Indirect Nuclear Spin-spin Coupling Research Articles

Enantiospecificity in NMR enabled by chirality-induced spin selectivity

Spin polarization in chiral molecules is a magnetic molecular response associated with electron transport and enantioselective bond polarization that occurs even in the absence of an external magnetic field. An unexpected finding by Santos and co-workers reported enantiospecific NMR responses in solid-state cross-polarization (CP) experiments, suggesting a possible additional contribution to the indirect nuclear spin-spin coupling in chiral molecules induced by bond polarization in the presence of spin-orbit coupling. Herein we provide a theoretical treatment for this phenomenon, presenting an effective spin-Hamiltonian for helical molecules like DNA and density functional theory (DFT) results on amino acids that confirm the dependence of J-couplings on the choice of enantiomer. The connection between nuclear spin dynamics and chirality could offer insights for molecular sensing and quantum information sciences. These results establish NMR as a potential tool for chiral discrimination without external agents.

Indirect Nuclear Spin-Spin Exchange Coupling through Solvated Electron in Small Sizes of Cyclic and Cage-Shaped Perfluoroalkanes.

Small perfluorocycloalkanes (hexafluorocyclopropane (c-C3 F6 ), octafluorocyclobutane (c-C4 F8 ) and decafluorocyclopentane (c-C5 F10 ) and cage-shaped perfluoroalkanes (perfluoro tetrahedral alkane (C4 F4 ), perfluoro prismane (C6 F6 ) and perfluoro cubane (C8 F8 )) are better electron scavengers. The captured excess electrons are weakly bound inside their backbone voids or over their backbones, forming the solvated electron ( ) systems (e@c-Cn F2n s (n=3, 4, 5) and e@Cn Fn (n=4, 6, 8)). There have been many studies on the structures and properties of such systems. However, the effect of on the indirect nuclear spin-spin coupling (J-coupling) is unknown. In this work, we explore how affects Ne J-coupling between two coupled F nuclei (Ne JFF -coupling) in perfluoroalkane systems through density functional theory calculations. We find unusual trans-Ne JFF -couplings (two coupled F nuclei in trans-position) in e@c-Cn F2n (n=3, 4, 5) and Ne JFF -couplings in e@Cn Fn (n=4, 6, 8). One excess electron not only changes the molecular structures, but also enforces unique distributions and properties, depending on the structural characteristics. We also confirm that such unusual Ne JFF -couplings are realized by through- (T-SE) transmission mechanism, rather than the conventional through-bonds (T-B)/through-space (T-S) ones. The novel transmission mechanism consists of the T-SE coupling path (path 1) and -enhanced T-B T-S coupling path (path 2), and the two paths jointly control Ne JFF through cooperation and competition. Interestingly, the former plays a dominant role for long-range Ne JFF -coupling (N=5), while the latter plays a role in the short-range Ne JFF -coupling (N=3, 4). Path bending angle mainly influences path 1, while path 2 is mainly influenced by the path length. This work not only provides novel insights into the mediating role of in the coupling information exchange, but also proposes a new -based coupling mechanism, possibly opening up potential applications for the -based indirect nuclear spin couplings.

Indirect nuclear spin-spin couplings with third-order contributions added to the SOPPA method.

In this article, a modification of the second-order polarization propagator approximation (SOPPA) method is introduced and illustrated for the calculation of the indirect nuclear spin-spin couplings. The standard SOPPA method, although cheaper in terms of computational cost, offers less accurate results than the ones obtained with coupled cluster methods. A new method, named SOPPA+A3-3, was therefore developed by adding the terms of the third-order A matrix that rely on the second-order double amplitudes. The performance of this third-order contribution was studied using the coupled cluster singles and doubles method as a reference, calculating the spin-spin couplings of molecules of diverse sizes and compositions, and comparing them to the SOPPA method. The results show that inclusion of this third-order contribution gives more accurate results than the standard SOPPA method with a level of accuracy close to that of the coupled cluster method with only a small increase in the computational cost of the response calculation that dominates the computational cost for small- to medium-sized molecules. The implementation of the first contributions to the third-order polarization propagator approximation in the Dalton program, thus, already shows a significant change in these molecular properties over those obtained with the standard SOPPA method.

Distinguishing “Through-Space” from “Through-Bonds” Contribution in Indirect Nuclear Spin–Spin Coupling: General Approaches Applied to Complex JPP and JPSe Scalar Couplings

We present herein two complementary theoretical approaches for analyzing the transmission pathways of indirect nuclear spin-spin couplings in high-resolution nuclear magnetic resonance. This phenomenon is notably conceptually poorly understood in complex experimental situations in which both nonbonded ["through-space" (TS)] and more "classical" bonding ("through-bond") spin-spin coupling pathways are potentially involved. The computational approaches we propose allow the visualization and discussion of individual transmission pathways and estimation of their relative weight from numerical contributions to the spin-spin coupling constant J-value. The first approach is based on the analysis of contributions limited to occupied molecular orbitals [focused on occupied molecular orbitals (FOMO)]. The second approach encompasses the consideration of both occupied and vacant orbitals [global molecular orbital contributions (GMOC)], and, besides the contributions from individual pathways, also considers their cross contributions. Both approaches are applicable to large systems with complex interactions of nuclear magnetic moments. Herein, we have first applied the FOMO and GMOC computational approaches to simple diphosphine models and then extended the analysis to JPP and JPSe experimentally measured in a constrained selenated (diphosphino)naphthalene compound. The new computational tools contributed evidence for the importance of the single lone pair not only from phosphorus but also from selenium in TS spin-spin transmission. It evidenced and modeled for the first time the existence of spin-spin transmission pathways mixing classical covalent bonding parts with a lone pair overlap of proximate heteroatoms (P and Se).

Efficient J‐oriented tin basis sets for the correlated calculations of indirect nuclear spin–spin coupling constants

New J-oriented tin basis sets, acvXz-J (X=2, 3, 4), have been developed at the level of the second-order polarization propagator approximation with the coupled-cluster single and double amplitudes, SOPPA (CCSD), for the purpose of correlated calculations of indirect nuclear spin-spin coupling constants involving tin nucleus. High-quality coupled-cluster calculations of several tin-proton and tin-carbon spin-spin coupling constants, performed with one of the newly developed basis sets, namely, the acv3z-J, taking into account relativistic, solvent, and vibrational corrections showed that the acv3z-J basis set is capable to provide reliable results, as compared with the experimental data.

Molecular parity nonconservation in nuclear spin couplings

The weak interaction does not conserve parity, which is apparent in many nuclear and atomic phenomena. However, thus far, parity nonconservation has not been observed in molecules. Here we consider nuclear-spin-dependent parity nonconserving contributions to the molecular Hamiltonian. These contributions give rise to a parity nonconserving indirect nuclear spin-spin coupling which can be distinguished from parity conserving interactions in molecules of appropriate symmetry, including diatomic molecules. We estimate the magnitude of the coupling, taking into account relativistic corrections. Finally, we propose and simulate an experiment to detect the parity nonconserving coupling using liquid- or gas-state zero-field nuclear magnetic resonance of electrically oriented molecules and show that $^{1}$H$^{19}$F should give signals within the detection limits of current atomic vapor-cell magnetometers.

SCFit: Software for single-crystal NMR analysis. Free vs constrained fitting

The design and implementation of a software package for the analysis of single-crystal NMR data is presented. The SCFit software can treat spectra arising from various interactions: (i) chemical shift tensor only; (ii) chemical shift tensor and quadrupolar coupling tensor; (iii) dipolar and indirect nuclear spin-spin coupling tensors; (iv) all four interactions. The software is demonstrated on recently reported 17O and 31P single-crystal NMR data for triphenylphosphine oxide and for two of its halogen-bonded cocrystals. The 17O single-crystal NMR data represent a case where all four above-mentioned interactions simultaneously affect the spectra. SCFit can fit the chemical shift and quadrupolar coupling in two ways: (i) through an unconstrained fitting process where all tensor parameters are freely optimized or (ii) through a constrained fitting process where the principal components of the tensors may be fixed to values known previously with high precision via the analysis of powder samples. The second strategy is explored in an effort to reduce the number of unknowns in the fitting process; an improvement in the precision of the resulting tensor orientations is noted in some cases.

Hierarchical Basis Sets for the Calculation of Nuclear Magnetic Resonance Spin-Spin Coupling Constants Involving Either Selenium or Tellurium Nuclei.

New basis sets, acvXz-J (X = 2, 3, 4), were designed for tellurium and selenium atoms for the calculation of indirect nuclear spin-spin coupling constants involving selenium or tellurium nuclei. Saturation of angular spaces was performed in an even-tempered manner till achieving the convergence of spin-spin coupling constants under consideration. The high-accuracy correlated SOPPA(CCSD) method was employed in this procedure. Saturated basis sets were contracted by approximately 30% using the coefficients obtained from the atomic self-consistent field (SCF) closed-shell calculations of selenium and tellurium anions, Se2- and Te2-. Final basis sets of acvXz-J showed sufficiently high accuracy in comparison with previous special basis sets.

Single-Crystal NMR Characterization of Halogen Bonds.

Oxygen-17-enriched triphenylphosphine oxide and three of its halogen-bonded cocrystals featuring 1,4-diiodotetrafluorobenzene and 1,3,5-trifluoro-2,4,6-triiodobenzene as halogen bond donors have been characterized by 31P and 17O single-crystal NMR spectroscopy. Single-crystal NMR allows for the measurement of not only the magnitudes of various NMR interaction tensors, but also their orientations relative to the crystal lattice and therefore relative to the halogen bonds themselves. 31P chemical shift tensors, 17O chemical shift tensors, 17O quadrupolar coupling tensors, and 31P-17O indirect nuclear spin-spin (J) coupling tensors are reported here for P═O···I halogen bonds. The angular deviations in the directions of the pseudo-unique components of the 31P chemical shift tensors, the 17O chemical shift tensors, and the 17O quadrupolar coupling tensors from the direction of the oxygen-iodine halogen bond correlate with the deviations in linearity of the P═O···I halogen bond. There is also a clear decrease in anisotropy and an increase in asymmetry of the J(31P,17O) coupling tensors attributable to the formation of iodine-oxygen halogen bonds. The small but quantifiable changes in the tensors are consistent with the weak nature of these halogen bonds relative to the P═O motif. Overall, this work establishes single-crystal NMR as a novel probe of halogen bonds in solids. Analysis of the results has provided insights into the correlations between the magnitude and orientation of various NMR interaction tensors and the local geometry of the halogen bond. Gauge-including projector-augmented wave computations corroborate the experimental findings.

RPA(D) and HRPA(D): Two new models for calculations of NMR indirect nuclear spin-spin coupling constants.

In this article, the RPA(D) and HRPA(D) models for the calculation of linear response functions are presented. The performance of the new RPA(D) and HRPA(D) models is compared to the performance of the established RPA, HRPA, and SOPPA models in calculations of indirect nuclear spin-spin coupling constants using the CCSD model as a reference. The doubles correction offers a significant improvement on both the RPA and HRPA models; however, the improvement is more dramatic in the case of the RPA model. For all coupling types investigated in this study, the results obtained using the HRPA(D) model are comparable in accuracy to those given by the SOPPA model, while requiring between 30% and 90% of the calculation time needed for SOPPA. The RPA(D) model, while of slightly lower accuracy compared to the CCSD model than HRPA(D), offered calculation times of only approximately 25% of those required for SOPPA for all the investigated molecules. © 2018 Wiley Periodicals, Inc.

Relativistic Effect on 1J(M,C) in Me4M, Me3M−, Ph4M, and Ph3M− (M=Pb, Sn, Ge, Si, and/or C): Role of s‐Type Lone Pair Orbitals in the Distinct Effect for the Anionic Species

Indirect one-bond nuclear spin-spin couplings between M and C [1 J(M,C)] in Me4 M, Me3 M- , Ph4 M, and Ph3 M- (M=Pb, Sn, Ge, Si, C) are analyzed with consideration of the relativistic effect and by employing Slater-type basis sets. The evaluated total values 1 JTL (M,C) reproduced the observed values with some systematic calculation errors. Fermi contact terms 1 JFC (M,C) contribute predominantly to 1 JTL (M,C) (≈99 %). A distinct relativistic effect on 1 J(Pb,C) is predicted for Me3 Pb- and Ph3 Pb- . The mechanisms for the distinct effect are elucidated by using the comparison between Me3 Pb- and Me4 Pb as an example. The contributions to 1 JFC (M,C) [or 1 JSD+FC (M,C), where SD denotes the spin-dipolar term] are decomposed into those of occupied orbitals and occupied-to-unoccupied transitions. The s-type lone-pair orbitals are demonstrated to contribute to the distinct relativistic effect on 1 J(Pb,C) of Me3 Pb- (and Ph3 Pb- ). The results are in sharp contrast to the cases of 1 J(M,C) for M atoms lighter than Pb, such as Si, and are explained by the s character of the M-C bonds. This treatment enables visualization and clear recognition the origin of the nuclear couplings for the species exhibiting a relativistic effect.

Calculation of NMR Spin-Spin Coupling Constants in Strychnine.

We compare the NMR indirect nuclear spin-spin coupling constants in strychnine calculated using density functional theory (DFT) with the semiempirical relativistic force field (RFF) method of Kutateladze and Mukhina (KM) (J. Org. Chem. 2015, 80, 10838-10848). DFT values significantly more accurate than those obtained by KM for their comparison with RFF values can be obtained, at a lower cost, by an appropriate selection of basis set.

Computation of indirect nuclear spin-spin couplings with reduced complexity in pure and hybrid density functional approximations.

We present a (sub)linear-scaling algorithm to determine indirect nuclear spin-spin coupling constants at the Hartree-Fock and Kohn-Sham density functional levels of theory. Employing efficient integral algorithms and sparse algebra routines, an overall (sub)linear scaling behavior can be obtained for systems with a non-vanishing HOMO-LUMO gap. Calculations on systems with over 1000 atoms and 20 000 basis functions illustrate the performance and accuracy of our reference implementation. Specifically, we demonstrate that linear algebra dominates the runtime of conventional algorithms for 10 000 basis functions and above. Attainable speedups of our method exceed 6 × in total runtime and 10 × in the linear algebra steps for the tested systems. Furthermore, a convergence study of spin-spin couplings of an aminopyrazole peptide upon inclusion of the water environment is presented: using the new method it is shown that large solvent spheres are necessary to converge spin-spin coupling values.

Relativistic four-component calculations of indirect nuclear spin-spin couplings with efficient evaluation of the exchange-correlation response kernel.

In this work, we report on the development and implementation of a new scheme for efficient calculation of indirect nuclear spin-spin couplings in the framework of four-component matrix Dirac-Kohn-Sham approach termed matrix Dirac-Kohn-Sham restricted magnetic balance resolution of identity for J and K, which takes advantage of the previous restricted magnetic balance formalism and the density fitting approach for the rapid evaluation of density functional theory exchange-correlation response kernels. The new approach is aimed to speedup the bottleneck in the solution of the coupled perturbed equations: evaluation of the matrix elements of the kernel of the exchange-correlation potential. The performance of the new scheme has been tested on a representative set of indirect nuclear spin-spin couplings. The obtained results have been compared with the corresponding results of the reference method with traditional evaluation of the exchange-correlation kernel, i.e., without employing the fitted electron densities. Overall good agreement between both methods was observed, though the new approach tends to give values by about 4%-5% higher than the reference method. On the average, the solution of the coupled perturbed equations with the new scheme is about 8.5 times faster compared to the reference method.

Revisiting NMR through-space J(FF) spin-spin coupling constants for getting insight into proximate F---F interactions.

At present times it is usual practice to mark biological compounds replacing an H for an F atom to study, by means of (19)F NMR spectroscopy, aspects such as binding sites and molecular folding features. This interesting methodology could nicely be improved if it is known how proximity interactions on the F atom affect its electronic structure as gauged through high-resolution (19)F NMR spectroscopy. This is the main aim of the present work and, to this end, differently substituted peri-difluoronaphthalenes are chosen as model systems. In such compounds are rationalized some interesting aspects of the diamagnetic and paramagnetic parts of the (19)F nuclear magnetic shielding tensor as well as the transmission mechanisms for the PSO and FC contributions to (4)JF1F8 indirect nuclear spin-spin coupling constants.

Novel 1,3-dichalcogeno-2-phospholanes with an annelated 1,2-dicarba-closo-dodecaborane(12) Unit

The most efficient strategies for the synthesis of novel 1,3dichalcogeno-2-phospholanes (chalcogen E = O, S, Se, Te) are introduced, starting from 1,2-dicarba-closo-dodecaborane(12) (ortho-carborane), its 1,2-di-lithiated derivative, and various phosphorus halides. The annelation of the phospholane ring with the rigid three-dimensional carborane framework causes markedly different properties when compared with other phospholanes. Most noteworthy are the structural alternatives concerning the orientation of the lone pair of electrons at phosphorus, the instability of Phalides in particular for E = O, and the pronounced tendency for dimerization in the case of P-organo derivatives, which increases from E = Te < Se < S << O. The latter is a consequence of spatial proximity between P-R or electron density at phosphorus and the carborane skeleton. Direct structural evidence is provided for monomers and dimers by single crystal X-ray structural analysis. The solution-state structures follow from consistent sets of multinuclear magnetic resonance data ( 1 H, 11 B, 13 C, 31 P, 77 Se, 125 Te NMR). This is complemented by calculations leading to optimized gas-phase geometries at the B3LYP/6-311+G(d,p) level of theory. Most NMR parameters (chemical shifts δ and indirect nuclear spinspin coupling constants n J) are calculated at the same level of theory. These studies indicate that there are cases, for which important features of the solid-state structures may not be retained in solution.

Calculation of nuclear spin-spin coupling constants using frozen density embedding

We present a method for a subsystem-based calculation of indirect nuclear spin-spin coupling tensors within the framework of current-spin-density-functional theory. Our approach is based on the frozen-density embedding scheme within density-functional theory and extends a previously reported subsystem-based approach for the calculation of nuclear magnetic resonance shielding tensors to magnetic fields which couple not only to orbital but also spin degrees of freedom. This leads to a formulation in which the electron density, the induced paramagnetic current, and the induced spin-magnetization density are calculated separately for the individual subsystems. This is particularly useful for the inclusion of environmental effects in the calculation of nuclear spin-spin coupling constants. Neglecting the induced paramagnetic current and spin-magnetization density in the environment due to the magnetic moments of the coupled nuclei leads to a very efficient method in which the computationally expensive response calculation has to be performed only for the subsystem of interest. We show that this approach leads to very good results for the calculation of solvent-induced shifts of nuclear spin-spin coupling constants in hydrogen-bonded systems. Also for systems with stronger interactions, frozen-density embedding performs remarkably well, given the approximate nature of currently available functionals for the non-additive kinetic energy. As an example we show results for methylmercury halides which exhibit an exceptionally large shift of the one-bond coupling constants between (199)Hg and (13)C upon coordination of dimethylsulfoxide solvent molecules.

First-principles electronic structure study of rhizoferrin and its Fe(III) complexes

We have determined the structure and coordination chemistry of rhizoferrin (Rf), which is a particular type of siderophore, and its Fe(III) complexes using density functional theory calculations. Our results show that the Fe(III) ion binds in an octahedral coordination, with a low-spin (S = 1/2) charge-neutral chiral complex having the largest binding energy of the investigated complexes. We have also calculated nuclear magnetic resonance parameters, such as chemical shifts for (1)H and (13)C, and indirect nuclear spin-spin couplings for (1)H-(1)H and (13)C-(1)H in free Rf and in a low-spin neutral Rf metal complex, as well as nuclear quadrupole interaction parameters, such as asymmetry parameter and nuclear quadrupole coupling constants for (14)N. Our calculated values for the chemical shifts for free Rf are in excellent agreement with experimental data while the calculated NMR parameters for Fe(III) complexes are predictions for future experimental work.

Nuclear magnetic resonance J coupling constant polarizabilities of hydrogen peroxide: A basis set and correlation study

In this article, we present the so far most extended investigation of the calculation of the coupling constant polarizability of a molecule. The components of the coupling constant polarizability are derivatives of the nuclear magnetic resonance (NMR) indirect nuclear spin-spin coupling constant with respect to an external electric field and play an important role for both chiral discrimination and solvation effects on NMR coupling constants. In this study, we illustrate the effects of one-electron basis sets and electron correlation both at the level of density functional theory as well as second-order polarization propagator approximation for the small molecule hydrogen peroxide, which allowed us to perform calculations with the largest available basis sets optimized for the calculation of NMR coupling constants. We find a systematic but rather slow convergence with the one-electron basis set and that augmentation functions are required. We observe also large and nonsystematic correlation effects with significant differences between the density functional and wave function theory methods.

Spin–Spin Artificial DNA Intercalated with Silver Cations: Theoretical Prediction

The indirect nuclear spin-spin coupling constants of Ag(+) cation intercalated between imidazole rings in DNA chains are calculated by means of DFT with relativistic effects taken into account by the use of the zeroth-order regular approximation Hamiltonian (DFT-ZORA). The calculations model how the (1)J((15)N,(109)Ag) coupling constant is affected by different types of geometry deformations and by the presence of water, which is simulated by means of the polarizable continuum model and explicitly present water molecules. Calculations for systems containing two and three imidazole pairs are also carried out to model the influence of stacking interactions. The computed (1)J((15)N,(109)Ag) spin-spin coupling constant is in the range of 85-105 Hz (depending on the computational model) and is in good agreement with the experimental value (ca. 92 Hz). This coupling constant is very little affected by the presence of solvent, stacking interactions, and geometry deformations. Such behavior is explained by visualization of the coupling path by means of coupling energy density (CED). Bigger models allow the coupling constant between two adjacent silver ions to be computed, and give a value of approximately 1 Hz, which is probably too small to be of practical interest. The (2)J((15)N,(15)N) value is calculated to be about 2.5 Hz, and is therefore of measurable magnitude.