Chlorine Anions Research Articles

SERS spectroscopy of nanocomposite porous films containing silver nanoparticles

It is demonstrated that surface-enhanced Raman scattering spectroscopy allows detecting 10−10 M Rhodamine 6G (Rh 6G) on nanocomposite films containing silver nanoparticles with an amplification factor of 3 × 107. The films used for SERS, which exhibit gradients of thickness and have silver particles and pores of different size, were obtained by pulse laser deposition from the low-energy backward erosion flux. To activate the SERS signal, the films were treated in solutions of metal chlorides and hydrogen chloride to achieve formation of anions of [AgCl2]− complexes. The composition of shells of silver nanoparticles, in particular, replacement of silver compounds preventing Rh 6G adsorption by anions of [AgCl2]− complexes enabling adsorption of Rh 6G cation between them, has been monitored by means of SERS spectroscopy. The obtained SERS spectra of Rh 6G in several locations on the film surface allowed determining the area with an optimal size of silver nanoparticles that gives rise to highest SERS signal intensity. The transmission spectra of the films revealed narrowing of the band corresponding to the local surface plasmon absorption, its shift toward the blue spectral region, and enhancement of plasmon resonance upon introduction of chlorine anion. The changes in absorption spectra of the films correlate with the activation of the Rh 6G SERS spectra.

Understanding complex phase transition mechanism by crystal structure analysis

Xylazine hydrochloride (2-(2,6-xylidino)-5,6-dihydro-4H-1,3-thiazine hydrochloride) is an adrenergic α-agonist used as a sedative, analgesic, and muscle relaxant in veterinary medicine. It has four polymorphous forms (A, Z, M and X), monohydrate (H), hemihydrate and solvates with dichloromethane and 2-propanol. It has been reported that the polymorph X is thermodynamically the least stable of these polymorphs, while the A is the most stable form at temperatures above 500C. The X forms only in H dehydration process, and at elevated temperature X transforms to polymorph A [1]. The crystal structures of the polymorphs A and X as well as hydrate H have been reported. Crystal structure of A and X have been determined from the powder X-ray diffraction data (PXRD), whereas that of hydrate have been determined from single crystal X-ray diffraction data [2-3]. In this study structure of A have been determined from single crystal data and compared to that determined by PXRD data. Crystal structures of A, X and H have been compared and analysed. Molecule conformation in crystal structure of all three forms is the same and molecular packing is similar. However, that in monohydrate H and polymorph X is basically the same and the only difference is the inclusion of the water molecules next to the chlorine anions, whereas relative xylazine moiety orientation and arrangement of the chlorine anions is different in the structure of polymorph A. The structural similarity or differences between all three forms noted above were also approved by the 2D-fingerprint plots of the Hirshfeld surfaces. Analysis of all three form crystal structures allowed to better understand complex solid-state phase transition from xylazine hydrochloride polymorph X to polymorph A during and after the dehydration of it monohydrate H.

Structure and Anion Exchangeability of Ni-Al-Type Layered Double Hydroxides

Layered double hydroxide (LDH) is one of promising inorganic materials for cleaning the environmental water polluted by toxic anions. The crystal structure of LDH is composed of the positively-charged metal hydroxide nanosheets and the anions with water molecules intercalated between the nanosheet layers. To put LDHs for practical use, it is necessary to understand why only special anions can be intercalated into the crystal structure from the aqueous solution. In this study, the anion exchange experiments and the synchrotron radiation x-ray powder diffraction measurements of Ni-Al-type LDHs of several kinds of Ni/Al ratios with chlorine and nitrate anions were performed to investigate the relationship between the anion exchange selectivity and crystal structures. The nitrate ion selectivity is normally poor in most of LDHs with different metal ions in the hydroxide nanosheet [1]. However, the nitrate ions were preferred to the chlorine ions in Ni-Al-type LDH when Ni/Al = 4, whereas the chlorine ions were selected when Ni/Al = 2. The crystal structure analysis revealed that the interlayer distance decreased and the thermal motion of the nitrate ions suppressed in Ni-Al-nitrate-type LDH with increasing the Ni/Al ratio, whereas those of the chlorine ions in Ni-Al-chlorine-type LDH increased and enhanced with increasing the Ni/Al ratio. These results indicate that the nitrate ions are more stable than the chlorine ions in the crystal structure of the Ni-Al-type LDH when the positive charge of the nanosheet is small, i.e. the number of anions is small. The short interlayer distance and the small thermal vibration of anions in the crystal structure are the key to understand the anion selectivity of LDH.

Water vapor clustering in the field of a chlorine anion occurring in a planar nanopore with structureless walls

The Monte Carlo bicanonical statistical ensemble method has been employed to calculate the free energy, entropy, and work of Cl− ion hydration in model planar pores 0.5 and 0.7 nm wide at 298 and 400 K. A detailed model of many-body interactions with the ion has been used, the model being matched to experimental data with respect to the free energy and enthalpy of attachment reaction in water vapor. Under the conditions of a restricted volume, the equilibrium size of a hydration shell substantially decreases, with the effect becoming stronger in the range of moderate and large sizes. In moderately supersaturated vapors, under the conditions of a nanopore, the ion loses its hydration shell as the temperature is decreased. In supersaturated vapors, the hydration shell formed on the ion is thermodynamically stable, while the stability crisis shifts to the region of larger sizes. The enhancement of the thermodynamic stability in the pore results from a rise in the chemical potential of molecules due to the deficiency of closet neighbors and a reduction in the entropy under the conditions of the restricted volume. As the temperature is elevated, the effect of ion displacement out of its hydration shell is leveled. The regularities derived in terms of the estimation model based on the capillary approximation are in qualitative agreement with the results of computer simulation.

Electrochemical Removal Cyanide in Wastewater by Ti/RuO<sub>2</sub>-Pt Electrodes

A laboratory-scale electrolytic cell with a Ti/RuO2-Pt anode and a Ti cathode was developed to treat high concentration cyanide-contained wastewater. The effects of the different electrode distances, concentration of chlorine anion and current densities, on the CN- removal were investigated. The results shown the too short and long electrode distance resulted in high energy consumption and low current, the appropriate electrode distance was essential. The CN- removal was very significant at the electrode distance was 9 cm, and the removal efficiency reached 99.2%. The removal CN- electrochemical oxidation was mainly attributed the success to in direct oxidation effect of chlorine /hypo-chlorite produced during the electrochemical reaction process. The CN- removal efficiency increased with increasing the concentration of chloride ion and operating current density. The optimum experimental condition was set at the electrode distance of 9 cm, NaCl dosage of 0.5 g/L, the current density of 10 mA/cm2, and pH of 12. At the optimum experimental condition, the CN- concentration in the solution decreased from 150.33 mg/L to 1.20 mg/L, and the CN- removal efficiency reached 99.2%.

Insight into Capture of Greenhouse Gas (CO2) based on Guanidinium Ionic Liquids

Quantum mechanics and molecular dynamics are used to simulate guanidinium ionic liquids. Results show that the stronger interaction exists between guanidine cation and chlorine anion with interaction energy about 109.216 kcal/mol. There are two types of spatial distribution for the title system: middle and top. Middle mode is a more stable conformation according to energy and geometric distribution. It is also verified by radial distribution function. The continuous increase of carbon dioxide (CO2) does not affect the structure of ionic liquids, but CO2 molecules are always captured by the cavity of ionic liquids.

Topological reaction sites – very strong chalcogen bonds

The analysis of interactions in complexes of S(CN)2, Se(CN)2, SFCl and SeFCl with F(-) and Cl(-) anions is performed here. The sulphur and selenium atoms act in these complexes as Lewis acid centres interacting with fluorine and chlorine anions. The arrangement of sub-units in complexes is in agreement with the σ-hole concept; particularly it is a result of contacts between positive and negative electrostatic potential sites. The interactions in complexes analyzed may be classified as very strong charge assisted chalcogen bonds and they possess numerous characteristics typical for covalent bonds. Even in the case of complexes of SFCl and SeFCl, i.e. SFCl2(-) and SeFCl2(-), the trivalency of the chalcogen atom is observed. The calculations were carried out at the MP2(full)/aug-cc-pVTZ level of approximation, the analyses were performed with the use of the Natural Bond Orbital (NBO) method, the Quantum Theory of 'Atoms in Molecules' (QTAIM) and the Electron Localization Function (ELF) approach. The results obtained by these methods are in agreement giving the consistent picture of the complexes' configurations and their electron charge distribution. The QTAIM and ELF approaches allow us to predict for S(CN)2, Se(CN)2, SFCl and SeFCl molecules the directions of nucleophilic attack. They are in line with the prediction based on the σ-hole concept. The Symmetry Adapted Perturbation Theory (SAPT) approach was also applied.

Nanocompósitos poliméricos de polietileno de alta densidade contendo hidróxidos duplos lamelares intercalados com anions derivados de corantes azo

O presente trabalho descreve a sintese e caracterizacao de hidroxidos duplos lamelares (HDL) de Zn/Al na razao molar 2:1, os quais foram intercalados com ions cloreto hidratados e ânions derivados dos corantes azo alaranjado de metila (AM) e alaranjado II (AII). Apos caracterizacao, os materiais foram utilizados como cargas em polietileno de alta densidade (PEAD) e nanocompositos foram preparados por extrusao e injecao, seguindo a norma ASTM D638-10. Os teores de cargas variaram de 0,1 ate 2% (incluindo-se os sais de sodio dos corantes) e os nanocompositos homogeneos foram avaliados em relacao as suas propriedades estruturais, termicas e mecânicas. De modo geral, apos a adicao das cargas existe somente uma pequena influencia na temperatura de fusao e cristalizacao do PEAD. Para os HDLs contendo o pigmento intercalado com o ânion do corante AM e sais de sodio de ambos os corantes, as propriedades mecânicas apresentaram leve aumento do modulo e tensao de ruptura e diminuicao do alongamento em relacao ao polimero puro e um comportamento inverso foi observado para o ânion AII, alem do HDL contendo ânions cloreto hidratados.

The relationship between enhanced enzyme activity and structural dynamics in ionic liquids: a combined computational and experimental study

Candida antarctica lipase B (CALB) is an efficient biocatalyst for hydrolysis, esterification, and polymerization reactions. In order to understand how to control enzyme activity and stability we performed a combined experimental and molecular dynamics simulation study of CALB in organic solvents and ionic liquids (ILs). Our results demonstrate that the conformational changes of the active site cavity are directly related to enzyme activity and decrease in the following order: [Bmim][TfO] > tert-butanol > [Bmim][Cl]. The entrance to the cavity is modulated by two isoleucines, ILE-189 and ILE-285, one of which is located on the α-10 helix. The α-10 helix can substantially change its conformation due to specific interactions with solvent molecules. This change is acutely evident in [Bmim][Cl] where interactions of LYS-290 with chlorine anions caused a conformational switch between α-helix and turn. Disruption of the α-10 helix structure results in a narrow cavity entrance and, thus, reduced the activity of CALB in [Bmim][Cl]. Finally, our results show that the electrostatic energy between solvents in this study and CALB is correlated with the structural changes leading to differences in enzyme activity.

Calculating Hyperfine Couplings in Large Ionic Crystals Containing Hundreds of QM Atoms: Subsystem DFT Is the Key

We present an application of the linear scaling frozen density embedding (FDE) formulation of subsystem DFT to the calculation of isotropic hyperfine coupling constants (hfcc's) of atoms belonging to a guanine radical cation embedded in a guanine hydrochloride monohydrate crystal. The model systems range from an isolated guanine to a 15,000 atom QM/MM cluster where the QM region is comprised of 36 protonated guanine cations, 36 chlorine anions, and 42 water molecules. Our calculations show that the embedding effects of the surrounding crystal cannot be reproduced by small model systems nor by a pure QM/MM procedure. Instead, a large QM region is needed to fully capture the complicated nature of the embedding effects in this system. The unprecedented system size for a relativistic all-electron isotropic hfcc calculation can be approached in this work because the local nature of the electronic structure of the organic crystals considered is fully captured by the FDE approach.

Chlorine anion–π and π−–π− interactions in two tetrazolyl derivative based Cu2+ complexes and quantum chemical calculations

Two bis(tetrazolyl)amine (H2BTA) and 5,5′-azotetrazolate (AT) based Cu2+ supramolecular complexes [Cu(H2BTA)Cl2(H2O)]·2H2O (1) and [Cu2(AT)2(pn)3]·2H2O (2) (pn=1,3-diaminopropane) have been synthesized and characterized by single crystal X-ray diffraction analysis. In 1, each Cu2+ ion displays a tetragonal pyramidal structure and an anion–π of Cl−–π interaction has been observed. The Cl−–π binding interaction together with O–H···Cl, N–H···Cl, N–H···O and O–H···N four hydrogen bonds link the complex units and lattice water molecules to form a 3D supramolecular network structure. In 2, the Cu2+ ions show an elongated octahedral structure and a 1D chain structure bridged by μ2-trans-AT2− ligands is found. An unusual face-to-face π−–π− stacking interaction between trans-AT2− anions in 2 is found. Complex 2 also exhibits a 3D supramolecular structure in which the π−–π− stacking, O–H···N and N–H···O hydrogen bonding and electrostatic interactions are responsible for the stabilization of the complex. The aqueous solution of 2 shows photochromic property. The Cl−–π and π−–π− interaction energies in 1 and 2 were calculated at MP2 level using gaussian 09 suite and demonstrated.

Molecular Dynamic Simulations and Vibrational Analysis of an Ionic Liquid Analogue

Deep eutectic solvents, considered ionic liquid (IL) analogues, show promise for many material science and engineering applications over typical ILs because they are readily available and relatively inexpensive. Atomistic molecular dynamics simulations have been performed over a range of temperatures on one eutectic mixture, 1:2 choline chloride/urea, using different force field modifications. Good agreement was achieved between simulated density, volume expansion coefficient, heat capacity, and diffusion coefficients and experimental values in order to validate the best performing force field. Atom-atom and center-of-mass radial distribution functions are discussed in order to understand the atomistic interactions involved in this eutectic mixture. Experimental infrared (IR) spectra are also reported for choline chloride-urea mixtures, and band assignments are discussed. The distribution of hydrogen-bond interactions from molecular simulations is correlated to curve-resolved bands from the IR spectra. This work suggests that there is a strong interaction between the NH2 of urea and the chlorine anion where the system wants to maximize the number of hydrogen bonds to the anion. Additionally, the disappearance of free carbonyl groups upon increasing concentrations of urea suggests that at low urea concentrations, urea will preferentially interact with the anion through the NH2 groups. As this concentration increases, the complex remains but with additional interactions that remove the free carbonyl band from the spectra. The results from both molecular simulations and experimental IR spectroscopy support the idea that key interactions between the moieties in the eutectic mixture interrupt the main interactions within the parent substances and are responsible for the decrease in freezing point.

Formation and crystallization of chlorine- and bromine-containing hafnium fluoride-based glasses

We have studied glass-forming regions for ZBLAN-type hafnium fluoride-based glasses with the compositions (63–53)HfF4 · 20BaF2 · 4LaF3 · (1–3)InF3 · (0–20)NaF in which fluorine anions are partially replaced by chlorine and bromine anions. The crystallization mechanism of the glasses has been investigated by differential thermal analysis and X-ray diffraction. The results demonstrate that characteristic features of the glasses are a significant decrease in glass transition temperature (t g) and the precipitation of fine-particle crystalline chloride and bromide phases at temperatures well below the crystallization temperature (t x) of their fluoride analogs. We have studied the effect of the Cl/F and Cl/Br ratios in the glass batch and the melt cooling rate after glass preparation on the crystallization behavior of the glasses and determined the heat treatment temperature and time for the formation of transparent glass-ceramic samples upon heat treatment in the temperature range where chloride and bromide phases precipitate. Doping of the glasses with 1 at % or smaller amounts of rare-earth metals is found to have no significant effect on the phase segregation process during heat treatment.

Sheets of Tetranuclear Ni(II) [2 × 2] Square Grids Structure with Infinite Orthogonal Two-Dimensional Water–Chlorine Chains

The tetranuclear nickel(II) complex [Ni4(HL)4]Cl4·4H2O {H2L = 1,5-bis[1-(pyridin-2-yl)ethylidene]carbono hydrazone} has been prepared by reaction in methanol of nickel(II) chloride and H2L in 2:1, M:L molar ratio. The single crystal X-ray diffraction analysis revealed a 2 × 2 square grid of tetramer units with the metal ions joined in pairs by the alkoxide oxygen atom in the μ2 mode with octahedral geometry around each nickel ion. The supramolecular structure shows that the tetramer units are linked through edge-to-face (T shape) C–H···π interactions, forming sheets with hydrophobic- (occupied by infinite 2D water–chlorine chains) and hydrophilic- (occupied by chlorine anions) channels. Variable temperature magnetic studies suggest an antiferromagnetic coupling between the adjacent Ni(II) centers with a coupling constant of J = −6.6 cm–1.

Synthesis, Crystal Structure, and Characterization of a New Organic-Inorganic Hybrid Material:

The title compound is an organic-inorganic hybrid material. The single crystal X-ray diffraction investigation reveals that the studied compound crystallizes in the orthorhombic system, space group Pbca with the following lattice parameters: (4) Å, (3) Å, (6) Å, and . The crystal lattice is composed of a discrete anion surrounded by piperazinium cations, chlorine anions, and water molecules. Complex hydrogen bonding interactions between , , organic cations, and water molecules form a three-dimensional network. Room temperature IR, Raman spectroscopy, and optical absorption of the title compound were recorded and analysed. The observed crystal morphology was compared to the simulated one using the Bravais-Friedel, Donnay-Harker model.

Structure and Resistance to Electrochemical Corrosion of NiTi Alloy

The NiTi alloy (50.6 at.% Ni) passivated for 30 min at 130°C by autoclaving has been studied towards corrosion resistance in aqueous solutions of 3% NaCl, 0.1 M H2SO4, 1 M H2SO4 and HBSS. Structure and thickness of the passive layer (TiO2, rutile) were examined by X-ray reflectivity method and high resolution electron microscopy. Corrosion behavior of this oxide layer was investigated by open circuit potential method and polarization curves. It was found that the corrosion resistance of the passivated NiTi alloy is strongly dependent on the type of corrosive environment. The higher corrosion resistance of the tested samples was revealed in sulfate solutions as compared to chloride ones. The highest resistance to electrochemical corrosion of the NiTi alloy was observed in 0.1 M H2SO4 solution. Susceptibility to pitting corrosion of the tested samples was observed which increased with the concentration rise of chlorine anions in solution. Electrochemical tests for 316L stainless steel carried out under the same experimental conditions revealed a weaker corrosion resistance in all solutions as compared to the highly corrosion resistant NiTi alloy.

Complexes of carboxyl-containing polymer and monosubstituted bipyridinium salts

Semi-empirical PM3 method for the quantum calculations of molecular electronic structure based on NDDO integral approximation is used to investigate the complex formation of monosubstituted 4,4′-bipyridinium salts BpyR (Hal) containing a halide anion interacting with the quaternary nitrogen atom and carboxylic group of the two-units construct. Significant effect of the BpyR (Hal) electronic structure is unveiled that contributes in two different structures of these salts, namely, partial charge transfer complex and ion pair structure, both having stable energy minima. We demonstrate that (i) the structure of the N-substituent modulates the energy and electronic characteristics of monosubstituted salts BpyR with chlorine and bromine anions and (ii) the coulomb interactions between quaternary N-atom, halogen anion, and the proton of carboxylic group stimulate the transformation of the charge transfer complex into the ion pair structure. Results of calculations are compared with the experimental FTIR spectra of blends of BpyR(Hal) with Eudragit copolymer.

A model study of the negative chlorine ion chemistry in the Earth’s mesosphere

An ion chemistry model is used to investigate the negative chlorine ion chemistry of the mesosphere for quiet ionospheric conditions. Model results are presented for high latitudes in February as well as for the equator in Summer. For nighttime, Cl-, Cl-(HCl), and NO3−(HCl) are the most abundant chlorine anions in the mesosphere. The concentration of ClO3− depends significantly on its stability against collision-induced dissociation. In contrast to previous model predictions, the abundance of Cl-(H2O) is small. For daytime, photoelectron detachment and photodissociation have pronounced impact on the negative chlorine ion chemistry in the mesosphere. The abundance of all anion cluster is considerably smaller than at night. While Cl- decreases in the upper mesosphere, its abundance increases at lower altitudes.

Temporal signal stability of KCl:Eu2+ storage phosphor dosimeters

Current KCl:Eu(2+) prototype dosimeters require a wait time of 12 h between irradiation and dosimetric readout. Although irradiating the dosimeters in the evening and reading on the following day works well in the clinical schedule, reducing the wait time to few hours is desirable. The purposes of this work are to determine the origin of the unstable charge-storage centers and to determine if these centers respond to optical or thermal excitation prior to dosimetric readout. Pellet-style KCl:Eu(2+) dosimeters were fabricated in-house for this study. A 6 MV photon beam was used to irradiate the dosimeters. After x ray irradiation, dosimeters were subjected to external excitation with near-infrared (NIR) light, ultraviolet (UV) light, or thermal treatment. Photostimulated luminescence (PSL) signal's temporal stability was subsequently measured at room temperature over a few hours using a laboratory PSL readout system. The dosimeters were also placed in a cryostat to measure the temperature dependence of the temporal stability down to 10 K. Strong F-band was present in the PSL stimulation spectrum, indicating that F-centers were the electron-storage centers in KCl:Eu(2+) where an electron was stored at a chlorine anion vacancy. Due to deep energy-depth (2.2 eV), F-centers were probably not responsible for the fast fading in the first a few hours post x ray irradiation. In addition, weak NIR bands were present. However, there was no change in PSL stabilization rate with intense NIR excitation, suggesting that the NIR bands played no role in the PSL fading. At temperatures lower than 77 K there was almost no signal fading with time. Noticeable PSL was observed for undoped KCl samples at room temperature, suggesting that Cl(2) (-) V(k) centers served as hole-storage centers for both undoped and doped KCl where a hole was trapped by a chlorine molecular ion. V(k) centers were stable at low temperature and became mobile at room temperature, probably causing the observed PSL fading with time. On the other hand, V(k) center could be stabilized by Eu(2+) activator or oxygen in the lattice, leading to the stable component in the PSL. A thermal process at elevated temperatures (60 °C or higher) was able to significantly accelerate the migration process resulting in a fast stabilization of PSL. However, this could not be accomplished using intense UV excitation. Thermal treatment enables KCl:Eu(2+) prototypes to be ready for readout in 1 h without the need of applying a large time-dependent correction factor. However, this cannot be achieved using optical preexcitation.

Synthesis, Characterizations and Luminescent Properties of Two Cadmium(II) Coordination Polymers Derived from Bis(Benzimidazole)-Based Ligands

Two Cd(II) coordination polymers, namely, {[Cd(L1)(chdc)]·(CH3CN)·(H2O)2}n (1) and [Cd(L2)Cl2]n (2) (L1 = 1,4-bis(5,6-dimethylbenzimidazole-1-ylmethyl)benzene, L2 = 1,2-bis(5,6-dimethylbenzimidazole-1-ylmethyl)benzene, H2chdc = 1,4-cyclohexanedicarboxylic acid) have been obtained by hydrothermal methods and characterized by IR, TG, elemental analysis, XPRD and single crystal structure analysis. The Cd(II) atom has a distorted octahedral coordination geometry in 1 and a roughly square-pyramidal coordination geometry in 2. Polymer 1 possesses a two-dimensional (2D) flat (6,3) network constructed with L1 and chdc bridging ligands. Polymer 2 displays a one-dimensional (1D) loop-like chain structure bridged by chlorine anions and L2 ligand, which is further arranged into a 2D supramolecular layer through face-to-face π–π stacking interactions. The luminescent properties of the polymers 1 and 2 were investigated in the solid-state. Two new coordination polymers of cadmium have been synthesized by different bis(benzimidazole) ligands. Both the complexes are characterized by X-ray single crystal structure, thermal and photoluminescence study.