Nuclear Magnetic Resonance Characterization Research Articles

Structural properties of glucan from Russula griseocarnosa and its immunomodulatory activities mediated via T cell differentiation

The polysaccharide, RGP2, was isolated from Russula griseocarnosa and its immunostimulatory effects were confirmed in cyclophosphamide (CTX)-induced immunosuppressed mice. Following purification via chromatography, structural analysis revealed that RGP2 had a molecular weight of 11.82 kDa and consisted of glucose (Glc), galactose (Gal), mannose, glucuronic acid and glucosamine. Bond structure analysis and nuclear magnetic resonance characterization confirmed that the main chain of RGP2 was formed by →6)-β-D-Glcp-(1→, →3)-β-D-Glcp-(1→ and →6)-α-D-Galp-(1→, which was substituted at O-3 of →6)-β-D-Glcp-(1→ by β-D-Glcp-(1→. RGP2 was found to ameliorate pathological damage in the spleen and enhance immune cell activity in immunosuppressed mice. Based on combined multiomics analysis, RGP2 altered the abundance of immune-related microbiota (such as Lactobacillus, Faecalibacterium, and Bacteroides) in the gut and metabolites (uridine, leucine, and tryptophan) in the serum. Compared with immunosuppressed mice, RGP2 also restored the function of antigen-presenting cells, promoted the polarization of macrophages into the M1 phenotype, positively affected the differentiation of helper T cells, and inhibited regulatory T cell differentiation through the protein kinase B (AKT)/mechanistic target of rapamycin (mTOR) pathway, ultimately exerting an immune boosting function. Overall, our findings highlight therapeutic strategies to alleviate CTX-induced immunosuppression in a clinical setting.

NMR characterization of RNA binding property of the DEAD-box RNA helicase DDX3X and its implications for helicase activity

The DEAD-box RNA helicase (DDX) plays a central role in many aspects of RNA metabolism by remodeling the defined structure of RNA molecules. While a number of structural studies have revealed the atomistic details of the interaction between DDX and RNA ligands, the molecular mechanism of how this molecule unwinds a structured RNA into an unstructured single-stranded RNA (ssRNA) has largely remained elusive. This is due to challenges in structurally characterizing the unwinding intermediate state and the lack of thermodynamic details underlying this process. In this study, we use solution nuclear magnetic resonance (NMR) spectroscopy to characterize the interaction of human DDX3X, a member of the DDX family, with various RNA ligands. Our results show that the inherent binding affinity of DDX3X for ssRNA is significantly higher than that for structured RNA elements. This preferential binding, accompanied by the formation of a domain-closed conformation in complex with ssRNA, effectively stabilizes the denatured ssRNA state and thus underlies the unwinding activity of DDX3X. Our results provide a thermodynamic and structural basis for the DDX function, whereby DDX can recognize and remodel a distinct set of structured RNAs to participate in a wide range of physiological processes.

Topological characterizations on hexagonal and rectangular tessellations of antikekulenes and its computed spectral, nuclear magnetic resonance and electron spin resonance characterizations

AbstractTessellations of antikekulenes are of interest from the standpoints of antiaromaticity, ring currents, unusual ‐electron characteristics, magnetism and their highly reactive nature. Although precursors of antikekulenes have been synthesized, up to now synthesis of antikekulenes has been proven to be formidably difficult. Yet they are predicted to have intriguing properties and their antiaromatic nature together with a combination of four and six‐membered rings makes them intriguing candidates for theoretical indices. In the present study, we have computed the topological indices of antikekulene by employing graph‐theoretical cut methods that simplify the parent tessellations of antikekulenes into simpler graphs. We have derived exact mathematical expressions of several topological descriptors for hexagonal and rectangular antikekulene structures. Furthermore we have obtained the graph‐spectral properties, algebraic structure counts, resonance stabilization and delocalization energies as well as nuclear magnetic resonance and electron spin resonance spectroscopic patterns of the two tessellations of antikekulenes.

Investigating the effects of base oil type on microstructure and tribological properties of polyurea grease

The soaring prices and physiological toxicity of lithium-based grease make polyurea grease a promising alternative due to its balanced cost and performance. Employing preformed thickeners to avoid toxic raw materials has become a preferred method for eco-friendly preparation of polyurea grease. However, the underlying mechanism of base oil modulates the microstructure of polyurea greases prepared with preformed thickeners, subsequently influencing their macroscopic performance remains unclear. Herein, three polyurea greases were synthesized by regulating the base oil types ((poly(α-olefin) oil (PAO40), alkyl naphthalene oil (AN30), and polyether oil (OSP320)) with the same preformed thickener. The real-time polarizing microscope observation of the grease structure evolution process revealed that the preformed thickeners gradually expanded in the base oil and formed a fiber structure. An increased polarity disparity between thickener and base oil leads to a reduced swelling rate and increased fiber length. As a result, compared with high polarity OSP320 and low polarity AN30, non-polar PAO40 induces a more interconnected 3D network composed of long fiber in obtained grease (PG). Low field nuclear magnetic resonance characterization and molecular simulations reveal this network exhibits significant binding ability towards base oil, reducing the movement ability of the base oil, endowing PG with the highest structural strength, achieving effective lubrication and low noise performance. These in-depth understandings will help promote the research and development of polyurea greases.

A commercially viable solution process to control long-chain branching in polyethylene.

In polyolefins, long-chain branching is introduced through an energy-intensive, high-pressure radical process to form low-density polyethylene (LDPE). In the current work, we demonstrated a ladder-like polyethylene architecture through solution polymerization of ethylene and less than 1 mole % of α,ω-dienes, using a dual-chain catalyst. The ladder-branching mechanism requires catalysts with two growing polymer chains on the same metal center, thus enchaining the diene without the requirement of a steady-state concentration of pendant vinyl groups. Molecular weight distributions lacking a high-molecular weight tail, distinctive Mark-Houwink signatures, nuclear magnetic resonance characterization, and shear and extensional rheology consistent with highly branched polyethylene architectures are described. This approach represents an industrially viable solution-polymerization process capable of producing controlled long-chain branched polyethylene with rheological properties comparable to those of LDPE or its blends with linear low-density polyethylene (LLDPE).

A Novel Approach for Post-Mortem Analysis in All-Solid-State Batteries: Isolating Solid Polymer Electrolytes from Lithium Anodes

Polymeric electrolytes are currently at the forefront of research for the next generation of lithium all-solid-state batteries. Polyethylene oxide (PEO), a commonly used polymer for these batteries, operates at elevated temperatures at which it reacts with active metal electrodes (e.g., lithium). Rich surface chemistry is developed at the Li-PEO interfaces, thereby controlling these batteries’ electrochemical behavior. Interfacial studies are essential to comprehend batteries’ stabilization or capacity fading mechanisms. For that, post-mortem analysis with an emphasis on interfaces is a necessary approach to underpinning these mechanisms. While it can be readily done with liquid electrolytes, post-mortem characterization of similar interfaces with solid electrolytes is hampered by the Li-PEO stack firm adhesion, which is impossible to separate. Here, various methods were attempted to separate polymer electrolytes from metallic anodes after Li symmetric cells’ operation, which is a necessary step for solid-state NMR characterization. By a simple method involving exposure to N2(g) atmosphere, PEO-based solid electrolyte samples were successfully isolated from lithium anodes while preserving their morphology and chemical characteristics to enable their direct analysis. This method’s concept was approved by Solid-state NMR spectroscopy. This work opens the door for post-operative analysis of many kinds of solid-state Li batteries.

NMR characterization of uniformly 13C- and/or 15N-labeled, unsulfated chondroitins with high molecular weights.

Solution nuclear magnetic resonance (NMR) analysis of polysaccharides can provide valuable information not only on their primary structures but also on their conformation, dynamics, and interactions under physiological conditions. One of the main problems is that non-anomeric 1H signals typically overlap, and this often hinders detailed NMR analysis. Isotope enrichment, such as with 13C and 15N, will add a new dimension to the NMR spectra of polysaccharides, and spectral analysis can be performed with enhanced sensitivity using isolated peaks. For this purpose, here we have prepared uniformly 13C- and/or 15N-labeled chondroitin polysaccharides -4)-β-D-glucuronopyranosyl-(1-3)-2-acetamido-2-deoxy-β-D-galactopyranosyl-(1- with molecular weights in the range from 310 to 460 k by bacterial fermentation. The enrichment ratios for 13C and 15N were 98.9 and 99.8%, respectively, based on the mass spectrometric analysis of the constituent chondroitin disaccharides. 1H and 13C NMR signals were assigned mainly based on HSQC and 13C-detection experiments including INADEQUATE, HETCOR, and HETCOR-TOCSY. The carbonyl carbon signal of the N-acetyl-β-D-galactosamine residue was unambiguously distinguished from the C6 carbon of the β-D-glucuronic acid residue by the observation of 13C peak splitting due to 1JCN coupling in 13C- and 15N-labeled chondroitin. The T2* and T1 were measured and indicate that both rigid and mobile sites are present in the long sequence of chondroitin. The conformation, dynamics, and interactions of chondroitin and its derivatives will be further analyzed based on the results obtained in this study.

Insertion of fluorine into a LiFePO4 electrode material by gas-solid fluorination.

In this study, the insertion of fluorine into LiFePO4 was carried out under molecular fluorine F2 at different temperatures. The reactivity strongly depends on the applied fluorination temperature, leading to very different products: core delithiation of the material is observed at low temperatures with the formation of a LiF shell around particles, while the material decomposes to gradually form a mixture of α-FeF3 and α-Li3FeF6 iron fluorides at higher temperatures. A second thermal treatment under N2 leads to the formation of LiFePO4F in a new way that has not been reported before. Supported by X-ray diffraction, Raman, infrared, Mössbauer spectroscopies, 7Li nuclear magnetic resonance and electrochemical characterization of the different materials, this report demonstrates various fluorination mechanisms for LiFePO4, from chemical delithiation to the stable pure fluorinated form LiFePO4F and illustrates an innovative method that can be extended to obtain the triphylite form of NaFePO4.

Eudragit® L100 Post-Modification via Ugi Multicomponent Reaction

This work investigated the post-modification of commercial poly(methyl mechacrylate-coacrylic acid) using the versatile multicomponent Ugi reaction. This reaction introduces diverse functionalities to tailor the polymer properties effectively. The commercial copolymer which is known for biocompatibility and drug delivery application was subjected to the Ugi reaction, altering its chemical structure. The structure of the modified polymer was checked by Fourier transform infrared spectroscopic and nuclear magnetic resonance and thermal characterizations, confirming successful Ugi component integration. Additionally, gel permeation chromatography assessed molecular weight changes. Results revealed enhanced thermal stability of the modified polymers compared to unmodified polymer, potentially advantageous in high-temperature applications. In summary, the study demonstrates efficient poly(methyl mechacrylate-co-acrylic acid) post-modification through a multicomponent Ugi reaction, yielding tailored polymers. Comprehensive spectroscopic, thermal, and gel permeation analyses shed light on structural changes and improved stability, pivotal for innovative applications like drug delivery.

Injectable in situ gelling methylcellulose-based hydrogels for bone tissue regeneration.

Injectable bone substitutes (IBSs) represent a compelling choice for bone tissue regeneration, as they can be exploited to optimally fill complex bone defects in a minimally invasive manner. In this context, in situ gelling methylcellulose (MC) hydrogels may be engineered to be free-flowing injectable solutions at room temperature and gels upon exposure to body temperature. Moreover, incorporating a suitable inorganic phase can further enhance the mechanical properties of MC hydrogels and promote mineralization, thus assisting early cell adhesion to the hydrogel and effectively guiding bone tissue regeneration. In this work, thermo-responsive IBSs were designed selecting MC as the organic matrix and calcium phosphate (CaP) or CaP modified with graphene oxide (CaPGO) as the inorganic component. The resulting biocomposites displayed a transition temperature around body temperature, preserved injectability even after loading with the inorganic components, and exhibited adequate retention on an ex vivo calf femoral bone defect model. The addition of CaP and CaPGO promoted the in vitro mineralization process already 14 days after immersion in simulated body fluid. Interestingly, combined X-ray diffraction and solid state nuclear magnetic resonance characterizations revealed that the formed biomimetic phase was constituted by crystalline hydroxyapatite and amorphous calcium phosphate. In vitro biological characterization revealed the beneficial impact of CaP and CaPGO, indicating their potential in promoting cell adhesion, proliferation and osteogenic differentiation. Remarkably, the addition of GO, which is very attractive for its bioactive properties, did not negatively affect the injectability of the hydrogel nor the mineralization process, but had a positive impact on cell growth and osteogenic differentiation on both pre-differentiated and undifferentiated cells. Overall, the proposed formulations represent potential candidates for use as IBSs for application in bone regeneration both under physiological and pathological conditions.

A Urea Modified Ternary Aqueous Electrolyte with Tuned Intermolecular Interactions and Confined Water Activity for Highly Stable Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have gained attention as potential energy storage devices due to their high safety.1 However, the narrow electrochemical window and unfavorable side reactions (i.e., hydrogen and oxygen evolution reactions) induced by water decomposition restrict their development.2,3 Thus, constraining water activity is necessary to enhance stability and enlarge electrochemical window. In this study, we prepare a 2.9 m (mol kgsolvent −1) Zn(ClO4)2−CO(NH2)2−H2O ternary aqueous electrolyte with restricted water activity at room temperature. Raman, Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) characterization techniques suggest strong intermolecular interactions between CO(NH2)2 and H2O, which decrease the free H2O molecules and reduce their associated activity to suppress the parasitic reactions at the electrodes. Density functional theory (DFT) calculations substantiate the strong hydrogen bonds between urea and water. Compared with eutectic electrolyte and water-in-salt electrolyte, this aqueous electrolyte exhibits a high ionic conductivity (6.83 mS cm−1) as conventional aqueous electrolytes without sacrificing the voltage window (2.5 V). Furthermore, DFT computations reveal the preferential adsorption of urea molecules onto the zinc surface, mediating zinc deposition process. The reduction of urea generates a robust organic solid electrolyte interphase (SEI), promoting homogeneous zinc deposition on the anode and hindering parasitic reactions. Consequently, this ternary aqueous electrolyte not only imparts Zn/Zn symmetric cells with prolonged cycling stability exceeding 1000 h at various current densities but also endows zinc−vanadium batteries a capacity of 250 mAh g−1 for 400 cycles at 1 A g−1. This finding highlights a promising approach for the development of stable aqueous zinc-ion batteries with an expanded electrochemical window.Reference A. Konarov et al. ACS Energy Letters 2018, 3 (10), 2620–2640.C. Li et al. Joule 2022, 6 (8), 1733–1738.J. Zhou et al. Advanced Materials 2021, 33 (33), 2101649. Figure 1

Operando NMR Characterization of Cycled and Calendar Aged Si Anodes

Replacing graphite anodes with Si anodes can greatly increase the capacity of current Li-ion batteries. Detailed characterization of Si lithiation reactions, solid electrolyte interphase (SEI) formation, and reversibility are therefore active areas of research. Solid-state nuclear magnetic resonance (NMR) spectroscopy is useful for characterizing different local environments within Si anodes as well as differentiating surface and bulk environments. Furthermore, non-invasive and non-destructive NMR methods can reveal metastable LixSi phases or SEI species forming on (dis)charge that may be too reactive to detect via ex situ methods. Here, we use an in situ and in operando NMR methodology to characterize full pouch cells comprising of Si anodes and NMC cathodes. We can observe changes in the relative amounts of Li in different environments within the same Si anode before/during/after charge & discharge and with various amounts of cycling or calendar aging using in situ 7Li NMR. The pouch cells used in our in situ NMR study are comparable to pouch cells made using mid- to large-scale fabrication methods as opposed to laboratory scale; in other words, challenges of cell-to-cell variability are minimized. We hypothesize “trapped” lithiated phases formed in the Si anode no longer contribute to electrochemical cycling and thus limit capacity in subsequent cycles/aging. We also characterized the SEI/surface species in situ with aging via 13C NMR measurements, identifying reactions of lithium silicides with electrolyte solvents and their subsequent decomposition.

Learnings From Impact and Implications of Signal-To-Noise in NMR T1-T2 Logging of Unconventional Reservoirs

We study the impact of signal-to-noise ratio (SNR) on nuclear magnetic resonance (NMR) T1-T2 maps across data sets acquired in multiple wells of an unconventional field under various logging and processing conditions. The mean and standard deviation of NMR porosity error between continuous moving-pass and stationary measurements are used to obtain insights into the impact of SNR on accuracy and precision. In a proof-of-concept experiment, we introduce a novel semi-analytical smeared-peak (SASP) technique that compensates for the over-regularized smearing due to poor SNR, of T1-T2 relaxation responses of different fluids. The SASP approximation to de-smear volumes of different fluid types is validated with field measurements from multiple wells. The uplift of the SASP technique in improving fluid volume interpretations is apparent in the in-situ calibration of low-SNR moving-pass NMR measurements with high-quality stationary measurements. The learnings show that logging protocols that are designed to increase SNR by combining specific acquisition parameters with processing strategies, within acceptable compromises, are mandatory for reliable NMR characterization of unconventional reservoirs.

Insights into the adsorption of perfluoroalkyl substances (PFASs) on excess sludge from an on-site leachate treatment plant

The disposal and reduction of excess sludge is one of the most challenging aspects of wastewater treatment. Recycling excess sludge as functional materials is an innovative approach that has garnered broad attention, as it can address environmental concerns and reduce the consumption of valuable materials. However, this approach is still challenging due to the low mixed liquor suspended solids in sewage treatment plants and the high synthesis costs involved. In this study, we proposed the application of excess sludge from an on-site leachate treatment plant for the efficient removal of perfluoroalkyl substances (PFASs) from wastewater. A simple thermal treatment was conducted and the obtained sludge-based adsorbents enable effective PFASs removal. Through the use of low field nuclear magnetic resonance and structural characterizations, results demonstrated that denitrifying sludge had higher hydrophobicity and specific surface area (30.85 m2/g) than nitrifying sludge, resulting in enhanced PFASs adsorption capacity and initial adsorption rates. Kinetic and isotherm simulations indicated that the adsorption was efficient and controlled by surface and intraparticle diffusion. Characterization and regulation results showed that the adsorption was dominated by hydrophobic and electrostatic interactions. These findings suggest a promising recycling approach of excess sludge while elucidating the dominant mechanisms involved.

Water partitioning and migration in unsaturated bentonites by low‐field NMR characterization

AbstractWater behavior in bentonite clay pores is influenced by soil–water interaction mechanisms such as capillary and adsorptive forces. Quantitative measurement of these water statuses remains challenging, leading to the adoption of advanced techniques. This study uses low‐field nuclear magnetic resonance (NMR) technique to investigate water partitioning dynamics and changes in the water state in sodium‐rich Wyoming bentonite and calcium‐rich Denver bentonite under various humidity conditions. NMR T2 relaxation and T1–T2 mapping techniques, along with a multi‐Gaussian decomposition method, enable a quantitative analysis of capillary and adsorptive water in both bentonites. A conceptual water partitioning model is derived to explain water molecule trajectories of water molecules under unsaturated conditions. Our findings indicate distinct transitions in hydrated layers for Na+‐smectite and Ca2+‐smectite at different relative humidity (RH) ranges. Characteristic T2 ranges are identified for capillary and adsorptive water in both clays and provide valuable insights into their water behavior. This study advances our understanding of soil properties at different RH environments and highlights the potential of low‐field NMR techniques in characterizing capillary and adsorptive water in bentonite clays.

NMR characterization of the structure of the intrinsically disordered region of human origin recognition complex subunit 1, hORC1, and of its interaction with G-quadruplex DNAs

Human origin recognition complex (hORC) binds to the DNA replication origin and then initiates DNA replication. However, hORC does not exhibit DNA sequence-specificity and how hORC recognizes the replication origin on genomic DNA remains elusive. Previously, we found that hORC recognizes G-quadruplex structures potentially formed near the replication origin. Then, we showed that hORC subunit 1 (hORC1) preferentially binds to G-quadruplex DNAs using a hORC1 construct comprising residues 413 to 511 (hORC1413−511). Here, we investigate the structural characteristics of hORC1413−511 in its free and complex forms with G-quadruplex DNAs. Circular dichroism and nuclear magnetic resonance (NMR) spectroscopic studies indicated that hORC1413−511 is disordered except for a short α-helical region in both the free and complex forms. NMR chemical shift perturbation (CSP) analysis suggested that basic residues, arginines and lysines, and polar residues, serines and threonines, are involved in the G-quadruplex DNA binding. Then, this was confirmed by mutation analysis. Interestingly, CSP analysis indicated that hORC1413−511 binds to both parallel- and (3 + 1)-type G-quadruplex DNAs using the same residues, and thereby in the same manner. Our study suggests that hORC1 uses its intrinsically disordered G-quadruplex binding region to recognize parallel-type and (3 + 1)-type G-quadruplex structures at replication origin.

The differentiation of N-butyl pentylone isomers using GC-EI-MS and NMR

Forensic laboratories are faced with an ever-expanding seized drug landscape including the increasing prevalence of novel psychoactive substances (NPS), such as synthetic cathinones, that have varying potencies and scheduling. This study demonstrates a combined gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) and nuclear magnetic resonance (NMR) spectroscopy approach for the differentiation of N-butyl pentylone isomers based on distinct retention times, characteristic EI mass spectra, and NMR characterization. Retention time reproducibility was assessed from 60 replicate measurements for each isomer over the course of a month. In addition, the effect of the mass spectrometer tune and the stability of an identified characteristic ion ratio using spectral data from ± 1 scan on either side of the peak apex were also statistically assessed using Welch’s ANOVA testing.The presence of diastereomers for N-sec-butyl pentylone was identified using the developed GC-EI-MS method, which was confirmed using one-dimensional and two-dimensional NMR spectroscopy. The retention time reproducibility of the chromatographic method was ± 0.076% or less over the course of a month. An identified characteristic ion ratio between the abundance of the fragment ion at m/z 128 and the fragment ion at m/z 72 enabled the differentiation of the four N-butyl pentylone isomers, even when accounting for the effect of the mass spectrometer tune and mass spectral scans used to calculate the characteristic ion ratio. The 95% confidence interval mean abundance ratio of the fragment ions at m/z 128 and m/z 72 was 17.14 ± 0.14 for N-butyl pentylone, 6.44 ± 0.05 for N-isobutyl pentylone, 3.38 ± 0.02 for N-sec-butyl pentylone, and 0.75 ± 0.01 for N-tert-butyl pentylone. These results highlight the capabilities of a combined GC-EI-MS and NMR approach for the differentiation and characterization of synthetic cathinone isomers.

Experimental and Computational Study on SEI Composition and Electrochemical Performance of Lithium-Ion Battery with Silicon Oxide-Graphite Composite Electrode

Demand on batteries with high energy density is surging. Conventionally, carbon materials have been used as an anode active material, but recently silicon materials are likely to be incorporated to form a composite anode in lithium-ion batteries (LIBs) for higher energy density. However, LIBs which include silicon materials in anode tend to show a low cycle performance especially the ratio of silicon materials in the anode increases. Commercial LIBs still have difficulty in incorporating large amount of silicon materials especially under the requirements where multiple aspects like safety, charging rate and energy density should be totally met.One potential pathway to improve the cycle performance in LIBs with silicon materials is to tune the nature of solid electrolyte interphase (SEI), a thin film which forms at the interface between anode active material and electrolyte. The nature of SEI is particularly important for LIBs with silicon materials because such silicon active materials show large volume changes during battery operation and SEI is dynamically reconstructed. It has been qualitatively reported so far that LiF is an important component for better battery performance. Our work suggests that the ratio of LiF in initially formed SEI is a crucial factor to realize improved cycle performance in such LIBs.In our work, anode with silicon oxide (SiOx)-graphite composite is considered. We investigated the relationship between electrochemical performance of the cell with such composite electrode and the nature of the film estimated by characterization and molecular simulation. We systematically changed the composition of liquid electrolyte to form various types of SEI on anode surface. For characterization, both fresh and aged cells with different electrolytes were dismantled, and SEI components were extracted by designated solvents, then NMR (nuclear magnetic resonance) was applied to identify the SEI species and quantify the amounts of major SEI components. Comparison between the evolution of SEI amount and an impedance element in electrochemical impedance spectroscopy during aging indicates that degradation of the cells is closely related to the growth of SEI. To further deepen understanding the role of LiF, molecular dynamics simulation was carried out, where the mixture of LiF and typical organic SEI was modelled. Correlation between calculated mechanical property and measured electrochemical performance of the cells were revealed. In our presentation, the requirements that SEI should satisfy will be discussed from the insight of electrochemical measurements, NMR characterization and modeling approaches.

Electrochemical and NMR Characterization of ZIF-67

Metal Organic Frameworks (MOFs) are attractive materials for their tunable porosities and chemistries. Zeolitic Imidazolate Frameworks (ZIF) are a class of MOFs recognized for their relative ease in synthesis and stability. In this work we study ZIF-67 for energy storage applications. We use a host of characterization techniques, including XRD, BET, EDS and 1H and 13C nuclear magnetic resonance (NMR), to better understand the neat ZIF-67. The ZIF-67 particle size is shown to be 150-300 nm, exhibiting good crystallinity with specific surface area of 850 m2/g. NMR reveals hyperfine interactions of the paramagnetic cobalt with 1H and 13C that are in good agreement with calculated values from first principles. Additionally, high resolution NMR spectra of “guest” molecules within the pores of the MOF are demonstrated. Composite electrodes based on ZIF-67 are characterized for their energy storage capacity in KOH electrolytes using cyclic voltammetry and electrochemical impedance spectroscopy. These electrodes are shown to display capacities greater than traditional carbons. Cyclic voltammetry is used to distinguish redox contributions from double layer capacity. Finally, in-situ NMR spectra of two electrode devices are presented to understand charging and discharging mechanisms.

NMR Characterization of the Papain-like Protease from SARS-CoV-2 Identifies the Conformational Heterogeneity in Its Inhibitor-Binding Site.

Papain-like protease (PLpro) from severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) is a prime target for the development of antivirals for Coronavirus disease 2019 (COVID-19). However, drugs that target the PLpro protein have not yet been approved. In order to gain insights into the development of a PLpro inhibitor, conformational dynamics of PLpro in complex with GRL0617, the most well-characterized PLpro inhibitor, were investigated using nuclear magnetic resonance (NMR) spectroscopy in solution. Although mutational analyses demonstrated that the L162 sidechain interaction is responsible for the affinity for GRL0617, NMR analyses revealed that L162 in the inhibitor-binding pocket underwent conformational exchange and was not fixed in the conformation in which it formed a contact with ortho-methyl group of GRL0617. The identified conformational dynamics would provide a rationale for the binding mechanism of a covalent inhibitor designed based on GRL0617.