Isotropic Shifts Research Articles

Unravelling of a [High Spin—Low Spin] ↔ [Low Spin—High Spin] Equilibrium in Spin‐Crossover Iron(II) Dinuclear Helicates Using Paramagnetic NMR Spectroscopy

AbstractSpin‐crossover between high‐spin (HS) and low‐spin (LS) states of selected transition metal ions in polynuclear and polymeric compounds is behind their use as multistep switchable materials in breakthrough electronic and spintronic devices. We report the first successful attempt to observe the dynamics of a rarely found broken‐symmetry spin state in binuclear complexes, which mixes the states [HS‐LS] and [LS‐HS] on a millisecond timescale. The slow exchange between these two states, which was identified by paramagnetic NMR spectroscopy in solutions of two spin‐crossover iron(II) binuclear helicates that are amenable to molecular design, opens a path to double quantum dot cellular automata for information storage and processing.

Unravelling of a [High Spin-Low Spin] ↔ [Low Spin-High Spin] Equilibrium in Spin-Crossover Iron(II) Dinuclear Helicates Using Paramagnetic NMR Spectroscopy.

Spin-crossover between high-spin (HS) and low-spin (LS) states of selected transition metal ions in polynuclear and polymeric compounds is behind their use as multistep switchable materials in breakthrough electronic and spintronic devices. We report the first successful attempt to observe the dynamics of a rarely found broken-symmetry spin state in binuclear complexes, which mixes the states [HS-LS] and [LS-HS] on a millisecond timescale. The slow exchange between these two states, which was identified by paramagnetic NMR spectroscopy in solutions of two spin-crossover iron(II) binuclear helicates that are amenable to molecular design, opens a path to double quantum dot cellular automata for information storage and processing.

Solid-State Structural Properties of Alloxazine Determined from Powder XRD Data in Conjunction with DFT-D Calculations and Solid-State NMR Spectroscopy: Unraveling the Tautomeric Identity and Pathways for Tautomeric Interconversion.

We report the solid-state structural properties of alloxazine, a tricyclic ring system found in many biologically important molecules, with structure determination carried out directly from powder X-ray diffraction (XRD) data. As the crystal structures containing the alloxazine and isoalloxazine tautomers both give a high-quality fit to the powder XRD data in Rietveld refinement, other techniques are required to establish the tautomeric form in the solid state. In particular, high-resolution solid-state 15N NMR data support the presence of the alloxazine tautomer, based on comparison between isotropic chemical shifts in the experimental 15N NMR spectrum and the corresponding values calculated for the crystal structures containing the alloxazine and isoalloxazine tautomers. Furthermore, periodic DFT-D calculations at the PBE0-MBD level indicate that the crystal structure containing the alloxazine tautomer has significantly lower energy. We also report computational investigations of the interconversion between the tautomeric forms in the crystal structure via proton transfer along two intermolecular N–H···N hydrogen bonds; DFT-D calculations at the PBE0-MBD level indicate that the tautomeric interconversion is associated with a lower energy transition state for a mechanism involving concerted (rather than sequential) proton transfer along the two hydrogen bonds. However, based on the relative energies of the crystal structures containing the alloxazine and isoalloxazine tautomers, it is estimated that under conditions of thermal equilibrium at ambient temperature, more than 99.9% of the molecules in the crystal structure will exist as the alloxazine tautomer.

Supramolecular structure and spectroscopic characterization of new 1,3,5-triaza-2-boracyclohex-3-en derivative formed under mild conditions between 2-imino-4-thiobiuret and boric acid

Reaction of 2-imino-4-thiobiuret with boric acid (in molar ration of 1:1) in aqueous solution at the mild conditions leads to formation of a heterocyclic compound of 2,2-dihdroxy-4-amino-6-thio-1,3,5-trihydrotriaza-2-boracyclohex-3-en (1). This compound crystallizes directly from the reaction solution after a few days, giving light yellowish transparent monoclinic crystals (P21/n). X-ray single crystal analysis shows that the heteroring and the thio- and amine groups are co-planar, whereas the plane of hydroxyl groups linked to boron are almost perpendicular to plane of the ring. The 2,2-dihdroxy-4-amino-6-thio-1,3,5-trihydrotriaza-2-boracyclohex-3-en molecules are arrangement via O–H...S hydrogen bonds in the stacks along b-axis, and the stacks are interacting each other via N–H...O hydrogen bonds forming a three-dimensional supramolecular architecture. The qualitative and quantitative intermolecular interactions in the crystal were analyzed using the Hirshfeld surface and 2D-fingerprint plots. The compound was also characterised by the FT-IR and Raman spectroscopy. The IR and FT-Raman spectra were made for protiated (1) and its deuterated analogue (1d). The IR and FT-Raman spectra for molecule in the gas-phase were calculated using DFT. DFT calculations and the isotropic frequency shift are helpful in assignments of the vibration bands. The calculated HOMO and LUMO energy gap explain the charge transfer interactions taking place within the molecule.

Lanthanide complexes with polyaminopolycarboxylates as prospective NMR/MRI diagnostic probes: peculiarities of molecular structure, dynamics and paramagnetic properties.

The paramagnetic lanthanide complexes with polyaminopolycarboxylate (PAPC) ligands attract considerable attention from the standpoint of potential applications thereof as relaxation agents used in medical magnetic resonance imaging (MRI) and in luminescent materials, as well as owing to promising use thereof as paramagnetic labels for studying the properties of biopolymers since they exhibit thermodynamic stability, good solubility in aqueous media and moderate toxicity. For the last decades, the NMR methods have been used to determine the physical and chemical properties of paramagnetic Ln compounds. The studies concerning paramagnetic NMR lanthanide-induced shifts (LISs) in dissolved Ln complexes, as well as the analysis of band shape as a function of temperature make it possible to obtain valuable information on the structure, intra- and intermolecular dynamics and paramagnetic properties thereof. This review is devoted solely to the following features: firstly, the processes of intramolecular dynamics of lanthanide complexes with polyamino-polycarboxylate ligands such as DOTA, EDTA and DTPA and their derivatives studied by NMR; secondly, the LISs of lanthanide complexes with EDTA, DOTA, DTPA and some of their derivatives depending on temperature and pH. Moreover, in this review, for the first time, the dependence of the activation energy of molecular dynamics in complexes with polydentate ligands on the atomic number of the lanthanide cation is analyzed and a monotonic change in energy is detected, which is due to the effect of lanthanide contraction. It should be noted that this phenomenon is quite general and may also appear in the future in many other series of lanthanide complexes with both other multidentate ligands and with bidentate and monodentate ligands. In the future, it is possible to predict the dependence of the properties of certain lanthanide complexes on the ionic radius of the lanthanide cation based on the approaches presented in the review. In this review, we have also presented the dynamic NMR as the main research method widely used to analyze the processes of molecular dynamics, and the structural studies based on the NMR relaxation spectroscopy and LIS analysis.

Paramagnetic NMR Shielding Tensors and Ring Currents: Efficient Implementation and Application to Heavy Element Compounds.

We present an efficient implementation of paramagnetic NMR shielding tensors and shifts in a nonrelativistic and scalar-relativistic density functional theory framework. For the latter, we make use of the scalar exact two-component Hamiltonian in its local approximation, and generally we apply the well established (multipole-accelerated) resolution of the identity approximation and the seminumerical exchange approximation. The perturbed density matrix of a paramagnetic NMR shielding calculation is further used to study the magnetically induced current density and ring currents of open-shell systems as illustrated for [U@Bi12]3-. [U@Bi12]3- features delocalized highest occupied molecular orbitals and sustains a net diatropic ring current of ca. 18 nA/T through the Bi12 torus similar to the all-metal aromatic heavy-element cluster [Th@Bi12]4-.

Phase distortion-free paramagnetic NMR spectra

The NMR spectra of paramagnetic substances can feature shifts over thousands of ppm. In high magnetic field instruments, this corresponds to extreme offsets, which make it challenging or impossible to achieve uniform excitation without phase distortion. Furthermore, because of the intrinsic presence of a dead time during which spins freely evolve, a further phase distortion occurs. A decade ago, a processing approach based on the analysis of the statistics of the phase of the spectrum was proposed to denoise NMR spectra. In this manuscript it is demonstrated that this approach is applicable to obtain paramagnetic NMR spectra that are free of phase distortion, even though the quantitative information of peaks intensities is lost. This is demonstrated on the high field spectra of a prototypical nickel(II)-complex and through the analysis of simulated data.

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se-NHC Adducts*.

N-heterocyclic carbene ligands (NHC) are widely utilized in catalysis and material science. They are characterized by their steric and electronic properties. Steric properties are usually quantified on the basis of their static structure, which can be determined by X-ray diffraction. The electronic properties are estimated in the liquid state; for example, via the 77 Se liquid state NMR of Se-NHC adducts. We demonstrate that 77 Se NMR crystallography can contribute to the characterization of the structural and electronic properties of NHC in solid and liquid states. Selected Se-NHC adducts are investigated via 77 Se solid state NMR and X-ray crystallography, supported by quantum chemical calculations. This investigation reveals a correlation between the molecular structure of adducts and NMR parameters, including not only isotropic chemical shifts but also the other chemical shift tensor components. Afterwards, the liquid state 77 Se NMR data is presented and interpreted in terms of the quantum chemistry modelling. The discrepancy between the structural and electronic properties, and in particular the π-accepting abilities of adducts in the solid and liquid states is discussed. Finally, the 13 C isotropic chemical shift from the liquid state NMR and the 13 C tensor components are also discussed, and compared with their 77 Se counterparts. 77 Se NMR crystallography can deliver valuable information about NHC ligands, and together with liquid state 77 Se NMR can provide an in-depth outlook on the properties of NHC ligands.

Evidence for amylose inclusion complexes with multiple acyl chain lipids using solid-state NMR and theoretical approaches

Amylose is known to form inclusion complexes in the presence of hydrophobic guests. Among lipids, only single-chain fatty acids have been reported as possible guests with the surrounding amylose in a well-defined V-helix conformation. Using experimental 13C solid-state NMR, we studied the formation of inclusion complexes between amylose and a variety of multiple-chains lipids of increasing complexity. Molecular dynamics simulations and calculations of 13C isotropic chemical shifts using the Density Functional Theory approach were performed to support the interpretation of experimental spectra. We provide unambiguous evidences that amylose forms inclusion complexes with lipids bearing multiple acyl chains. Amylose conformations around these lipids are characterized by {ϕ,ψ} anomeric bond dihedral angles near {115°,105°}. In the 13C NMR spectra, this translates into C1 and C4 chemical shifts of 102.5 ppm and 81.1 ppm, regardless of the helical conformation of the amylose surrounding the acyl chains.

Rigid, Highly Reactive and Stable DOTA-like Tags Containing a Thiol-Specific Phenylsulfonyl Pyridine Moiety for Protein Modification and NMR Analysis*.

Site specific installation of a paramagnetic ion with magnetic anisotropy in a biomolecule generates valuable structural restraints, such as pseudocontact shifts (PCSs) and residual dipolar couplings (RDCs). These paramagnetic effects can be used to characterize the structures, interactions and dynamics of biological macromolecules and their complexes. Two single-armed DOTA-like tags, BrPSPy-DO3M(S)A-Ln and BrPSPy-6M-DO3M(S)A-Ln, each containing a thiol-specific reacting group, that is, a phenylsulfonyl pyridine moiety, are demonstrated as rigid, reactive and stable paramagnetic tags for protein modification by formation of a reducing resistant thioether bond between the protein and the tag. The two tags present high reactivity with the solvent exposed thiol group in aqueous solution at room temperature. The introduction of Br at the meta-position in pyridine enhances the reactivity of 4-phenylsulfonyl pyridine towards the solvent exposed thiol group in a protein, whereas the ortho-methyl group in pyridine increases the rigidity of the tag in the protein conjugates. The high performance of these two tags has been demonstrated in different cysteine mutants of ubiquitin and GB1. The high reactivity and rigidity of these two tags can be added in the toolbox of paramagnetic tags suitable for the high-resolution NMR measurements of biological macromolecules and their complexes.

Local Structure and Magnetism of La1–xMxPO4 (M = Sm, 239Pu, 241Am) Explained by Experimental and Computational Analyses

With their high chemical and self-irradiation stability, crystalline monazites are among the most promising materials for the encapsulation of nuclear wastes. Yet, the local and magnetic structures of the matrices doped with low-content actinide cation, depicted as most resistant, are still unclear. This limits the development of theoretical approaches predicting their behavior under extreme conditions—self-irradiation and long-term leaching. Here, we characterize the model matrices La1–xMxPO4 (0 ≤ x ≤ 0.10)—with M = Sm, 239Pu, 241Am—by X-ray diffraction and solid-state 31P NMR. As an example, we confirm that La0.96241Am0.04PO4 has higher self-irradiation resistance compared to 241AmPO4. Further, computational analyses show that magnetic properties of the Pu complex are strongly affected by the J-mixing and the paramagnetic NMR shifts are dominated by the Fermi contact contribution, arising from delocalization of the spin density of the cation toward the phosphorus through the bonds.

Failure Rates in Contact versus Non-Contact Athletes Following Arthroscopic Inferior Capsular Shift at 10-Year Follow-Up (237)

Objectives:Arthroscopic Bankart repair has become the surgical procedure of choice for many in the United States, over the Latarjet in Europe, for first time anterior shoulder instability with minimal bone loss, less than 20%. However, high recurrence rates in contact athletes have led many to proceed with open type procedures. Our purpose was to compare failure rates and functional outcomes of the arthroscopic inferior capsular shift in contact and non-contact athletes. We hypothesized that contact and non-contact athletes would exhibit excellent functional outcomes and return to sport with low recurrence rates.Methods:A consecutive series of 69 shoulders in 61 contact and non-contact athletes underwent an arthroscopic inferior capsular shift with ≥3 suture anchors by a single surgeon (1999-2018). Thirty shoulders in 26 contact athletes (6 women; 25.3±8.1 years) and 39 shoulders in 35 non-contact athletes (7 women; 34.8±10.0 years) were included. Inclusion criteria were complete anterior inferior labral detachment (6 unit hours) and ≥2-year follow-up. Exclusion criteria included multidirectional instability, engaging Hill Sachs lesion or glenoid bone loss >30%. A modified 3-portal technique utilizing the outside-in method was employed. A conservative rehabilitation program was followed with return to sport no sooner than 3 months in non-contact, 4-5 months in contact, and 9 months in throwing athletes. Functional outcomes were measured using Constant Scores, American Shoulder and Elbow Surgeons (ASES) Score, Western Ontario Shoulder Instability Index (WOSI), Melbourne Instability Shoulder Scale (MISS), and Rowe. Forward elevation, external rotation at side and 90° abduction and internal rotation range of motion (ROM) were measured. Independent samples t-tests were used to assess differences in outcomes between contact and non-contact athletes (Bonferroni correction: p<0.006).Results:Follow-up was 11.0±3.5 years (range 2-16 years) in contact athletes and 12.2±4.3 years (range 2-21 years) in non-contact athletes (p=0.264). Contact athletes were significantly younger than non-contact athletes (p<0.0001). An average of 3.9±1.7 and 3.1±1.0 suture anchors were used in contact and non-contact groups, respectively (p=0.348). There were no significant differences in post-operative functional scores (all p>0.053) or shoulder ROM (all p>0.034) between groups. Forward flexion was 163.75±16.8° pre-operatively and 168.89±13.0° post-operatively in contact athletes (p=0.212) and 162.5±13.7° preoperatively and 170±7.7° post-operatively in non-contact athletes (p=0.005). External rotation at the side was 59.04±19.4° pre-operatively and 67.9±18.6° value post-operatively in contact athletes (p=0.094) and 52.94±25.1° pre-operatively and 62.83±14.3° post-operatively in non-contact athletes (p=0.062). External rotation at 90° abduction was 92.61±20.1° pre-operatively and 93.39±12.9° post-operatively in contact athletes (p=0.867) and 88.33±21.1° pre-operatively and 87.5±8.1° post-operatively in non-contact athletes (p=0.842).Internal rotation behind the back was to an average of T11 pre-operatively and T9 post-operatively in contact athletes (p=0.004) and L1 pre-operatively and T9 post-operatively in non-contact athletes (p=0.001).In contact and non-contact athletes, respectively, Rowe scores were 65.35±17.6 and 51.25±13.2 preoperatively and 89.22±17.6 and 96.25±12.4 post-operatively (p=0.002 and p<0.001); Constant Scores were 75.69±12.6 and 61.67±11.3 pre-operatively 85.79±19.6 and 89.71±13.6 post-operatively; ASES scores were 80.40±15.3 and 62.14±22.2 pre-operatively and 93.91±9.9 and 86.06±20.7 post-operatively (p<0.001 and p<0.001); MISS scores were 59.36±12.4 and 48.39±15.5 preoperatively and 88.20±13.5 and 75.75±19.7 post-operatively (p<0.001 and p<0.001); WOSI was 3.50±1.3 and 4.55±1.4 pre-operatively and 1.70±3.0 and 2.94±2.7 post-operatively (p=0.101 and p=0.066). Overall recurrence rate was 4.3% (3/69). Two contact athletes (2/30; 6.7%) and one non-contact athlete (1/39; 2.6%) experienced a traumatic recurrent instability event requiring revision surgery (p=0.439). These three patients underwent a revision arthroscopic inferior capsular shift with an additional 3-4 plication sutures and returned to pre-injury sports including hockey, football, skiing, and tennis without recurrence of instability at greater than 7 years following the revision surgery.Conclusions:Modified arthroscopic inferior capsular shift utilizing ≥3 suture anchors with plication sutures returns contact and non-contact athletes to sports with excellent functional outcomes, low recurrence rates (3/69), and full unrestricted ROM. While loss of ROM is a concern, particularly in overhead athletes, ROM was successfully restored in all patients, most notably in external rotation at 90° abduction. We recommend a modified arthroscopic inferior capsular shift with plication sutures as the primary procedure in all athletes with anterior instability with less than 30% bone loss excluding those with high Beighton scores rather than a Latarjet.

Refined Structures of O-Phospho-l-serine and Its Calcium Salt by New Multinuclear Solid-State NMR Crystallography Methods.

O-phospho-l-serine (Pser) and its Ca salt, Ca[O-phospho-l-serine]·H2O (CaPser), play important roles for bone mineralization and were recently also proposed to account for the markedly improved bone-adhesive properties of Pser-doped calcium phosphate-based cements for biomedical implants. However, the hitherto few proposed structural models of Pser and CaPser were obtained by X-ray diffraction, thereby leaving the proton positions poorly defined. Herein, we refine the Pser and CaPser structures by density functional theory (DFT) calculations and contrast them with direct interatomic-distance constraints from two-dimensional (2D) nuclear magnetic resonance (NMR) correlation experimentation at fast magic-angle spinning (MAS), encompassing double-quantum–single-quantum (2Q–1Q) 1H NMR along with heteronuclear 13C{1H} and 31P{1H} correlation NMR experiments. The Pser and CaPser structures before and after refinements by DFT were validated against sets of NMR-derived effective 1H–1H, 1H–31P, and 1H–13C distances, which confirmed the improved accuracy of the refined structures. Each distance set was derived from one sole 2D NMR experiment applied to a powder without isotopic enrichment. The distances were extracted without invoking numerical spin-dynamics simulations or approximate phenomenological models. We highlight the advantages and limitations of the new distance-extraction procedure. Isotropic 1H, 13C, and 31P chemical shifts obtained by DFT calculations using the gauge including projector augmented wave (GIPAW) method agreed very well with the experimental results. We discuss the isotropic and anisotropic 13C and 31P chemical-shift parameters in relation to the previous literature, where most data on CaPser are reported herein for the first time.

Paramagnetic Relaxation Enhancement for Detecting and Characterizing Self-Associations of Intrinsically Disordered Proteins.

Intrinsically disordered proteins and intrinsically disordered regions within proteins make up a large and functionally significant part of the human proteome. The highly flexible nature of these sequences allows them to form weak, long-range, and transient interactions with diverse biomolecular partners. Specific yet low-affinity interactions promote promiscuous binding and enable a single intrinsically disordered segment to interact with a multitude of target sites. Because of the transient nature of these interactions, they can be difficult to characterize by structural biology methods that rely on proteins to form a single, predominant conformation. Paramagnetic relaxation enhancement NMR is a useful tool for identifying and defining the structural underpinning of weak and transient interactions. A detailed protocol for using paramagnetic relaxation enhancement to characterize the lowly-populated encounter complexes that form between intrinsically disordered proteins and their protein, nucleic acid, or other biomolecular partners is described.

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

AbstractWe report an experimental observation of 31P NMR resonances shifted by over 10 000 ppm (meaning percent range, and a new record for solutions), and similar 1H chemical shifts, in an intermediate‐spin square planar ferrous complex [tBu(PNP)Fe‐H], where PNP is a carbazole‐based pincer ligand. Using a combination of electronic structure theory, nuclear magnetic resonance, magnetometry, and terahertz electron paramagnetic resonance, the influence of magnetic anisotropy and zero‐field splitting on the paramagnetic shift and relaxation enhancement is investigated. Detailed spin dynamics simulations indicate that, even with relatively slow electron spin relaxation (T1 ≈10−11 s), it remains possible to observe NMR signals of directly metal‐bonded atoms because pronounced rhombicity in the electron zero‐field splitting reduces nuclear paramagnetic relaxation enhancement.

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts.

We report an experimental observation of 31P NMR resonances shifted by over 10 000 ppm (meaning percent range, and a new record for solutions), and similar 1H chemical shifts, in an intermediate‐spin square planar ferrous complex [ tBu(PNP)Fe‐H], where PNP is a carbazole‐based pincer ligand. Using a combination of electronic structure theory, nuclear magnetic resonance, magnetometry, and terahertz electron paramagnetic resonance, the influence of magnetic anisotropy and zero‐field splitting on the paramagnetic shift and relaxation enhancement is investigated. Detailed spin dynamics simulations indicate that, even with relatively slow electron spin relaxation (T 1 ≈10−11 s), it remains possible to observe NMR signals of directly metal‐bonded atoms because pronounced rhombicity in the electron zero‐field splitting reduces nuclear paramagnetic relaxation enhancement.

Partial Opening of Cytochrome P450cam (CYP101A1) Is Driven by Allostery and Putidaredoxin Binding.

Cytochrome P450cam (CYP101A1) catalyzes the regio- and stereo-specific 5-exo-hydroxylation of camphor via a multistep catalytic cycle that involves two-electron transfer steps, with an absolute requirement that the second electron be donated by the ferrodoxin, putidaredoxin (Pdx). Whether P450cam, once camphor has bound to the active site and the substrate entry channel has closed, opens up upon Pdx binding, during the second electron transfer step, or it remains closed is still a matter of debate. A potential allosteric site for camphor binding has been identified and postulated to play a role in the binding of Pdx. Here, we have revisited paramagnetic NMR spectroscopy data and determined a heterogeneous ensemble of structures that explains the data, provides a complete representation of the P450cam/Pdx complex in solution, and reconciles alternative hypotheses. The allosteric camphor binding site is always present, and the conformational changes induced by camphor binding to this site facilitates Pdx binding. We also determined that the state to which Pdx binds comprises an ensemble of structures that have features of both the open and closed state. These results demonstrate that there is a finely balanced interaction between allosteric camphor binding and the binding of Pdx at high camphor concentrations.

Structure elucidation by Sparkle/RM1, and solution behavior of lanthanideIII complexes: NMR, 4f‒4f absorption spectra and Photoluminescent properties

This paper presents the paramagnetic NMR, 4f‒4f absorption and photoluminescence properties of the complexes of Sm, Eu, Ho and Er with hexafluoroacetylacetone (hfaa) and 1,10‒phenanthroline (phen) in various coordinating and non‒coordinating solvents. The ground state molecular structure of the ternary complexes, [Ln(hfaa)3(phen)](Ln = Ho and Er) and their hydrated parent molecules, [Ln(hfaa)3(H2O)2] were determined using semi‒empirical Sparkle/RM1 method. The optimized structures reflect the effect of lanthanide contraction as the average bond distances [Ln‒O and Ln‒N] decreases on going from Ho to Er. The shape analyses reveal that the geometry of these eight-coordinated complexes is very close to triangular dodecahedron with D2d symmetry. The NMR spectra of the complexes show that the complexes are stable in both coordinating and non‒coordinating solvents. In the 4f‒4f absorption spectra, the solvents’ effect is reflected on the band shape and oscillator strength of the hypersensitive transitions of ternary Ho (5G6 ← 5I8) and Er (2H11/2 ← 4I15/2 and 4G11/2 ← 4I15/2) complexes. These changes suggest solvents influence in changing the symmetry of the field around the Ho and Er ions. The photophysical properties of Sm and Eu complexes are superior in non‒coordinating solvents than those observed in the coordinating solvents .

Intrinsic anisotropy parameters of a series of lanthanoid complexes deliver new insights into the structure-magnetism relationship

Intrinsic anisotropy parameters of a series of lanthanoid complexes deliver new insights into the structure-magnetism relationship

An Examination of Factors Influencing Small Proton Chemical Shift Differences in Nitrogen-Substituted Monodeuterated Methyl Groups

Monodeuterated methyl groups have previously been demonstrated to provide access to long-lived nuclear spin states. This is possible when the CH2D rotamers have sufficiently different populations and the local environment is chiral, which foments a non-negligible isotropic chemical shift difference between the two CH2D protons. In this article, the focus is on the N-CH2D group of N-CH2D-2-methylpiperidine and other suitable CH2D-piperidine derivatives. We used a combined experimental and computational approach to investigate how rotameric symmetry breaking leads to a 1H CH2D chemical shift difference that can subsequently be tuned by a variety of factors such as temperature, acidity and 2-substituted molecular groups.