Molecular Cations Research Articles

Polarizability Plays a Decisive Role in Modulating Association between Molecular Cations and Anions.

Electrostatic interactions involving proteins depend on not only the ionic charges involved but also their chemical identities. Here we examine the origins of incompletely understood differences in the strength of association of different pairs of monovalent molecular ions that are relevant to protein-protein and protein-ligand interactions. Cationic analogues of the basic amino acid side chains are simulated, along with oxyanionic analogues of cation-exchange ligands and acidic amino acids. Experimentally observed association trends with respect to the cations, but not anions, are captured by a nonpolarizable model. An effective continuum correction to account for electronic polarizability can capture both trends better but at the expense of fidelity to the underlying free energy landscape for ion-pair association. A polarizable model proves decisive in capturing experimentally suggested trends with respect to both cations and anions; critically, the free energy landscape for ion-pair association is itself altered, thus altering configurational sampling.

Molecular Architecture Effects on Bulk Nanostructure in Bis(Orthoborate) Ionic Liquids.

A series of 19 ionic liquids (ILs) based on phosphonium and imidazolium cations of varying alkyl-chain lengths with the orthoborate anions bis(oxalato)borate [BOB]- , bis(mandelato)borate, [BMB]- and bis(salicylato)borate, [BScB]- , are synthesized and studied using small-angle neutron scattering (SANS). All measured systems display nanostructuring, with 1-methyl-3-n-alkyl imidazolium-orthoborates forming clearly bicontinuous L3 spongelike phases when the alkyl chains are longer than C6 (hexyl). L3 phases are fitted using the Teubner and Strey model, and diffusely-nanostructured systems are primarily fitted using the Ornstein-Zernicke correlation length model. Strongly-nanostructured systems have a strong dependence on the cation, with molecular architecture variation explored to determine the driving forces for self-assembly. The ability to form well-defined complex phases is effectively extinguished in several ways: methylation of the most acidic imidazolium ring proton, replacing the imidazolium 3-methyl group with a longer hydrocarbon chain, substitution of [BOB]- by [BMB]- , or exchanging the imidazolium for phosphonium systems, irrespective of phosphonium architecture. The results suggest there is only a small window of opportunity, in terms of molecular amphiphilicity and cation:anion volume matching, for the formation of stable extensive bicontinuous domains in pure bulk orthoborate-based ILs. Particularly important for self-assembly processes appear to be the ability to form H-bonding networks, which offer additional versatility in imidazolium systems.

Diffusiophoresis of latex driven by anionic nanoparticles and their counterions

HypothesisDiffusiophoresis of colloidal latex particles has been reported for molecular anions and cations of comparable size. In the present study, this phenomenon is observed for two types of charged colloids acting as multivalent electrolyte: (i) anionic charge-stabilised silica nanoparticles or (ii) minimally-charged sterically-stabilised diblock copolymer nanoparticles. ExperimentsUsing a Hele-Shaw cell, a thin layer of relatively large latex particles is established within a sharp concentration gradient of nanoparticles by sequential filling with water, latex particles and nanoparticles. Asymmetric diffusion is observed, which provides strong evidence for diffusiophoresis. Quantification involves turbidity measurements from backlit images. FindingsThe latex particles diffuse across a concentration gradient of charged nanoparticles and the latex concentration front scales approximately with time1/2. Moreover, the latex particle flux is inversely proportional to the concentration of background salt, confirming electrostatically-driven motion. These observations are consistent with theory recently developed to account for diffusiophoretic motion driven by multivalent ions.

Zwitterions Functionalized by Optical Cycling Centers: Toward Laser-Coolable Polyatomic Molecular Cations.

Functionalization of large aromatic compounds and biomolecules with optical cycling centers (OCC) is of considerable interest for the design and engineering of molecules with a highly selective optical photoresponse. Both internal and external dynamics in such molecules can be precisely controlled by lasers, enabling their efficient cooling and opening up broad prospects for high-precision spectroscopy, ultracold chemistry, enantiomer separation, and various other fields. The way the OCC is bonded to a molecular ligand is crucial to the optical properties of the OCC, first of all, for the degree of closure of the optical cycling loop. Here we introduce a novel type of functionalized molecular cation where a positively charged OCC is bonded to various organic zwitterions with a particularly high permanent dipole moment. We consider strontium(I) complexes with betaine and other zwitterionic ligands and show the possibility of creating efficient and highly closed population cycling for dipole-allowed optical transitions in such complexes.

Local cation-tuned reversible single-molecule switch in electric double layer

The nature of molecule-electrode interface is critical for the integration of atomically precise molecules as functional components into circuits. Herein, we demonstrate that the electric field localized metal cations in outer Helmholtz plane can modulate interfacial Au-carboxyl contacts, realizing a reversible single-molecule switch. STM break junction and I-V measurements show the electrochemical gating of aliphatic and aromatic carboxylic acids have a conductance ON/OFF behavior in electrolyte solution containing metal cations (i.e., Na+, K+, Mg2+ and Ca2+), compared to almost no change in conductance without metal cations. In situ Raman spectra reveal strong molecular carboxyl-metal cation coordination at the negatively charged electrode surface, hindering the formation of molecular junctions for electron tunnelling. This work validates the critical role of localized cations in the electric double layer to regulate electron transport at the single-molecule level.

Using pressure to unravel the structure–dynamic-disorder relationship in metal halide perovskites

The exceptional optoelectronic properties of metal halide perovskites (MHPs) are presumed to arise, at least in part, from the peculiar interplay between the inorganic metal-halide sublattice and the atomic or molecular cations enclosed in the cage voids. The latter can exhibit a roto-translative dynamics, which is shown here to be at the origin of the structural behavior of MHPs as a function of temperature, pressure and composition. The application of high hydrostatic pressure allows for unraveling the nature of the interaction between both sublattices, characterized by the simultaneous action of hydrogen bonding and steric hindrance. In particular, we find that under the conditions of unleashed cation dynamics, the key factor that determines the structural stability of MHPs is the repulsive steric interaction rather than hydrogen bonding. Taking as example the results from pressure and temperature-dependent photoluminescence and Raman experiments on MAPbBr_3 but also considering the pertinent MHP literature, we provide a general picture about the relationship between the crystal structure and the presence or absence of cationic dynamic disorder. The reason for the structural sequences observed in MHPs with increasing temperature, pressure, A-site cation size or decreasing halide ionic radius is found principally in the strengthening of the dynamic steric interaction with the increase of the dynamic disorder. In this way, we have deepened our fundamental understanding of MHPs; knowledge that could be coined to improve performance in future optoelectronic devices based on this promising class of semiconductors.

Occurrence, Identification and Preliminary Biological Control of Bulb Rot of Onion (Allium cepa)

Onion bulb rot was observed in low-temperature warehouses in Mae Wang District, Chiang Mai, Thailand in 2022. The pathogens were isolated and identifi ed as Pantoea agglomerans and Burkholderia gladioli based on morphological and biochemical characterization, pathogenicity tests, and 16S rRNA gene sequences. Biological control is regarded as a safer and more sustainable strategy than chemical control and has elicited great attention for disease control. Bacillus sp. isolate BB22 was isolated from rhizosphere soil and was evaluated for its preliminary potential to inhibit the growth of onion bulb rot bacterial pathogens by the dual culture technique. The results showed inhibition zones of P. agglomerans of 30.1 mm and B. gladioli of 13.0 mm. Molecular identifi cation of Bacillus sp. isolate BB22 was performed by using 16S rRNA and gyrA gene sequences and confi rmed as Bacillus velezensis. PCR amplifi cation of the bmyB, fenD, ituA, and srfAA genes coding for bacillomycin, fengycin D, iturin A, and surfactin, respectively, showed the potential for the production of these antibiotics. This study revealed the potential application of B. velezensis as a biocontrol agent against bulb rot-causing bacterial pathogens of onions.

Charge-Transfer Spectroscopy of Ag+(Benzene) and Ag+(Toluene).

Gas-phase ion-molecule complexes of silver cation with benzene or toluene are produced via laser vaporization in a pulsed supersonic expansion. These ions are mass-selected and photodissociated with tunable UV-visible lasers. In both cases, photodissociation produces the organic cation as the only fragment via a metal-to-ligand charge-transfer process. The wavelength dependence of the photodissociation produces electronic spectra of the charge-transfer process. Broad structureless spectra result from excitation to the repulsive wall of the charge-transfer excited states. Additional transitions are detected correlating to the forbidden 1S → 1D silver cation-based atomic resonance and to the HOMO-LUMO excitation on the benzene or toluene ligand. Transitions to these states produce the same molecular cation photofragments produced in the charge-transfer transitions, indicating an unanticipated excited-state curve-crossing mechanism. Spectra measured for these ions are compared to those for ions tagged with argon atoms. The presence of argon causes a significant shift on the energetic positions of these electronic transitions for both Ag+(benzene) and Ag+(toluene).

Evaluation of Molecular Fragmentation in Polycyclic Aromatic Hydrocarbons by Time-of-Flight Secondary Ion Mass Spectrometry

In time-of-flight secondary ion mass spectrometry (TOF-SIMS), ionized molecules and molecular fragments (secondary ions) are generated in collisions of high-energy ions (primary ions) with a solid sample surface. Mass spectra of the emitted secondary ions are typically used to identify molecular species and to determine their spatial distribution on the sample surface. Here, we extend this application in a TOF-SIMS study of a series of polycyclic aromatic hydrocarbons (PAHs) where we focus on the fragmentation of these molecules, with the purpose of better understanding the fragmentation patterns of heavy aromatic molecules in petroleum. For all PAHs, the collision process generated (i) a series of smaller cation fragments and (ii) cations close in size to the original PAH (molecular cations). Stark differences are measured for various PAHs regarding the abundance of smaller fragments versus molecular cations. Observation of hydrogen-deficient (H-deficient) cation fragments indicates the formation of polyynes and allenes. For PAHs producing higher fractions of small cation fragments, these ions are surprisingly hydrogen rich (H-rich). The H/C ratio of fragments does not scale with the fraction of Clar sextet carbon, nor with energies of low-lying electronic transitions. Free radical cation fragments tend to be suppressed. For sufficiently large fragments, aromatic cations appear to be formed and include some free radical aromatics. There is ample production of molecular ions with loss of a single carbon atom or a methine group, which corresponds to the reduction of a 6-membered aromatic ring to a 5-membered ring. There is some enhancement of free radical molecular cations due to the corresponding formation of neutral polyynes. Fragment anions are also produced with a strong preference for very H-deficient carbon clusters, in some cases being the same as carbon cluster anions observed in space. Comparisons of PAH TOF-SIMS spectra with those of asphaltenes are discussed in detail.

Structure stabilized with robust molecular cation N(CH3)4+ in high efficiency perovskite solar cells

Polarity and acid–base equilibrium of the A-site ions in organic-inorganic hybrid perovskites are the major origins of structure instability that limits the efficiency of perovskite solar cells (PSCs). It is effective to stabilize the structure of perovskite by partial replacement of A-site ions with larger radius and non-polar ions. Here, we fabricate tetramethylammonium ions N(CH3)4+ (TMA+) substituting perovskite, MA1-xTMAxPbI3, by partially replacing MA+ in MAPbI3 with large and rigid TMA+. Theoretical and experimental study demonstrates that the introduction of TMA+ cation in MA1-xTMAxPbI3 perovskite leads to a more stable crystal structure and reduces the defects state density in perovskite films. The PSCs based on MA1-xTMAxPbI3 (x = 0.15) films demonstrate a champion efficiency of 22.23% and an improved stability against air environment. This work highlights the significance of A-site ionic characteristics of perovskite structure and provides a new strategy in constructing high efficiency and stable hybrid PSCs.

Attosecond photoionization delays in the vicinity of molecular Feshbach resonances

Temporal delays extracted from photoionization phases are currently determined with attosecond resolution by using interferometric methods. Such methods require special care when photoionization occurs near Feshbach resonances due to the interference between direct ionization and autoionization. Although theory can accurately handle these interferences in atoms, in molecules, it has to face an additional, so far insurmountable problem: Autoionization is slow, and nuclei move substantially while it happens, i.e., electronic and nuclear motions are coupled. Here, we present a theoretical framework to account for this effect and apply it to evaluate time-resolved and vibrationally resolved photoelectron spectra and photoionization phases of N2 irradiated by a combination of an extreme ultraviolet (XUV) attosecond pulse train and an infrared pulse. We show that Feshbach resonances lead to unusual non-Franck-Condon vibrational progressions and to ionization phases that strongly vary with photoelectron energy irrespective of the vibrational state of the remaining molecular cation.

Ultrahigh energy density solid state supercapacitor based on metal halide perovskite nanocrystal electrodes: Real-life applications

Inorganic lead halide perovskite nanocrystals have now become an emerging material for modern nanodevice applications. But, the huge toxicity of lead to the ecosystem has limited its applications in modern technology. In this view, a large organic cation-based metal halide perovskite may be considered the most efficient supercapacitor electrode material. Here, a new type and high molecular organic cations based low-dimensional metal halide perovskite (LDMHP) nanocrystals (NCs) are synthesized by a chemical process and their performances as supercapacitor electrode is tested. An excellent charge storage capacity and especially the Tin (Sn)-based perovskite NCs showed a very high specific capacitance and energy density of ~1536 Fg−1 and ~213 Whkg−1 at a current density of 2.0 Ag−1, respectively. The calculated variable parameter (b) value from cyclic voltammetry showed that the total capacity of the Sn-based perovskite NCs electrode is controlled by capacitor-like behaviour. The Sn NCs also found to have a very high DC dielectric constant at room temperature, possibly responsible for their superior supercapacitor performance. A solid-state supercapacitor based on synthesized NCs was used for real-life applications of supplying sufficient power to light emitting diodes (LEDs) for a long time.

Electron-Impact Excitation and Dissociation of Heavy Rare Gas Heteronuclear Ions via Transitions to Charge Transfer States

Heteronuclear diatomic rare gas molecular cations feature excited electronic terms with charge transfer character located several eV above the ground term. The role of such terms in collisions involving heteronuclear ions is studied theoretically under conditions typical of the plasma-based sources of UV and IR radiation. Calculations were carried out for processes of dissociative excitation, dissociative recombination and electron impact bound–bound excitation in Ar/Xe and Kr/Xe plasmas using the recently developed semiclassical approach combined with the ab initio data for potential energy curves and oscillator strengths of electronic transitions. The approach consistently describes the contributions from the entire rovibrational manifold to the processes studied. The cross sections of the processes mentioned are calculated for wide ranges of gas temperatures and electron energies. We show that the processes considered are quite effective when they are accompanied by transitions to charge transfer terms. For the range of electron energies typical of active media of UV and IR radiation sources the cross sections exceed those reported for the processes usually considered to involve transitions between the ground and first excited electronic state. The excitation of charge transfer electronic terms can play an important role in the kinetics of rare gas mixture plasmas.

Electronic and Topological Properties of UIO66-ILs Interaction through a Computational Study

A high surface area adsorbent, such as MOFs, is an attractive option to evacuate heavy metals from wastewater. However, due to the possibility of the MOF structure collapsing when exposed to water, the stability and selectivity of MOFs for wastewater treatment remain a debatable task. Depending on the application, it has been shown that the consolidation of IL into MOF could improve the stability and reusability of pure MOF; nevertheless, research on the molecular interactions between the MOF framework and IL is still lacking. The stability, compatibility, and selectivity of this hybrid material are significantly influenced by the fundamental interactions between the MOFs and ILs moieties (cation and anion molecules), particularly the sorts of interactions. In this work, we focused on the topological properties of ILs and utilization of molecular docking calculations to assess the binding energy (ΔGbind) and binding affinity between UIO66 with TFSI-imidazole and TFSI-pyridinium ILs studied. The properties of ILs such as aromaticity of the structures, bond critical point (BCP), and electrostatic potential map surface were carried out using the Gaussian and Multiwfn software while the binding energies were computed using the AutoDock software to identify particular binding sites for IL toward MOF. The Autodock software's default setting was used to prepare all of the structures. To determine the binding locations of MOF, the IL was successively incorporated into the MOF pores inside the grid box of 90 x 90 x 90 Å (x, y, and z) dimensions. The results showed that both ILs; TFSI-imidazole, and TFSI-pyridinium IL, interacted favorably with the MOFs, having binding energies varying from -4.12 to -8.60 kcal mol-1. The stability of UIO66-ILs system increases with the addition of anion and cation. According to docking molecular structures, both cation and anion tend to bind in the corner of the MOF pore, which is in line with the previous work.

Solid‐State Confinement Effects in Selective exo‐H/D Exchange in the Rhodium σ‐Norbornane Complex [(Cy2PCH2CH2PCy2)Rh(η2:η2‐C7H12)][BArF4

AbstractDensity functional theory calculations modelling selective exo‐H/D exchange observed in the Rh σ‐alkane complex [(Cy2PCH2CH2PCy2)Rh(η2:η2‐endo‐NBA)][BArF4], [1‐NBA][BArF4], are reported, where ArF=3,5‐C6H3(CF3)2 and NBA=norbornane, C7H12. Two models were considered 1) an isolated molecular cation, [1‐NBA]+ and 2) a full model in which [1‐NBA][BArF4] is treated in the solid state through periodic DFT. After an initial endo‐exo rearrangement, both models predict H/D exchange to proceed through D2 addition and oxidative cleavage followed by a rate‐limiting C−H activation of the norbornane through a σ‐CAM step to form a [1‐Rh(D)(η2‐HD)(norbornyl)]+ intermediate. HD rotation followed by a σ‐CAM C−D bond formation, HD reductive coupling and HD loss then complete the H/D exchange process. exo‐H/D exchange is facilitated by a supporting agostic interaction and is consistently more accessible kinetically than the potentially competing endo‐H/D exchange (isolated cation: ΔG≠exo=+15.9 kcal/mol, ΔG≠endo=+18.4 kcal/mol; solid state: ΔG≠exo=+22.1 kcal/mol, ΔG≠endo=+25.1 kcal/mol). The solid‐state environment has a significant impact on the computed energetics, with barriers increasing by ca. 7 kcal/mol, while only the solid‐state model correctly predicts the endo‐bound NBA complex to be the resting state of the system. These outcomes reflect solid‐state confinement effects within the pocket occupied by the [1‐NBA]+ cation and defined by the pseudo‐octahedral array of neighbouring [BArF4]− anions. The asymmetry of the solid‐state environment also requires a second H/D exchange pathway to be defined to account for reaction at all four exo‐C−H bonds. These entail slightly higher barriers (ΔG≠exo=+24.8 kcal/mol, ΔG≠endo=+27.5 kcal/mol) but retain a distinct preference for exo‐ over endo‐H/D exchange.

3-Chloro-N,N-di-methyl-propan-1-aminium chloride.

The organic cation in the title mol-ecular salt, C5H13NCl+·Cl-, exhibits the gauche effect with a C-H bond of the C atom β to the chloro group donating electrons to the anti-bonding orbital of the C-Cl bond to stabilize the gauche conformation [Cl-C-C-C = -68.6 (6)°], as confirmed by DFT geometry optimizations that show a lengthening of the C-Cl bond relative to that of the anti conformation. Of further inter-est is the higher point group symmetry of the crystal (), compared that of the that of the mol-ecular cation, which arises from a supra-molecular head-to-tail square arrangement of four mol-ecular cations that circulate in a counterclockwise direction when viewed down the tetra-gonal c axis.

High-order harmonic generation by aligned homonuclear diatomic cations.

We introduce the theory of high-order harmonic generation by aligned homonuclear diatomic cations using a strong-field approximation. The target cation is represented as a system which consists of two atomic (ionic) centres and one active electron, while the driving field is either a monochromatic or bichromatic field. For a linearly polarised driving field, we investigate the differences between the harmonic spectra obtained with a neutral molecule and the corresponding molecular cation. Due to the larger ionisation potential, the molecular cations can withstand much higher laser-field intensity than the corresponding neutral molecule before the saturation effects become significant. This allows one to produce high-order harmonics with energy in the water-window interval or beyond. Also, the harmonic spectrum provides information about the structure of the highest-occupied molecular orbital. In order to obtain elliptically polarised harmonics, we suggest that an orthogonally polarised two-colour field is employed as a driving field. In this case, we analyse the harmonic ellipticity as a function of the relative orientation of the cation in the laser field. We show that the regions with large harmonic ellipticity in the harmonic energy-orientation angle plane are the broadest for cations whose molecular orbital does not have a nodal plane. Finally, we show that the molecular cations exposed to an orthogonally polarised two-colour field represent an excellent setup for the production of elliptically polarised attosecond pulses with a duration shorter than 100 as.

The role of small molecular cations in the chemical flow of the interstellar environments.

Molecular ions have been ubiquitous in a variety of environments in the interstellar medium, from Circumstellar Envelopes to Dark Molecular Clouds and to Diffuse Clouds. Their role in the multitude of molecular processes which have been found to occur in those environments has been the subject of many studies over the years, so that we have acquired by now a complex body of data on their chemical structures, their possible function within chemical reactions and their most likely paths to formation. In the present work we review a broad range of such molecular ions, focusing exclusively on positive ions involving the smallest and simplest cations which have been either detected or conjectured as present in the interstellar medium (ISM). We therefore consider mainly molecular cations formed with components like H, H+, He and He+, atomic species which are by far the most abundant baryons in the ISM in general. Their likely structures and their roles in a variety of chemical energy flow paths are discussed and presented within the context of their interstellar environments.

ANTIBIOTIC RESISTANCE PROFILE AND MOLECULAR CONFORMATION AND MRSA ISOLATE BY MULTIPLEX PCR FROM CLINICAL SAMPLE AT A TERTIARY CARE HOSPITAL IN INDIA

Methicillin Resistant Staphylococcus aureus (MRSA) is an important human pathogen. They are emerging as a serious public-health issue. It causes nosocomial and community acquired infections. MRSA is present throughout hospitals in many countries. Nowadays it is the most commonly isolated antimicrobial resistant pathogen worldwide. The study include Material Method – d 450 isolates of Staphylococcus species from various clinical samples. The samples received from outpatient departments (OPDs), inpatient departments (IPDs) & various intensive care units (ICUs) included urine, blood, pus, sputum, vaginal swab, tissue, pleural uid. All clinical samples were processed as per standard bacteriological techniques. Molecular identication of Antibiotic Resistance Gene-mecA gene was also performed. Out of 450 Result– Staphylococcus species, 150 isolates were Staphylococcus aureus & 300 isolates were Coagulase Negative Staphylococci (CONS). Conclusion – Methicillin resistance is caused by the presence of mec- A gene, which encodes a low afnity penicillin binding protein (PBP)-2a or PBP2' which has a low afnity for β-lactam antibiotics. Therefore, presence of mec-A gene indicates methicillin resistance in Staphylococci. Detecting mec-A gene by polymerase chain reaction is now considered the gold standard for identifying methicillin resistance in S. aureus.

Molecular photodissociation dynamics revealed by Coulomb explosion imaging.

Coulomb explosion imaging (CEI) methods are finding ever-growing use as a means of exploring and distinguishing the static stereo-configurations of small quantum systems (molecules, clusters, etc). CEI experiments initiated by ultrafast (femtosecond-duration) laser pulses also allow opportunities to track the time-evolution of molecular structures, and thereby advance understanding of molecular fragmentation processes. This Perspective illustrates two emerging families of dynamical studies. 'One-colour' studies (employing strong field ionisation driven by intense near infrared or single X-ray or extreme ultraviolet laser pulses) afford routes to preparing multiply charged molecular cations and exploring how their fragmentation progresses from valence-dominated to Coulomb-dominated dynamics with increasing charge and how this evolution varies with molecular size and composition. 'Two-colour' studies use one ultrashort laser pulse to create electronically excited neutral molecules (or monocations), whose structural evolution is then probed as a function of pump-probe delay using an ultrafast ionisation pulse along with time and position-sensitive detection methods. This latter type of experiment has the potential to return new insights into not just molecular fragmentation processes but also charge transfer processes between moieties separating with much better defined stereochemical control than in contemporary ion-atom and ion-molecule charge transfer studies.