Mass Spectrometric Identification of [4Fe–4S](NO)x Intermediates of Nitric Oxide Sensing by Regulatory Iron–Sulfur Cluster Proteins

Nitric oxide (NO) can function as both a cytotoxin and a signalling molecule. In both cases, reaction with iron–sulfur (Fe–S) cluster proteins plays an important role because Fe–S clusters are reactive towards NO and so are a primary site of general NO-induced damage (toxicity). This sensitivity to nitrosylation is harnessed in the growing group of regulatory proteins that function in sensing of NO via an Fe–S cluster. Although information about the products of cluster nitrosylation is now emerging, detection and identification of intermediates remains a major challenge, due to their transient nature and the difficulty in distinguishing spectroscopically similar iron-NO species. Here we report studies of the NO-sensing Fe–S cluster regulators NsrR and WhiD using non-denaturing mass spectrometry, in which non-covalent interactions between the protein and Fe/S/NO species are preserved. The data provide remarkable insight into the nitrosylation reactions, permitting identification, for the first time, of protein-bound mono-, di- and tetranitrosyl [4Fe–4S] cluster complexes ([4Fe–4S](NO), [4Fe–4S])(NO)₂ and [4Fe–4S](NO)₄) as intermediates along pathways to formation of product Roussin's red ester (RRE) and Roussin's black salt (RBS)-like species. The data allow the nitrosylation mechanisms of NsrR and WhiD to be elucidated and clearly distinguished.     

Catalytic CO Oxidation by O2 Mediated with Single Gold Atom Doped Titanium Oxide Cluster Anions AuTi2O4–6−

Gas-phase studies on catalytic CO oxidation by O₂ mediated with gold-containing heteronuclear metal oxide clusters are vital to obtain the structure−reactivity relationship of supported gold catalysts, while it is challenging to trigger the reactivity of clusters with closed-shell electronic structure in O₂ activation. Herein, we identified that CO oxidation by O₂ can be catalyzed by the AuTi₂O_4–6⁻ clusters, among which AuTi₂O₄⁻ with closed-shell electronic structure can effectively activate O₂. The reactions were characterized by mass spectrometry and quantum chemical calculations. Theoretical calculations showed that in the initial stage of O₂ activation, the Ti₂O₄ moiety in AuTi₂O₄⁻ contributes dominantly to activate O₂ into superoxide (O₂⁻⋅) without participation of the Au atom. In subsequent steps, the intimate charge transfer interaction between Au and the Ti₂O₄ moiety drives the direct dissociation of the O₂⁻⋅ unit.     

Unimolecular Gas-Phase Oxidation of Terminal Hydroxy Groups in [FeO(CH2)nOH]+ Complexes (n = 2–8). A Case for O?H Bond Activation by Late Transition-Metal Ions. Preliminary Communication

In contrast to Fe⁺/diol complexes, gas-phase dehydrogenation of the corresponding Fe^II alkoxides, [FeO(CH₂)_nCH₂OH]⁺, is a highly specific process in the course of which oxidation of the terminal OH group takes place. Based on labeling studies, this is the exclusive mechanism for n = 2 and 3 (Scheme: path ); for higher homologues, as for example [FeOf(CH₂)₇CH₂OH]⁺, the labeling data demonstrate that an additional mechanism is operative, involving the dehydrogenation of internal positions of the alkyl chain (path ). The Fe⁺-mediated oxidation –CH₂OH → –CHO +H₂: constitutes one of the rare examples of O-H bond activation by late cationic transition-metal ions.     

Sorption–Desorption of Copper and Strontium Ions by the Soil. The Influence of Microorganisms on the State of Metals

Sorption of heavy metal (copper and strontium) ions by the meadow chernozem and grey forest soils differing in the content of organic substance was described using the Langmuir equation. The analysis of characteristic sorption coefficients demonstrated that copper possesses the enhanced affinity for the studied soil samples compared to strontium. Maximal values of the sorption of copper (0.085 mmol/g) and strontium (0.045 mmol/g) obtained for the colloidal fraction of meadow chernozem soil (particle diameter d < 1 m) are approximately 1.5 times larger than for the same fraction of grey forest soil; this ratio remains almost the same even when using the coarser fraction (d < 50 m). It was established that up to 90% of metal ions could be present in the soil in an immobile form. An increase in the concentration of heavy metal ions in the soil causes their redistribution between the components of absorbing soil complex and an increase in the fraction of metal in mobile forms (water-soluble, exchange, soluble in weakly acidic medium). Upon the microbiological treatment (bioleaching in the suspension variant) of the soils containing copper or strontium ions, the total content of metal, including its mobile forms, decreases by an order of magnitude.     

Mixed Ruthenium–Iridium Carbonyl Cluster Complexes. Synthesis of the Anions [Ru3Ir2(CO)14]2− and [Ru3Ir2(CO)14H]− and Crystal Structures of Their [tetraphenylphosphonium]+ Salts

The reaction of Ru₃(CO)₁₂ and [Ir(CO)₄]^- (as [PPh₄]⁺ or [N(PPh₃)₂]⁺ salts) yields the anion [Ru₃Ir₂(CO)₁₄]^2- (1) which has been found to derive from the intermediate [Ru₃Ir(CO)₁₃]^- anion. Treatment of (1) with acids gives the conjugated hydrido species [Ru₃Ir₂(CO)₁₄H]^- (2). The two anions were characterized by single-crystal X-ray diffraction of their [PPh₄]⁺ salts. [PPh₄]₂[Ru₃Ir₂(CO)₁₄]: space group C2/c, Z=4, a=22.121(5) Å, b=10.546(5) Å, c=25.931(5) Å, =103.870(5)°, R=0.052 and R_w=0.130 for 3128 independent reflections with I>2(I ). [PPh₄][Ru₃Ir₂(CO)₁₄H]: space group P2₁/c, Z=8, a=22.833(5) Å, b=13.893(5) Å, c=25.810(5) Å, =92.650(5)°, R=0.070 and R_w=0.150 for 12141 independent reflections with I>2(I). Both anions 1 and 2 have a trigonal bipyramidal metal frame. There are two independent anions in the asymmetric unit of 2 differing in their ligand stereochemistry.     

C−H Activation by Iron-Vanadium Bimetallic Oxide Cluster Anions FeV3O10− and FeV5O15−: A Comparison with Scandium-Vanadium Oxide Clusters

Late transition metal-bonded atomic oxygen radicals (LTM−O⋅⁻) have been frequently proposed as important active sites to selectively activate and transform inert alkane molecules. However, it is extremely challenging to characterize the LTM−O⋅⁻-mediated elementary reactions for clarifying the underlying mechanisms limited by the low activity of LTM−O⋅⁻ radicals that is inaccessible by the traditional experimental methods. Herein, benefiting from our newly-designed ship-lock type reactor, the reactivity of iron-vanadium bimetallic oxide cluster anions FeV₃O₁₀⁻ and FeV₅O₁₅⁻ featuring with Fe−O⋅⁻ radicals to abstract a hydrogen atom from C₂−C₄ alkanes has been experimentally characterized at 298 K, and the rate constants are determined in the orders of magnitude of 10⁻¹⁴ to 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹, which are four orders of magnitude slower than the values of counterpart ScV₃O₁₀⁻ and ScV₅O₁₅⁻ clusters bearing Sc−O⋅⁻ radicals. Theoretical results reveal that the rearrangements of the electronic and geometric structures during the reaction process function to modulate the activity of Fe−O⋅⁻. This study not only quantitatively characterizes the elementary reactions of LTM−O⋅⁻ radicals with alkanes, but also provides new insights into structure-activity relationship of M−O⋅⁻ radicals.     

Thermal Activation of N?H Bonds by Transition‐metal Oxide Cations: Does a Hierarchy Exist in the First Row?

The thermal reactions of first-row transition-metal oxide cations [MO](+) (M=Sc-Ni, Zn) with ammonia have been studied by gas-phase experiments and computational methods. The activation of N-H bonds is brought about by the monoxides of the middle and late 3d metals Mn-Ni and Zn. The two primary reaction channels correspond to dehydration, which leads to [M(NH)](+), and hydrogen-atom abstraction to form [M(OH)](+). Oxygen-atom transfer from [MO](+) to NH(3) to produce neutral or ionized hydroxylamine was observed as a minor channel for some of the late transition-metal oxides. The computational analysis of these reactions, which was aimed at elucidating the reaction mechanisms and to uncover possible periodic trends across the first row, have been performed for the couples [MO](+) /NH(3) (M=Sc-Zn). Dehydration is found to be endothermic for the oxides of scandium to vanadium and exothermic for the other systems. Hydrogen-atom abstraction becomes exothermic starting with [MnO](+) and, finally, oxygen-atom transfer is feasible for the cationic oxides of nickel to zinc.     

Synthesis and structures of zirconium complexes [Et2H2N]+2[ZrCl6]2–, [Me3NCH2Ph]+2[ZrCl6]2–•MeCN, [Ph3PC6H4(CHPh2-4)]+2[ZrCl6]2–•2 MeCN,and [Ph4Sb]+2[ZrCl6]2–

Russian Chemical Bulletin - The complexes [Et2H2N]+2[ZrCl6]2– (1), [Me3NCH2Ph]+2[ZrCl6]2–?MeCN (2), [Ph3PC6H4(CHPh2-4)]+2[ZrCl6]2–?2 MeCN (3), and...     

Frontispiz: Biomass Oxidation: Formyl C?H Bond Activation by the Surface Lattice Oxygen of Regenerative CuO Nanoleaves

An integrated experimental and computational investigation reveals that surface lattice oxygen of copper oxide (CuO) nanoleaves activates the formyl C H bond in glucose and incorporates itself into the glucose molecule to oxidize it to gluconic acid. The reduced CuO catalyst regains its structure, morphology, and activity upon reoxidation. The activity of lattice oxygen is shown to be superior to that of the chemisorbed oxygen on the metal surface and the hydrogen abstraction ability of the catalyst is correlated with the adsorption energy. Based on the present investigation, it is suggested that surface lattice oxygen is critical for the oxidation of glucose to gluconic acid, without further breaking down the glucose molecule into smaller fragments, because of C C cleavage. Using CuO nanoleaves as catalyst, an excellent yield of gluconic acid is also obtained for the direct oxidation of cellobiose and polymeric cellulose, as biomass substrates.     

Unusual Thermal Quenching of Photoluminescence from an Organic–Inorganic Hybrid [MnBr4]2−-based Halide Mediated by Crystalline–Crystalline Phase Transition

The ability to generate and manipulate photoluminescence (PL) behavior has been of primary importance for applications in information security. Excavating novel optical effects to create more possibilities for information encoding has become a continuous challenge. Herein, we present an unprecedented PL temporary quenching that highly couples with thermodynamic phase transition in a hybrid crystal (DMML)₂MnBr₄ (DMML=N,N-dimethylmorpholinium). Such unusual PL behavior originates from the anomalous variation of [MnBr₄]²⁻ tetrahedrons that leads to non-radiation recombination near the phase transition temperature of 340 K. Remarkably, the suitable detectable temperature, narrow response window, high sensitivity, and good cyclability of this PL temporary quenching will endow encryption applications with high concealment, operational flexibility, durability, and commercial popularization. Profited from these attributes, a fire-new optical encryption model is devised to demonstrate high confidential information security. This unprecedented optical effect would provide new insights and paradigms for the development of luminescent materials to enlighten future information encryption.     

Chlorination of charged buckyballs: reactions of C60x+ cations (x = 1–3) with Cl2, CCl4, CDCl3, CH2Cl2, and CH3Cl

The chlorination of singly and multiply charged C₆₀ cations has been investigated with the selected-ion flow tube technique. Observations are reported for the reactions of C₆₀^·+, C₆₀²⁺ and C₆₀^·3+ with Cl₂, CCl₄, CDCl₃, CH₂Cl₂ and CH₃Cl at room temperature (295 ± 2 K) in helium at a total pressure of 0.35 ± 0.02 Torr. C₆₀^·+ and C₆₀²⁺ were observed not to chlorinate, or react in any other way, with these five molecules. Chlorine also did not react with C₆₀^·3+, but bimolecular chloride transfer and electron transfer reactions, reactions that result in charge reduction/charge separation, were observed to occur with CCl₄, CDCl₃, CH₂Cl₂ and CH₃Cl. Chloride transfer was the predominant channel seen with CCl₄, CDCl₃ and CH₂Cl₂ while electron transfer dominates the reaction with CH₃Cl. These results are consistent with trends in chloride affinity and ionization energy. The reluctant chlorination of the first two charge states of C₆₀ is attributed to the energy required to distort the carbon cage upon bond formation, while the observed chloride transfer to C₆₀^·3+ is attributed to the greater electrostatic interactions with this ion.     

Tuning the Reactivities of the Heteronuclear [AlnV3−nO7−n]+ (n=1, 2) Cluster Oxides towards Methane by Varying the Composition of the Metal Centers

The thermal gas-phase reactions of [Al₂VO₅]⁺ and [AlV₂O₆]⁺ with methane have been explored by using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry complemented by high-level quantum chemical calculations. Both cluster ions chemisorbed methane as the major reaction channels at room temperature. [Al₂VO₅]⁺ could break only one C−H bond to liberate CH₃, whereas [AlV₂O₆]⁺ exhibited higher oxidizing ability such that it brings about the selective generation of formaldehyde. Mechanistic aspects are revealed and the crucial roles of the metal centers are discussed.     

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of N?H Imines and Alkynes by C?H/N?H Activation

Described herein is a manganese‐catalyzed dehydrogenative [4+2] annulation of N H imines and alkynes, a reaction providing highly atom‐economical access to diverse isoquinolines. This transformation represents the first example of manganese‐catalyzed C H activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H₂ as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition‐metal‐catalyzed C H activation. Mechanistic studies revealed the five‐membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.     

The Kinetic Isotope Effect as a Probe of Spin Crossover in the C?H Activation of Methane by the FeO+ Cation

Two‐state reactivity (TSR) is often used to explain the reaction of transition‐metal–oxo reagents in the bare form or in the complex form. The evidence of the TSR model typically comes from quantum‐mechanical calculations for energy profiles with a spin crossover in the rate‐limiting step. To prove the TSR concept, kinetic profiles for C H activation by the FeO⁺ cation were explored. A direct dynamics approach was used to generate potential energy surfaces of the sextet and quartet H‐transfers and rate constants and kinetic isotope effects (KIEs) were calculated using variational transition‐state theory including multidimensional tunneling. The minimum energy crossing point with very large spin–orbit coupling matrix element was very close to the intrinsic reaction paths of both sextet and quartet H‐transfers. Excellent agreement with experiments were obtained when the sextet reactant and quartet transition state were used with a spin crossover, which strongly support the TSR model.     

Thermal studies on Li(CH3CN)4PF6 and Li(C4H10O2)2PF6 complexes by the TG–DTA–MS and DSC

Journal of Thermal Analysis and Calorimetry - Li(CH3CN)4PF6 and Li(C4H10O2)2PF6 complexes are important intermediates created in the synthetic process of high-purity LiPF6 electrolyte via...     

The Synthesis and Characterization of [4-CH3OC6H4CH2NH3]4P2O7·6H2O

Inorganic–organic hybrid compounds exhibit interesting properties in several application areas. In this regard, chemical preparation and characterization by X-ray diffraction, thermal analysis, and IR spectroscopy are given for a new organic cation diphosphate [4-CH₃OC₆H₄CH₂NH₃]₄P₂O₇·6H₂O. This later crystallizes in a C2/c unit cell with a = 38.238(6)Å, b = 6.453(1)Å, c = 16.942(7)Å; β = 97.60(4)°; Z = 4; and V = 4144(2)ų and D_x = 1.377 g·cm^?3. Its crystal structure has been determinated and refined to R = 0.044, using 7978 independent reflections. This atomic arrangement consists of inorganic layers built up from P₂O₇ ^4? anions and water molecules. On these layers, which are parallel to the (b, c) planes, the (4-CH₃OC₆H₄CH₂NH₃)⁺ cations are anchored through multiple hydrogen bonds.     

Heats of reaction of HMo(CO)3C5H5 with CCl4 and CBr4 and of NaMo(CO)3C5H5 with I2 and CH3. Solution thermochemical study of the MoX bond for X = H,Cl, Br,I and CH3

The heats of reaction of HMo(CO)₃C₅H₅ with CX₄ (X = Cl, Br) producing XMo(CO)₃C₅H₅ have been measured by solution calorimetry and are −31.8±0.9 and −34.4±2.0 kcal/mole, respectively. The heats of reaction of NaMo(CO)₃C₅H₅ with I₂ and CH₃I producing IMo(CO)₃C₅H₅ and H₃CMo(CO)₃C₅H₅ are −32.3± 1.3 and −7.7± 0.3 kcal/mole. Oxidation with Br₂CCl₄ yielding Br₃Mo(CO)₂C₅H₅ was measured for the following complexes: (C₅H₅(CO)₃Mo)₂, (−92.0±1.0 kcal/mole), BrMo(CO)₃C₅H₅ (−24.9± 2.0 kcal/mole) and HMo(CO)₃C₅H₅ (−60.7± 2.0 kcal/mole). These and other data are used to calculate the Mo–X bond strength for X = H, Cl, Br, I, and CH₃. These bond strength estimates are compared to those reported for X₂Mo(C₅H₅)₂. Iodination of H₃CMo(CO)₃C₅H₅, reported in the literature to yield CH₃I and IMo(CO)₃C₅H₅, actually produces CH₃C(O)I and I₃Mo(CO)₂C₅H₅.     

Control of the Transition between Ni‐C and Ni‐SIa States by the Redox State of the Proximal Fe?S Cluster in the Catalytic Cycle of [NiFe] Hydrogenase

[NiFe] hydrogenase catalyzes the reversible cleavage of H₂. The electrons produced by the H₂ cleavage pass through three Fe–S clusters in [NiFe] hydrogenase to its redox partner. It has been reported that the Ni‐SI_a, Ni‐C, and Ni‐R states of [NiFe] hydrogenase are involved in the catalytic cycle, although the mechanism and regulation of the transition between the Ni‐C and Ni‐SI_a states remain unrevealed. In this study, the FT‐IR spectra under light irradiation at 138–198 K show that the Ni‐L state of [NiFe] hydrogenase is an intermediate between the transition of the Ni‐C and Ni‐SI_a states. The transition of the Ni‐C state to the Ni‐SI_a state occurred when the proximal [Fe₄S₄]_p^2+/+ cluster was oxidized, but not when it was reduced. These results show that the catalytic cycle of [NiFe] hydrogenase is controlled by the redox state of its [Fe₄S₄]_p^2+/+ cluster, which may function as a gate for the electron flow from the NiFe active site to the redox partner.