Neutral Species Research Articles

Longitudinal Extension of Double π-Helix Enables Near-Infrared Amplified Dissymmetry and Chiroptical Response.

Near-infrared (NIR) circularly polarized light absorbing or emitting holds great promise for highly sensitive and precise bioimaging, biosensing, and photodetectors. Aiming at designing NIR chiral molecular systems with amplified dissymmetry and robust chiroptical response, herein, we present a series of double π-helical dimers with longitudinally extended π-entwined substructures via Ullmann or Yamamoto homocoupling reactions. Circular dichroism (CD) spectra revealed an approximate linear bathochromic shift with the rising number of naphthalene subunits, indicating a red to NIR chiroptical response. Particularly, the terrylene diimide-entwined dimers exhibited the strongest CD intensities, with the maximal |Δε| reaching up to 393 M-1 cm-1 at 666 nm for th-TDI[2]; and a record-high chiroptical response (|ΔΔε|) between the neutral and dianionic species of 520 M-1 cm-1 at 833 nm for th-TDI[2]Cl was achieved upon further reduction to its dianionic state. Time-dependent density functional theory (TDDFT) calculations suggested that the pronounced intensification of the CD spectra originated from a simultaneous enhancement of both electric (μ) and magnetic (m) transition dipole moments, ultimately leading to an overall increase in the rotatory strength (R). Notably, the circularly polarized luminescence (CPL) brightness (BCPL) reached 77 M-1 cm-1 for th-TDI[2]Cl, among the highest values reported for NIR-CPL emitters. Furthermore, all chiral dianions exhibited excellent air stability under ambient conditions with half-life times of up to 10 days in N-methylpyrrolidone (NMP), which is significant for future biological applications and chiroptic switches.

Solvation Properties of Neutral Gold Species in Supercritical Water Studied By THz Spectroscopy

Supercritical water provides distinctly different solvation properties compared to what is known from liquid water. Despite its prevalence deep in the Earth’s crust and its role in chemosynthetic ecosystems in the vicinity of hydrothermal vents, molecular insights into its solvation mechanisms are still very scarce compared to what is known for liquid water. Recently, neutral metal particles have been detected in hydrothermal fluids and proposed to explain the transport of gold species to ore deposits on Earth. Using ab initio molecular dynamics, we elucidate the solvation properties of small gold species at supercritical conditions. The neutral metal clusters themselves contribute enormous THz intensity not because of their intramolecular vibrations, but due to their pronounced electronic polarization coupling to the dynamical supercritical solvent, leading to a continuum absorption up to about 1000 cm‐1 . On top, long‐lived interactions between the gold clusters and solvation water leads at these supercritical conditions to a sharp THz resonance that happens to be close to the one due to H‐bonding in liquid water at ambient conditions. The resulting distinct resonances can be used to analyse the solvation properties of neutral metal particles in supercritical aqueous solutions.

Solvation Properties of Neutral Gold Species in Supercritical Water Studied By THz Spectroscopy.

Supercritical water provides distinctly different solvation properties compared to what is known from liquid water. Despite its prevalence deep in the Earth's crust and its role in chemosynthetic ecosystems in the vicinity of hydrothermal vents, molecular insights into its solvation mechanisms are still very scarce compared to what is known for liquid water. Recently, neutral metal particles have been detected in hydrothermal fluids and proposed to explain the transport of gold species to ore deposits on Earth. Using ab initio molecular dynamics, we elucidate the solvation properties of small gold species at supercritical conditions. The neutral metal clusters themselves contribute enormous THz intensity not because of their intramolecular vibrations, but due to their pronounced electronic polarization coupling to the dynamical supercritical solvent, leading to a continuum absorption up to about 1000 cm-1 . On top, long-lived interactions between the gold clusters and solvation water leads at these supercritical conditions to a sharp THz resonance that happens to be close to the one due to H-bonding in liquid water at ambient conditions. The resulting distinct resonances can be used to analyse the solvation properties of neutral metal particles in supercritical aqueous solutions.

Spectrophotometric and DFT study of Germanium(IV) interaction with 6,7-dihydroxy-2,4-diphenyl-1-benzopyran-1-ium bromide in solutions: Room-temperature cloud point extraction and its analytical application

In the current study, a novel and fast procedure for room-temperature cloud point extraction of Germanium (VI) followed by spectrophotometric detection is developed. A 6,7-dihydroxy-2,4-diphenyl-1-benzopyran-1-ium bromide (DPBP) reagent was proposed for binding Ge (IV) into the extractable colored complex. The interaction of Ge (IV) with the reagent DPBP was studied using spectrophotometry and density functional theory (DFT) calculations. It was established that the complex stoichiometry is 1:2. It was shown that with the increase of the charge of the resulting complex, the Gibbs free energy of the complex formation increases considerably. This means that the formation of neutral species with cis- location of the hydroxyl ligands is the most preferable process. The cloud point phenomenon at room temperature was immediately initiated via ammonium benzoate. The calibration plot for Ge (IV) was obtained in the concentration range of 4–490 μg L−1 under optimized conditions: pH = 1, concentration of DPBP 1.8–2∙10-5 mol/L, 0.12 mol/L aqueous ammonium benzoate and 1 % (v/v) Triton X-100). The limit of detection is 1.2 μg L−1. The method was successfully applied to the determination of Ge(IV) traces in vegetable and rock samples.

Building a New Platform for Significantly Improving Performance of Hartree-Fock and CCSD(T) Correlation Energy Based on Two-Point Complete Basis Set Extrapolation Schemes.

The leading cause of high expense in gold standard coupled cluster theory is that calculations of electronic energies converge exceedingly slowly with an increased basis set size. Extrapolation principally allows for achieving higher-quality outcomes at reduced costs. Numerous extrapolation formulas have been developed, with attempts to predict energies up to the complete basis set limit. Unfortunately, since the intricate shape of the function hinges on the molecular properties with the highest angular momentum of the basis set, the accuracy of the extrapolated energies highly depends on the fitted empirical parameters, which rely on the quality of the data sets for fitting. In this work, to overcome the extrapolation deficiency caused by the very limited data sets and smaller basis sets in the early stages, we constructed a new benchmark platform that includes a broader data set of 183 species (containing open-shell, closed-shell, ionic, and neutral species) and a larger basis set up to aug-cc-pV6Z. The newly optimized parameters can significantly improve the energy-predictive abilities of ten published formulas. Notably, all ten formulas perform quite similarly under the new platform with the reoptimized parameters. Finally, we built an online calculator for researchers to use for these extrapolation schemes. Our work would reignite the interest and applications of the underestimated formulas.

Intrinsic rotation modulation by diffusive neutral particles in tokamaks

The modulated transport model, a model kinetic ion transport equation for the pedestal and scrape-off layer (SOL), is generalized to self-consistently include effects of a single neutral particle species. The neutrals contribute additional transport terms, modifying the v∥ -dependent orbit-averaged ion diffusivities of the original work and the resulting predicted intrinsic rotation of the ions. After making simplifying assumptions of the neutral transport, in particular taking the continuous transport limit via a short charge-exchange step expansion, we derive relatively simple analytic expressions that capture the diffusive neutral physics. Within the scope of the model’s validity, the neutral-driven intrinsic rotation can compete with the turbulence-driven intrinsic rotation. However, for physically motivated parameters, the neutral-driven intrinsic rotation appears negligible, either on a term-by-term basis or due to a strong cancellation between the neutral-driven momentum diffusion and pinch terms. It appears that a treatment containing finite charge-exchange steps is necessary to capture neutral transport of strong flow momentum into the confined region from the SOL.

Kelvin-Helmholtz-induced mixing in multi-fluid partially ionized plasmas.

Turbulence is a fundamental process that drives mixing and energy redistribution across a wide range of astrophysical systems. For warm ([Formula: see text]) plasma, the material is partially ionized, consisting of both ionized and neutral species. The interactions between ionized and neutral species are thought to play a key role in heating (or cooling) of partially ionized plasmas. Here, mixing is studied in a two-fluid partially ionized plasma undergoing the shear-driven Kelvin-Helmholtz instability to evaluate the thermal processes within the mixing layer. Two-dimensional numerical simulations are performed using the open-source (PIP) code that solves for a two-fluid plasma consisting of a charge-neutral plasma and multiple excited states of neutral hydrogen. Both collisional and radiative ionization and recombination are included. In the mixing layer, a complex array of ionization and recombination processes occur as the cooler layer joins the hotter layer, and vice versa. In localized areas of the mixing layer, the temperature exceeds the initial temperatures of either layer with heating dominated by collisional recombinations over turbulent dissipation. The mixing layer is in approximate ionization-recombination equilibrium, however the obtained equilibrium is different to the Saha-Boltzmann local thermal equilibrium. The dynamic mixing processes may be important in determining the ionization states, and with that intensities of spectral lines, of observed mixing layers. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'.

On the ambipolar diffusion formulation for ion-neutral drifts in the non-negligible drift velocity limit.

The ambipolar diffusion approximation is used to model partially ionized plasma dynamics in a single-fluid setting. To correctly apply the commonly used version of ambipolar diffusion, a set of criteria should be satisfied including the requirement that the difference in velocity between charges and neutral species (known as drift velocity) is much smaller than the thermal velocity, otherwise the drift velocity will drive a non-negligible level of further collisions between the two species. In this paper, we explore the consequences of relaxing this assumption. We show that a new induction equation can be formulated without this assumption. This formulation reduces to the ambipolar induction equation in the case the drift velocity is small. In the large drift velocity limit, the feedback of the drift velocity on the collision frequency results in decreased diffusion of the magnetic field compared with the standard ambipolar diffusion approximation for the same parameters. This has a natural consequence of reducing the frictional heating that can occur. Applying this to results from flux emergence simulations where the expansion of the magnetic field leads to strong adiabatic cooling of the partially ionized chromosphere resulted in a noticeable reduction in the magnitude of the predicted drift velocities. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'.

The Mechanism of Rh(I)-Catalyzed Coupling of Benzotriazoles and Allenes Revisited: Substrate Inhibition, Proton Shuttling, and the Role of Cationic vs Neutral Species.

Direct coupling of benzotriazole to unsaturated substrates such as allenes represents an atom-efficient method for the construction of biologically and pharmaceutically interesting functional structures. In this work, the mechanism of the N2-selective Rh complex-catalyzed coupling of benzotriazoles to allenes was investigated in depth using a combination of experimental and theoretical techniques. Substrate coordination, inhibition, and catalyst deactivation was probed in reactions of the neutral and cationic catalyst precursors [Rh(μ-Cl)(DPEPhos)]2 and [Rh(DPEPhos)(MeOH)2]+ with benzotriazole and allene, giving coordination, or coupling of the substrates. Formation of a rhodacycle, formed by unprecedented 1,2-coupling of allenes, is responsible for catalyst deactivation. Experimental and computational data suggest that cationic species, formed either by abstraction of the chloride ligand or used directly, are relevant for catalysis. Isomerization of benzotriazole and cleavage of its N-H bond are suggested to occur by counteranion-assisted proton shuttling. This contrasts with a previously proposed scenario in which oxidative N-H addition at Rh is one of the key steps. Based on the mechanistic analysis, the catalytic coupling reaction could be optimized, leading to lower reaction temperature and shorter reaction times compared to the literature.

Hydrogen Bonds Are Never of an "Anti-electrostatic" Nature: A Brief Tour of a Misleading Nomenclature.

A large amount of scientific works have contributed through the years to rigorously reflect the different forces leading to the formation of hydrogen bonds, the electrostatic and polarization ones being the most important among them. However, we have witnessed lately with the emergence of a new terminology, anti-electrostatic hydrogen bonds (AEHBs), that seems to contradict this reality. This nomenclature is used in the literature to describe hydrogen bonds between equally charged systems to justify the existence of these species, despite numerous proofs showing that AEHBs are, as any other hydrogen bond between neutral species, mostly due to electrostatic forces. In this Viewpoint, we summarize the state of the art regarding this issue, try to explain why this terminology is very misleading, and strongly recommend avoiding its use based on the hydrogen bond physical grounds.

[N−I−N] Type Halogen Bonding: Structure, Synthesis and Applications

AbstractHalogen bond has received widespread attention in recent years due to the vast applications in supramolecular chemistry, sensing and crystal engineering. In contrast to the normal halogen bonds, [N−I−N] type halogen bond exhibits enhanced strength and solvent resistance capabilities. It adopts a bonding geometry of the three‐center four‐electron bond, where the nitrogen can be a neutral, positive, or negative species such as pyridine, saccharin, and urotropine moieties. The emerging new type halogen bond has found specific potentials in constructing supramolecular architectures and catalysis. This concept provides a brief summary based on recent developments of [N−I−N] type halogen bonding, reviewing and summarizing its synthesis, structure and application.

Glutamate Leaching of Spent Lithium-Ion Battery Cathode in Weak Acidic-Neutral Condition: New Insight on Kinetics and Dissolution Mechanism

ABSTRACT Organic acid leaching receives less attention than inorganic acids for Li-ion battery recycling process at the industrial scale due to the high consumption rate of the acids as leaching reagents. This paper reports an effective leaching of cobalt (Co) and lithium (Li) from spent battery cathode using low concentration of monosodium glutamate as lixiviants. More than 95% of Co and Li could be dissolved at leaching conditions MSG 0.1 M (18 g/L), pH 5, sodium sulfite 0.5 M as reductant, pulp density 20 g/L, room temperature and leaching time 6 h. Increasing the temperature to 80°C sped up the leaching process, where maximum recovery could be attained within 1 h. pH played a major role in the leaching efficiency (effective range pH 4–6). pH lower than 4 led to neutral and cationic glutamate species, which were ineffective in attracting cobalt ion. pH higher than 6 initiated the surface passivation by Co(OH)2. In the absence of a passivation layer, cobalt dissolution mechanism followed the chemical reaction-controlled model, while in the presence of the layer, the mechanism switched to diffusion through product layer. Kinetic studies demonstrated that aside from pH, the formation of passivation layer was hypothetically regulated by adjusting the other leaching parameters. Aside from the observation on kinetic study, the proposed leaching mechanism was supported by characterization (particle size analysis, SEM-EDS, FT-IR) results.

Remote inductively coupled plasmas in Ar/N2 mixtures and implications for plasma enhanced ALD

Plasma enhanced atomic layer deposition (PEALD) is a cyclic atomic layer deposition (ALD) process that incorporates plasma-generated species into one of the cycle substeps. The addition of plasma is advantageous as it generally provides unique reactants and a substantially reduced growth temperature compared to thermal approaches. However, the inclusion of plasma, coupled with the increasing variety of plasma sources used in PEALD, can make these systems challenging to understand and control. This work focuses on the use of plasma diagnostics to examine the plasma characteristics of a remote inductively coupled plasma (ICP) source, a type of plasma source that is commonly used for PEALD. Ultraviolet to near-infrared spectroscopy and spatially resolved Langmuir probe measurements are employed to characterize a remote ICP system using nitrogen-based gas chemistries typical for III-nitride growth processes. Spectroscopy is used to characterize the relative concentrations of important reactive and energetic neutral species generated in the remote ICP as a function of gas flow rate, Ar/N2 flow fraction, and gas pressure. In addition, the plasma potential and plasma density for the same process parameters are examined using an RF compensated Langmuir probe downstream from the ICP source. The results are also discussed in terms of their impact on materials growth.

Molecular Logic Gates Based on Ferrocene-Containing Compounds

Ferrocene has a unique structure, i.e., a central iron atom neatly sandwiched between two cyclopentadienyl rings, which has revolutionized the chemists’ views about how metals bind to organic π-systems. This structural arrangement leads to some fascinating chemical and photophysical properties. The last three decades, there were reports about receptor molecules that could be considered to perform simple logic operations via coupling ionic bonding or more complex molecular-recognition processes with photonic (fluorescence) signals. In these systems, chemical binding (‘input’) results in a change in fluorescence intensity (‘output’) from the receptor. It has been proven that molecules respond to changes in their environment, such as the presence of various ions, neutral species, pHs, temperatures, and viscosities. Since their first realization by de Silva, molecular logic gates have been intensively experimentally studied, with purely theoretical studies being less common. Here, we present the research that has been conducted on Molecular Logic Gates (MLGs) containing ferrocene and their applications. We categorized such systems into three families of MLGs: long-chain molecules (oligomers or polymers) that incorporate ferrocene, medium-sized molecules that incorporate ferrocene, and systems where ferrocene or its derivatives are used as external additives. Furthermore, MLGs including metal cations without the ferrocene moiety are briefly presented, while computational methodologies for an accurate theoretical study of MLG, including metal cations, are suggested. Finally, future perspectives of MLGs containing ferrocene and their applications are also presented.

Enhancing Energy Storage Capacity of 3D Carbon Electrodes Using Soft Landing of Molecular Redox Mediators.

The incorporation of redox-active species into the electric double layer is a powerful strategy for enhancing the energy density of supercapacitors. Polyoxometalates (POM) are a class of stable, redox-active species with multielectron activity, which is often used to tailor the properties of electrochemical interfaces. Traditional synthetic methods often result in interfaces containing a mixture of POM anions, unreactive counter ions, and neutral species. This leads to degradation in electrochemical performance due to aggregation and increased interfacial resistance. Another significant challenge is achieving the uniform and stable anchoring of POM anions on substrates to ensure the long-term stability of the electrochemical interface. These challenges are addressed by developing a mass spectrometry-based subambient deposition strategy for the selective deposition of POM anions onto engineered 3D porous carbon electrodes. Furthermore, positively charged functional groups are introducedon the electrode surface for efficient trapping of POM anions. This approach enables the deposition of purified POM anions uniformly through the pores of the 3D porous carbon electrode, resulting in unprecedented increase in the energy storage capacity of the electrodes. The study highlights the critical role of well-defined electrochemical interfaces in energy storage applications and offers a powerful method to achieve this through selective ion deposition.

Influence of salinity gradients on the diffusion of water and ionic species in dual porosity clay samples

Most of the available data on diffusion in natural clayey rocks consider tracer diffusion in the absence of a salinity gradient despite the fact that such gradients are frequently found in natural and engineered subsurface environments. To assess the role of such gradients on the diffusion properties of clayey materials, through-diffusion experiments were carried out in the presence and absence of a salinity gradient using salt-diffusion and radioisotope tracer techniques. The experiments were carried out with vermiculite samples that contained equal proportions of interparticle and interlayer porosities so as to assess also the role played by the two types of porosities on the diffusion of water and ions. Data were interpreted using both a classical Fickian diffusion model and with a reactive transport code, CrunchClay that can handle multi-porosity diffusion processes in the presence of charged surfaces. By combining experimental and simulated data, we demonstrated that (i) the flux of water diffusing through vermiculite interlayer porosity was minor compared to that diffusing through the interparticle porosity, and (ii) a model considering at least three types of porous volumes (interlayer, diffuse layer interparticle, and bulk interparticle) was necessary to reproduce consistently the variations of neutral and charged species diffusion as a function of salinity gradient conditions.

Investigation of O atom kinetics in O2 plasma and its afterglow

We have developed a comprehensive kinetic model to study the O atom kinetics in an O2 plasma and its afterglow. By adopting a pseudo-1D plug-flow formalism within the kinetic model, our aim is to assess how far the O atoms travel in the plasma afterglow, evaluating its potential as a source of O atoms for post-plasma gas conversion applications. Since we could not find experimental data for pure O2 plasma at atmospheric pressure, we first validated our model at low pressure (1–10 Torr) where very good experimental data are available. Good agreement between our model and experiments was achieved for the reduced electric field, gas temperature and the densities of the dominant neutral species, i.e. O2(a), O2(b) and O. Subsequently, we confirmed that the chemistry set is consistent with thermodynamic equilibrium calculations at atmospheric pressure. Finally, we investigated the O atom densities in the O2 plasma and its afterglow, for which we considered a microwave O2 plasma torch, operating at a pressure between 0.1 and 1 atm, for a flow rate of 20 slm and an specific energy input of 1656 kJ mol−1. Our results show that for both pressure conditions, a high dissociation degree of ca. 92% is reached within the discharge. However, the O atoms travel much further in the plasma afterglow for p = 0.1 atm (9.7 cm) than for p = 1 atm (1.4 cm), attributed to the longer lifetime (3.8 ms at 0.1 atm vs 1.8 ms at 1 atm) resulting from slower three-body recombination kinetics, as well as a higher volumetric flow rate.

Modeling of ion transport from ionization region to entrance of mass spectrometer in HiPIMS argon/Cr target

Plasma global kinetic model coupled with the Monte Carlo method is used to study the ion transport in HiPIMS Ar/Cr target. The plasma kinetic global model is developed to study the time evolution of neutral, ion, and electron species created in the ionization region. To analyze the ion temporal spectra at the entrance of the mass spectrometer, a simple model based on the Monte Carlo technique is developed to track the ion trajectories from the ionization region to the mass spectrometer. The ion temporal spectra obtained by the global kinetic model in the ionization region are introduced in the Monte Carlo model as input data. The simulation results reveal a temporal shift of the ion spectra as well as their spreading in comparison with those obtained in the ionization region. Such temporal shapes of the ion spectra are more sensitive to the ion temperatures in the ionization region, and the position of the mass spectrometer is connected to the reactor. A satisfactory agreement between simulated ion temporal spectra and those measured by the mass spectrometer is obtained when we have represented the ion population energies by two Maxwellian distributions, where the first one corresponds to the low temperature and the second to the high temperature.

Ionic Route to Atmospheric Relevant HO2 and Protonated Formaldehyde from Methanol Cation and O2.

Gas-phase ion chemistry influences atmospheric processes, particularly in the formation of cloud condensation nuclei by producing ionic and neutral species in the upper troposphere-stratosphere region impacted by cosmic rays. This work investigates an exothermic ionic route to the formation of hydroperoxyl radical (HO2) and protonated formaldehyde from methanol radical cation and molecular oxygen. Methanol, a key atmospheric component, contributes to global emissions and participates in various chemical reactions affecting atmospheric composition. The two reactant species are of fundamental interest due to their role in atmospheric photochemical reactions, and HO2 is also notable for its production during lightning events. Our experimental investigations using synchrotron radiation reveal a fast hydrogen transfer from the methyl group of methanol to oxygen, leading to the formation of CH2OH+ and HO2. Computational analysis corroborates the experimental findings, elucidating the reaction dynamics and hydrogen transfer pathway. The rate coefficients are obtained from experimental data and shows that this reaction is fast and governed by capture theory. Our study contributes to a deeper understanding of atmospheric processes and highlights the role of ion-driven reactions in atmospheric chemistry.

Observation of Solvent-Dependence in the Mechanism of Neutral-Catalyzed Isomerization of para-Aminobenzoic Acid Protomers.

Proton-transfer reactions are commonplace during electrospray ionization (ESI) mass spectrometry experiments and are often responsible for imparting charge to analyte molecules. Multiple protonation-site isomers (protomers) can arise for polyfunctional molecules and these isomers can interconvert via solvent-mediated proton transfer reactions during various stages of the ESI process. Studying the populations and interconversion of protonation isomers provides key insight into the ESI process, ion-molecule interactions, and ion dissociation mechanisms. An archetype molecule to study protomer interconversion fundamentals in this context is para-aminobenzoic acid (pABA), where both the amino and carboxylic acid protomers are typically formed under ESI and the mechanisms for interconversion are still under refinement. Using ion-trap mass spectrometry reaction kinetics (2.5 mTorr, 300 K), this study examines gas-phase interconversion catalysis of pABA protomers by seven neutral species, which are commen solvents and additives used for ESI: water, formic acid, methanol, ethanol, propanol, ammonia, and acetonitrile. Three distinct reaction cases are reported: (i) formic acid, methanol, ethanol, propanol, and ammonia each catalyze the interconversion between the amino and carboxylic acid protomers via a n = 1 solvent-molecule vehicle mechanism; (ii) for water, however, a n = 6 adduct complex is detected and this suggests that the observed protomer interconversion occurs through a Grotthuss mechanism, in accord with literature reports; (iii) acetonitrile inhibits proton transfer by the formation of particularly stable n = 1 and 2 adduct complexes. The second-order rate constants for the protomer interconversion are observed to increase in the following order: H2O < HCO2H < MeOH < EtOH < PrOH < NH3. Potential energy schemes are reported for all neutral-catalyzed proton transfer reactions using the DSD-PBEP86-D3(BJ)/aug-cc-pVDZ level of theory. A central transition state, which connects the protonation site adducts, is shown to be the key rate-limiting step. The energy of this transition state is sensitive to the proton affinity of the neutral solvent, and this is supported by the correlation between the reaction rate and the solvent proton affinity.