Heteronuclear Decoupling Research Articles

Assignment of resonances in the Escherichia coli 5 S RNA fragment proton NMR spectrum using uniform nitrogen-15 enrichment

The downfield proton NMR spectrum of aqueous uniformly nitrogen-15 enriched 5 S RNA fragment is presented. Selective nitrogen-15 decoupling difference proton spectroscopy revealed nitrogen-15 chemical shifts of fragment imino nitrogens. Nitrogen chemical shifts of nucleic acid guanine and uracil imino nitrogens have separate small ranges. Nitrogen-15 and proton chemical shift correlation by the heteronuclear decoupling permitted the identification of the base type of some previously unassigned imino proton resonances in the 5 S RNA fragment spectrum. Corresponding resonances in the natural isotopic abundance 5 S RNA fragment spectrum are assigned to base types by comparison with the enriched sample spectrum. 5 S RNA fragment Proton NMR Uniform 15N enrichment Heteronuclear decoupling Chemical shift correlation Assignment strategy

Heteronuclear correlation spectroscopy in rotating solids

Coherence transfer by an isotropic mixing process is used for two-dimensional heteronuclear shift correlation in magic-angle-spinning solid-state spectroscopy. Selective coherence transfer is combined with efficient homonuclear and heteronuclear dipolar decoupling to obtain well-resolved shift correlation spectra.

The illusions of spin decoupling

The action of heteronuclear decoupling applied to I spins while observing the resonance of a second nuclear species S is examined for systems prepared in an arbitrary initial state. It is shown that unexpected effects may be produced: The removal of heteronuclear interactions by strong decoupling fields does not guarantee that the two spin systems behave independently. In particular it is demonstrated that antiphase multiplet magnetization of the S spins remains directly responsive to the radio-frequency I spin perturbation, and to I-I interactions, even when the decoupling removes the heteronuclear coupling interactions completely. Some simple illustrative examples are examined theoretically and experimentally.

Evaluation of a new broadband decoupling sequence: WALTZ-16

A new scheme for low-power broadband heteronuclear decoupling is described, based on the use of a composite radiofrequency pulse sequence 90°(+ X) 180°(− X) 270°(+ X), incorporated into a repeated cycle or supercycle. Its principal attribute is that the residual splittings on the observed resonances (usually carbon-13) are very small (less than 0.1 Hz) for a wide range of decoupler offsets (approximately − B 2 < ΔB < + B 2). Existing theories of broadband decoupling are used to calculate the effects of various possible instrumental imperfections on decoupling performance. It is concluded that spatial inhomogeneity of the B 2 field has a perceptible influence near the extremes of the decoupler bandwidth. Only 180° shifts of the radiofrequency phase are used, and the performance is remarkably insensitive to the exact setting of this phase shift. Any decoupler which employs a systematic modulation scheme runs the risk of introducing “cycling sidebands” into the observed spectrum; it is demonstrated that with the proposed sequence these sidebands are very weak, particularly when the decoupling cycle and the signal acquisition processes are not synchronized. As an illustration, the broadband-decoupled carbon-13 spectrum of an aniline derivative is recorded showing natural-abundance carbon-13 satellite signals but no appreciable cycling sidebands. The circuit for a practical implementation of this decoupling sequence is described.

Molecular movement and magnetic relaxation of 13C-nuclei of organic ions in the ion exchange resin phase

Fourier spectroscopy in the regime of the total hetero nuclear decoupling of 13C—{ 1H} has been used to measure the spin-spin and spin-lattice relaxation times of the 13C nuclei of the triethylbenzyl ammonium ion in completely saturated Dowex-50 and KRS resins with a content of crosslinker 2, 4, 8 and 12% at 33°C. Analysis of the findings coupled with the results of measurement of the Overhausser nuclear coefficient indicates the strongly hindered character of the movement of the ion rising with increase in the degree of crosslinking of the resin, slowing of the molecular movement of the counter-ion is not accompanied by appreciable changes in the position of the resonance signals of the 13C nuclei. In all the resins studied major deviations of the ratio of the relaxation times T 1/ T 2 from unity were observed. The lower boundary of the correlation times of the total rotation of the ion is 0·1 nsec.

31P nuclear magnetic resonance of phosphoenzyme intermediates of alkaline phosphatase.

Covalent (E-P) and noncovalent (E X P) phosphoenzyme intermediates exist on the reaction path of alkaline phosphatase of Escherichia coli. Zn(II) and Cd(II) alkaline phosphatases both form E-P and E X P from inorganic phosphate. These intermediates show well separated 31P NMR resonances in slow chemical exchange with respect to each other and to unbound phosphate. The 31P signals of E X P of all forms of the 113Cd(II) enzyme are doublets (J = approximately 30 Hz) due to 113Cd-O-31P coupling. Heteronuclear decoupling shows the phosphate of E X P to be coordinated to the A site metal of the two metal ions, A and B, approximately 3.9 A apart at each catalytic center. The chemical shifts of E X P vary from approximately 4 ppm for the Zn(II) enzyme to 12.6-13.4 ppm for forms of the Cd(II) enzyme and indicate a major influence of the metal ions on the conformation around phosphorus. The phosphoryl group of E-P is not coordinated to either of the two metal ions at the active center as shown by the absence of 113Cd-O-31P coupling on the 31P signals of E-P formed by the 113Cd(II) enzymes. The chemical shift of E-P is not sensitive to metal ion species or stoichiometry and is 8-9 ppm for all forms of the Zn(II) and Cd(II) enzymes. The E-P in equilibrium E X P in equilibrium E + Pi equilibria are described by analogous pH functions for the Zn(II) and Cd(II) enzymes. At acid pH E-P predominates and is converted to E X P as the pH is raised, following a sigmoid pH profile. For the Zn(II) enzyme the midpoint of the E-P in equilibrium E X P equilibrium occurs at pH 5, while for the Cd(II)6 and Cd(II)2 enzymes the midpoints are pH 8.7 and 10, respectively. The ionization controlling the equilibrium between E-P and E X P may be that of a metal-bound H2O (-OH nucleophile) whose pKa will depend strongly on the hardness of the coordinating metal ion. For the Zn(II)4 enzyme one of 2 mol of E-P formed by the enzyme at acid pH dissociates readily at pH 7.5-8 where dissociation of E X P (Kd approximately equal to mM) is rate-limiting. Phosphate binds more tightly to the Cd(II) enzyme and 2 mol of phosphate remain bound until above pH 9 where E X P begins to dissociate at mM concentrations. The low Kd for E X P and the alkaline shift in the E-P in equilibrium E X P pH profile probably account for the slow turnover of the Cd(II) enzyme. Precise chemical shifts of the 113Cd and 31P NMR signals as well as the ratio of E-P/E X P at one active center of the dimer are altered by metal ion binding at the other active center indicating significant subunit-subunit interactions.

ChemInform Abstract: HETERONUCLEAR TWO‐DIMENSIONAL NUCLEAR MAGNETIC RESONANCE: DECABORANE

Boron-11/proton two-dimensional n.m.r. spectroscopy with heteronuclear decoupling in both frequency dimensions has been used to study decaborane. The chemical-shift correlation map shows clearly how resonances from the various boron and proton sites are related, and in particular demonstrates the association of the bridging protons with B5,7,8,10 and with B6,9.

Investigation of poly(arylenevinylene)s, 24. High‐resolution solid‐state 13C NMR spectroscopy of poly(1,4‐phenylenevinylene)s

AbstractHigh‐resolution 13C NMR spectra of solid poly(1,4‐phenylenevinylene), poly(1,4‐phenylene‐1,2‐diphenylvinylene) and of three related, substituted polymers (CN, OCH3, O) were obtained with a combined technique of heteronuclear decoupling, cross‐polarization and magic angle spinning. The reported chemical shifts were assigned by means of solid model compounds (trans‐stilbene, trans, trans‐1,4‐distyrylbenzene, tetraphenylethylene). Utilizing the high sensitivity of 13C NMR chemical shifts to chemical structure, this method is applied to structure confirmation, the determination of sp3‐defects in poly(phenylenevinylene)s PPV, and the determination of sterical and electronical effects of phenyl and phenylene groups.

Heteronuclear two-dimensional nuclear magnetic resonance: decaborane

Boron-11/proton two-dimensional n.m.r. spectroscopy with heteronuclear decoupling in both frequency dimensions has been used to study decaborane. The chemical-shift correlation map shows clearly how resonances from the various boron and proton sites are related, and in particular demonstrates the association of the bridging protons with B5,7,8,10 and with B6,9.

1H–13C n.m.r. chemical shift correlation

A 1H–13C n.m.r. correlation map is obtained by low-power heteronuclear decoupling, with carbon signal acquisition under proton broad-band decoupling in order to suppress off-resonance effects.

Assignment of polypeptide 1H and 13C signals according to the amino acid sequence by multifrequency heteronuclear decoupling

By 13C{ 1H} heteronuclear selective multifrequency decoupling one can assign the NMR signals in polypeptide spectra to specific positions of amino acid residues in the primary structure. Use was made of decoupling of the interresidue spin-spin interaction of carbonyl carbon 13C′ and H α proton in the natural-abundance 13C NMR spectrum. Interactions of the carbonyl carbon with H α and H β protons of the same amino acid residue are suppressed by additional irradiation. The assignment technique is illustrated by lysine and alanine signal assignment in the NMR spectra of apamin, an 18-membered bee-venom polypeptide neurotoxin.

The composite physical and chemical approach to the solution spatial structure of polypeptide neurotoxins

The most fruitful approach to the solution structure of peptides and proteins is a dovetailing of physical (experimental and theoretical) and chemical (selective modification) methods so as to best attain the common purpose of assessing the intra-and intermolecular interactions of the give substance. Of the physical methods the most informative in such study is high resolution NMR spectroscopy. We have made extensive use of this technique within the framework of the above approach in an analysis of the spatial structures os some polypeptide neurotoxin components of bee and snake venoms. For signal assignment in the 1H and 13C NMR spectra of the bee venom component apamin (18 amino acid residues, two disulfide bonds) a multifrequency homo- and heteronuclear decoupling procedure was developed, aimed at identification of the spin systems of the particular amino acid residues and determination of the residue position in the amino sequence. The apamin spatial structure has been elucidated by selection of the optimal calculated conformation on the basis of the NMR parameters of the native toxin and its selectively modified analogs. In a study of snake neurotoxins, mainly neurotoxin II (61 amino acid residues, four disulfide bonds) isolated from the venom of the Central Asian cobra Naja naja oxiana, use was made of the dependence of the 1H NMR parameters on the conditions of the aqueous medium, and of selective chemical modification, in particular, insertion of spin labels. Additional information was obtained from comparison of the spectra with those of homologous toxins from other snake. The contacts revealed between the amino acid side chains provided a general picture of the holding of the backbone and detailed information on the antiparallel β-structure of its central segment. A comparison snake venom erabutoxins, as well as with NMR data for Naja naja oxiana cytotoxins I and II. An EPR study of the binding of selectivity spin labeled neurotoxin II derivatives to the Torpedo marmorata acetylcholine receptor revealed the role played by lysine residues in this specific interaction

Utilization of chirp frequency modulation with 180°-phase modulation for heteronuclear spin decoupling

Heteronuclear decoupling with Chirp modulation in conjunction with 180°-phase alternation is demonstrated to be a more efficient decoupling method than 180°-phase alternation alone. A theory that predicts the results of Chirp modulation alone is developed, and it is used to explain the results of decoupling with Chirp modulation and 180°-phase alternation. This method allows for efficient spin decoupling with as little as 2 W of decoupling power.

Applications of homonuclear two-dimensional J spectroscopy: an alternative to broad band heteronuclear and homonuclear decoupling

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTApplications of homonuclear two-dimensional J spectroscopy: an alternative to broad band heteronuclear and homonuclear decouplingLaurance D. Hall and Subramaniam SukumarCite this: J. Am. Chem. Soc. 1979, 101, 11, 3120–3121Publication Date (Print):May 1, 1979Publication History Published online1 May 2002Published inissue 1 May 1979https://doi.org/10.1021/ja00505a049RIGHTS & PERMISSIONSArticle Views37Altmetric-Citations27LEARN 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 (295 KB) Get e-Alerts Get e-Alerts

Pseudo heteronuclear INDOR experiments using a fourier transform NMR spectrometer

A circuit is described that allows partial computer control of a Schomandl ND-100M frequency synthesizer by a JEOL EC-100 computer fitted with a Diablo Series 30 disc drive. A specified number of free-induction decays are accumulated and stored on the backing disc; a computer pulse increments the synthesizer frequency, and the cycle is repeated allowing automatic heteronuclear selective decoupling experiments. This method is used to measure 1H (by 13C-{ 1H}) and 195Pt (by 1H-{ 195Pt}) chemical shifts.

Quantitative aspects of deuteron (spin 1) spin decoupling in solid-state N M R

The dynamics of heteronuclear spin decoupling in solids is treated rigorously in the case of deuterons ($^{2}\mathrm{D}$) decoupled from protons ($^{1}\mathrm{H}$). Dipole-dipole interaction among each spin species is neglected. Deuteron decoupling in the presence of strong quadrupolar interaction ${\ensuremath{\omega}}_{Q}$ is governed by a double-quantum process, which is demonstrated by experiments and by double-quantum-limit calculations as compared with the rigorous treatment. Double-quantum satellites are observed in the proton NMR spectra due to coherent double-quantum motion of the deuteron spins.

Dynamics of heteronuclear spin coupling and decoupling in solids

Dynamics of heteronuclear spin coupling and decoupling in solids

19F and 1H shielding tensors and crystal structure of 4,4′-difluorobiphenyl

The fluorine and proton magnetic shielding tensors of 4,4′-difluorobiphenyl have been determined at 89·3 and 93 MHz, respectively. Heteronuclear decoupling was applied during a WAHUHA multiple pulse sequence in an effort to suppress heteronuclear H-F dipolar couplings in addition to homonuclear dipolar couplings. Principal values of the almost completely asymmetric fluorine shielding tensor are σ xx F = -107·4 ± 0·4, σ yy F = -49·3 ± 0·4 and σ zz F = -0·7 ± 0·4 p.p.m. relative to liquid hexafluorobenzene. The proton data could be analysed to yield two different sets of principal shielding values: σ xx I = -1·5 ± 1·5, σ yy I = -6·5 ± 1·5, σ zz I = -11·5 ± 1·5 p.p.m. and σ xx II = -5·5 ± 1·5, σ yy II = -7·5 ± 1·5 and σ zz II = - 9·5 ± 1·5 p.p.m. relative to TMS. The crystal structure of 4,4′-difluorobiphenyl has not yet been determined. As part of this work we determined its space group. Proton dipolar interactions (from wide line spectra) and 19F principal shielding directions were used to determine the orientation of the molecules in the unit cell and to ascertain that the molecules are planar in the crystal.

1H and 31P NMR spectra of substituted methylphosphonic acids with indirect determination of 31P shifts

AbstractProton and phosphorus magnetic resonance spectra of substituted methylphosphonic acids have been determined as a function of pH. A method has been developed for measuring the 31P shift indirectly by optimal heteronuclear decoupling of the 1H spectra of samples and standards. Control experiments have demonstrated the broad applicability of this technique to the characterization of low milligram samples of N‐phosphonomethylglycine and potential metabolites.

Rotational isomerism. Part XIX. Nuclear magnetic resonance spectral analysis and conformation of 1,1,1,4,4,4-hexafluorobutane

The combined techniques of heteronuclear noise decoupling and carbon-13 satellite analysis were used to provide initial parameters for a complete analysis of the ten-spin system of CF3·CH2·CH2·CF3. The results demonstrate clearly that the compound exists predominantly in the trans-conformation, both as the neat liquid and in acetone solution. 1H, 19F, and 13C spectra were observed and the significance of the couplings, particularly the 13C couplings, is discussed.