B1-B2 phase transition of ferropericlase at planetary interior conditions

Using ab initio simulations based on density functional theory, we have analyzed the crystal structure and thermodynamic stability of Mg_{x} Fe_{1-x}O ferropericlase, showing how the P-T phase diagram associated with the B1-B2 phase transition of pure MgO is influenced by the presence of iron substitutional alloys. We find that a small concentration of Fe atoms contribute to an increase of the transition pressure at fixed temperature, extending the stability of B1 crystalline structure. Moreover, we find a significant nonhomogeneous distribution of the iron atoms between the two phases at low temperatures, with strong partitioning in the B1 phase, an interesting phenomena that could lead to important dynamic consequences. Finally, we analyze the effect of the iron impurities on the volume thermal expansion

Natural frequency discontinuity of vertical liquid sheet flows at transcritical threshold

The natural and forced dynamic response of a gravitational plane liquid sheet (curtain) of finite length interacting with an unconfined gaseous ambient is numerically and experimentally investigated. The global eigenvalue spectrum obtained by means of a linear inviscid one-dimensional model, accounting for the coupling between the curtain motion and the ambient pressure disturbances, clearly shows an abrupt increase (jump) in the characteristic natural frequency of the flow when the supercritical (We>1) to subcritical (We<1) transition occurs, with the Weber number defined as the ratio between inertia and capillary forces. On the other hand, the numerical simulation of the forced sheet response does not show any discontinuity between supercritical and subcritical conditions, as recently found by Torsey et al. (J. Fluid Mech., vol. 910, 2021, pp. 1-14) in the case of an infinite liquid sheet subjected to imposed ambient pressure disturbances not coupled with the curtain motion. It is argued that the forced liquid sheet behaviour varies continuously in shape and amplitude between the two regimes, not depending on the specific liquid-gas interaction model considered, whilst the natural frequency of the finite flow system does undergo a discontinuity, which can be theoretically predicted by the model of sheet-ambient interaction employed here. As a major result, the experimental evidence of the natural frequency jump is for the first time provided as well

DMC-ICE13: ambient and high pressure polymorphs of ice from Diffusion Monte Carlo and Density Functional Theory

Ice is one of the most important and interesting molecular crystals exhibiting a rich and evolving phase diagram. Recent discoveries mean that there are now twenty distinct polymorphs; a structural diversity that arises from a delicate interplay of hydrogen bonding and van der Waals dispersion forces. This wealth of structures provides a stern test of electronic structure theories, with Density Functional Theory (DFT) often not able to accurately characterise the relative energies of the various ice polymorphs. Thanks to recent advances that enable the accurate and efficient treatment of molecular crystals with Diffusion Monte Carlo (DMC), we present here the DMC-ICE13 dataset; a dataset of lattice energies of 13 ice polymorphs. This dataset encompasses the full structural complexity found in the ambient and high-pressure molecular ice polymorphs and when experimental reference energies are available our DMC results deliver sub-chemical accuracy. Using this dataset we then perform an extensive benchmark of a broad range of DFT functionals. Of the functionals considered, we find revPBE-D3 and RSCAN to reproduce reference absolute lattice energies with the smallest error, whilst optB86b-vdW and SCAN+rVV10 have the best performance on the relative lattice energies. Our results suggest that a single functional achieving reliable performance for all phases is still missing, and that care is needed in the selection of the most appropriate functional for the desired application.The insights obtained here may also be relevant to liquid water and other hydrogen bonded and dispersion bonded molecular crystals

Single molecule conduction of engineered cytochrome b562 bonded to metallic electrodes

Measuring single molecule conductance is a fundamental step in order to realise the basic elements of future electronic circuits. This work describes the use of an engineered electron transfer protein, cytochrome 6562 (cyt 6562), as a single molecule junction point between a gold surface and a metallic tip through defined thiol-metal interactions. Two separate cysteine residues were introduced in the cyt b562 amino acid sequence at strategic positions the single-molecule conductivity of the two double cysteine mutants SH-SA and SH-LA was investigated using atomic force microscopy (AFM), scanning tunnelling microscopy (STM), current-volt age (TV) and current-distance (I-z) experiments. The haem binding properties of the cysteine variants were similar to that of the wild-type cyt 6562 confirming that the mutations had not altered the protein's core properties. AFM and STM studies revealed that the SH-SA and SH-LA molecules bound to gold electrode in defined orientations, dictated by the thiol-pair utilised. A strong and stable interaction between the proteins bearing the thiol groups and a Au(lll) surface was achieved, and a single-molecule conductance of 1 nS w is measured in air. In contrast, the unengineered wild-type cyt 6562 bound much less robustly to the gold surface and the measured conductance was at least one order of magnitude less. Crucially, using electrochemical STM (EC-STM) approaches a change in conductance of the cytochrome over different overpotentials was observed, demonstrating that the molecule can act as an electrochemical gate. The protein became most conducting when the substrate potential was set close to the redox potential of the protein. The electrochemical, I-V and I-z STM measurements sug gested a two-step model for electron transfer. This study illustrates the possibility of exploiting a haem binding nrotein directly adsorbed onto a conducting surface as a nanoelectronic element and offers nw perspectives for future biomolecular electronic circuits

An overview on plants cannabinoids endorsed with cardiovascular effects.

Nowadays cardiovascular diseases (CVDs) are the major causes for the reduction of the quality of life. The endocannabinoid system is an attractive therapeutic target for the treatment of cardiovascular disorders due to its involvement in vasomotor control, cardiac contractility, blood pressure and vascular inflammation. Alteration in cannabinoid signalling can be often related to cardiotoxicity, circulatory shock, hypertension, and atherosclerosis. Plants have been the major sources of medicines until modern eras in which researchers are experiencing a rediscovery of natural compounds as novel therapeutics. One of the most versatile plant is Cannabis sativa L., containing phytocannabinoids that may play a role in the treatment of CVDs. The aim of this review is to collect and investigate several less studied plants rich in cannabinoid-like active compounds able to interact with cannabinoid system; these plants may play a pivotal role in the treatment of disorders related to the cardiovascular system

Application of nanodisc technology for direct electrochemical investigation of plant cytochrome P450s and their NADPH P450 oxidoreductase

Direct electrochemistry of cytochrome P450 containing systems has primarily focused on investigating enzymes from microbes and animals for bio-sensing applications. Plant P450s receive electrons from NADPH P450 oxidoreductase (POR) to orchestrate the bio-synthesis of a plethora of commercially valuable compounds. In this report, full length CYP79A1, CYP71E1 and POR of the dhurrin pathway in Sorghum bicolor were reconstituted individually in nanoscale lipid patches, “nanodiscs”, and directly immobilized on unmodified gold electrodes. Cyclic voltammograms of CYP79A1 and CYP71E1 revealed reversible redox peaks with average midpoint potentials of 80 ± 5 mV and 72 ± 5 mV vs. Ag/AgCl, respectively. POR yielded two pairs of redox peaks with midpoint potentials of 90 ± 5 mV and −300 ± 10 mV, respectively. The average heterogeneous electron transfer rate constant was calculated to be ~1.5 s(−1). POR was electro-catalytically active while the P450s generated hydrogen peroxide (H(2)O(2)). These nanodisc-based investigations lay the prospects and guidelines for construction of a simplified platform to perform mediator-free, direct electrochemistry of non-engineered cytochromes P450 under native-like conditions. It is also a prelude for driving plant P450 systems electronically for simplified and cost-effective screening of potential substrates/inhibitors and fabrication of nano-bioreactors for synthesis of high value natural products

Fast electron transfer through a single molecule natively structured redox protein

The electron transfer properties of proteins are normally measured as molecularly averaged ensembles. Through these and related measurements, proteins are widely regarded as macroscopically insulating materials. Using scanning tunnelling microscopy (STM), we present new measurements of the conductance through single-molecules of the electron transfer protein cytochrome b562 in its native conformation, under pseudo-physiological conditions. This is achieved by thiol (SH) linker pairs at opposite ends of the molecule through protein engineering, resulting in defined covalent contact between a gold surface and a platinum–iridium STM tip. Two different orientations of the linkers were examined: a long-axis configuration (SH-LA) and a short-axis configuration (SH-SA). In each case, the molecular conductance could be ‘gated’ through electrochemical control of the heme redox state. Reproducible and remarkably high conductance was observed in this relatively complex electron transfer system, with single-molecule conductance values peaking around 18 nS and 12 nS for the SH-SA and SH-LA cytochrome b562 molecules near zero electrochemical overpotential. This strongly points to the important role of the heme co-factor bound to the natively structured protein. We suggest that the two-step model of protein electron transfer in the STM geometry requires a multi-electron transfer to explain such a high conductance. The model also yields a low value for the reorganisation energy, implying that solvent reorganisation is largely absent