experimental REDOR data, and instead provides the information necessary to construct models based on unbiased data analysis. Examples include application to membrane-associated Alzheimer's β peptide. In the case of chemical shift tensor analysis, we have applied the method to arbitrarily complex phospholipid mixtures for analysis of subtle perturbations, for example, by association of antimicrobial peptides with model membrane systems.

Blue and red shift hydrogen bonds in crystalline cobaltocinium complexes

Typical hydrogen-bonded cobaltocinium salts of formula [Cp2Co+][A−] [with Cp = C5H5 and A = PF6 ( 1), AsF6 ( 2), SbF6 ( 3), I ( 4), I3 ( 5), Co(CN)6 ( 6), Co(CO)4 ( 7), Br3 ( 8), FeI4 ( 9) and HCl2 ( 10)] were studied by means of a combined structural, spectroscopic (IR, Raman, solid-state NMR) and theoretical approach. The solid-state vibrational spectra show blue or red shift hydrogen bond behavior depending on the anionic species, i.e. high- or low-frequency ν(CH) shift with respect to the solution value. The crystal structure of the new complex [Cp2Co+][SbF6−], a blue-shifted system, is reported while the [Cp2Co+][I−] complex, a red-shifted system disordered at room temperature, reveals a novel ordered polymorph at 150 K. The weak interactions (C⋯H, H⋯H, H⋯X, C⋯X) between cations and anions were analyzed by means of the Hirshfeld surfaces model, which permits their clear graphic visualization. HS fingerprint plots and normalized contact distances visually describe the difference between blue- and red-shifted complexes. Chemical shift tensors and shielding anisotropy values of the Cp carbon atoms, extracted from 13C CPMAS solid-state NMR spectra, allow the evaluation of Cp rotational motions which are related to the intermolecular contact extent. Finally, a DFT computational model is able to rationalize all the experimental data. It shows that the prevalence of one between two forces, that is, the attractive polarization of C–H bonds and the repulsive effect of electronic clouds, leads to the blue or red shift phenomenon.

Solid-state 17O NMR and computational studies of terminal transition metal oxo compounds

We report solid-state NMR characterization of the 17O (I = 5/2) chemical shift and quadrupole coupling tensors in two terminal oxo compounds, 17O≡Ti(IV)(TMP) and 17O≡Cr(IV)(TMP), in which TMP is 5,10,15,20-tetramesitylporphyrin and the oxo ligand is enriched by 17O (ca. 40%). This is the first time that 17O NMR tensors are determined for this important class of compounds. The 17O nuclei in the O≡Ti and O≡Cr triple bonds are found to exhibit very large chemical shift anisotropies but rather small 17O quadrupole coupling constants. Terminal oxo compounds represent one of the rare cases where the atomic nucleus under study simultaneously experiences a highly anisotropic magnetic shielding environment, but a highly symmetrical electric field distribution. The solid-state 17O NMR data are consistent with solid-state 13C, 15N and 31P NMR results on carbido, nitrido and phosphido compounds. The density functional theory (DFT) computations using the zeroth-order regular approximation (ZORA) to account for spin-orbital relativistic effects reproduce the experimental 17O NMR results reasonably well. DFT computations also reveal the origins at the molecular orbital level of the observed 17O NMR properties for terminal oxo compounds.

Rapid calculation of protein chemical shifts using bond polarization theory and its application to protein structure refinement

Although difficult to analyze, NMR chemical shifts provide detailed information on protein structure. We have adapted the semi-empirical bond polarization theory (BPT) to protein chemical shift calculation and chemical shift driven protein structure refinement. A new parameterization for BPT amide nitrogen chemical shift calculation has been derived from MP2 ab initio calculations and successfully evaluated using crystalline tripeptides. We computed the chemical shifts of the small globular protein ubiquitin, demonstrating that BPT calculations can match the results obtained at the DFT level of theory at very low computational cost. In addition to the calculation of chemical shift tensors, BPT allows the calculation of chemical shift gradients and consequently chemical shift driven geometry optimizations. We applied chemical shift driven protein structure refinement to the conformational analysis of a set of Trypanosoma brucei (the causative agent of African sleeping sickness) tryparedoxin peroxidase Px III structures. We found that the interaction of Px III with its reaction partner Tpx seems to be governed by conformational selection rather than by induced fit.

Investigation of drug delivery on anticancer drug by SWCNT with theoretical studies

The interaction of anticancer drug Sn(CH3)2(N-acetyl-L-cysteinate), that is called (N-acetyl-L-cysteinato-O,S) dimethyl tin(IV), with single walled carbon nanotube (SWCNT) is investigated by Quantum chemical ab initio calculations at HF/(LanL2DZ+STO-3G) and HF/(LanL2DZ+6-31G) levels in gas phase and solution. The solvent effect is taken into account via the self-consistent reaction field (SCRF) method. Carbon nanotubes can act as a suitable drug delivery vehicle for internalization, transportation and translocation of Sn(CH3)2(N-acetyl-L-cysteinate) within biological systems. Thermodynamical analysis indicates that the relative energies (ΔE), enthalpies (ΔH) and free Gibbs energies (ΔG) are negative for Sn(CH3)2(N-acetyl-L-cysteinate)-CNT system, but the calculated entropies (ΔS) are positive, suggesting thermodynamic favorability for covalent attachment of Sn(CH3)2(N-acetyl-L-cysteinate) into carbon nanotube. Also, the results show that with increasing dielectric constant of solvent, the stability of Sn(CH3)2(N-acetyl-L-cysteinate)-CNT complex decreases. Furthermore, anisotropic chemical shift tensor (Δσ), total atomic charge and asymmetry parameter (η) have been calculated using the gauge-including atomic orbital (GIAO) method, results being compared with CGST data. From the nuclear magnetic resonance (NMR) calculations, it can be seen that the NMR (Δσ, η) parameters at the sites of nitrogen and oxygen, as well as C-2 and C-3 nuclei 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(CH3)2(N-acetyl-L-cysteinate), nuclear magnetic resonance (NMR) parameters, single walled nanotube (SWNT), solvent.

Solid state NMR studies of oligourea foldamers: Interaction of 15N-labelled amphiphilic helices with oriented lipid membranes

Synthetic oligomers that are derived from natural polypeptide sequences, albeit with unnatural building blocks, have attracted considerable interest in mimicking bioactive peptides and proteins. Many of those compounds adopt stable folds in aqueous environments that resemble protein structural elements. Here we have chemically prepared aliphatic oligoureas and labeled them at selected positions with (15)N for structural investigations using solid-state NMR spectroscopy. In the first step, the main tensor elements and the molecular alignment of the (15)N chemical shift tensor were analyzed. This was possible by using a two-dimensional heteronuclear chemical shift/dipolar coupling correlation experiment on a model compound that represents the chemical, and thereby also the chemical shift characteristics, of the urea bond. In the next step (15)N labeled versions of an amphipathic oligourea, that exert potent antimicrobial activities and that adopt stable helical structures in aqueous environments, were prepared. These compounds were reconstituted into oriented phospholipid bilayers and the (15)N chemical shift and (1)H-(15)N dipolar couplings of two labeled sites were determined by solid-state NMR spectroscopy. The data are indicative of an alignment of this helix parallel to the membrane surface in excellent agreement with the amphipathic character of the foldamer and consistent with previous models explaining the antimicrobial activities of α-peptides.

Behavior of [2.2]paracyclophane in magnetic fields: A survey of the magnetic response properties from chemical shift tensor maps

[2.2]Paracyclophane, is a fascinating compound that consist of two π-stacked benzene rings in parallel planes which are held together by two p-ethyl bridges, where the close proximity of the aromatic rings leads to unique properties and distinctive features. The graphical analysis of each component of the chemical shift tensor ( δ), reveals the magnetic complexity of such entity dominated by both ring current and anisotropic effects. In addition to the enhance magnetic response due to the additive interaction between the magnetic fields generated by the diatropic ring currents on each aromatic ring ( ring current effect). The analysis of the δ xx and δ yy components, reveals the influence of the anisotropic effect from the p-ethyl bridges leading to deshielding regions at the center of [2.2]paracyclophane, which contribute to the anisotropic behavior observed.

Ultrahigh resolution protein structures using NMR chemical shift tensors

NMR chemical shift tensors (CSTs) in proteins, as well as their orientations, represent an important new restraint class for protein structure refinement and determination. Here, we present the first determination of both CST magnitudes and orientations for (13)Cα and (15)N (peptide backbone) groups in a protein, the β1 IgG binding domain of protein G from Streptococcus spp., GB1. Site-specific (13)Cα and (15)N CSTs were measured using synchronously evolved recoupling experiments in which (13)C and (15)N tensors were projected onto the (1)H-(13)C and (1)H-(15)N vectors, respectively, and onto the (15)N-(13)C vector in the case of (13)Cα. The orientations of the (13)Cα CSTs to the (1)H-(13)C and (13)C-(15)N vectors agreed well with the results of ab initio calculations, with an rmsd of approximately 8°. In addition, the measured (15)N tensors exhibited larger reduced anisotropies in α-helical versus β-sheet regions, with very limited variation (18 ± 4°) in the orientation of the z-axis of the (15)N CST with respect to the (1)H-(15)N vector. Incorporation of the (13)Cα CST restraints into structure calculations, in combination with isotropic chemical shifts, transferred echo double resonance (13)C-(15)N distances and vector angle restraints, improved the backbone rmsd to 0.16 Å (PDB ID code 2LGI) and is consistent with existing X-ray structures (0.51 Å agreement with PDB ID code 2QMT). These results demonstrate that chemical shift tensors have considerable utility in protein structure refinement, with the best structures comparable to 1.0-Å crystal structures, based upon empirical metrics such as Ramachandran geometries and χ(1)/χ(2) distributions, providing solid-state NMR with a powerful tool for de novo structure determination.

NMR study of size effects in relaxor PMN nanoparticles

93Nb − NMR line shape and spin–lattice measurements show that microcrystalline PbMg1/3Nb2/3O3 (PMN) powder is dynamically disordered at room temperature, whereas nanocrystalline PMN powder is orientationally frozen out and long-range ordered at room temperature. The dynamical disorder of the microcrystalline powder results in a motional averaging of the anisotropic part of the 93Nb chemical shift tensor and second order quadrupole shift, whereas this averaging is absent in the nanocrystalline powder, resulting in a broader central line and a longer spin–lattice relaxation time. This seems to be the first observation of such size effects in a relaxor.

First-principles calculations of 17O nuclear magnetic resonance chemical shielding in Pb(Zr1/2Ti1/2)O3 and Pb(Mg1/3Nb2/3)O3: Linear dependence on transition-metal/oxygen bond lengths

First-principles density functional theory oxygen chemical shift tensors were calculated for A(B,B′)O3 perovskite alloys Pb(Zr1/2Ti1/2)O3 (PZT) and Pb(Mg1/3Nb2/3)O3 (PMN). Quantum chemistry methods for embedded clusters and the gauge including projector augmented waves (GIPAW) method [C. J. Pickard and F. Mauri, Phys. Rev. B 63, 245101 (2001)]10.1103/PhysRevB.63.245101 for periodic boundary conditions were used. Results from both methods are in good agreement for PZT and prototypical perovskites. PMN results were obtained using only GIPAW. Both isotropic δiso and axial δax chemical shifts were found to vary approximately linearly as a function of the nearest-distance transition-metal/oxygen bond length, rs. Using these results, we argue against Ti clustering in PZT, as conjectured from recent 17O NMR magic-angle-spinning measurements. Our findings indicate that 17O NMR measurements, coupled with first-principles calculations, can be an important probe of local structure in complex perovskite solid solutions.

Calculation of chemical shift anisotropy in proteins

Individual peptide groups in proteins must exhibit some variation in the chemical shift anisotropy (CSA) of their constituent atoms, but not much is known about the extent or origins of this dispersion. Direct spectroscopic measurement of CSA remains technically challenging, and theoretical methods can help to overcome these limitations by estimating shielding tensors for arbitrary structures. Here we use an automated fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach to compute (15)N, (13)C' and (1)H chemical shift tensors for human ubiquitin and the GB1 and GB3 fragments of staphylococcal protein G. The average and range of variation of the anisotropies is in good agreement with experimental estimates from solid-state NMR, and the variation among residues is somewhat smaller than that estimated from solution-state measurements. Hydrogen-bond effects account for much of the variation, both between helix and sheet regions, and within elements of secondary structure, but other effects (including variations in torsion angles) may play a role as well.

The Influence of the Stereochemistry of Alanine Residue on the Solid State Conformation and Crystal Packing of Opioid Peptides Containing d-Ala or l-Ala in Message Domain – XRD and NMR Study

In this work, an X-ray diffraction (XRD) and solid state NMR study of two tetrapeptides with different stereochemistry of alanine residue is presented using Tyr-(D-Ala)-Phe-Gly (1), an N-terminal sequence of opioid peptide dermorphin, and its biologically inactive analog Tyr-(L-Ala)-Phe-Gly (2). Single-crystal XRD proved that 1 crystallized under different conditions from exclusively one structure: a monoclinic crystal with P2(1) space group. In contrast, 2 very easily formed at least three crystallographic modifications, 2a (monoclinic P2(1)), 2b (orthorhombic P2(1)2(1)2) and 2c (tetragonal P4(1)2(1)2). Solid-state NMR spectroscopy was employed to investigate the structure and molecular dynamics of 1, 2a, and 2b. By employing different NMR experiments (dipolar dephasing and PILGRIM) and an analysis of the (13)C principal elements of the chemical shift tensor (CST), it was proven that the main skeleton of tetrapeptides is rigid, whereas significant differences in the molecular motion of the aromatic residues were observed. Comparing current data with those of previous studies (J. Phys. Chem. B2004, 108, 4535-4545 and Cryst. Growth Des. 2009, 9, 4050-4059), it can be assumed that an important preorganization mechanism anticipating the formation of peptide crystals containing D-Ala in sequence is the intramolecular CH-π interaction, which occurs for the amino acid with D stereochemistry. This effect may be responsible for the formation of only one crystallographic form of D-Ala peptides.

A multinuclear solid-state magnetic resonance and GIPAW DFT study of anhydrous calcium chloride and its hydrates

The group 2 metal halides and corresponding metal halide hydrates serve as useful model systems for understanding the relationship between the electric field gradient (EFG) and chemical shift (CS) tensors at the halogen nuclei and the local molecular and electronic structure. Here, we present a 35/37Cl and 43Ca solid-state nuclear magnetic resonance (SSNMR) study of CaCl2. The 35Cl nuclear quadrupole coupling constant, 8.82(8) MHz, and the isotropic chlorine CS, 105(8) ppm (with respect to dilute NaCl(aq)), are different from the values reported previously for this compound, as well as those reported for CaCl2·2H2O. Chlorine-35 SSNMR spectra are also presented for CaCl2·6H2O, and when taken in concert, the SSNMR observations for CaCl2, CaCl2·2H2O, and CaCl2·6H2O clearly demonstrate the sensitivity of the chlorine EFG and CS tensors to the local symmetry and to changes in the hydration state. For example, the value of δiso decreases with increasing hydration. Gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) calculations are used to substantiate the experimental SSNMR findings, to rule out the presence of other hydrates in our samples, to refine the hydrogen positions in CaCl2·2H2O, and to explore the isostructural relationship between CaCl2 and CaBr2. Finally, the 43Ca CS tensor span is measured to be 31(5) ppm for anhydrous CaCl2, which represents only the fifth CS tensor span measurement for calcium.