Molecular Anions Research Articles

Co-intercalated layered double hydroxides as thermal and photo-oxidation stabilizers for polypropylene.

An elegant and efficient approach consisting in the co-intercalation of stabilizing molecular anions is described here. The thermal stabilizer calcium diethyl bis[[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphonate] (Irganox 1425, MP-Ca) and a photo-oxidation stabilizer (hindered amine light stabilizer, HALS) are co-intercalated into the interlayer regions of layered double hydroxides (LDH) in a one-step coprecipitation. These hybrid organic–inorganic materials are successively dispersed in polypropylene to form HnMn′-Ca2Al/PP composite films (with H = HALS and M = MP) through a solvent casting method. The corresponding crystalline structure, chemical composition, morphology as well as the resistance against thermal aging and photo-oxidation are carefully investigated by various techniques. The results show that the powdered HnMn′-Ca2Al-LDHs hybrid materials have a much higher thermal stability than MP-Ca and HALS before intercalation. In addition, the HnMn′-Ca2Al/PP composites exhibit a higher overall resistance against thermal degradation and photo-oxidation compared to LDHs intercalated with only HALS or MP. This underlines the benefit of the co-intercalation. The co-intercalated LDH materials pave a new way in designing and fabricating high-performance multifunctional additives for polymers.

Five‐, Four‐ and Three‐Dentate Europium Chelates for Anion Sensing and Their Applicability to Enzymatic Dephosphorylation Reactions

AbstractThe design of anion‐sensitive probes with sufficient sensitivity and selectivity is a demanding task in analytical sciences and chemical sensor technology. The reversible binding of anions to lanthanide centers is a possible approach for the development of molecular anion sensors, as reversibility is a prerequisite for continuous sensing and monitoring of enzymatic reactions. Some anion species lead to a strong increase of luminescence intensities and lifetimes by the replacement of luminescence quenching water molecules, though the selectivity of the luminescence response is still a major problem. We synthesized a series of positively charged pyridyl‐based multidentate europium complexes (five‐, four‐ and three dentate) including sensitizing chromophores and studied their luminescence intensity and lifetime responses to different polyphosphates, pyrophosphate, phosphate anions, and carboxyanions. The results revealed that the number and symmetry of the binding sites have a significant impact on the response. The five‐dentate complex was used for the real‐time monitoring of the activity of the ATP hydrolyzing enzyme apyrase.

Photoelectron Spectroscopy of Molecular Anion of Alq3: An Estimation of Reorganization Energy for Electron Transport in the Bulk.

A molecular anion of tris(8-hydroxyquinolinato)aluminum (Alq3) was generated by a pulsed discharge to the solid sample under supersonic expansion and its photoelectron spectrum was recorded after mass selection. The vertical detachment energy of Alq3– and the adiabatic electron affinity of Alq3 were determined to be 1.24 ± 0.01 and 0.89 ± 0.04 eV, respectively. By using these energies determined for monomeric Alq3, the reorganization energy for the intermolecular electron transport in bulk Alq3 was estimated to be 0.70 ± 0.08 eV.

Lateral Graphene p–n Junctions Realized by Nanoscale Bipolar Doping Using Surface Electric Dipoles and Self‐Organized Molecular Anions

AbstractLateral p–n junctions take the unique advantages of 2D materials, such as graphene, to enable single‐atomic layer microelectronics. A major challenge in fabrication of the lateral p–n junctions is in the control of electronic properties on a 2D atomic sheet with nanometer precision. Herein, a facile approach that employs decoration of molecular anions of bis‐(trifluoromethylsulfonyl)‐imide (TFSI) to generate p‐doping on the otherwise n‐doped graphene by positively polarized surface electric dipoles (pointing toward the surface) formed on the surface oxygen‐deficient layer “intrinsic” to an oxide ferroelectric back gate is reported. The characteristic double conductance minima V Dirac− and V Dirac + illustrated in the obtained lateral graphene p–n junctions can be tuned in the range of −1 to 0 V and 0 to +1 V, respectively, by controlling the TFSI anions and surface dipoles quantitatively. The unique advantage of this approach is in adoption of polarity‐controlled molecular ion attachment on graphene, which could be further developed for various lateral electronics on 2D materials.

Polyiodide structures in thin single-walled carbon nanotubes: A large-scale density-functional study

Using automatic structure generation algorithms and large-scale density functional computations we study polyiodide structures encapsulated within a 1 nm diameter single-walled carbon nanotube. The most energetically preferable confined iodine structures are the I3−, I5− and I82− molecular anions and periodic single, double and triple chain systems. The formation energy drops with increasing number of iodine atoms, reaching a minimum for a single iodine chain. Double and triple chains are metastable but have higher formation energies due to spatial confinement within the thin carbon nanotube. The calculated electron transfer from the nanotube to the molecular structures is close to the integer charge values of the molecular anions. The corresponding Fermi energy shift depends on the iodine concentration. For the single, double and triple chains the calculated Fermi shift is ∼0.13, ∼0.23 and ∼0.19 eV below the top of the nanotube valence band, respectively. The computational approaches presented here require minimal a priori knowledge of the system under study, yet are able to predict stable iodine structures observed in experiment.

Accurate Predictions of Electron Binding Energies of Dipole-Bound Anions via Quantum Monte Carlo Methods.

Neutral molecules with sufficiently large dipole moments can bind electrons in diffuse nonvalence orbitals with most of their charge density far from the nuclei, forming so-called dipole-bound anions. Because long-range correlation effects play an important role in the binding of an excess electron and overall binding energies are often only on the order of 10s-100s of wave numbers, predictively modeling dipole-bound anions remains a challenge. Here, we demonstrate that quantum Monte Carlo methods can accurately characterize molecular dipole-bound anions with near-threshold dipole moments. We also show that correlated sampling Auxiliary Field Quantum Monte Carlo is particularly well-suited for resolving the fine energy differences between the neutral and anionic species. These results shed light on the fundamental limitations of quantum Monte Carlo methods and pave the way toward using them for the study of weakly bound species that are too large to model using traditional electron structure methods.

Exotic molecules consisting of an antiproton and a hydrogen atom

A theoretical study is conducted on the stability of exotic antiproton-hydrogen molecular anions ($\overline{p}\mathrm{H}$), which in the separated atom limit correlate with $\overline{p}+\mathrm{H}(n=2)$ ($n$ being the principal quantum number). The $\overline{p}\mathrm{H}$ molecule in the electronic ground state is highly unstable due to pair annihilation and autodetachment ($\ensuremath{\rightarrow}\overline{p}p+e$). However, if the $\overline{p}\mathrm{H}$ molecule is electronically excited, the molecular stability can be drastically improved. Since the excited states of the $\mathrm{H}$ atom have accidental degeneracy, the asymptotic form of the Born-Oppenheimer potential curve of $\overline{p}+\mathrm{H}(n=2)$ behaves as $1/{R}^{2}$ ($R$ being the relative distance), which can play a critical role in the bonding and stability of the molecule. It is found that the $\overline{p}\mathrm{H}$ molecule in the first electronic excited state and in a high rotational state is sufficiently stable and has a lifetime dominated by spontaneous radiative emission ($\ensuremath{\rightarrow}\overline{p}+\mathrm{H}+h\ensuremath{\nu}$). The $\overline{p}\mathrm{H}$ system is dynamically similar to ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$, which had been commonly considered to be unstable due to autodetachment. However, recent measurements of ion-beam sputtering unambiguously verified the existence of long-lived ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$ molecules in high rotational states. This suggests that the $\overline{p}\mathrm{H}$ molecules may actually be created if one employs experimental means such as the chemical sputtering of hydrogen-rich targets with $\overline{p}$ beams.

Electron Propagator Methods for Vertical Electron Detachment Energies of Anions: Benchmarks and Case Studies.

Ab initio electron propagator methods are efficient and accurate means of calculating vertical electron detachment energies of closed-shell, molecular anions with nuclei from the first three periods. Basis set extrapolations enable definitive comparisons between electron propagator results and benchmarks defined by total energy differences obtained with coupled-cluster, single, double, plus perturbative triple substitution theory. The best compromises of accuracy and efficiency are provided by the renormalized, partial third-order, diagonal (P3+) self-energy and by the nondiagonal, renormalized, second-order (NR2) approximation. The outer-valence Green function, the two-particle-one-hole Tamm-Dancoff approximation, the third-order algebraic diagrammatic construction, and the renormalized third-order methods also are examined. A detailed analysis of errors for small anions is performed. Case studies include F-(H2O) and Cl-(H2O) complexes, C5H5-, two P2N3- pentagonal rings, and a superhalide, Al(BO2)4-, whose electron detachment energy is more than double those of the halide anions. These applications illustrate the versatility of electron propagator methods, their utility for interpreting negative-ion photoelectron spectra, and their promise in the discovery of unusual properties and patterns of chemical bonding. Composite methods, which combine basis set effects calculated at the relatively efficient diagonal, second-order level and higher correlation effects calculated with small basis sets, provide excellent estimates of basis set-extrapolated P3+ or NR2 results and facilitate applications to large molecules. In the P3+ and NR2 methods, a judicious choice of low-order couplings between hole operators that correspond to the assumptions of Koopmans's theorem and operators that describe final-state relaxation and polarization and initial-state correlation leads to predictive accuracy, computational efficiency, and interpretive lucidity.

Dissociation of methyl formate (HCOOCH3) molecules upon low-energy electron attachment

Context. The methyl formate molecule (HCOOCH3) is considered to be a key molecule in astrochemistry. The abundance of this molecule in space depends on the stability upon irradiation with particles like low-energy electrons. Aims. We have investigated the decomposition of the molecule upon electron capture in the electron energy range from about 0 eV up to 15 eV. All experimentally obtained fragmentation channels of the molecular anion were investigated by quantum chemical calculations. Methods. A high resolution electron monochromator coupled with quadrupole mass spectrometer was used for the present laboratory experiment. Quantum chemical calculations of the electron affinities of the generated fragments, the thermodynamic thresholds and the activation barriers for the associated reaction channels were carried out to complement the experimental studies. Results. Electron attachment is shown to be a purely dissociative process for this molecule and proceeds within two electron energy regions of about 1 eV to 4 eV and from 5 eV to 14 eV. In our experiment five anionic fragments with m/z (and possible stoichiometric structure) 59 (C2H3O2−), 58 (C2H2O2−), 45 (CHO2−) 31 (CH3O−), and 29 (CHO−) were detected. The most abundant anion fragments that are formed through dissociative electron attachment to methyl formate are the complementary anions CH3O− and CHO−, associated with the same single bond cleavage and different survival probability. Conclusions. The low-energy electron induced dissociation of methyl formate differs from its isomers acetic acid and glycolaldehyde, which leads to possible chemical selectivity in the chemical evolution.

Molecular analysis of selective gas adsorption within composites of ionic polyimides and ionic liquids as gas separation membranes

The CO2 separation characteristics of ionic polyimides (i-PIs) are modeled using molecular dynamics simulations in combination with grand canonical Monte Carlo calculations. The performance of neat i-PI systems is evaluated, as well as composite structures containing both i-PIs and various ionic liquids (ILs). The i-PI + IL composites are based on combinations of 1-n-butyl-3-methylimidazolium ([C4mim+]) cations with three common molecular anions: (bis(trifluoromethylsulfonyl)imide ([Tf2N−]), tetrafluoroborate ([BF4−]), and hexafluorophosphate ([PF6−]). It is found that 50 mol% IL inclusion can increase CO2/CH4 selectivity by 16% in [BF4−]-based materials and by 36% in [PF6−]-based materials from mixtures of 5% CO2/95% CH4. While the [BF4−]-based system shows higher CO2/CH4 selectivity, the [Tf2N−]-based system shows higher CO2/N2 gas selectivity. A comprehensive structural analysis (fractional free volume (FFV), pore size distribution, surface area, etc.) is used to highlight the underlying differences among the different i-PI + IL systems that lead to the different adsorption properties.

Analysis of the Frequency and Diversity of 1,3-Dialkylimidazolium Ionic Liquids Appearing in the Literature

The hypothetical assertion that there are potentially millions of ionic liquids (ILs) can be validated using basic knowledge of IL precursors and simple calculations. While it is an interesting thought exercise to ponder the possibilities of ILs, it is important to investigate how many discrete ILs (i.e., unique cation and anion pairings) have actually been synthesized and reported in the literature. A complete analysis of all ILs is a daunting task, especially if the definition of what constitutes an IL is broad. Nonetheless, insight can be gained into the use of ILs over the past ∼20 years from a focused analysis of systematically varied 1,3-dialkylimidazolium-based ILs (i.e., [R1R2im][X], where R1 and R2 are n-alkyl chains and X is either a halide or molecular anion). This family of ILs includes many of the most widely used and most thoroughly studied IL substances, including 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) and 1-ethyl-3-methylimidazolium bistriflimide ([C2mim][Tf2N]). Us...

What is the effect of lipophilic polymeric ionic liquids on friction and wear?

In this work, methacrylate-type ionic liquid (IL) monomers containing a quaternary ammonium cation and two different counter-anions were synthesized and used as co-monomers to obtain functional poly(alkyl methacrylates) (PAMAs). They were then evaluated as friction and wear reducing additives for lubricants. The effect of molecular weight, polymer topology (random or diblock), and IL counter anion on friction and wear behavior of polymer PAO (poly-alpha olefin) solutions have been investigated. The results were compared to those of PAO solutions additized with a small molecule, non-polymeric ionic liquid, or non-ionic copolymers containing 2-(dimethylamino)ethyl methacrylate (DMAEMA) as the polar comonomer. No clear correlation between polymer molecular weight and friction or wear behavior was observed. Random ionic liquid copolymers led to lower wear volumes than their block counterparts. Polymers containing dicyanamide (DCA) counter anion showed lower wear volume compared to those containing bis((trifluoromethyl)sulfonyl)imide (TFSI) anion. Surprisingly, none of the IL copolymers studied outperformed the DMAEMA containing block copolymer in terms of wear volume reduction, suggesting the IL moiety had no beneficial effect on wear.

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F.

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound electrons with neutral molecules/atoms. State-of-the-art in vacuo anion generation techniques allow application to a broad range of atomic, molecular, and cluster anion systems. These are separated and selected using time-of-flight mass spectrometry. Electrons are removed by linearly polarized photons (photo detachment) using table-top laser sources which provide ready access to excitation energies from the infra-red to the near ultraviolet. Detecting the photoelectrons with a velocity mapped imaging lens and position sensitive detector means that, in principle, every photoelectron reaches the detector and the detection efficiency is uniform for all kinetic energies. Photoelectron spectra extracted from the images via mathematical reconstruction using an inverse Abel transformation reveal details of the anion internal energy state distribution and the resultant neutral energy states. At low electron kinetic energy, typical resolution is sufficient to reveal energy level differences on the order of a few millielectron-volts, i.e., different vibrational levels for molecular species or spin-orbit splitting in atoms. Photoelectron angular distributions extracted from the inverse Abel transformation represent the signatures of the bound electron orbital, allowing more detailed probing of electronic structure. The spectra and angular distributions also encode details of the interactions between the outgoing electron and the residual neutral species subsequent to excitation. The technique is illustrated by the application to an atomic anion (F-), but it can also be applied to the measurement of molecular anion spectroscopy, the study of low lying anion resonances (as an alternative to scattering experiments) and femtosecond (fs) time resolved studies of the dynamic evolution of anions.

Anion-Dependent Doping and Charge Transport in Organic Electrochemical Transistors

We study the effects of different electrolyte anions on the mixed ionic/electronic transport properties of organic electrochemical transistors (OECTs) based on poly(3-hexylthiophene-2,5-diyl). We show that the transport properties depend on the anion present in the electrolyte, with greater source-drain currents resulting from the use of molecular anions such as hexafluorophosphate and trifluoromethanesulfonylimide than from the use of smaller atomic anions such as fluoride or chloride. Using spectroelectrochemistry, we show the maximum doping level that can be achieved in an aqueous environment is also anion-dependent. Furthermore, we find that the average electronic carrier mobility at a given doping level depends on the chemistry of the compensating counterion. We further investigate this dependence by electrochemical quartz crystal microbalance measurements, showing the solvation of the dopant anions within the polymer is drastically different depending on the choice of the anion. Surprisingly, we fin...

Water Dynamics in Polyacrylamide Hydrogels.

Polymeric hydrogels have wide applications including electrophoresis, biocompatible materials, water superadsorbents, and contact lenses. The properties of hydrogels involve the poorly characterized molecular dynamics of water and solutes trapped within the three-dimensional cross-linked polymer networks. Here we apply ultrafast two-dimensional infrared (2D IR) vibrational echo and polarization-selective pump-probe (PSPP) spectroscopies to investigate the ultrafast molecular dynamics of water and a small molecular anion solute, selenocyanate (SeCN-), in polyacrylamide hydrogels. For all mass concentrations of polymer studied (5% and above), the hydrogen-bonding network reorganization (spectral diffusion) dynamics and reorientation dynamics reported by both water and SeCN- solvated by water are significantly slower than in bulk water. As the polymer mass concentration increases, molecular dynamics in the hydrogels slow further. The magnitudes of the slowing, measured with both water and SeCN-, are similar. However, the entire hydrogen-bonding network of water molecules appears to slow down as a single ensemble, without a difference between the core water population and the interface water population at the polymer-water surface. In contrast, the dissolved SeCN- do exhibit two-component dynamics, where the major component is assigned to the anions fully solvated in the confined water nanopools. The slower component has a small amplitude which is correlated with the polymer mass concentration and is assigned to adsorbed anions strongly interacting with the polymer fiber networks.

Rotational Spectroscopy of a Triatomic Molecular Anion.

Rotational transitions of the nonlinear triatomic molecular anion NH_{2}^{-} have been observed by terahertz spectroscopy in a cryogenic radio frequency ion trap. Absorption of terahertz photons has been probed by rotational state-dependent photodetachment of the trapped negative ions near the detachment threshold. Using this two-photon scheme, the two lowest rotational transitions for the asymmetric top rotor NH_{2}^{-} have been found. For the para nuclear spin configuration, the 1_{0}←0_{0} transition frequency was determined to be 933 954(2)MHz, and for the ortho configuration the 1_{+1}←1_{-1} transition frequency was determined to be 447 375(3)MHz. This result appears to preclude the recent tentative assignment of an interstellar absorption feature to NH_{2}^{-}.

Modeling Quantum Kinetics in Ion Traps: State-changing Collisions for OH+ (3Σ- ) Ions with He as a Buffer Gas.

We present quantum scattering calculations for rotational state‐changing cross sections and rates, up to about 50 K of ion translational temperatures, for the OH+ molecular ion in collision with He atoms as the buffer gas in the trap. The results are obtained both by using the correct spin‐rotation coupling of angular momenta and also within a recoupling scheme that treats the molecular target as a pseudo‐(1Σ+ ) state, and then compares our findings with similar data for the OH−(1Σ+ ) molecular partner under the same conditions. This comparison intends to link the cation behaviour to the one found earlier for the molecular anion. The full calculations including the spin‐rotation angular momenta coupling effects have been recently reported (L. González‐Sánchez and R. Wester and F.A. Gianturco, Mol.Phys.2018, DOI 10.1080/00268976.2018.14425971) with the aim of extracting specific propensity rules controlling the size of the cross sections. The present study is instead directed to modelling trap cooling dynamics by further obtaining the solutions of the corresponding kinetics equations under different trap schemes so that, using the presently computed rates can allow us to indicate specific optimal conditions for the experimental setup of the collisional rotational cooling in an ion trap for the system under study.

MOLECULAR RELAXATION IN BINARY SYSTEMS NaNO3 – NaNO2, KNO3 – KNO2

In the present study, the molecular relaxation processes in crystalline sodium nitrate NaNO3, crystalline sodium nitrite NaNO2, crystalline potassium nitrate KNO3, crystalline potassium nitrite KNO2, and in solid binary salt systems sodium nitrate – sodium nitrite NaNO3 – NaNO2 and potassium nitrate - potassium nitrite KNO3 – KNO2 were studied with the Raman spectroscopic methods. We have found that the relaxation time of the fully symmetric vibration of n1 (A) of the molecular nitrate anion NO3– in the solid binary salt systems “nitrate – nitrite” NaNO3 – NaNO2 or KNO3 – KNO2 is lower than in the individual crystalline nitrate NaNO3 or KNO3, respectively. It is shown that the increase in the rate of intramolecular relaxation is explained by the presence in the binary system of an additional relaxation mechanism of the vibrationally excited states of the nitrate ion NO3–. This relaxation mechanism of the nitrate ion NO3– in a binary system is associated with the excitation of a lower-frequency vibration of another anion (nitrite ion NO2–) and the "birth" of a lattice vibration (phonon). The frequency of this phonon is equal to the difference in the vibration frequencies of the nitrate ion NO3– and nitrite ion NO2–. It is established that the condition for the realization of such a relaxation mechanism is that the difference in the frequency of these oscillations of the nitrate ion NO3– and nitrite ion NO2– must correspond to the region of a sufficiently high density of states of the phonon spectrum of the solid binary salt system under study. The maximum frequency of the phonon spectrum of the system is determined by its Debye temperature. For ionic salt systems, the Debye temperature is always higher than 200 K, and often more than 300 K. Therefore, in the solid binary salt systems, the proposed relaxation mechanism is almost always relevant.Forcitation:Aliev A.R., Akhmedov I.R., Kakagasanov M.G., Aliev Z.A., Amirov A.M. Molecular relaxation in the binary systems NaNO3 – NaNO2, KNO3 – KNO2. Izv. Vyssh.Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 23-30

Hg4 Te8 (Te2 )4 ]8- : A Heavy Metal Porphyrinoid Embedded in a Lamellar Structure.

The use of ionic liquids (Cn C1 Im)[BF4 ] with long alkyl chains (n=10, 12) in the ionothermal treatment of Na2 [HgTe2 ] led to lamellar crystal structures with molecular macrocyclic anions [Hg8 Te16 ]8- (1), the heaviest known topological relative of porphyrin. [Hg8 Te16 ]8- differs from porphyrin by the absence of an electronic π-system, which prevents a "global" aromaticity. Quantum chemical studies reveal instead small ring currents in the pyrrole-type five-membered rings that indicate weak local (σ) aromaticity. As a result of their lamellar nature, the compounds are promising candidates for the formation of sheets containing chalcogenidometalate anions.

Chitosan-based particles for protection of proteins during storage and oral administration

Crosslinked chitosan particles have been developed to improve the storage stability of bioactive proteins and to ensure adequate bioavailability by targeting release to the colon. The characteristics of these chitosan-based particles, formed using different molecular weight chitosans and different anion cross-linkers, were demonstrated using small angle X-ray scattering, ζ-potential, particle size, and morphology. An in vitro release study showed that protein release from the particles in the upper gastrointestinal tract was <30%, suggesting the possibility for target release to the colon. Some of the particles were shown to retain colon-targeted protein delivery after storage in PBS buffer. By controlling the structure of the chitosan-based particles, it was possible to both reduce protein leakage during short-term storage and achieve colon-targeted delivery.