We examine theoretically the signatures of magnetic adatoms in graphene probed by scanning tunneling spectroscopy (STS). When the adatom hybridizes equally with the two graphene sublattices, the broadening of the local adatom level is anomalous and can scale with the cube of the energy. In contrast to ordinary metal surfaces, the adatom local moment can be suppressed by the proximity of the probing scanning tip. We propose that the dependence of the tunneling conductance on the distance between the tip and the adatom can provide a clear signature for the presence of local magnetic moments. We also show that tunneling conductance can distinguish whether the adatom is located on top of a carbon atom or in the center of a honeycomb hexagon.

Introduction of polar azulenes and further functionalization significantly enhance the NLO properties of carbon based materials.

These authors contributed equally to this work. SUMMARYThe chloroplast NAD(P)H dehydrogenase-like (NDH) complex consists of about 30 subunits from both the nuclear and chloroplast genomes and is ubiquitous across most land plants. In some orchids, such as Phalaenopsis equestris, Dendrobium officinale and Dendrobium catenatum, most of the 11 chloroplast genomeencoded ndh genes (cp-ndh) have been lost. Here we investigated whether functional cp-ndh genes have been completely lost in these orchids or whether they have been transferred and retained in the nuclear genome. Further, we assessed whether both cp-ndh genes and nucleus-encoded NDH-related genes can be lost, resulting in the absence of the NDH complex. Comparative analyses of the genome of Apostasia odorata, an orchid species with a complete complement of cp-ndh genes which represents the sister lineage to all other orchids, and three published orchid genome sequences for P. equestris, D. officinale and D. catenatum, which are all missing cp-ndh genes, indicated that copies of cp-ndh genes are not present in any of these four nuclear genomes. This observation suggests that the NDH complex is not necessary for some plants. Comparative genomic/transcriptomic analyses of currently available plastid genome sequences and nuclear transcriptome data showed that 47 out of 660 photoautotrophic plants and all the heterotrophic plants are missing plastid-encoded cp-ndh genes and exhibit no evidence for maintenance of a functional NDH complex. Our data indicate that the NDH complex can be lost in photoautotrophic plant species. Further, the loss of the NDH complex may increase the probability of transition from a photoautotrophic to a heterotrophic life history.

An α-diimine-stabilized Al-Al-bonded compound [L(2-)Al(II)-Al(II)L(2-)] (L = [{(2,6-iPr(2)C(6)H(3))NC(Me)}(2)]; 1) consists of dianionic α-diimine ligands and sub-valent Al(2+) ions and thus could potentially behave as a multielectron reductant. The reactions of compound 1 with azo-compounds afforded phenylimido-bridged products [L(-)Al(III)(μ(2)-NPh)(μ(2)-NAr)Al(III)L(-)] (2-4). During the reaction, the dianionic ligands and Al(2+) ions were oxidized into monoanions and Al(3+), respectively, whilst the [NAr](2-) imides were produced by the four-electron reductive cleavage of the N=N double bond. Upon further reduction by Na, the monoanionic ligands in compound 2 were reduced to the dianion to give [(L(2-))(2)Al(III)(2)(μ(2)-NPh)(2)Na(2)(thf)(4)] (5). Interestingly, when asymmetric azo-compounds were used, the asymmetric adducts were isolated as the only products (compounds 3 and 4). DFT calculations indicated that the reaction was quite feasible in the singlet electronic state, but the final product with the triplet-state monoanionic ligands could result from an exothermic singlet-to-triplet conversion during the reaction process.

We present exact analytical calculations of scanning tunneling currents in locally disordered graphene using a multimode description of the microscope tip. Analytical expressions for the local density of states (LDOS) are given for energies beyond the Dirac cone approximation. We show that the LDOS at the A and B sublattices of graphene are out of phase by π implying that the averaged LDOS, as one moves away from the impurity, shows no trace of the 2q F (with q F the Fermi momentum) Friedel modulation. This means that a STM experiment lacking atomic resolution at the sublattice level will not be able of detecting the presence of the Friedel oscillations [this seems to be the case in the experiments reported in Phys. Rev. Lett. 101, 206802 (2008)]. The momentum maps of the LDOS for different types of impurities are given. In the case of the vacancy, 2q F features are seen in these maps. In all momentum space maps, K and K + K ′ features are seen. The K + K ′ features are different from what is seen around zero momentum. An interpretation for these features is given. The calculations reported here are valid for chemical substitution impurities, such as boron and nitrogen atoms, as well as for vacancies. It is shown that the density of states close to the impurity is very sensitive to type of disorder: diagonal, non-diagonal, or vacancies. In the case of weakly coupled (to the carbon atoms) impurities, the local density of states presents strong resonances at finite energies, which leads to steps in the scanning tunneling currents and to suppression of the Fano factor. New J. Phys.

This work demonstrates that non-redox metal ions as Lewis acids can sharply improve the oxygen transfer efficiency of a manganese(II) catalyst having a non-heme ligand. In the absence of Lewis acid, oxidation of a manganese(II) complex will generate the known di-μ-oxo-bridged dinuclear Mn2(III,IV) core which is very sluggish for olefin epoxidation. Adding non-redox metal ions causes the dissociation of the dinuclear core, leading to sharp improvement in its oxygen transfer efficiency.

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Escherichia coli inorganic pyrophosphatase (E-PPase) is a tetranuclear divalent metal dependent enzyme that catalyzes the reversible interconversion of pyrophosphate (PPi) and orthophosphate (Pi), with Mg(2+) conferring the highest activity. In the present work, the reaction mechanism of E-PPase is investigated using the hybrid density functional theory (DFT) method B3LYP with a large model of the active site. Our calculated results shed further light on the detailed reaction mechanism. In particular, the important residue Asp67, either protonated or unprotonated, was taken into account in the present calculations. Our calculations indicated that a protonated Asp67 is crucial for the reverse reaction to take place; however, it is lost sight of in the forward reaction. The bridging hydroxide is shown to be capable of performing nucleophilic in-line attack on the substrate from its bridging position in the presence of four Mg(2+) ions. During the catalysis, the roles of the four magnesium ions are suggested to provide a necessary conformation of the active site, facilitate the nucleophile formation and substrate orientation, and stabilize the trigonal bipyramid transition state, thereby lowering the barrier for the nucleophilic attack.