New mixed alkaline-earth nitridomolybdate(VI) nitride oxides with anion-ordered sub-structures

New molybdenum(VI) nitride oxides were synthesised by the reaction of strontium nitride and calcium nitride with molybdenum foil at high temperature in sealed stainless steel crucibles. The reactions yielded single crystalline products determined by X-ray diffraction to form complex structures in the triclinic space group P1(no. 2). The mixed alkaline earth compounds with composition Ca38Sr13[MoN4]12N8O3 and Ca36Sr15[MoN4]12N8O3 are isostructural with the quaternary nitride oxides Sr51[WN4]12N8O3 and Ca51[WN4]12N8O3. The structures contain isolated [MoN4](6-) tetrahedra, partially disordered alkaline earth cations and an ordered sublattice of N(3-) and O(2-) anions. Oxide anions are coordinated only to the alkaline earth metals. The title compounds are the first mixed alkaline earth metal nitride oxides.     

Common solutions to the Lyapunov equations

Let A be an n×n matrix with complex entries. A necessary and sufficient condition is established for the existence of a Hermitian solution H to the equations

$\text{AH+HA}{}^1\text{=HA+A}{}^1\text{H=I}$

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Fast second order electron transfer reactions coupled to redox protein electrochemistry: Experiment and digital simulation

Chemical modification of metal surfaces by chemisorption provides a versatile method for the production of electrode interfaces which can be selective for the direct electrochemistry of one redox protein over another. The electrochemistry of a mixture of horse heart cytochrome c and spinach plastocyanin has been investigated at gold surfaces made selective for first one and then the other protein. The resulting cyclic voltammetry is quite unusual, containing pre-shoulders to both reduction current and reoxidation current peaks. The results have been interpreted in terms of fast second order electron transfer reactions taking place between the two proteins in homogeneous solution. This rationalisation has been corroborated by an explicit digital simulation of the proposed reaction scheme, using second order RKI. There are three independently variable parameters to the simulation: forward kinetic parameter, reverse kinetic parameter, and concentration ratio of non-electrode-active species to electrode-active species. The simulation has been used to explore a number of interesting trends in these parameters. Five such sequences of simulated cyclic voltammograms are reported, together with peak current and potential data in most cases. Attention is drawn to the possibility for further interesting experimental mixed redox protein electrochemistry at selective surfaces.     

The crucial role of the nitrogen substituent in the desymmetrisation of cyclic meso-imides using B-Me and B-OMe oxazaborolidine catalysts

Various cyclic meso-imides have been desymmetrised via enantioselective reduction using two chiral oxazaborolidine catalysts derived from (1R,2S)-cis-1-amino-indan-2-ol followed by the reduction of the hydroxylactam product to give the γ-lactam. The enantiomeric excesses were shown to be 27-99% by chiral HPLC and chiral GC of the γ-lactam products with the nitrogen substituent playing a pivotal role in determining yield and selectivity.     

Facile oxygenation of organic sulfides with H2O2 catalyzed by Mn-Me3TACN compounds

Two binuclear Mn-Me₃TACN (Me₃TACN is 1,4,7-N,N′,N″-trimethyl-1,4,7-triazacyclononane) compounds catalyze the oxygenation of organic sulfides utilizing H₂O₂ under ambient conditions. Both phenyl sulfide and ethyl phenyl sulfide were converted to the corresponding sulfones and chloroethyl phenyl sulfide proceeds to its elimination product of phenyl vinyl sulfone.     

Origin of the quadrupole splitting in the Mössbauer 57Fe spectrum of cubic (disordered) LiFeO2

The room-temperature Mössbauer ⁵⁷Fe spectrum of polycrystalline disordered cubic α-LiFeO₂ contains a quadrupole splitting |Δ_obs| of 0.65(2) mm/sec. This value is relatively large for an Fe atom in an essentially Fe³⁺_HS state. To account for its magnitude, the distribution of the electric-field gradient (EFG) values associated with the Fe atoms was investigated by means of exact geometric analysis involving the 12 nearest cation neighbors (model A) as well as large-scale computer simulation involving more distant cations (models B to E). It is found that (1) the major contribution to |Δ_obs| comes from the distribution of +1 and +3 charges among the 12 nearest cation neighbors of a reference Fe atom; (2) this contribution by itself largely accounts for |Δ_obs|; (3) the contribution from cations beyond the seventh-nearest neighbors is marginal; (4) displacing the oxygen atoms from their lattice sites toward adjacent Fe atoms produces a significant effect on the distribution of EFG values at a reference Fe atom, while incipient cation ordering appears to have a relatively small effect; and (5) the contribution of the EFG = 0 component to model |EFG| distributions will be overemphasized unless cations beyond the first-nearest neighbors are included in the EFG summation. The 144 distinct (up to rotation and reflection) Li¹⁺_12?kFe³⁺_k configurations on the coordination cuboctahedron of nearest cation neighbors (required for the examination of model A) are listed, together with their symmetries and multiplicities, and it is shown that the 144 configurations engender only 17 distinct |EFG| values. Observations are also made on various geometric aspects of calculating EFG at ⁵⁷Fe³⁺_HS on cubic lattices.     

Hydroaromatic equilibration during biosynthesis of shikimic acid

The expense and limited availability of shikimic acid isolated from plants has impeded utilization of this hydroaromatic as a synthetic starting material. Although recombinant Escherichia coli catalysts have been constructed that synthesize shikimic acid from glucose, the yield, titer, and purity of shikimic acid are reduced by the sizable concentrations of quinic acid and 3-dehydroshikimic acid that are formed as byproducts. The 28.0 g/L of shikimic acid synthesized in 14% yield by E. coli SP1.1/pKD12.138 in 48 h as a 1.6:1.0:0.65 (mol/mol/mol) shikimate/quinate/dehydroshikimate mixture is typical of synthesized product mixtures. Quinic acid formation results from the reduction of 3-dehydroquinic acid catalyzed by aroE-encoded shikimate dehydrogenase. Is quinic acid derived from reduction of 3-dehydroquinic acid prior to synthesis of shikimic acid? Alternatively, does quinic acid result from a microbe-catalyzed equilibration involving transport of initially synthesized shikimic acid back into the cytoplasm and operation of the common pathway of aromatic amino acid biosynthesis in the reverse of its normal biosynthetic direction? E. coli SP1.1/pSC5.214A, a construct incapable of de novo synthesis of shikimic acid, catalyzed the conversion of shikimic acid added to its culture medium into a 1.1:1.0:0.70 molar ratio of shikimate/quinate/dehydroshikimate within 36 h. Further mechanistic insights were afforded by elaborating the relationship between transport of shikimic acid and formation of quinic acid. These experiments indicate that formation of quinic acid during biosynthesis of shikimic acid results from a microbe-catalyzed equilibration of initially synthesized shikimic acid. By apparently repressing shikimate transport, the aforementioned E. coli SP1.1/pKD12.138 synthesized 52 g/L of shikimic acid in 18% yield from glucose as a 14:1.0:3.0 shikimate/quinate/dehydroshikimate mixture.     

Electrochemical synthesis and study of polydiphenylamine

The electrochemical oxidation of diphenylamine in acetonitrile produces an adherent conducting polymer film at the electrode. Conductivity measurements on pressed pellets of this polymer give a room temperature conductivity of 10 S cm⁻¹. The polymer can be cycled between 25 and 200°C without deterioration in the conductivity. Preliminary SEM/EDS studies suggest that there is one BF⁻₄ counter ion for every four monomer units in the oxidised polymer film.