Heteronuclear Coupling Research Articles

One- and two-dimensional gradient-selected HSQMBC NMR experiments for the efficient analysis of long-range heteronuclear coupling constants

One- and two-dimensional gradient-selected HSQMBC NMR experiments for the efficient analysis of long-range heteronuclear coupling constants

1H and 13C-NMR Spectroscopic Study of Some 1H-4,5-Dihydroimidazolium Salts

first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessAbstract 1H and 13C-NMR Spectroscopic Study of Some 1H-4,5-Dihydroimidazolium Salts by Alejandra Salerno and Isabel A. Perillo * Departamento de Química Orgánica. Facultad de Farmacia y Bioquímica. Universidad de Buenos Aires. Junín 956 (1113), Argentina * Author to whom correspondence should be addressed. Molecules 2000, 5(3), 479-480; https://doi.org/10.3390/50300479 Published: 22 March 2000 Download Download PDF Download PDF with Cover Download XML Versions Notes Abstract: The 1H y 13C-NMR spectra of some 1,3 and 1,2,3-trisubstituted 1H-4,5-dihydroimidazolium salts are analyzed. Introduction1H-4,5-Dihydroimidazolium salts are typical cyclic amidinium compounds where the cation is resonance stabilized and the positive charge can be delocalized either on the nitrogen atoms or on the C2:NMR spectra analysis and its comparison with the corresponding saturated compounds (imidazoli-dines 2), allows to reach conclusions about the contribution of such structures. Experimental1H and 13C NMR spectra were recorded on a Bruker MSL-300 spectrometer using deuterochloro-form as the solvent. Results and DiscussionThe 1H and 13C-NMR spectroscopic study of a series of 1,3-di and 1,2,3-trisubstituted 1H-4,5-dihydroimidazoliom salts 1 (Table) is presented. Table 1. Table 1. R1R2R3X-C6H5HC6H5Cl-p-CH3C6H4Hp-CH3C6H4Cl-p-Cl-C6H4HCH2-C6H5Cl-C6H5C6H5CH3I-p-CH3C6H4C6H5CH3I-p-CH3OC6H4C6H5CH3I-p-NO2C6H4C6H5CH3I- In order to assign the heterocyclic hydrogens and carbons in the 1,2-diaryl-3-methyl substituted compounds, the spectroscopic study of the parent 1H-4,5-dihydroimidazoles 3 and their salts 4 had been carried out.The unequivocal assignment of the hydrogen and carbon signals of the 1,2,3-trisubstituted salts has been done by the HMQC and HMBC spectra.The important electronic deficit at the level of the heterocyclic ring in compounds 1 has been clearly demonstrated by comparison of the spectroscopic features of the salts 1 with the corresponding imidazolidines 2. The iminium structure contribution (A,C) was analyzed according to the chemical shifts and the heteronuclear 1J13C-H coupling constants of the heterocyclic ring carbons and N-CH3. Share and Cite MDPI and ACS Style Salerno, A.; Perillo, I.A. 1H and 13C-NMR Spectroscopic Study of Some 1H-4,5-Dihydroimidazolium Salts. Molecules 2000, 5, 479-480. https://doi.org/10.3390/50300479 AMA Style Salerno A, Perillo IA. 1H and 13C-NMR Spectroscopic Study of Some 1H-4,5-Dihydroimidazolium Salts. Molecules. 2000; 5(3):479-480. https://doi.org/10.3390/50300479 Chicago/Turabian Style Salerno, Alejandra, and Isabel A. Perillo. 2000. "1H and 13C-NMR Spectroscopic Study of Some 1H-4,5-Dihydroimidazolium Salts" Molecules 5, no. 3: 479-480. https://doi.org/10.3390/50300479 Find Other Styles Article Metrics No No Article Access Statistics For more information on the journal statistics, click here. Multiple requests from the same IP address are counted as one view.

Demonstration of quantum logic gates in liquid crystal nuclear magnetic resonance

H– 13 1 C heteronuclear dipolar couplings are used to produce the NMR (nuclear magnetic resonance) version of a two bit controlled-NOT quantum logic gate. This gate is coupled with the Hadamard gate to complete a circuit which generates the Einstein–Podolsky–Rosen (EPR) state which is the maximally entangled state of a pair of spins. The EPR state is crucial for the potential exponential speed advantage of quantum computers over their classical counterparts. We sample the deviation density matrix of the two spin system to verify the presence of the EPR state. EPR state lifetimes are also measured with this technique, thereby demonstrating the viability of liquid crystals as a platform for quantum computing.

Direct measurement of heteronuclear long-range coupling constants from phase-sensitive HMBC spectra

A simple pulse sequence in inverse-detection mode is proposed for the detection of heteronuclear long-range couplings. In the resulting 2D heteronuclear multiple-bond correlation (HMBC) spectra, pure-absorptive peak patterns are obtained along both frequency dimensions. Since the heteronuclear couplings result in anti-phase splittings over the proton homonuclear multiplets along the ω2-dimension, the phase-sensitive HMBC experiment can be provided as an easy and direct means for the measurement of heteronuclear long-range coupling constants. Copyright © 2000 John Wiley & Sons, Ltd.

A new method for the simultaneous measurement of magnitude and sign of 1DCH and 1DHH dipolar couplings in methylene groups.

Heteronuclear dipolar couplings of the protein backbone have proven to have a big impact on the accuracy of protein NMR structures. H,H dipolar couplings might have the same impact on side chains. Here we present a method that combines both heteronuclear and homonuclear dipolar couplings to investigate the local conformation of methylene groups. A new pulse sequence (SPITZE-HSQC) is presented, that allows to measure the two C,H and the H,H dipolar couplings at the same time, using spin state selective transfers. The new method has been applied to the methylene groups of glycines in the protein ubiquitin. The C,H and the H,H dipolar couplings might have a key role in fast stereospecific assignment of protons in CH2 groups.

Natural abundance heteronuclear NMR studies of the T3 mini-loop hairpin in the terminal repeat of the adenoassociated virus 2.

A DNA hairpin containing a T3 loop, as occurs in the terminal repeat of a popular gene therapy vector (Adenoassociated Virus 2, AAV2), has been extensively studied using homo- and heteronuclear NMR experiments. Almost complete assignment of the proton and carbon resonances, including H5'(Pro-S) and H5'(Pro-R) protons, has been accomplished at natural abundance. NOESY spectra in H2O and D2O have revealed many unusual NOEs, which, when combined with the epsilon, beta, gamma, and chi torsion angles determined from heteronuclear 1H-13C, 1H-31P, and 13C-31P coupling constants, have allowed for a more detailed picture of the T3 mini-loop hairpin. The three loop thymidines are all unpaired, yet are highly structured when bracketed by a 5'-GC...GC-3' stem sequence. The structure determined in this manuscript is considerably different from several other structures reported so far. Contrary to an RNA oligomer with a central U3 sequence that has the tendency to form a duplex with three U*U mismatches, the d(GAAGC-TTT-GCTTC) sequence exists mostly as a hairpin under millimolar NMR conditions. Since T3 triloop was found to be an essential element for the site-specific non-homologous integration of the AAV2 virus, and modification of the T3 loop residue abolishes such capability, the structure we report here may be of biological significance.

Hartmann–Hahn polarization transfer in liquids: An ideal tool for selective experiments

Cross-polarization using continuous-wave spin-locking fields has never become routine in liquid-state nuclear magnetic resonance. Efficiency of cross-polarization tends to be strongly attenuated if radio-frequency (RF) fields are not perfectly homogeneous. It has recently been demonstrated that imperfections in RF-fields have little effect on efficiency of polarization transfer, provided that RF-amplitudes are comparable to magnitudes of heteronuclear scalar coupling constants, rendering this method ideal for selective experiments. The technique can be exploited for the excitation of nuclei with a low gyromagnetic factor like 13C and 15N, as well as of nuclei with a high gyromagnetic factor like 1H. Several useful applications are discussed. © 2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 103–124, 2000

15] Filamentous bacteriophage for aligning RNA, DNA, and proteins for measurement of nuclear magnetic resonance dipolar coupling interactions

Publisher Summary This chapter describes the application of filamentous bacteriophage as a versatile tool for generating partially ordered solutions of nucleic acids and proteins. The Pfl phage system described in the chapter is an ideal method for obtaining a tunable degree of alignment of RNA and DNA oligomers and some proteins in solution, which then allows the measurement of homonuclear and heteronuclear dipolar coupling interactions. The Pfl filamentous phage system is ideally suited for obtaining a tunable degree of alignment in RNA and DNA molecules and acidic proteins for the observation of dipolar couplings. The phage particles are fully aligned at magnetic fields as low as 300 MHz and are stable indefinitely at a range of temperatures and buffer conditions. These dipolar couplings provide long-range structural information that is presently unavailable by standard solution nuclear magnetic resonance (NMR) techniques; therefore, in the future, dipolar coupling data may prove to be as indispensable as 1 H– 1 H nuclear Overhauser effect (NOE) in the solution structure determinations of macromolecules. This should be especially true for structure determinations of RNA and DNA oligomers where the low density of protons compared to proteins leads to fewer useful NOE distance constraints, and therefore generally less well-defined structures. In addition, the current solution NMR techniques are generally unable to determine global structural features, such as bending in nucleic acids, due because of the local nature of the NOE distance constraints.

Synthesis and characterisation of unsymmetrical metal (RuII, OsII) and ferrocenyl complexes of 1,3,5-triethynylbenzene

A series of complexes featuring metal (trans-[RuCl(dppm)2], trans-[OsCl(dppm)2] or [Ru(η-C5H5)(PPh3)2]) and ferrocenyl (C5H5FeC5H4) units unsymmetrically arranged around the periphery of a 1,3,5-triethynylbenzene core have been synthesized in good to reasonable yields by various synthetic routes. A crystal structure determination of trans-[(C5H5FeC5H4CC)2C6H3{CCRu(dppm)2Cl}] shows that the two ferrocenyl units are positioned on the same side of the trisubstituted aromatic core and that all three ethynyl linkages are bent ‘down’ out of the plane of the central ring. Electrochemical studies show that in the heteronuclear coupling of osmium(II) or ruthenium(II) fragment(s) with ferrocenyl unit(s) the oxidation of OsII or RuII precedes that of the ferrocene unit(s). In addition, whereas in diruthenium or diosmium complexes the oxidation of the two metal centres proceeds separately, in the diferrocenyl complexes the oxidation of the two ferrocene units occurs at the same potential values. This result shows that on appending different groups to the same skeletal core (namely, triethynylbenzene) some can interact electronically (the RuII- and OsII-containing fragments) whereas others do not (the ferrocenyl units).

Transverse relaxation optimized triple-resonance NMR experiments for nucleic acids.

Triple resonance HCN and HCNCH experiments are reliable methods of establishing sugar-to-base connectivity in the NMR spectra of isotopicaly labeled oligonucleotides. However, with larger molecules the sensitivity of the experiments is drastically reduced due to relaxation processes. Since the polarization transfer between 13C and 15N nuclei relies on rather small heteronuclear coupling constants (11-12 Hz), the long evolution periods (up to 30-40 ms) in the pulse sequences cannot be avoided. Therefore any effort to enhance sensitivity has to concentrate on manipulating the spin system in such a way that the spin-spin relaxation rates would be minimized. In the present paper we analyze the efficiency of the two known approaches of relaxation rate control, namely the use of multiple-quantum coherence (MQ) and of the relaxation interference between chemical shift anisotropy and dipolar relaxation - TROSY. Both theoretical calculations and experimental results suggest that for the sugar moiety (H1'-C1'-N1/9) the MQ approach is clearly preferable. For the base moiety (H6/8-C6/8-N1/9), however, the TROSY shows results superior to the MQ suppression of the dipole-dipole relaxation at moderate magnetic fields (500 MHz) and the sensitivity improvement becomes dramatically more pronounced at very high fields (800 MHz). The pulse schemes of the triple-resonance HCN experiments with sensitivity optimized performance for unambiguous assignments of intra-residual sugar-to-base connectivities combining both approaches are presented.

Predicted Influence of N-Acetyl Group Content on the Conformational Extension of Chitin and Chitosan Chains

ABSTRACT Conformational analysis of chitosan molecules has been performed using the MM3(92) force field to investigate the role played by the acetamido groups on the stiffness of these chains. A high dielectric constant value was needed to model an aqueous environment and to reproduce the distribution of the N-acetyl glucosamine group orientation that is observed by NMR. Disaccharidic fragments, differently substituted at C2, were selected as models for chitin and chitosan chains. Their conformational space has been explored by means of adiabatic mapping of the glycosidic Φ,Ψ torsion angles. Although the overall features of all the potential energy surfaces created appear similar, the accessible conformational space of a glycosidic bond is affected by the nature of the substituent at C2 on the non-reducing residue of the disaccharide unit. This is illustrated by the differences in the calculated partition functions together with the predicted average homonuclear and heteronuclear coupling constants. Computed maps were used to predict polymeric unperturbed dimensions, characteristic ratio and persistence length of idealized chitin and chitosan chains, by Monte Carlo methods. Pure chitosan is predicted to be more coiled than pure chitin chains. At low N-acetyl group contents, chain extension appears to be dependent on the degree of substitution. Average chain dimensions increase monotonically for increases in content up to 60% of N-acetyl groups, but show no significant variation at higher contents. For molecules consisting of 50% amino and 50% N-acetylated residues, random, alternate and block patterns of substitution have been investigated. It has also been shown that the spatial extension of the polymer chains is dependent on the primary structure. Comparison with the literature experimental data is difficult because of the extreme diversity of the reported conformationally dependent values. However, such study provides a unique insight into the dependence of these two factors (degree of acetylation and distribution of acetyl groups) on the stiffness and flexibility of different chitin and chitosan chains.

Magnitude and absolute orientation of 1H chemical shielding tensors in polycrystalline powders: a 1H CRAMPS NMR study of KH 2PO 4

It is shown that the magnitude and absolute orientation of 1H chemical shielding tensors may be determined from polycrystalline powders using combined rotation and multiple pulse spectroscopy (CRAMPS) by simultaneous evolution under chemical shielding and heteronuclear dipolar coupling interactions. An experimental approach based on the broadband high-order truncating MSHOT-3 homonuclear decoupling sequence is demonstrated for the hydrogen bonded proton within the 31P– 1H– 31P three-spin systems of a powder of KH 2PO 4.

Simultaneous Measurement of 3JHN,Hα and 3JHα,Hβ Coupling Constants in 13C,15N-Labeled Proteins

A triple-resonance NMR pulse sequence termed HA[HB,HN](CACO)NH is proposed that provides two types of 3JHH coupling constants sharing the Cα proton in amino acid spin systems. The experiment is of the quantitative J correlation-type and takes advantage of the favorable relaxation properties of 1Ha−13Cα multiple-quantum coherence as compared to schemes relying on antiphase magnetization. The problem of signal overlap is considerably reduced by calculating J values from cross-peak−cross-peak intensity ratios rather than referencing diagonal peaks. Application to flavodoxin from Desulfovibrio vulgaris yields a total of 282 3JHα,Hβ and 3JHN,Hα coupling constants, normally determined in two separate experiments, to be used in conjunction with heteronuclear couplings to derive angular constraints for the protein's backbone and side chains. While 3JHα,Hβ coupling constants indicate some extent of conformational averaging not in accord with fixed side chain torsion, excellent correlation of the experimental 3JHN,...

Recoupled Polarization Transfer Heteronuclear 1H–13C Multiple-Quantum Correlation in Solids under Ultra-fast MAS

A new approach for high-resolution solid-state heteronuclear multiple-quantum MAS NMR spectroscopy of dipolar-coupled spin-12 nuclei is introduced. The method is a heteronuclear chemical shift correlation technique of abundant spins, like 1H with rare spins, like 13C in natural abundance. High resolution is provided by ultra-fast MAS and high magnetic fields, high sensitivity being ensured by a direct polarization transfer from the abundant protons to 13C. In a rotor-synchronized variant, the method can be used to probe heteronuclear through-space proximities, while the heteronuclear dipolar coupling constant can quantitatively be determined by measuring multiple-quantum spinning-sideband patterns. By means of recoupling, even weak heteronuclear dipolar interactions are accessible. The capabilities of the technique are demonstrated by measurements on crystalline l-tyrosine hydrochloride salt.

Distinguishing diastereomeric organic compounds based on the concerted use of3J(C,H) and3J(N,H) values

The relative stereochemistry of the two acyclic carbons separated by a single bond was determined from three-bond homo- and heteronuclear coupling constants. The analysis of data was based on a purely qualitative interpretation of the Karplus relationships. The methodology presented could resolve acyclic diastereoisomers if adequate sets of three-bond coupling constants can be measured. Copyright © 1999 John Wiley & Sons, Ltd.

Anomalous Rotational Resonance Spectra in Magic-Angle Spinning NMR

Magic-angle spinning NMR spectra of samples containing dilute spin-12 pairs display broadenings or splittings when a rotational resonance condition is satisfied, meaning that a small integer multiple of the spinning frequency matches the difference in the two isotropic shift frequencies. We show experimental rotational resonance NMR spectra of a 13C2-labeled retinal which are in qualitative disagreement with existing theory. We propose an explanation of these anomalous rotational spectra involving residual heteronuclear couplings between the 13C nuclei and the neighboring 1H nuclei. These couplings strongly influence the rotational resonance 13C spectrum, despite the presence of a strong radiofrequency decoupling field at the 1H Larmor frequency. We model the residual heteronuclear couplings by differential transverse relaxation of the 13C single-quantum coherences. We present a superoperator theory of the phenomenon and describe a numerical algorithm for rapid Liouville space simulations in periodic systems. Good agreement with experimental results is obtained by using a biexponential transverse relaxation model for each spin site.

Concentration dependence of [formula omitted] nuclear magnetic resonance decay shapes and second moments in bone mineral

19 F nuclear magnetic resonance (NMR) spin-echoes and free induction decays (FIDs) have been observed from samples of fluoridated trabecular canine bone powder, with fluoride concentrations ([F]) ranging from approximately 10 to 33 mg F/g Ca. Curve fitting of echo envelopes and FIDs was performed using a two-component model function, where one of the components incorporates the effects of one-dimensional dipolar coupling. This function provides a good match for both echo envelopes and FIDs. Estimates of the total second moment and its homonuclear (F–F coupling) component were obtained from the fitting procedure. Based on the second moment measurements, it is argued that 19 F spins in bone mineral typically experience weaker heteronuclear dipolar coupling than those in the mineral hydroxyapatite (HAP), which is often considered to be a prototype for bone mineral.

J-Resolved HMBC, a new NMR technique for measuring heteronuclear long-range coupling constants

A new NMR pulse sequence that incorporates J-scaling into HMBC enables efficient measurement of heteronuclear long-range coupling.

Heteronuclear Double-Quantum MAS NMR Spectroscopy in Dipolar Solids

A new pulse sequence for high-resolution solid-state heteronuclear double-quantum MAS NMR spectroscopy of dipolar-coupled spin-12 nuclei is introduced. It is based on the five-pulse sequence known from solution-state NMR, which is here applied synchronously to both spin species. The heteronuclear double-quantum (HeDQ) spinning-sideband patterns produced by this experiment are shown to be sensitive to the heteronuclear distance, as well as the relative orientations of the chemical-shift and dipolar tensors. In particular, it is shown that the HeDQ patterns exhibit an enhanced sensitivity to the chemical shielding tensors as compared with the single-quantum spinning-sideband patterns. The detection of HeDQ patterns via the I and S spins is discussed. The isolated 13C–1H spin pair in deuterated ammonium formate with 13C in natural abundance was chosen as a model system, and the perturbing influence of dipolar couplings to surrounding protons on the 13C–1H DQ coherence is discussed. The pulse sequence can also be used as a heteronuclear double-quantum filter, hence providing information about heteronuclear couplings, and thus allowing the differentiation of quaternary and CHn bonded carbons. The elucidation of 13C–1H dipolar proximities is presented for a sample of bisphenol A polycarbonate with 13C in natural abundance, recorded with a broadband version of the synchronized five-pulse sequence.

Heteronuclear coupling constants of hydroxyl protons in a water solution of oligosaccharides: trehalose and sucrose

Relatively few details are known about the conformational preferences of hydroxyl groups in carbohydrates in water solution, though these would be informative about solvation and H-bonding. We show that highly concentrated solutions of sucrose and trehalose exhibit surprisingly well-resolved 1H NMR spectra in a deuterium oxide–water solvent mixture at subzero temperatures. Measurement conditions are suitable to extract nearly all homonuclear and, for the first time, heteronuclear coupling constants of OH groups of carbohydrates in their natural abundance. For 2,3 J HO,C coupling constants new, powerful variants of HETLOC and HECADE techniques were applied. The present data do not support the presence of persistent H-bonds in these two cryogenic disaccharides.