Shcherbin, Dmitri; Thorvaldsen, Andreas johan; Jonsson, Dan Johan; Ruud, Kenneth(Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
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Abstract:
We present the first gauge-origin independent formulation of Jones birefringence at the Hartree–Fock level of theory. Gauge-origin independence is achieved through the use of London atomic orbitals. The implementation is based on a recently proposed atomic orbital-based response theory formulation that allows for the use of both time- and perturbation-dependent basis sets [Thorvaldsen, Ruud, Kristensen, Jørgensen, and Coriani, J. Chem. Phys. 129, 214108 (2008)]. We present the detailed expressions for the response functions entering the Jones birefringence when London atomic orbitals are used. The implementation is tested on a set of polar and dipolar molecules at the Hartree–Fock level of theory. It is demonstrated that London orbitals lead to much improved basis-set convergence, and that the use of small, conventional basis sets may lead to the wrong sign for the calculated birefringence. For large basis sets, London orbitals and conventional basis sets converge to the same results.
Dedicated to the memory of Björn Roos (1937–2010), one of the fathers of modern multiconfigurational quantum chemistry, who also cared deeply about chemical applications, and a fun and inspiring friend to countless theoretically oriented chemists.
The circularly polarized luminescence (CPL) and electronic circular dichroism (CD) spectroscopic parameters corresponding to the n ← π* and n → π* transitions, respectively, have been calculated for selected β,γ-enones using density functional theory. For the smallest β,γ-enone, (1R,4R)-bicyclo[2.2.1]hept-5-en-2-one (norbornenone), coupled-cluster calculations have also been carried out. The excited-state potential energy surface for three of the five enones studied reveals two minima with different C[double bond, length as m-dash]OC[double bond, length as m-dash]C dihedral angles, and with rotatory strengths of opposite sign. The relative energies of the minima determine the sign of the CPL intensity, which may be the same or opposite as in the CD spectrum, in agreement with experimental data. The results obtained in this first computational study of CPL demonstrate its usefulness as an indicator of excited-state structures of chiral species.
We present the first relativistic study of the electric-field-gradient induced birefringence (Buckingham birefringence), with application to the series of molecules CX2 (X = O, S, Se, Te). A recently developed atomic-orbital-driven scheme for the calculation of time-dependent molecular properties using one-, two- and four-component relativistic wave functions (Bast et al. in Chem Phys 356:177, 2009) is extended to first-order frequency-dependent magnetic-field perturbations, using London atomic orbitals to ensure gauge-origin independent results and to improve basis-set convergence. Calculations are presented at the Hartree–Fock and Kohn–Sham levels of theory and results for CO2 and CS2 are compared with previous high-level coupled-cluster calculations. Except for the heaviest member of the series, relativistic effects are small—in particular for the temperature-independent contribution to the birefringence. By contrast, the effects of electron correlation are significant. However, the reliability of standard exchange-correlation functionals in describing Buckingham birefringence remains unclear based on the comparison with high-level coupled-cluster singles-and-doubles calculations.
Cold-adaptation strategies have been studied in multiple psychrophilic organisms, especially for psychrophilic enzymes. Decreased enzyme activity caused by low temperatures as well as a higher viscosity of the aqueous environment require certain adaptations to the metabolic machinery of the cell. In addition to this, low temperature has deleterious effects on the lipid bilayer of bacterial membranes and therefore might also affect the embedded membrane proteins. Little is known about the adaptation of membrane proteins to stresses of the cold. In this study we investigate a set of 66 membrane proteins from the core genome of the bacterial family Vibrionaceae to identify general characteristics that discern psychrophilic and mesophilic membrane proteins. Bioinformatical and statistical methods were used to analyze the alignments of the three temperature groups mesophilic, intermediate and psychrophilic. Surprisingly, our results show little or no adaptation to low temperature for those parts of the proteins that are predicted to be inside the membrane. However, changes in amino acid composition and hydrophobicity are found for complete sequences and sequence parts outside the lipid bilayer. Among others, the results presented here indicate a preference for helix-breaking and destabilizing amino acids Ile, Asp and Thr and an avoidance of the helix-forming amino acid Ala in the amino acid composition of psychrophilic membrane proteins. Furthermore, we identified a lower overall hydrophobicity of psychrophilic membrane proteins in comparison to their mesophilic homologs. These results support the stability-flexibility hypothesis and link the cold-adaptation strategies of membrane proteins to those of loop regions of psychrophilic enzymes.
The criteria for defining bacterial species and even the concept of bacterial species itself are under debate, and the discussion is apparently intensifying as more genome sequence data is becoming available. However, it is still unclear how the new advances in genomics should be used most efficiently to address this question. In this study we identify genes that are common to any group of genomes in our dataset, to determine whether genes specific to a particular taxon exist and to investigate their potential role in adaptation of bacteria to their specific niche. These genes were named unique core genes. Additionally, we investigate the existence and importance of unique core genes that are found in isolates of phylogenetically non-coherent groups. These groups of isolates, that share a genetic feature without sharing a closest common ancestor, are termed genophyletic groups.
The bacterial family Vibrionaceae was used as the model, and we compiled and compared genome sequences of 64 different isolates. Using the software orthoMCL we determined clusters of homologous genes among the investigated genome sequences. We used multilocus sequence analysis to build a host phylogeny and mapped the numbers of unique core genes of all distinct groups of isolates onto the tree. The results show that unique core genes are more likely to be found in monophyletic groups of isolates. Genophyletic groups of isolates, in contrast, are less common especially for large groups of isolate. The subsequent annotation of unique core genes that are present in genophyletic groups indicate a high degree of horizontally transferred genes. Finally, the annotation of the unique core genes of Vibrio cholerae revealed genes involved in aerotaxis and biosynthesis of the iron-chelator vibriobactin.
The presented work indicates that genes specific for any taxon inside the bacterial family Vibrionaceae exist. These unique core genes encode conserved metabolic functions that can shed light on the adaptation of a species to its ecological niche. Additionally, our study suggests that unique core genes can be used to aid classification of bacteria and contribute to a bacterial species definition on a genomic level. Furthermore, these genes may be of importance in clinical diagnostics and drug development.
Simpson, David; Benedictow, Anna; Berge, Halldis; Bergström, Robert; Emberson, Lisa D.; Fagerli, Hilde; Flechard, Chris R.; Hayman, Garry D.; Gauss, Michael; Jonson, Jan Eiof; Jenkin, Michael E.; Nyiri, Agnes; Richter, Cornelia; Semeena, Valiyavetil S.; Tsyro, Svetlana; Tuovinen, Juha Pekka; Valdebenito, Alvaro; Wind, Peter(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
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The Meteorological Synthesizing Centre-West (MSC-W) of the European Monitoring and Evaluation Programme (EMEP) has been performing model calculations in support of the Convention on Long Range Transboundary Air Pollution (CLRTAP) for more than 30 years. The EMEP MSC-W chemical transport model is still one of the key tools within European air pollution policy assessments.
Traditionally, the model has covered all of Europe with a resolution of about 50 km × 50 km, and extending vertically from ground level to the tropopause (100 hPa). The model has changed extensively over the last ten years, however, with flexible processing of chemical schemes, meteorological inputs, and with nesting capability: the code is now applied on scales ranging from local (ca. 5 km grid size) to global (with 1 degree resolution). The model is used to simulate photo-oxidants and both inorganic and organic aerosols.
In 2008 the EMEP model was released for the first time as public domain code, along with all required input data for model runs for one year. The second release of the EMEP MSC-W model became available in mid 2011, and a new release is targeted for summer 2012. This publication is intended to document this third release of the EMEP MSC-W model. The model formulations are given, along with details of input data-sets which are used, and a brief background on some of the choices made in the formulation is presented. The model code itself is available at www.emep.int, along with the data required to run for a full year over Europe.
Colonization of host tissues is a first step taken by many pathogens during the initial stages of infection. Despite the impact of bacterial disease on wild and farmed fish, only a few direct studies have characterized bacterial factors required for colonization of fish tissues. In this study, using live-cell and confocal microscopy, rainbow trout skin epithelial cells, the main structural component of the skin epidermis, were demonstrated to phagocytize bacteria. Mutant analyses showed that the fish pathogen Vibrio anguillarum required the lipopolysaccharide O-antigen to evade phagocytosis and that O-antigen transport required the putative wzm-wzt-wbhA operon, which encodes two ABC polysaccharide transporter proteins and a methyltransferase. Pretreatment of the epithelial cells with mannose prevented phagocytosis of V. anguillarum suggesting that a mannose receptor is involved in the uptake process. In addition, the O-antigen transport mutants could not colonize the skin but they did colonize the intestines of rainbow trout. The O-antigen polysaccharides were also shown to aid resistance to the antimicrobial factors, lysozyme and polymyxin B. In summary, rainbow trout skin epithelial cells play a role in the fish innate immunity by clearing bacteria from the skin epidermis. In defense, V. anguillarum utilizes O-antigen polysaccharides to evade phagocytosis by the epithelial cells allowing it to colonize rapidly fish skin tissues.