Nuclear Magnetic Resonance Coupling Constants Research Articles

A local hybrid exchange functional approximation from first principles.

Local hybrid functionals are a more flexible class of density functional approximations, allowing for a position-dependent admixture of exact exchange. This additional flexibility, however, comes with a more involved mathematical form and a more complicated design. A common denominator for previously constructed local hybrid functionals is the usage of thermochemical benchmark data to construct these functionals. Herein, we design a local hybrid functional without relying on benchmark data. Instead, we construct it in a more ab initio manner, following the principles of modern meta-generalized gradient approximations and considering theoretical constraints. To achieve this, we make use of the density matrix expansion and a local mixing function based on an approximate correlation length. The accuracy of the developed density functional approximation is assessed for thermochemistry, excitation energies, polarizabilities, magnetizabilities, nuclear magnetic resonance (NMR) spin-spin coupling constants, NMR shieldings, and shifts, as well as EPR g-tensors and hyperfine coupling constants. Here, the new exchange functional shows a robust performance and is especially well suited for atomization energies, barrier heights, excitation energies, NMR coupling constants, and EPR properties, whereas it loses some ground for the NMR shifts. Therefore, the designed functional is a major step forward for functionals that have been designed from first principles.

NMR Coupling Constants Based on the Bethe–Salpeter Equation in the GW Approximation

We present the first steps to extend the Green's function GW method and the Bethe-Salpeter equation (BSE) to molecular response properties such as nuclear magnetic resonance (NMR) indirect spin-spin coupling constants. We discuss both a nonrelativistic one-component and a quasi-relativistic two-component formalism. The latter describes scalar-relativistic and spin-orbit effects and allows us to study heavy-element systems with reasonable accuracy. Efficiency is maintained by the application of the resolution of the identity approximation throughout. The performance is demonstrated using conventional central processing units (CPUs) and modern graphics processing units (GPUs) for molecules involving several thousand basis functions. Our results show that a large amount of Hartree-Fock exchange is vital to provide a sufficient Kohn-Sham starting point to compute the GW quasi-particle energies. As the GW-BSE approach is generally less accurate for triplet excitations or related properties such as the Fermi-contact interaction, the admixture of the Kohn-Sham correlation kernel through the contracted BSE (cBSE) method improves the results for NMR coupling constants. This leads to remarkable results when combined with the eigenvalue-only self-consistent variant (evGW) and Becke's half and half functional (BH&HLYP) or the CAM-QTP family. The developed methodology is used to calculate the Karplus curve of tin molecules, illustrating its applicability to extended chemically relevant molecules. Here, the GW-cBSE method improves upon the chosen BH&HLYP Kohn-Sham starting points.

Revisiting the structure of Heliannuol L: A computational approach.

Recently, structural elucidation of natural products has undergone a revolution. The combined use of different modern spectroscopic methods has allowed obtaining a complete structural assignment of natural products using small amounts of sample. However, despite the extraordinary ongoing advances in spectroscopy, the mischaracterization of natural products has been and remains a recurrent problem, especially when the substance presents several stereogenic centers. The misinterpretation of nuclear magnetic resonance (NMR) data has resulted in frequent reports addressing structural reassignment. In this context, a great effort has been devoted to developing quantum chemical calculations that simulate NMR parameters accurately, allowing to achieve a more precise spectral interpretation. In this work, we employed a protocol for theoretical calculations of 1 H NMR chemical shifts and coupling constants using density functional theory (DFT), followed by the application of the DP4+ method to revisit the structure of Heliannuol L, a member of the Heliannuol class, isolated from Helianthus annuus. Our results indicate that the originally proposed structure of Heliannuol L needs a stereochemical reassignment, placing the hydroxyl bonded to C10 in the opposite side of the methyl and hydroxyl groups bonded to C7 and C8, respectively.

Concomitant disorder and high-affinity zinc binding in the human zinc- and iron-regulated transport protein 4 intracellular loop.

The human zinc- and iron-regulated transport protein 4 (hZIP4) protein is the major plasma membrane protein responsible for the uptake of zinc in the body, and as such it plays a key role in cellular zinc homeostasis. hZIP4 plasma membrane levels are regulated through post-translational modification of its large, disordered, histidine-rich cytosolic loop (ICL2) in response to intracellular zinc concentrations. Here, structural characteristics of the isolated disordered loop region, both in the absence and presence of zinc, were investigated using nuclear magnetic resonance (NMR) spectroscopy. NMR chemical shifts, coupling constants and temperature coefficients of the apoprotein, are consistent with a random coil with minor propensities for transient polyproline Type II helices and β-strand in regions implicated in post-translational modifications. The ICL2 protein remains disordered upon zinc binding, which induces exchange broadening. Paramagnetic relaxation enhancement experiments reveal that the histidine-rich region in the apoprotein makes transient tertiary contacts with predicted post-translational modification sites. The residue-specific data presented here strengthen the relationship between hZIP4 post-translational modifications, which impact its role in cellular zinc homeostasis, and zinc sensing by the intracellular loop. Furthermore, the zinc sensing mechanism employed by the ICL2 protein demonstrates that high-affinity interactions can occur in the presence of conformational disorder.

Dissection of the Structural Features of a Fungicidal Antibody-Derived Peptide.

The synthetic peptide T11F (TCRVDHRGLTF), derived from the constant region of human IgM antibodies, proved to exert a significant activity in vitro against yeast strains, including multidrug resistant isolates. Alanine substitution of positively charged residues led to a decrease in candidacidal activity. A more dramatic reduction in activity resulted from cysteine replacement. Here, we investigated the conformational properties of T11F and its alanine-substituted derivatives by circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. Peptide interaction with Candida albicans cells was studied by confocal and scanning electron microscopy. T11F and most of its derivatives exhibited CD spectra with a negative band around 200 nm and a weaker positive band around 218 nm suggesting, together with NMR coupling constants, the presence of a polyproline II (PPII) helix, a conformational motif involved in a number of biological functions. Analysis of CD spectra revealed a critical role for phenylalanine in preserving the PPII helix. In fact, only the F11A derivative presented a random coil conformation. Interestingly, the loss of secondary structure influenced the rate of killing, which turned out to be significantly reduced. Overall, the obtained results suggest that the PPII conformation contributes in characterising the cell penetrating and fungicidal properties of the investigated peptides.

13C-1H coupling constants as a conformational tool for structural assignment of quinic and octulosonic acid

A complete set of NMR coupling constants (1JC-H, 2JC-H, 3JC-H, and 3JH-H) were calculated for the eight stereoisomers of quinic acid, at the B3LYP/6-311G(d,p)/PCM(methanol) level of theory. The Fermi contact term of the coupling constants was computed with a modified, uncontracted, version of the 6-311G(d,p) basis set, with additional tight polarization functions. 1H and 13C NMR chemical shifts were determined at the same level using the gauge-invariant atomic orbital (GIAO) method. The magnitude of the spin-spin coupling constants was found to be affected by the orientation (axial or equatorial) of the coupling proton and the orientation of the hydroxy group on the coupling carbon, whereas the chemical shifts depend on the presence or absence of electron-withdrawing hydroxy groups attached to the carbon atoms involved.Graphical Nuclear magnetic resonance coupling constants, computed with density functional theory, can be used to differentiate and identify the different stereoisomers of quinic acid.

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.

On the Configuration of Five‐Membered Rings: A Spin–Spin Coupling Constant Approach

Five-membered rings are clearly among the most common structural motifs found in chemistry and biology. Nevertheless, the configuration of conformationally mobile five-membered rings is often difficult to assign from nuclear magnetic resonance (NMR) data. A simple, reliable, and efficient approach for the stereochemical analysis of five-membered rings based on the measurement of NMR coupling constants is presented. Density functional theory calculations using representative conformations of the full conformational space available to rings with different substitution patterns were used to identify differences between the accessible coupling constant values for cis and trans relative orientations of the substituents. The calculations were assessed experimentally using NMR data obtained from a number of models. This approach can be easily used to analyze different five-membered rings, such as oxolanes, cyclopentanes, furanosides and pyrrolidines, and their relative configuration can be determined without the need for making further conformational considerations.

Approximating correlation effects in multiconfigurational self-consistent field calculations of spin-spin coupling constants

The multiconfigurational self-consistent field (MCSCF) method in their approximations restricted and complete active spaces (RAS and CAS) provides a theoretically accurate description of the coupling constants of a wide range of molecules. To obtain accurate results, however, very large basis sets and large configuration spaces must be used. Nuclear magnetic resonance coupling constants for the equilibrium geometry have been calculated for a series of small molecules using approximated correlation contributions. The four contributions to the coupling constants (Fermi contact, spin dipolar, orbital paramagnetic, and orbital diamagnetic) have been calculated at the CAS and RAS MCSCF and second-order polarization propagator approximation levels using a large basis set. An additive model that considers the effect on the coupling constants from excitation of more than two electrons and from core-electron correlation is used to estimate the coupling constants. Compared with the experimental couplings, the best calculated values, which correspond to the MCSCF results, present a mean absolute error of 3.6 Hz and a maximum absolute deviation of 13.4 Hz. A detailed analysis of the different contributions and of the effects of the additive contributions on the coupling constants is carried out.

Vicinal fluorine-fluorine coupling constants: Fourier analysis.

Stereochemical dependences of vicinal fluorine-fluorine nuclear magnetic resonance coupling constants (3JFF) have been studied with the multiconfigurational self-consistent field in the restricted active space approach, with the second-order polarization propagator approximation (SOPPA), and with density functional theory. The SOPPA results show the best overall agreement with experimental couplings. The relationship with the dihedral angle between the coupled fluorines has been studied by Fourier analysis, the result is very different from that of proton-proton couplings. The Fourier coefficients do not resemble those of a typical Karplus equation. The four nonrelativistic contributions to the coupling constants of 1,2-difluoroethane configurations have been studied separately showing that up to six Fourier coefficients are required to reproduce the calculated values satisfactorily. Comparison with Fourier coefficients for matching hydrogen fluoride dimer configurations suggests that the higher order Fourier coefficients (Cn> or =3) originate mainly from through-space Fermi contact interaction. The through-space interaction is the main reason 3JFF do not follow the Karplus equation.

Nuclear spin–spin coupling density functions and the Fermi hole

Nuclear spin–spin coupling density functions yield a three-dimensional picture of the interaction between two nuclear dipole moments mediated by electron spin density. A physical interpretation of the Fermi contact coupling density maps can be readily arrived at on account of the Fermi correlation between same-spin electrons as the mechanism whereby the spin polarization induced about one nucleus is transmitted to another nucleus coupled to it. It is shown that the Fermi hole density function, evaluated by an opportune choice of the reference electron, is characterized by morphological aspects very similar to those appearing in the plots of one- and two-bonds Fermi contact density functions. A comparison has been made for hydrogen fluoride, water, ammonia, and methane molecules at the Hartree–Fock level of theory. The results confirm the role of the Fermi correlation as the fundamental vehicle propagating nuclear-spin/electron-spin contact interaction, i.e., the process mainly responsible for nuclear spin–spin coupling. The plots of Fermi hole density show that the geminal H–H coupling would not be possible without the essential contribution of the spin density in the vicinity of the heavier nucleus. The combined use of Fermi contact density functions and Fermi hole distributions yields a very promising approach to the study of nuclear magnetic resonance coupling constants, and provides a sound physical basis for their interpretation.

Conformation of the Dipeptide Cyclo(L-Pro-L-Pro) Monitored by the Nuclear Magnetic Resonance and Raman Optical Activity Spectra. Experimental and ab Initio Computational Study

Nuclear magnetic resonance (NMR) and Raman optical activity (ROA) spectra of the cyclic dipeptide were measured and analyzed with respect to their ability to sense molecular structure and conformation. Data obtained by both techniques were simulated using ab initio quantum mechanical computations. Calculated chemical shifts, hydrogen−hydrogen spin−spin coupling constants and ROA intensities agreed well with the experimental values. The spin−spin NMR coupling constants were found to be most suitable for estimating of the conformational ratio. The ROA intensities provided additional information about the absolute configuration. The relation of the NMR chemical shifts to molecular structure was obscured by the solvent effect. The experimental results and calculated relative conformer energies suggest that equilibrium of three conformations takes place in the solution at the room temperature with a prevalence (∼80%) of the conformation present in the crystalline state.

Phosphorylation disrupts the central helix in Op18/stathmin and suppresses binding to tubulin.

Protein phosphorylation represents a ubiquitous control mechanism in living cells. The structural prerequisites and consequences of this important post-translational modification, however, are poorly understood. Oncoprotein 18/stathmin (Op18) is a globally disordered phosphoprotein that is involved in the regulation of the microtubule (MT) filament system. Here we document that phosphorylation of Ser63, which is located within a helix initiation site in Op18, disrupts the transiently formed amphipathic helix. The phosphoryl group reduces tubulin binding 10-fold and suppresses the MT polymerization inhibition activity of Op18's C-terminal domain. Op18 represents an example where phosphorylation occurs within a regular secondary structural element. Together, our findings have implications for the prediction of phosphorylation sites and give insights into the molecular behavior of a globally disordered protein.

Accurate determination of small nuclear magnetic resonance coupling constants from decoupling experiments

A new technique is described for the accurate determination of small NMR spin coupling constants. The multiplet under investigation is recorded under coupled and decoupled conditions, and then corresponding ordinates of the time-domain signals are divided, leaving only the modulation term, cosn(πJISt) where n is the number of equivalent protons in the irradiated group. Precautions are taken to avoid division by zero or near-zero values. The Fourier transform of the quotient is a single multiplet (1 : 1 doublet, 1 : 2 : 1 triplet, or 1 : 3 : 3 : 1 quartet) giving a direct measure of the coupling constant. The technique is illustrated with reference to the proton–proton couplings in furan-2-aldehyde in various solvents. The reproducibility of the measurements is superior to ±0.04 Hz and the results are in good agreement with those from a related technique where the decoupled multiplet is reconvoluted with a trial coupling J* which is varied to give best fit with the fully coupled multiplet.

15] Furanose sugar conformations in DNA from NMR coupling constants

The flexible five-membered sugar ring plays a pivotal role in nucleic acid structure and dynamic behavior. Structural differences between A-, B-, and Z-type duplexes are intimately correlated with specific conformational ranges of individual (deoxy)-riboses. Moreover, within the B-DNA family at least, each sugar responds to its surroundings (e.g., the basestacking pattern) by an appropriate adaptation of its geometry. For this reason, it is highly desirable to obtain a maximum of detailed quantitative information on the “atomic” level for each individual sugar in a DNA chain with the aid of existing experimental techniques. The chapter provides information content embodied in sets of vicinal 1 H– 1 H nuclear magnetic resonance (NMR) coupling constants. The complete conformational analysis of a given interconverting furanose in the ideal case involves the determination of five independent parameters: P s , Ф s , P N , Ф N , and X s . This is done by the creation of a simultaneous and consistent fit of a set of experimental coupling constants for predicted values with the aid of a graphical method or a computer least squares fit.

Nuclear magnetic resonance coupling constants and electronic structure in molecules

Describes the theory of NMR spin-spin coupling constants, the nature of the three types of coupling mechanisms contributing to the overall spin-spin coupling constant, and the results for two different types of coupling constants in molecules (carbon-carbon and carbon-nitrogen coupling).

Cyclotetraphosphanes: geometry, 1J(PP) nuclear magnetic resonance coupling constants, and phosphorus chemical shift anisotropy. A nuclear magnetic resonance study in liquid crystals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCyclotetraphosphanes: geometry, 1J(PP) nuclear magnetic resonance coupling constants, and phosphorus chemical shift anisotropy. A nuclear magnetic resonance study in liquid crystalsJ. P. Albrand, A. Cogne, and J. B. RobertCite this: J. Am. Chem. Soc. 1978, 100, 9, 2600–2604Publication Date (Print):April 1, 1978Publication History Published online1 May 2002Published inissue 1 April 1978https://doi.org/10.1021/ja00477a002RIGHTS & PERMISSIONSArticle Views144Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (590 KB) Get e-Alerts Get e-Alerts

Correlation of nuclear magnetic resonance coupling constants with transition metal–ligand bond lengths in tertiary phosphine complexes

N.m.r. coupling constants 1J(M–P) are reported for complexes of WIV, PtI, and PtIV. Results for 1J(Pt–P) in the complexes [PtCl4–n(R3P)n](n-2)+ and [PtCl6–n(R3P)n](n–2)+(n= 1–3) are discussed in terms of the M.O. expression for the Fermi contact interaction. Interpretation of coupling constants in terms of the s-orbital bond order is supported by the correlation of bond lengths with 1J(Pt–P) for PtII complexes and by the similarity of trends in bond lengths and M–P coupling constants in mer-tris(phosphine) complexes of WIV, RhI, RhIII, PtII, and PtIV. It is also shown that, for both 1J(Pt–P) and 2J(PtCH), ratios of coupling constants in related PtIV and PtII complexes reflect bond-length differences in the two oxidation states.

Metal satellite spectra of tetracyclopropyltin, tetracyclopropyllead, and dicyclopropylmercury and the implication on general nuclear magnetic resonance coupling constants

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMetal satellite spectra of tetracyclopropyltin, tetracyclopropyllead, and dicyclopropylmercury and the implication on general nuclear magnetic resonance coupling constantsP. A. Scherr and J. P. OliverCite this: J. Am. Chem. Soc. 1972, 94, 23, 8026–8031Publication Date (Print):November 1, 1972Publication History Published online1 May 2002Published inissue 1 November 1972https://doi.org/10.1021/ja00778a016RIGHTS & PERMISSIONSArticle Views80Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (689 KB) Get e-Alerts Get e-Alerts

Nuclear magnetic resonance coupling constants in tin in 3,3,3-trifluoropropyltin compounds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNuclear magnetic resonance coupling constants in tin in 3,3,3-trifluoropropyltin compoundsDwight Edward Williams, Louis H. Toporcer, and Gary M. RonkCite this: J. Phys. Chem. 1970, 74, 10, 2139–2142Publication Date (Print):May 1, 1970Publication History Published online1 May 2002Published inissue 1 May 1970https://doi.org/10.1021/j100909a016RIGHTS & PERMISSIONSArticle Views138Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (472 KB) Get e-Alerts