Global NMR Discussion Meetings

NMR Methods / Theory

  • Ions dance, nuclei talk: understanding intermolecular Overhauser transfer in ionic liquids.

    Florin Teleanu (New York University, United States)

    LinkedIn: @Florin Teleanu; X: @teleanuflorin; BlueSky: ‪@teleanuflorin.bsky.social‬

    Abstract: Intermolecular dipolar interactions between nuclear spins residing on different ions is used to map spatial proximities in ionic liquids. This study investigates how temperature impacts the observed polarization transfer among ions in different molecular shells. We provide a detailed explanation of measured intermolecular cross-relaxation rates in two ionic liquids using molecular dynamics simulations.

    1. Jonas Koppe Avatar
      Jonas Koppe

      Thank you for the presentation. Do you use a special experimental setup to run the 1H-19F NMR experiments?

      Reply
      1. Florin Teleanu Avatar
        Florin Teleanu

        Hi, Jonas. Thanks for the question. There’s nothing special about our experimental setup. Just a standard BBO probe to pulse simultaneously on 1H and 19F channels.

        Reply
    2. Blake Wilson Avatar
      Blake Wilson

      Hi Florin, thank you for this interesting presentation! Can this technique be used to measure local solvent dynamics and local viscosity around larger molecules, which may have more complicated interactions with the solvent?

      Reply
      1. Florin Teleanu Avatar
        Florin Teleanu

        Hi, Blake. Great question! Indeed, we expect averaged bulk properties to be different than the ones in the first solvation shell, similar to how water strongly binds to solvated cations. There are two aspects that change across shells: the correlation time and the radial distribution function. The correlation time scales quadratically as you go further away (see slide 5) and RDF has several maxima. However, molecules are constantly changing shells (and rotational tumbling regime) so it seems quite difficult to quantify each shell’s contribution at a given time, though we have been thinking if there’s a way to deconvolute the observed cross-relaxation rates to different shells’ averaged contributions (like a Voronoi tessellation) at different temperatures, which would be quite informative. Alternatively, we can use a simple model for the intermolecular dipolar coupling that doesn’t take strong binding into account and predict the temperature dependency of the cross relaxation rate and see how much it deviates from MD simulations and experiments. Another approach would be to use 11B/10B quadrupolar interactions with the first solvation shells to span local dynamics which we have already done (https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5355636), but with no clear multiple quantum coherences. For now, a simple way would be to have a very reliable force field that predicts many basic (density, bulk viscosity, bulk diffusion) and more complex (auto- and cross-relaxation rates for intra- and intermolecular interactions) and then rely on the FF predictions to get the local descriptors you want. Still, your question is very interesting and I think a clear answer could be provided only if we manage to develop something like a pulse sequence to separate each shell’s contribution to the observed rate.

        Reply

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  • Removing t1-noise in DNP-enhanced NMR at natural isotopic abundance using two-spin order filter

    Quentin Reynard-Feytis (CEA Grenoble, France)

    LinkedIn: @Quentin Reynard-Feytis

    Abstract: Recent developments in MAS-DNP have dramatically enhanced the sensitivity of solid-state NMR, making it possible to perform increasingly complex experiments. Notably, this includes 13C–13C and 13C–15N correlation spectroscopy on powdered samples at natural isotopic abundance (NA), without the need for isotopic enrichment. Working with low-abundance nuclei also reduces dipolar truncation, thereby facilitating the observation of long-range polarization transfers. However, the potential of these techniques is often compromised by strong artefacts such as t₁-noise, which arises from instabilities during indirect evolution. Because t₁-noise is multiplicative, signals from abundant but uncorrelated nuclei can mask weaker cross-peaks, particularly problematic in NA samples where signal overlap is common.

    In this study, we present a new approach to suppress t₁-noise in natural-abundance 13C–13C DQ-SQ correlation spectra. The method involves converting double-quantum (DQ) coherences into longitudinal two-spin order (zz-terms), followed by the application of a “zz-filter” to selectively remove magnetization from uncorrelated 13C spins. We describe the theoretical basis of the technique and demonstrate its application to both J-coupling and dipolar-based DQ-SQ experiments at NA. At 100 K, using a standard Bruker MAS-DNP system, we show that this filtering enables the clear identification of long-range cross-peaks previously obscured by noise. Furthermore, at 30 K on a helium-cooled MAS-DNP setup, where t₁-noise is typically more severe due to higher sensitivity, we observe substantial SNR improvements in the indirect dimension (up to 10×). These advances make it possible to acquire, for the first time, a reliable 13C–13C DQ-SQ spectrum at natural abundance and 30 K.

    1. Amit Bhattacharya Avatar
      Amit Bhattacharya

      Hi Quentin, great work and nice presentation! Could you elaborate how zz-filter distinguish between “correlated” and “uncorrelated” nuclei at the quantum mechanical level? What happens to the overall sensitivity when you apply this filtering – is there a trade-off between noise suppression and signal intensity?

      Reply
      1. Quentin Reynard-Feytis Avatar
        Quentin Reynard-Feytis

        Hi Amit,

        thank you very much !

        before the DQ excitation block, the spins are prepared among the z-axis and from there you apply the DQ-excitation. At this stage, there is two possibilities:

        – correlated spins: you generate DQCs (which are for instance DQy = I1xI2y + I2yI1x)

        – uncorrelated spins: they cannot create DQCs so they stay along the z-axis

        When we apply the zz-filter, we convert these terms such as:

        – correlated spins: the first pulse will create I1zI2z terms from the DQy (cannot be completely converted)

        – uncorrelated spins: the Iz magnetization is put in the x.y plan

        The subsequent delay will diphase uncoupled spins’ Ix.y magnetization, but will preserve the I1zI2z terms that can only be formed from coupled spin pairs.

        The second pulse will convert the I1zI2z terms back into DQCs, and the sequence keeps running 🙂

        Let me know if that was clear or if you have any more questions !

        Reply
        1. Quentin Reynard-Feytis Avatar
          Quentin Reynard-Feytis

          update: I forgot to answer the 2nd part of your question.

          Yes, there is a trade-off. For isotropic DQ-excitation (i.e., all the DQCs generated have the same phase in the DQ subspace), we loose a factor 2 when applying the zz-filter.

          This is problematic, although we obtain a 5 to 12-fold noise reduction with the zz-filter, which leads to SNR improvements of ~2.5 to 6.

          When facing relatively “low” t1-noise, the applicability of the zz-filter isn’t straightforward and there might be other solution more viable. (for instance Fred Perras paper 10.1016/j.jmr.2018.11.008 )

          I hope this was clear !

          Best,

          Quentin

          Reply
          1. Amit Bhattacharya Avatar
            Amit Bhattacharya

            Thank you Quentin, for your detailed answer.

            Reply
    2. Chloé Gioiosa Avatar
      Chloé Gioiosa

      Dear Quentin,

      Thank you vor the very nice presentation!

      I was wondering if the efficiency of the zz-filter depends on the refocused lifetime of the coherences (T2′) and/or on the spinning frequency ?

      Reply
      1. Quentin Reynard-Feytis Avatar
        Quentin Reynard-Feytis

        Dear Chloé,

        thank you very much for your comment !

        You’re perfectly right, since we want the SQCs associated to uncoupled spins to diphase during the delay of the zz-filter, this needs to be done through various (Zeeman truncated) interactions: CSA, 1H-X couplings, 1H-1H couplings, etc…

        Although all of these interactions are supposely averaged out by MAS, their still quite present in rather slow MAS speed regime (<10kHz). At higher spinning speeds, the time necessary to diphase the SQCs (which create the t1-noise) might be exceedingly high ! The T2' partially transcripts for how present these residual interactions influence the spectrum, so this is definitely linked ! A really long T2' might mean that the residual interactions are not strong enough to quickly diphase the SQCs, which can affect the zz-filter efficiency…

        However:

        – at natural abundance, the zz-terms lifetime is reeeaaaally long since they don't face spin diffusion issues, so in principle there is no limitation to extend the zz-filter delay.

        – It is possible to add a DARR-field on the 1H channel, which reintroduces 1H-13C coupling, to speed up the decay of the SQCs during the zz-filter delay.

        So in conclusion, yes it definitely matters and the stategy needs to be adapted, but one shouldn't face any major limitations….although this still needs to be proved 🙂

        Reply
        1. Chloé Gioiosa Avatar
          Chloé Gioiosa

          Thank you for the detailed answer

          Reply

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  • DNP Semianalytical Calculations and Quantum Mechanical Simulations in MAS and Static Conditions

    Raj Chaklashiya (Northwestern University and University of California, Santa Barbara, United States)

    LinkedIn: @Raj Chaklashiya

    Abstract: Dynamic Nuclear Polarization (DNP) continues to transform NMR spectroscopy by enhancing its signal by several orders of magnitude via polarization transfer from unpaired electron spins to nuclear spins, enabling studies of objects consisting of very few spins such as cells. However, maximizing its potential towards subcellular components consisting of even fewer spins would significantly benefit from optimization of signal enhancement towards its theoretical maximum, which is nontrivial to achieve due to the many different factors that go into signal enhancement. DNP Semianalytical Calculations via simple numerical model assumptions and first principles Quantum Mechanical Simulations via time-evolved Hamiltonian propagators are two distinct methods that can be used to predict DNP performance and assess potential sources of missing enhancement via comparison with experimental DNP frequency profiles. This talk is a tutorial that applies these methods to the analysis of DNP from a highly efficient DNP biradical, TEMTriPol-1, which consists of one part Trityl and another part TEMPO. Inclusion of the effects of microwave saturation and electron spin relaxation in semianalytical calculations and use of the QUEST Northwestern computing cluster in Spinevolution quantum mechanical simulations both provide key improvements to these methods that enable closer matching between experiment and simulation. The results point towards the critical need to understand the J-coupling distribution of DNP radicals to fully understand the underlying DNP mechanism and optimize DNP performance.

    1. Arianna Actis Avatar
      Arianna Actis

      Dear Raj, very interesting study. Could you comment more on the role of the J coupling on the shape of the DNP profile? How would a reduction of J affect the profile? Have you studied other biradicals with different combinations of relaxation times/J couplings?

      Reply
      1. Raj Chaklashiya Avatar
        Raj Chaklashiya

        Dear Arianna, thank you, and thanks for the questions!
        So regarding J coupling and the profile shape, we found that reducing the J coupling narrows the Trityl part of the DNP profile significantly, removing the “bump” in the DNP profile that shows up on the left side of the profile during experiment. It seems that reducing J has the net effect of making the overall DNP profile narrower, leading to clear discrepancies with the broader experimental DNP profile.
        This is the first established biradical that I have done this kind of study on, but I have done simulation studies in the past of multiradicals and coupled monoradicals with varying dipolar, J, and/or relaxation times, and the results can get quite interesting. I’m happy to go more in-depth on this if you’d like! Here are a couple papers where we discuss those cases in detail:
        Multi Electron Spin Cluster Enabled Dynamic Nuclear Polarization with Sulfonated BDPA –in our simulation section we see the impact of J coupling and relaxation times on coupled BDPA and find that there is a combination that matches experimental trends. J coupling matching the nuclear larmor frequency combined with a strong differential in t1e’s can result in an absorptive central feature in the DNP profile lineshape: https://pubs.acs.org/doi/full/10.1021/acs.jpclett.3c02428
        Dynamic Nuclear Polarization Using Electron Spin Cluster – this paper has detailed simulations on Trityl-based multiradicals and the conditions in which dipolar couplings are strong enough to result in strong DNP enhancements, as well as the impact of relaxation time differentials on the DNP profile: https://pubs.acs.org/doi/full/10.1021/acs.jpclett.4c00182

        Reply
    2. Kuntal Mukherjee Avatar
      Kuntal Mukherjee

      Dear Raj, very nice talk! I would like to know that in second method, when you are observing for static case, the dipolar interaction is also present there (which is primarily averaged out in case of MAS), how the role of dipolar interaction and J-coupling can be separately understood?
      Thank you.

      Reply
      1. Raj Chaklashiya Avatar
        Raj Chaklashiya

        Hi Kuntal,

        Thank you! Good question–so first to clarify, the dipolar coupling definitely plays a role in both the MAS and Static simulations–even though there is averaging of dipolar orientations that would make seeing their effects in the NMR spectra harder, its effects can still be seen in the DNP profile itself, because in both cases the dipolar coupling strength directly determines how coupled the two electron spins are–if they are too weakly coupled, the Cross Effect DNP cannot occur, while if they have strong enough coupling it can occur. So in this sense, it needs to be understood for both static and MAS.

        As to your question–in these simulations I assume a dipolar coupling constant at 12.5 MHz because I don’t expect the distance between the Trityl electron and the TEMPO electron of TEMTriPol-1 to change. However, J-Coupling is a different story, as it is already known based on liquid state EPR experiments that there is a broad distribution of J couplings.

        However, if we assume both the dipolar and J couplings can change, what happens, and how do the effects differentiate from one another? I think in this case, the key difference lies in how they impact the EPR spin populations:
        – Dipolar coupling acts as a means to broaden electron spin populations. Stronger dipolar coupling results in broader EPR lines, while weaker dipolar coupling results in narrower EPR lines
        – J coupling acts as a means of splitting electron spin populations. Stronger +J coupling results in a wider split in the EPR line, while weaker +J coupling results in a narrower split in the EPR line. And crucially, negative J coupling when strong vs weak can flip this dependence (which results in the better fit with -J as opposed to +J)

        From this, one can see how dipolar coupling alone would result in different a different input EPR line, and therefore a different DNP profile–while it can broaden the already existing electron spin populations, it cannot necessarily create new populations further away. This means it would be harder for a small “bump” to suddenly appear due to dipolar broadening as opposed to J couplings–that bump however could easily be created if a population were shifted due to J couplings.

        The beauty of these simulations, however, is that it can be easy to test these hypotheses! We could input a range of dipolar coupling values and compare that with what happens if we input a range of J coupling values, and vice-versa, all while keeping the other coupling fixed.

        Let me know if you have any more questions!

        Reply
        1. Kuntal Mukherjee Avatar
          Kuntal Mukherjee

          Ok, that clears the query, thank you!

          Reply
          1. Raj Chaklashiya Avatar
            Raj Chaklashiya

            No problem!

            Reply

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  • An NICS study on Modulation of Aromaticity of Nitroaniline Isomers in Binary Solvent Mixtures

    Prince Sebastian (St.Berchmans College, Changanacherry, India)

    LinkedIn: @Prince Sebastian

    Abstract: The stability and chemical reactivity of substituted benzene derivatives are largely determined by their aromatic nature. Using the Nucleus-Independent Chemical Shift at 1 Å above the ring center [NICS(1)] as an aromaticity probe, we examine how binary solvent mixtures affect the modulation of aromaticity in ortho, meta, and para-nitroaniline isomers. To simulate different solvation environments, binary mixtures comprising water, chloroform, dimethyl sulfoxide, acetonitrile, trifluroethanol, N,N-Dimethylformamide, dioxane, and tetrahydrofuran were employed. Less negative NICS(1) values in solvent combinations indicate that solvation reduces aromaticity for all three nitroaniline isomers, according to our computational analysis. Solvent-induced polarisation and hydrogen bonding effects, which affect electron delocalisation within the aromatic ring, are responsible for this decrease in aromaticity. Interestingly, the type of isomer and solvent composition affect the amount of aromaticity loss, with para-nitroaniline exhibiting the highest sensitivity to solvation effects. The reactivity and mechanism of chemical transformations involving nitroaniline derivatives may be influenced by solvent-dependent aromaticity, according to these findings, which also emphasise the critical role of solvent environment in modulating electronic properties.

    1. Blake Wilson Avatar
      Blake Wilson

      Hi Prince, great presentation. I have two questions.

      1) From your data it seems like NICS(0) values in binary mixtures are often lower than the NICS(0) values for each solvent making up the mixture. Can you comment on this?
      2) How are your calculated NICS values validated? Or is that the next step?

      Reply
    2. PRINCE SEBASTIAN Avatar
      PRINCE SEBASTIAN

      Hi Blake,

      1)Yes, our observations indicate that the NICS(0) values for binary mixtures are generally lower than those of the individual pure solvents. This suggests a decrease in aromaticity when two solvents are mixed. The possible reason for this decrease is the presence of specific intermolecular interactions, such as hydrogen bonding or other non-covalent interactions, that alter the electronic environment of the aromatic ring.

      In particular, inter-hydrogen bonding appears to play a crucial role in modulating aromaticity within the mixtures. These interactions can lead to redistribution of electron density, thereby reducing the magnetic shielding experienced in the aromatic system, which manifests as a lower NICS(0) value. To further support this interpretation, we carried out AIM (Atoms in Molecules) analysis, which confirmed the presence and nature of these intermolecular interactions in the mixtures.

      2)The calculated NICS values were validated by comparison with literature data, ensuring that the observed trends match previously reported results, and by verifying consistency across computational methods, confirming that variations in the computational approach did not significantly affect the trends.

      Reply

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  • The Quantum Gate Recipe: Simulation of Nuclear Magnetic Resonance Pulse Protocols for the CNOT and SWAP Quantum gates

    Lena Aly (New York University Abu Dhabi, UAE)

    LinkedIn: @Lena Aly

    Abstract: In this work, we develop a MATLAB-based simulation model for NMR pulse protocols in weakly coupled spin-½ systems, with a focus on implementing quantum logic gates such as the Controlled-NOT (CNOT) gate. The model connects the unitary matrix representation of quantum gates to experimentally realizable pulse sequences using angular momentum operator formalism. It allows direct evaluation of pulse performance and provides quantitative error estimates for various sequences. The model enables informed comparisons between alternative pulse schemes, and lays the groundwork for future extensions to include advanced techniques such as composite pulses for NMR based quantum information science.

    1. Kirill Sheberstov Avatar
      Kirill Sheberstov

      Hi, what is the classical analogy of the CNOT gate, and what is the main difference between the two?

      Reply
      1. Lena Aly Avatar
        Lena Aly

        Hi!

        The action of the CNOT gate is analogous to the classical XOR operation, and the output of the XOR gate can be thought of as the target qubit in a CNOT. Unlike the XOR, however, the CNOT does not reduce the two qubits into one qubit: the control qubit remains as it is, and the target undergoes the XOR operation. This makes the operation of the CNOT reversible and can be represented by a unitary matrix, as required for all quantum gates.

        It can be more challenging to implement the CNOT gate, though, because it is important to only flip the state of the target qubit without changing the coherence of the states.

        Also, the CNOT is an essential component in implementing quantum entanglement, which is necessary to give quantum computers an advantage over their classical counterparts.

        Reply
    2. Jonas Koppe Avatar
      Jonas Koppe

      Thank you for the presentation. How easily can this expanded to investigate e.g., the Toffoli gate?

      Reply
      1. Lena Aly Avatar
        Lena Aly

        Such an interesting question!

        The current work lays the framework for transforming the desired projection operators in the form of idempotents into realizable pulse sequences and testing them. Since any desired expansions would be unitary, they can also be modeled as idempotents and follow the same logic with a minor modification in the defined Hamiltonian.

        Reply
    3. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Lena, nice presentation! I am curious, what are some examples of those small mistakes that could occur when trying to go from the matrices to the pulse sequences?

      Reply
    4. Lena Aly Avatar
      Lena Aly

      Thank you so much!

      Well, since the process of going from the matrices to pulse sequences includes identifying the desired projection operators, factorizing them to include complex numbers, using idempotent identities to rewrite them as exponents, and then trying to separate the exponents such that each exponent applies only to one axis, many mistakes could happen, especially with signs.

      The one I identified in Price et al 1999 (https://doi.org/10.1006/jmre.1999.1851) using the program was in their application of the identity highlighted in the presentation. It was inconsistent with their choice of axis, which did not end well in the simulation as shown (they should have used U^-1 where they have used U). This also makes sense why their result was different from the one by Volkov and Salikhov 2011 (10.1007/s00723-011-0297-2), although they both used the same mathematical foundation to derive the pulse sequence for the CNOT gate.

      Reply
      1. Raj Chaklashiya Avatar
        Raj Chaklashiya

        Thank you! That is very interesting–it turns out sign mistakes are crucial to avoid for these kinds of calculations!

        Reply

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  • An operational perspective on the Magnus-Fer conundrum in time-dependent quantum mechanics

    Kuntal Mukherjee (IISER Mohali, India)

    LinkedIn: @Kuntal Mukherjee; X: @kuntalsherlock

    Abstract: Development of analytical methods for studying periodically driven quantum systems has been key for gaining insights into the physical phenomena in spectroscopy. The success of analytic methods relies on its operational aspects and exactness in replicating (known) experimental results. The analytical methods based on the Magnus expansion (ME) scheme have been preferred in time-evolution studies, though recently, the splitting of the time-propagator into a product of exponential operators in the Fer expansion (FE) scheme has gained wider attention. Hence, the operational advantages between the two has always remained contentious and is discussed herein with a two-spin model system supported by the numerical simulations with a heteronuclear spin system based on CP (Cross-Polarization) and a homonuclear spin system based on DQ-HORROR (Double Quantum Homonuclear Rotary Resonance) experiments. Here, we highlight the serious discrepancies observed in time-evolution studies based on time-propagators derived from both the FE and ME schemes. The exactness of the FE scheme is problem specific and highly dependent on the commutator relations among propagator operator. Only in certain cases, it results in agreement to those obtained from exact numerical methods. By contrast, the ME scheme in an appropriate interaction frame presents a reliable framework for evaluating the observables at stroboscopic time-intervals.

    1. Jonas Koppe Avatar
      Jonas Koppe

      Thank you for the presentation. Is there a scenario where you would recommend using the Fer expansion?

      Reply
      1. Kuntal Mukherjee Avatar
        Kuntal Mukherjee

        Hi Jonas,
        Unfortunately, there are very limited opportunities to use Fer expansion to obtain exact results. In general, It would work when following conditions are satisfied.
        [Fn(t),ρ(0)] ≠ 0 & [Fn(t), D] ≠ 0
        There must be non-commutating operators present in the F-operators with the initial density matrix operator and detection operator simultaneously, since, the terms showing the effect of anisotropic interactions must be reflected in the final signal expression. In case of CP and DQ-HORROR experiments, one of the F-operator commutes with the density operator, the anisotropic terms do not participate in the final signal expression. Hence, we have to choose such experiments where the above relation holds and the choice of experiment is totally contextual and need to verify the applicability of the Fer expansion.

        Reply
    2. Kuntal Mukherjee Avatar
      Kuntal Mukherjee

      Hi Jonas,
      Unfortunately, there are very limited opportunities to use Fer expansion to obtain exact results. In general, It would work when following conditions are satisfied.
      [Fn(t),ρ(0)] ≠ 0 & [Fn(t), D] ≠ 0
      There must be non-commutating operators present in the F-operators with the initial density matrix operator and detection operator simultaneously, since, the terms showing the effect of anisotropic interactions must be reflected in the final signal expression. In case of CP and DQ-HORROR experiments, one of the F-operator commutes with the density operator, the anisotropic terms do not participate in the final signal expression. Hence, we have to choose such experiments where the above relation holds and the choice of experiment is totally contextual and need to verify the applicability of the Fer expansion.

      Reply
    3. Nicolas Bolik-Coulon Avatar
      Nicolas Bolik-Coulon

      Thank you for the effort in presenting such a topic!
      It seems that the Fer expansion cannot work in the presence of CSA, as you discuss. So how and why was this method introduced in the first place?
      Based on your conclusions, would there be any reason moving forward to use the Fer expansion over the Magnus one?

      Reply
      1. Kuntal Mukherjee Avatar
        Kuntal Mukherjee

        Hi Nicolas, thank you for watching my presentation.

        The original Fer expansion was applied to the classical systems. But for quantum mechanical systems, the commutation relations play a big role. In this presentation as well as the publication, to keep things simple, we have shown the applicability of Fer expansion over cycle time detection or stroboscopic detection. The conclusion is straightforward in this case which is presented. But for continuous detection or non-stroboscopic detection, the form of Fn-operators become very complex upon going to higher order. Hence, to work with Magnus expansion, you need to add all the Fn-operators in a single exponent and operate it on density operator to evaluate signal (through BCH expansion). It is highly probable that in such scenario, deducing closed form expression is quite cumbersome though possible and in worse cases, the presence of off-diagonal terms will not give any closed form solution. On the other hand, Fer expansion would allow to operate the Fn-operators individually and obtain a product of simpler expressions, although, it still needs to satisfy the following two conditions, i.e. [Fn(t),ρ(0)] ≠ 0 & [Fn(t), D] ≠ 0 for which the applicability of Fer expansion becomes limited. To sum up, in stroboscopic detection, Magnus expansion’s efficiency is greater or equal to Fer expansion’s efficiency. For non-stroboscopic detection, Fer expansion is convenient to use if the above two conditions satisfy. There is a paper by Shreyan et. al. (https://doi.org/10.1080/00268976.2023.2231107)on decoupling that discuss on the non-stroboscopic detection also.
        I hope this explanation helps and answers your query.
        Thank you again.

        Reply
    4. Sajith V Sadasivan Avatar
      Sajith V Sadasivan

      Hi Kuntal,

      Great to see your work here!

      Have you ever explored using the Fer expansion approach for systems involving quadrupolar nuclei?

      Reply
      1. Kuntal Mukherjee Avatar
        Kuntal Mukherjee

        Hi Sajith,

        Thank you very much for watching my presentation.
        I have been exploring the Fer expansion scheme involving spin-1/2 nuclei only. Although, for systems involving quadrupolar nuclei, the method would be same, like evaluating the time-propagator by writing down the F1 and F2 operators. Due to quadrupolar nuclei, there will be addition of Quadrupolar interaction. So, starting with a single spin quadrupolar nuclei under single pulse followed by stroboscopic detection of signal and assuming no anisotropic interaction present with offset=0 kHz, we can have simplest problem to start with. As a time-independent Hamiltonian, we would have external RF-Hamiltonian and as a time-dependent Hamiltonian, we would have internal Quadrupolar Hamiltonian. Then, we can write down the F1 and F2-operators. During detection, we would know how much Fer expansion is exact depending upon the condition it needs to satisfy, i.e. [Fn(t),ρ(0)] ≠ 0 & [Fn(t), D] ≠ 0. Further addition of anisotropies like CSA would only bring new set of challenges that Fer expansion has to deal with. As of now, I can comment on a primitive level about it. For better assessment, we have to calculate it thoroughly.
        I hope this satisfies your query.
        Thank you again for showing the interest.

        Reply
        1. Sajith V Sadasivan Avatar
          Sajith V Sadasivan

          Yes. Thank you.

          Reply

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  • Advancing GHz-class NMR: High sensitivity through larger volume cryoprobe and optimal control sequences

    David Joseph (Max Planck Institute for Multidisciplinary Sciences, Germany)

    X: @DaJo_1729

    Abstract: Improving the sensitivity of nuclear magnetic resonance (NMR) spectroscopy requires advancements in both instrument technology and experimental methodology. In this study, we introduce the first proton-detected large volume cryoprobe designed for 1.2 GHz instruments, leveraging optimal control pulse sequences to enhance performance (Sci. Adv. 9,eadj1133, 2023). Our results demonstrate up to a 56% increase in sensitivity and more than a twofold reduction in experimental time compared to the small volume cryoprobes in use at the moment. Additionally, we systematically optimized the experimental conditions to fully exploit the capabilities of GHz-class magnets. To further extend the benefits of our approach, we developed a library of optimal control triple resonance experiments, enabling boosted sensitivity for advanced NMR applications.

    1. Cory Widdifield Avatar
      Cory Widdifield

      When comparing the results from the 5 mm TCI probe at 1.2 GHz with the 5 mm TCI probe at 950 MHz, what is the most surprising/interesting/useful insight that you have personally encountered? In the future, what do you think might be the most useful/interesting insights enabled by performing experiments at 1.2 GHz?

      Reply
      1. David Joseph Avatar
        David Joseph

        The most useful insight is that bio-NMR experiments perform much better using optimal control pulses. A 5 mm TCI at 950 MHz approaches the power availability limit for broadband pulses, particularly for the 13C and 15N channels. At 1.2 GHz, a 5 mm TCI can only be used with optimal control pulses. However, using optimal control pulses with fields starting from 800 MHz would provide free signal enhancement and save valuable experimental time.

        The most interesting insights would come from performing experiments at 1.2 GHz to study biomolecular dynamics. All B₀-dependent parameters, such as CSA and alignment, reach their maximum values at this frequency, enabling access to data on motions that would otherwise be impossible to observe with lower field magnets. Increased resolution at 1.2 GHz would also be useful for studying larger proteins and intrinsically disordered proteins.

        Reply
        1. Cory Widdifield Avatar
          Cory Widdifield

          Thank you for your response, David.

          Reply
    2. Gottfried Otting Avatar
      Gottfried Otting

      These are important reference data.
      1) Wouldn’t one expect that the sensitivity obtained with a Shigemi tube is either the same or less than that obtained with a conventional 5 mm tube?
      2) Which compound and signal did you use to measure the sensitivities in the presence of different salt concentrations – ubiquitin or sucrose?
      3) Does CSA relaxation of ubiquitin amide protons broaden their 1H NMR signals noticeably more than at, say, 950 MHz?

      Reply
      1. David Joseph Avatar
        David Joseph

        1) The sensitivity of a Shigemi depends on the amount of sample available. It is especially sensitive when a lower volume of sample is available. There is also an optimal height that provides the best signal-to-noise ratio when using a Shigemi tube. Our concern here was B_1 inhomogeneity, which is lower with a Shigemi tube. However, since the pulses also compensate for ±20% inhomogeneity, we only see only a slight improvement in sensitivity when using a Shigemi tube.

        2) It was p53 1-73, a disordered protein, in a Tris-Bis buffer, using optimal control HNCA sequence.

        3) Thanks for the question! I just looked it up, and for an HNCO experiment, the difference is around 3 Hz, while for an HSQC, it’s around 1 Hz (along the proton dimension). It is broader at 1.2 GHz.

        Reply
    3. David Joseph Avatar
      David Joseph

      1) The sensitivity of a Shigemi depends on the amount of sample available. It is especially sensitive when a lower volume of sample is available. There is also an optimal height that provides the best signal-to-noise ratio when using a Shigemi tube. Our concern here was B_1 inhomogeneity, which is lower with a Shigemi tube. However, since the pulses also compensate for ±20% inhomogeneity, we only see only a slight improvement in sensitivity when using a Shigemi tube.

      2) It was p53 1-73, a disordered protein, in a Tris-Bis buffer, using optimal control HNCA sequence.

      3) Thanks for the question! I just looked it up, and for an HNCO experiment, the difference is around 3 Hz, while for an HSQC, it’s around 1 Hz (along the proton dimension). It is broader at 1.2 GHz.

      Reply
    4. Bijaylaxmi Patra Avatar
      Bijaylaxmi Patra

      Hi David, brilliant presentation. Clear, concise, and insightful.
      You mentioned a useful tip about using buffers with lower conductivity and larger ions. Could you please elaborate on why this is beneficial and how exactly it helps in practice?

      Reply
      1. David Joseph Avatar
        David Joseph

        Hi, thank you! This has to do with noise contribution from the sample, which is especially problematic for the cryoprobe. The noise from the sample is proportional to its conductivity and dielectric properties. Using a buffer with larger ions will lower the mobility, thus lowering the conductivity of the buffer and reducing the noise from the sample. This increases the signal-to-noise ratio of the spectrum.

        Reply
    5. David Joseph Avatar
      David Joseph

      Hi, thank you! This has to do with noise contribution from the sample, which is especially problematic for the cryoprobe. The noise from the sample is proportional to its conductivity and dielectric properties. Using a buffer with larger ions will lower the mobility, thus lowering the conductivity of the buffer and reducing the noise from the sample. This increases the signal-to-noise ratio of the spectrum.

      Reply

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  • A BOTTOM-UP APPROACH: COMPLIMENTING NMR RELAXOMETRY WITH THEORY AND SIMULATIONS

    Angel Mary Chiramel Tony (University of Rostock, Germany)

    LinkedIn: @Angel Mary C T; X: @AngelMaryCT1; Bluesky: @angelchirameltony.bsky.social

    Abstract: By using Fast Field Cycling (FFC) NMR spectroscopy, dynamical processes can be studied over many orders of magnitude. However, interpreting FFC-NMR data often requires models that are specific to certain systems. Here we propose a novel approach for computing the inter- and intramolecular contribution to the magnetic dipolar relaxation from molecular dynamics (MD) simulations. This method is enabling us to predict NMR relaxation rates, addressing the full FFC frequency range, covering many orders of magnitude, while also avoiding influences due to limitations in system size and the accessible time interval. Our methodology is based on combining the analytical theory of Hwang and Freed (HF) for the long-range intermolecular contribution of the magnetic dipole-dipole correlation function with MD simulations. Here we apply this approach to compute the inter- and intramolecular NMR relaxation of 19F nuclei in the ionic liquid C5Py-NTf2 to study the dynamics of the NTf2 anion. By employing our MD simulation-based approach, we could show that the correlation functions due to the HF theory does asymptotically converge with our MD simulation results at long times. This approach is successful in disentangling the different contributions to the intramolecular 19F-NMR relaxation rate due to the complex intramolecular dynamics of the anion. We successfully described the rotational anisotropy, differentiating between the overall tumbling of the anion and internal rotation of the CF3 group, which is difficult to decipher with the fitting models.

    1. Amit Bhattacharya Avatar
      Amit Bhattacharya

      Hi Angel, nice presentation! I was wondering—on slide 11, why doesn’t the 283 K data fit as well as the 303 K and 323 K data, which show excellent fit?

      Reply
      1. Angel Mary Chiramel Tony Avatar
        Angel Mary Chiramel Tony

        Hello Amit,
        Many thanks for the question.
        The lines are indicated for the Relaxation rate calculated from MD(with correction term) in the bottom approach manner. It’s not a fit for experimental data points obtained from FFC NMR.
        The mismatch we have for 283K can probably be attributed to the quadrupolar nuclei(Deuterium on cation) and dipolar nuclei (Fluorine on anion) interaction. As this effect becomes pronounced at lower temperature, we see the effect for 283K compared to the other two higher temperatures.

        Let me know if it clarifies your question and if you have any other questions/curiosity.

        Best regards
        Angel

        Reply
        1. Amit Bhattacharya Avatar
          Amit Bhattacharya

          Thanks Angel, it clarifies my question.

          Reply
    2. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Angel, nice talk! I was wondering, is it possible to apply this method or a modified version of this method to vitrified samples (e.g. frozen solutions at ultralow temperatures)? I am assuming this would be in a regime of significantly less tumbling, but there would still be processes (e.g. vibrational, rotational) that contribute to and create a relaxation time.

      Reply

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  • Spin now, Think later: Understanding relaxation rates of nuclear spins in electrolytes from spin and molecular dynamics simulations

    Florin Teleanu – @teleanuflorin

    One way to investigate batteries’s health is by analyzing the state of its electrolytes. Here, we develop a computational methodology to predict magnetization lifetimes in multi-spin systems like NaBF4 electrolyte through a combination of molecular and spin dynamics simulations.

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  • Elucidation of Bicalutamide Conformers in DMSO-d6: A Combined NMR and Computational Study

    Anna Mololina – @Anikkks

    Our research addresses the challenges posed by polymorphism in pharmaceuticals, focusing on bicalutamide, a treatment for prostate cancer. Using NOESY spectroscopy and computational methods, we analyzed the spatial structure of bicalutamide in DMSO-d6, providing detailed insights into its conformational behavior.

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