There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Multiwfn is a multifunctional program for wavefunction analysis. Its main functions are: (1) Calculating and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population analysis. (3) Bond order analysis. (4) Orbital composition analysis. (5) Plot density-of-states and spectrum. (6) Topology analysis for electron density. Some other useful utilities involved in quantum chemistry studies are also provided. The built-in graph module enables the results of wavefunction analysis to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com.

Multiwfn: a multifunctional wavefunction analyzer.

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

Denitrification is a distinct means of energy conservation, making use of N oxides as terminal electron acceptors for cellular bioenergetics under anaerobic, microaerophilic, and occasionally aerobic conditions. The process is an essential branch of the global N cycle, reversing dinitrogen fixation, and is associated with chemolithotrophic, phototrophic, diazotrophic, or organotrophic metabolism but generally not with obligately anaerobic life. Discovered more than a century ago and believed to be exclusively a bacterial trait, denitrification has now been found in halophilic and hyperthermophilic archaea and in the mitochondria of fungi, raising evolutionarily intriguing vistas. Important advances in the biochemical characterization of denitrification and the underlying genetics have been achieved with Pseudomonas stutzeri, Pseudomonas aeruginosa, Paracoccus denitrificans, Ralstonia eutropha, and Rhodobacter sphaeroides. Pseudomonads represent one of the largest assemblies of the denitrifying bacteria within a single genus, favoring their use as model organisms. Around 50 genes are required within a single bacterium to encode the core structures of the denitrification apparatus. Much of the denitrification process of gram-negative bacteria has been found confined to the periplasm, whereas the topology and enzymology of the gram-positive bacteria are less well established. The activation and enzymatic transformation of N oxides is based on the redox chemistry of Fe, Cu, and Mo. Biochemical breakthroughs have included the X-ray structures of the two types of respiratory nitrite reductases and the isolation of the novel enzymes nitric oxide reductase and nitrous oxide reductase, as well as their structural characterization by indirect spectroscopic means. This revealed unexpected relationships among denitrification enzymes and respiratory oxygen reductases. Denitrification is intimately related to fundamental cellular processes that include primary and secondary transport, protein translocation, cytochrome c biogenesis, anaerobic gene regulation, metalloprotein assembly, and the biosynthesis of the cofactors molybdopterin and heme D1. An important class of regulators for the anaerobic expression of the denitrification apparatus are transcription factors of the greater FNR family. Nitrate and nitric oxide, in addition to being respiratory substrates, have been identified as signaling molecules for the induction of distinct N oxide-metabolizing enzymes.

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Cell biology and molecular basis of denitrification.

N2OR has been found to have two structural forms of its tetranuclear copper active site, the 4CuS CuZ* form and the 4Cu2S CuZ form EPR, resonance Raman, and MCD spectroscopies have been used to determine the redox states of these sites under different reductant conditions, showing that the CuZ* site accesses the 1-hole and fully reduced redox states, while the CuZ site accesses the 2-hole and 1-hole redox states Single-turnover reactions of N2OR for CuZ and CuZ* poised in these redox states and steady-state turnover assays with different proportions of CuZ and CuZ* show that only fully reduced CuZ* is catalytically competent in rapid turnover with N2O

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Determination of the active form of the tetranuclear copper sulfur cluster in nitrous oxide reductase.

Enzymatic properties and effect of ionic strength on periplasmic nitrate reductase (NAP) from Desulfovibrio desulfuricans ATCC 27774.

Relations between mercury, methyl-mercury and selenium in tissues of Octopus vulgaris from the Portuguese coast.

Resonance Raman spectra of rubredoxin: new assignments and vibrational coupling mechanism from iron-54/iron-56 isotope shifts and variable-wavelength excitation

The multicopper enzyme nitrous oxide reductase (N2OR) catalyzes the final step of denitrification, the two-electron reduction of N2 Ot o N 2. This enzyme is a functional homodimer containing two different multicopper sites: CuA and CuZ. CuA is a binuclear copper site that transfers electrons to the tetranuclear copper sulfide CuZ, the catalytic site. In this study, Pseudomonas nautica cytochrome c552 was identified as the physiological electron donor. The kinetic data show differences when physiological and artificial electron donors are compared (cytochrome vs methylviologen (MV)). In the presence of cytochrome c552, the reaction rate is dependent on the ET reaction and independent of the N2O concentration. With MV, electron donation is faster than substrate reduction. From the study of cytochrome c552 concentration dependence, we estimate the following kinetic parameters: Kmc552 ) 50.2 ( 9.0 µM and Vmaxc552 ) 1.8 ( 0.6 units/mg. The N2O concentration dependence indicates a KmN2O of 14.0 ( 2.9 µM using MV as the electron donor. The pH effect on the kinetic parameters is different when MV or cytochrome c552 is used as the electron donor (pKa ) 6.6 or 8.3, respectively). The kinetic study also revealed the hydrophobic nature of the interaction, and direct electron transfer studies showed that CuA is the center that receives electrons from the physiological electron donor. The formation of the electron transfer complex was observed by 1 H NMR protein-protein titrations and was modeled with a molecular docking program (BiGGER). The proposed docked complexes corroborated the ET studies giving a large number of solutions in which cytochrome c552 is placed near a hydrophobic patch located around the CuA center.

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Electron transfer complex between nitrous oxide reductase and cytochrome c552 from Pseudomonas nautica: kinetic, nuclear magnetic resonance, and docking studies.

Isabel Moura

Papers

Determination of the active form of the tetranuclear copper sulfur cluster in nitrous oxide reductase.

Enzymatic properties and effect of ionic strength on periplasmic nitrate reductase (NAP) from Desulfovibrio desulfuricans ATCC 27774.

Relations between mercury, methyl-mercury and selenium in tissues of Octopus vulgaris from the Portuguese coast.

Resonance Raman spectra of rubredoxin: new assignments and vibrational coupling mechanism from iron-54/iron-56 isotope shifts and variable-wavelength excitation

Electron transfer complex between nitrous oxide reductase and cytochrome c552 from Pseudomonas nautica: kinetic, nuclear magnetic resonance, and docking studies.