Effect Of Ion Pairs Research Articles

Effect of Ion Pairs on the Dispersion Parameters (SAR, MCAR, CROSS) of some Calcareous and Saline Soils in Nineveh Governorate

The study included selected soils from locations within Nineveh Governorate (Tal-Kaif, Al Hamdaniya, represent calcareous soils),(Rabie’a, Tal-Abta, represent saline soils) three depths were determined for soil sampling (0-20) (20-50) (50-80) cm. The results showed that there was a difference in the effect of dispersion parameters on the structural composition of soil and the degradation of soil properties, where it was observed that the values of the parameters, SAR, MCAR, CROSS were high after correcting the ion pairs values. The increase in the SAR value appeared in calcareous soils at a average of (0.031) and for saline soils at a average of (0.463) after correcting the ion pairs. The MCAR values increased in calcareous soils by (0.025) and saline soils by (0.508) after correcting the ion pairs. CROSS increased in calcareous soils by (0.027) and saline soils by (0.532) after correcting the ion pairs.

Insights into the effect of contact ion-pairs on C[sbnd]H bond activation for the synthesis of Ru(III)-NHC complexes: A combined experimental and computational study

The effect of contact ion pairs and comparison of the three halide ions on the electrophilic CH activation during the base-free synthesis of Ru(III)-NHC complexes [RuIII(PyNHCR)(Cl)3(H2O)] (1a; R = Me, and 1b; R = iPr) have been investigated. DFT modelling of two pathways for the formation of Ru(III)-NHC complexes, viz. halide coordination pathway and ion-pair pathway, reveals the effect of halide ions during electrophilic CH activation for the generation of carbene. The ion-pair path is preferred for azolium salts with Cl− and I−, whereas with Br−, the reaction follows the halide coordination route leading to the mixed halide complex. The synthetic route follows concerted-metalation-deprotonation (CMD) mechanism for ion pair pathway. The higher activation barrier for the reaction with Cl− ions can be explained in terms of greater stabilization of the intermediates, compared to the transition states, due to halide coordination or hydrogen bonding with Cl− ions. Furthermore, the successful synthesis of 1b from the reaction of RuCl3·3H2O and the corresponding imidazolium salt precursor with Cl− in dioxane at 100 °C validates the conclusions of the DFT studies.

Boron isotope fractionation between B(OH)3 and B(OH)4− in aqueous solution: A theoretical investigation beyond the harmonic and Born−Oppenheimer approximations

Boron isotope fractionation between boric acid and borate ion in aqueous solution (hereafter, α3–4) is a key coefficient for reconstructing paleo-pH and paleo-pCO2 records, and a valuable parameter for understanding boron isotope geochemistry related to mineral-water interactions. Although boron isotopes have wide geologic application, the effect of temperature and ion pairing on boron isotope fractionation is poorly described. Moreover, conventional density functional theory (DFT) calculations do not provide an accurate estimate of the boron isotope fractionation factor. Here, we provide a new strategy to accurately calculate α3–4 values in aqueous solution by evaluating harmonic frequencies, higher-order energy terms, and solvation effects. Using benchmark coupled cluster (CCSD(T)) calculations, our 25 °C results for α3–4 ranges from 1.0259 to 1.0275, which is in good agreement with recent experimental data. Solvation effects reduced the α3–4 value by ∼6‰, while high-order corrections raised the α3–4 value by ∼2‰. Our calculations evaluating the effect of aqueous ion pairs suggest that the α3–4 values in seawater and pure water should be almost identical. Our results provide a reasonable estimation of the partition function ratios of dissolved boron species, which will benefit studies of boron isotope fractionation in aqueous environments.

Influence of Ion Pairs and Activity on the Index of Irrigation Water Quality Relying on Some Modern Terms in Erbil Governorate. *

Influence of Ion Pairs and Activity on the Index of Irrigation Water Quality Relying on Some Modern Terms in Erbil Governorate. *

Adopted ion-pair effect to construct bicontinuous starch-based gel and its application in humidity sensitivity and strain-responsiveness

Along with the growing consume of disposable electronic devices, the development of biodegradable and sustainable resources is highly desired to address the contaminated footprints from petroleum-based materials. However, it is still a challenge to overcome obstacles of the dispersion of additives and flexibility for fabricating starch-based strain-responsiveness device. Herein, we developed a facile method to fabricate mechanically stretchable starch-based gel (SGZn gel) with humidity-conductivity through thermal mixing starch and ions-pairing solution, which was a kind of transparent gel without region of stress concentration and hysteresis effect. Attributed to disorganization effect and dipole interaction of ion pairs, SGZn gels achieved homogeneous matrix, increased elongation at break (243%) and high transparency (87%). Meanwhile, the continuous ionic conductivity paths in gel matrix constructed by ions-pairing solution could endow SGZn gels with excellent humidity sensitivity, obtaining an ionic conductivity of 10−3 S/cm after absorbing 10 wt% water from humidity environment. Benefiting from these features, SGZn gels were capable of sensing human motions, both tiny motion in fingers and intense force in feet, satisfying the basic requirements for sustainable wearable devices. This study provided a facile approach for preparing multifunctional starch-based gels to meet the requirements in various applications such as flexible material, humidity detection and smart devices.

The effect of ion pairs on coacervate-driven self-assembly of block polyelectrolytes.

The incorporation of oppositely charged polyelectrolytes into a block copolymer system can lead to formation of microphase separated nanostructures driven by the electrostatic complex between two oppositely charged blocks. It is a theoretical challenge to build an appropriate model to handle such coacervate-driven self-assembly, which should capture the strong electrostatic correlations for highly charged polymers. In this paper, we develop the self-consistent field theory considering the ion paring effect to predict the phase behavior of block polyelectrolytes. In our model, two types of ion pairs, the binding between two oppositely charged monomers and the binding between charged monomers and counterions, are included. Their strength of formation is controlled by two parameters Kaa and Kac, respectively. We give a detailed analysis about how the binding strength Kac and Kaa and salt concentration affect the self-assembled nanostructure of diblock polyelectrolyte systems. The results show that the binding between two oppositely charged blocks provides driven force for microphase separation, while the binding between charged monomers and counterions competes with the polyion pairing and thus suppresses the microphase separation. The addition of salt has a shielding effect on the charges of polymers, which is a disadvantage to microphase separation. The phase diagrams as a function of polymer concentration and salt concentration at different situations are constructed, and the influence of Kaa, Kac, and charged block composition fa is analyzed in depth. The obtained phase diagrams are in good agreement with currently existing experimental and theoretical results.

A dual-ion battery has two sides: the effect of ion-pairs.

There is mutual interference between the positive and negative electrodes in a dual-ion battery. In Li4Ti5O12/graphite batteries, strong ion-pairs between Li+ and anions may have a detrimental effect on intercalation at both sides: Li+ into Li4Ti5O12, and anions into graphite.

The unexpected effect of aqueous ion pairs on the forbidden n →π* transition in nitrate.

Aqueous nitrate is ubiquitous in the environment, found for example in stratospheric clouds, tropospheric particulate matter, rain and snow, fertilized fields, rivers and the ocean. Its photolysis is initiated by absorption into the strongly forbidden n →π* transition. Photolysis reactivates deposited nitrate, releasing nitrogen oxides, and UV light is commonly used to break down nitrate pollution. The transition is doubly forbidden unless its symmetry is broken, giving a powerful means of probing the interactions of nitrate with its environment and of using experiment to validate the results of theory. In this study we demonstrate the remarkably different effects of the addition of a series of mono- and di-valent metal chlorides on the nitrate UV transition. While they all shift the transition to shorter wavelengths, the shift changes significantly from one to another. For the monovalent series Li+, Na+, K+, the blue shift decreases down the column being strongest for Li+ and weakest for K+. For the divalent series Mg2+, Ca2+, Ba2+, the opposite effect is observed with the energy shift of Ba2+ being an order of magnitude larger than for Mg2+. The absorption intensity also changes; the addition of Na+ and K+ decrease intensity whereas Li+ increases intensity. For the divalent cations an increase is seen for all three members of the series Mg2+, Ca2+ and Ba2+. Paradoxically, the effect of addition of CaCl2 to the solution is to decrease the environmental photolysis rate of nitrate; despite the increase in intensity, Ca2+ blue shifts the peak position above the tropospheric photolysis threshold around 300 nm. Using computational chemistry we conclude that the effects are due to the microscopic interactions of the nitrate anion and not continuum effects. Two microscopic mechanisms are investigated in detail, the formation of a nitrate monohydrate cluster and a contact ion pair. The contact ion pair shows the potential for significant impact on the energy and intensity of the transition.

Effect of Ion Pairs on Nonlinear Optical Properties of Crystal Violet: Surfactants, Nano-droplets, and In Vitro Culture Conditions

Crystal violet (CV) has nonlinear optical (NLO) properties that make it suitable for photodynamic therapy. In this respect, Z-scan technique is applied to find the influence of surfactants and nano-droplets on NLO properties of CV. Nonlinear absorption coefficient and nonlinear refractive index can be further determined. The NLO parameters are also enhanced by the increase in anionic surfactant concentrations, while they remain constant with the rise in cationic ones. Moreover, the NLO parameters are extremely improved in dye-doped water droplets prepared with anionic surfactant and a continuous phase of low-polarity oils. It has been demonstrated that the interaction of ion pairs can change linear optical and NLO properties of CV that in turn can change the charge density distribution. To study the behavior of dye during in vitro culture conditions, the effect of cell culture media and fetal bovine serum on NLO properties of CV was examined.

Effect of ion pairs and ion activity on calculation of groundwater salinity-potential in different soil depths

Effect of ion pairs and ion activity on calculation of groundwater salinity-potential in different soil depths

Mechanism of Ion-Pair Strategy in Modulating Skin Permeability of Zaltoprofen: Insight from Molecular-Level Resolution Based on Molecular Modeling and Confocal Laser Scanning Microscopy

The study was carried out to investigate the mechanism of the ion-pair strategy in modulating zaltoprofen (ZAL) skin permeability. Seven organic amines were chosen as counter ions and the formation of ion pairs was confirmed by Fourier transform infrared and proton nuclear magnetic resonance spectroscopy. In vitro permeation studies showed that the permeation of ZAL was significantly promoted with alkylamines and cycloalkanolamines, while significantly retarded with alkanolamines. The results were further visualized by confocal laser scanning microscopy studies. Investigations from the standpoint of solubility, partition, and diffusion indicated that the modulation mechanism of ion pairs was mainly attributed to an alteration of ZAL diffusion in the skin, which was accomplished by masking the carboxyl of ZAL and adding the hydrogen-bonding groups of counter ions. A negative correlation was observed between the enhancement ratio of ion pairs and the polar surface area of counter ions. Molecular modeling revealed that ion pairs acted with the nature of different affinity to ceramide, which would be responsible for the diffusion retardation. The study indicated that the maximum effect of ion pairs tended to be achieved with counter ions of lower hydrogen-bonding potential. Besides, ZAL-triethylamine ion pair might be a promising strategy for transdermal delivery of ZAL.

Origin of reversal of stereoselectivity for [4+2] cycloaddition reaction between cyclopentadiene and methyl methacrylate in the presence of the chloroloaluminate ionic liquid (1-ethyl-3-methyl-imidazolium chloride): in silico studies

The origin of stereoselectivity for [4+2] cycloaddition reaction of methyl methacrylate with cyclopentadiene was investigated with the B3LYP-D3(BJ)/6-31+G(d)//B3LYP/6-31+G(d) level of theory in the presence of the ionic liquid 1-ethyl-3-methyl-imidazolium chloride (EMI+Cl–) and its acidic chloroaluminate melt, 1-ethyl-3-methyl-imidazolium heptachlorodialuminate (EMI+Al2Cl7–). The reaction of methyl methacrylate with cyclopentadiene was examined in the gas phase to rationalize the effect of the ionic liquid ion pairs EMI+Cl– and EMI+Al2Cl7–. The DFT calculated results were found to be in good agreement with the experimentally observed results. The much-discussed hydrogen bonding effect of the imidazolium cation with the dienophile is less important to govern the stereoselectivity for the cycloaddition reaction. The atoms in molecules theory was used to examine the role of hydrogen bonding between the EMI+ cation and methyl methacrylate in the transition state geometries. The calculated activation barriers with the M062X/6-31+G(d)//B3LYP/6-31+G(d) and MP2/6-311+G(d,p)//B3LYP/6-31+G(d) levels of theory also predict the similar exo/endo-stereoselectivity trend for the cycloaddition reactions.

Improvement of Thermal Stability via Outer-Loop Ion Pair Interaction of Mutated T1 Lipase from Geobacillus zalihae Strain T1

Mutant D311E and K344R were constructed using site-directed mutagenesis to introduce an additional ion pair at the inter-loop and the intra-loop, respectively, to determine the effect of ion pairs on the stability of T1 lipase isolated from Geobacillus zalihae. A series of purification steps was applied, and the pure lipases of T1, D311E and K344R were obtained. The wild-type and mutant lipases were analyzed using circular dichroism. The Tm for T1 lipase, D311E lipase and K344R lipase were approximately 68.52 °C, 70.59 °C and 68.54 °C, respectively. Mutation at D311 increases the stability of T1 lipase and exhibited higher Tm as compared to the wild-type and K344R. Based on the above, D311E lipase was chosen for further study. D311E lipase was successfully crystallized using the sitting drop vapor diffusion method. The crystal was diffracted at 2.1 Å using an in-house X-ray beam and belonged to the monoclinic space group C2 with the unit cell parameters a = 117.32 Å, b = 81.16 Å and c = 100.14 Å. Structural analysis showed the existence of an additional ion pair around E311 in the structure of D311E. The additional ion pair in D311E may regulate the stability of this mutant lipase at high temperatures as predicted in silico and spectroscopically.

Microphase Separation in Sulfonated Block Copolymers Studied by Monte Carlo Simulations

The underpinnings of microphase separation in symmetric poly(styrenesulfonate-block-methylbutylene) (PSS−PMB) copolymer melts were examined by Monte Carlo lattice simulations. The main challenge is understanding the effect of ion pairs in the PSS block on thermodynamics. We assume that experimentally determined Flory−Huggins interaction parameters are adequate for describing intermonomer interactions. Our model does not account for either electrostatic or dipolar interactions. This enables comparisons between simulated and experimentally observed microphases reported by Park and Balsara [Macromolecules 2008, 41, 3678] without resorting to any adjustable parameters. The PSS block in both experiments and theory is partially sulfonated. We quantified the effect of sequence distribution on phase behavior by using alternating and blocky PSS chains in the simulations. Depending on temperature and sequence distribution, simulations show perforated lamellae, gyroid, and hexagonally packed cylinders in addition to...

Effect of ion pairs in fast-light bandwidth in high-concentration erbium-doped fibers

The effect of ion pairs in high-concentration erbium-doped fibers on slow- and fast-light propagation enabled by coherent population oscillations at room temperature has been experimentally investigated. We find that an increase of the erbium ion concentration increases the fractional advancement although it degrades the bandwidth of the modulated signals that propagate at superluminal velocities due to the presence of ion pairs in the fiber.

Determination of synthetic polypeptide conformations and molecular geometrical parameters by nonaqueous CE

The aim of this work was to study changes in homopolypeptide chain conformation as a function of the number of residues by the modeling of the electrophoretic mobility. For this purpose, the frictional coefficients of poly(N(epsilon)-trifluoroacetyl-L-lysine) with different number of residues (up to 11) were determined from the absolute ionic mobilities and modeled by the hydrodynamic frictional coefficient of an equivalent cylinder. This approach allowed determination of geometrical parameters of the polypeptide chain in a liquid phase (nonaqueous solution of the BGE). The fact that the BGE and analyte are dissolved in mixed (methanol-ACN) organic solvent implied to take into account different effects and corrections that are generally not considered in aqueous solvent: namely, the effect of ion-pairs between constituents of the BGE for the calculation of the ionic strength, the effect of ion-pairs between the solutes and the electrolyte counterions and the correction due to the dielectric friction (Hubbard-Onsager equations). In addition, the influence of the ionic strength on the electrophoretic mobility was corrected using the Pitts equation, and the effect of lateral charges due to a slight deprotonation of the -NH- group in the lateral chain was also considered. From this modeling, molecular geometrical parameters relative to the linear and helicoïdal conformations were obtained with very good correlation coefficients. Interestingly, this work also points out that the use of ionic mobility modeling for extracting molecular geometrical parameters can also be applied to end-charged polypeptides with slightly charged lateral chains (3% of elementary charge per residue).

Terminal ion pairs stabilize the second β‐hairpin of the B1 domain of protein G

The effects of terminal ion pairs on the stability of a beta-hairpin peptide corresponding to the C-terminal residues of the B1 domain of protein G were determined using thermal unfolding as monitored by nuclear magnetic resonance and circular dichroism spectroscopy. Molecular dynamics (MD) simulations were also performed to examine the effect of ion pairs on the structures. Eight peptides were studied including the wild type (G41) and the N-terminal modified sequences that had the first residue deleted (E42), replaced with a Lys (K41), or extended by an additional Gly (G40). Acetylated variants were made to examine the effect of removing the positive N-terminal charge on beta-hairpin stability. The rank in stability determined experimentally is K41 > E42 approximately G41 approximately G40 > Ac-K41 > Ac-E42 approximately Ac-G41 > Ac-G40. The Tm of the K41 peptide is 12 degrees C higher than G41, while the Tm values for the acetylated peptides are less than their unacetylated forms by more than 15 degrees C. NOE cross-peaks between side-chain methylene groups at the N- and C-termini and larger CalphaH shifts compared to random values are seen for K41. The addition of 20% methanol increases the stability in K41 and G41. The MD studies complement these results by showing that the charged N-terminus is important to stability. The type of ion pair observed varies with peptide, and when formed the simulations show that the ion pair can prevent fraying of the beta-strands through electrostatic and hydrophobic contacts. Therefore, introducing favorable electrostatic interactions at the N- and C-termini can substantially enhance beta-hairpin stability and help define the structure.

Neutron Scattering Reveals the Dynamic Basis of Protein Adaptation to Extreme Temperature

To explore protein adaptation to extremely high temperatures, two parameters related to macromolecular dynamics, the mean square atomic fluctuation and structural resilience, expressed as a mean force constant, were measured by neutron scattering for hyperthermophilic malate dehydrogenase from Methanococcus jannaschii and a mesophilic homologue, lactate dehydrogenase from Oryctolagus cunniculus (rabbit) muscle. The root mean square fluctuations, defining flexibility, were found to be similar for both enzymes (1.5 A) at their optimal activity temperature. Resilience values, defining structural rigidity, are higher by an order of magnitude for the high temperature-adapted protein (0.15 Newtons/meter for O. cunniculus lactate dehydrogenase and 1.5 Newtons/meter for M. jannaschii malate dehydrogenase). Thermoadaptation appears to have been achieved by evolution through selection of appropriate structural rigidity in order to preserve specific protein structure while allowing the conformational flexibility required for activity.

Synthesis, optical and magnetic properties of homo- and heteronuclear systems and glasses containing them

To study the effect of ion pairs (f and d–f) coupled in a polymeric system on their optical and magnetic properties, syntheses of homo- and heteronuclear systems were undertaken. Single crystals of the polynuclear Nd glutarate of formula [Nd(Glut)(H2O)4]Cl·2H2O (1) were obtained. The X-ray diffraction analysis shows the triclinic system and the P1 space group. The structure consists of polynuclear two-dimensional chains built of dimeric units with two nonequivalent Nd3+ centres. The two Nd3+ ions are coordinated by carboxyl groups of the glutarate anion and water molecules. Two different coordination modes of the carboxylate group occur in the structure: simple bridging (bidentate) and chelating bridging (tridentate). There are five oxygen atoms of four carboxylate groups in the direct environment of each Nd ion and four water molecules complete the coordination number at nine. The network of hydrogen bonds stabilises the crystal structure. The above structural characteristics are well manifested in the spectroscopic properties of crystalline 1. Using the sol–gel technique, neodymium (2) and Nd3+:Cu2+ glutarate (3) were incorporated in glass. Glasses of good optical quality were obtained, enabling an analysis of the spectroscopic properties of the investigated systems and consideration of the heteronuclear forms in the glass. The optical and magnetic behaviour of these systems were analysed down to 1.8 K. The effect of the dimensionality of the systems on their optical and magnetic properties is also discussed.

Ion Pairs Involved in Maintaining a Thermostable Structure of Glutamate Dehydrogenase from a Hyperthermophilic Archaeon

Intersubunit ion pairs are considered to be involved for maintaining a stable structure of the glutamate dehydrogenase (GDH) from hyperthermophiles. In order to demonstrate an effect of intersubunit ion pairs on the structural stability, two kinds of mutation (T138E, Thr at position 138 was replaced by Glu; E158Q, Glu at position 158 was replaced by Gln) which add and remove ion pairs, respectively, were introduced intoPk-gdhAgene encoding GDH fromPyrococcus kodakaraensisKOD1. Addition of one ion pair (Pk-GDH-T138E) increased the optimum temperature and thermostability. In contrast,Pk-GDH-E158Q showed lower optimum temperature and less thermostability than wild type GDH. Structure analysis of GDHs was performed by circular dichroism (CD) and indicated that all recombinant enzymes (Pk-GDH,Pk-GDH-T138E,Pk-GDH-E158Q) possess different structures from that of natural GDH. Upon heat treatment (60°C, 2h), the structures ofPk-GDH andPk-GDH-T138E were converted to another form close to the natural structure. However, no structural conversion by heat treatment was observed inPk-GDH-E158Q. These results indicate that intersubunit ion pairs play an important role in forming thermostable structure ofPk-GDH.