Total Correlation Spectroscopy(TOCSY) across All NMR-Active Nuclei by Mixing at Zero Field https://doi.org/10.1021/acs.jpclett.0c02032

[Audio] Total Correlation Spectroscopy(TOCSY) across All NMR-Active Nuclei by Mixing at Zero Field.

[Audio] TOCSY (Total Correlation Spectroscopy) is a two-dimensional nuclear magnetic resonance (NMR) experiment used to identify scalar-coupled spin networks, or to determine the connectivity of atoms within molecules. The TOCSY experiment is based on the principle of mixing homonuclear spins by a strong radio-frequency field and exploiting the resulting spin diffusion to obtain information about the spin system. This technique is widely applied to small molecules and is also useful for larger molecules such as proteins, nucleic acids, and polysaccharides..

Article title: Total Correlation Spectroscopy across All NMR-Active Nuclei by Mixing at Zero Field Authors: Ivan V. Zhukov, Alexey S. Kiryutin , Fabien Ferrage , Gerd Buntkowsky , Alexandra V. Yurkovskaya , and Konstantin L. Ivanov* Link to paper: https://doi.org/10.1021/acs.jpclett.0c02032.

[Audio] ZULF stands for Zero or Ultra-Low Field. It is a technique used in nuclear magnetic resonance (NMR) spectroscopy to efficiently transfer spin polarization between heteronuclear nuclei across a spin network. It uses a combination of fast field switches and isotropic mixing at an ultralow field, allowing one to obtain high-resolution 2D spectra of complex mixtures..

[Audio] Summary of the article nuclear Overhauser spectroscopy (NOESY) This article introduces the concept of Total Correlation Spectroscopy (TOCSY) across all NMR-active nuclei by mixing at Zero Field (ZULF-TOCSY). This method combines the advantages of high-resolution NMR experiments and isotropic spin mixing under ZULF-NMR conditions to provide correlations among all NMR-active nuclei in a coupled network. The authors demonstrate the potential of ZULF-TOCSY to analyze complex mixtures on a growth medium of isotope-labeled biomolecules by illustrating the method on isotopically enriched amino acids. The ZULF-TOCSY spectra allow one to highlight heteronuclear coupling networks and quickly identify individual compounds in the mixture by their coupled spin networks. The authors also discuss the potential of ZULF-TOCSY as an analytical tool for a complex mixture, as well as its clear advantage over traditional heteronuclear NOESY experiments..

[Audio] Figure 1 from this article is a schematic of two different protocols used in total correlation spectroscopy (TOCSY) experiments. The first protocol (Figure 1a) involves preparing nuclear spin coherence of interest (step 1), evolving the coherence under an interaction during time t₁ (step 2), mixing (step 3), and finally observing the free induction decay (FID) signal as a function of time t₂ (step 4). The second protocol (Figure 1b) involves using the ZULF-TOCSY pulse sequence to polarize a sample at a high magnetic field (Bo), followed by a nonadiabatic field jump back to a higher field (BUL). Finally, the amount of polarization transfer is measured after the field jump back to high field..

[Audio] Figure 2 shows a block diagram which depicts four steps for performing two-dimensional NMR experiments. The first step is to prepare the nuclear spin coherence of interest. The second step is to let the coherence evolve under an interaction for a set period of time, t₁. The third step is mixing, and the fourth step is the observation of the Free Induction Decay (FID) signal as a function of time, t₂..

[Audio] Figure 3 shows the NMR spectra of compounds used, the kinetics of polarization transfer under ZULF conditions, and the figures of experimental results. Figure 3 displays a ZULF-TOCSY spectrum of L-lysine. The spectrum is composed of 2048 x 256 data points and is given by an 90°-shifted squared sinusoidal window function in both dimensions. The figure displays extensive 1H-13C and 1H-15N correlations, with the e-CH2 protons exhibiting cross-peaks with all carbons. The figure highlights the heteronuclear coupling networks, which allows one to identify individual molecules in complex mixtures..

[Audio] Figure 4 shows a two-dimensional correlation spectrum of an ISOGRO sample, which highlights the coupling networks of its various isotopically labeled small biomolecules. The spectrum shows correlations between hydrogen and carbon atoms, as well as hydrogen and nitrogen atoms, allowing for the identification of individual molecules in the mixture. ISOGRO is a complex mixture of uniformly isotopically enriched 13C and 15N molecules: amino acids and small peptides (65%), glucose (2%), and salts (30%)..

[Audio] The experiment was performed using a commercial 9.4 T NMR spectrometer (Avance III HD, Bruker) equipped with TXI and BBO probes. The ZULF-TOCSY method was used to analyze the sample, which utilizes isotropic spin mixing under zero-field NMR conditions to highlight heteronuclear coupling networks. The protocol of the experiment consists of four steps. The first step is the preparation of the nuclear spin coherence of interest. The second step is the evolution of this coherence under an interaction during a set time period, t1. The third step is mixing, and the fourth step is the observation of the free induction decay (FID) signal as a function of a set time period, t2. The spectrum was given by 2048 × 256 data points. The ZULF-TOCSY method allows one to identify coupling networks of all NMR-active nuclei, displayed in 1H-13C or 1H-15N 2D correlations. High sensitivity is obtained by polarizing the sample at a high magnetic field Bo. The simultaneous correlation of all active nuclei makes ZULF-TOCSY particularly suited for parallel detection. We demonstrate 1H-13C and 1H-15N correlations in ZULF-TOCSY spectra of labeled amino acids, which allow one to obtain cross-peaks among all heteronuclei belonging to the same coupled network, even when the direct interaction between them is negligible. The ZULF-TOCSY method will lead to the development of a new toolbox of experiments to analyze complex mixtures by NMR. We also demonstrate the potential of ZULF-TOCSY to analyze complex mixtures on a growth medium of isotope-labeled biomolecules..

[Audio] The novel application of this article is the development of a new toolbox of experiments to analyze complex mixtures by NMR, specifically the utilization of the coherent polarization transfer among heteronuclear spin systems to implement an analogue of the widely used TOCSY experiment, which is applied to homonuclear spin systems. The next step experiment proposed by the authors is to further optimize the ZULF-TOCSY mixing time with a simple field-jump experiment..

References:. Zhukov, I. V.; Kiryutin , A. S.; Ferrage , F.; Buntkowsky , G.; Yurkovskaya , A. V.; Ivanov, K. L. Total Correlation Spectroscopy across All NMR-Active Nuclei by Mixing at Zero Field. The Journal of Physical Chemistry Letters 2020 , 11 (17), 7291–7296..