Radical Cation Complexes Research Articles

Structural modification of nickel tetra(thiocyano)corroles during electrochemical water oxidation.

In this study, we present two fully characterized nickel tetrathiocyanocorroles, representing a novel class of 3d-metallocorroles. These nickel(II) ions form square planar complexes, exhibiting a d8-electronic configuration. These anionic complexes are stabilized by the electron-withdrawing SCN groups on the bipyrrole unit of the corrole. The reduced aromaticity in these anionic nickel(II) corrole complexes is evidenced by single crystal X-ray diffraction (XRD) data and a markedly altered absorption profile, with stronger Q bands compared to Soret bands. Notably, the UV-Vis and electrochemical data exhibit significant differences from previously reported nickel(II) corrole radical cation and nickel(II) porphyrin complexes. While these electrochemical data bear a resemblance to those of the anionic nickel(II) corrole by Gross et al., the UV-Vis data show substantial distinctions. Additionally, we explore the utilization of nickel(II)-corrole@CC (where CC denotes carbon cloth) as an electrocatalyst for the oxygen evolution reaction (OER) in an alkaline medium. During electrochemical water oxidation, the molecular catalyst is partially converted to nickel (oxy)hydroxide, Ni(O)OH. The structure reveals the coexistence of the molecular complex and Ni(O)OH in the active catalyst, achieving a turnover frequency (TOF) of 3.32 × 10-2 s-1. The synergy between the homogeneous and heterogeneous phases improves the OER activity, providing more active sites and edge sites and enhancing interfacial charge transfer.

Reliable Isotropic Electron-Paramagnetic-Resonance Hyperfine Coupling Constants from the Frozen-Density Embedding Quasi-Diabatization Approach.

We present a systematic benchmark of isotropic electron-paramagnetic-resonance hyperfine coupling constants calculated for radical cation and anion complexes of molecules contained in the S22 test set using the frozen-density embedding quasi-diabatization (FDE-diab) approach. The results are compared to those from Kohn-Sham density-functional theory and frozen-density embedding, employing the domain-based local pair natural orbital coupled cluster singles and doubles method as a reference. We demonstrate that our new approach outperforms frozen-density embedding in all cases and provides reliable hyperfine couplings for radical cations using rather simple generalized-gradient approximation-type functionals. By contrast, more sophisticated and computationally less efficient exchange-correlation approximations are required for Kohn-Sham density-functional theory. For the radical anions, FDE-diab can at least provide an accuracy similar to that of Kohn-Sham density-functional theory. Finally, we demonstrate the computational advantages of FDE-diab for a π-stacked benzene octamer radical cation.

Bis(imidazolium)-1,3-diphosphete-diide: A Building Block for FeC2 P2 Complexes and Clusters.

Reaction of the 6π-electron aromatic four-membered heterocycle (IPr)2 C2 P2 (1) (IPr=1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) with [Fe2 CO9 ] gives the neutral iron tricarbonyl complex [Fe(CO)3 -η3 -{(IPr)2 C2 P2 }] (2). Oxidation with two equivalents of the ferrocenium salt, [Fe(Cp)2 ](BArF24 ), affords the dicationic tricarbonyl complex [Fe(CO)3 -η4 -{(IPr)2 C2 P2 }](BArF24 )2 (4). The one-electron oxidation proceeds under concomitant loss of one CO ligand to give the paramagnetic dicarbonyl radical cation complex [Fe(CO)2 -η4 -{(IPr)2 C2 P2 }](BArF24 ) (5). Reduction of 5 allows the preparation of the neutral dicarbonyl complex [Fe(CO)2 -η4 -{(IPr)2 C2 P2 }] (6). An analysis by various spectroscopic techniques (57 Fe Mössbauer, EPR) combined with DFT calculations gives insight into differences of the electronic structure within the members of this unique series of iron carbonyl complexes, which can be either described as electron precise or Wade-Mingos clusters.

Bis(imidazolium)‐1,3‐diphosphete‐diide: A Building Block for FeC2P2 Complexes and Clusters

AbstractReaction of the 6π‐electron aromatic four‐membered heterocycle (IPr)2C2P2 (1) (IPr=1,3‐bis(2,6‐diisopropylphenyl)‐1,3‐dihydro‐2H‐imidazol‐2‐ylidene) with [Fe2CO9] gives the neutral iron tricarbonyl complex [Fe(CO)3‐η3‐{(IPr)2C2P2}] (2). Oxidation with two equivalents of the ferrocenium salt, [Fe(Cp)2](BArF24), affords the dicationic tricarbonyl complex [Fe(CO)3‐η4‐{(IPr)2C2P2}](BArF24)2 (4). The one‐electron oxidation proceeds under concomitant loss of one CO ligand to give the paramagnetic dicarbonyl radical cation complex [Fe(CO)2‐η4‐{(IPr)2C2P2}](BArF24) (5). Reduction of 5 allows the preparation of the neutral dicarbonyl complex [Fe(CO)2‐η4‐{(IPr)2C2P2}] (6). An analysis by various spectroscopic techniques (57Fe Mössbauer, EPR) combined with DFT calculations gives insight into differences of the electronic structure within the members of this unique series of iron carbonyl complexes, which can be either described as electron precise or Wade–Mingos clusters.

Electron-transfer induced photo-oxidation of 4,5-dihydro-1,2,4-oxadiazoles: Experimental and computational studies

A series of 3,5-disubstituted 4,5-dihydro-1,2,4-oxadiazoles (DHOZs) were considered to elucidate electronic effects of the substitutions on their UV-light sensitivities. Based on the proposed electron-transfer induced photo-oxidation in this study, the rate of photoreaction is dependent more on the electronic nature of the substituent on the C5-position of the heterocyclic ring than on the C3-position. Also, the electron-accepting ability of solvent significantly facilitates this photo-induced electron-transfer process. In addition, results of the computational studies carried out on the species along the photochemical reaction path steps approve that the photo-oxidation reaction proceeds via tunneling electron transfer process from the excited state of DHOZs to the solvent molecule, forming a radical cation complex intermediate, followed by proton transfer resulting in the formation of the radical pair complex intermediate. Structural relaxation of this radical pair intermediate resulted in the formation of the final oxidized product in a single step, which shows that the last step of photo-oxidation reaction consists of the transfer of the second electron/proton (hydrogen) to the solvent. These computational results thus explain how the relative rate of the photo-oxidation reaction affected by the nature of the substitutions. In addition, photo-isomerization of oxadiazole (OZ) containing the trans-5-styryl substitution to the cis-5-styryl isomer and the following photo-cyclization reaction are studied experimentally and computationally.

Metalloradical Cations and Dications Based on Divinyldiphosphene and Divinyldiarsene Ligands.

Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3‐E)GaCl4 [(3‐E).+ = [{(IPr)C(Ph)E}2Fe(CO)3].+, E = P or As; IPr = C{(NDipp)CH}2, Dipp = 2,6‐iPr2C6H3] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E}2 (1‐E) with Fe2(CO)9 affords [{(IPr)C(Ph)E}2Fe(CO)3] (2‐E), in which 1‐E binds to the Fe atom in an allylic (η3‐EECvinyl) fashion and functions as a 4e donor ligand. Complexes 2‐E undergo 1e oxidation with GaCl3 to yield (3‐E)GaCl4. Spin density analysis revealed that the unpaired electron in (3‐E).+ is mainly located on the Fe (52–64 %) and vinylic C (30–36 %) atoms. Further 1e oxidation of (3‐E)GaCl4 leads to unprecedented η3‐EECvinyl to η3‐ECvinylCPh coordination shuttling to form the dications (4‐E)(GaCl4)2.

A Highly Reactive Chromium(V)–Oxo TAML Cation Radical Complex in Electron Transfer and Oxygen Atom Transfer Reactions

We report the synthesis, characterization, and electron-transfer (ET) oxidation reactivity of a chromium(V)–oxo TAML cation radical complex binding Sc3+ ion, {[CrV(O)(TAML•+)]-Sc3+}3+ (2-Sc). Its p...

Balancing Density Functional Theory Interaction Energies in Charged Dimers Precursors to Organic Semiconductors.

The pursuit of an increasingly accurate description of intermolecular interactions within the framework of Kohn-Sham density functional theory (KS-DFT) has motivated the construction of numerous benchmark databases over the past two decades. By far, the largest efforts have been spent on closed-shell, neutral dimers for which today the interaction energies and geometries can be accurately reproduced by various combinations of dispersion-corrected density functional approximations (DFAs). In sharp contrast, charged, open-shell dimers remain a challenge as illustrated by the analysis of the OREL26rad benchmark set, composed of π-dimer radical cations. Aside from the methodological aspect, achieving a proper description of radical cationic complexes is appealing due to their role as models for charge carriers in organic semiconductors. In the interest of providing an assessment of more realistic dimer systems, we construct a data set of large radical cationic dimers (CryOrel9) and jointly train the 19 parameters of a dispersion corrected, range-separated hybrid density functional (ωB97X-dDsC). The main objective of ωB97X-dDsC is to provide the maximum balance between the treatment of long-range London dispersion and reduction of the delocalization error, which are essential conditions to obtain accurate energy profiles and binding energies of charged, open-shell dimers. The performance of ωB97X-dDsC, its parent ωB97X functional series, and a selection of wave function-based methods is reported for the CryOrel9 data set. The robustness of the reoptimized variant (ωB97X-dDsC) is also tested on other GMTKN30 data sets.

Oriented (Local) Electric Fields Drive the Millionfold Enhancement of the H-Abstraction Catalysis Observed for Synthetic Metalloenzyme Analogues.

This contribution follows the recent remarkable catalysis observed by Groves et al. in hydrogen-abstraction reactions by a) an oxoferryl porphyrin radical-cation complex [Por⋅+ FeIV (O)Lax ] and b) a hydroxoiron porphyrazine ferric complex [PyPzFeIII (OH)Lax ], both of which involve positively charged substituents on the outer circumference of the respective macrocyclic ligands. These charge-coronated complexes are analogues of the biologically important Compound I (Cpd I) and synthetic hydroxoferric species, respectively. We demonstrate that the observed enhancement of the H-abstraction catalysis for these systems is a purely electrostatic effect, elicited by the local charges embedded on the peripheries of the respective macrocyclic ligands. Our findings provide new insights into how electrostatics can be employed to tune the catalytic activity of metalloenzymes and can thus contribute to the future design of new and highly efficient hydrogen-abstraction catalysts.

Electron-Transfer and Redox Reactivity of High-Valent Iron Imido and Oxo Complexes with the Formal Oxidation States of Five and Six.

We report for the first time electron-transfer (ET) properties of mononuclear nonheme iron-oxo and -imido complexes with the formal oxidation states of five and six, such as an iron(V)-imido TAML cation radical complex, which is formally an iron(VI)-imido complex [FeV(NTs)(TAML+•)] (1; NTs = tosylimido), an iron(V)-imido complex [FeV(NTs)(TAML)]- (2), and an iron(V)-oxo complex [FeV(O)(TAML)]- (3). The one-electron reduction potential (Ered vs SCE) of 1 was determined to be 0.86 V, which is much more positive than that of 2 (0.30 V), but the Ered of 3 is the most positive (1.04 V). The rate constants of ET of 1-3 were analyzed in light of the Marcus theory of adiabatic outer-sphere ET to determine the reorganization energies (λ) of ET reactions with 1-3; the λ of 1 (1.00 eV) is significantly smaller than those of 2 (1.98 eV) and 3 (2.25 eV) because of the ligand-centered ET reduction of 1 as compared to the metal-centered ET reduction of 2 and 3. In oxidation reactions, reactivities of 1-3 toward the nitrene transfer (NT) and oxygen atom transfer (OAT) to thioanisole and its derivatives and the C-H bond activation reactions, such as the hydrogen atom transfer (HAT) of 1,4-cyclohexadiene, were compared experimentally. The differences in the redox reactivity of 1-3 depending on the reaction types, such as NT and OAT versus HAT, were interpreted by performing density functional theory calculations, showing that the ligand-centered reduction seen on ET reactions can switch to metal-centered reduction in NT and HAT.

Balancing DFT Interaction Energies in Charged Dimers Precursors to Organic Semiconductors

Accurately describing intermolecular interactions within the framework of Kohn-Sham density functional theory (KS-DFT) has resulted in numerous benchmark databases over the past two decades. By far, the largest efforts have been spent on closed-shell, neutral dimers for which today, the interaction energies and geometries can be accurately reproduced by various combinations of dispersion-corrected density functional approximations (DFAs). In sharp contrast, charged, open-shell dimers remain a challenge as illustrated by the analysis of the OREL26rad benchmark set consisting of pi-dimer radical cations. Aside from the methodological aspect, achieving a proper description of radical cationic complexes is appealing due to their role as models for charge carriers in organic semiconductors. In the interest of providing an assessment of more realistic dimer systems, we construct a dataset of large radical cationic dimers (CryOrel) and jointly train the 19 parameters of a dispersion corrected, range-separated hybrid density functional (wB97X-dDsC), with the objective of providing the maximum balance between the treatment of long-range London dispersion and reduction of the delocalization error. These conditions are essential to obtain accurate energy profiles and binding energies of charged, open-shell dimers. Comparisons with the performance of the parent wB97X functional series and state-of-the-art wavefunction based methods are provided.

Quercetin@ZIF-90 as a novel antioxidant for label-free colorimetric ATP sensing at neutral pH

Quercetin is a nature polyphenolic flavonoid compound, which act as antioxidant and radical scavengers in cells. However, such activities strongly depend on the intracellular microenvironment, which has become an urgency to develop a more stable method for better use of quercetin. Herein, we report a facile approach to fabricate Quercetin@ZIF-90 (QZ) with a narrow size distribution about 100 nm, the synthesized QZ exhibits considerable antioxidant and radical scavenger ability comparing to bare quercetin. Moreover, the experiment results indicated that QZ was sensitive to adenosine 5′-triphosphate (ATP) and pH, thus QZ was applied as a novel antioxidant for the determination of ATP. In brief, though 3, 3′, 5, 5′-tetramethylbenzidine (TMB) could be oxidized to blue cation radical complex by oxidase-like BSA-MnO2 nanosheets (MNs) at neutral pH, QZ could sufficiently protect against MNs-induced TMB cation radicals reaction, which means no obvious color change in MNs-TMB system after the addition of QZ. However, ATP could induced collapse of QZ due to the interaction between ATP and Zn2+ allowing the release of quercetin from ZIF-90 shell, and the inhibition effect to the MNs was weakened, leading to the recovery of blue oxTMB. In this way, a novel “Off-On” colorimetric method for ATP sensing was established, and the method displayed a good linear relationship ranging from 2.0 μ mol L−1 to 80.0 μ mol L−1. The reported strategy is also capable of ATP sensing in MCF-7 cell lysates, which illustrated our method exhibited high sensitivity and selectivity.

Substitution effects on olefin epoxidation catalyzed by Oxoiron(IV) porphyrin π-cation radical complexes: A dft study.

The effects of peripheral fluorine atoms on epoxidation reactions of ethylene by oxoiron(IV) porphyrin cation radical complex in the quartet and sextet spin multiplicities are systematically investigated using the DFT method. The overall reaction routes are determined using a model system of ethylene and Fe(IV)OCl-porphyrin with substituted fluorine atoms. By obtaining the energy diagrams and electron- and spin-density difference contour maps of the transition states and intermediate compounds, we confirm that the electron-withdrawing by peripheral fluorine atoms enhances the reactivity as the number of fluorine atoms increases, as is observed experimentally. The intersystem crossing between the quartet and sextet spin multiplicities is discussed by means of the intrinsic reaction coordinate method. We conclude that the rate-determining step is located at the first transition state (TS1) for the activation of CC and FeO bonds, and the ground electronic state changes from quartet to sextet around the TS1. © 2019 Wiley Periodicals, Inc.

A Manganese(V)-Oxo Tetraamido Macrocyclic Ligand (TAML) Cation Radical Complex: Synthesis, Characterization, and Reactivity Studies.

A mononuclear manganese(V)-oxo complex with tetraamido macrocyclic ligand (TAML), [MnV (O)(TAML)]- (1), is a sluggish oxidant in oxidation reactions. Herein, a mononuclear manganese(V)-oxo TAML cation radical complex, [MnV (O)(TAML+. )] (2), is reported. It was synthesized by reacting [MnIII (TAML)]- with 3.0 equivalents of [RuIII (bpy)3 ]3+ or upon addition of one-electron oxidant to 1 and then characterized thoroughly with various spectroscopic techniques along with DFT calculations. Although 1 is a sluggish oxidant, 2 is a strong oxidant capable of activating C-H bonds of hydrocarbons (i.e., hydrogen atom transfer reaction) and transferring its oxygen atom to thioanisoles and olefins (i.e., oxygen atom transfer reaction).

Observation of alkaline earth complexes M(CO)8 (M = Ca, Sr, or Ba) that mimic transition metals.

The alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) typically engage in chemical bonding as classical main-group elements through their ns and np valence orbitals, where n is the principal quantum number. Here we report the isolation and spectroscopic characterization of eight-coordinate carbonyl complexes M(CO)8 (where M = Ca, Sr, or Ba) in a low-temperature neon matrix. Analysis of the electronic structure of these cubic Oh -symmetric complexes reveals that the metal-carbon monoxide (CO) bonds arise mainly from [M(dπ)] → (CO)8 π backdonation, which explains the strong observed red shift of the C-O stretching frequencies. The corresponding radical cation complexes were also prepared in gas phase and characterized by mass-selected infrared photodissociation spectroscopy, confirming adherence to the 18-electron rule more conventionally associated with transition metal chemistry.

A Nitrido-bridged Heterometallic Ruthenium(IV)/Iron(IV) Phthalocyanine Complex Supported by A Tripodal Oxygen Ligand, [Co(η5-C5H5){P(O)(OEt)2}3]−: Synthesis, Structure, and Its Oxidation to Give Phthalocyanine Cation Radical and Hydroxyphthalocyanine Complexes

Dinuclear iron nitrido phthalocyanine complexes are of interest owing to their applications in catalytic oxidation of hydrocarbons. While nitrido-bridged diiron phthalocyanine complexes are well documented, the oxidation chemistry of heterodinuclear iron(IV) phthalocyanine nitrides has not been well explored. In this paper we report on the synthesis of a heterometallic FeIV/RuIV phthalocyanine nitride and its oxidation to yield phthalocyanine cation radical and hydroxyphthalocyanine complexes. Treatment of [FeII(Pc)] (Pc2- = phthalocyanine dianion) with [RuVI(LOEt)(N)Cl2] (LOEt- = [Co(η5-C5H5){P(O)(OEt)2}3]-) (1) afforded the heterometallic μ-nitrido complex [Cl2(LOEt)RuIV(μ-N)FeIV(Pc)(H2O)] (2) that contains an RuIV=N = FeIV linkage with the Ru-N and Fe-N distances of 1.689(6) and 1.677(6) Å, respectively, and Ru-N-Fe angle of 176.0(4)°. Substitution of 2 with 4- tert-butylpyridine (Bupy) gave [Cl2(LOEt)RuIV(μ-N)FeIV(Pc)(Bupy)]. The cyclic voltammogram of 2 displayed a reversible Pc-centered oxidation couple at +0.18 V versus Fc+/0 (Fc = ferrocene). The oxidation of 2 with [N(4-BrC6H4)3]SbCl6 led to isolation of the cationic complex [Cl2(LOEt)RuIV(μ-N)FeIV(Pc·+)(H2O)][SbCl6]0.85[SbCl5(OH)]0.15 (2[SbCl6]0.85[SbCl5(OH)]0.15), whereas that with PhICl2 yielded the chloride complex [Cl2(LOEt)RuIV(μ-N)FeIV(Pc·+)Cl] (3). Complexes 2[SbCl6]0.85[SbCl5(OH)]0.15 and 3 have been characterized by X-ray crystallography. The UV/visible spectra of 2+ (λmax = 515 and 747 nm) and 3 (λmax = 506 and 748 nm) displayed absorption bands that are characteristic of Pc cation radical. The EPR spectrum of 3 showed a signal with the g value of 2.0012 (width = 5 G) that is consistent with an organic radical. The spectroscopic data support the formulation of 2+ and 3 as RuIV-FeIV Pc cation radical complexes. The reaction of 2 with PhI(CF3CO2)2 in dried CH2Cl2 afforded a mixture of [Cl2(LOEt)RuIV(μ-N)FeIV(Pc·+)(CF3CO2)] (4) and a hydroxyphthalocyanine complex, [Cl2(LOEt)RuIV(μ-N)FeIV(Pc-OH)(H2O)](CF3CO2) (5), whereas that in wet CH2Cl2 (containing ca. 0.5% water) led to isolation of 5 as the sole product. Complex 4 was independently prepared by salt metathesis of 3 with AgCF3CO2.

Hydrogen Atom vs. Hydride Transfer in Cytochrome P450 Oxidations: A Combined Mass Spectrometry and Computational Study

Biomimetic models of short‐lived enzymatic reaction intermediates can give useful insight into the properties and coordination chemistry of transition metal complexes. In this work, we investigate a high‐valent iron(IV)‐oxo porphyrin cation radical complex, namely [FeIV(O)(TPFPP+·)]+, for which TPFPP is the dianion of 5,10,15,20‐tetrakis(pentafluorophenyl) porphyrin. The [FeIV(O)(TPFPP+·)]+ ion was studied by ion‐molecule reactions in a Fourier transform ion cyclotron resonance mass spectrometer through reactivities with 1,3,5‐cycloheptatriene, 1,3‐cyclohexadiene and toluene. The different substrates give dramatic changes in reaction mechanism and efficiencies, whereby cycloheptatriene leads to hydride transfer, whereas cyclohexadiene and toluene react through hydrogen atom abstraction. Detailed computational studies point to major differences in ionization energy, as well as C–H bond energies of the substrates that influence the hydrogen atom abstraction vs. electron transfer pathways. The various variables that determine the pathways for hydride transfer vs. hydrogen atom transfer are elucidated and discussed.

Iron versus Ruthenium: Clarifying the Electronic Differences between Prototypical Mixed-Valence Organometallic Butadiyndiyl Bridged Molecular Wires

The electronic structures of the prototypical bimetallic buta-1,3-diyn-1,4-diyl-bridged radical cation complexes [{M(dppe)Cp′}2(μ-C≡CC≡C)]+ (M= Fe, Cp′ = Cp* (1a), Cp (1b); M = Ru, Cp′ = Cp* (2a), Cp (2b)) have been (re)investigated using a combination of UV–vis–NIR and IR spectroelectrochemistry, and quantum chemical calculations based on both dispersion-corrected global (BLYP35-D3) and local (Lh-SsirPW92-D3) hybrid functionals. Following analysis of new and existing data, including the IR-active ν(C≡C) bands, the iron compounds [1]+ are reclassified as valence-trapped (Robin and Day Class II) mixed-valence complexes, in contrast to the ruthenium complexes [2]+, which are delocalized (Robin and Day Class III) systems. All members of the series exist as a thermally populated distribution of conformers in solution, and the overlapping spectroscopic profiles make the accurate extraction of the parameters necessary for the analysis of [1]+ and [2]+ within the framework of the Marcus–Hush model extremely chal...

Nucleophilic Aromatic Addition in Ionizing Environments: Observation and Analysis of New C-N Valence Bonds in Complexes between Naphthalene Radical Cation and Pyridine.

Radical organic ions can be stabilized by complexation with neutral organics via interactions that can resemble chemical bonds, but with much diminished bond energies. Those interactions are a key factor in cluster growth and polymerization reactions in ionizing environments such as regions of the interstellar medium and solar nebulae. Such radical cation complexes between naphthalene (Naph) and pyridine (Pyr) are characterized using mass-selected ion mobility experiments. The measured enthalpy of binding of the Naph+•(Pyr) heterodimer (20.9 kcal/mol) exceeds that of the Naph+•(Naph) homodimer (17.8 kcal/mol). The addition of 1-3 more pyridine molecules to the Naph+•(Pyr) heterodimer gives 10-11 kcal/mol increments in binding enthalpy. A rich array of Naph+•(Pyr) isomers are characterized by electronic structure calculations. The calculated Boltzmann distribution at 400 K yields an enthalpy of binding in reasonable agreement with experiment. The global minimum is a distonic cation formed by Pyr attack on Naph+• at the α-carbon, changing its hybridization from sp2 to distorted sp3. The measured collision cross section in helium for the Naph+•(Pyr) heterodimer of 84.9 ± 2.5 Å2 at 302 K agrees well with calculated angle-averaged cross sections (83.9-85.1 Å2 at 302 K) of the lowest energy distonic structures. A remarkable 16 kcal/mol increase in the binding energy between Naph+•(Pyr) and Bz+•(Pyr) (Bz is benzene) is understood by energy decomposition analysis. A similar increase in binding from Naph+•(NH3) to Naph+•(Pyr) (as well as between Bz+•(NH3) and Bz+•(Pyr)) is likewise rationalized.

Gas-Phase Intercluster Thiyl-Radical Induced C-H Bond Homolysis Selectively Forms Sugar C2-Radical Cations of Methyl D-Glucopyranoside: Isotopic Labeling Studies and Cleavage Reactions.

A suite of isotopologues of methyl D-glucopyranosides is used in conjunction with multistage mass spectrometry experiments to determine the radical site and cleavage reactions of sugar radical cations formed via a recently developed 'bio-inspired' method. In the first stage of CID (MS2), collision-induced dissociation (CID) of a protonated noncovalent complex between the sugar and S-nitrosocysteamine, [H3NCH2CH2SNO + M]+, unleashes a thiyl radical via bond homolysis to give the noncovalent radical cation, [H3NCH2CH2S• + M]+. CID (MS3) of this radical cation complex results in dissociation of the noncovalent complex to generate the sugar radical cation. Replacement of all exchangeable OH and NH protons with deuterons reveals that the sugar radical cation is formed in a process involving abstraction of a hydrogen atom from a C-H bond of the sugar coupled with proton transfer to the sugar, to form [M - H• + D+]. Investigation of this process using individual C-D labeled sugars reveals that the main site of H/D abstraction is the C2 position, since only the C2-deuterium labeled sugar yields a dominant [M - D• + H+] product ion. The fragmentation reactions of the distonic sugar radical cation, [M - H•+ H+], were studied by another stage of CID (MS4). 13C-labeling studies revealed that a series of three related fragment ions each contain the C1-C3 atoms; these arise from cross-ring cleavage reactions of the sugar. Graphical Abstract ᅟ.