Homonuclear Broadband Decoupling Research Articles

1H NMR with Partial Transition Selectivity.

1H NMR has unique strengths, owing, for one, to 1H being the most sensitive NMR nucleus. However, the limited frequency range of 1H chemical shifts implies spectral crowding, leading to difficulties in assignment and interpretation of the spectra. Homonuclear broadband decoupling has been developed as a means of simplifying 1H NMR spectra but clearly leads to the inevitable and complete loss of precious information on homonuclear scalar couplings in solution state. A novel experiment is introduced in this work, which leads to partial 1H multiplet selectivity, thereby reducing spectral crowding, while at the same time permitting couplings to be inferred. The present one-dimensional (1D) experiment relies on two-way coherence transfer starting from 1H to coupled 13C carbons at natural abundance and ending finally with 1H detection. The experiment may be termed CArbon Single transition EDited (CASED) 1H NMR. The unusual spectral patterns that result are summarized, demonstrated, and rationalized for various molecular fragments. Artifacts in the present version of the CASED experiment are also described, and an application to the 1H NMR of a disaccharide is demonstrated as a first practical example.

NMR supersequences with real-time homonuclear broadband decoupling: Sequential acquisition of protein and small molecule spectra in a single experiment.

NOAH (NMR byOrderedAcquisition using 1H-detection) type of pure shift NMR pulse scheme has been designed for the efficient utilization of magnetization that presents in a spin-system under consideration. The proposed strategy, PROSMASH-HSQC2 (PROtein-HSQC and SMAll molecule-HSQC Signals with Homodecoupling) uses the real-time BIRD pure shift NMR strategy and two HSQC spectra (13C-HSQC for small molecules and 15N-HSQC for 15N-isotopic labelled proteins) can be recorded in a single NMR experiment. Thus, this method permits precise determination of drug-protein interactions at atomic levels by monitoring the chemical shift perturbations, and will have potential applications in drug discovery programs.

Measurement of 1H NMR relaxation times in complex organic chemical systems: application of PSYCHE

In complex organic molecules, relaxation times measured from the PSYCHE homonuclear broadband decoupling methods provide a wealth of information on intramolecular dynamics and intermolecular interactions.

Viva la Resolución! Enhancing the Resolution of 1H NMR Spectra by Broadband Homonuclear Decoupling

The structural characterization of synthetic organic and natural products often relies on proton-detected NMR spectra. While the sensitivity of protons is the highest of all NMR-active nuclei, their spectral resolution is rather poor. The removal of scalar couplings leads to a large resolution enhancement by collapsing all signals to singlets. Such homonuclear broadband decoupled proton spectra, which resemble proton-decoupled ¹³C NMR spectra, can be obtained by several techniques, most of which require the acquisition of an additional dimension and/or special data processing. Recently introduced homonuclear decoupling during acquisition yields free induction decays (FIDs), which can be processed and analyzed like regular proton data. This approach can also be implemented in the proton dimension of any two- and multidimensional NMR spectroscopic experiment and is particularly useful when significant signal overlap renders the assignment of scalar-coupled signals impossible. 1 Introduction 2 Direct Homonuclear Broadband Decoupling 3 Experimental Considerations of Slice-Selective Decoupling

Enhancing the resolution of multi-dimensional heteronuclear NMR spectra of intrinsically disordered proteins by homonuclear broadband decoupling

Limited spectral resolution in the proton dimension of NMR spectra is a severe problem in intrinsically disordered proteins. Here we show that homonuclear broadband proton decoupling of the direct and indirect dimensions of multi-dimensional NMR spectra significantly enhances their resolution.

Boosting the Resolution of 1H NMR Spectra by Homonuclear Broadband Decoupling

Broadband homonuclear decoupling of proton spectra, that is, the collapse of all multiplets into singlets, has the potential of boosting the resolution of (1)H NMR spectra. Several methods have been described in the last 40 years to achieve this goal. Most of them can only be applied in the indirect dimension of multi-dimensional NMR spectra or special data processing is necessary to yield decoupled 1D proton spectra. Recently, complete decoupling of proton spectra during acquisition has been introduced; this not only significantly reduced the experimental time to record these spectra, but also removed the need for any sophisticated processing schemes. Here we present an introduction and overview of the techniques and applications of broadband proton-decoupled proton experiments.

Simplifying Proton NMR Spectra by Instant Homonuclear Broadband Decoupling

However, these techniques have not been widelyused, since they are insensitive and usually complicatedprocessing schemes have to be applied to achieve the desiredhomonuclear decoupling. Recently, the slice-selective broad-band-decoupling during a weak gradient field (also calledZangger–Sterk or ZS method)

HECADE: HMQC- and HSQC-Based 2D NMR Experiments for Accurate and Sensitive Determination of Heteronuclear Coupling Constants from E.COSY-Type Cross Peaks

Two-dimensional pulse sequences for the determination of heteronuclear long-range coupling constants are presented. The sequences are based on the HMQC/HMBC or HSQC technique with subsequent optional homonuclear I-spin transfer. However, they yield tilted cross-peak patterns displaying antiphase heteronuclear coupling constants in the projections of both dimensions, which allow accurate determination of the couplings even in cases where the linewidth is of comparable magnitude. Two characteristic pulse-sequence elements were implemented to shape theF1domain: the first element allows an arbitrary scaling of the heteronuclear coupling splittings relative to S-spin chemical-shift differences, whereas the second element achieves homonuclear broadband decoupling among the I spins in the HMQC/HMBC experiments and thus allows purely absorptive representations of such spectra. In comparison with established (ω1) X-half-filtered TOCSY spectra, the signal dispersion inF1is significantly improved and largely under experimental control. Furthermore, heteronuclear couplings of (I1, S) pairs where S is either quaternary or carries one or more I spins that do not belong to the same I-coupling network as I1can also be measured. The implementation of pulsed field gradients results in good suppression of spectral artifacts.

α&β HSQC, an HSQC-Type Experiment with Improved Resolution for I2S Groups

Abstract A new HSQC-type pulse scheme is introduced that effectively improves the spectral resolution by what corresponds to the size of geminal J HH coupling constants, i.e., on the order of −14 Hz in CH 2 groups of peptides and proteins. The gain in resolution comes from the fact that, in I 2 S groups with I-spin detection, only those resonances with the passive I spin being in either the α or the β state are excited. The experiment α HSQC has two versions: one that is α and β selective in the echo and antiecho parts, respectively, or the opposite combination. This selection of polarizing only one half of the I-spin resonances works even when the two I spins are strongly coupled. Pure-absorption, selective α HSQC or β HSQC spectra are obtained by the two combinations of the echo part of one of the α HSQC spectra with the antiecho part of the other. These two spectra (α HSQC and β HSQC) can be merged into another spectrum, Mab HSQC, which has the appearance of an HSQC spectrum with homonuclear broadband decoupling of geminal scalar interactions. The method is demonstrated on aqueous solutions of a decapeptide at the natural-abundance level of isotopes and on the protein rhodniin (103 residues) uniformly labeled with 13 C and 15 N.

Broadband-decoupled proton spectroscopy

Proton NMR spectra are presented in a form that incorporates chemical-shift effects but excludes spin-spin splittings, as if homonuclear broadband decoupling had been employed. By Fourier transformation of spin echoes modulated by proton-proton coupling, a two-dimensional J spectrum is obtained. A 50 ms purging pulse at the end of the evolution period suppresses antiphase product-operator terms; this changes the character of the two-dimensional spin-multiplet patterns and ensures that the signals are in the pure absorption mode. In the limit of weak coupling, each multiplet pattern possesses C 4 symmetry and a software “symmetry filter” separates overlapping multiplets and rejects all other signal components. By the appropriate projection of the processed J spectrum, a one-dimensional spectrum is obtained with narrow singlet responses at the chemical-shift frequencies and no spin-spin splittings. The peak heights are proportional to the numbers of equivalent protons at each site. A separate spin-multiplet pattern from each site is available in the other frequency dimension ( F 1). The technique can be incorporated into more complicated experiments such as spin-lattice relaxation studies.

Broadband homonuclear decoupling in heteronuclear shift correlation NMR spectroscopy

Recently, Garbow, Weitekamp, and Pines introduced a new approach to homonuclear broadband decoupling (I). Independently, a closely related experiment has been proposed for semiselective heteronuclear J spectroscopy (2). The two types of experiments have the common feature that all protons which are not directly attached to a 13C nucleus experience an effect as if a nonselective 180” pulse were applied, while protons bonded to a r3C nucleus are not affected. This type of behavior can be used conveniently in many of the heteronuclear types of two-dimensional experiments (3-9). Here, its use for sensitivity and resolution enhancement in heteronuclear spectroscopy will be demonstrated. It is mentioned here that other approaches to homonuclear broadband decoupling in heteronuclear shift correlation spectroscopy have been proposed by Frenkiel (JO), but those experiments rely on a different principle (II), and are of a less general nature. The experimental scheme is sketched in Fig. 1. The theory of the conventional heteronuclear decoupled shift correlation experiment (3) has been described elsewhere (3-6) and will be repeated here. The difference between the conventional heteronuclear decoupled shift correlation experiment and the scheme of Fig. 1 is that the single 180 o 13C pulse at the center of the evolution period has now been replaced by a 90”,(‘H)-1/(2J)-180°,(‘H), 180”,(‘3C)-l/(2J)-900-,(‘H) sequence, where J is the magnitude of the heteronuclear coupling constant in hertz. It has been shown (I, 2) that this sequence has the effect of a single 180” pulse for those protons that are not attached to a 13C nucleus, while other protons (those attached to 13C) are essentially

Homonuclear broad band decoupling and two-dimensional J-resolved NMR spectroscopy

Homonuclear broad band decoupling and two-dimensional <i>J</i>-resolved NMR spectroscopy