Multidimensional Nuclear Magnetic Resonance Research Articles

The role of Nuclear Magnetic Resonance (NMR) spectroscopy in cattle metabolism

Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical tool that has significantly advanced the understanding of cattle metabolism. Nuclear Magnetic Resonance (NMR) spectroscopy plays a pivotal role in the study of cattle metabolism, offering distinct advantages over other spectrometric methods. NMR spectroscopy is a powerful analytical tool that provides detailed molecular insights by exploiting the magnetic properties of atomic nuclei. Unlike mass spectrometry and infrared spectroscopy, NMR does not require extensive sample preparation or destruction, preserving the integrity of biological samples. This non-invasive nature is particularly beneficial for longitudinal studies in cattle, where metabolic changes over time are of interest. One of the key strengths of NMR spectroscopy is its ability to simultaneously detect and quantify a broad range of metabolites in complex biological matrices, such as blood, urine, and tissue extracts. This comprehensive metabolic profiling is crucial for understanding the biochemical pathways and physiological states in cattle. NMR's high reproducibility and quantitative accuracy further enhance its suitability for metabolic studies, enabling precise monitoring of metabolic fluctuations in response to dietary changes, environmental stressors, or disease conditions. NMR spectroscopy also offers unique advantages in elucidating structural information about metabolites. Through multidimensional NMR techniques, researchers can determine the molecular structure and conformation of metabolites, providing deeper insights into metabolic functions and interactions. This structural elucidation is often challenging with other spectrometric methods, which may lack the resolution or require derivatization of samples. Moreover, NMR spectroscopy's non-destructive nature allows for the analysis of living tissues and in vivo studies, facilitating real-time monitoring of metabolic processes. This capability is instrumental in studying dynamic metabolic responses and adaptations in cattle under different physiological states. Additionally, the development of advanced NMR techniques, such as high-resolution magic angle spinning (HR-MAS) and hyperpolarization, has further expanded the scope of NMR applications in metabolic research. NMR spectroscopy stands out as a superior method for studying cattle metabolism due to its non-destructive approach, comprehensive metabolic profiling, structural elucidation capabilities, and potential for in vivo analysis. These advantages make NMR an indispensable tool in advancing our understanding of cattle metabolism and improving livestock health and productivity. Keywords: Nuclear Magnetic Resonance (NMR), Cattles, Metabolomics.

Overhauser enhanced liquid state nuclear magnetic resonance spectroscopy in one and two dimensions

Nuclear magnetic resonance (NMR) is fundamental in the natural sciences, from chemical analysis and structural biology, to medicine and physics. Despite its enormous achievements, one of its most severe limitations is the low sensitivity, which arises from the small population difference of nuclear spin states. Methods such as dissolution dynamic nuclear polarization and parahydrogen induced hyperpolarization can enhance the NMR signal by several orders of magnitude, however, their intrinsic limitations render multidimensional hyperpolarized liquid-state NMR a challenge. Here, we report an instrumental design for 9.4 Tesla liquid-state dynamic nuclear polarization that enabled enhanced high-resolution NMR spectra in one and two-dimensions for small molecules, including drugs and metabolites. Achieved enhancements of up to two orders of magnitude translate to signal acquisition gains up to a factor of 10,000. We show that hyperpolarization can be transferred between nuclei, allowing DNP-enhanced two-dimensional 13C–13C correlation experiments at 13C natural abundance. The enhanced sensitivity opens up perspectives for structural determination of natural products or characterization of drugs, available in small quantities. The results provide a starting point for a broader implementation of DNP in liquid-state NMR.

NMR spectroscopic investigations of transition metal complexes in organometallic and bioinorganic chemistry

AbstractThe field of coordination chemistry has evolved to intersect with organic chemistry and biochemistry, giving rise to the disciplines of organometallic and bioinorganic chemistry. Nuclear magnetic resonance (NMR) spectroscopy can be applied for characterizing transition metal complexes, spanning both diamagnetic and paramagnetic complexes prevalent in organometallic compounds and metalloproteins. This review offers a comprehensive overview of a wide variety of characterization techniques, ranging from basic 1H and 13C NMR spectroscopy to advanced methods such as heteronuclear experiments, polarization transfer techniques, relaxometry, and multidimensional NMR spectroscopy. The diverse array of NMR spectroscopic methods outlined here promises to enhance our comprehension of transition metal complexes, facilitating the development of innovative catalysts and therapeutics.

Multidimensional Spectroscopy of Nuclear Spin Clusters in Diamond.

Optically active spin defects in solids offer promising platforms to investigate nuclear spin clusters with high sensitivity and atomic-site resolution. To leverage near-surface defects for molecular structure analysis in chemical and biological contexts using nuclear magnetic resonance (NMR), further advances in spectroscopic characterization of nuclear environments are essential. Here, we report Fourier spectroscopy techniques to improve localization and mapping of the test bed ^{13}C nuclear spin environment of individual, shallow nitrogen-vacancy centers at room temperature. We use multidimensional spectroscopy, well-known from classical NMR, in combination with weak measurements of single-nuclear-spin precession. We demonstrate two examples of multidimensional NMR: (i)improved nuclear spin localization by separate encoding of the two hyperfine components along spectral dimensions and (ii)spectral editing of nuclear-spin pairs, including measurement of internuclear coupling constants. Our work adds important tools for the spectroscopic analysis of molecular structures by single-spin probes.

Hiding in plain sight: Complex interaction patterns between Tau and 14-3-3ζ protein variants

Tau protein is an intrinsically disordered protein that plays a key role in Alzheimer's disease (AD). In brains of AD patients, Tau occurs abnormally phosphorylated and aggregated in neurofibrillary tangles (NFTs). Together with Tau, 14-3-3 proteins – abundant cytosolic dimeric proteins – were found colocalized in the NFTs. However, so far, the molecular mechanism of the process leading to pathological changes in Tau structure as well as the direct involvement of 14-3-3 proteins are not well understood. Here, we aimed to reveal the effects of phosphorylation by protein kinase A (PKA) on Tau structural preferences and provide better insight into the interaction between Tau and 14-3-3 proteins. We also addressed the impact of monomerization-inducing phosphorylation of 14-3-3 at S58 on the binding to Tau protein. Using multidimensional nuclear magnetic resonance spectroscopy (NMR), chemical cross-linking analyzed by mass spectrometry (MS) and PAGE, we unveiled differences in their binding affinity, stoichiometry, and interfaces with single-residue resolution. We revealed that the interaction between 14-3-3 and Tau proteins is mediated not only via the 14-3-3 amphipathic binding grooves, but also via less specific interactions with 14-3-3 protein surface and, in the case of monomeric 14-3-3, also partially via the exposed dimeric interface. In addition, the hyperphosphorylation of Tau changes its affinity to 14-3-3 proteins. In conclusion, we propose quite complex interaction mode between the Tau and 14-3-3 proteins.

Structural and Dynamical Insights of Cu-Coordinated Cellulose Nanofibers for Li+ Battery by NMR Spectroscopy

In the quest of novel sustainable research to meet the global surge of clean energy demand, cellulose nanofibers (CNF) derived from natural wood materials offer exceptional properties for safe, cost-effective, efficient Li+ batteries. A new strategy has been established via introducing Cu2+ into the CNF to achieve a greater mobility of Li+, where Cu2+ opens up one-dimensional nanofibrils and creates molecular channels.1 Various experimental methods and molecular dynamic simulations have been used to characterize these materials. In this context, Nuclear Magnetic Resonance (NMR), a highly sensitive technique plays a significant role in providing new insights into the structure and dynamics of Li-Cu-CNF materials. In collaboration with Prof. Liangbing Hu, University of Maryland, current research focusses on studying highly conductive Li-Cu-CNF materials prepared with different Li-salt via different synthetic approaches in the ARPA-E project. Fast magic angle spinning (MAS) detecting 1H helps in estimating the residual solvent/H2O present in Li-Cu-CNF materials, which is crucial to determine the Li+ transport mechanism. Pulsed Field Gradient (PFG) NMR has been used to measure the diffusivity of Li+ and anion and to estimate the Li+ transference number (t Li+). We found that the estimated t Li+ of studied Li-Cu-CNF materials is much greater as compared to the other polymer-based electrolytes. Additionally, the anisotropic diffusion of Li+ and anion in aligned cellulose wood materials have been well-established through PFG NMR. Lastly, the local structure of cellulose fibers and their spatial interactions with ionic species are probed through multi-dimensional (1D and 2D) solid state NMR detecting 1H, 7Li, 19F, 13C nuclei. Reference. Yang, Q. Wu, W. Xie, X. Zhang, A. Brozena, J. Zheng, M. N. Garaga, B. H. Ko, Y. Mao, S. He, Y. Gao, P. Wang, M. Tyagi, F. Jiao, R. Briber, P. Albertus, C. Wang, S. Greenbaum, Y.-Y. Hu, A. Isogai, M. Winter, K. Xu, Y. Qi, and L. Hu, Copper-coordinated cellulose ion conductors for solid-state batteries. Nature (2021) 598, 590–596.

Optimal control pulses for the 1.2-GHz (28.2-T) NMR spectrometers

The ability to measure nuclear magnetic resonance (NMR) spectra with a large sample volume is crucial for concentration-limited biological samples to attain adequate signal-to-noise (S/N) ratio. The possibility to measure with a 5-mm cryoprobe is currently absent at the 1.2-GHz NMR instruments due to the exceedingly high radio frequency power demands, which is four times compared to 600-MHz instruments. Here, we overcome the high-power demands by designing optimal control (OC) pulses with up to 20 times lower power requirements than currently necessary at a 1.2-GHz spectrometer. We show that multidimensional biomolecular NMR experiments constructed using these OC pulses can bestow improvement in the S/N ratio of up to 26%. With the expected power limitations of a 5-mm cryoprobe, we observe an enhancement in the S/N ratio of more than 240% using our OC sequences. This motivates the development of a cryoprobe with a larger volume than the current 3-mm cryoprobes.

Interfacial Bonding between a Crystalline Metal-Organic Framework and an Inorganic Glass.

The interface within a composite is critically important for the chemical and physical properties of these materials. However, experimental structural studies of the interfacial regions within metal-organic framework (MOF) composites are extremely challenging. Here, we provide the first example of a new MOF composite family, i.e., using an inorganic glass matrix host in place of the commonly used organic polymers. Crucially, we also decipher atom-atom interactions at the interface. In particular, we dispersed a zeolitic imidazolate framework (ZIF-8) within a phosphate glass matrix and identified interactions at the interface using several different analysis methods of pair distribution function and multinuclear multidimensional magic angle spinning nuclear magnetic resonance spectroscopy. These demonstrated glass-ZIF atom-atom correlations. Additionally, carbon dioxide uptake and stability tests were also performed to check the increment of the surface area and the stability and durability of the material in different media. This opens up possibilities for creating new composites that include the intrinsic chemical properties of the constituent MOFs and inorganic glasses.

Application of 15N-Edited 1H-13C Correlation NMR Spectroscopy─Toward Fragment-Based Metabolite Identification and Screening via HCN Constructs.

Many key building blocks of life contain nitrogen moieties. Despite the prevalence of nitrogen-containing metabolites in nature, 15N nuclei are seldom used in NMR-based metabolite assignment due to their low natural abundance and lack of comprehensive chemical shift databases. However, with advancements in isotope labeling strategies, 13C and 15N enriched metabolites are becoming more common in metabolomic studies. Simple multidimensional nuclear magnetic resonance (NMR) experiments that correlate 1H and 15N via single bond 1JNH or multiple bond 2-3JNH couplings using heteronuclear single quantum coherence (HSQC) or heteronuclear multiple bond coherence are well established and routinely applied for structure elucidation. However, a 1H-15N correlation spectrum of a metabolite mixture can be difficult to deconvolute, due to the lack of a 15N specific database. In order to bridge this gap, we present here a broadband 15N-edited 1H-13C HSQC NMR experiment that targets metabolites containing 15N moieties. Through this approach, nitrogen-containing metabolites, such as amino acids, nucleotide bases, and nucleosides, are identified based on their 13C, 1H, and 15N chemical shift information. This approach was tested and validated using a [15N, 13C] enriched Daphnia magna (water flea) metabolite extract, where the number of clearly resolved 15N-containing peaks increased from only 11 in a standard HSQC to 51 in the 15N-edited HSQC, and the number of obscured peaks decreased from 59 to just 7. The approach complements the current repertoire of NMR techniques for mixture deconvolution and holds considerable potential for targeted metabolite NMR in 15N, 13C enriched systems.

Machine learning assisted interpretation of 2D solid-state nuclear magnetic resonance spectra

A machine learning methodology using deep neural network (DNN) for interpreting multidimensional solid-state nuclear magnetic resonance (SSNMR) of various synthetic and natural polymers is presented. The separated local field (SLF) SSNMR which correlates local well-defined heteronuclear dipolar with the tensor orientation of the chemical shift anisotropy (CSA) of spin in the solid state can provide valuable structure and molecular dynamics information of synthetic and biopolymers. Compared with the traditional linear least-square fitting, the proposed DNN-based methodology can efficiently and accurately determine the tensor orientation of CSA of both 13C and 15N in all four samples. The method achieves prediction precisions of the Euler angles with < ±5° and is characterized by low training costs and high efficiency (<1 s). The feasibility and robustness of the DNN-based analysis methodology are confirmed by comparison to reported-literature values. This strategy is expected to aid in the interpretation of complex multidimensional NMR spectra of complicated polymer system.

A robust t1 noise suppression method in NMR spectroscopy.

Artefacts in high-resolution multidimensional nuclear magnetic resonance (NMR) spectra, known as t1 noise, can significantly downgrade the spectral quality and remain a significant noise source, limiting the sensitivity of most two-dimensional NMR experiments. In addition to highly sensitive hardware and experimental designs, data post-processing is a relatively simple and cost-effective method for suppressing t1 noise. In this study, histograms and quantiles were used to obtain a robust estimation of noise level. We constructed a weighted matrix to suppress the t1 noise. The weighted matrix was calculated from the logistic functions, which were adaptively computed from the spectrum. The proposed method is robust and effective in both simulations and actual experiments. Further, it can maintain the quantitative relationship of the spectrogram and is suitable for various complex peak types.

Elongated galactan side chains mediate cellulose-pectin interactions in engineered Arabidopsis secondary cell walls.

The plant secondary cell wall is a thickened matrix of polysaccharides and lignin deposited at the cessation of growth in some cells. It forms the majority of carbon in lignocellulosic biomass, and it is an abundant and renewable source for forage, fiber, materials, fuels, and bioproducts. The complex structure and arrangement of the cell wall polymers mean that the carbon is difficult to access in an economical and sustainable way. One solution is to alter the cell wall polymer structure so that it is more suited to downstream processing. However, it remains difficult to predict what the effects of this engineering will be on the assembly, architecture, and properties of the cell wall. Here, we make use of Arabidopsis plants expressing a suite of genes to increase pectic galactan chain length in the secondary cell wall. Using multi-dimensional solid-state nuclear magnetic resonance, we show that increasing galactan chain length enhances pectin-cellulose spatial contacts and increases cellulose crystallinity. We also found that the increased galactan content leads to fewer spatial contacts of cellulose with xyloglucan and the backbone of pectin. Hence, we propose that the elongated galactan side chains compete with xyloglucan and the pectic backbone for cellulose interactions. Due to the galactan topology, this may result in comparatively weak interactions and disrupt the cell wall architecture. Therefore, introduction of this strategy into trees or other bioenergy crops would benefit from cell-specific expression strategies to avoid negative effects on plant growth.

Solvent-derived defects suppress adsorption in MOF-74

Defects in metal-organic frameworks (MOFs) have great impact on their nano-scale structure and physiochemical properties. However, isolated defects are easily concealed when the frameworks are interrogated by typical characterization methods. In this work, we unveil the presence of solvent-derived formate defects in MOF-74, an important class of MOFs with open metal sites. With multi-dimensional solid-state nuclear magnetic resonance (NMR) investigations, we uncover the ligand substitution role of formate and its chemical origin from decomposed N,N-dimethylformamide (DMF) solvent. The placement and coordination structure of formate defects are determined by 13C NMR and density functional theory (DFT) calculations. The extra metal-oxygen bonds with formates partially eliminate open metal sites and lead to a quantitative decrease of N2 and CO2 adsorption with respect to the defect concentration. In-situ NMR analysis and molecular simulations of CO2 dynamics elaborate the adsorption mechanisms in defective MOF-74. Our study establishes comprehensive strategies to search, elucidate and manipulate defects in MOFs.

Design Principle of a Water-Dispersed Photocatalytic Perovskite through Ligand Deconstruction

Strategically designed surface modifiers that produce stable perovskite nanocrystals (NCs) and allow efficient charge extraction in polar solvents are critical for perovskite photocatalysis. We designed a multifunctional bolaamphiphilic ligand (NKE-12) with multidentate ionic groups at both ends, which significantly increases the colloidal stability of CsPbBr3 NCs in an aqueous medium without affecting their structural integrity and catalytic attributes. Ligand deconstruction via K and E fragmented ligands revealed synergistic actions of the cationic and anionic functionalities in surface passivation, phase separation, and water localization away from the surface of NKE-12-modified CsPbBr3 NCs. Multidimensional nuclear magnetic resonance experiments and contact angle measurements further suggested surface interactions and improved hydrophilicity via ionic terminal groups that account for water stability. Photogenerated hole-transfer dynamics of CsPbBr3/NKE-12 NCs to a probe molecule 6,7-dihydroxycoumarin was studied using transient absorption spectroscopy. Overall, this study paves the way for ligand design principles for surface engineering to develop water-stable perovskite photocatalysts.

Abstract 3844: A biophysical investigation into the binding interactions of novel anti-cancer inhibitors of atypical protein kinase C (aPKCs)

Abstract The aim of this study is to address the challenge of the expression of recombinant atypical protein kinase C (aPKCs) in a bacterial system and understand the binding interactions of novel anti-cancer inhibitors of aPKCs. The Protein kinase Cs (PKCs) expression at a high rate is a key indicator of cancer cell proliferation and survival. In particular, the over-expressions of aPKCs were found to be directly associated with various cancer cells in benign and malignant stages. Several cancer growth blockers (inhibitors) are available for targeted therapy. However, these inhibitors had to pass through rigorous in silico screening, in vitro, and in vivo assays before FDA approval. During the characterization studies of the protein, insights into binding interactions between aPKCs and drug molecules are crucial. For successive studies such as for biophysical characterization, the recombinant bioactive full-length PKC- ι (an aPKC) expression in the bacterial system is still a challenge. In addition, the binding interaction studies of aPKCs with inhibitors in physiological conditions providing structural details are limited to some X-ray crystallography structures and computational studies. Here we addressed these two challenges and report a protocol detailing the bioactive full-length and catalytic domain of PKC- ι expression and purification from the bacterial system. The further characterization of the recombinant protein by the determination of melting temperature, functional activity, and circular dichroism reported here provides important information on the characteristics of the protein in its native state. Moreover, we show the chemical interactions of five novel anti-cancer inhibitors ICA-1S (Nucleosidic homolog) 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide), ICA-1T (Phosphorylated nucleosidic homolog of ICA-1S, [4-(5-amino-4-carbamoylimidazol-1-yl)-2,3-dihydroxycyclopentyl] methyl dihydrogen phosphate), ACPD (2-acetyl-1,3-cyclopentanedione), DNDA (3,4-diaminonaphthalene-2,7-disulfonic acid) and ζ(ZETA)-Stat (8-hydroxy-1,3,6- naphthalenetrisulfonic acid) to locate their regions of binding on the catalytic domain of the aPKCs (PKC- ι and PKC- ζ). We have utilized the chemical shift changes obtained from various multi-dimensional Nuclear Magnetic Resonance (NMR) experiments. Moreover, we have applied the isothermal calorimetry method to understand the biophysical properties of the aPKCs in presence of these inhibitors. The observed biophysical properties of the protein and chemical shift perturbations in the amide backbone of the catalytic domain upon binding shed light on the molecular recognition process, binding characteristics, and atomic-level structural details of the aPKCs. Citation Format: Radwan Ebna Noor, Tracess B. Smalley, Mildred Acevedo-Duncan. A biophysical investigation into the binding interactions of novel anti-cancer inhibitors of atypical protein kinase C (aPKCs). [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3844.

Mixed Ligand Passivation as the Origin of Near-Unity Emission Quantum Yields in CsPbBr3 Nanocrystals

Key features of syntheses, involving the quaternary ammonium passivation of CsPbBr3 nanocrystals (NCs), include stable, reproducible, and large (often near-unity) emission quantum yields (QYs). The archetypical example involves didodecyl dimethyl ammonium (DDDMA+)-passivated CsPbBr3 NCs where robust QYs stem from interactions between DDDMA+ and NC surfaces. Despite widespread adoption of this synthesis, specific ligand-NC surface interactions responsible for large DDDMA+-passivated NC QYs have not been fully established. Multidimensional nuclear magnetic resonance experiments now reveal a new DDDMA+-NC surface interaction, beyond established "tightly bound" DDDMA+ interactions, which strongly affects observed emission QYs. Depending upon the existence of this new DDDMA+ coordination, NC QYs vary broadly between 60 and 85%. More importantly, these measurements reveal surface passivation through unexpected didodecyl ammonium (DDA+) that works in concert with DDDMA+ to produce near-unity (i.e., >90%) QYs.

Analysis of Heparin Samples by Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy in the Solid State.

Heparin is a polydisperse, heterogeneous polysaccharide of the glycosaminoglycan (GAG) class that has found widespread clinical use as a potent anticoagulant and is classified as an essential medicine by the World Health Organization. The importance of rigorous monitoring and quality control of pharmaceutical heparin was highlighted in 2008, when the existing regulatory procedures failed to identify a life-threatening adulteration of pharmaceutical heparin with oversulfated chondroitin sulfate (OSCS). The subsequent contamination crisis resulted in the exploration of alternative approaches for which the use of multidimensional nuclear magnetic resonance (NMR) spectroscopy techniques and multivariate analysis emerged as the gold standard. This procedure is, however, technically demanding and requires access to expensive equipment. An alternative approach, utilizing attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) combined with multivariate analysis, has been developed. The method described enables the differentiation of diverse GAG samples, the classification of samples of distinct species provenance, and the detection of both established heparin contaminants and alien polysaccharides. This methodology has sensitivity comparable to that of NMR and can facilitate the rapid, cost-effective monitoring and analysis of pharmaceutical heparin. It is therefore suitable for future deployment throughout the supply chain.

Synthesis of Alpha-Linked Glucosides from Soybean Isoflavone Aglycones Using Amylosucrase from Deinococcus geothermalis.

Soybean isoflavone aglycones (SIAs) have many biological activities but are poorly water-soluble in the human body. Glycosylation provides structural diversity to SIAs and can alter their physicochemical properties, including water solubility. An alpha-linked glucosylation of SIA was achieved using amylosucrase from Deinococcus geothermalis. A total of 13 alpha-linked glucosyl SIAs were obtained, and their colors in solution were confirmed. The structures of the isolated compounds were identified by mass spectrometry and multidimensional nuclear magnetic resonance spectroscopy. The amylosucrase transglycosylation formed new isoflavone glycosides with alpha glycosidic bonds at C-7 and/or C-4' of SIAs, followed by the production of isoflavone glycosides with alpha (1 → 6) glycosidic bonds. The products with a glucosyl moiety attached to the C-4' of SIAs were found to be more water-soluble than their counterparts attached to the C-7 and/or beta-linkages. This study suggests a strategy for the synthesis of bioactive compounds with enhanced water solubility through alpha-linked glucosylation.

Conformational heterogeneity suggests multiple substrate binding modes in CYP106A2

CYP106A2 (cytochrome P450meg) is a bacterial enzyme originally isolated from B. megaterium, and has been shown to hydroxylate a wide variety of substrates, including steroids. The regio- and stereochemistry of CYP106A2 hydroxylation has been shown to be dependent on a variety of factors, and hydroxylation often occurs at more than one site and/or with lack of stereospecificity for some substrates. Comprehensive backbone 15N, 1H and 13C resonance assignments based on multidimensional nuclear magnetic resonance (NMR) experiments performed with uniform and selective isotopically labeled CYP106A2 samples are reported herein, and broadening and splitting of resonances assigned to regions of the enzyme shown to be affected by substrate binding in other P450 enzymes indicate that substrate binding does not reduce structural heterogeneity as has been observed previously in P450 enzymes CYP101A1 and MycG. Paramagnetic relaxation enhancement (PRE) due to proximity between substrate protons and the heme iron were measured for three different substrates, and the relatively uniform nature of the PREs support the proposal that multiple substrate binding modes are occupied at saturating substrate concentrations.

Selecting the Optimal Fluorinated Ether Co-Solvent for Lithium Metal Batteries.

To guide the selection of a suitable fluorinated ether (FE) co-solvent for lithium metal batteries, it is crucial to understand the relationship between the organic structures of the FEs and the electrochemical performance of an FE-containing electrolyte. In this work, 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane (FEE), 1,1,2,2-tetrafluoro-3-(1,1,2,2-tetrafluoroethoxy)propane (TTE), and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (OFDEE) were chosen as representative FE co-solvents because of their distinct structural properties. The structure-activity relationship between the FEs and the electrochemical performance of Li||LiNi0.6Mn0.2Co0.2O2 (Li||NMC622) cells was correlated and quantified by Fourier-transform infrared and multi-dimensional nuclear magnetic resonance techniques. Sand's model was also employed to assess the extent of lithium dendrite formation in the cells using various FE electrolytes. The cycling performance of Li||NMC622 cells using different FE co-solvents follows the order FEE > TTE > OFDEE. Since the direct measurement of Sand's time is difficult, we introduced relative Sand's time to probe the diffusion behavior of each electrolyte, and the results showed that the best performance was obtained in the electrolyte with the longest relative Sand's time. Moreover, the lithium metal cell using the electrolyte with FEE co-solvent showed similar capacity retention compared with the baseline electrolyte at room temperature, but it demonstrated significantly improved low-temperature performance. The results indicate that FEE is a promising co-solvent candidate for improving the low-temperature performance of lithium metal batteries because it possesses not only non-solvating behavior but also very low viscosity and non-flammability. The advanced electrolyte LiPF6-FEC-DMC-FEE enables very stable cycling of lithium metal batteries at various temperatures.