17O Labeling Research Articles

Decomposition of Electrolyte Solutions at Positive Electrodes

Preventing the decomposition reactions of electrolyte solutions is essential for extending the lifetime of lithium-ion batteries. However, the high voltage (>4.5 V) reactivity of commonly used electrolyte solutions is still poorly understood; electrolyte decomposition at the positive electrode is generally believed to proceed via electrochemical oxidation of the organic carbonate solvent,1 while more recent work has revealed an alternative pathway involving reactive lattice oxygen species originating from the positive electrode (i.e., singlet oxygen).2 Unfortunately, we still have a limited understanding of these reactions, the products that form, and which chemical structural units in the electrolyte solution make them reactive - all of which make it challenging to assess and mitigate the impact of electrolyte decomposition on the battery’s lifetime.In this work, operando gas measurements and solution NMR were combined to study the electrochemical and chemical decomposition of widely used electrolyte salts, solvents, and additives. First, the electrochemical stability of the electrolyte components was reviewed against C65 electrodes in a standard H-cell setup: all solvents reveal little decomposition up to 5.5 V (vs Li/Li+), consistent with previous electrochemical measurements.3,4 Based on the experimentally detected soluble and gaseous products, the electrochemical decomposition mechanism is inferred. Subsequently, the chemical stability against reactive oxygen species (i.e., singlet oxygen; 1O2, peroxide anion; O2 2 −, and superoxide radical anion, O2 −) was explored. All carbonate solvents demonstrated instability against reactive oxygen species. As before, the experimentally detected gaseous and soluble products were used to infer the decomposition mechanisms. The proposed mechanisms were verified using 17O and 18O isotopic labeling for NMR spectroscopy and mass spectrometry measurements, respectively. The findings on the reactivity between the electrolyte components and reactive oxygen species provide a deeper understanding of electrolyte decomposition processes occurring at high voltage positive electrodes (e.g., Li-rich layered and disordered rocksalt oxides, high-voltage spinels, and polyanionic materials). Moreover, these insights will support the development of more stable electrolyte formulations, further extending the lifetime of lithium-ion batteries.(1) Imhof, R.; Novak, P. Oxidative Electrolyte Solvent Degradation in Lithium-Ion Batteries: An In Situ Differential Electrochemical Mass Spectrometry Investigation. J Electrochem Soc 1999, 146 (5), 1702–1706.(2) Jung, R.; Metzger, M.; Maglia, F.; Stinner, C.; Gasteiger, H. A. Oxygen Release and Its Effect on the Cycling Stability of LiNi x Mn y Co z O 2 (NMC) Cathode Materials for Li-Ion Batteries. J Electrochem Soc 2017, 164 (7), A1361–A1377. https://doi.org/10.1149/2.0021707jes.(3) Zhang, X.; Soc, J. E.; Zhang, X.; Kostecki, R.; Richardson, T. J.; Pugh, J. K.; Ross, P. N. Electrochemical and Infrared Studies of the Reduction of Organic Carbonates Electrochemical and Infrared Studies of the Reduction of Organic Carbonates. Journal of The Electrochemical Society 2001, 148 (12), A1341–A1345. https://doi.org/10.1149/1.1415547.(4) Moshkovich, M.; Cojocaru, M.; Gottlieb, H. E.; Aurbach, D. The Study of the Anodic Stability of Alkyl Carbonate Solutions by in Situ FTIR Spectroscopy, EQCM, NMR and MS. Journal of Electroanalytical Chemistry 2001, 497, 84–96. https://doi.org/http://dx.doi.org/10.1016/S0022-0728(00)00457-5.

Origin of Oxygen in Graphene Oxide Revealed by 17O and 18O Isotopic Labeling.

Wet-chemical oxidation of graphite in a mixture of sulfuric acid with a strong oxidizer, such as potassium permanganate, leads to the formation of graphene oxide with hydroxyl and epoxide groups as the major functional groups. Nevertheless, the reaction mechanism remains unclear and the source of oxygen is a subject of debate. It could theoretically originate from the oxidizer, water, or sulfuric acid. In this study, we employed 18O and 17O labeled reagents to experimentally elucidate the reaction mechanism and, thus, determine the origin of oxo-functional groups. Our findings reveal the multifaceted roles of sulfuric acid, acting as a dispersion medium, a dehydrating agent for potassium permanganate, and an intercalant. Additionally, it significantly acts as a source of oxygen next to manganese oxides. Through 17O solid-state magic-angle spinning (MAS) NMR experiments, we exclude water as a direct reaction partner during oxygenation. With labeling experiments, we conclude on mechanistic insights, which may be exploited for the synthesis of novel graphene derivatives.

Unveiling the Structure and Reactivity of Fatty-Acid Based (Nano)materials Thanks to Efficient and Scalable 17O and 18O-Isotopic Labeling Schemes.

Fatty acids are ubiquitous in biological systems and widely used in materials science, including for the formulation of drugs and the surface-functionalization of nanoparticles. However, important questions regarding the structure and reactivity of these molecules are still to be elucidated, including their mode of binding to certain metal cations or materials surfaces. In this context, we have developed novel, efficient, user-friendly, and cost-effective synthetic protocols based on ball-milling, for the 17O and 18O isotopic labeling of two key fatty acids which are widely used in (nano)materials science, namely stearic and oleic acid. Labeled molecules were analyzed by 1H and 13C solution NMR, IR spectroscopy, and mass spectrometry (ESI-TOF and LC-MS), as well as 17O solid state NMR (for the 17O labeled species). In both cases, the labeling procedures were scaled-up to produce up to gram quantities of 17O- or 18O-enriched molecules in just half-a-day, with very good synthetic yields (all ≥84%) and enrichment levels (up to an average of 46% per carboxylic oxygen). The 17O-labeled oleic acid was then used for the synthesis of a metal soap (Zn-oleate) and the surface-functionalization of ZnO nanoparticles (NPs), which were characterized for the first time by high-resolution 17O NMR (at 14.1 and 35.2 T). This allowed very detailed insight into (i) the coordination mode of the oleate ligand in Zn-oleate to be achieved (including information on Zn···O distances) and (ii) the mode of attachment of oleic-acid at the surface of ZnO (including novel information on its photoreactivity upon UV-irradiation). Overall, this work demonstrates the high interest of these fatty acid-enrichment protocols for understanding the structure and reactivity of a variety of functional (nano)materials systems using high resolution analyses like 17O NMR.

Unleashing the Potential of 17O NMR Spectroscopy Using Mechanochemistry

Abstract17O NMR spectroscopy has been the subject of vivid interest in recent years, because there is increasing evidence that it can provide unique insight into the structure and reactivity of many molecules and materials. However, due to the very poor natural abundance of oxygen‐17, 17O labeling is generally a prerequisite. This is a real obstacle for most research groups, because of the high costs and/or strong experimental constraints of the most frequently used 17O‐labeling schemes. Here, we show for the first time that mechanosynthesis offers unique opportunities for enriching in 17O a variety of organic and inorganic precursors of synthetic interest. The protocols are fast, user‐friendly, and low‐cost, which makes them highly attractive for a broad research community, and their suitability for 17O solid‐state NMR applications is demonstrated.

Investigating Local Structure in Layered Double Hydroxides with 17O NMR Spectroscopy

A new method based on the “memory effect” for efficient and economical 17O labeling of layered double hydroxides (LDHs) is introduced. High‐quality 17O solid‐state NMR spectra are obtained, for the first time, for LDHs prepared with only several hundred microliters of 17O‐enriched H2O. The 17O resonances due to the different oxygen ions in the structure of LDHs can be resolved with better resolution than the results obtained from 1H ultrafast magic angle spinning (MAS) NMR spectroscopy. The results show clear evidence for Al–O–Al avoidance. Since only intermediate MAS speeds and fields are used, this new approach can be incorporated easily with a variety of dipolar recoupling schemes to explore the key interactions and applications of LDHs.

On the Track to Silica-Supported Tungsten Oxo Metathesis Catalysts: Input from 17O Solid-State NMR

The grafting of an oxo chloro trisalkyl tungsten derivative on silica dehydroxylated at 700 °C was studied by several techniques that showed reaction via W-Cl cleavage, to afford a well-defined precatalyst for alkene metathesis. This was further confirmed by DFT calculations on the grafting process. (17)O labeling of the oxo moiety of a series of related molecular and supported tungsten oxo derivatives was achieved, and the corresponding (17)O MAS NMR spectra were recorded. Combined experimental and theoretical NMR studies yielded information on the local structure of the surface species. Assessment of the (17)O NMR parameters also confirmed the nature of the grafting pathway by ruling out other possible grafting schemes, thanks to highly characteristic anisotropic features arising from the quadrupolar and chemical shift interactions.

Hydroxy-β-Thiolactams to Oxazole-2-thiones. A Novel DMSO-Promoted Oxidation

3-Aryl-3-hydroxy-1-methylazetidine-2-thiones react with HCl in DMSO to give 3-methyl-5-aryloxazole-2-thiones. Substituent effects correlate with rate effects on hydrolyses of acetals of benzaldehyde. An (17)O labeling experiment indicates that the oxygen atom of the product is derived from the hydroxyl group. Trifluoroacetic anhydride/DMSO in CH2Cl2 can also promote the reaction. Mechanisms involving a Grob-type fragmentation of an activated substrate, followed by recyclization, or a cyclopropylcarbinyl type of rearrangement can account for this oxidative rearrangement.

Loading of MOF-5 with Cu and ZnO Nanoparticles by Gas-Phase Infiltration with Organometallic Precursors: Properties of Cu/ZnO@MOF-5 as Catalyst for Methanol Synthesis

The loading of [Zn4O(bdc)3] (MOF-5; bdc = 1,4-benzenedicarbocylate) with nanocrystalline Cu and ZnO species was achieved in a two-step process. First, the solvent-free gas-phase adsorption of the volatile precursors [CpCuL] (L = PMe3, CNtBu) and ZnEt2 leads to the isolable inclusion compounds precursor@MOF-5. These intermediates were then converted into Cu@MOF-5 and ZnO@MOF-5 by hydrogenolysis or photoassisted thermolysis at 200−220 °C in the case of Cu and hydrolysis or dry oxidation at 25 °C followed by annealing 250 °C in the case of ZnO. 17O labeling studies using H217O (30%) revealed that neither the bdc linkers nor the central oxide ion of the Zn4O unit exchange oxygen atoms/ions with the imbedded ZnO species. The obtained material Cu@MOF-5 (11 wt % Cu), exhibiting an equivalent Langmuir surface of 1100 m2·g−1, was further characterized by powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). The Cu nanoparticles are homogeneously distributed over the MOF-5 microcrystals, occupying only about 1% of the cavities. Their size distribution appears to be polydisperse with a majority around 1 nm in size (by EXAFS) together with a minority of larger particles up to 3 nm (PXRD). Cu@MOF-5 was reversibly surface oxidized/reduced by N2O/H2 treatment, resulting in a (Cu2O/Cu)@MOF-5 material as revealed by PXRD and XAS. Depending on the preparation conditions of the ZnO@MOF-5 materials a variation of the ZnO loading from 10 to 35 wt % was achieved. PXRD, TEM, UV−vis, and 17O-MAS NMR spectroscopy gave evidence for a largely intact MOF-5 matrix with imbedded ZnO nanoparticles <4 nm being in the quantum size regime. Doubly-loaded (Cu/ZnO)@MOF-5 samples were prepared by gas-phase loading of ZnO@MOF-5 with [CpCuL] followed by thermally activated hydrogenolysis. The initial catalytic productivity in methanol synthesis from a CO/CO2/H2 gas mixture at 1 atm and 220 °C peaked at about 60% of an industrial reference catalyst. This result is particular surprising because of the comparably low Cu loading (1.4 wt %) and small Cu specific surface area <1 m2·g−1, thus suggesting a superior interfacial contact between the Cu and ZnO nanophases. However, the materials (Cu/ZnO)@MOF-5 were unstable under catalytic conditions over several hoours, the metal organic framework collapsed, and the final catalytic activities were poor.

Solid-state 17O NMR in Biological Solids: Efficient 17O Labeling of Amino Acids and Peptides

Abstract A highly effective labeling method for 17O-enriched amino acids and peptides at moderate experimental conditions (Japanese Patent 2006-8666) has been presented, which has enabled us to readily carry out solid-state 17O NMR experiments in almost all amino acids and peptides.

A convenient and rapid method for the selective oxygen-17 enrichment of aspartyl peptides during solid-phase synthesis

In this work we describe, for the first time, a rapid and efficient method for 17O selective labeling on the β-carboxyl group of an aspartic acid residue already incorporated into a peptide sequence anchored on a solid-phase support. The β-O-benzyl ester of the Asp residue of the Ac-RGD-benzydrylamine resin was successfully saponified using Na17OH in a methanol/dichloromethane mixture. The 17O selective enriched peptide was then released from the solid support by acidic cleavage. The 17O NMR spectrum confirmed the 17O labeling of the Asp β-carboxylate.

Synthesis, Characterization, and Reactivity of W2Ru3 Clusters That Contain Oxo and Carbido Ligands, Obtained by Direct C−O Bond Activation

Treatment of CpWRu3(CO)12(μ-H) with CpW(CO)3H in refluxing heptane afforded the cluster compound Cp2W2Ru3(CO)13 (1). Single-crystal X-ray analysis indicates a trigonal-bipyramidal cluster arrangement with both W atoms located at the equatorial positions. Pyrolysis of 1 in refluxing toluene gave the oxo−carbido cluster CpW(O)CpWRu3(μ5-C)(CO)11 (2a) in moderate yield, whereas the condensation of LWRu3(CO)12(μ-H) and L‘W(CO)3H (L = L‘ = Cp*; L, L‘ = Cp, Cp* or Cp*, Cp) afforded the derivatives LW(O)L‘WRu3(μ5-C)(CO)11 (2b, L = L‘ = Cp*; 2c, L = Cp; L‘ = Cp*) exclusively. A combination of spectroscopic and structural data suggests that the complexes 2 adopt a wingtip-bridged butterfly structure and possess a terminal oxo and an interstitial carbide ligand. Thus, the transformation from 1 to 2 illustrates an example of metal-assisted cleavage of the carbonyl C−O bond. Mechanistic considerations based on the result of 17O labeling studies are discussed. Furthermore, extensive heating of 2b,c in toluene leads via elimination of two CO ligands to the formation of the new cluster complexes LL‘W2(μ-O)Ru3(μ5-C)(CO)9 (3b, L = L‘ = Cp*; 3c, L = Cp; L‘ = Cp*), in which a distorted-square-pyramidal core structure has been confirmed by single-crystal X-ray analysis. Treatment of 3 with CO gives regeneration of the complexes 2 in high yield.

The effect of 17O on the relaxation of an amide proton within a hydrogen bond.

The relaxation rates of the multiple-quantum coherence for the amide hydrogen of Gly13 in ras p21.GDP were determined in the presence and absence of 17O labeling in the beta-phosphate of GDP. No significant difference could be observed between labeled and unlabeled samples, in spite of the fact that the hydrogen bond from the amide group of Gly13 to the beta-phosphate is shorter than is typical, based on its chemical shift. For macromolecules in which an oxygen atom is the acceptor of a hydrogen bond, dipolar coupling between 17O and hydrogen is unlikely to be observable, except for extremely short H-bonds.

Polynuclear Titanium Oxoalkoxides: Molecular Building Blocks for New Materials?

ABSTRACTThe [Ti7O4](OEt)20 molecule, Et = C2H5, is very reactive toward ethanol, and its [Ti7O4] metal oxide core structure is largely decomposed in &lt;10 minutes. The [Ti16O16](OEt232 molecule, however, has a [Ti16O16] core structure which is relatively stable toward alcoholysis, and solid state 17O MAS NMR experiments using selective 17O labeling techniques show that this core structure is preserved in good yield during sol-gel polymerization.

Sequence-dependent variations in the 31P NMR spectra and backbone torsional angles of wild-type and mutant Lac operator fragments.

Assignment of the 31P resonances of a series of six sequenced-related tetradecamer DNA duplexes, d(TGTGAGCGCTCACA)2, d(TATGAGCGCTCATA)2, d(TCTGAGCGCTCAGA)2, d(TGTGTGCGCACACA)2, d(TGTGACGCGTCACA)2 and d(CACAGTATACTGTG)2, related to the lac operator DNA sequence was determined either by site-specific 17O labeling of the phosphoryl groups or by two-dimensional 1H-31P pure absorption phase constant time (PAC) heteronuclear correlation spectroscopy. J(H3'-P) coupling constants for each of the phosphates of the tetradecamers were obtained from 1H-31P J-resolved selective proton flip 2D spectra. By use of a modified Karplus relationship the C4'-C3'-O3'-P torsional angles (epsilon) were obtained. Comparison of the 31P chemical shifts and J(H3'-P) coupling constants of these sequences has allowed greater insight into those various factors responsible for 31P chemical shift variations in oligonucleotides and provided an important probe of the sequence-dependent structural variation of the deoxyribose phosphate backbone of DNA in solution. These sequence-specific variations in the conformation of the DNA sugar phosphate backbone of various lac operator DNA sequences can possibly explain the sequence-specific recognition of DNA by DNA binding proteins, as mediated through direct contacts between the phosphates and the protein.

Two-dimensional proton and phosphorus-31 NMR spectra and restrained molecular dynamics structure of an extrahelical adenosine tridecamer oligodeoxyribonucleotide duplex

Assignment of the 1H and 31P NMR spectra of an extrahelical adenosine tridecamer oligodeoxyribonucleotide duplex, d(CGCAGAATTCGCG)2, has been made by two-dimensional 1H-1H and heteronuclear 31P-1H correlated spectroscopy. The downfield 31P resonance previously noted by Patel et al. (1982) has been assigned by both 17O labeling of the phosphate as well as a pure absorption phase constant-time heteronuclear 31P-1H correlated spectrum and has been associated with the phosphate on the 3' side of the extrahelical adenosine. JH3'-P coupling constants for each of the phosphates of the tridecamer were obtained from the 1H-31P J-resolved selective proton-flip 2D spectrum. By use of a modified Karplus relationship the C4-C3'-O3-P torsional angles (epsilon) were obtained. There exists a good linear correlation between 31P chemical shifts and the epsilon torsional angle. The 31P chemical shifts and epsilon torsional angles follow the general observation that the more internal the phosphate is located within the oligonucleotide sequence, the more upfield the 31P resonance occurs. Because the extrahelical adenosine significantly distorts the deoxyribose phosphate backbone conformation even several bases distant from the extrahelical adenosine, 31P chemical shifts show complex site- and sequence-specific variations. Modeling and NOESY distance-restrained energy minimization and restrained molecular dynamics suggest that the extrahelical adenosine stacks into the duplex. However, a minor conformation is also observed in the 1H NMR, which could be associated with a structure in which the extrahelical adenosine loops out into solution.

Assignments of phosphorus-31 NMR resonances in oligodeoxyribonucleotides: origin of sequence-specific variations in the deoxyribose phosphate backbone conformation and the phosphorus-31 chemical shifts of double-helical nucleic acids

It is now possible to unambiguously assign all 31P resonances in the 31P NMR spectra of oligonucleotides by either two-dimensional NMR techniques or site-specific 17O labeling of the phosphoryl groups. Assignment of 31P signals in tetradecamer duplexes, (dTGTGAGCGCTCACA)2, (dTAT-GAGCGCTCATA)2, (dTCTGAGCGCTCAGA)2, and (dTGTGTGCGCACACA)2, and the dodecamer duplex d(CGTGAATTCGCG)2 containing one base-pair mismatch, combined with additional assignments in the literature, has allowed an analysis of the origin of the sequence-specific variation in 31P chemical shifts of DNA. The 31P chemical shifts of duplex B-DNA phosphates correlate reasonably well with some aspects of the Dickerson/Calladine sum function for variation in the helical twist of the oligonucleotides. Correlations between experimentally measured P-O and C-O torsional angles and results from molecular mechanics energy minimization calculations show that these results are consistent with the hypothesis that sequence-specific variations in 31P chemical shifts are attributable to sequence-specific changes in the deoxyribose phosphate backbone. The major structural variation responsible for these 31P shift perturbations appears to be P-O and C-O backbone torsional angles which respond to changes in the local helical structure. Furthermore, 31P chemical shifts and JH3'-P coupling constants both indicate that these backbone torsional angle variations are more permissive at the ends of the double helix than in the middle. Thus 31P NMR spectroscopy and molecular mechanics energy minimization calculations appear to be able to support sequence-specific structural variations along the backbone of the DNA in solution.

ChemInform Abstract: 17O and 18O Labeling Studies by NMR. Mechanism of Rearrangement of an α‐Thiophosphoryl Trifluoroacetate to an α‐Phosphoryl Thiotrifluoroacetate.

AbstractThe labeled derivatives (VIa) of the thiophosphoryl trifluoroacetate (VIb) are prepared from the acetal (I).