2,507 research outputs found
Assembly, Structure, and Reactivity of Cu\u3csub\u3e4\u3c/sub\u3eS and Cu\u3csub\u3e3\u3c/sub\u3eS Models for the Nitrous Oxide Reductase Active Site, Cu\u3csub\u3eZ\u3c/sub\u3e*
Bridging diphosphine ligands were used to facilitate the assembly of copper clusters with single sulfur atom bridges that model the structure of the CuZ* active site of nitrous oxide reductase. Using bis(diphenylphosphino)amine (dppa), a [CuI4(Ī¼4-S)] cluster with NāH hydrogen bond donors in the secondary coordination sphere was assembled. Solvent and anion guests were found docking to the NāH sites in the solid state and in the solution phase, highlighting a kinetically viable pathway for substrate introduction to the inorganic core. Using bis(dicyclohexylphosphino)methane (dcpm), a [CuI3(Ī¼3-S)] cluster was assembled preferentially. Both complexes exhibited reversible oxidation events in their cyclic voltammograms, making them functionally relevant to the CuZ* active site that is capable of catalyzing a multielectron redox transformation, unlike the previously known [CuI4(Ī¼4-S)] complex from Yam and co-workers supported by bis(diphenylphosphino)methane (dppm). The dppa-supported [CuI4(Ī¼4-S)] cluster reacted with N3ā, a linear triatomic substrate isoelectronic to N2O, in preference to NO2ā, a bent triatomic. This [CuI4(Ī¼4-S)] cluster also bound Iā, a known inhibitor of CuZ*. Consistent with previous observations for nitrous oxide reductase, the tetracopper model complex bound the Iā inhibitor much more strongly and rapidly than the substrate isoelectronic to N2O, producing unreactive Ī¼3-iodide clusters including a [Cu3(Ī¼3-S)(Ī¼3-I)] complex related to the [Cu4(Ī¼4-S)(Ī¼2-I)] form of the inhibited enzyme
Crystal structure of \u3cem\u3ecis\u3c/em\u3e-2-(2-carboxycyclopropyl)-glycine (CCG-III) monohydrate
The title compound, C6H9NO4Ā·H2O [systematic name: (Ī±R,1R,2S)-rel-Ī±-amino-2-carbĀoxyĀcycloĀpropaneĀacetic acid monohydrate], crystallizes with two organic molĀecules and two water molĀecules in the asymmetric unit. The space group is P21 and the organic molĀecules are enantiĀomers, thus this is an example of a `false conglomerate\u27 with two molĀecules of opposite handedness in the asymmetric unit (r.m.s. overlay fit = 0.056 Ć
for one molĀecule and its inverted partner). Each molĀecule exists as a zwitterion, with proton transfer from the amino acid carbĀoxyĀlic acid group to the amine group. In the crystal, the components are linked by N-HĀ·Ā·Ā·O and O-HĀ·Ā·Ā·O hydrogen bonds, generating (100) sheets. Conformationally restricted glutamate analogs are of interĀest due to their selective activation of different glutamate receptors, and the naturally occurring (+)-CCG-III is an inhibitor of glutamate uptake and the key geometrical parameters are discussed
Charge-Transfer Forces in the Self-Assembly of Heteromolecular Reactive Solids:ā Successful Design of Unique (Single-Crystal-to-Single-Crystal) DielsāAlder Cycloadditions
Electron donor/acceptor (EDA) interactions are found to be a versatile methodology for the engineering of reactive heteromolecular crystals. In this way, a series of the charge-transfer Ļ-complexes between bis(alkylimino)-1,4-dithiin acceptors and anthracene donors are shown to form heteromolecular (1:1) crystalline solids that spontaneously undergo stereoselective [2 + 4] DielsāAlder cycloadditions. The flexible nature of the 1,4-dithiin moiety allows this homogeneous topochemical transformation to proceed with minimal distortion of the crystal lattice. As a result, a unique (single) crystal phase of the DielsāAlder adduct can be produced anti-thermodynamically with a molecular arrangement very different from that in solvent-grown crystals. Such a topochemical reaction between bis(methylimino)-1,4-dithiin and anthracene proceeds thermally and homogeneously up to very high conversions without disintegration of the single crystal. This ideal case of the mono-phase topochemical conversion can be continuously monitored structurally (X-ray crystallography) and kinetically (NMR spectroscopy) throughout the entire range of the crystalline transformation. The resultant āartificialā crystal of the DielsāAlder adduct is surprisingly stable despite its different symmetry and packing mode compared to the naturally grown (thermodynamic) crystal
Molecular Actuator: Redox-Controlled Clam-Like Motion in a Bichromophoric Electron Donor
The one-electron oxidation of tetramethoxydibenzobicyclo[4.4.1]undecane (4) prompts it to undergo a clam-like electromechanical actuation into a cofacially Ļ-stacked conformer as established by (i) electrochemical analysis, (ii) by the observation of the intense charge-resonance transition in the near IR region in its cation radical spectrum, and (iii) by X-ray crystallographic characterization of the isolated cation radical salt (4+ā¢ SbCl6ā)
Practical Synthesis of Unsymmetrical Tetraarylethylenes and Their Application for the Preparation of [TriphenylethyleneāSpacerāTriphenylethylene] Triads
We have demonstrated that reactions of diphenylmethyllithium with a variety of substituted benzophenones produces corresponding tertiary alcohols that are easily dehydrated, without any need for purification, to produce various unsymmetrical and symmetrical tetraarylethylenes in excellent yields. The simplicity of the method allows for the preparation of a variety of ethylenic derivatives in multigram (10ā50 g) quantities with great ease. The methodology was successfully employed for the preparation of various triphenylethylene (TPE)-based triads (i.e., TPEāspacerāTPE) containing polyphenylene and fluoranyl-based spacers. The ready availability of various substituted tetraarylethylenes allowed us to shed light on the effect of substituents on the oxidation potentials (Eox) of various tetraarylethylenes. Moreover, the electronic coupling among the triphenylethylene moieties in various TPEāspacerāTPE triads was briefly probed by electrochemical and optical methods
Simultaneous Ejection of Six Electrons at a Constant Potential by Hexakis(4-ferrocenylphenyl)benzene
A simple synthesis of a dendritic hexaferrocenyl electron donor (5) is described in which six ferrocene moieties are connected at the vertices of the propeller of the hexaphenylbenzene core. The molecular structure of 5 is confirmed by X-ray crystallography. An electrochemical analysis along with redox titrations (which are tantamount to coulometry) confirmed that it ejects six electrons at a single potential
Accessing Spin-Crossover Behaviour In Iron(II) Complexes Of N-Confused Scorpionate Ligands
The first examples of a class of N-confused tris(pyrazolyl)methane āscorpionateā ligands have been prepared. The magnetic properties of their iron(II) tetrafluoroborate complexes are dictated by changing one substituent per ligand rather than three as is typical for normal scorpionate ligands
Reaction Chemistry of Silver(I) Trifluoromethanesulfonate Complexes of Nitrogen-Confused \u3cem\u3eC\u3c/em\u3e-Scorpionates
Two new C-scorpionate ligands with a bis(3,5-dimethylpyrazol-1-yl)methyl group bound to the 3 position of either an N-tosyl (TsL*) or an NāH pyrazole (HL*) ring have been prepared. The silver(I) complexes of these new ligands and the two previously reported analogous ligands with unsubstituted bis(pyrazol-1-yl)methyl groups (TsL and HL) in both 1:1 and 2:1 ligand/metal ratios were investigated to explore the effects of ligand sterics on their physical and chemical properties. The structurally characterized derivatives of the type [Ag(L)2](OTf) are four-coordinate, where the confused pyrazolyl is not bound to the metal. On the other hand, three 1:1 complexes [Ag(L)](OTf) had all pyrazolyls bound, while the Ī¼āĪŗ1,Īŗ1-TsL derivative had an unbound confused pyrazolyl. The molecularity of the latter four ranged from polymeric to dimeric to monomeric in the solid with increasing steric bulk of the ligand. The utility of these complexes in stoichiometric ligand-transfer reactions and in styrene aziridination was demonstrated. Thus, tricarbonylmanganese(I) complexes were prepared as kinetically inert models for comparative solution diffusion NMR studies. Also, [Fe(HL)2](OTf)2 was prepared for similar reasons and to compare the effects of anion on spin-crossover properties
A One-Hole Cu\u3csub\u3e4\u3c/sub\u3eS Cluster with N\u3csub\u3e2\u3c/sub\u3eO Reductase Activity: A Structural and Functional Model for Cu\u3csub\u3eZ\u3c/sub\u3e
During bacterial denitrification, two-electron reduction of N2O occurs at a [Cu4(Ī¼4-S)] catalytic site (CuZ*) embedded within the nitrous oxide reductase (N2OR) enzyme. In this Communication, an amidinate-supported [Cu4(Ī¼4-S)] model cluster in its one-hole (S = 1/2) redox state is thoroughly characterized. Along with its two-hole redox partner and fully reduced clusters reported previously, the new species completes the two-electron redox series of [Cu4(Ī¼4-S)] model complexes with catalytically relevant oxidation states for the first time. More importantly, N2O is reduced by the one-hole cluster to produce N2 and the two-hole cluster, thereby completing a closed cycle for N2O reduction. Not only is the title complex thus the best structural model for CuZ* to date, but it also serves as a functional CuZ* mimic
A Cu\u3csub\u3e4\u3c/sub\u3eS Model for the Nitrous Oxide Reductase Active Sites Supported Only by Nitrogen Ligands
To model the (His)7Cu4Sn (n = 1 or 2) active sites of nitrous oxide reductase, the first Cu4(Ī¼4-S) cluster supported only by nitrogen donors has been prepared using amidinate supporting ligands. Structural, magnetic, spectroscopic, and computational characterization is reported. Electrochemical data indicates that the 2-hole model complex can be reduced reversibly to the 1-hole state and irreversibly to the fully reduced state
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