Global NMR Discussion Meetings

2025

  • Lighting Up the Hidden Nuclear Spins: Revisiting the Three-Spin Mixing Photo-CIDNP Mechanism in Solids under Static and MAS Conditions

    Sajith V Sadasivan (New York University Abu Dhabi, United Arab Emirates)

    LinkedIn: @Sajith V Sadasivan; X: @v_sadasivan

    Abstract: Nuclear Magnetic Resonance (NMR) spectroscopy, a key tool for probing molecular structure and dynamics, is fundamentally limited by the intrinsically low thermal polarization of nuclear spins, resulting in weak signal intensities. Dynamic Nuclear Polarization (DNP) enhances NMR sensitivity by transferring polarization from electron spins via microwave irradiation, yet it often demands cryogenic conditions and complex instrumentation. Photochemically induced DNP (photo-CIDNP) offers a promising, microwave-free alternative by exploiting optically generated spin polarization, with recent work using synthetic donor–chromophore–acceptor systems demonstrating significant 1H and 13C hyperpolarization in the solid state. Building on these advances, our present study expands the three-spin mixing (TSM) framework by establishing a generalized resonance condition valid across coupling regimes of radical pairs under both static and magic angle spinning (MAS) conditions. Through an operator-based effective Hamiltonian approach, it is shown that coherent singlet–triplet mixing, driven by hyperfine interactions, is central to the hyperpolarization mechanism through photo-CIDNP. Additionally, a Landau–Zener treatment captures the periodic level anti-crossings enabled by MAS, providing mechanistic insight into polarization transfer pathways. These findings offer critical guidance for optimizing photo-CIDNP transfer and rationally designing photoactive molecular systems for next-generation applications in biomedical imaging and materials characterization.

    1. KSHAMA SHARMA Avatar
      KSHAMA SHARMA

      Questions:
      1. How do the polarization levels and build-up times you are seeing with photo-CIDNP compare to what’s typically achieved using microwave-driven DNP? Are there any trade-offs or unexpected advantages in Photo-CIDNP?
      2. In developing the operator-based effective Hamiltonian model, what kinds of assumptions or simplifications did you have to make? And how do those choices affect the accuracy of your predictions?

      Reply
      1. Sajith V Sadasivan Avatar
        Sajith V Sadasivan

        Dear Kshama,

        Hope you are doing well. Thanks for your questions.

        Please find the responses to your questions below.

        1. How do the polarization levels and build-up times you are seeing with photo-CIDNP compare to what’s typically achieved using microwave-driven DNP? Are there any trade-offs or unexpected advantages in Photo-CIDNP?

        Response: Photo-CIDNP achieves moderate polarization enhancements but offers faster build-up and the possibility of operating towards room temperature with simpler hardware and high‐field compatibility.
        In De Biasi et al.’s experiments, the ¹H polarization builds up within seconds under continuous 450 nm laser irradiation. Please refer to https://doi.org/10.1021/jacs.4c06151 (Fig. 3). They obtained bulk NMR signal enhancements by factors of ∼100 at both 9.4 and 21.1 T for the 1H signal under MAS at 100 K. Since this is a non-thermal polarization, it’s not limited as in DNP (by a factor of ~660). It can be improved depending on radical chromophore efficiency and experimental conditions. Microwave DNP achieves larger enhancements but has slower build-up, higher complexity, and requires cryogenics.

        We have mentioned this in our article (Sec. III B): https://doi.org/10.1063/5.0265957. The perturbation strength, E1, responsible for three-spin mixing (TSM) at level crossings and net transition probabilities in photo-CIDNP can be compared to the three-spin flip process in the cross-effect DNP under MAS using Landau-Zener model. In photo-CIDNP, the corresponding perturbation term, which drives TSM, can be derived from the coefficients of the ZQ and DQ effective TSM Hamiltonian. For the cross-effect (CE), E1 is given by E1 = d*B/ωn. Please refer to https://doi.org/10.1063/1.4747449. E1 in CE DNP is weaker than in photo-CIDNP because, in CE, it is scaled down by the nuclear Larmor frequency, which increases significantly at high magnetic fields.

        2. In developing the operator-based effective Hamiltonian model, what kinds of assumptions or simplifications did you have to make? And how do those choices affect the accuracy of your predictions?

        Response: Our approach employs an operator-based theoretical framework to model the photo-CIDNP process in a three-spin system. This framework unifies Zeeman, hyperfine, and electron–electron (e–e) coupling interactions into a single effective Hamiltonian that governs the coherent dynamics driving three-spin mixing (TSM) and, ultimately, photo-CIDNP under zero- and double-quantum (ZQ/DQ) matching conditions.

        To facilitate analytical treatment, we analyze the Hamiltonian within the separate α and β manifolds of the nuclear spin using polarization (or polar) operators. A fictitious zero-quantum operator is introduced for the electron spins (radical pair) to simplify the spin dynamics. We also perform a transformation into a tilted frame, aligning the effective rotation axis with the quantization (z) axis. This allows us to extract effective precession frequencies for the nuclear spin in the α and β manifolds, which appear on the right-hand side of the ZQ/DQ matching conditions. To further analyze nuclear hyperpolarization, we transform the tilted-frame Hamiltonian into the interaction frame, following the strategy used in CP and DNP frameworks. This yields generalized resonance conditions for both ZQ and DQ transitions.

        Our model establishes these generalized matching conditions in a form that remains valid across all regimes of spin parameters, including variations in the g-tensor isotropic shift (Δ), electron–electron coupling strength (d), and hyperfine coupling constants (A and B). The resulting effective Hamiltonians introduce a dipolar scaling factor, which directly governs the rate of polarization transfer. An analytical solution for the time evolution of the density matrix under the effective Hamiltonian, along with the corresponding expression for the trace of the nuclear spin polarization ⟨Iz(t)⟩, reveals an intensity factor that defines the maximum achievable polarization. The total efficiency of nuclear hyperpolarization is determined by the interplay between this dipolar scaling and intensity factor, providing key insights into the rational design of photoactive sensitizer molecules and the optimization of experimental conditions for efficient photo-CIDNP. The excellent agreement between numerical simulations and analytical predictions under three distinct electron–electron coupling regimes—strong, intermediate, and weak—relative to Δ supports the reliability of our model and its ability to identify optimal conditions for three-spin mixing and photo-CIDNP. Overall, this study lays a robust theoretical foundation for optimizing nuclear polarization transfer in diverse photo-CIDNP applications.

        For more detailed information, please refer to https://doi.org/10.1063/5.0265957 or contact us.

        Thank you.

        Reply
        1. KSHAMA SHARMA Avatar
          KSHAMA SHARMA

          Dear Sajith,
          Yes, I’m doing well and hope you’re doing great too! Thank you for answering all the questions so thoroughly.

          Reply
          1. Sajith V Sadasivan Avatar
            Sajith V Sadasivan

            Good to know! I’m also doing good.

            You’re welcome.

            Reply
    2. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Sajith, nice talk! I am excited to see Photo-CIDNP is improved under MAS conditions. I was wondering, how high in magnetic field can you do this technique, whether that is modified by going from static to MAS conditions, and what fields it is optimal.

      Reply
    3. Sajith V Sadasivan Avatar
      Sajith V Sadasivan

      Hi Raj,

      Thank you for the nice comment and thoughtful question.

      Photo-CIDNP transfer under MAS relies on periodic anti-level crossings, which are governed by the matching conditions mentioned. MAS modulates the Hamiltonian terms periodically, which helps drive matching conditions repeatedly per rotor cycle, leading to better build-up and more uniform polarization (as compared to CE DNP as explained in Sec. IIIB, https://doi.org/10.1063/5.0265957). Under MAS, the effective fields can transiently match the conditions for efficient TSM, even if the static field would otherwise be unfavorable.

      At low fields, nuclear Larmor frequencies (ωₙ) are small, so matching conditions are relatively easy to satisfy. At higher fields, ωₙ becomes large, and achieving the matching becomes more stringent. The efficiency of polarization transfer can drop if the anti-level crossings shift away from optimal conditions. Having said this, it’s not just B₀, but also the relative g-shift (Δg), e-e coupling, and anisotropic hyperfine terms that matter (which are the important factors appearing in the matching condition). With proper molecular design (e.g., adjusting Δg and couplings), photo-CIDNP can still work efficiently even at 9.4 T, 21.1 T, or possibly higher fields.

      In De Biasi et al.’s recent experiments, they obtained bulk 1H NMR signal enhancements by factors of ~100 at both 9.4 and 21.1 T under MAS at 100 K using PhotoPol-S (as compared to their experiments at 0.3 T, yielding enhancement ~ 16 fold under STATIC conditions using Photopol). Please refer to https://doi.org/10.1021/jacs.4c06151 (Fig.  2) and https://doi.org/10.1021/jacs.3c03937 (Fig. 3). In this case, the matching conditions at 21.1 T are achieved by significantly increasing the e-e coupling from 5.5 MHz in PhotoPol to 570 MHz in PhotoPol-S by eliminating the spacer segment. Since the 1H hyperfine couplings in PhotoPol and PhotoPol-S are expected to be less than 50 MHz, there is less flexibility to adjust this as compared to e-e couplings towards higher fields.

      Hope this answers your question.

      Reply
      1. Raj Chaklashiya Avatar
        Raj Chaklashiya

        Thank you for your detailed response! That is very interesting, and makes sense to me–so it is harder to make it work at higher fields, but better molecular design can improve it. It’s very interesting to know that already there are some designs that work at 9.4 and even at 21.1 T up to 100x enhancement. I am excited to see such optimized molecular designs in the future!

        Reply
    4. Sajith V Sadasivan Avatar
      Sajith V Sadasivan

      Same here!

      Reply

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  • Rapid Melting Strategies for benchtop DNP: A Step Toward Replenishable Hyperpolarization in Liquid-State NMR

    Yang Wang (Very High Field NMR Center of Lyon (CRMN Lyon), France)

    LinkedIn: @Yang Wang; X: @WangYan35529716; Bluesky: @yangwangcz.bsky.social‬

    Abstract: Hyperpolarization techniques can boost NMR sensitivity by over 10,000-fold [1]. Among these, dissolution dynamic nuclear polarization (dDNP) is well established but suffers major drawbacks: it is destructive, single-use, and results in dilution upon sample dissolution, leading to rapid signal decay and incompatibility with multi-scan NMR experiments [2].
    We are developing a benchtop DNP platform designed to enable replenishable hyperpolarization without dilution. This approach uses hyperpolarizing materials (HYPOPs) [3] within a compact benchtop polarizer [4], coupled directly to a benchtop NMR spectrometer for solution-state detection. Our long-term goal is a closed-loop system allowing repeated freeze-DNP-melt-flow cycles.
    A critical challenge is maintaining polarization during the melt. In our current system, the sample is transferred from a 77 K DNP cryostat inside a 1 T benchtop polarizer into a dedicated melting station. This first prototype uses a guided high-flux (500 L/min), high-temperature (630 °C) air stream to melt a 250 µL sample in 5 seconds.
    We are now working to reduce the melt time below 1 second by increasing airflow, temperature, and integrating high-power laser light. Ultimately, we aim to couple this rapid melt setup with DNP and solution-state hyperpolarized NMR for multi-scan acquisition capability.
    References:
    [1] Ardenkjær-Larsen, J. H., et al. PNAS 100.18 (2003): 10158-10163.
    [2] Golman, K., et al. Cancer Res. 66.22 (2006): 10855-10860.
    [3] El Daraï, T., Cousin, S.F., Stern, Q., et al. Nat. Commun. 12 (2021): 4695.
    [4] Bocquelet, C., et al. Sci. Adv. 10 (2024): eadq3780.

    1. KSHAMA SHARMA Avatar
      KSHAMA SHARMA

      Hi Yang! Thank you for the presentation.

      I was wondering if you observe any noticeable time lag associated with activating the heat gun during the melting process? If so, have you considered alternative heating methods, such as infrared or laser-based systems that might allow for a more rapid and controlled melt?

      Regarding the freeze-melt and then flow cycles, how reproducible are your polarization levels across repeated runs?

      Reply
      1. Yang Wang Avatar
        Yang Wang

        Hi Kshama,

        Thank you for your questions !

        Indeed, the heat gun does require a few seconds after activation to reach the target temperature. To address this, I preheat the gun to the desired temperature before exposing the sample, so that the hot air is already at the setpoint at the very start of the melting process.

        I have also considered three alternative heating strategies. Among them, infrared laser heating is particularly promising. We have recently acquired a 1 kW, 1 μm wavelength IR laser system, which is currently being installed. I hope to begin testing it in the coming months and are looking forward to sharing new results with you.

        In parallel, we are also simulating microwave heating approaches, although the heating speed appears to be limited in this case…

        Regarding your question on reproducibility, we unfortunately do not yet have experimental data. However, we are planning a series of repeated melt-DNP experiments in the coming months to verify the polarization reproducibility across cycles.

        Best regards,
        Yang

        Reply
        1. KSHAMA SHARMA Avatar
          KSHAMA SHARMA

          Sounds great Yang! All the best and thank you!

          Reply

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  • Folding, Stability, and Oligomerization of HSPB8: An NMR-Based Investigation of Its α-Crystallin Domain

    Zainab Amin (IISER Pune, India)

    LinkedIn: @Zainab Khan; X: @ZAINAB_KHAN_7

    Abstract: HSPB8 (Heat Shock Protein B8) is an important chaperone that acts independently of ATP. Perturbations in HSPB8 function have thus been implicated in various protein aggregation disorders. Despite its biological importance, the structural and dynamic behaviour of HSPB8 under different stress conditions remains poorly understood. Understanding these perturbations is a key to elucidating the role of HSPB8 in protein quality control mechanisms. In this study, we performed a biophysical characterization of the α-crystallin domain (ACD) of HSPB8, involved in dimer formation, using solution-state nuclear magnetic resonance spectroscopy under different environmental perturbations. The effect on the structural integrity was characterized by monitoring changes in chemical shifts and linewidths of ACD in response to stressors. The results suggest that the ACD domain of HSPB8 is highly sensitive to environmental perturbations. In parallel, an initial investigation into the folding process of the protein has been carried out using multidimensional NMR spectroscopy. The backbone amide resonances of the unfolded protein were assigned through a combination of 3D NMR experiments, allowing mapping of amino acid residues to their respective peaks in the 2D 15N-1H HSQC spectrum. With the unfolded state characterized, this study aims to further elucidate the conformational landscape of the protein during refolding by gradually reducing the denaturant concentration and monitoring changes using the dynamic NMR techniques. These experiments are expected to yield mechanistic insights into the folding pathway of HSPB8, including the identification of transient, low-population intermediate states that may play critical roles in its chaperone activity and cellular function under stress.

    1. Chandan Singh Avatar
      Chandan Singh

      Thanks for a nice presentation. I have following questions regarding the same:
      What happens if you go in reverse order i.e. If the protein is denatured slowly with the help of urea and HSQC is recorded?

      Reply
    2. Zainab Amin Avatar
      Zainab Amin

      Thanks for asking! We have not tried that as it is difficult to assign the protein its folded monomeric form as of now. I think the protein may or may not follow the same folding pathway as we slowly unfold the protein from the folded form. To have an exact answer ,we may need to perform the experiments.

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

      Thank you for this nice presentation!
      Your CEST profiles are quite pretty. I was wondering though if you had any information about the intermediate state, i.e. what is its nature? I thought that if it is was a folding intermediate, its chemical shift would be closer to the folded state but it seems like the major peak is moving away as you decrease the urea concentration.
      In addition, as you progress toward folding, do you expect to form oligomeric species? How do the R2 of the ground and excited states compare?

      Reply
      1. Zainab Amin Avatar
        Zainab Amin

        The observation that the chemical shifts of the minor (excited) state are distinct from both the unfolded and native conformations suggests that the intermediate represents a unique conformational ensemble. While it may involve local structure formation, it remains structurally distinct from the final folded state, a point further supported by our HSQC spectra. Although the fully folded state has not yet been assigned, overlay analysis shows that the intermediate does not fully converge with it, particularly at 2 M urea, where the HSQC profile deviates from the native-like pattern. The minor-state chemical shifts remain relatively consistent across decreasing urea concentrations, which indicates that the intermediate is structurally persistent. Regarding oligomerization, our concentration-dependent HSQC experiments for the folded construct showed only subtle line shape changes, consistent with weak self-association. This suggests a tendency towards dimer formation, though not strong enough to classify as higher-order oligomerization under the conditions tested. At 2 M urea, we do observe increased R₂ values and modest peak broadening, yet not to the extent typically seen with large oligomeric assemblies. Further validation is required to confirm this behavior.
        I hope this helps clarify some of your questions!
        Thank you!

        Reply
    4. Zainab Amin Avatar
      Zainab Amin

      The observation that the chemical shifts of the minor (excited) state are distinct from both the unfolded and native conformations suggests that the intermediate represents a unique conformational ensemble. While it may involve local structure formation, it remains structurally distinct from the final folded state, a point further supported by our HSQC spectra. Although the fully folded state has not yet been assigned, overlay analysis shows that the intermediate does not fully converge with it, particularly at 2 M urea, where the HSQC profile deviates from the native-like pattern. The minor-state chemical shifts remain relatively consistent across decreasing urea concentrations, which indicates that the intermediate is structurally persistent. Regarding oligomerization, our concentration-dependent HSQC experiments for the folded construct showed only subtle line shape changes, consistent with weak self-association. This suggests a tendency towards dimer formation, though not strong enough to classify as higher-order oligomerization under the conditions tested. At 2 M urea, we do observe increased R₂ values and modest peak broadening, yet not to the extent typically seen with large oligomeric assemblies. Further validation is required to confirm this behavior.
      I hope this helps clarify some of your questions!
      Thank you!

      Reply
    5. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Zainab, nice talk! I am curious about how you can use this technique to distinguish between different possible outcomes–like for example, if there were 2 or 3 intermediate states, how would that look like as compared to having one (which is what is shown)? I ask because I can imagine this method could be applied also to other proteins as well, which may have more than one intermediate state. Thanks!

      Reply
      1. Zainab Amin Avatar
        Zainab Amin

        Thank you!
        In case of multiple intermediates, you will see multiple minor dips and you can fit them to other models rather than two state model. Also, you can record the experiment at different B1 fields to check if you are missing any hidden or merged minor dips.
        I hope that answers the query to some extend!

        Reply
        1. Raj Chaklashiya Avatar
          Raj Chaklashiya

          Yes it does! Thank you for your response!

          Reply

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  • Solid-state NMR methods for characterization of ions embedded in graphenic materials for supercapacitors application

    Paulo Cesar de Mello Correa (University of Espírito Santo (UFES), Brasil)

    X: @pcmspin; Bluesky: @spinplus.bsky.social‬

    Abstract: Solid-state NMR is widely employed to study the structural properties of activated carbon and other graphenic materials. Activated carbon is extensively utilized in industrial and consumer applications, particularly in energy storage devices such as supercapacitors, which serve as an environmentally sustainable alternative for integration into electrical systems alongside conventional batteries, or potentially replacing them in the future. In supercapacitor design, activated carbon functions as an electrode material due to its highly porous network, which provides a large surface area, thereby enhancing capacitance. Another approach to improving energy storage capacity of a supercapacitor involves synthesizing activated carbon with controlled pore dimensions, confining ions near the surface for optimized charge accumulation. Solid-state NMR can measure the nucleus-independent chemical shift (NICS), defined as the chemical shift difference (in ppm) between extra-pore and intra-pore peaks in NMR spectra. In this study, solid-state ¹H and ¹⁹F NMR spectra were acquired for activated carbon samples soaked in distilled water and aqueous solutions of NaF and NaBF₄. The results reveal an increase in NICS with surface area, consistent with steam activation that introduce micropores, which leads to larger NICS values, indicating reduced ion-surface distances. Furthermore, NMR spectral deconvolution of extra-pore and intra-pore peaks enables indirect estimation of pore volume for the carbon material.

    1. Jonas Koppe Avatar
      Jonas Koppe

      Thank you for the presentation. Have you considered using 10/11B NMR to study the BF4- ions?

      Reply
      1. Paulo Cesar de Mello Correa Avatar
        Paulo Cesar de Mello Correa

        Hello Jonas!

        It would really be interesting to measure with 11B and compare the results, thank you for the suggestion. We are also working to carry out measurements with 23Na and possibly confirm some particular aspect of the BF4 ion in accessing the pores of samples B240 and B400. In addition, this analysis would provide a perspective on a possible difference between cations and anions in accessing the pores of the studied material.

        thank you for the comment!!

        Reply
    2. Riley Hooper Avatar
      Riley Hooper

      Nice presentation Paulo. Adding on to Jonas’ Boron suggestion, have you thought to look at 23Na or 35/37Cl to see whether these ions show similar behaviour as the ones studied? Additionally, have you performed any VT NMR to try to assess ion dynamics in the activated carbon?

      Reply
      1. Paulo Cesar de Mello Correa Avatar
        Paulo Cesar de Mello Correa

        Hello Riley!

        Thank you for the suggestion, we do have plans to measure with 23Na (for the NaBF4 1.0 M solution) and possibly with 35/37Cl (for the LiCl 1.0 M solution) to investigate possible relationships with the ion charge (cation or anion) for accessing the porous network of the studied carbons, thank you for the suggestion. Although the results have already shown that Li+ and BF4- ions do not access the pores of the B240 and B400 samples, a more careful analysis is necessary to draw such conclusions. Regarding VT NMR measurements, unfortunately, we do not have the apparatus for this type of measurement. However, we are conducting Exchange NMR (EXSY) measurements to investigate the dynamic aspects of ions in the exchange regimes between the bulk electrolyte and the porous network, as well as in the intra-particle exchange regime.

        Thank you very much for the comment!!

        Reply
        1. Riley Hooper Avatar
          Riley Hooper

          Cool! I would be curious if the Na/Li and F/Cl would have similar behaviours, and the quadrupolar parameters (particularly for Cl) could be instructive on whether the Cl ions are more immobilized in the pores vs. bulk.

          Reply
          1. Paulo Cesar Correa Avatar
            Paulo Cesar Correa

            Hello, it would be very interesting to analyze all the nuclei present in NaBF4 and LiCl. We are working on taking these measurements to complement our work. Thanks again for your comment!

            Reply
    3. Bijaylaxmi Patra Avatar
      Bijaylaxmi Patra

      Hi Paulo,
      Interesting presentation!
      My question is quite simple: Is there any specific reason you chose 5 kHz MAS for your experiment?

      Reply
      1. Paulo Cesar Correa Avatar
        Paulo Cesar Correa

        Hello Bijaylaxmi, interesting question!

        There is indeed a reason: our experiments are being conducted using an unsealed rotor, which allows for potential solution leakage during centrifugation in the MAS experiment. To mitigate this, we are operating at a spinning frequency of 5 kHz. In fact, we are actively investigating this leakage through NMR measurements, using a method that enables us to monitor the decay in intensity of both the ex-pore and in-pore peaks over time. Our results confirm the occurrence of leakage, as evidenced by a consistent decrease in the ex-pore peak intensity, particularly within the first 15 minutes of spinning. Therefore, all measurements are carefully limited to under 15 minutes and using the lower spinning frequency possible to prevent damage to the spectrometer.

        Thank you for the comment!!

        Reply
    4. Tales Gomes Avatar
      Tales Gomes

      Nice work!

      Reply
    5. Gabriel Sampaio Avatar
      Gabriel Sampaio

      Thanks for the presentation!

      Reply

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  • Probing interfacial water via color-center-enabled spin magnetometry

    Kang Xu (CUNY–The City College of New York, United States)

    LinkedIn: @Kang Xu‬

    Abstract: We use shallow nitrogen-vacancy (NV) centers in diamond to probe the nanoscale dynamics of interfacial water confined between diamond and a fluorinated oil layer. By selectively detecting 1H and 19F nuclei using NV-NMR, we resolve distinct diffusion behaviors of water and oil near the interface. Our results reveal that water diffuses much faster than oil and is gradually displaced over days. Molecular dynamics simulations and surface-sensitive X-ray spectroscopy support the observation of slow, thermally driven reorganization. This work highlights NV-NMR as a powerful tool for studying molecular-scale interfacial processes under ambient conditions.

    1. Yunfan Qiu Avatar
      Yunfan Qiu

      Hi Kang,
      Exciting experiments and results! Regarding the H signal with a broad linewidth of 70 kHz, do you have any thoughts on how to achieve a narrower signal with better resolution? Looking forward to hearing your insights.

      Reply
    2. Kang Avatar
      Kang

      Hi Yunfan,

      Thanks for your comment! The 70 KHz signal is FFT result from correlation measurement protocol. Which is FID like signal resulted from diffusion out the detection zone of NV. Narrower linewidth could be down by deeper NV for micrometer scale detectio or hyperpolarize the target nuclei to overcome the thermal polarization limit. However, I don’t think these two approach would work for H signal from interfacial water. Firstly, micrometer scale detection may not gain more signal from thin interfacial water; secondly, hyperpolarize interfacial water maybe not that easy? Thanks for your comment agian!

      Reply
    3. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Kang,
      Nice presentation! One thing I am confused about is, why do 19F and 1H have these differing behaviors around the diamond? Is it only because 19F is more “slow” or are there other factors involved?

      Reply
      1. Kang Avatar
        Kang

        Hi Raj,

        Thanks for your comment! I think “slow” should be the main factor of there diffusion behavior. But the two dimensional nature of 2D of 1H and 3D nature of 19F may also cause some difference, althrough we did not go very detail about this difference. There is a paper considering this model as a difference. “Power-law scaling of correlations in statistically polarised nano-NMR”. Have a nice weekend!

        Best
        Kang

        Reply

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  • Dynamic Nuclear Polarization Mechanisms in Diamond Defect Systems: Analytical Models and Transfer Dynamics

    Shubham Kumar Debdatta (Indian Institute of Science, Bangalore, India)

    Abstract: Nitrogen-vacancy (NV) centers in diamond have become prominent platforms for dynamic nuclear polarization (DNP), offering a robust route to hyperpolarize surrounding ¹³C nuclear spins under ambient conditions. Experimental observations have revealed both microwave-assisted and microwave-independent DNP pathways, frequently rationalized in terms of level anti-crossings between coupled electronic and nuclear spin manifolds.
    In this work, we construct an analytical treatment of spin polarization transfer from NV centers to proximal ¹³C nuclei, employing the density matrix formalism in conjunction with average Hamiltonian theory. Under the condition of selective excitation of a single electronic transition, we invoke a reduced Hilbert space description to derive compact expressions for spin polarization resonance conditions, effective spin Hamiltonians, and transfer efficiency as a function of external magnetic field, hyperfine interaction strength, and applied microwave fields.
    The model is further generalized to incorporate NV–P1–¹³C configurations, where P1 centers—substitutional nitrogen defects with spin-½—mediate cross-relaxation pathways that enable microwave-free spin polarization transfer. This extension elucidates key dynamical features such as field-dependent polarization oscillations, resonance-enhanced transfer channels, and timescales associated with transient spin exchange processes.
    This theoretical framework offers a detailed understanding of DNP mechanisms across both isolated and interacting defect configurations. The results delineate optimal regimes for maximizing nuclear spin polarization in diamond-based systems, particularly under low magnetic fields and ambient conditions, with direct implications for enhancing the sensitivity of nuclear magnetic resonance (NMR) and other hyperpolarization-enabled techniques.

    1. Arianna Actis Avatar
      Arianna Actis

      Dear Shubham, thank you for the presentation, it is a very interesting study. If I understand correctly, the graph showing “Normalized Signal vs Time” shows the the polarization buildup on 13C. Could you comment on the factors that affect this polarization transfer? Thank you.

      Reply
    2. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Thank you! I assume you’re referring to the NV–P1–13C cluster-based study. In this context, the transfer rate mostly depends on A_zz^Δ and A_zx^Δ, which represent the differences in secular and pseudo-secular hyperfine couplings. These differences are key factors governing the transfer rate.
      In the plot, the purple plot indicates no spin polarization transfer. This occurs when the 13C nuclear spin is positioned exactly midway between the NV center and the P1 center, resulting in zero difference in both secular and pseudo-secular hyperfine couplings—hence, no transfer takes place.
      Additionally, there is a dependence on θ (theta) and φ (phi), which are related to nuclear and electronic couplings. These angular dependencies reflect how spin polarization transfer is influenced by the relative positioning of the 13C nucleus—whether it’s closer to the NV or the P1 center—and by the physical distance between NV and P1.

      Reply
    3. Sajith V Sadasivan Avatar
      Sajith V Sadasivan

      Nice work, Shubham.

      Have you explored the simulations under MAS?

      Reply
    4. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Thank you! I haven’t looked into the matching conditions under MAS yet.

      Reply
      1. Sajith V Sadasivan Avatar
        Sajith V Sadasivan

        Okay.

        Reply
    5. Arianna Actis Avatar
      Arianna Actis

      Hello Shubham, thank you for your answer. Did you try also to study clusters composed by multiple NV and P1 centres?

      Reply
    6. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Yes, I am currently exploring cluster-based systems. At the moment, our primary focus is on the 14N nucleus (associated with the P1 center) within the NV–P1–13C spin system, examining its dynamics as a four-spin system.

      Reply
    7. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Dear Shubham,
      Nice presentation! I was wondering, while your simulations show that the optimal matching conditions are at X Band, is there any way that you’ve seen to manipulate the spin system (e.g. via couplings) such that the optimal matching condition can occur at higher field? Like basically–what about the system would have to be changed for the optimal condition to be at high field?

      Reply
    8. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Hi Raj, Thank you! I believe I may not be fully understanding your question. The matching conditions remain the same and are highly valid in the high-field regime. However, as the magnetic field strength increases, the range over which spin polarization transfer occurs becomes narrower. This is because, at higher fields, the matching condition primarily depends on the nuclear Larmor frequency, with much less influence from hyperfine couplings. This trend is also demonstrated in the presentation at 9.4 Tesla.

      Reply
      1. Raj Chaklashiya Avatar
        Raj Chaklashiya

        Thanks! That makes sense to me–so it would have to require tuning the nuclear larmor frequency for it to work well at high fields.

        Reply

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  • Seeing the unseen with Dynamic Nuclear Polarization

    Ribal Jabbour (New York University Abu Dhabi, UAE)

    Abstract: Dynamic Nuclear Polarization (DNP) is a technique that utilizes the sensing capability of electron spins to significantly enhance the sensitivity of NMR signals, particularly for low-sensitivity samples. Glassing agents are essential in the DNP process, as they facilitate the transfer of polarization from unpaired electron spins to nuclear spins while providing cryoprotection. Glycerol/D2O/H2O mixtures have been widely used as glassing agents for this purpose over the past two decades. However, glycerol exhibits two prominent peaks in NMR spectra, which can obscure signals in certain regions. Using alternative glassing agents can mitigate this issue, uncovering these regions for clearer analysis. Additionally, DNP without any glycerol can be employed to study off-the-shelf insulin, which can enable detailed structural of this critical biomolecule.

    1. Chloé Gioiosa Avatar
      Chloé Gioiosa

      Hi Ribal, Thank you for your presentation.

      Did you estimate the proton concentration in your final sample and how does it compare with a more traditional DNP juice formulation, and did you try different concentrations of radical to optimize the enhancement?

      Reply
    2. Ribal Jabbour Avatar
      Ribal Jabbour

      Hi Chloé,

      We did not estimate the proton concentration in the final sample yet.

      We did try different radical optimizations. 10 mM seems to be the optimal. For 20 mM the enhancement goes down to 30.

      Reply
    3. Arianna Actis Avatar
      Arianna Actis

      Hi Ribal, thank you for the presentation.
      Did you try radicals of different types, do you think they might give a better enhancement? And, following the previous question by Chloé, do you have an explanation why increasing the concentration of the radical you used decreases the enhancement?

      Reply
    4. Ribal Jabbour Avatar
      Ribal Jabbour

      Hi Arianna,

      We did not try different radicals. The radical we used (ASYMPol-POK) is, to my latest knowledge, the best-performing and commercially available one at this field. There is a plan to try AMUPol and see the difference between both. In general, when you increase your radical concentration, you are adding more paramagnetic species to your sample (sometimes high concentration may also overcouple your radicals and can terminate them), which leads to more paramagnetic relaxation and broadening, and this can affect your enhancement.

      Reply
    5. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Ribal, nice presentation! The different results depending on glassing agent used made me very curious, and I have a couple questions to this effect:
      1) What would you expect to occur if you tried DMSO solvent?
      2) There are some papers that use a special freezing method (https://www.jove.com/v/61733/cryogenic-sample-loading-into-magic-angle-spinning-nuclear-magnetic) that requires only 10-15% glycerol or DMSO for cryopreservation to run MAS DNP experiments without breaking cells:
      https://pubs.acs.org/doi/full/10.1021/jacs.1c06680 and https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2021.789478/full — I am wondering if you would expect that decreasing glycerol content could potentially mimic the results you see in just insulin, while simultaneously providing some of the benefits of glycerol (which appear to be stronger signal based on the slide)

      Reply

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  • Long-lived states that can survive a phase transition!

    Vishal Varma (Indian Institute of Science Education and Research (IISER) Pune, India)

    Abstract: In NMR spectroscopy, the longitudinal relaxation that destroys both classical and quantum information by restoring the spin populations to thermal equilibrium has traditionally hindered our ability to harness the full potential of spin dynamics. However, the emergence of long-lived states (LLS) has challenged this notion. With lifetimes significantly exceeding the spin-lattice relaxation time constant T1, LLS has revolutionized the field, enabling advanced medical imaging, chemical analysis, and quantum information processing applications.

    While LLS has predominantly been observed in isotropic phases, its presence in anisotropic phases has remained an intriguing question. I will show that LLS can be prepared in a two-spin system oriented in a liquid crystal solvent and, even more strikingly, demonstrate that it can survive the phase transition from the oriented phase to the isotropic phase when subjected to heating. This resilience highlights the untapped potential of LLS in various applications.

    Reference(s):

    V. Varma and T. S. Mahesh, “Long-Lived Singlet State in an Oriented Phase and its Survival across the Phase Transition Into an Isotropic Phase,” Phys. Rev. Applied 20, 034030 (2023).

    1. Kirill Sheberstov Avatar
      Kirill Sheberstov

      Why do you use M2S in the partially oriented phase and smth like the Sarkar sequence in the isotropic phase? How long does it take for the phase transition to occur, and how does this time compare to the lifetime(s) of LLS in the oriented phase and in the isotropic phases?

      Reply
    2. Vishal Varma Avatar
      Vishal Varma

      Hi Kirill Sheberstov. The spins are strongly coupled in the partially oriented phase; therefore, we use the M2S sequence. We use the Sarkar sequence in the isotropic phase due to weak coupling between the two spins.

      The phase transition takes less than 30 seconds. We turn on the probe heater 10 seconds before the M2S, because it takes a few seconds before a significant temperature rise is observed. The rest of the time is spent during storage when the WALTZ-16 sequence is applied.

      Near the transition temperature, the LLS lifetime is 4.6 seconds (in oriented phase) and above 8 seconds (in isotropic phase). So we give minimum 16 seconds of storage time before acquiring the signal with the Sarkar sequence in isotropic phase. This delay is above 5*T_lls for both the oriented and isotropic phases.

      Thanks for your interest.

      Reply
    3. Cory Widdifield Avatar
      Cory Widdifield

      Hello, this presentation appears to be from the viewpoint that survival of the long-lived singlet (LLS) state would be unexpected upon a phase transition. Could you clarify why undergoing a phase transition might eliminate all the coherent signal associated with the LLS state? Did your understanding change as a result of making these experimental measurements? Are you able to comment on whether there is a ‘scaling’ in the amount of LLS coherence when undergoing the phase transition (for example, is some portion irreversibly lost, or does it appear to be quantitatively ‘all there’ after accounting for otherwise ‘normal’ relaxation processes that would occur during the time associated with the phase transition)?

      Reply
      1. Vishal Varma Avatar
        Vishal Varma

        Hello. Thank you for your questions.

        As the phase transition happens, the structure of the Hamiltonian changes. The residual dipolar coupling is decreasing with the temperature, and we were unsure whether the LLS would survive this change! We found that the LLS survives this, and we verified that the signal observed in the isotropic phase originates from the LLS coherence prepared in the oriented phase.

        Regarding the question of scaling in the amount of LLS coherence, I think some part is irreversibly lost because the heating of the sample is non-uniform. Some parts of the sample might not have been entirely converted to the liquid phase, making it a mixed phase. Moreover, since the detection sequence in the isotropic phase is designed to detect the LLS coherence in the isotropic phase, it might also be that some LLS coherence was not observed.

        I appreciate your questions. Please let me know if my answer is unclear or if I have misunderstood the question. I would be happy to discuss. Thanks again.

        Reply
        1. Cory Widdifield Avatar
          Cory Widdifield

          Thank you for your responses.

          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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