Soft Ions Research Articles

Electronic Structure and Magnetic Properties of a Titanium(II) Coordination Complex.

Stable coordination complexes of TiII (3d2) are relatively uncommon, but are of interest as synthons for low oxidation state titanium complexes for application as potential catalysts and reagents for organic synthesis. Specifically, high-spin TiII ions supported by redox-inactive ligands are still quite rare due to the reducing power of this soft ion. Among such TiII complexes is trans-[TiCl2(tmeda)2], where tmeda = N,N,N',N'-tetramethylethane-1,2-diamine. This complex was first reported by Gambarotta and co-workers almost 30 years ago, but it was not spectroscopically characterized and theoretical investigation by quantum chemical theory (QCT) was not feasible at that time. As part of our interest in low oxidation state early transition metal complexes, we have revisited this complex and report a modified synthesis and a low temperature (100 K) crystal structure that differs slightly from that originally reported at ambient temperature. We have used magnetometry, high-frequency and -field EPR (HFEPR), and variable-temperature variable-field magnetic circular dichroism (VTVH-MCD) spectroscopies to characterize trans-[TiCl2(tmeda)2]. These techniques yield the following S = 1 spin Hamiltonian parameters for the complex: D = -5.23(1) cm-1, E = -0.88(1) cm-1, (E/D = 0.17), g = [1.86(1), 1.94(2), 1.77(1)]. This information, in combination with electronic transitions from MCD, was used as input for both classical ligand-field theory (LFT) and detailed QCT studies, the latter including both density functional theory (DFT) and ab initio methods. These computational methods are seldom applied to paramagnetic early transition metal complexes, particularly those with S > 1/2. Our studies provide a complete picture of the electronic structure of this complex that can be put into context with the few other high-spin and mononuclear TiII species characterized to date.

Combining soft electrode and ion exchange membranes for increasing salinity difference energy efficiency

A large variety of routes have been envisaged for improving the efficiency of methods aimed at producing clean, renewable energy. One of them includes the so-called capmix techniques, whereby clean electrical energy is obtained by alternately contacting salty and fresh solutions with capacitive electrodes. Investigations in this area have focused on optimizing materials, cycle implementation, up-scaling, and so on. One possibility that has been explored regards the use of ion exchange membranes for producing the necessary voltage differences between electrodes when in contact with concentrated and dilute ionic solutions. A related, but different approach consists in treating the electrodes with charged layers, notably polyelectrolytes. In this work, we propose an original combination of the two most efficient capmix techniques by simultaneously coating the carbon electrodes with membranes and polyelectrolytes. With the objective of analyzing the benefit of this new proposal in terms of energy and power, CAPMIX cycles were performed and carefully examined. These results will lead to the first insight into the ensemble behavior of polyelectrolyte layers and exchange membranes which will be key for the overall improvement of the CAPMIX methods.

Kx[Bi4-xMnxS6], Design of a Highly Selective Ion Exchange Material and Direct Gap 2D Semiconductor.

Layered sulfides with high selectivity for binding heavy metal ions and radionuclide ions are promising materials in effluent treatment and water purification. Here we present a rationally designed layered sulfide Kx[Bi4-xMnxS6] (x = 1.28) deriving from the Bi2Se3-structure type by targeted substitution to generate quintuple [Bi4-xMnxS6]x- layers and K+ cations between them. The material has dual functionality: it is an attractive semiconductor with a bandgap of 1.40 eV and also an environmental remediation ion-exchange material. The compound is paramagnetic, and optical adsorption spectroscopy and DFT electronic structure calculations reveal that it possesses a direct band gap and a work function of 5.26 eV. The K+ ions exchange readily with alkali or alkaline-earth ions (Rb+, Cs+, and Sr2+) or soft ions (Pb2+, Cd2+, Cr3+, and Zn2+). Furthermore, when the K+ ions are depleted the Mn2+ ions in the Bi2Se3-type slabs can also be replaced by soft ions, achieving large adsorption capacities. The ion exchange reactions of Kx[Bi4-xMnxS6] can be used to create new materials of the type Mx[Bi4-xMnxS6] in a low temperature kinetically controlled manner with significantly different electronic structures. The Kx[Bi4-xMnxS6] (x = 1.28) exhibits efficient capture of Cd2+ and Pb2+ ions with high distribution coefficient, Kd (107 mL/g), and exchange capacities of 221.2 and 342.4 mg/g, respectively. The material exhibits excellent capacities even in high concentration of competitive ions and over a broad pH range (2.5-11.0). The results highlight the promise of the Kx[Bi4-xMnxS6] (x = 1.28) phase to serve not only as a highly selective adsorbent for industrial and nuclear wastewater but also as a magnetic 2D semiconductor for optoelectronic applications.

フォトニクス（X線からテラヘルツ波まで）／ソフトマターのナノテクノロジー／イオンビーム

フォトニクス（X線からテラヘルツ波まで）／ソフトマターのナノテクノロジー／イオンビーム

Assembly of Soft Electrodes and Ion Exchange Membranes for Capacitive Deionization.

The responsible use of water, as well as its reuse and purification, has been a major problem for decades now. In this work, we study a method for adsorbing ions from aqueous solutions on charged interfaces using highly porous electrodes. This water purification process is based on the electric double layer concept, using the method known as capacitive deionization (CDI): If we pump salty solutions through the volume comprised between two porous electrodes while applying a potential difference to them, ions present in the solution are partially removed and trapped on the electrode surfaces. It has been well established that the use of carbon electrodes in combination with ion exchange membranes (membrane-CDI) improves the efficiency of the method above that achieved with bare activated carbon. Another approach that has been tested is based on coating the carbon with polyelectrolyte layers, converting them into “soft electrodes” (SEs). Here we investigate the improvement found when combining SEs with membranes, and it is shown that the amount of ions adsorbed and the ratio between ions removed and electrons transported reach superior values, also associated with a faster kinetics of the process. The method is applied to the partial desalination of up to 100 mM NaCl solutions, something hardly achievable with bare or membrane-covered electrodes. A theoretical model is presented for the ion transport in the presence of both the membrane and the polyelectrolyte coating.

Characterizing TDP-43307-319 Oligomeric Assembly: Mechanistic and Structural Implications Involved in the Etiology of Amyotrophic Lateral Sclerosis.

Aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) is a salient feature of amyotrophic lateral sclerosis (ALS), a debilitating neurodegenerative disorder affecting over 200 000 people worldwide. The protein undergoes both functional and pathogenic aggregation; the latter is irreversible and hypothesized to produce soluble oligomers that are toxic to neurons in addition to inclusions made of stable fibrous deposits. Despite progress made toward identifying disease-related proteins, the underlying pathogenic mechanism associated with these toxic oligomers remains elusive. Utilizing a multimodal approach that combines several measurement techniques (circular dichroism (CD), thioflavin T spectroscopy (ThT), Fourier transform infrared spectroscopy (FTIR)) and high spatial resolution imaging tools (electron microscopy (EM) and atomic force microscopy (AFM)), with soft ion mobility mass spectrometry (IM-MS) and atomistic molecular dynamics (MD) simulations, we explore the oligomerization mechanisms, structures, and assembly pathways of TDP-43307-319. This fragment is both amyloidogenic and toxic and is within the glycine-rich C-terminal domain essential for both toxicity and aggregation of the full-length protein. In addition to the wild-type peptide, two ALS-related mutants (A315T and A315E) and a non-axon-toxic mutant (G314V) were investigated to determine how mutations affect the oligomerization of TDP-43307-319 and structures of toxic oligomers. The results of our study provide new insights into how ALS-related mutants, A315T and A315E, accelerate or alter the pathogenic mechanism and highlight the role of an internal glycine, G314, in maintaining efficient packing known to be critical for functional oligomer assembly. More importantly, our data demonstrate that G314 plays a vital role in TDP-43 assembly and prevents cytotoxicity via its unique aversion to oligomers larger than trimer. Our observation is consistent with previous studies showing that G314V mutation of the full-length TDP-43 induced remediation of both axonotoxicity and neuronal apoptosis. Our findings reveal a distinct aggregation mechanism for each peptide and elucidate oligomeric species and possible structures that may be involved in the pathology of ALS.

Relations between metal ion characteristics and adsorption performance of graphene oxide: A comprehensive experimental and theoretical study

The adsorption performance of graphene oxide (GO) towards metallic hard (Na+, Mg2+), soft (Cd2+ and Pb2+) and borderline ions (Ni2+, Cu2+, Zn2+, Co2+) was studied experimentally giving the sequence of maximum Langmuir adsorption capacities Qm, mmol/g, as Na+ < Mg2+ < Co2+ < Cd2+ < Zn2+ < Ni2+ < Cu2+ < Pb2+. The results showed that the adsorption capacities Qm of hard ions were substantially lower than that of soft and borderline ones. The relationship between the Qm values of metal ions and their characteristics was studied using relative correlation analysis. The ion characteristics include atomic number AN, ionic radius r, change in ionization potential ΔIP, electronegativity Xm, atomic weight AW, covalent index Xm2r, absolute difference between electrochemical potential of the ion and that of its first stable reduced state ΔE0, absolute value of the first hydrolysis constant decimal logarithm |lgKOH|, atomic radius AR, atomic radius to atomic weight ratio AR/AW, polarization force or ionic index Z2/r and softness index σp. The Qm value exhibited positive correlation with r, △IP, Xm, Z2/r, AN/△IP, AW, Xm2/r and AN, while negative correlation was observed with △E0, |lgKOH|, σp, AR and AR/AW. The results allow the Qm values being predicted by the equation, the correlation coefficient R2 of which exceeds 0.885:Qm=0.338ΔIP-0.110|lgKOH|+0.114Z2/r+26.934σp-1.479AR-1.162Xm2r+0.115AN-3.059Density functional theory (DFT) was adopted to study the adsorption mechanism of metal ions at GO, taking Na+, Cu2+ and Pb2+ ions as examples. The results showed the adsorption energy Ead of GO-Na+ bond being negative indicating Na+ adsorption less likely resulting possibly in relatively low adsorption capacity of GO towards hard ions. The Ead values of GO bonds with Cu2+ and Pb2+ comprised the rows GO(O)-Cu2+ > GO(COOH)-Cu2+ > GO(OH)-Cu2+, and GO(COOH)-Pb2+ > GO(OH)-Pb2+ > GO(O)-Pb2+, respectively. The results provide guidelines in predicting the adsorption ability of GO adsorbent towards metal ions.

Surface Penetration without Enrichment: Simulations Show Ion Surface Propensities Consistent with Both Elevated Surface Tension and Surface Sensitive Spectroscopy.

Molecular dynamics was used to investigate ion surface propensities in NaCl, KBr, and CsI solutions with an MP2-based force field. Although NaCl is found to be strongly repelled from the liquid-vapor interface, softer ions, such as I-, penetrate closely to the interface. Despite the surface penetration, the concentration of CsI near the interface is still lower than that in the bulk, thus leading to no surface enrichment. The salt concentration is found to affect relative surface propensities of the ions. More significant surface penetration is observed at higher salt concentrations. Softer ions at higher concentrations form a complex multilayer arrangement that can not be characterized as a simple surface bilayer. The simulated ion distributions explain the spectroscopic evidence of surface perturbation by soft ions with a negative surface excess consistent with an increased surface tension of salt solutions.

Electrical double layer in molten salts with account of soft repulsions.

Results of Monte Carlo simulations of the electrode-molten salt interface are reported. The system was modeled by soft ions in contact with a soft wall using the Lennard-Jones potential restricted to the repulsion part. The soft wall was formed of C (graphite), Hg, and Pb atoms. Calculations were carried out for the parameter values which would permit making comparison with the real system. The paper presents information on physicochemical properties of the interfacial region, such as the ion singlet distribution functions, the mean electrostatic potential as a function of the distance from the electrode surface, and differential capacitance results as a function of the electrode charges. The differential capacitance curves have a flat and distorted bell shape which vary depending on the kind of the electrode material. The differential capacitance results are discussed and compared with the data obtained from ionic liquid simulations, density functional theory, and mean field calculations.

Quantifying correlations of metal ionic characters with ecological soil screening levels (Eco-SSLs) of metals using QICAR models

Soil pollution by heavy metals is a major challenge for soil ecosystems; therefore, many countries have published thresholds or standards for protecting soil organisms based on toxicity testing. However, there have been few studies on the mechanism of metal toxicity on organisms in soils, especially relationships between metal's ionic properties and its toxicity. Herein, we selected environmental soil screening levels (Eco-SSLs), which are internationally recognized ecotoxicity values recommended by the United States Environmental Protection Agency (USEPA), and investigated relationships between Eco-SSLs and metal ionic characteristics. The results showed that several ionic characteristics were significantly correlated with Eco-SSL using a classification of metal ions according to hard and soft acids and bases. Electrochemical potential, atomic ionization potential, the first hydrolysis constant, the maximum complex stability constant, a polarization force parameter and covalent radius showed significant correlations with Eco-SSLs for borderline plus hard ions, while the soft index exhibited significant fitting for borderline plus soft ions, suggesting that ionic bonding and covalent bonding played important roles in metal toxicity on borderline plus hard ions and soft ions, respectively. Then, we chose characteristics that had the strongest correlations with Eco-SSLs, and developed quantitative ion character–activity relationship (QICAR) for soil organisms. The QICARs predicted Eco-SSLs for metals that were reasonably consistent with those recommended by USEPA, with differences between them generally <0.5 orders of magnitude. Overall, QICAR provide a basis for ecological risk assessment and could be useful to interpret relationships between metal's ionic properties and its toxicity.

Study of stainless steel electrodes after electrochemical analysis in sea water condition

For water electrolysis, a rare earth material (eg., platinum) is often used as an electrode, but because of the high cost and toxicity of chemicals, researchers are searching for cost effective and eco-friendly alternative materials. Various alloys and metals have been long explored for use as electrode materials in different media. Stainless steel (SS 304) electrodes are cost effective and have a large surface area; further their catalytic performance is comparable to that of carbon coated noble metals cathodes. Stainless steel has good mechanical properties and durability so it is widely used in desalination plants, oil and gas industries, ship building, etc. However, over a period of time it corrodes very quickly in saline water. To improve the stability and durability of the electrodes (i.e., to minimize corrosion), we anneal the samples under two different sets of conditions and test the electrodes in 3.5% NaCl solution. The anodic peak (−0.25 V) observed for bare stainless steel result from the formation of iron (II) hydroxide [Fe(OH)2]. The Raman bands observed at 210 and 274 cm−1 for bare stainless steel result from the formation of α-Fe2O3 owing to partial, anodic, and cathodic reactions occurring on the electrode which disrupts the surface layers. High intensity X-ray diffraction (XRD) and Raman peaks of Cr2O3 and MnCr2O4 observed in argon and hydrogen annealed sample after cyclic voltammetry reveal that this sample is more stable than bare and air annealed samples. XRD reveals mixed oxide phases in addition to eskolaite and magnetite phases. Scanning electron microscope (SEM) images show that although the air-annealed sample has a soft, spongy structure, Na and Cl ions are adsorbed in the voids on the outer surface of the electrode leading to quick degradation. For the air-annealed sample the oxide appears to adhere poorly to the stainless steel. Oxygen (ie., oxide composition) may play a key role in adherence and growth of Cr2O3 formed at high temperature. X-ray photoelectron spectroscopy (XPS) reveals that large amounts of Cr and Mn are dissolved/corroded into the electrolyte for air annealed sample which is in good agreement with the Raman and SEM results.

Thiol-Functionalized Pores via Post-Synthesis Modification in a Metal-Organic Framework with Selective Removal of Hg(II) in Water.

Owing to the rapid increase of Hg(II) ions in water resources, the design and development of new adsorbents for Hg(II) removal are becoming a significant challenge in environmental protection. Herein, a thiol-functionalized metal-organic framework (SH-MiL-68(In)) was successfully prepared through a post-synthesis modification procedure, and the framework intactness and porosity were well maintained after this process. SH-MiL-68(In) exhibited selective adsorption performance for Hg(II) ions in water. Meanwhile, SH-MiL-68(In) also shows a high adsorption capacity (450 mg g-1), large adsorption rate (rate constant k2 = 1.25 g mg-1 min-1), and good recycling of adsorption capacity toward Hg(II) ions. The excellent adsorption performance resulted from the strong binding interactions between -SH soft basic groups and Hg(II) soft acidic ions.

Development of Soft Ion Gel Based Touch Sensor

Ionic liquids and ion gels have useful properties such as conductivity, non-volatility and thermal stability. The purpose of this research is development of touch sensor composed only of soft material. Silicone rubber layers with micro-channel patterns, were fabricated against 3D printed molds. These silicone rubber layers were bonded to create enclosed micro-channels, and a conductive ionic gel is injected into the micro-channels. Changes in electrical resistance of the ionic gel under strain ( that is on being pressed, bent, twisted and stretched) were measured. Results indicate predictable behavior of the developed sensor.

Soft hydrogen plasma induced phase transition in monolayer and few-layer MoTe2

Phase transition from the semiconducting hexagonal (2H) phase to the metallic monoclinic (1T′) phase in two-dimensional (2D) transition metal dichalcogenides like MoTe2 is not only of great importance in fundamental study but also of technological significance for broad device applications. Here we report a universal, facile, scalable and reversible phase engineering technique (between 2H and 1T′ phases) for both monolayer and few-layer MoTe2 based on a soft hydrogen plasma treatment. The 2H → 1T′ transition was confirmed by a series of characterizations including Raman spectra and mapping studies, XPS analysis and FET device measurements at varying temperatures. We attribute the phase transition to the warping of Te–Mo bonds and the lateral sliding of the top Te-layer induced by the soft hydrogen ion bombardment according to both the structural and electronic characterizations as well as the horizontal comparison with the cases of Ar or O2 plasma treatment. We have also prepared a 2D heterostructure containing periodical 2H and 1T′ MoTe2 and showed that such phase transition can be readily reversed by post annealing. These results thus provide a robust and efficient approach for the phase engineering of monolayer and few-layer MoTe2 and could aid the development of 2D optoelectronic, memory and reconfigurable devices.

Evaluation of effective treatment depth in skin cancer treatments with electronic brachytherapy

PurposeTo evaluate changes in the percent depth dose (PDD) and effective depth of treatment due to force applied by the applicator during treatments of nonmelanoma skin cancer with the Xoft electronic brachytherapy system. MethodsTo simulate compressible tissue, a 5-mm tissue-equivalent bolus was used. A soft x-ray ion chamber was used for output measurements, which were performed for all Xoft surface applicators with plastic endcaps in place. Output was first measured at 5 mm depth with minimal pressure from the applicator on the bolus and then repeated after applying uniform pressure on the applicator to calculate the change in PDD and effective treatment depth. ResultsFor the 10-mm cone, a moderate force of 5 N changed the PDD by more than 20%. The effect was also pronounced for the 20-mm cone, while minimal for the 35- and 50-mm cones. Even when only a moderate force was applied, the effective prescription depth changed by several millimeters, on the order of a typical prescription depth. ConclusionBased on the results of this simulation, excessive pressure applied on the skin by the applicator can drastically alter the PDD and effective treatment depth. The effect is most pronounced for the 10- and 20-mm cones, which tend to be used most frequently. Inappropriate applicator placement may therefore result in significant consequences such as excessive dose to the target, severe skin reaction, permanent discoloration, skin indentation, and poor overall cosmesis upon completion of treatment.

Study of a Superconducting Magnetic Diverter for the ATHENA X-Ray Space Telescope

The advanced telescope for high energy astrophysics (ATHENA) is an X-ray telescope of the European space agency which is planned to be launched in 2028. It will carry out observations in the X-ray band, exploiting two focal plane detectors where X-ray photons will be focused by silicon pore optics. Previous X-ray missions have shown a serious issue with soft protons and ions (below 150 keV/n), which could enter the telescope mirror aperture and be concentrated toward the focal plane. These particles must be blocked or diverted to avoid excess background loading on the detectors. The proposed solution is to deflect protons away from the instruments field of view by means of magnets located between the optics and the focal plane. A 160000 amp-turns HTS superconducting toroidal magnet, composed by three or four round coils located between 0.6 and 1.2 m from the focal plane, can efficiently deflect most of the incoming particles. The rejection rate for protons till 120 keV is better than 99%, to be compared with about 80% of a previously proposed diverter based on permanent magnets. The magnetic field requirement at the detectors level (B <; 1 mT) is widely satisfied, as well as the mass budget of 110 kg. Challenging aspects related to the operation and reliability of the superconducting magnet will be discussed.

Mercury Trithiolate Binding (HgS3) to a de Novo Designed Cyclic Decapeptide with Three Preoriented Cysteine Side Chains.

Mercury(II) is an unphysiological soft ion with high binding affinity for thiolate ligands. Its toxicity lies in the interactions with low molecular weight thiols including glutathione and cysteine-containing proteins that disrupt the thiol balance and alter vital functions. However, mercury can also be detoxified via interactions with Hg(II)-responsive regulatory proteins such as MerR, which coordinates Hg(II) with three cysteine residues in a trigonal planar fashion (HgS3 coordination). The model cyclodecapeptide P3C, c(GCTCSGCSRP) was designed to promote Hg(II) chelation in a HgS3 coordination environment through the parallel orientation of three cysteine side chains. The binding motif is derived from the dicysteine P2C cyclodecapeptide validated previously as a model for d10 metal transporters containing the binding sequence CxxC. The formation of the mononuclear HgP3C complex with a HgS3 coordination is demonstrated using electrospray ionization mass spectrometry, UV absorption, and 199Hg NMR. Hg LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy indicates that the Hg(II) coordination environment is T-shaped with two short Hg-S distances at 2.45 Å and one longer distance at 2.60 Å. The solution structure of the HgP3C complex was refined based on 1H-1H NMR constraints and EXAFS results. The cyclic peptide scaffold has a rectangular shape with the three binding cysteine side chains pointing toward Hg(II). The HgP3CH complex has a p Ka of 4.3, indicating that the HgS3 coordination mode is stable over a large range of pH. This low p Ka value suggests that the preorientation of the three cysteine groups is particularly well-achieved for Hg(II) trithiolate coordination in P3C.

Highlights from LHCb

The recent highlights from LHCb in soft QCD and Heavy Ion physics are presented. This includes measurements from collisions of proton and lead [see formula in PDF] ion beams with other beams as well as noble gas targets. An outlook on future analyses of [see formula in PDF] collisions is presented.

Research Progress on the Effect of Stray Current on Properties of Cement-Based Materials in China

In recent years, more and more attention has been paid to the effect of stray current on the properties of cement-base materials in subway engineering. In the actual service process, reinforced cement-based systems suffer from various erosive conditions, the degradation mechanisms in reinforced cement-based systems due to the combined effects of stray current and environmental multi-factors have been a serious problem in civil engineering for many years. This paper reviews the research achievements on the properties of cement-based materials under the multi-factor coupling conditions such as stray current and soft water, chloride ion, sulfate, stress, freezing and thawing cycle and so on. Furthermore, the improvement of cement-based materials on stray current resistance is also generalized in it. Prospects of cement-based materials for durability under environment multi-factor coupling actions are also presented.

Preliminary assessment of the ATHENA/WFI non-X-ray background

We present a preliminary assessment of the non-X-ray background for the WFI on board ATHENA conducted at IAAT in the context of the collaborative background and radiation damage working group activities. Our main result is that in the baseline configuration originally assumed for the camera the requirement on the level of non-X-ray background could not be met. In light of the results of Geant4 simulations we propose and discuss a possible optimization of the camera design and pinpoint some open issues to be addressed in the next phase of investigation. One of these concerns the possible contribution to the non-X-ray background from soft protons and ions funneled to the focal plane through the optics. This is not quantified at this stage, here we just briefly report on our ongoing activities aimed at validating the mechanisms of proton scattering at grazing incidence.