Effect Of Counterions Research Articles

Mechanistic studies on counter-ionic effects of camphorsulfonate-based ionic liquids on kinetics, thermodynamics and stereoselectivity of β-amino carbonyl compounds

Catalysis is important in various applications of organic chemistry and its output product control for stereoselective compounds is outrageous. Establishment of experimental facts of stereoselective compounds from catalysis and their validation using theoretical evidences is the key to understand various mechanisms of optically active compounds. A family of new ionic liquids (ILs) with various imidazolium cations and camphorsulfonate anion as environmentally benign liquid salts have been synthesized and deployed for catalysis of β-amino carbonyl compounds. The products were formed using ILs as a homogeneous catalyst with excellent product yield and diastereoselectivity. The effect of counter ions, Hammett acidity and viscosity of ILs along with solvent and temperature are explored in terms of reaction kinetics and product yields. Density functional theory (DFT) was used to investigate thermodynamical study of mechanistic pathway of the reaction. The DFT calculations predicted that the catalysis mechanism involved both counterions of the IL. Moreover, it is evidenced that the syn-pathway required lower activation energy while anti-pathway led to thermodynamically stable product. This study explores new avenues for using ILs as potential homogeneous catalysts for the production of stereoselective species.

Transition-State Expansion: A Quantitative Model for Counterion Effects in Ionic Reactions.

SummaryIonic reactions are the most common reactions used in chemical synthesis. In relatively low dielectric constant solvents (e.g., dichloromethane, toluene), ions usually exist as ion pairs. Despite the importance of counterions, a quantitative description of how the paired 'counterion' affects the reaction kinetic is still elusive. We introduce a general and quantitative model, namely transition-state expansion (TSE), that describes how the size of a counterion affects the transition-state structure and the kinetics of an ionic reaction. This model could rationalize the counterion effects in nucleophilic substitutions and gold-catalyzed enyne cycloisomerizations.

NaTePO5, SrTeP2O8 and Ba2TeP2O9: Three tellurite-phosphates with large birefringence

Two new tellurite-phosphates NaTePO5, SrTeP2O8 and the previously reported Ba2TeP2O9 were synthesized successfully via high-temperature solid-state reactions and their structures were determined by single-crystal X-ray diffraction. The structures of NaTePO5 and SrTeP2O8 feature two-dimensional (2D) [TePO5]- and [TeP2O8]2- anionic layers interleaved with Na+ and Sr2+ cations, respectively. The 31P NMR spectra show that electron density around phosphorus atoms in SrTeP2O8 is slightly larger than that in Ba2TeP2O9, owing to the connection modes of [TeO5] and [PO4] units and counter-ion effects. The calculated electric field strength (Z/a2) based on the 31P chemical shift indicate as the chemical shift increases the Z/a2 also increases, as evidenced by the binding energy of P 2p determined by the X-ray photoelectron spectroscopy. Further, first-principle calculations show that the NaTePO5, SrTeP2O8 and Ba2TeP2O9 exhibit large birefringence of 0.212, 0.133 and 0.126 at 1064 nm, respectively, compared to other phosphates.

Micro-solvation and counter ion effects on ionic reactions: Activation of potassium fluoride with 18-crown-6 and tert-butanol in aprotic solvents

Ionic reactions have an important solvent effect and the first solvation shell makes the most important contribution for determining the reactivity. In the case of nucleophilic fluorination with potassium fluoride, the solubilization of the salt is another aspect which needs be considered. In the present work, the effect of adding stoichiometric quantity of 18-crown-6 and the bulky alcohol tert-butanol to the reaction of potassium fluoride with alkyl bromide in toluene and acetonitrile solvents was investigated by theoretical methods as molecular dynamics and electronic structure calculations, as well as by experiments. The calculations indicate that the fluoride ion in the KF (18-crown-6) complex interacts with tert-butanol molecules forming aggregates with one (acetonitrile solvent) and three (toluene solvent) tert-butanol molecules. The calculations predict that formation of these aggregates increase the solubilization of KF and produces and important rate acceleration effect in both acetonitrile and toluene solvents, which is experimentally observed. In the concentration around 0.75 mol L−1 of the tert-butanol, the reaction rate is proportional to the alcohol concentration and the rate of alkyl halide decay becomes 10 times higher than the rate without this alcohol. The present results point out that both the interactions of KF with crown ether and tert-butanol molecules have a synergic effect, increasing its reactivity towards SN2 reactions.

Influence of the ancillary ligands on the luminescence of platinum(II) complexes with a triazole-based tridentate C^N^N luminophore

The effect of different ancillary ligands and counterions in platinum(II) complexes has been investigated. Based on the previously reported tridentate C^N^N ligand precursor 2-(1-benzyl-1H-1,2,3-triazol-4-yl)-6-phenylpyridine (HL), the photophysical properties of complexes of the type [Pt(L)(X)]n+ have been varied by changing the fourth (monodentate) ligand (X) of the square-planar platinum(II) complexes. Different lifetimes and quantum yields were observed, depending on the identity of this ancillary ligand. The most favorable photophysical properties within this series of complexes were obtained for neutral complexes with the phenylacetylido ligand with a quantum yield of 35% and a lifetime of 2.22 µs, while for cationic complexes bearing nitrile, isonitrile and triphenylphosphane units gave comparable results with quantum yields ranging from 11% to 16% and lifetimes from 3.59 µs to 4.93 µs. Introducing a ferrocene moiety attached to an acetylido ligand, the complex became hardly emissive. The investigated counterions perchlorate, tetrafluoroborate and hexafluorophosphate of positively charged complexes regarding their photophysical properties were found to affect the non-radiative decay rates. To understand the minor effect observed for the emission maxima of the complexes, density functional theory (DFT) was applied. The experimental emission spectra of the complexes were reproduced by using simplified model systems. The distribution of the frontier orbitals used for the description of the emissive T1 state in its optimized geometry mainly involves the tridentate luminophore rather than the ancillary ligand. This explains why the emission is dominated by the pincer unit with perturbative participation of the metal center while excluding significant influence of the ancillary ligand.

Thiourea-Derived Chelating Ligands and Their Organometallic Compounds: Investigations into Their Anticancer Activity.

Thiones have been investigated as ligands in metal complexes with catalytic and biological activity. We report the synthesis, characterization, and biological evaluation of a series of MII/III complexes of the general formulae [MII(cym)(L)Cl]X (cym = η6-p-cymene) or [MIII(Cp*)(L)Cl]X (Cp* = η5-pentamethylcyclopentadienyl), where X = Cl− or PF6−, and L represents heterocyclic derivatives of thiourea. The thiones feature a benzyl-triazolyl pendant and they act as bidentate ligands via N,S-coordination to the metal centers. Several derivatives have been investigated by single-crystal X-ray diffraction analysis. NMR investigations showed a counterion-dependent shift of several protons due to the interaction with the counterions. These NMR investigations were complemented with X-ray diffraction analysis data and the effects of different counterions on the secondary coordination sphere were also investigated by DFT calculations. In biological studies, the Ir benzimidazole derivative was found to accumulate in the cytoplasm and it was the most cytotoxic derivative investigated.

The Effect of Counterions in Hydrophobic Ion Pairs on Oral Bioavailability of Exenatide.

The aim of this study was to evaluate the potential of n-octadecyl sulfate (SOS) as a counterion for hydrophobic ion pairing (HIP) with exenatide-a potent glucagon-like peptide-1 (GLP-1) analogue in the treatment of diabetes mellitus-to improve its oral bioavailability. Exenatide was ion-paired with SOS and docusate (DOC) serving as the gold standard followed by the incorporation in a self-emulsifying drug delivery system (SEDDS) comprising Capmul MCM EP, Captex 355, Kolliphor RH40, and propylene glycol at a mass ratio of 41:15:40:4. The hydrophobicity of exenatide-SOS and exenatide-DOC was characterized by determining the butanol-water partition coefficient (log Pbutanol/water). Droplet size and zeta potential of the ion pair-loaded SEDDS were characterized followed by intestinal membrane permeability determination on freshly excised rat intestines compared to exenatide solution. Furthermore, the oral bioavailability of exenatide-SOS- and exenatide-DOC-loaded SEDDS was also evaluated in vivo in healthy male Sprague-Dawley rats. Hydrophobic ion pairing increased the log Pbutanol/water of exenatide from -1.9 to 2.0 for exenatide-SOS and to 1.2 for exenatide-DOC. SEDDSs loaded with 0.26% (m/m) exenatide-SOS and 0.17% (m/m) exenatide-DOC had mean droplet size less than 30 nm and negative zeta potential. Ex vivo permeation experiments revealed 3.5-fold and 6.4-fold improvement in membrane permeability of the exenatide-SOS-loaded SEDDS vs. the exenatide-DOC-loaded SEDDS and exenatide solution, respectively. The orally administered exenatide-SOS-loaded SEDDS and exenatide-DOC-loaded SEDDS resulted in relative oral bioavailability vs. subcutaneous injection (SC) of 19.6 and 15.2%, respectively. Within this study, the key role of counterions for oral peptide delivery via HIP could be confirmed, and SOS was identified as a promising surfactant for this purpose.

Morphologies of spherical bidisperse polyelectrolyte brushes in the presence of trivalent counterions

We study surface morphologies of a bimodal polyelectrolyte brush grafted onto a surface of spherical colloid in the presence of trivalent counterions, using molecular dynamics simulations. Both the good and poor solvent conditions are considered. Grafting density and charge fraction are varied to generate a series of microphase separated structures, which represents the competition between the excluded volume interaction and trivalent counterion mediated bridging. The short chains are more extended than the long counterparts under good solvent conditions, which are different with those under poor solvent conditions through a careful analysis on shape factor of grafted chains as well as distributions of monomers and counterions. Furthermore, the electrostatic bridging effect of trivalent counterions is analyzed carefully by classifying them into four states. Also, our simulation results can sever as a guide for improving the performance of polydisperse polyelectrolyte brushes as smart stimuli-responsive materials.

Coumarin substituted 4–aryl–1,2,4–triazolium salts and their silver(I) N–heterocyclic carbene complexes: Effects of counterions on the antioxidant and antihaemolytic properties

Although numerous silver complexes have been found to target human derived leukemia cells, the nature and reactivity of such species with normal human red blood cells and targeting oxidants remain unexplored. In this contribution, we report the synthesis and characterization of three series of structurally varied silver complexes derived from biologically active coumarin substituted 1,2,4–triazol–5–ylidine ligands. 1,2,4–Triazolium salts (6–13) that serve as NHC precursors have been prepared by treating 4–(2,6–dimethylphenyl) triazole with substituted 4–bromomethylcoumarin derivatives, and corresponding silver NHC complexes (14–25) by in situ deprotonation method using appropriate silver sources. Complexes 14, 15 and 18 have been studied for their structure following single crystal X–ray diffraction technique, which adjudicates the presence of silver atom in an almost linear coordination geometry. Complexes 21 and 22 displayed promising antioxidant potential with the IC50 (a concentration of test sample required to neutralize DPPH radicals by 50%) value of 7.49 ± 0.702, 7.42 ± 0.125 μM, respectively; while the triazolium salt displayed no activity in the working concentration range (10–250 μM). Likewise, at a concentration of 100 μM the silver complexes showed significantly less percentage lysis of human red blood cells in the range 2.36 ± 0.59 to 8.49 ± 0.27% (except 18, 24 and 25).

Municipal solid waste incineration fly ash exposed to carbonation and acid rain corrosion scenarios: Release behavior, environmental risk, and dissolution mechanism of toxic metals

This study investigated the leaching behavior, environmental risk, and dissolution mechanism of toxic metals (TMs) in solidified/stabilized municipal solid waste incineration fly ash (MSWI FA) exposed to alternative “carbonation + acid rain corrosion” disposal scenarios. The content of TMs (mg/kg) showed a trend of Zn (12,187.10 ± 168.60) > Pb (3374.43 ± 66.12) > Cu (1055.14 ± 32.52) > Cr (127.95 ± 8.12) > Cd (119.05 ± 6.26) > Ni (49.50 ± 3.20). Initial leaching of CO2-saturated water (CSW) and replacement of simulated acid rain (SAR) increased the environmental risk of leached TMs. The results of “average release rate” (mg/(kg·d)) of TMs indicated that Zn (0.8307)/Cu (0.0278)/Cd (0.0109) and Cu (0.0581)/Cr (0.001176)/Ni (0.004339) in phosphoric acid stabilized FA and Pb (0.0753)/Cr (0.001921)/Ni (0.00111) and Pb (0.0656)/Zn (1.0560)/Cd (0.0050) in Portland cement solidified FA were the key “problem TMs” during carbonation and acid rain corrosion, respectively. CSW leaching increased the independent environmental risk of most TMs in residual FA (especially Zn/Cd) due to the increased carbonate-bound fraction. Compared with independent carbonation, alternative “carbonation + acid rain corrosion” contributed to a higher comprehensive environmental risk for TMs in residual FA. CSW leaching system was an indirect carbonation based on CO2-water and FA matrix, in which “nucleation and dissolution” of carbonates and “immobilization and dissolution” of TMs coexisted. The dissolution mechanism of TMs was mainly controlled by reaction equilibrium of nucleation and dissolution of carbonates containing TMs. Dissolution and nucleation were the dominant mechanism in the early and later periods of CSW leaching, respectively. Carbonate layer dissolution, H+ corrosion/displacement, and counter-ion effect (SO42− > NO3− > Cl−) were the main mechanisms affecting TM dissolution during SAR leaching.

Aqueous solubility of kinase inhibitors: III the effect of acidic counter ion on the dovitinib/γ-cyclodextrin complexation

Dovitinib, a hydrophobic kinase inhibitor (KI), is lipophilic anticancer agent that forms water-soluble complexes with cyclodextrins (CDs). However, dovitinib’s very low intrinsic solubility hampers the complex formation and, consequently, the CD solubilization. The aim of the study was to enhance the CD solubilization through formation of more water soluble dovitinib salts. When dovitinib is unionized (i.e. at pH above its pKa value) the phase-solubility profile of the binary dovitinib/γCD complex is of Bs-type with K1:1 of 684 M−1. Then the complex has limited solubility in water. Upon protonization, (i.e. at pH below the pKa value) the solubility of dovitinib was increased but the increase was dependent on the negatively charged counter ion. Citrate, acetate, EDTA and chloride resulted in the greatest solubility enhancement and, thus, were selected to further studies. The ternary phase-solubility profiles of dovitinib/γCD/counter ion were also of Bs-type while those of dovitinib/HPγCD/counter ion and dovitinib/SBEγCD/counter ion were of AN-type. The counter ions had greater solubilizing effect in SBEγCD solutions than in γCD and HPγCD solutions. This is due to the influence of charge-charge interaction between the positively charged dovitinib and negatively charged SBEγCD. Citrate was the most effective counter ion particularly in aqueous SBEγCD solutions. The complexation was verified by NMR. The highest dovitinib flux through semi-permeable membrane was observed from medium containing dovitinib/CDs/citrate complexes. In conclusion, citrate provided the highest dovitinib solubilization and complexation.

Theoretical Rationalization of Self-Assembly of Cellulose Nanocrystals: Effect of Surface Modifications and Counterions.

The hierarchical self-assembly of cellulose nanocrystals (CNCs) is an important phenomenon occurring naturally in plant cell walls. Utilization of this assembly for advanced applications requires a fundamental theoretical understanding of interactions between the CNCs, which is still incomplete. Hence, in this work, we used molecular dynamics simulations to study the effect of surface modification on the interactions between the CNCs and the resulting bundling process. We consider two types of common surface modifications of native CNCs, sulfated CNCs (SCNCs) and TEMPO-oxidized CNCs (TCNCs), in the presence of two types of counterions, Na+ and Ca2+, in solution. We used the umbrella sampling method to calculate the potential of the mean force (PMF), and we found that the strength of interaction between the modified CNCs decreases, compared with the native CNCs. The strength of interaction for TCNCs is almost similar to that for SCNCs at the same level of surface substitution, whereas the type of counterion has a strong effect on the PMF with a higher interaction energy between the CNCs in the presence of a divalent counterion as compared to a monovalent counterion. Finally, we studied the self-assembly of CNCs into a hexagonal bundle for the native CNCs and sulfated CNCs focusing on the twist of the bundle, bound water inside the bundle, inter-CNC gap, and interaction energy between the CNCs in the bundle, and the effect of the counterions on the morphology of the bundle. The equilibrium spacing of the CNCs within the bundle is found to be consistent with the results of PMF calculations for the minimum separation distance between the respective crystal surfaces.

STRUCTURE-ACTIVITY RELATIONSHIPS AND SURFACE IMMOBILIZATION OF POLYCATIONIC ANTIMICROBIALS

Antimicrobial agents have been the subject of scientific interest for the last few decades. However, the emergence of a novel coronavirus and pandemic that ensued has brought a new sense of urgency to the field of antibacterial research. The most urgent needs to mitigate the pandemic are self-disinfecting health equipment and antimicrobial protective equipment such as gowns for healthcare workers and face masks for the general public. At a time of high demand for antimicrobial products, understanding the mechanisms involved in antimicrobial polymers will be a benefit. In this review, the definition of antimicrobials and their classification according to the mode of action, as well as their chemical structure, were explained and used to build the fundamental understanding about antimicrobials and the working principles behind their action. The discussion continued with factors that affect the antimicrobial activity, which is the focus of the review. The first part of the review deals with free antimicrobial polymers in solution. The effect of molecular weight, counterions, spacer length and alkyl chain to the efficacy of antimicrobial polymers are highlighted and discussed at length. Focus in the second part shifts towards surface-immobilized antimicrobial polymers and their methods of immobilization.

Molecular Au(I) complexes in the photosensitized photocatalytic CO2 reduction reaction

Abstract

High-Throughput Salt Screening of Synthetic Intermediates: Effects of Solvents, Counterions, and Counterion Solubility

Using a statistical Z-score methodology, the yield data from 65 high-throughput acid screens and 45 base screens on synthetic intermediates were analyzed. The results show that salt screening outco...

Assessment of the SCAN Functional for Spin-State Energies in Spin-Crossover Systems.

The strongly constrained and appropriately normed (SCAN) functional has been tested toward the calculation of spin-state energy differences in a data set of 20 spin-crossover (SCO) systems, ranging from d4 to d7. Results show that the SCAN functional is able to correctly predict the low-spin state as the ground state for all systems, and the energy window provided by the calculations falls in the approximate range of energies that will allow for SCO to occur. Moreover, the SCAN functional can be used in periodic boundary condition calculations, accounting for the effect of collective crystal vibrations and counterions in the thermochemistry of the spin transition. Our results validate this functional as a potential method for in silico screening of new SCO systems at both, molecular and crystal-packed levels.

Computational Assessment of Counterion Effect of Borate Anions on Ethylene Polymerization by Zirconocene and Hafnocene Catalysts

The olefin polymerization performance of metallocene catalysts strongly depends on the nature of the counteranion provided by the activator system. The relative effect of two borate anions [B(C6F5)...

Effects of counterions and solvents on the geometrical and vibrational features of dinucleoside-monophosphate (dNMP): case of 3',5'-dideoxycytidine-monophosphate (dDCMP).

The effects of the interaction of the monovalent (Li+, Na+, K+) and divalent (Mg2+) counterions hexahydrated (6H2O), with the PO2- group, on the geometrical and vibrational characteristics of 3', 5'-dDCMP, were studied using the DFT/B3LYP/6-31++G(d) method. These calculations were performed using the explicit (6H2O) and hybrid (6H2O/Continuum) solvation models. The optimizations reveal that in the conformation g-g- and in the explicit model of solvation, the small ions (Li+, Na+) deviate from the bisector plane of the angle O1-P-O2 and the large ions (K+ and Mg2+) remain in this plane, whereas in the hybrid model of solvation, the counterions deviate from this plane. However, when the conformer is g+g+, the monovalent counterions deviate and divide the remainder of the plane regardless of the type of solvation model. In addition, the g-g- conformer is the most stable in the presence of the explicit solvent, while the g+g+ conformer is the most stable in the presence of the hybrid solvent. Finally, the normal modes of the conformers g-g- and g+g+ in the presence of the counterions in the hybrid model show a better agreement with the available experimental data of the DNA forms A, B (g-g-), and Z (g+g+) relatively to the explicit model. This very good agreement is illustrated by the very small deviations ≤ 0.08% (g-g-) and ≤ 0.41% (g+g+) observed between the calculated and experimental data for the PO2- (asymmetric) stretching mode in the presence of the counterion K+ in the hybrid model. Graphical abstract.

Lanthanide Intra-series Separation by a 1,10-Phenanthroline Derivative: Counterion Effect

ABSTRACT The demand for rare earths is expected to keep increasing throughout the following years. Separation of lanthanides in particular is especially challenging because of their chemical similarities. Therefore, improving the separation process is essential. In this work, we present the effect of the counterion nature on the lanthanide extraction by a 1,10-phenanthroline derivative, the N-octyl-N-tolyl-1,10-phenanthroline-2-carboxamide in chloroform. Modification of the counterion yields a drastic change in selectivity, with a shift in the maximum of extraction from the light lanthanides (Pr, Nd, Sm) in the nitrate system to the heavy lanthanides (Dy, Ho) in the perchlorate system. Other salts (NaCl, NaNO2) showed a gradual increase in extraction along the whole lanthanide series or no effect (Na2SO4). This selectivity shift was explained by possible different coordination in the organic phase. The reversed behavior depending on the anion is especially interesting because a cycling extraction/back-extraction of light lanthanides in nitrate/chloride media or a cycling extraction/back-extraction of heavy lanthanides in perchlorate/nitrate media can enhance the separation factors of Nd and Dy/Ho, respectively.

The size and affinity effect of counterions on self-assembly of charged block copolymers.

The effect of counterions' size and affinity on the microphase separated morphologies of neutral-charged diblock copolymers is investigated systematically using a random phase approximation (RPA) and self-consistent field theory (SCFT). The phase diagrams as a function of χAB and fA at different counterion sizes and different affinities to neutral blocks are constructed, respectively. Stability limits calculated using the RPA are in good agreement with the disorder-body-centered cubic phase boundaries from SCFT calculations. It was found that increasing the size of counterions causes the phase diagram to shift upward and leftward, which is attributed to electrostatic interactions and the intrinsic volume of counterions. The domain size of the ordered phase shows an unexpected tendency that it decreases with increasing counterions' size. The counterions' distributions in H and G phases demonstrate that it is electrostatic interaction, instead of packing frustration, that plays a leading role in such systems. For finite size counterions, with the increase in affinity between counterions and neutral blocks, the phase diagram shifts upward, indicating the improved compatibility between different blocks. Furthermore, the affinity effect between counterions and neutral blocks can be mapped into an effective Flory parameter χAB ' = χAB + 0.27χBC.