Calculation of Vapour-Liquid Equilibria of Lennard-Jones Binary Systems by the Gibbs Ensemble Monte Carlo Simulation

Abstract

The Gibbs ensemble Monte Carlo simulation has been used to calculate vapour-liquid equilibria of a Lennard-Jones (LJ) binary mixture. The mixture studied is the LB-2-1 model which has been used in our previous calculations on PVT relation and density-dependent local composition. The P-x-y relation has been established at two different temperatures and used to determine vapour-liquid coexistence region in the PVTx space.     

New software for finding transition states by probing accessible,or ergodic,regions

An automated, iterative approach to finding the lowest energy, ionic diffusion paths through a periodic structure has been developed within our new code (written in FORTRAN 77 and named Bubble). The approach is quite general in that it can be applied to find, at a chosen temperature, the accessible (ergodic) regions of a hyper-surface, which is defined across a uniform grid [1 Schön, J.C., Putz, H. and Jansen, M. 1996. Studying the energy hypersurface of continuous system—The threshold algorithm. J. Phys.-Conden. Matt., 8: 143[Crossref] , [Google Scholar]]. We describe both our implementation within the Bubble code and its application to locating the approximate transition states for Mg interstitial diffusion in forsterite, which can then be refined using standard transition state searching [2 Banerjee, A., Adams, N., Simons, J. and Shepard, R. 1985. Search for stationary points on surfaces. J. Phys. Chem., 89: 52[Crossref], [Web of Science ®] , [Google Scholar]].     

Did the prion protein become vulnerable to misfolding after an evolutionary divide and conquer event?

Despite high sequence identity among mammalian prion proteins (PrPs), mammals have varying rates of susceptibility to prion disease resulting in a so-called species barrier. The species barrier follows no clear pattern, with closely related species or similar sequences being no more likely to infect each other, and remains an unresolved enigma. Variation of the conformationally flexible regions may alter the thermodynamics of the conformational change, commonly referred to as the conformational conversion, which occurs in the pathogenic process of the mammalian prion protein. A conformational ensemble scenario is supported by the species barrier in prion disease and evidence that there are strains of pathogenic prion with different conformations within species. To study how conformational flexibility has evolved in the prion protein, an investigation was undertaken on the evolutionary dynamics of structurally disordered regions in the mammalian prion protein, non-mammalian prion protein that is not vulnerable to prion disease, and remote homologs Doppel and Shadoo. Structural disorder prediction analyzed in an evolutionary context revealed that the occurrence of increased or altered conformational flexibility in mammalian PrPs coincides with key events among PrP, Doppel, and Shadoo. Comparatively rapid evolutionary dynamics of conformational flexibility in the prion protein suggest that the species barrier is not a static phenomenon. A small number of amino acid substitutions can repopulate the conformational ensemble and have a disproportionately large effect on pathogenesis.     

Subunit Secondary Structure in Filamentous Viruses: Predictions and Observations

Abstract

The algorithm of Gamier, Osguthorpe and Robson (J. Mol. Biol. 120, 97–120, 1978) for prediction of protein secondary structure has been applied to the coat protein sequences of six filamentous bacteriophages: fd, Ifl, IKe, Pfl, Xf and Pf3. For subunits of Class I virions (fd, Ifl, IKe), the algorithm predicts a very high percentage of helix in comparison to other structure types, which is in accord with the results of laser Raman and circular dichroism measurements. For subunits of the Class II virions (Pfl, Xf, Pf3), the algorithm consistently predicts a predominance of β structure, which is compatible with the demonstrated facility for conversion of Class II subunits from α-helix to β-strand under appropriate experimental conditions (Thomas, Prescott and Day, J. Mol. Biol. 165, 321–356, 1983). Even when the algorithm is biased to favor helix, the Class II virion subunits are predicted to contain considerably more strand than helix. Qualitatively similar results are obtained using the algorithm of Chou and Fasman {Adv. Enzym. 47, 45–148,45-148). Therefore, both predictive and experimental methods indicate a distinction between Gass I and II subunits, which is reflected in a greater tendency of the latter to adopt other than uniform β-helical conformation. The results suggest a possible model for the disassembly of filamentous viruses which may involve the unraveling of coat protein helices at the N terminus.     

Ocean energy and the law of the sea: The need for a protocol

Although fossil fuels are the overwhelming source of energy for the world, and will continue to be so for the foreseeable future, demographic, environmental, political, and economic factors indicate that interest in alternative, renewable sources of energy will grow. There is a need for both global and national policies on ocean energy management. In particular, coastal states and the energy industry would benefit from guidelines that helped to create a predictable, stable environment in which long‐term, high‐cost research, development, and investment decisions could be made with confidence. Coastal states have jurisdiction over the maritime zones most relevant to energy production, but many lack the expertise and funds to develop this potential source. Industry must operate within the control of coastal states and will not be served well by a plethora of differing legal interpretations and unilaterally imposed restrictions and obligations from state to state. An Ocean Energy Protocol to the 1982 UN Convention on the Law of the Sea would afford governments and industry the opportunity to clarify their respective obligations and address particular interests for mutual benefit.     

Trade‐Off between Trap Filling,Trap Creation,and Charge Recombination Results in Performance Increase at Ultralow Doping Levels in Bulk Heterojunction Solar Cells

Doping of organic bulk heterojunction solar cells has the potential to improve their power conversion efficiency (PCE). Deconvoluting the effect of doping on charge transport, recombination, and energetic disorder remains challenging. It is demonstrated that molecular doping has two competing effects: on one hand, dopant ions create additional traps while on the other hand free dopant‐induced charges fill deep states possibly leading to V _OC and mobility increases. It is shown that molar dopant concentrations as low as a few parts per million can improve the PCE of organic bulk heterojunctions. Higher concentrations degrade the performance of the cells. In doped cells where PCE is observed to increase, such improvement cannot be attributed to better charge transport. Instead, the V _OC increase in unannealed P3HT:PCBM cells upon doping is indeed due to trap filling, while for annealed P3HT:PCBM cells the change in V _OC is related to morphology changes and dopant segregation. In PCDTBT:PC70BM cells, the enhanced PCE upon doping is explained by changes in the thickness of the active layer. This study highlights the complexity of bulk doping in organic solar cells due to the generally low doping efficiency and the constraint on doping concentrations to avoid carrier recombination and adverse morphology changes.     

Hybrid Flora of the British Isles by Clive A. Stace,Chris D. Preston and David A. Pearman. Bristol: Botanical Society of Britain and Ireland, 2015. 500 pp. Hardback. ISBN 978‐0‐901158‐48‐2. £45.00.

In this commentary, we discuss evidence for the phylogenetic affiliations of Tortotubus protuberans, the subject of Martin Smith's 2016 paper in the Botanical Journal of the Linnean Society entitled, ‘Cord‐forming Palaeozoic fungi in terrestrial assemblages’. We agree that the fossilized, branching, somatic filaments probably represent fungal hyphae. We were not convinced by Smith's proposal that T. protuberans represents Dikarya, the clade of fungi that includes most modern moulds, yeasts and mushrooms. To justify classification, Smith relied on structures that are analogous between T. protuberans and modern fungi, and argued ‘that Dikarya can produce the range of morphologies expressed by T. protuberans’. We review available information about homologies of the characteristics of T. protuberans, including mycelial cords, retrograde growth, septal pores and ornamented hyphae. Retrograde growth in T. protuberans is intriguing from an evolutionary developmental point of view, but it differs sufficiently in fine detail when compared with growth patterns in croziers or clamp connections of Dikarya, so that homologies are unclear. Tortotubus protuberans is an important fossil form, but we suggest taking a step back and relating it to the distribution of character evolution through the fungal phylogeny rather than to derived characters of modern taxa.