Chloride Counterions Research Articles

Single-molecule magnet of a tetranuclear dysprosium complex disturbed by a salen-type ligand and chloride counterions.

A series of three salen-type lanthanide complexes, e.g., [Dy4(L)2(HL)2Cl2(μ3-OH)2]2Cl2(OH)2·3CH3CH2OH·H2O (1) and [Ln4(L)2(HL)2Cl2(μ3-OH)2]Cl2·5CH3OH·4CH2Cl2 (Ln = Tb(III), 2; Ho(III), 3) have been isolated by the reactions of H2L (H2L = N,N'-bis(3-methoxysalicylidene)cyclohexane-1,2-diamine) with LnCl3·6H2O. X-ray crystallographic analysis reveals that all complexes 1-3 are isostructural, in which four Ln ions and eight O atoms form the distorted defective dicubane {Dy4O8} cores. Magnetic studies indicate that complex 1 exhibits two slow magnetic relaxation processes with effective energy barrier Ueff = 55.71 K under a zero direct-current field, which is attributed to the two coordination geometries of the Dy(III) ions with a salen-type ligand and coordination of a chloride counterion. It represents the highest energy barrier among the salen-type tetranuclear lanthanide single-molecule magnets.

On the function and fate of chloride ions in amyloidogenic self-assembly of insulin in an acidic environment: salt-induced condensation of fibrils.

Formation of amyloid fibrils is often facilitated in the presence of specific charge-compensating ions. Dissolved sodium chloride is known to accelerate insulin fibrillation at low pH that has been attributed to the shielding of electrostatic repulsion between positively charged insulin molecules by chloride ions. However, the subsequent fate of Cl(-) anions; that is, possible entrapment within elongating fibrils or escape into the bulk solvent, remains unclear. Here, we show that, while the presence of NaCl at the onset of insulin aggregation induces structural variants of amyloid with distinct fingerprint infrared features, a delayed addition of salt to fibrils that have been already formed in its absence and under quiescent conditions triggers a "condensation effect": amyloid superstructures with strong chiroptical properties are formed. Chloride ions appear to stabilize these superstructures in a manner similar to stabilization of DNA condensates by polyvalent cations. The concentration of residual chloride ions trapped within bovine insulin fibrils grown in 0.1 M NaCl, at pD 1.9, and rinsed extensively with water afterward is less than 1 anion per 16 insulin monomers (as estimated using ion chromatography) implying absence of defined solvent-sequestered nesting sites for chloride counterions. Our results have been discussed in the context of mechanisms of insulin aggregation.

Adsorption of Transition Metal Chlorides by Silica with Grafted 1-n-Propyl-3-Methylimidazolium Chloride

Silica with grafted 1-n-propyl-3-methylimidazolium chloride was investigated as adsorbent for the removal of cobalt(II), copper(II), zinc(II), cadmium(II) and mercury(II) chlorides from alcoholic and aqueous solutions. The adsorption proceeds via the formation of metal-chloride anionic complexes detained near the grafted organic cations as counterions. This conclusion is corroborated by the electronic and Raman spectra. The high removal degrees of the metal chlorides from solutions are easily reached. The adequate models of adsorption equilibria consider dissociation and auto-complexation of chlorides in solutions and formation of tri- and tetrachlorometallate anions in the solid phase. Also, the equilibrium constants for the CoCl 2 and CuCl 2 adsorption by several materials containing grafted organic cations and chloride counterions were recalculated in the framework of this model. The weak dependence of equilibrium constants on the nature of immobilized cations and carriers agrees with the established chemistry of metal chlorides fixation.

Modelling the effects of competing anions on fluoride removal by functionalized polyacrylonitrile coated with iron oxide nanoparticles

Fe 2 O 3 nano particles supported on functionalized poly-acrylonitrile was prepared. PAN-oxime-nano Fe 2 O 3 was characterized by XRD, FTIR andTEMand used for fluoride adsorption. The adsorption capacity increased with increasing initial fluoride concentration and reaction time. Fluoride-removal performance of PAN-oxime-nano Fe 2 O 3 was also tested in the presence of various competing anions usually found in drinking water. Competitive sorption between fluoride and competing anions showed a minimum preference for chloride counterions. Carbonate was the greatest competitor for fluoride removal followed by phosphate and sulphate. Counterion presence decreased fluoride adsorption capacity in order of CO 3 2− > PO 4 3− > SO 4 2− > Cl − . The presence of anions at various concentrations decreased fluoride adsorption capacity on PAN-oxime-nano Fe 2 O 3 by 1.22 to 6.51 mg g –1 . Effects of each two anions exist simultaneously in aqueous solution on fluoride adsorption was investigated using Tukey’s test (called also a pairwise comparison). Tukey’s HSD results indicate that the differences between various pairs of anions are significant (P < 0.05), except for chloride–sulphate (P = 0.08). In the design of PAN-oxime-nano Fe 2 O 3 for environmental applications, the strong influence of the counter ions must be considered. KEYWORDS Fluoride, PAN-oxime- nano Fe 2 O 3 , counterion, adsorption.

Understanding Aqueous Electrolyte Stability through Combined Computational and Magnetic Resonance Spectroscopy: A Case Study on Vanadium Redox Flow Battery Electrolytes

AbstractThe investigation of the vanadium electrolyte stability issue on the molecular‐level solvation structure and the dynamics has led to the successful designing of mixed acid‐based vanadium electrolytes. This new mixed‐acid based electrolyte system render approximately 70 % increase in energy density (≈40 Wh L−1) and approximately 80 % increase in stable temperature window (−10 to +50 °C) compared with conventional sulfuric acid‐based vanadium electrolyte. Through a comprehensive study by density functional theory and nuclear magnetic resonance spectroscopies, the improved stability is attributed to the hydrochloric acid as optimal cosolvent providing chloride anions for a ligand‐exchange process in the vanadium solvation structure. The role of the chloride counteranion in the solvation structure and dynamics of vanadium species was studied using combined magnetic resonance spectroscopy and DFT‐based theoretical methods. The solvation phenomenon of multiple vanadium species and their impact on vanadium redox flow battery electrolyte chemical stability are discussed.

Structure of the electrical double layer at aqueous gold and silver interfaces for saline solutions

We report the structure of the electrical double layer, determined from molecular dynamics simulations, for a range of saline solutions (NaCl, KCl, MgCl2 and CaCl2) at both 0.16 and 0.60molkg−1 on different facets of the gold and silver aqueous interfaces. We consider the Au/Ag(111), native Au/Ag(100) and reconstructed Au(100)(5×1) facets. For a given combination of metallic surface and facet, some variations in density profile are apparent across the different cations in solution, with the corresponding chloride counterion profiles remaining broadly invariant. All density profiles at the higher concentration are predicted to be very similar to their low-concentration counterparts. We find that each electrolyte responds differently to the different metallic surface and facets, particularly those of the divalent metal ions. Our findings reveal marked differences in density profiles between facets for a given metallic interface for both Mg2+ and Ca2+, with Na+ and K+ showing much less distinction. Mg2+ was the only ion for which we find evidence of materials-dependent differences in interfacial solution structuring between the Ag and Au.

Crystal structure of bis-{N-[2-(di-methyl-amino)-eth-yl]quinolin-8-amine-κ(3) N,N',N''}nickel(II) dichloride 3.5-hydrate.

In the title compound, [Ni(C13H17N3)2]Cl2·3.5H2O, the geom­etry of the NiN6 complex cation is slightly distorted octa­hedral, with a facial arrangement of the two tridentate N-[2-(di­­methyl­amino)­eth­yl]quinolin-8-amine ligands around the metal ion. The asymmetric unit consists of two independent complex half-mol­ecules located on centres of inversion, together with two chloride counter-anions and 3.5 water mol­ecules of solvation, one of which is disordered across an inversion centre. In the crystal, O—H⋯O, O—H⋯Cl and N—H⋯Cl hydrogen-bonding inter­actions form a three-dimensional network structure.

Counterion-assisted cation transport in a biological calcium channel.

How ions pass through the lumen of an ion channel is a key question underlying cellular communication. The effects of water and pore-lining residues (channel design) have been extensively explored. However, the role of counterions is less well understood. The pore subunit of the calcium release-activated calcium channel, Orai, provides a useful model to explore the effect of anions on the permeation of cations. Herein, we employ computer simulations molecular dynamics (MD) to explore ion permeation through the V174A Orai mutant, a constitutively open pore, in a phospholipid membrane hydrated by a 150 mM NaCl solution. When an external voltage is applied in the MD simulations, it induces only a moderate conformational change to the channel, which facilitates the passage of ions. Infrequent sodium permeation is observed on the microsecond time scale, which is consistent with experiment. In contrast, the chloride counterions exhibit higher mobility in the channel and are actively involved in sodium transport. The anion-assisted cation permeation identified here likely highlights a more general functional role for counterions, especially in ion channels with medium pore-size. Experiments with a variety of counterions might further illuminate the nature of their active role.

Crystal structure of bis-(4-nitro-aniline-κN (1))(5,10,15,20-tetra-phenyl-por-phy-rin-ato-κ(4) N)cobalt(III) chloride di-chloro-methane monosolvate.

The reaction of [CoIII(TPP)Cl] (TPP is the dianion of 5,10,15,20-tetra­phenyl­porphyrin) with an excess of 4-nitro­aniline in di­chloro­methane leads to the title compound, [CoIII(C44H28N4)(C6H6N2O2)2]Cl·CH2Cl2. The CoIII ion lies on an inversion centre and is octa­hedrally coordinated by two N atoms of the NH2 groups of the two 4-nitro­aniline trans-axial ligands and four pyrrole N atoms of the porphyrin. The asymmetric unit contains one half of the [CoIII(TPP)(4-nitro­aniline)2]+ ion complex, one chloride counter-ion (lying on a twofold rotation axis) and one half di­chloro­methane solvent mol­ecule, where the C atom lies on a twofold rotation axis. The average equatorial Co—N(pyrrole) distance (Co—Np) is 1.982 (2) Å and the axial Co—N(4-nitro­aniline) bond length is 2.006 (2) Å. The crystal packing is stabilized by an N—H⋯Cl hydrogen bond between the N atom of the amino group of the 4-nitro­aniline axial ligand and the chloride counter-ion. The supra­molecular architecture is further stabilized by weak C—H⋯π inter­actions.

Crystal structure of chlorido-penta-kis(dimethyl sulfoxide-κO)chromium(III) dichloride.

In the complex cation of the title salt, [CrCl(C2H6OS)5]Cl2, the CrIII ion is coordinated by one chloride ligand and five O atoms from dimethyl sulfoxide (DMSO) ligands, leading to a slightly distorted octa­hedral coordination environment [O—Cr—O angles range from 86.69 (16) to 92.87 (16)°]. In the crystal, complex cations are arranged in hexa­gonally packed rows parallel to [010], with the chloride counter-anions situated in between. The inter­actions between cations and anions are mainly ionic in nature.

P2 The detection of propofol glucuronide in human hair using LC-MS/MS: Case study and survey of high-risk health professionals

Background Propofol (2,6-diisopropylphenol) is a commonly used agent for general anesthesia because of its short duration, quick recovery time, and minimal side effects. Although not a controlled substance in the United States, propofol abuse and misuse by medical professionals has increased 5-fold between 1997 and 2011. Propofol detection in biological fluids has a very short detection window and the presence of propofol in hair does not distinguish between ingestion and environmental exposure. A metabolite, propofol glucuronide, is formed in the liver and may be detected in the hair. The purpose of this study is to validate a method for the detection of propofol glucuronide in hair and apply this method to a case study and a survey of high-risk health professionals. Methods A method for the detection of propofol glucuronide was developed and validated according commonly recognized guidelines. Briefly, hair specimens were powdered and extracted into water while incubating in a sonicating water batch without heat over night. Extracts were subjected to solid phase extraction using quaternary amine with chloride counter ion extraction cartridges. The eluates were evaporated under nitrogen at 40 °C, reconstituted in 100 μL of DI water. Extracts were separated using Synergy Polar RP column (50mm x 2mm x 2.5 μm particle size) on an Agilent 1200 HPLC system. The compounds were detected on an AB Sciex 5500 tandem mass spectrometer (LC-MS/MS) following the transitions of 353,1 m/z to 176,7 m/z , 112,6 m/z , 84,7 m/z for propofol glucuronide and 370,1 m/z to 193,7 m/z and 369,7 m/z for the internal standard, propofol glucuronide- d 17 . A hair specimen that originated from a 50 year old woman that was anesthetized for 15 minutes was analyzed. Additionally, a survey of 300 de-identified hair specimen remnants that originated from health professionals undergoing treatment for substance abuse. Results The empirically determined LOD and LOQ for this assay were 4 pg/mg and 8 pg/mg, respectively. The intra- and inter-assay bias and imprecision studies were all acceptable ( Conclusion This method demonstrated sufficient precision, accuracy and robustness with an analytical measurement range between 8 pg/mg and 100 pg/mg. While being sensitive enough to identify two individuals in a survey of high-risk substance abuse treatment participants, the method was not able to identify propofol metabolite in the hair of a woman receiving a routine quantity of propofol administered during a short surgical procedure. This method provides substance abuse treatment professionals with another objective tool to identify propofol abusers.

Synthesis, supramolecular assemblies and luminescence of nickel(II) complexes based on a series of N-(2-pyridylmethyl) amino acid derivatives

N-(2-Pyridylmethyl)-l-alanine (l-Hpana), and N-(2-pyridylmethyl)-aspartic acid (l-H2pasp) have been solvothermally prepared and structurally characterized by X-ray single-crystal diffraction. Complexes 1 and 2 crystallize in the monoclinic P21/c and orthorhombic C2221 space groups, respectively, due to the dissimilar ligand features (chirality of l-Hpana). They show similar mononuclear coordination structures with two kinds of five-member chelating rings, which are assembled into 2D supramolecular networks through multiple N–H⋯O and O–H⋯O interactions. For complex 3, the formation of a Ni–O bond between Ni(II) and the side-chain carboxylate lead to a left-handed helical coordination polymer with helical water chains inclusion. The most striking feature is that the helical hydrogen-bonding motif represents rare hydrated hydronium aggregation that formed by strong interactions between hydronium ions and guest water molecules. This helical aggregate is further stabilized by multiple hydrogen bonds with other lattice water molecules and chloride counteranions. The thermal and luminescent properties of these complexes have also been investigated.

Photo‐Induced Water Oxidation Based on a Mononuclear Cobalt(II) Complex

AbstractPhoto‐induced water oxidation based on first row transition metal complexes has drawn much attention recently as a part of the efforts to design systems for solar fuel production. Here, the classic tetradentate ligand TPA (tris(2‐pyridylmethyl)amine) is used together with cobalt(II) in CH3CN to form a mononuclear cobalt complex [Co(TPA)Cl]Cl. Single crystal X‐ray diffraction shows that [Co(TPA)Cl]Cl is composed of discrete cationic units with a penta‐coordinate cobalt center, along with chloride counter ions. In borate buffer, the Co complex acts as a water oxidation catalyst, as shown by the presence of a catalytic wave in electrochemistry. Under visible light irradiation, in the presence of photosensitizer and electron acceptor, the Co complex catalyzes O2 evolution with a turnover frequency (TOF) of 1.0 mol(O2)·mol(Co)−1·s−1 and a turnover number (TON) of 55 mol(O2)·mol(Co)−1 in pH 8 borate buffer.

Reaction between [Ir(COD)(PMe3)3]Cl and 2-aminopent-4-enoic acid: Tridentate N, O and C bonding

The reaction between the electron-rich iridium(I) complex, [Ir(COD)(PMe3)3]Cl, and the amino acid, 2-aminopent-4-enoic acid leads to the direct formation of a product with facial geometry about the iridium center with three PMe3 groups, and tripodal coordination of the amino acid via N, O and C. The synthesis of this product can be visualized as involving the formation of an iridium hydride followed by insertion of the pendant alkene. Two different crystal structures of the product were determined, one containing a chloride counterion and one with a tetraphenylborate counterion. The change in counterion leads to very different intermolecular interactions.

Charge distribution in Mn(salen) complexes

The charge and spin distribution in manganese-salen complexes were analyzed using different basis sets and density functionals. Five population analysis methods [Mulliken, Löwdin, Natural population analysis (NPA), atoms in molecules (AIM), and CHelpG] were used to characterize the charge distribution. Results show that NPA and AIM were the only methods capable of giving charges with the correct sign for all cases under study. According to the analysis of the natural charge and spin distributions, the salen ligand shows a complex behavior, counteracting the effect of the chloro and oxo ligands on the metal center. Furthermore, the presence of a chloride counter ion increases the oxo-radical character of Oxo-Mn(salen) complexes, which may play an important role in the rationalization of the catalytic properties of Mn(salen) complexes. © 2014 Wiley Periodicals, Inc.

A DFT study on the NHC catalysed Michael addition of enols to α,β-unsaturated acyl-azoliums. A base catalysed C–C bond-formation step

The NHC catalysed nucleophilic additions of enols to α,β-unsaturated acyl-azolium intermediates have been investigated using DFT methods at the MPWB1K/6-31G** computational level. In the direct and the conjugate additions, formation of a hydrogen bond (HB) with the carboxyl oxygen is not sufficient to favour the C-C bond formation as a consequence of the low nucleophilic character of enols. Interestingly, when enols form a HB with the chloride counterion, the activation energies associated with the conjugate addition decrease as a consequence of the increased nucleophilic character of enols and the increased electrophilic character of the 'acyl-azolium + Cl' ion pair. Analysis of the DFT reactivity indices allows establishing a base catalysed C-C bond-formation step promoted by the chloride counterion.

An enzymatic biomimetic system: enhancement of catalytic efficiency with new polymeric chiral ionic liquids synthesised by controlled radical polymerisation

The controlled radical polymerization of monomeric units containing chiral ionic liquids (CILs) allows the synthesis of intrinsically chiral polymers through a bottom-up design. These polymeric chiral ionic liquids (PCILs) show a well-defined three dimensional structure organized as the result of a complex non-covalent network of hydrogen-bonding contacts driven by the C2 hydrogen atoms of the imidazolium aromatic rings and the OH moieties present in the side functionalities of the main polymeric chain. The exchange of the chloride counter ion by the L-prolinate anion leads to new types of polymeric catalysts, which behave as efficient artificial aldolase biomimetic systems, being highly active and selective for the aldol reaction in water. These new polymeric catalysts are significantly more active than the corresponding monomeric counterpart when the reaction is performed either in water or in the presence of water. The increase in catalytic efficiency can be related to their 3D structure, displaying helical chirality in the polymeric chain as a function of their preparation methodology. Under suitable experimental conditions, these polymers are able to catalyse the consecutive aldol-dehydration process, behaving as synthetic mimics of the aldolase-dehydrogenase enzymatic system. Moderate enantioselectivities can be achieved under suitable conditions.

Simulation study of the G=4 PAMAM dendrimer in water at different pH conditions

We report an analysis of Molecular Dynamics simulations carried out for the PAMAM-EDA dendrimer in water, considering neutral dendrimer, or high pH conditions, or assuming that all the amine groups are fully protonated at low pH (the addition of chloride counterions ensures the global charge neutrality of the system in this case). These simulations were performed considering the PCFF force-field with explicit consideration of hydrogen bonds and using the TIP3P molecular parameters for the water molecules. Our data indicate a remarkably different orientational distribution of dendrimer units for the two systems, low or high pH, with stronger segregation of dendrons in the former case Neutral dendrimers adsorb more water molecules.

Cyanobiphenyl versus Alkoxybiphenyl: Which Mesogenic Unit Governs the Mesomorphic Properties of Guanidinium Ionic Liquid Crystals?

A series of phenylguanidinium salts 3·X, which are linked via an alkoxy spacer either to a 4-decyloxy- or 4-cyano-substituted biphenyl mesogen, was prepared and the mesomorphism studied. A decyloxybiphenyl core and a spacer of at least C6 chain length were required for mesophase formation. Replacement of the chloride counterion by other anions like bromide or tetrafluoroborate improved the thermal stability of the mesophase. A comparison of substitution pattern (meta v. para) on the phenyl ring revealed decreased melting and clearing points for the bent cationic head group. All guanidinium ionic liquid crystals 3 displayed only smectic A (SmA) phases. A packing model is assumed where the molecules in a bilayer stack over each other in opposite direction with interdigitated terminal decyloxy groups and spacers.

Measurement of the Electrostatic Interaction between Polyelectrolyte Brush Surfaces by Optical Tweezers

We demonstrated an optical tweezers method to measure the electrostatic interaction between the strong polyelectrolyte brushes, poly(2-(methacryloyloxy)ethyltrimethylammonium chloride) (PMTAC), grafted on silica particles in aqueous media. The weak electrostatic interaction was successfully detected with a resolution of less than 0.1 μN m(-1). The apparent Debye length, including the charge distribution in the polymer brush and the surface potential, decreased as the salt concentration in the medium increased. The experimentally obtained surface charge density was much smaller than that estimated from the amount of polyelectrolyte on the surface. Furthermore, the dissociation of ionic groups was enhanced by decreasing the grafting density of the polyelectrolyte brush. The results suggest that the majority of chloride counterions was immobilized in the dense polyelectrolyte brush layer to neutralize the high charge density.