Publications by authors named "Fabian S Menges"

20 Publications

  • Page 1 of 1

Probing Microbiome Genotoxicity: A Stable Colibactin Provides Insight into Structure-Activity Relationships and Facilitates Mechanism of Action Studies.

J Am Chem Soc 2021 Sep 15;143(38):15824-15833. Epub 2021 Sep 15.

Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.

Colibactin is a genotoxic metabolite produced by commensal-pathogenic members of the human microbiome that possess the (aka ) biosynthetic gene cluster. bacteria induce tumorigenesis in models of intestinal inflammation and have been causally linked to oncogenesis in humans. While colibactin is believed underlie these effects, it has not been possible to study the molecule directly due to its instability. Herein, we report the synthesis and biological studies of colibactin 742 (), a stable colibactin derivative. We show that colibactin 742 () induces DNA interstrand-cross-links, activation of the Fanconi Anemia DNA repair pathway, and G/M arrest in a manner similar to . The linear precursor , which mimics the biosynthetic precursor to colibactin, also recapitulates the bacterial phenotype. In the course of this work, we discovered a novel cyclization pathway that was previously undetected in MS-based studies of colibactin, suggesting a refinement to the natural product structure and its mode of DNA binding. Colibactin 742 () and its precursor will allow researchers to study colibactin's genotoxic effects independent of the producing organism for the first time.
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http://dx.doi.org/10.1021/jacs.1c07559DOI Listing
September 2021

Chemical Reduction of Ni Cyclam and Characterization of Isolated Ni Cyclam with Cryogenic Vibrational Spectroscopy and Inert-Gas-Mediated High-Resolution Mass Spectrometry.

J Phys Chem A 2021 Aug 29;125(31):6715-6721. Epub 2021 Jul 29.

Sterling Chemistry Laboratory, Chemistry Department, Yale University, New Haven, Connecticut 06520, United States.

Ni cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) is an efficient catalyst for the selective reduction of CO to CO. A crucial elementary step in the proposed catalytic cycle is the coordination of CO to a Ni cyclam intermediate. Isolation and spectroscopic characterization of this labile Ni species without solvent has proven to be challenging, however, and only partial IR spectra have previously been reported using multiple photon fragmentation of ions generated by gas-phase electron transfer to the Ni cyclam dication at 300 K. Here, we report a chemical reduction method that efficiently prepares Ni cyclam in solution. This enables the Ni complex to be transferred into a cryogenic photofragmentation mass spectrometer using inert-gas-mediated electrospray ionization. The vibrational spectra of the 30 K ion using both H and N messenger tagging over the range 800-4000 cm were then measured. The resulting spectra were analyzed with the aid of electronic structure calculations, which show strong method dependence in predicted band positions and small molecule activation. The conformational changes of the cyclam ligand induced by binding of the open shell Ni cation were compared with those caused by the spherical, closed-shell Li cation, which has a similar ionic radius. We also report the vibrational spectrum of a Ni cyclam complex with a strongly bound O ligand. The cyclam ligand supporting this species exhibits a large conformational change compared to the complexes with weakly bound N and H, which is likely due to significant charge transfer from Ni to the coordinated O.
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http://dx.doi.org/10.1021/acs.jpca.1c05016DOI Listing
August 2021

Characterization of the non-covalent docking motif in the isolated reactant complex of a double proton-coupled electron transfer reaction with cryogenic ion spectroscopy.

J Chem Phys 2020 Jun;152(23):234309

Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA.

The solution kinetics of a proton-coupled electron transfer reaction involving two-electron oxidation of a Ru compound with concomitant transfer of two protons to a quinone derivative have been interpreted to indicate the formation of a long-lived intermediate between the reactants. We characterize the ionic reactants, products, and an entrance channel reaction complex in the gas phase using high-resolution mass spectrometry augmented by cryogenic ion IR photodissociation spectroscopy. Collisional activation of this trapped entrance channel complex does not drive the reaction to products but rather yields dissociation back to reactants. Electronic structure calculations indicate that there are four low-lying isomeric forms of the non-covalently bound complex. Comparison of their predicted vibrational spectra with the observed band pattern indicates that the C=O groups of the ortho-quinone attach to protons on two different -NH groups of the reactant scaffold, exhibiting strong O-H-N contact motifs. Since collisional activation does not lead to the products observed in the liquid phase, these results indicate that the reaction most likely proceeds through reorientation of the H-atom donor ligand about the metal center.
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http://dx.doi.org/10.1063/5.0012176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7304996PMC
June 2020

Base-Directed Photoredox Activation of C-H Bonds by PCET.

J Org Chem 2020 06 15;85(11):7175-7180. Epub 2020 May 15.

Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States.

Photoredox catalysis using proton-coupled electron transfer (PCET) has emerged as a powerful method for bond transformations. We previously employed traditional chemical oxidants to achieve multiple-site concerted proton-electron transfer (MS-CPET) activation of a C-H bond in a proof-of-concept fluorenyl-benzoate substrate. As described here, photoredox oxidation of the fluorenyl-benzoate follows the same rate constant driving force trend determined for thermal MS-CPET. Analogous photoredox catalysis enables C-H activation and H/D exchange in a number of additional substrates with favorably positioned bases. Mechanistic studies support our hypothesis that MS-CPET is a viable pathway for bond activation for substrates in which the C-H bond is weak, while stepwise carboxylate oxidation and hydrogen atom transfer likely predominate for stronger C-H bonds.
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http://dx.doi.org/10.1021/acs.joc.0c00333DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7275901PMC
June 2020

Chain Length Dependence of Hydrogen Bond Linkages between Cationic Constituents in Hydroxy-Functionalized Ionic Liquids: Tracking Bulk Behavior to the Molecular Level with Cold Cluster Ion Spectroscopy.

J Phys Chem Lett 2020 Feb 14;11(3):683-688. Epub 2020 Jan 14.

Sterling Chemistry Laboratory , Yale University , New Haven , Connecticut 06520 , United States.

Hydroxy functionalization of cations in ionic liquids (ILs) can lead to formation of contacts between their OH groups [so-called (c-c) interactions]. One class of these linkages involves cooperatively enhanced hydrogen bonds to anionic partners that are sufficiently strong to overcome the repulsion between two positively charged centers. Herein, we clarify how the propensity for the formation of (c-c) contacts depends on the alkyl chain length between two cationic rings and their OH groups by analyzing the temperature-dependent IR spectra of bulk ILs as well as the vibrational predissociation spectra of ∼35 K complexes comprised of two cations and one anion. This study compares the behavior of two cationic derivatives with ethyl and propyl chains complexed with two different anions: bis(trifluoromethylsulfonyl)imide and tetrafluoroborate. Only the bulk ILs with the longer chain propyl derivative [HPMPip = 1-(3-hydroxypropyl)-1-methylpiperidinium] display (c-c) interactions. Molecular-level aspects of this docking arrangement are revealed by analyzing the OH stretching fundamentals displayed by the ternary complexes.
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http://dx.doi.org/10.1021/acs.jpclett.9b03359DOI Listing
February 2020

Comment on "C-D Vibration at C2 Position of Imidazolium Cation as a Probe of the Ionic Liquid Microenvironment".

J Phys Chem A 2020 01 17;124(4):755-756. Epub 2020 Jan 17.

Sterling Chemistry Laboratory , Yale University , New Haven , Connecticut 06520 , United States.

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http://dx.doi.org/10.1021/acs.jpca.9b10728DOI Listing
January 2020

Cooperatively enhanced hydrogen bonds in ionic liquids: closing the loop with molecular mimics of hydroxy-functionalized cations.

Phys Chem Chem Phys 2019 Aug;21(33):18092-18098

Department of Chemistry, University of Rostock, 18059 Rostock, Germany.

We address the cooperative hydrogen bonding interactions in play between the ionic constituents of ionic liquids (ILs) with particular attention to those involving the attractive interactions between two cations in the system 1-(2-hydroxyethyl)pyridinium tetrafluoroborate [HEPy][BF4]. This is accomplished by comparing the temperature-dependent linear infrared spectra of [HEPy][BF4] with that of the molecular mimic of its cation, 2-phenylethanol (PhenEthOH). We then explored the structural motifs of these H-bonded configurations at the molecular level by analyzing the cryogenic ion vibrational predissociation spectroscopy of cold (∼35 K) gas phase cluster ions with quantum chemical methods. The analysis of the OH stretching bands reveals the formation of the various binding motifs ranging from the common +OHBF4- interaction in ion-pairs (c-a) to the unusual +OH+OH interaction (c-c) in linear and cyclic, homodromic H-bonding domains. Replacing ion-pairs by the molecular (neutral) analogue of the IL cation also results in the formation of positively charged cyclic motifs, with the bands of the gas phase cationic cyclic tetramer (HEPy+)(PhenEthOH)3 appearing quite close to those assigned previously to cyclic tetramers in the liquid. These conclusions are supported by density functional theory (DFT) calculations of the cationic and neutral clusters as well as the local structures in the liquid. Our combined experimental and theoretical approach for the gas and the liquid phases provides important insight into the competition between differently H-bonded and charged constituents in liquids.
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http://dx.doi.org/10.1039/c9cp03300aDOI Listing
August 2019

Integration of High-Resolution Mass Spectrometry with Cryogenic Ion Vibrational Spectroscopy.

J Am Soc Mass Spectrom 2019 Sep 10;30(9):1551-1557. Epub 2019 Jun 10.

Department of Chemistry, Yale University, New Haven, CT, 06520, USA.

We describe an instrumental configuration for the structural characterization of fragment ions generated by collisional dissociation of peptide ions in the typical MS scheme widely used for peptide sequencing. Structures are determined by comparing the vibrational band patterns displayed by cryogenically cooled ions with calculated spectra for candidate structural isomers. These spectra were obtained in a linear action mode by photodissociation of weakly bound D molecules. This is accomplished by interfacing a Thermo Fisher Scientific Orbitrap Velos Pro to a cryogenic, triple focusing time-of-flight photofragmentation mass spectrometer (the Yale TOF spectrometer). The interface involves replacement of the Orbitrap's higher-energy collisional dissociation cell with a voltage-gated aperture that maintains the commercial instrument's standard capabilities while enabling bidirectional transfer of ions between the high-resolution FT analyzer and external ion sources. The performance of this hybrid instrument is demonstrated by its application to the a, y and z fragment ions generated by CID of a prototypical dipeptide precursor, protonated L-phenylalanyl-L-tyrosine (H-Phe-Tyr-OH or FY-H). The structure of the unusual z ion, nominally formed after NH is ejected from the protonated tyrosine (y) product, is identified as the cyclopropane-based product is tentatively identified as a cyclopropane-based product.
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http://dx.doi.org/10.1007/s13361-019-02238-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6813835PMC
September 2019

Spectroscopic Evidence for an Attractive Cation-Cation Interaction in Hydroxy-Functionalized Ionic Liquids: A Hydrogen-Bonded Chain-like Trimer.

Angew Chem Int Ed Engl 2018 Nov 24;57(47):15364-15368. Epub 2018 Oct 24.

Sterling Chemistry Laboratory, Yale University, New Haven, CT, 06520, USA.

We address the formation of hydrogen bonded domains among the cationic constituents of the ionic liquid (IL) 1-(3-hydroxypropyl)pyridinium tetrafluoroborate [HPPy][BF ] by means of cryogenic ion vibrational predissociation spectroscopy of cold (ca. 35 K) gas-phase cluster ions and quantum chemistry. Specifically, analysis of the OH stretching bands reveals a chain-like OH⋅⋅⋅OH⋅⋅⋅OH⋅⋅⋅BF binding motif involving the three cations in the cationic quinary cluster ion (HPPy ) (BF ) . Calculations show that this cooperative H-bond attraction compensates for the repulsive Coulomb forces and results in stable complexes that successfully compete with those in which the OH groups are predominantly attached to the counter anions. Our combined experimental and theoretical approach provides insight into the cooperative effects that lead to the formation of hydrogen bonded domains involving the cationic constituents of ILs.
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http://dx.doi.org/10.1002/anie.201808381DOI Listing
November 2018

Structural Motifs in Cold Ternary Ion Complexes of Hydroxyl-Functionalized Ionic Liquids: Isolating the Role of Cation-Cation Interactions.

J Phys Chem Lett 2018 Jun 21;9(11):2979-2984. Epub 2018 May 21.

Department of Chemistry , University of Rostock , 18059 Rostock , Germany.

We address the competition between intermolecular forces underlying the recent observation that ionic liquids (ILs) with a hydroxyl-functionalized cation can form domains with attractive interactions between the nominally repulsive positively charged constituents. Here we show that this behavior is present even in the isolated ternary (HEMIm)NTf complex (HEMIm = 1-(2-hydroxyethyl)-3-methylimidazolium) cooled to about 35 K in a photodissociation mass spectrometer. Of the three isomers isolated by double resonance techniques, one is identified to exhibit direct contact between the cations. This linkage involves a cooperative H-bond wherein the OH group on one cation binds to the OH group on the other, which then attaches to the basic N atom of the anion. Formation of this motif comes at the expense of the usually dominant interaction of the acidic CH group on the Im ring with molecular anions, as evidenced by isomer-dependent shifts in the CH vibrational fundamentals.
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http://dx.doi.org/10.1021/acs.jpclett.8b01130DOI Listing
June 2018

Trapping and Structural Characterization of the XNO·NO (X = Cl, Br, I) Exit Channel Complexes in the Water-Mediated X + NO Reactions with Cryogenic Vibrational Spectroscopy.

J Phys Chem Lett 2017 Oct 18;8(19):4710-4715. Epub 2017 Sep 18.

Institute of Chemistry and the Fritz-Haber Center for Molecular Dynamics, The Hebrew University , Jerusalem 9190401, Israel.

The heterogeneous reaction of NO with sea spray aerosols yields the ClNO molecule, which is postulated to occur through water-mediated charge separation into NO and NO ions followed by association with Cl. Here we address an alternative mechanism where the attack by a halide ion can yield XNO by direct insertion in the presence of water. This was accomplished by reacting X(DO) (X = Cl, Br, I) cluster ions with NO to produce ions with stoichiometry [XNO]. These species were cooled in a 20 K ion trap and structurally characterized by vibrational spectroscopy using the D messenger tagging technique. Analysis of the resulting band patterns with DFT calculations indicates that they all correspond to exit channel ion-molecule complexes based on the association of NO with XNO, with the NO constituent increasingly perturbed in the order I > Br > Cl. These results establish that XNO can be generated even when more exoergic reaction pathways involving hydrolysis are available and demonstrate the role of the intermediate [XNO] in the formation of XNO.
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http://dx.doi.org/10.1021/acs.jpclett.7b02120DOI Listing
October 2017

Identification and Partial Structural Characterization of Mass Isolated Valsartan and Its Metabolite with Messenger Tagging Vibrational Spectroscopy.

J Am Soc Mass Spectrom 2017 11 11;28(11):2414-2422. Epub 2017 Aug 11.

Department of Chemistry, Yale University, New Haven, CT, 06520, USA.

Recent advances in the coupling of vibrational spectroscopy with mass spectrometry create new opportunities for the structural characterization of metabolites with great sensitivity. Previous studies have demonstrated this scheme on 300 K ions using very high power free electron lasers in the fingerprint region of the infrared. Here we extend the scope of this approach to a single investigator scale as well as extend the spectral range to include the OH stretching fundamentals. This is accomplished by detecting the IR absorptions in a linear action regime by photodissociation of weakly bound N molecules, which are attached to the target ions in a cryogenically cooled, rf ion trap. We consider the specific case of the widely used drug Valsartan and two isomeric forms of its metabolite. Advantages and challenges of the cold ion approach are discussed, including disentangling the role of conformers and the strategic choices involved in the selection of the charging mechanism that optimize spectral differentiation among candidate structural isomers. In this case, the Na complexes are observed to yield sharp resonances in the high frequency NH and OH stretching regions, which can be used to easily differentiate between two isomers of the metabolite. Graphical Abstract ᅟ.
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http://dx.doi.org/10.1007/s13361-017-1767-zDOI Listing
November 2017

Hidden role of intermolecular proton transfer in the anomalously diffuse vibrational spectrum of a trapped hydronium ion.

Proc Natl Acad Sci U S A 2017 06 31;114(24):E4706-E4713. Epub 2017 May 31.

Sterling Chemistry Laboratory, Yale University, New Haven, CT 06525;

We report the vibrational spectra of the hydronium and methyl-ammonium ions captured in the C binding pocket of the 18-crown-6 ether ionophore. Although the NH stretching bands of the CHNH ion are consistent with harmonic expectations, the OH stretching bands of HO are surprisingly broad, appearing as a diffuse background absorption with little intensity modulation over 800 cm with an onset ∼400 cm below the harmonic prediction. This structure persists even when only a single OH group is present in the HDO isotopologue, while the OD stretching region displays a regular progression involving a soft mode at about 85 cm These results are rationalized in a vibrationally adiabatic (VA) model in which the motion of the HO ion in the crown pocket is strongly coupled with its OH stretches. In this picture, HO resides in the center of the crown in the vibrational zero-point level, while the minima in the VA potentials associated with the excited OH vibrational states are shifted away from the symmetrical configuration displayed by the ground state. Infrared excitation between these strongly H/D isotope-dependent VA potentials then accounts for most of the broadening in the OH stretching manifold. Specifically, low-frequency motions involving concerted motions of the crown scaffold and the HO ion are driven by a Franck-Condon-like mechanism. In essence, vibrational spectroscopy of these systems can be viewed from the perspective of photochemical interconversion between transient, isomeric forms of the complexes corresponding to the initial stage of intermolecular proton transfer.
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http://dx.doi.org/10.1073/pnas.1705089114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5474800PMC
June 2017

Exploring the Gas-Phase Activation and Reactivity of a Ruthenium Transfer Hydrogenation Catalyst by Experiment and Theory in Concert.

J Phys Chem A 2017 Jun 2;121(23):4422-4434. Epub 2017 Jun 2.

Fachbereich Chemie and Forschungszentrum OPTIMAS, Technische Universität Kaiserslautern , 67663 Kaiserslautern, Germany.

This study elucidates structures, activation barriers, and the gas-phase reactivity of cationic ruthenium transfer hydrogenation catalysts of the structural type [(η-cym)RuX(pympyr)]. In these complexes, the central ruthenium(+II) ion is coordinated to an η-bound p-cymene (η-cym), a bidentate 2-R-4-(2-pyridinyl)pyrimidine ligand (pympyr) with R = NH or N(CH), and an anion X = I, Br, Cl, or CFSO. We present infrared multiple-photon dissociation (IR-MPD) spectra of precursors (before HCl loss) and of activated complexes (after HCl loss), which elucidates C-H activation as the key step in the activation mechanism. A resonant two-color IR-MPD scheme serves to record several otherwise "dark" bands and enhances the validity of spectral assignments. We show that collision-induced dissociation (CID)-derived activation energies of the [(η-cym)RuX(pympyr)] (R = N(CH)) complexes depend crucially on the anion X. The obtained activation energies for the HX loss correlate well with quantum chemical activation barriers and are in line with the HSAB concept. We further elucidate the reaction of the activated complexes with D under single-collision conditions. Quantum mechanical simulations substantiate that the resulting species represent analogues for hydrido intermediates formed after abstraction of H and H from isopropanol, as postulated for the catalytic cycle of transfer hydrogenation by us before.
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http://dx.doi.org/10.1021/acs.jpca.7b02459DOI Listing
June 2017

Mechanistic Studies on Ruthenium(II)-Catalyzed Base-Free Transfer Hydrogenation Triggered by Roll-Over Cyclometalation.

Chempluschem 2017 Feb 22;82(2):212-224. Epub 2016 Nov 22.

Fachbereich Chemie, Technische Universität Kaiserslautern, Erwin-Schrödinger-Strasse 54, 67663, Kaiserslautern, Germany.

The synthesis of 2-substituted pyridine-pyrimidine ligands and their complexation with arene ruthenium(II) chloride moieties is reported. Depending on the electronic and steric influences of the ligand, the catalysts undergo CH activation by roll-over cyclometalation. This process opens up the route to the catalytic transfer hydrogenation of ketones with isopropanol as the hydrogen source under base-free and mild conditions. Barriers related to the roll-over cyclometalation process can be determined experimentally by collision-induced dissociation ESI mass spectrometry. They are supported by DFT calculations and allow the classification of the ligands according to their electronic and steric properties, which is also in accordance with critical bond parameters derived from X-ray structure data. DFT calculations furthermore reveal that the formation of a ruthenium(II) hydrido species is plausible through β-hydride elimination from isopropanol.
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http://dx.doi.org/10.1002/cplu.201600526DOI Listing
February 2017

Catalytic Oxygen Evolution from Manganese Complexes with an Oxidation-Resistant N,N,O-Donor Ligand.

Chempluschem 2016 Oct;81(10):1129-1132

Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT, 06511, USA.

There is great interest in developing Mn water-splitting catalysts due to their low cost, abundance, and relevance to the oxygen-evolving complex (OEC). Three ligands with highly donating pyridine alkoxide moieties, including 2-(pyridin-2-yl)propan-2-ol (pyalkH), 2,2'-(pyridine-2,6-diyl)bis(propan-2-ol) (py-dialkH ), and 2-[(2,2'-bipyridin)-6-yl]propan-2-ol (bipy-alkH), have been screened with Mn for oxygen-evolution catalysis. Complexes with the ligand bipy-alkH were shown to evolve O when driven by Oxone (potassium peroxymonosulfate). The catalytic mixture generated from the precursor complex [Mn(bipy-alkH)Cl ] retained activity in unbuffered solution beyond 160 h.
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http://dx.doi.org/10.1002/cplu.201600353DOI Listing
October 2016

Alkali-Controlled C-H Cleavage or N-C Bond Formation by N2-Derived Iron Nitrides and Imides.

J Am Chem Soc 2016 09 29;138(35):11185-91. Epub 2016 Aug 29.

Department of Chemistry, Yale University , 225 Prospect Street, New Haven, Connecticut 06520, United States.

Formation of N-H and N-C bonds from functionalization of N2 is a potential route to utilization of this abundant resource. One of the key challenges is to make the products of N2 activation reactive enough to undergo further reactions under mild conditions. This paper explores the strategy of "alkali control," where the presence of an alkali metal cation enables the reduction of N2 under mild conditions, and then chelation of the alkali metal cation uncovers a highly reactive species that can break benzylic C-H bonds to give new N-H and Fe-C bonds. The ability to "turn on" this C-H activation pathway with 18-crown-6 is demonstrated with three different N2 reduction products of N2 cleavage in an iron-potassium system. The alkali control strategy can also turn on an intermolecular reaction of an N2-derived nitride with methyl tosylate that gives a new N-C bond. Since the transient K(+)-free intermediate reacts with this electrophile but not with the weak C-H bonds in 1,4-cyclohexadiene, it is proposed that the C-H cleavage occurs by a deprotonation mechanism. The combined results demonstrate that a K(+) ion can mask the latent nucleophilicity of N2-derived nitride and imide ligands within a trimetallic iron system and points a way toward control over N2 functionalization.
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http://dx.doi.org/10.1021/jacs.6b04984DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5266523PMC
September 2016

Capture of CO2 by a Cationic Nickel(I) Complex in the Gas Phase and Characterization of the Bound, Activated CO2 Molecule by Cryogenic Ion Vibrational Predissociation Spectroscopy.

Angew Chem Int Ed Engl 2016 Jan 24;55(4):1282-5. Epub 2015 Nov 24.

Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT, 06511, USA.

We describe a systematic method for the preparation and spectroscopic characterization of a CO2 molecule coordinated to an activated bisphenoidal nickel(I) compound containing a tetraazamacrocyclic ligand in the gas phase. The resulting complex was then structurally characterized by using mass-selected vibrational predissociation spectroscopy. The results indicate that a highly distorted CO2 molecule is bound to the metal center in an η(2)-C,O coordination mode, thus establishing an efficient and rational method for the preparation of metal-activated CO2 for further studies using ion chemistry techniques.
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http://dx.doi.org/10.1002/anie.201507965DOI Listing
January 2016

Synthesis, Characterization, and Nitrogenase-Relevant Reactions of an Iron Sulfide Complex with a Bridging Hydride.

J Am Chem Soc 2015 Oct 12;137(41):13220-3. Epub 2015 Oct 12.

Department of Chemistry, Yale University , New Haven, Connecticut 06520, United States.

The FeMoco of nitrogenase is an iron-sulfur cluster with exceptional bond-reducing abilities. ENDOR studies have suggested that E4, the state that binds and reduces N2, contains bridging hydrides as part of the active-site iron-sulfide cluster. However, there are no examples of any isolable iron-sulfide cluster with a hydride, which would test the feasibility of such a species. Here, we describe a diiron sulfide hydride complex that is prepared using a mild method involving C-S cleavage of added thiolate. Its reactions with nitrogenase substrates show that the hydride can act as a base or nucleophile and that reduction can cause the iron atoms to bind N2. These results add experimental support to hydride-based pathways for nitrogenase.
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http://dx.doi.org/10.1021/jacs.5b06841DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4818001PMC
October 2015

Thermodynamics of water dimer dissociation in the primary hydration shell of the iodide ion with temperature-dependent vibrational predissociation spectroscopy.

J Phys Chem A 2015 Mar 20;119(10):1859-66. Epub 2015 Feb 20.

Sterling Chemistry Laboratory, Yale University , New Haven, Connecticut 06525, United States.

The strong temperature dependence of the I(-)·(H2O)2 vibrational predissociation spectrum is traced to the intracluster dissociation of the ion-bound water dimer into independent water monomers that remain tethered to the ion. The thermodynamics of this process is determined using van't Hoff analysis of key features that quantify the relative populations of H-bonded and independent water molecules. The dissociation enthalpy of the isolated water dimer is thus observed to be reduced by roughly a factor of three upon attachment to the ion. The cause of this reduction is explored with electronic structure calculations of the potential energy profile for dissociation of the dimer, which suggest that both reduction of the intrinsic binding energy and vibrational zero-point effects act to weaken the intermolecular interaction between the water molecules in the first hydration shell. Additional insights are obtained by analyzing how classical trajectories of the I(-)·(H2O)2 system sample the extended potential energy surface with increasing temperature.
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http://dx.doi.org/10.1021/jp510250nDOI Listing
March 2015
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