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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.
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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? -
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.
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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?-
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!
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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! -
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!
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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!-
Yes it does! Thank you for your response!
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High-resolution ssNMR study of Collagen Protein in Native Bone under Fast Magic Angle Spinning
Bijaylaxmi Patra (Centre of Biomedical Research, India)
LinkedIn: @Bijaylaxmi Patra; X: @BijaylaxmiNMR; Bluesky: @bijaylaxmi.bsky.social
Abstract: Fast magic angle spinning (MAS) is a powerful technique in solid-state nuclear magnetic resonance (ssNMR) spectroscopy that effectively decreases line broadening and enables high-resolution structural study of biological systems. Nevertheless, its utility in probing complex and heterogeneous biomaterials in their native form has been constrained. In this study, we leveraged fast MAS (70KHz) to perform 2D ¹H-detected ¹³C–¹H double cross-polarization (CP) heteronuclear correlation experiments on native bone. This high-resolution method enabled the detection of previously unobserved inter-residue correlations within the aliphatic region of collagen. Additionally, our findings suggest potential π-interactions between aromatic amino acids and spatially proximal anionic or imino acids within the collagen triple helix. Our study paves the way for advanced ¹H-detected heteronuclear correlation experiments under fast MAS to more effectively elucidate the complex and heterogeneous structural organization of other native collagen-rich biological systems.
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Hello Patra, nice presentation!
I was wondering if you can observe the same inter-residue correlation also exploiting other SS-NMR experiments such as the C-C DARR or similar.-
Hi Marco, thanks for showing interest in my work.
Yes, we may observe the same inter-residue correlations using other ssNMR experiments as well, and our future plans include performing such experiments to obtain ¹³C–¹³C correlations.
However, as an initial study, we preferred ¹H-detected ¹³C–¹H experiments because they require significantly less experimental time compared to ¹³C–¹³C correlation experiments, especially since the experiments are conducted at natural isotopic abundance.Fast MAS techniques have not been widely used to study collagen in native bone due to concerns about friction-induced sample instability during long experimental durations. In our previous study (https://doi.org/10.1002/mrc.5508), we demonstrated the feasibility of acquiring ¹H–¹H correlations. Building on that, we now report ¹³C–¹H correlations, and we believe that ¹³C–¹³C experiments will be even more interesting in future studies.
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Hi Marco, thanks for showing interest in my work.
Yes, we may observe the same inter-residue correlations using other ssNMR experiments as well, and our future plans include performing such experiments to obtain ¹³C–¹³C correlations.
However, as an initial study, we preferred ¹H-detected ¹³C–¹H experiments because they require significantly less experimental time compared to ¹³C–¹³C correlation experiments, especially since the experiments are conducted at natural isotopic abundance.Fast MAS techniques have not been widely used to study collagen in native bone due to concerns about friction-induced sample instability during long experimental durations. In our previous study (https://doi.org/10.1002/mrc.5508), we demonstrated the feasibility of acquiring ¹H–¹H correlations. Building on that, we now report ¹³C–¹H correlations, and we believe that ¹³C–¹³C experiments will be even more interesting in future studies.
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Very nice presentation. I was just wondering if it would be interesting to study other components of the bone and how they are structured within the bone e.g the lipids.
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Yes, it is indeed very interesting to study other components in bone, as it is rich in various types of molecules within its extracellular matrix.
Bone is a fascinating biomaterial that my lab has been working on for many years. My seniors have already explored water–lipid interactions (https://doi.org/10.1016/j.ssnmr.2020.101666), water–mineral interactions (https://doi.org/10.1021/acsomega.2c01133), and citrate–collagen interactions within the bone matrix (https://doi.org/10.1021/acs.jpcb.1c01431).
Specifically, regarding lipids in bone, the major type found in the matrix is triglycerides. Nidhi et al. studied lipids in hydrated, dehydrated, and H₂O–D₂O exchanged bone samples. They found that dehydration and H/D exchange significantly affect the transverse relaxation times (T₂) of triglycerides. These changes reflect alterations in the hydrogen bonding network and the local conformational dynamics of the lipid environment. Dehydration increased the mobility of triglycerides, indicating greater freedom of motion when water is removed. For further insights into other components, I recommend reading this book chapter: https://doi.org/10.1039/9781839165702-00614
Thank you for your curiosity and engagement with our research.
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Hi Bijaylakshmi, Thank you for the presentation.
So if I understood correctly, you just ground the native bone and packed it directly into the rotor? Were there any other steps involved in preparing the sample for the fast MAS experiments?
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Studies have shown that cryogenic grinding can alter the structure and hydration of bone. Therefore, we avoided both cryogenic and mechanical grinding. Instead, we carefully prepared small bone flakes (tiny pieces) using a scalpel and directly packed them into the rotor without any further processing. These flakes retained the structural and morphological features of the native intact bone.
For further queries, you can refer to our published article: https://doi.org/10.1002/mrc.5508.
I’m grateful for your interest and curiosity about my work.
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HSQC/F1-PSYCHE TOCSY NOAH Supersequence for the Analysis of Biofluids
Aditi Pandey (Centre of BioMedical Research, India)
Abstract: Accurate metabolite assignment is essential for effective metabolomics research. 2D NMR spectroscopy such as 1H-13C HSQC and 1H-1H TOCSY plays vital role in the identification of metabolites when combined with spectral databases. However, collecting high quality HSQC data from biofluids at natural 13C abundance requires large number of scans and hence NMR time typically of the order of 12-24 hours even at high fields (600-800MHz) with cryogenic probes. Performing further COSY and TOCSY in high resolution mode can result in additional hours. While NOAH (NMR by Ordered Acquisition using 1 H detection) supersequences offer
time-efficient acquisition by combining multiple experiments in a single pulse sequence using a single recovery delay without sacrificing sensitivity. This is achieved by reusing unused magnetization from one experiment (e.g. HSQC) for subsequent ones (e.g. TOCSY). However due to high complexity of biofluids standard TOCSY spectra often suffers from peak overlap.
The PSYCHE-TOCSY experiment helps resolve this by generating one sharp peak per resonance, thus minimizing overlap. Thus we want to introduce a novel HSQC+PSYCHE-TOCSY NOAH2 supersequence that combines HSQC with PSYCHE-TOCSY to provide fasterand clearer analysis of complex metabolite mixtures in biofluids.-
Hello! Very nice work congratulations!
I was wondering, in your NOAH-based sequence, how much sensitivity is lost (if any) compared to the two experiments acquired separately? How much time is then saved?
Thank you very much!-
Hello Marco, very insightful query indeed!
Actually when we record a PSYCHE-TOCSY separately at all the same acquisition parameters, there is negligible loss in the sensitivity. Here we have compared it with a regular TOCSY, which is although more sensitive but we are often not able to make full use of it due to the crowded peaks.
I hope you understand. You can further ask any more queries.
Thank you!
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That’s quite impressive!
How does the resolution of the NOAH sequence compares to the a PSYCHE-TOCSY, as opposed to a regular TOCSY?
The NOAH TOCSY (pannel D in the 1D and 2D NMR Spectra assignment pannel) seems to show some artifacts at 5ppm in F1. Can you comment on that? Also water suppression seems a lot better, what is the reason?
How does the signal-to-noise ratio compare between the experiments?Thanks!
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Hello Nicolas, thanks for your kind appreciation.
The resolution in PSYCHE-TOCSY from NOAH sequence is same as standalone PSYCHE-TOCSY. The artefact is due to some phase problem.
For water suppression we have used presaturation block before the start of TOCSY sequence and excitation sculpting, placed just before the acquisition in homonuclear module.
The SNR of the two experiments is very similar.
I hope this resolves your query. Thank you!
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Identification, Quantification, and Isolation of Synthetic Cannabinoids in Forensic Drug Seizures
Mariana Riccio (Universidade de Brasília, Brasil)
Abstract: Synthetic cannabinoids represent one of the most diverse classes of emerging psychoactive substances and are frequently seized in forensic operations. These substances, designed to mimic the effects of Δ9-tetrahydrocannabinol (Δ9-THC), exhibit diverse chemical structures, making their identification and quantification challenging using conventional methods. In this context, Nuclear Magnetic Resonance (NMR) spectroscopy has emerged as an advantageous analytical alternative, enabling structural characterization and accurate quantification without the need for commercial reference standards of the analyte itself. This study aimed to identify, quantify, and isolate the synthetic cannabinoids JWH-073, JWH-210, and JWH-250 from samples of plant material seized by the Brazilian Federal Police. For this purpose, gas chromatography-mass spectrometry (GC/MS) was used for the preliminary identification of cannabinoids in the samples, flash chromatography for separation, and NMR spectroscopy for characterization and quantification. The results obtained through NMR allowed for detailed structural characterization and confirmation of the identity of the cannabinoids JWH-073, JWH-210, and JWH-250, whose concentrations in the seized samples were 1.42%, 1.64%, and 0.87% (w/w), respectively. Additionally, purification via flash chromatography enabled the separation of the compounds with purities of 76.1% for JWH-073, 72.7% for JWH-210, and 89.0% for JWH-250. The data obtained demonstrate the efficiency of NMR as an analytical method for the quantification of synthetic cannabinoids, providing a reliable approach for forensic analysis without the need for commercial reference standards.
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Hello Mariana, thank you for the nice presentation!
I have two questions :
1. At which magnetic field and with what range of concentration did you do your analysis of the mixture with?
2. I was wondering if this methodology could be used in the future to discriminate the origin of the seized material based on their cannabinoid composition?-
Hello! Thank you so much for your kind feedback and for your thoughtful questions!
1. Magnetic field and concentration range:
The NMR analyses were performed on a 14.1 T spectrometer (600 MHz for ¹H NMR). For the preparation of the samples, 100 mg of plant material was extracted with 1 mL of CDCl₃, resulting in a crude extract that was directly analyzed. The cannabinoid concentrations within this extract ranged from 1 to 3 mg/mL.2. Discriminating the origin of the seized material:
In an ideal scenario, yes — the cannabinoid composition could potentially be used to discriminate the origin of seized material, but it’d have to be supported by a comprehensive database and chemometric tools.In Brazil, for instance, the Federal Police runs a project called PeQui (Perfil Químico das Drogas), which focuses on establishing standardized chemical profiles of seized drugs to support forensic intelligence. This includes the analysis of purity, minor constituents, adulterants, and solvent residues to help identify trafficking routes, distribution patterns, and — when possible — infer geographic origin.
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Thank you for your answers!
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Hello,
I assume that these samples provided by the police were initially as plants (or plant parts). Could you describe the workup stages (extractions?) that are required to isolate the relevant compounds from the plant? Also, I think you are showing 1H NMR results only. Would adding 13C NMR data be useful to help increase your confidence in assigning the spectra to chemical compounds in the samples?
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Hello, Cory! Thank you for your interest.
Yes, the samples provided by the Federal Police were plant materials — specifically herbal mixtures suspected to contain synthetic cannabinoids. Here’s a description of the extraction and isolation process for the enriched samples:
Extraction and isolation:
A total of 3.85 g of plant material, previously confirmed by GC/MS to contain a mixture of three synthetic cannabinoids, was extracted with 25 mL of methanol in a Falcon tube. The mixture was vortexed for 5 minutes, sonicated for 1 hour, and then centrifuged. The supernatant was collected, and the whole process was repeated another time under the same conditions. The combined extracts were evaporated at room temperature, yielding 165 mg of dry extract.This extract was then subjected to flash chromatography using a Biotage® Isolera One system, with a 10 g normal-phase silica column (25–33 µm). The elution was performed with an hexane/ethyl acetate mixture (95:5), allowing the isolation of enriched fractions of the cannabinoids for further analysis.
Regarding ¹³C NMR:
You’re absolutely right — while ¹³C NMR would certainly improve the confidence in compound identification, it was only feasible for the enriched fractions obtained through chromatography. In the crude extract, the analyte concentration was too low (~0.5-2%), and acquiring reliable ¹³C spectra would require prohibitively long acquisition times due to sensitivity limitations.-
Thank you for your responses.
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Hi Mariana,
Thank you for your presentation, and I enjoyed it! I have two questions: 1. Have you tried using 2D NMR to further validate the structures of the different isomers? 2. This may not be directly related to the NMR focus of this conference, but have you considered getting crystals to precisely determine the structures? look forward to your thoughts.-
Hi Yunfan,
Thank you for your kind words and thoughtful questions!1. Regarding the use of 2D NMR: yes, we employed 2D experiments—specifically COSY, HSQC, and HMBC—to support the assignment of chemical shifts and confirm the substitution pattern of the isomers. These correlations were essential to distinguish between JWH-250 and its positional isomer JWH-201.
2. As for crystallography: although single-crystal X-ray diffraction would certainly provide definitive structural confirmation, we didn’t pursue it in this project. The combination of GC/MS and 1D/2D NMR already provided sufficient information to identify the structures with confidence. Moreover, growing suitable crystals from the isolated fractions would have been particularly challenging, both because of the small amount of material and the need for pure, well-formed single crystals. So considering the analytical goals and the limited sample availability, we prioritized solution-state NMR techniques.
Best regards,
Mariana
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Identifying multiple quantum coherence in ionic liquids
Yanan Li (New York University, United States)
LinkedIn: @Yanan Li; X: @YananLi12451
Abstract: Multiple-quantum NMR spectroscopy has long been employed to selectively isolate specific magnetization components. Here, we combined CRAZED and triple-quantum-filtered (TQF) experiments to investigate multiple quantum coherences in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4). This approach offers detailed insights into the ion dynamics and intermolecular interactions characteristic of ionic liquids.
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Hi, on slide 5, you show the dependence of the signal intensity on the angle θ. Which experimental parameters set up this angle? Another question: how many coupled spins are necessary to have to expect triple quantum coherence? And zero order coherence?
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For the first question,we control the angle θ by adjusting the relative amplitudes of gradients along y and z (Gz, Gy).
For the second question, triple quantum coherence are required at least three coupled spins (like I1+I2+I3+ or I1-I2-I3-). Zero order coherences are formed with at least 2 spins (like I1+I2- or I1-I2+).
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Yanan,
Thank you for your presentation. You clearly demonstrated intermolecular contributions to the quantum coherence. Since this is an ionic compound, does the contribution come from the cationic counterpart of BF₄ anion or from other ionic liquid species? Do you expect certain nuclei to contribute more significantly? Looking forward to your insights. -
Thank you for the good question! I would say that the observed intermolecular quantum coherences of 11B likely originate from interactions between the BF4 anion and both neighboring anions and cations (11B-1H, 11B -19F, 11B-11B). It is difficult to draw a conclusion from the standard CRAZED experiments, but I tend to favor 1H due to its higher magnetic separation ratio and natural abundance.
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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.
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Thank you for the presentation. Do you use a special experimental setup to run the 1H-19F NMR experiments?
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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.
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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?
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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.
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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.
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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?-
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.
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Dear Sajith,
Yes, I’m doing well and hope you’re doing great too! Thank you for answering all the questions so thoroughly.-
Good to know! I’m also doing good.
You’re welcome.
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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.
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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.
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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!
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Same here!
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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).
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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?
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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.
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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)?
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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.
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Thank you for your responses.
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Microstructural and Dynamical Characterization of Polymer Electrolytes for Li-ion Batteries Using Advanced Solid-State NMR Techniques
Isha Isha (Indian Institute of Science, India)
Abstract: Solid-state lithium-ion batteries (SSLBs) with lithium metal anodes present significant advantages over conventional liquid electrolyte-based lithium-ion batteries (LIBs), including higher energy densities and improved safety. The flammability of liquid electrolytes and the formation of dendrites at the electrodes are critical safety concerns in traditional LIBs. Furthermore, the energy density of conventional LIBs (200–300 Wh kg⁻¹) is insufficient for long-distance applications in battery-powered devices, and their operational temperature range is limited to -20°C to 60°C.
Implementing solid electrolytes (SEs) offers a promising solution to these challenges. Solid polymer electrolytes (SPEs) exhibit superior mechanical properties and enhanced safety features. However, the primary limitation of SPEs is their low ionic conductivity, typically around 10-4 Scm-1 under ambient conditions, which remains a significant obstacle to their widespread adoption. Understanding the mechanism of conductivity is a crucial step. Our Research mainly focuses on understanding the conductivity mechanism of the polymer electrolytes. Ionic Conductivity depends on the structure and the dynamics of the polymer backbone, and the Solid-State NMR is the only technique that can probe both the local structure and the dynamics. The microscopic properties of the polymers, such as the local structures, phases, and dynamics significantly influence macroscopic conductivity. Understanding the structure-property relationships is crucial to design SPE(s). SS NMR spectroscopy allows non–invasive characterization with site-specific local structural and dynamical details of materials regardless of their crystallinity. The NMR interactions are susceptible to the local structures and dynamics that have been used to gain insight into ion–dynamics mechanism in SPE(s).-
Thank you for the presentation! Could explain the observed isotropic-shift evolution for the various salt concentrations observed in the 1H, 6/7Li, and 19F NMR?
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Thanks for your presentation Isha, have you extracted any Li hopping/transport rates from your VT 7Li data?
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Thank you for the question , the shift in the isotropic chemical shift represents the change in the phases when salt is added. In PEO, there are crystalline domains and amorphous domains. When the salt is added to the polymer matrix, there is a reformation of the phases dominating by the amorphous which is indicated by the shoulder peaks.
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Optically Addressable NV Centers for Quantum Sensing
Amaria Javed (NYU Abu Dhabi, United Arab Emirates)
Abstract: This talk presents our ongoing work on NV-diamond-based quantum sensing at the Center for Quantum and Topological Systems (CQTS) at NYU Abu Dhabi, with a focus on optical techniques for spin state readout and signal enhancement. Nitrogen-Vacancy (NV) centers in diamond are point defects that serve as atomic-scale quantum sensors, offering remarkable sensitivity to magnetic and electric fields, temperature, and strain. These color centers exhibit spin-dependent fluorescence under green laser excitation, enabling optical initialization and readout of their quantum state even at room temperature.
At the core of our experimental approach is Optically Detected Magnetic Resonance (ODMR), a technique that uses changes in NV center fluorescence to measure shifts in spin transitions, revealing information about the surrounding environment. We are currently building a custom NV-based sensing setup, which involves laser excitation at 532 nm, microwave control of spin transitions, and efficient fluorescence detection via optical filters and photodetectors.
Our work aims to optimize the optical alignment, fluorescence collection efficiency, and stability of the system for robust quantum sensing applications. We explore methods to enhance contrast in ODMR spectra, increase sensitivity, and suppress background noise, which are critical for real-time, high-resolution measurements. These efforts lay the foundation for emerging applications in nanoscale magnetometry, bioimaging, materials characterization, and lab-on-a-chip sensing technologies.
This presentation will give an overview of the NV center’s optical properties, practical design considerations in setting up an ODMR experiment, and the broader role of photonics in quantum sensing.-
Hi Amaria,
Thank you for your presentation. What specific object or system do you plan to detect using the NV center through ODMR? I assume it is something spin active, so it can interact with the NV and cause observable changes in the emission? Looking forward to hearing more about your project. -
Thank you for your interest! Yes, you’re absolutely right, the NV center is sensitive to spin-active species. In our project, we are focusing on EPR detection using the NV center, specifically targeting unpaired electron spins in external samples. The idea is to use the NV’s spin-dependent photoluminescence and ODMR contrast to detect and characterize these spins at the nanoscale.
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Polyelectrolyte Hydrogels for Water Desalination Examined via Sodium NMR Spectroscopy
Huijing Zou (New York University, United States)
LinkedIn: @Huijing Zou
Abstract: Hydrogel desalination is a recently developed method for removing salt from water. Its mechanism is based on the electrostatic imbalance between the fixed charge groups in the polyelectrolyte hydrogels and the surrounding solution. Combining polyelectrolyte hydrogels with thermoresponsive materials enables a temperature-driven swelling and shrinking cycle, which provides a more energy-efficient way to extract desalinated water from hydrogels by using solar energy. In this study, the interactions between salt ions and sodium polyacrylate hydrogels in NaCl solution were analyzed using NMR spectroscopy. The Na+ ion distribution was characterized by 23Na NMR imaging. The relaxation rates of Na+ in the supernatant and hydrogel phase were measured from 298 K to 318 K. The hydrogels in multi-salt environments were measured under two conditions: one with controlled concentrations of each type of salt, and another with controlled total ionic strength. Furthermore, multiple quantum filtered NMR was applied to analyze quadrupolar interactions between Na+ ions and hydrogels. Current state-of-the-art analyses for studying the ionic flux are based on conductivity measurements. The use of sodium NMR spectroscopy and imaging provides much deeper insights into the salt-rejection mechanisms. The results from this study provide valuable insights for the design of hydrogel structures and the improvement of desalination performance.
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Thank you for the presentation. Can the amount of Na+ ions in the supernatant quantified by both imaging and relaxation analysis? If so, do the results agree?
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Hi Jonas, thank you for your comment!
The Na+ ions in the supernatant can be quantified by NMR imaging by using a reference sample (NaCl solution only). We can compare the integrals to estimate the amount of Na+ ions within the detection region. The integral ratio (with half-tube hydrogels: without hydrogels) is 2.51 for 1dzg, and 2.72 for 1d imaging. The relaxation analysis help us understand the Na+ ion mobility. When comparing relaxation rates under different conditions (temperature, multi-salt…), we can get a rough view on how different conditions affect the bound Na+ and free Na+ ions.
Hope this answers your question.
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Hi Huijing, thank you for the presentation. What is the spatial resolution of your imaging measurements, and what is the size of the average piece of hydrogel?
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Hi Blake, thank you for your comment!
The 1D imaging is done on Bruker AVIII 400 MHz, and has TD=512 and swh=39682.5 Hz, spatial resolution is 152.3 μm. In fact, I haven’t done much measurement on the size of hydrogels and I assume you mean the dried hydrogels, most dried hydrogels I added has a length within 3 mm.
Hope this answers your question!
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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.
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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. -
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!
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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?-
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
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