Synthesis of the P-cluster inorganic core of nitrogenases

The [8Fe-7S] core of the P-clusters in nitrogenases is unique among the known [Fe-S] clusters which are essential to electron-transfer processes in nature. The [8Fe-7S] cluster has been thought unstable and to exist only in protein environments. We found that this unusual [8Fe-7S] structure can be self-assembled from the reaction of Fe(II) bis-amide, tetramethylthiourea, 2,4,6-triisopropylbenzenethiol, and elemental sulfur in a specific mole ratio. The structure of the complex isolated therefrom closely resembles that of the reduced form (PN) of the P-clusters, while the 6Fe(II)2Fe(III) oxidation state was manifested by the M?ssbauer study.     

A steep one-step [HS-HS] to [LS-LS] spin transition in a 4,4'-bipyridine linked one-dimensional coordination polymer constructed from a pyrazolato bridged Fe(II) dimer

The variable temperature magnetic susceptibility, X-ray crystallography, and M?ssbauer and Raman spectra of a new dinuclear complex-based one-dimensional coordination polymer [[Fe(II)2(NCS)2(mu-bpypz)2](micro-4,4'-bpy)].MeOH demonstrated a steep one-step [HS-HS] to [LS-LS] spin transition.     

Naphthalene and Anthracene Complexes Sandwiched by Two {(Cp*)FeI} Fragments: Strong Electronic Coupling between the FeI Centers

The reactions of the half‐sandwich iron(II) complex [FeCl(Cp*)(tmeda)] ( 1 ; Cp*=η⁵‐C₅Me₅, TMEDA=N,N,N′,N′‐tetramethylethylenediamine) with potassium naphthalenide or potassium anthracenide gave the diamagnetic complexes [(Cp*)Fe(μ‐polyarene)Fe(Cp*)] (polyarene=naphthalene ( 2 ), anthracene ( 3a )), which have two {(Cp*)Fe} units bound to opposite faces of the polyarene. One of two {(Cp*)Fe} units in 3a is located over the central ring of anthracene while the other is positioned over an outer ring. The {(Cp*)Fe} unit bound to the central ring of 3a migrates to the outer ring upon heating in the solid state to give the isomer 3b . The electrochemical potential separations between successive one‐electron redox events for complexes 2 and 3b are large. The mixed valence complexes [ [2]+ ]⁺ and [ [3b]+ ]⁺ were synthesized by chemical oxidation. The mixed‐valence complex [ [3b]+ ]⁺ is charge delocalized on the Mössbauer timescale at 78 K, and its absorption spectrum shows an intervalence charge‐transfer band. Complex [ [2]+ ]⁺ exhibits two absorption bands in the near‐IR region and a slightly broadened doublet in the Mössbauer spectrum. DFT calculations were carried out to examine the electronic structures of these dinuclear iron(I) complexes to elucidate the factors responsible for their diamagnetism and to determine the degree of charge delocalization in the mixed‐valence complexes.     

Mixed-valence states in TCNQ salts of monoalkylbiferrocenes and their mixed crystals with dialkyl derivative

TCNQ salts of 1-monoalkylbiferrocenes showed a temperature-independent trapped-valence state as expected for the unsymmetrical structure of cations. On the other hand, mixed crystals of 1-monobutyl- and 1.1-dibutylbiferrocenium⁺(TCNQ) ₃ ^– showed a temperature dependence of the mixed-valence states, showing that the lattice affects the mixed-valence states.     

A new time-resolved fluorometric microarray detection system using core–shell-type fluorescent nanosphere and its application to allergen microarray

We have developed a new time-resolved fluorometric (TRF) microarray detection system consisting of fluorescent NH₂ nanosphere, TRF microarray detector and gamma-irradiated polystyrene chip. Using the TRF microarray detector, we detected 500 particles of the fluorescent nanosphere in one channel. Cross-talk fluorescence from the adjacent channels was little observed in the TRF microarray detector (<0.0004 %). The TRF microarray detection system was further applied for serum allergen-specific immunoglobulin E (IgE) multi-analyses. As a labeled tag antibody, an anti-human IgE Fab’ fragment-conjugated fluorescent nanosphere (Fab’ nanosphere) was prepared as described previously. As a chip surface appropriate for allergen immobilization, the polystyrene chip surface was modified by gamma irradiation. The immunoassay reactivity using the gamma-irradiated polystyrene chip was approximately 2.5-times improved compared with that of the non-treated polystyrene chip. Non-specific adsorption of the Fab’ nanosphere onto the gamma-irradiated polystyrene chip surface was very low level (<0.0009 %). In only 20 μl of serum, six allergen-specific IgEs could be simultaneously determined in one reaction well in fewer than 90 min. Good correlation curves were obtained between the microarray immunoassay and the CAP RAST fluoro-enzyme immunoassay (CAP/RAST FEIA) method (r>0.961). Reproducibility (CVs) of the microarray immunoassay was 8.6 % to 19.0 % (n=5).     

Creep behavior of epoxy resin during irradiation at cryogenic temperature

Creep tests of an epoxy resin during bending and irradiation have been carried out to investigate the synergistic effects of radiation and stress on mechanical properties of the resin. Simultaneous application of stress and irradiation on the epoxy resin enhanced creep rates in comparison with the application of stress on an irradiated sample. In order to clarify the mechanism of the radiation-induced creep, measurements of solvent swelling of specimens have been performed. The swelling increased with the dose and the increase of the swelling corresponds to the increase of the chain scission. The mechanism of increased deformation of the resin during irradiation is proposed to be caused by increased chain scission following the release of the local strain energy.     

Frequency Measurement of Pure Rotational Transitions of D(2)O from 0.5 to 5 THz

Frequencies of pure rotational transitions of D(2)O were measured in the region 0.5-5 THz with a high-precision far-infrared spectrometer using a tunable radiation source. Measured frequencies of about 150 spectral lines, 30 of them being newly measured lines, provide an excellent frequency standard for the far-infrared region together with our previous measurements on H(2)(16)O, H(2)(17)O, and H(2)(18)O. Molecular parameters of Watson's A-reduced Hamiltonian have been obtained to reproduce the observed frequencies. Copyright 2001 Academic Press.