Gas-phase Mass Spectrometry Research Articles

Homoleptic Transition Metal Carbonyl Cations: Synthetic Approaches, Characterization and Follow-Up Chemistry.

ConspectusCarbon monoxide, CO, is one of the most important ligands in organometallic chemistry. It is an excellent π-acceptor and a moderate σ-donor. Therefore, most of the known transition metal carbonyls (TMCs) exhibit a zerovalent or even negative metal oxidation state (OS) of up to -4. However, given the right conditions, the carbonyl ligand also forms homoleptic cationic complexes with one or more transition metal atoms, the transition metal carbonyl cations (TMCCs), known with an OS of up to +3. Despite their long-standing history upon discovery of the first [M(CO)6]+ examples (M = Mn, Tc, Re) by E. O. Fischer in 1962 as well as their very fundamental nature, it took until the 1990s for the scope to be widened by Aubke, Strauss and Willner. Yet, many potential TMCC entries known from gas-phase mass spectrometry work remained unknown on preparative grounds. This is due to their high reactivity, which puts scientists to new challenges and encourages the development of suitable solvents, anions and oxidants, to cope with the demands of these fundamental salts─later referred to as pseudo-gas-phase conditions and innocent deelectronators and solvents.Hence, the utilization of extremely weakly coordinating perfluorinated alkoxyaluminates [Al(ORF)4]- and [F{Al(ORF)3}2]- (ORF = -OC(CF3)3) in combination with the polar but non- or weakly coordinating innocent solvents 1,2-difluorobenzene (oDFB) and 1,2,3,4-tetrafluorobenzene (TFB) yielded the first TMCC salts containing heptacoordinate [M(CO)7]+ (M = Nb, Ta) as well as paramagnetic [M(CO)6]+· (M = Cr, Mo, W) or [Ni(CO)4]+·. However, the use of typical inorganic oxidants Ag+, [NO]+ and Ag+/0.5 I2 regularly led to unwanted side reactions. For example, the Lewis acidic silver(I) cations form Lewis pairs with various Lewis basic TMCs yielding partly clustered [Agx{TMC}y]x+ complex salts, while nitrosonium cations may substitute for carbonyl ligands, forming [M(CO)x-1(NO)]+ complexes. The synergistic oxidizing reagent Ag+/0.5 X2 can add halonium ions X+ to the TMCs (X = Cl, Br, I). This prevented the synthesis of univalent group 8 TMCC salts. Yet, the application of radical cation salts of perfluorinated arenes as innocent deelectronators finally yielded salts of [Fe(CO)5]+· and [M3(CO)14]2+ (M = Ru, Os).TMCC salts are excellent starting materials, and the reaction of [Co(CO)5]+ and [Ni(CO)4]+· with benzene led to the previously unknown bis(benzene) sandwich complexes [Co(benzene)2]+ and [Ni(benzene)2]+·. Under the right conditions, even the very weakly bound oDFB-complex salts with [M(oDFB)2]+ (M = Co, Ni) cations form, useful as naked metal(I) synthons and for small-molecule activation.

Characterization of acetochlor degradation and role of microbial communities in biofilters with varied substrate types

Northeast China has a large area of cultivated land, and the application of various chemical herbicides is very high. As a high-efficiency herbicide widely used in dry fields, its residue in the environment is also concern. Therefore, low-cost and high efficient control measures are urgently needed. Twelve Biofilter simulation devices were designed to investigate the efficiency and mechanism of removing acetochlor under low-temperature conditions. Biochar (Bio-BF), ceramsite (CER-BF), and gravel (GRA-BF) were chosen to be substrates to compare the effect of substrate type on the removal of acetochlor. The results showed that the biochar (Bio-BF) treatment had the shortest onset time (<1 h), The gravel (GRA-BF) treatment had the longest onset of action (more than 8 h), but the removal effect was essentially the same as the biochar treatment. The 16S rRNA gene sequencing results revealed that different bacterial communities are formed due to different substrates. Proteobacteria and Actinobacteria are the dominant phyla in the three biofilters. Four metabolites, 2-ethyl-6-methyl-N-(ethoxymethyl) acetanilide, N-(2-ethyl-6-methyl phenyl) acetamide, N-(2-ethyl-6-methyl phenyl) formamide, and (2-ethyl-6-methyl phenyl) carbamic acid, were identified using gas phase mass spectrometry. The analysis and prediction of the degradation pathways of acetochlor revealed that Ferribacterium, Klebsiella, and Comamonadaceae belonging to the phylum Proteobacteria and Rhodococcus belonging to the phylum Actinobacteria were the key microorganisms involved in the degradation of acetochlor in the biofilter. Redundancy analysis (RDA) further indicates that dissolved oxygen and temperature are key environmental factors affecting the development of key microbial communities within the biofilter, and that future design of biofilters in Northeast China should focus on how to improve oxygen content and temperature.

Conductometric acetic anhydride gas sensors based on S-doped porous ZnO microspheres with enhanced Lewis base interaction

Acetic anhydride is an essential raw material for manufacturing the drug heroin. Its rapid detection using semiconductor sensors has great significance to curb the spread of drugs. However, there are few reports on the design of semiconductor sensors for acetic anhydride, and the sensing mechanism remains unclear. For this reason, the strategy enhancing the Lewis base sites on the ZnO surface via S-doped is proposed in view of the Lewis acid properties of acetic anhydride combined with Lewis acid base theory. The synthesized S-doped porous spherical ZnO (S-ZnO-600) sensor response (312.4) to 100 ppm acetic anhydride is 4.9 times than ZnO-600 (64.1) with a detection limit of 200 ppb. X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR) and the electron localization function (ELF) indicate that S-doped greatly modulates the electronic structure of ZnO through lattice defects. Meanwhile, the increase of Lewis basicity on the ZnO surface through S doping is further confirmed using CO2 temperature programmed desorption (CO2-TPD), the frontier molecular orbital and the charge density difference (CDD). Gas-phase mass spectrometry (GP-MS) combined with DFT further reveals the catalytic degradation of acetic anhydride sensing process.

(Invited) Nucleation and Growth of Small Atomic Aggregates into Superatom Nanoclusters

One of the challenges in nucleation and growth of small atomic aggregates is to develop the novel research field of solid-state chemistry and material science using gas-phase-synthesized superatom nanoclusters. Among various superatoms, the greatest advantage of the central-atom-encapsulating binary superatoms, such as M@Si16, is that their electronic structures can be designed by optimizing the central metal atom M while retaining the geometrical symmetry of the Si16 cage [1], as shown in the figure below. We have systematically investigated the nucleation and growth of M@Si16 superatoms with gas-phase mass spectrometry, and then performed the surface immobilization of the M@Si16 cations and anions on a substrate monodispersively with the size-selective soft-landing. Initial products prepared via the surface immobilization of M@Si16 superatoms on solid surfaces decorated with monolayer films of C60 molecules were investigated using scanning tunneling microscopy (STM) [2] and X-ray photoelectron spectroscopy (XPS) [3]. Furthermore, we have developed a large-scale synthesis method for M@Si16 (M = Ti and Ta) by scaling up the clean dry-process with a high-power impulse magnetron sputtering (HiPIMS, nanojima®) [4] and by a direct liquid embedded trapping (DiLET) method [5]. The spectroscopic results reveal that the structures of soft-landed and isolated M@Si16 superatoms are the metal-encapsulating tetrahedral silicon-cage (METS) [5,6].Furthermore, superatoms of group-5 metals (M = V, Nb, and Ta) encapsulating Si16 cage nanoclusters (M@Si16) can be efficiently generated to form assembled films [7]. Temperature-dependent current–voltage (I–V) characteristics of the M@Si16 assembled films revealed that the electrical conduction mechanism is not band transport, but hopping transport with Efros–Shklovskii variable range hopping for all central M atoms [8]. The results show that electrons involved in conduction are strongly correlated to localized electronic states.[1] K. Koyasu, A. Nakajima, et al. J. Am. Chem. Soc. 127, 4998 (2005).[2] M. Nakaya, A. Nakajima, et al. Nanoscale, 6, 14702 (2014).[3] M. Shibuta, A. Nakajima, et al. J. Am. Chem. Soc. 137, 14015 (2015).[4] C. H. Zhang, A. Nakajima, et al. J. Phys. Chem. A 117, 10211 (2013).[5] H. Tsunoyama, A. Nakajima, et al. J. Phys. Chem. C 121, 20507 (2017).[6] H. Tsunoyama, A. Nakajima, et al. Acc. Chem. Res. 51, 1735 (2018).[7] M. Shibuta, A. Nakajima, et al. J. Phys. Chem. C, 124, 28108 (2020).[8] T. Yokoyama, A. Nakajima, et al. J. Phys. Chem. C, 125, 18420 (2021). Figure 1

Extraction of cucumber phloem sap based on the capillary-air pressure principle.

Changes in the substances in phloem sap can effectively reflect the nutritional status of cucumber plants during their growth. Because of the limitations of the time-consuming and complex operations of existing phloem sap extraction methods, the authors proposed a new extraction method based on the capillary-air pressure principle and designed a new sap sampling device. To examine the feasibility of the new sampling device, sap sampled from the same plant with the new method and the common EDTA method was analyzed by gas-phase mass spectrometry. The data showed that the number of substances in the sap sampled using capillary-air pressure was higher than that observed using the EDTA method. The concentration of substances sampled using capillary-air pressure was much higher than that observed using EDTA.

Enhancement of norisoprenoid and acetoin production for improving the aroma of fermented mango juice by Bacillus subtilis-HNU-B3

Mango juice (MJ) has high nutritional value and decent flavor. However, its aroma could be easily changed by heat treatment during processing, which affects its acceptability and quality. In this study, Bacillus subtilis-HNU-B3 that could transfer carotenoid, was obtained from orchard soil to improve the aroma of fermented mango juice (FMJ). Compared with MJ, the organic acid content of FMJ by B. subtilis-HNU-B3 was significantly changed, and the contents of succinic acid and malic acid were increased to 3.68 mg/mL and 2.04 mg/mL, respectively. Moreover, volatile compounds identified by headspace solid-phase micro-extraction gas-phase mass spectrometry in FMJ were norisoprenoid and acetoin, accounting for 51.52 % of the total volatile substances. In addition, B. subtilis-HNU-B3 fermentation significantly increased the antioxidant capacity and total phenol contents of MJ, and the activity of carotenoid cleavage dioxygenase was 188 U/L. In conclusion, the aroma of FMJ could be improved by B. subtilis-HNU-B3 through increasing the content of norisoprenoid and acetoin. Our results provide theatrical support for Bacillus subtilis to improve the aroma quality of FMJ.

Breeding of High Yield β -glucosidase Yeast by Mutagenesis and Its Effect on the Aroma Characteristics of Rosa roxburghii Tratt Wine

To analyze the effects of β-glucosidase on the aroma characteristics of Rosa roxburghii Tratt (Rosa roxburghii) wine, a strain of Wickerhamomyces anomalus (W. anomalus) C4 producing β-glucosidase was used as the starting strain, and its β-glucosidase activity was further improved by mutagenesis using ethylmethanesulfonate (EMS). R. roxburghii wine was produced via pure or mixed inoculatation of W. anomalus or together with Saccharomyces cerevisiae. The β-glycosidase producing ability was examined using p-nitrophenyl-β-D-glucopyranoside colorimetry. Headspace solid phase microextraction (HS-SPME) and gas phase mass spectrometry (GC-MS) were performed to determine the volatile aroma substances of each group of R. roxburghii wine. A mutant strain W.anomalus E3 with stable β-glucosidase produced activity was obtained using the mutagenic agent EMS, and the enzyme activity of W.anomalus E3 was (55.05±1.74) U/L, which increased 31.70% compared with the starting strain W.anomalus C4. β-glucosidase activity increased gradually, reached its maximum at the 10th day, and then decreased rapidly during the fermentation process of R. roxburghii wine. Inoculation with W.anomalus C4 and E3 could reduce theacidity value including total acid, volatile acid and pH of the R. roxburghii wine, and the total sugar content was also decreased. Moreover, inoculation with W.anomalus C4 and E3 also regulate the aroma characteristics, such as increasing the volatile ester and alcohol content and the OAVs of the main aroma components. Therefore, it was helpful to regulate the aroma characteristics and increase the complexity and richness of the R. roxburghii wine when inoculation with W.anomalus strain producing β-glucosidase.

A Room-Temperature Stable Distonic Radical Cation.

Distonic radical cations (DRCs) with spatially separated charge and radical sites have, so far, largely been observed by gas-phase mass spectrometry and/or matrix isolation spectroscopy work. Herein, we disclose the isolation of a crystalline dicarbondiphosphide-based β-distonic radical cation salt 3.+ (BARF) (BARF=[B(3,5-(CF3 )2 C6 H3 )4 )]- ) stable at room temperature and formed by a one-electron-oxidation-induced intramolecular skeletal rearrangement reaction. Such a species has been validated by electron paramagnetic resonance (EPR) spectroscopy, single-crystal X-ray diffraction, UV/Vis spectroscopy and density functional theory (DFT) calculations. Compound 3.+ (BARF) exhibits a large majority of spin density at a two-coordinate phosphorus atom (0.74 a.u.) and a cationic charge located predominantly at the four-coordinate phosphorus atom (1.53 a.u.), which are separated by one carbon atom. This species represents an isolable entity of a phosphorus radical cation that is the closest to a genuine phosphorus DRC to date.

Synthesis and characterization of crystalline niobium and tantalum carbonyl complexes at room temperature.

A variety of homoleptic transition metal carbonyl complexes are known as bulk compounds for group 7-12 metals. These metals typically feature a maximum of 6 CO ligands to form complexes with 18 valence electrons. In contrast, group 3-5 metals, with fewer valence electrons, have been shown to form highly coordinated heptacarbonyl and octacarbonyl complexes-although they were only identified by gas-phase mass spectrometry and/or matrix isolation spectroscopy work. Now we have prepared heptacarbonyl cations of niobium and tantalum as crystalline salts that are stable at room temperature. The [M(CO)7]+ (M = Nb or Ta) complexes were formed by the oxidation of [M(CO)6]- with 2Ag+[Al(ORF)4]- (RF, C(CF3)3) under a CO atmosphere; their experimental characterization was supported by density functional theory calculations. Other unusual carbonyl compounds were also synthesized: two isostructural salts that contained the 84-valence-electron cluster cation [Ag6{Nb(CO)6}4]2+, the piano-stool complexes [(1,2-F2C6H4)M(CO)4]+ and two polymorphs of neutral Ta2(CO)12 with a long, unsupported Ta-Ta bond.

Study on the removal of aesthetic indicators by ozone during advanced treatment of water reuse

Aesthetics and water quality are primary issues of concern for sustainable water reuse since aesthetically unpleasant color and odor are likely to induce public misgiving. This study utilizes aesthetic indicators and other bulk water quality parameters for evaluation. It is found that ozonation during advanced treatment processes in a full-scale water reclamation plant (WRP) could achieve satisfactory performance in decolorization and oxidation of aromatic and humic contents. As limited efficacy on odor removal was detected in the WRP, this study further researched the removal of the main odorant substances 2-methylisokanol (2-MIB) and geosmin (GSM) with different ozone dosage using solid-phase extraction (SPE) and gas phase mass spectrometry (GC–MS) techniques. According to the first-order reaction kinetics, it is inferred that competitive reactions during ozonation by organic matters and restricted CT values are major factors affecting the odor removal. As such, additional treatment approaches such as nanofiltration (NF) are suggested to be consider for aesthetic control towards sustainable and long-term reclaimed water use.

Theoretical and Experimental Studies of Subnanoscale Molecules and Clusters

A brief review is given of theoretical and experimental studies of a series of subnanoscale molecules and clusters performed by the authors with the staff of the Institute of Atomic and Molecular Sciences and the Genomics Center, Academia Sinica (Taipei, Taiwan) using quantum chemical calculations and experimental means of laser spectroscopy and mass spectrometry in gas phase. Several systems are considered: (a) the fragmentation and association of heme, hemin, and beta-hematin; (b) the structure, stability and chirality of the isomers of the protonated octamer of serine; (c) the stability and structure of Li- and Na-substituted saccharides, fullerols, and fullerol-like polyhydroxyl clusters; and (d) the theoretical prediction and experimental synthesis and study of the endohedral methane–fullerene cluster CH4@C60.

How Peptides Dissociate in Plasmonic Hot Spots.

Plasmon-induced hot carriers enable dissociation of strong chemical bonds by visible light. This unusual chemistry has been demonstrated for several diatomic and small organic molecules. Here, the scope of plasmon-driven photochemistry is extended to biomolecules and the reactivity of proteins and peptides in plasmonic hot spots is described. Tip-enhanced Raman spectroscopy (TERS) is used to both drive the reactions and to monitor their products. Peptide backbone bonds are found to dissociate in the hot spot, which is reflected in the disappearance of the amide I band in the TER spectra. The observed fragmentation pathway involves nonthermal activation, presumably by dissociative capture of a plasmon-induced hot electron. This fragmentation pathway is known from electron transfer dissociation (ETD) of peptides in gas-phase mass spectrometry (MS), which suggests a general similarity between plasmon-induced photochemistry and nonergodic reactions triggered by electron capture. This analogy may serve as a design principle for plasmon-induced reactions of biomolecules.

Molecular mechanisms of influence of slow electrons on biological structures

Background: The article reviews investigations carried out by biophysicists of the Transcarpathian Branch of the Ukrainian Biophysical Society, dedicated to the memory of the prominent Ukrainian biophysicist, Professor Yuri Pavlovich Blagoi. Objectives: Study of the peculiarities of physical processes and structural changes in nucleic acid molecules initiated by low-energy electrons (10-1-102 eV). Materials and methods: Molecular components of nucleic acids – nucleobases, nucleosides – were chosen as objects of research. A complex of methods is applied: the spectral method for obtaining the luminescence spectra of molecules excited by an electron impact; the electric method in determining the complete cross-sections of the formation of positive and negative ions; the method of gas-phase mass spectrometry with electron impact ionization. A new approach is proposed, which is based on the development of the methods for obtaining biomolecules in an isolated (gas) state, the formation of molecular beams, and the implementation of a crossed electron and molecular beams method. Results: The processes of excitation, ionization and fragmentation of molecules of nucleic acid bases under electron impact are investigated. The radiation spectra of biomolecules in the wavelength region from 200 nm to 500 nm for different energies of incident electrons are obtained. For identification of spectral bands, the excitation functions of biomolecules are investigated, mass spectrometry analysis of the bases is performed, semi-empirical quantum-chemical calculations of structural parameters are carried out. It is established that the complex superpositional nature of the spectra reflects the simultaneous occurrence of various physical processes, including, in addition to the direct excitation of the singlet and triplet states of the base molecules, the dissociation excitation and excitation of ionized biomolecules and their fragments. The analysis of the excitation functions shows the presence of intersystem transitions with the formation of triplet metastable states of the nucleic acid bases molecules. It is shown that the processes of the appearance of negative ions are of resonant nature and are accompanied by the dissociation of molecules even at energies smaller than the thresholds for excitation and ionization.

Reactions of a Polyhalide Ionic Liquid with Copper, Silver, and Gold.

The reactions of copper, silver, and gold with the imidazolium‐based polyhalide ionic liquid (IL) [C6C1Im][Br2I] were investigated by using X‐ray photoelectron spectroscopy (XPS), weight‐loss measurements, and gas‐phase mass spectrometry. All three Group 11 metals are strongly corroded by the IL at moderate temperatures to give a very high content of dissolved CuI, AgI, and AuI species. The IL–metal solutions are stable against contact with water and air. The replacement of imidazolium with inorganic sodium cations decreased metal corrosion rates by orders of magnitude. Our results clearly indicate metal oxidation by iodide from dibromoiodide anions to form molecular iodine and anionic [Br‐MI‐Br]− (M=Cu, Ag, Au) complexes stabilized by imidazolium counterions. From experiments with a trihalide IL with imidazolium methylated at the 2‐position, we ruled out the formation of imidazole–carbene as a cause of the observed corrosion. In contrast to Group 11 metals, molybdenum is inert against the trihalide IL, which is attributed to surface passivation.

Phosphorus-Containing Mineral Evolution and Thermodynamics of Phosphorus Vaporization during Carbothermal Reduction of High-Phosphorus Iron Ore

High-phosphorus iron ore is not used because of its high phosphorus content. Phosphorus is mainly present in fluorapatite. In this work, the phosphorus vaporization that occurs during the carbothermal reduction of fluorapatite was investigated. The thermodynamic principle of vaporization, which removes phosphorus during carbothermal reduction, was elucidated, and the mineral evolution of high-phosphorus iron ore was summarized. The results demonstrate that it was difficult to reduce fluorapatite when only carbon was added. When Al2O3, SiO2, and Fe2O3 were added, the dephosphorization of fluorapatite was stimulated, and the dephosphorization temperature decreased. A phosphorus-containing gas was generated during this process. SiO2 had the strongest effect on the dephosphorization of fluorapatite. The carbothermal reduction rate of fluorapatite accelerated when SiO2, Al2O3, and Fe2O3 were concurrently added. These oxides were advantageous for vaporization dephosphorization. The gas-phase volatiles were detected through gas-phase mass spectrometry. The volatiles were primarily P2 or PO. The temperature range of 1000–1100 °C was the optimum for vaporization dephosphorization. This article provides a theoretical and experimental basis for the development and utilization of high-phosphorus iron ore through vaporization dephosphorization.

Studies on serum pharmacochemistry of effective parts of modified Xiaochaihu Tang for treatment of gastric ulcer

To conduct the studies on serum pharmacochemistry of effective parts of modified Xiaochaihu Tang for treatment of gastric ulcer by using chromatography-mass spectrometry. Absolute ethyl alcohol induced-gastric ulcer model of mouse was used in this study to investigate the pharmacology of modified Xiaochaihu Tang and its effective parts. Both groups could significantly decrease the absolute ethyl alcohol induced-ulcer. Gasphase-mass spectrometry (GC-MS) was used to detect chemical compositions of volatile fractions and the drug components after gastric administration. A total of 63 compounds were identified in extracts, accounting for more than 93% of the all volatile oil, including 23.51% α-curcumene, 11.96% zingiberene, 9.56% curzerene, 6.54% β-sesquinene, 4.77% camphene, and 6 prototype components were also detected in serum for gastric ulcer model. In liquid chromatography-mass spectrometry (LC-MS), a total of 17 compounds were identified in extracts, 6 prototype components and 2 metabolites (3,5-O-feruloylquinic acid and palmatine) were obtained in serum. In a conclusion, this study provides an important scientific basis for identifying the active ingredients in modified Xiaochaihu Tang, and also helps to reveal the pharmacological effect of modified Xiaochaihu Tang for treatment of gastric ulcer.

Comparative study on Artemisia halodendron Turcz. and its two related plants by GC-MS analysis and protective effect against carbon tetrachloride-induced hepatotoxicity in mice

A rapid method had been used for comparative study on Artemisia halodendron Turcz. and its two related plants by gas phase-mass spectrometry (GC-MS). The comparison of the volatile oils obtained in three plants by GC-MS were similar in 20 compositions. However, n-Hexadecanoic acid (10.40%), Biphenyl (7.867%) and 9,12-Octadecadienoic acid (7.25%) were the predominant in the volatile oils of A. halodendron Turcz., whereas these constituents did not exist in the other two plants. And the study investigated the effect of three plants against CCl4-induced hepatotoxicity in mice. 70% ethanol extracts of A. halodendron Turcz. showed weaker protective effect than the other two plants. It suggested that they provide a basis for the identification of the A. halodendron Turcz. from the other two plants and the ethanol extract from three plants exerted a protecting effect against hepatotoxicity.

Isotope geochemistry. Biological signatures in clumped isotopes of O₂.

The abundances of molecules containing more than one rare isotope have been applied broadly to determine formation temperatures of natural materials. These applications of "clumped" isotopes rely on the assumption that isotope-exchange equilibrium is reached, or at least approached, during the formation of those materials. In a closed-system terrarium experiment, we demonstrate that biological oxygen (O2) cycling drives the clumped-isotope composition of O2 away from isotopic equilibrium. Our model of the system suggests that unique biological signatures are present in clumped isotopes of O2—and not formation temperatures. Photosynthetic O2 is depleted in (18)O(18)O and (17)O(18)O relative to a stochastic distribution of isotopes, unlike at equilibrium, where heavy-isotope pairs are enriched. Similar signatures may be widespread in nature, offering new tracers of biological and geochemical cycling.

What controls clumped isotopes?

Isotope Geochemistry Stable isotopes of a molecule can clump together in several combinations, depending on their mass. Even for simple molecules such as O2, which can contain 16O, 17O, and 18O in various combinations, clumped isotopes can potentially reveal the temperatures at which molecules form. Away from equilibrium, however, the pattern of clumped isotopes may reflect a complex array of processes. Using high-resolution gas-phase mass spectrometry, Yeung et al. found that biological factors influence the clumped isotope signature of oxygen produced during photosynthesis (see the Perspective by Passey). Similarly, Wang et al. showed that away from equilibrium, kinetic effects causing isotope clumping can lead to overestimation of the temperature at which microbially produced methane forms. Science , this issue p. [431][1]; p. [428][2]; see also p. [394][3] [1]: /lookup/doi/10.1126/science.aaa6284 [2]: /lookup/doi/10.1126/science.aaa4326 [3]: /lookup/doi/10.1126/science.aab1604

Methane cycling. Nonequilibrium clumped isotope signals in microbial methane.

Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted "clumped" isotopologues (for example, (13)CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane's clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on (13)CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.