Hadamard magnetization transfers achieve dramatic sensitivity enhancements in homonuclear multidimensional NMR correlations of labile sites in proteins, polysaccharides and nucleic acids

EXSY, TOCSY and NOESY lie at the foundation of homonuclear NMR experiments in organic and pharmaceutical chemistry, as well as in structural biology. Limited magnetization transfer efficiency is an intrinsic downside of these methods, particularly when targeting rapidly exchanging species such as labile protons ubiquitous in polysaccharides, sidechains and backbones of proteins, and in bases and sugars of nucleic acids: the fast decoherence imparted on these protons through solvent exchanges, greatly reduces their involvement in homonuclear correlation experiments. We have recently discussed how these decoherences can be visualized as an Anti-Zeno Effect, that can be harnessed to enhance the efficiency of homonuclear transfers within Looped PROjected SpectroscopY (L-PROSY) leading to 200-300% enhancements in NOESY and TOCSY cross-peaks for amide groups in biomolecules. This study demonstrates that even larger sensitivity gains per unit time, equivalent to reductions by several hundred-folds in the duration of experiments, can be achieved by looping inversion or using saturation procedures. In the ensuing experiments a priori selected frequencies are encoded according to Hadamard recipes, and subsequently resolved along the indirect dimension via linear combinations. Magnetization-transfer (MT) processes reminiscent of those occurring in CEST provide significant enhancements in the resulting cross-peaks, in only a fraction of acquisition time of a normal 2D experiment. The effectiveness of the ensuing three-way polarization transfer interplay between water, labile and non-labile protons was corroborated experimentally for proteins, homo-oligosaccharides and nucleic acids. In all cases, cross-peaks barely detectable in conventional 2D NMR counterparts, were measured ca. 10-fold faster and with 200-600% signal enhancements by the Hadamard MT counterparts

Dataset for: Parallel NMR Spectroscopy With Simultaneous Detection of 1H and 19F Nuclei

Recording NMR signals of several nuclear species simultaneously by using parallel receivers provides more information from a single measurement and at the same time increases the measurement sensitivity per unit time. Here we present a comprehensive series of the most frequently used NMR experiments modified for simultaneous direct detection of two of the most sensitive NMR nuclei – 1H and 19F. We hope that the presented material will stimulate interest in and further development of this technique

Data from: Parallel NMR Spectroscopy With Simultaneous Detection of 1H and 19F Nuclei

NMR instruments equipped with multiple receivers can significantly increase the information content in experiments by recording multiple free induction decays (FID-s) from several nuclear species in a single pass. This in turn reduces the number of experiments required to solve a particular analytical or structure elucidation problem. We present a comprehensive series of such experiments that involve multi-receiver detection of two of the most sensitive NMR nuclei – ¹H and ¹⁹F. The experiment designs are categorized into three main groups – (i) interleaved experiments, (ii) parallel acquisition experiments and (iii) sequential acquisition experiments. The interleaved experiments are based on independent pulse programs that are typically dealing with more or less isolated spin systems and avoid perturbing spin system(s) that are recovering while the experiment involving the active spin system is conducted. The parallel acquisition experiments are based on simultaneous observation of the free induction decays (FID-s) of several spin systems in parallel. The multi-dimensional experiments of this type usually involve joint coherence transfer pathways and one or more joint frequency domains. Finally, the sequential acquisition experiments involve direct observation of one or more FID-s within the pulse sequence and otherwise are similar to the parallel acquisition experiments. Several examples of each type of multi-receive H/F experiments involving the most popular NMR pulse sequences including COSY, TOCSY, DOSY, HOESY, HETCOR, HSQC, HMQC, HMBC and T₁ measurement by inversion recovery method are presented and discussed. Furthermore, we demonstrate that efficiency of such experiments can be further improved by combining the multi-receiver methodology with the modern approaches of fast methods, such as relaxation optimization, non-uniform sampling, Hadamard encoding, computer-optimized folding and ultra-fast NMR by spatial encoding. We believe that the multi-receiver technology is set to become a routine way of multiplying the efficiency and throughput in high-resolution NMR spectroscopy

Hadamard acquisition of 13C-13C 2D correlation NMR spectra

International audienceWe show that a multiselective excitation with Hadamard encoding is a powerful tool for 2-D acquisition of 13 C─13 C homonuclear correlations. This method is not designed to improve the sensitivity, but rather to reduce the experiment time, provided there is sufficient sensitivity. Therefore, it allows fast acquisition of such 2-D spectra in labeled molecules. The technique has been demonstrated using a U─13 C─15 N histidine hydrochloride monohydrate sample allowing each point of the build-up curves of the 13 C─13 C cross-peaks to be recorded within 4 min 35 s, which is very difficult with conventional methods. Using the U─13 C─15 N f-MLF sample, we have demonstrated that the method can be applied to molecules with 14 13 C resonances with a minimum frequency separation of 240 Hz

Cross-Polarization Schemes for Improved Heteronuclear Transfers Involving Labile Protons in Biomolecular Solution NMR

INEPT-based experiments are widely used for ¹H→¹⁵N transfers, but often fail when involving labile protons due to solvent exchanges. J-based cross polarization (CP) strategies offer a more efficient alternative to perform such transfers, particularly when leveraging the Hʷᵃᵗᵉʳ ↔ Hᴺ exchange process to boost the ¹H→¹⁵N transfer process. This leveraging, however, demands the simultaneous spin-locking of both Hʷᵃᵗᵉʳ and Hᴺ protons by a strong ¹H RF field, while fulfilling the γₕB₁,ₕ=γₙB₁,ₙ Hartmann-Hahn matching condition. Given the low value of γₙ/γₕ, however, these demands are often incompatible—particularly when experiments are executed by the power-limited cryogenic probes used in contemporary high field NMR. The present manuscript discusses CP alternatives that can alleviate this limitation, and evaluates their performance on urea, amino acids, and intrinsically disordered proteins. These alternatives include new CP variants based on frequency-swept and phase-modulated pulses, designed to simultaneously fulfill the aforementioned conflicting conditions. Their performances vis-à-vis current options are theoretically analyzed with Liouville-space simulations, and experimentally tested with double and triple resonance transfer experiments.ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

19F DOSY diffusion-NMR spectroscopy of fluoropolymers

International audienceA new pulse sequence for obtaining 19F detected DOSY (diffusion ordered spectroscopy) spectra of fluorinated moleculesis presented and used to study fluoropolymers based on vinylidene fluoride and chlorotrifluoroethylene. The performanceof 19F DOSY NMRexperiments (and in general any type ofNMR experiment) on fluoropolymers creates someunique complicationsthat very often prevent detection of important signals. Factors that create these complications include: (1) the presence of manyscalar couplings among 1H, 19F and 13C; (2) the large magnitudes of many 19F homonuclear couplings (especially 2JFF); (3) the large19F chemical shift range; and (4) the low solubility of these materials (which requires that experiments be performed at high temperatures).A systematic study of the various methods for collecting DOSY NMR data, and the adaptation of these methods to obtain19F detected DOSY data, has been performed using a mixture of low molecular weight, fluorinated model compounds. Thebest pulse sequences and optimal experimental conditions have been determined for obtaining 19F DOSY spectra. The optimumpulse sequences for acquiring 19F DOSY NMR data have been determined for various circumstances taking into account the spectraldispersion, number and magnitude of couplings present, and experimental temperature. Pulse sequences and experimentalparameters for optimizing these experiments for the study of fluoropolymers have been studied