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Jeffbenite, ideally Mg.sub.3Al.sub.2Si.sub.3O.sub.12, has been identified as inclusions in super-deep diamonds originating from depths that exceed 300 km. Although Mg-end member jeffbenite has limited stability at upper-mantle conditions, iron-bearing jeffbenite may have broader P-T stability that extends to the transition zone or uppermost lower mantle, incorporating significant amounts of ferric iron. Using synchrotron-based, single-crystal X-ray diffraction (XRD) and synchrotron Mössbauer spectroscopy (SMS) at pressures up to 29 GPa, we report the crystal structure, compressibility, and likely spin transition of iron in ferromagnesian jeffbenite (Mg.sub.2.32Al.sub.0.03Fe.sup.2+.sub.1.28Fe.sup.3+.sub.1.77Si.sub.2.85O.sub.12). High-pressure structure refinements reveal that Fe.sup.3+ substitution for Si in the T2 site, which shares edges with the M2 octahedron, likely stabilizes jeffbenite at high pressure, because it increases the cation-to-cation distance between these sites. Although ferromagnesian jeffbenite does not undergo a structural phase transition below 30 GPa, SMS hyperfine parameters suggest the onset of an electronic spin transition of iron from high-spin (HS) to low-spin (LS) at around 22 GPa, which may increase its stability at high pressures. Pressure-volume data were fit to a third order Birch-Murnaghan equation of state, resulting in V.sub.0 = 816.54(9), K.sub.T0 = 181.54(1.39), and [Formula omitted] = 2.76(14). These equation of state parameters are applicable to evaluating the encapsulation pressures of super-deep diamonds. The density and bulk modulus of ferromagnesian jeffbenite are similar to or higher than pyrope-almandine, pyrope-majorite, and skiagite-majorite solid solution garnets, further suggesting that jeffbenite may be an important ferric-iron silicate in the deeper parts of the mantle transition zone and uppermost lower mantle. However, future studies on the influence of temperature and oxidation state on the stability and equations of state of iron-bearing jeffbennite are still needed to determine what role, if any, jeffbenite plays in transition-zone mineralogy., Author(s): Fei Wang [sup.1], Elizabeth C. Thompson [sup.2], Dongzhou Zhang [sup.3], Ercan E. Alp [sup.4], Jiyong Zhao [sup.4], Joseph R. Smyth [sup.5], Steven D. Jacobsen [sup.1] Author Affiliations: (1) grid.16753.36, [...]

Mononuclear non-haem iron (NHFe) enzymes catalyse a broad range of oxidative reactions, including halogenation, hydroxylation, ring closure, desaturation and aromatic ring cleavage reactions. They are involved in a number of biological processes, including phenylalanine metabolism, the production of neurotransmitters, the hypoxic response and the biosynthesis of secondary metabolites (1-3). The reactive intermediate in the catalytic cycles of these enzymes is a high-spin S = 2 Fe(IV)=O species, which has been trapped for a number of NHFe enzymes (4-8), including the halogenase SyrB2 (syringomycin biosynthesis enzyme 2). Computational studies aimed at understanding the reactivity of this Fe(IV)=O intermediate (9-13) are limited in applicability owing to the paucity of experimental knowledge about its geometric and electronic structure. Synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) is a sensitive and effective method that defines the dependence of the vibrational modes involving Fe on the nature of the Fe(IV)=O active site (14-16). Here we present NRVS structural characterization of the reactive Fe(IV)5O intermediate of a NHFe enzyme, namely the halogenase SyrB2 from the bacterium Pseudomonas syringae pv. syringae. This intermediate reacts via an initial hydrogen-atom abstraction step, performing subsequent halogenation of the native substrate or hydroxylation of non-native substrates (17). A correlation of the experimental NRVS data to electronic structure calculations indicates that the substrate directs the orientation of the Fe(IV)=O intermediate, presenting specific frontier molecular orbitals that can activate either selective halogenation or hydroxylation., SyrB2, an α-ketoglutarate (αKG)-dependent NHFe enzyme found in Pseudomonas syringae pv. syringae, halogenates the methyl group of L-threonine (L-Thr) using non-ribosomal peptide synthetase machinery (18). The Fe(II) active site is [...]

Bleomycin (BLM) is a glycopeptide anticancer drug capable of effecting single- and double-strand DNA cleavage. The last detectable intermediate prior to DNA cleavage is a low spin [Fe.sup.III] peroxy level species, termed activated bleomycin (ABLM). DNA strand scission is initiated through the abstraction of the C-4' hydrogen atom of the deoxyribose sugar unit. Nuclear resonance vibrational spectroscopy (NRVS) aided by extended X-ray absorption fine structure spectroscopy and density functional theory (DFT) calculations are applied to define the natures of [Fe.sup.III]BLM and ABLM as (BLM)[Fe.sup.III]--OH and (BLM/[Fe.sup.III]([[eta].sup.1]-OOH/species, respectively. The NRVS spectra of [Fe.sup.III]BLM and ABLM are strikingly different because in ABLM the [delta]Fe--O--O bending mode mixes with, and energetically splits, the doubly degenerate, intense O--Fe--[N.sub.ax] transaxial bends. DFT calculations of the reaction of ABLM with DNA, based on the species defined by the NRVS data, show that the direct H-atom abstraction by ABLM is thermodynamically favored over other proposed reaction pathways. nonheme iron | structure/reactivity doi/ 10.1073/pnas.1016323107

Recent studies have shown that high pressure (P) induces the metallization of the [Fe.sup.2+]--O bonding, the destruction of magnetic ordering in Fe, and the high-spin (HS) to low-spin (LS) transition of Fe in silicate and oxide phases at the deep planetary interiors. Hematite ([Fe.sub.2][O.sub.3]) is an important magnetic carrier mineral for deciphering planetary magnetism and a proxy for Fe in the planetary interiors. Here, we present synchrotron Mossbauer spectroscopy and X-ray diffraction combined with ab initio calculations for [Fe.sub.2][O.sub.3] revealing the destruction of magnetic ordering at the hematite [right arrow] [Rh.sub.2][O.sub.3]-II type (RhII) transition at 70 GPa and 300 K, and then the revival of magnetic ordering at the RhII [right arrow] postperovskite (PPv) transition after laser heating at 73 GPa. At the latter transition, at least half of [Fe.sup.3+] ions transform from LS to HS and [Fe.sub.2][O.sub.3] changes from a semiconductor to a metal. This result demonstrates that some magnetic carrier minerals may experience a complex sequence of magnetic ordering changes during impact rather than a monotonic demagnetization. Also local Fe enrichment at Earth's core-mantle boundary will lead to changes in the electronic structure and spin state of Fe in silicate PPv. If the ultra-low-velocity zones are composed of Fe-enriched silicate PPv and/or the basaltic materials are accumulated at the lowermost mantle, high electrical conductivity of these regions will play an important role for the electromagnetic coupling between the mantle and the core. spin ordering | electrical conductivity | high pressure | phase transition

The electronic spin state of [Fe.sup.2+] in ferropericlase, ([Mg.sub.0.75][Fe.sub.0.25])O, transitions from a high-spin (spin unpaired) to low-spin (spin paired) state within the Earth's mid-lower mantle region. To better understand the local electronic environment of high-spin [Fe.sup.2+] ions in ferropericlase near the transition, we obtained synchrotron Mossbauer spectra (SMS) of ([Mg.sub.0.75],[Fe.sub.0.25])O in externally heated and laser-heated diamond anvil cells at relevant high pressures and temperatures. Results show that the quadrupole splitting (QS) of the dominant high-spin [Fe.sup.2+] site decreases with increasing temperature at static high pressure. The QS values at constant pressure are fitted to a temperature-dependent Boltzmann distribution model, which permits estimation of the crystal-field splitting energy ([[DELTA].sub.3]) between the [d.sub.xy] and [d.sub.xz] or [d.sub.zy] orbitals of the [t.sub.2g] states in a distorted octahedral [Fe.sup.2+] site. The derived [[DELTA].sub.3] increases from approximately 36 meV at 1 GPa to 95 meV at 40 GPa, revealing that both high pressure and high temperature have significant effects on the 3d electronic shells of [Fe.sup.2+] in ferroperielase. The SMS spectra collected from the laser-heated diamond cells within the time window of 146 ns also indicate that QS significantly decreases at very high temperatures. A larger splitting of the energy levels at high temperatures and pressures should broaden the spin crossover in ferropericlase because the degeneracy of energy levels is partially lifted. Our results provide information on the hyperfine parameters and crystal-field splitting energy of high-spin [Fe.sup.2+] in ferropericlase at high pressures and temperatures, relevant to the electronic structure of iron in oxides in the deep lower mantle. Keywords: Ferroperielase, diamond-anvil cell, spin transition, Mossbauer spectroscopy, high pressures, high temperatures

The electronic environment of the Fe nuclei in two silicate perovskite samples, [Fe.sub.0.05][Mg.sub.0.95]Si[O.sub.3] (Pv05) and [Fe.sub.0.1][Mg.sub.0.9]Si[O.sub.3] (Pv10), have been measured to 120 GPa and 75 GPa, respectively, at room temperature using diamond anvil cells and synchrotron Mossbauer spectroscopy (SMS). Such investigations of extremely small and dilute [sup.57]Fe-bearing samples have become possible through the development of SMS. Our results are explained in the framework of the 'three-doublet' model, which assumes two [Fe.sup.2+]-like sites and one [Fe.sup.3+]-like site that are well distinguishable by the hyperfine fields at the location of the Fe nuclei. At low pressures, [Fe.sup.3+]/[SIGMA]Fe is about 0.40 for both samples. Our results show that at pressures extending into the lowermost mantle the fraction of [Fe.sup.3+] remains essentially unchanged, indicating that pressure alone does not alter the valence states of iron in (Mg,Fe)Si[O.sub.3] perovskite. The quadrupole splittings of all Fe sites first increase with increasing pressure, which suggests an increasingly distorted (noncubic) local iron environment. Above pressures of 40 GPa for Pv10 and 80 GPa for Pv05, the quadrupole splittings are relatively constant, suggesting an increasing resistance of the lattice against further distortion. Around 70 GPa, a change in the volume dependence of the isomer shift could be indicative of the endpoint of a continuous transition of [Fe.sup.3+] from a high-spin to a low-spin state.

NPAT, a substrate of the cyclin E-Cdk2 complex, has been found to link cyclin E-Cdk2 to the regulation of replication-dependent histone gene transcription. NPAT was shown to activate histone gene transcription, and the activation depends on promoter elements already thought to mediate cell cycle-dependent transcription.

Xenopus oocyte cell extracts administered to Xenopus egg extracts block the Xenopus sperm nuclei and double-stranded plasmid DNA template replication. The immature oocytes contain molecules that negatively control the replication of chromosomal DNA. Negative factors decrease during the maturation of the oocytes. The inhibitory process is not caused due to template DNA degradation or suppression of chain elongation by the oocytes.

Studies have revealed that four chromosomal replication origin regions in higher eukaryotes commonly share modular sequence elements such as DNA unwinding elements, pyrimidine tracts, scaffold-associated regions and transcriptional regulatory sequences. Initiator protein binding sites and inherently destabilized regions might also possibly be shared. A DNA replication initiation model which postulates uncoupled DNA duplex unwinding, transient single stranded intermediates and DNA synthesis at multiple sites is proposed.

Sound velocities of hexagonal close-packed iron (hcp-Fe) were measured at pressures up to 73 gigapascals and at temperatures up to 1700 kelvin with nuclear inelastic x-ray scattering in a laser-heated diamond anvil cell. The compressional-wave velocities ([V.sub.P]) and shear-wave velocities ([V.sub.S]) of hcp-Fe decreased significantly with increasing ternperature under rnoderately high pressures. [V.sub.P] and [V.sub.S] under high pressures and temperatures thus cannot be fitted to a linear relation, Birch's law, which has been used to extrapolate measured sound velocities to densities of iron in Earth's interior. This result means that there are more light elements in Earth's core than have been inferred from linear extrapolation at room temperature., The properties of Earth's iron-rich core have been inferred from estimates of iron density at high pressures and temperatures and from measurements of compressional-wave ([V.sub.P]) and shear-wave ([V.sub.S]) velocities passing [...]