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.

A colorimetric assay for nitrite determination in beer based on c-type multiheme enzyme Nitrite reductase (NiR) isolated from Desulfovibrio desulfuricans ATCC 27774, was developed. Using the enzyme in solution, nitrite assay was linear in the 10−8 – 10−2 M range with a detection limit of 10−8 M and a recovery ranging from 90 to 107%. The imprecision ranged from 4 to 10% on the entire calibration curve. With NiR immobilised onto a nylon coil, a flow reactor was developed which showed a narrower linear range (10−5 – 10−2 M) and a higher detection limit (10−5 M) than with the enzyme in solution, but made it possible to reuse the enzyme up to 100 times (50% residual activity). Sample preparation was simple and fast: only degassing and beer dilution by buffer was needed. This enzymatic assay was in good agreement with the results obtained using commercial nitrite determination kits.

Enzymatic Spectrophotometric Determination of Nitrites in Beer

Two azurins with unusual redox and spectroscopic properties isolated from the Pseudomonas chlororaphis strains DSM 50083T and DSM 50135.

Publisher Summary This chapter focuses on low-spin sulfite reductases, which are isolated from Desulfovibrio vulgaris (Hildenborough) (DvH), Methanosarcina barkeri ( Ms. Barkeri ), and Desulforomonas acetoxidans ( Drm. Acetoxidans ). Sulfite reductase catalyzes the six-electron reduction of SO 3 2- to S 2- .This enzyme contains an iron tetrahydroporphyrin prosthetic group, termed “siroheme,” in addition to nonheme iron. On the basis of physiological function, two types of sulfite reductases can be defined (1) the assimilatory type, which is involved in the synthesis of sulfur-containing compounds, and (2) the dissimilatory one, which participates in the respiratory pathway for sulfate-reducing bacteria (SRB). Under certain assay conditions of dissimilatory sulfite reductases, in addition to sulfide, trithionate and thiosulfate are irreversibly produced. All purification procedures of sulfite reductases are carried out at 4 and all buffers are adjusted to pH 7.6. The purified enzyme is stable for six months in 0.05 M Tris-HCl buffer at –80. The purified sulfite reductase has a molecular mass of 27.2 kDa, determined by amino-acid composition. The iron content is consistent with the existence of a single [4Fe-4S] cluster and a siroheme.

Low-spin sulfite reductases

Structural changes associated with calcium-dependent activation of the di-heme cytochrome c peroxidase of Paracoccus pantotrophus

The most thoroughly characterized non-heme iron center in biology is Rubredoxin, the simplest member of the iron-sulfur class of metalloproteins. Rubredoxin contains a highspin iron atom with tetrahedral coordination by four cysteinyl sulfur atoms. A structural variant of this center is found in Desulforedoxin, the smallest known Rubredoxin type protein. The 3D structure of both Rd and Dx has been determined at high resolution. These two proteins can therefore be used as case studies in which structural control by the polypeptide chain over the metal site can be discussed in detail.

Isabel Moura

Papers

Enzymatic Spectrophotometric Determination of Nitrites in Beer

Two azurins with unusual redox and spectroscopic properties isolated from the Pseudomonas chlororaphis strains DSM 50083T and DSM 50135.

Low-spin sulfite reductases

Structural changes associated with calcium-dependent activation of the di-heme cytochrome c peroxidase of Paracoccus pantotrophus

Analysis, Design and Engineering of Simple Iron-Sulfur Proteins: Tales from Rubredoxin and Desulforedoxin