Concentrated Aqueous Solutions Research Articles

Molecular Modeling of Water-in-Salt Electrolytes: A Comprehensive Analysis of Polarization Effects and Force Field Parameters in Molecular Dynamics Simulations.

Accurate modeling of highly concentrated aqueous solutions, such as water-in-salt (WiS) electrolytes in battery applications, requires proper consideration of polarization contributions to atomic interactions. Within the force field molecular dynamics (MD) simulations, the atomic polarization can be accounted for at various levels. Nonpolarizable force fields implicitly account for polarization effects by incorporating them into their van der Waals interaction parameters. They can additionally mimic electron polarization within a mean-field approximation through ionic charge scaling. Alternatively, explicit polarization description methods, such as the Drude oscillator model, can be selectively applied to either a subset of polarizable atoms or all polarizable atoms to enhance simulation accuracy. The trade-off between simulation accuracy and computational efficiency highlights the importance of determining an optimal level of accounting for atomic polarization. In this study, we analyze different approaches to include polarization effects in MD simulations of WiS electrolytes, with an example of a Na-OTF solution. These approaches range from a nonpolarizable to a fully polarizable force field. After careful examination of computational costs, simulation stability, and feasibility of controlling the electrolyte properties, we identify an efficient combination of force fields: the Drude polarizable force field for salt ions and non-polarizable models for water. This cost-effective combination is sufficiently flexible to reproduce a broad range of electrolyte properties, while ensuring simulation stability over a relatively wide range of force field parameters. Furthermore, we conduct a thorough evaluation of the influence of various force field parameters on both the simulation results and technical requirements, with the aim of establishing a general framework for force field optimization and facilitating parametrization of similar systems.

Electrodeposition of Cobalt from LiCl-Based Highly Concentrated Aqueous Solution: Crystal Phase and Hydrogen Content

The relationship between the crystal phase and absorbed hydrogen in cobalt electrodeposited from a LiCl-based highly concentrated (HC) aqueous solution was investigated using X-ray diffraction and thermal desorption spectroscopy. We expected that the use of an HC solution would enable the electrodeposition of cobalt without hydrogen evolution and the concomitant hydrogen absorption. The current efficiency of cobalt deposition was more than 99% at potentials above –0.8 V vs. Ag/AgCl, indicating that hydrogen evolution is really suppressed, and the electrodeposited cobalt accompanied the fcc phase irrespective of the deposition temperature. However, electrodeposited cobalt contained a large amount of hydrogen despite the high current efficiency. The hydrogen content of cobalt obtained at 100 °C was approximately 10% of that obtained at room temperature; however, the fcc phase was still co-deposited, suggesting that factors other than hydrogen could be responsible for fcc-Co formation. The reason for hydrogen inclusion from the HC solution is discussed in terms of the hydrogen reduction mechanism.

Unravelling the structural and dynamical properties of concentrated aqueous ammonium nitrate solutions: MD simulation studies

ABSTRACT In this work, we present, the concentration-dependent solvation structure and dynamics of an ammonium nitrate (AN) ion pair in aqueous media by means of classical molecular dynamics simulations. Structural properties were investigated by computing the potentials of mean force (PMFs), radial distribution functions (RDFs), cluster size distribution functions, and hydrogen bond dynamics. The change in the depth of the contact ion pair (CIP) and solvent-separated ion pair minima (SSIP) is marginal, whereas for the solvent-assisted ion pair (SAIP) is more stable at lower salt concentrations. The marginal difference in the depth of the CIP minimum of the PMF is explained based on cluster size distribution and hydrogen bonding. The solvation structure of the ions is not affected by the salt concentration. Ab-initio and classical molecular dynamics simulations (both constrained and unconstrained) give similar results for the solvation structure around the cation and the anion. The spatial density distribution functions of the anions around the cations show that the anions occupy the space around the ammonium hydrogen atoms. Profound differences in dynamical properties are found in the case of concentrated solutions as compared to dilute solutions.

CaF2(s) Solubility Isotherm in the CaF2–CaSO4–MSO4–H2O (M = Zn, Mn, Mg) Quaternary Systems and Their Subsystems at Various Temperatures

A ZnSO4 electrolyte solution with impurity salts such as MnSO4 and MgSO4 is often used in zinc hydrometallurgical processes over a wide temperature range. CaSO4·2H2O(s) scaling and fluorine corrosion are two encountered problems in the process. Understanding the CaF2(s) solubility behavior in MSO4 (M = Zn, Mn, Mg) aqueous solutions at various temperatures helps remove Ca2+ and F– ions from the solution. However, CaF2(s) solubility data, especially at temperatures >298 K, have not been published yet. In this work, CaF2(s) solubilities in the CaF2–CaSO4–MSO4–H2O (M = Zn, Mn, Mg) quaternary systems and its subsystems of the CaF2–MSO4–H2O (M = Zn, Mn, Mg) at 348.15 K and the CaF2–CaSO4–MSO4–H2O (M = Zn, Mg) quaternary systems and the CaF2–MgSO4–H2O ternary system at 298.15 K are systematically measured. The results show that the CaF2(s) solubility in the MSO4 (M = Zn, Mn, Mg) aqueous solution of a certain concentration at 348.15 K is considerably higher than that at 298.15 K. At 298.15 and 348.15 K, the salting-in effect of MSO4 (M = Zn, Mn, Mg) on CaF2(s) solubility is enhanced with the order ZnSO4 < MnSO4 < MgSO4. At both temperatures, CaF2(s) solubilities in CaSO4·2H2O(s)- or CaSO4(s)-saturated MSO4 (M = Zn, Mn, Mg) aqueous solutions are generally lower than those in pure MSO4 (M = Zn, Mn, Mg) aqueous solutions. Particularly, the salting-in effect of MgSO4 on CaF2 is so strong that CaF2(s) dissolves completely and is converted to CaSO4·2H2O(s) and MgF2(s) in a concentrated MgSO4 aqueous solution. Hence, this study indicates that high temperatures and high salt concentrations increase the CaF2(s) solubility, making the removal of Ca2+ and F– ions from the system challenging. Further, the existence of impurity salts MnSO4 and MgSO4 makes it more difficult.

Enabling long-cycling aqueous sodium-ion batteries via Mn dissolution inhibition using sodium ferrocyanide electrolyte additive

Aqueous sodium-ion batteries (AIBs) are promising candidates for large-scale energy storage due to their safe operational properties and low cost. However, AIBs have low specific energy (i.e., <80 Wh kg−1) and limited lifespans (e.g., hundreds of cycles). Mn-Fe Prussian blue analogues are considered ideal positive electrode materials for AIBs, but they show rapid capacity decay due to Jahn-Teller distortions. To circumvent these issues, here, we propose a cation-trapping method that involves the introduction of sodium ferrocyanide (Na4Fe(CN)6) as a supporting salt in a highly concentrated NaClO4-based aqueous electrolyte solution to fill the surface Mn vacancies formed in Fe-substituted Prussian blue Na1.58Fe0.07Mn0.97Fe(CN)6 · 2.65H2O (NaFeMnF) positive electrode materials during cycling. When the engineered aqueous electrolyte solution and the NaFeMnF-based positive electrode are tested in combination with a 3, 4, 9, 10-perylenetetracarboxylic diimide-based negative electrode in a coin cell configuration, a specific energy of 94 Wh kg–1 at 0.5 A g−1 (specific energy based on the active material mass of both electrodes) and a specific discharge capacity retention of 73.4% after 15000 cycles at 2 A g−1 are achieved.

Cations impact radical reaction dynamics in concentrated multicomponent aqueous solutions.

Ultraviolet (UV) photolysis of nitrite ions (NO2-) in aqueous solutions produces a suite of radicals, viz., NO·, O-, ·OH, and ·NO2. The O- and NO· radicals are initially formed from the dissociation of photoexcited NO2-. The O- radical undergoes reversible proton transfer with water to generate ·OH. Both ·OH and O- oxidize the NO2- to ·NO2 radicals. The reactions of ·OH occur at solution diffusion limits, which are influenced by the nature of the dissolved cations and anions. Here, we systematically varied the alkali metal cation, spanning the range from strongly to weakly hydrating ions, and measured the production of NO·, ·OH, and ·NO2 radicals during UV photolysis of alkaline nitrite solutions using electron paramagnetic resonance spectroscopy with nitromethane spin trapping. Comparing the data for the different alkali cations revealed that the nature of the cation had a significant effect on production of all three radical species. Radical production was inhibited in solutions with high charge density cations, e.g., lithium, and promoted in solutions containing low charge density cations, e.g., cesium. Through complementary investigations with multinuclear single pulse direct excitation nuclear magnetic resonance (NMR) spectroscopy and pulsed field gradient NMR diffusometry, cation-controlled solution structures and extent of NO2- solvation were determined to alter the initial yields of ·NO and ·OH radicals as well as alter the reactivity of NO2- toward ·OH, impacting the production of ·NO2. The implications of these results for the retrieval and processing of low-water, highly alkaline solutions that comprise legacy radioactive waste are discussed.

An Alkanethiol-Surfactant Bilayer To Prevent Shape Conversion of Anisotropic Silver Nanoparticles and Probe Their Formation Mechanisms.

Anisotropic nanoparticles can be synthesized under kinetic control but may undergo subsequent shape changes due to atomic reorganization. Furthermore, their synthesis involves rapid steps, which are challenging to monitor in situ. Here, we show how a nanoemulsion of alkanethiols with an ethoxylated surfactant, easily prepared and metastable for months, can simultaneously prevent shape reorganization and arrest reaction kinetics. We illustrate this generic method on the silver nanoplates synthesized in concentrated acetic acid aqueous solutions, in which rapid shape reorganization occurs. We show that there exists an optimum thiol concentration corresponding to full coverage of all silver surface atoms, which can be simply calculated from particle dimensions. Furthermore, we demonstrate that arresting nanoparticle formation can be achieved within milliseconds using a tandem rapid mixers scheme in a continuous flow setup, allowing ex situ monitoring of the reaction.

Speciation and Ammonia-Induced Precipitation of Neptunium and Uranium Ions.

The pH evolution and corresponding changes in the UV-Vis-NIR absorption spectra of oxygenated neptunium (NpO2+ and NpO22+) and uranyl ions (UO22+) in nitric acid are investigated during titration with an aqueous NH3 solution. The speciation and precipitation regimes between acidic (pH 1.5) and alkaline (pH 10) conditions at room temperature are discussed to assess the suitability of Np(V) or Np(VI) in sol-gel conversion processes for fuel target fabrication. Under the applied experimental conditions, Np(V) hydrolyzes and precipitates into the insoluble hydroxide NpO2OH only above pH values 7.5 and an increase up to pH 10.0 is required to precipitate quantitatively. Np(VI) displays changes in the coordination environment of NpO22+ ions in the pH interval 1.6-4.0, similar to what is observed for U(VI). Precipitation into NpO3·H2O or other hydroxide compounds takes place between pH 4.0 and 5.9, which overlaps largely with precipitation of ammonium diuranate species from the U(VI) solution. The use of concentrated NH3 aqueous solution, as commonly used in the external gelation process, will allow to quantitatively precipitate both Np(V) and Np(VI) species. Internal gelation process conditions, on the other hand, seem incompatible with the high pH required to precipitate Np(V) completely. For fabricating mixed-oxide (U,Np) targets using sol-gel conversion, a feed broth containing Np(VI) and U(VI) will be required to achieve homogeneous gelation.

Wet spinning and 3D printing of supramolecular hydrogels in acid-base and dynamic conditions

N-alkyl-D-galactonamides give biocompatible hydrogels that are very delicate and not injectable. To circumvent their mechanical fragility and the injectability issue, we have developed a method of injection based on solvent-water exchange. A solution of the gelator in a good solvent is injected vertically in a bath of water. The diffusion of water inside the solvent jet triggers the fast self-assembly of the N-alkyl-D-galactonamides into supramolecular fibers. It leads to the formation of well-defined gel filaments. We first used dimethylsulfoxide (DMSO) as the good solvent of N-alkyl-D-galactonamides. Then, we considered to get rid of this organic solvent by implementing an “all-aqueous method”, paving the way to green chemistry methods. Despite the fact that these molecules do not have conventional acid-base functions in water, N-alkyl-D-galactonamides can be deprotonated and solubilized in highly concentrated NaOH aqueous solutions. As with DMSO, the basic solution is denser than the solution in the bath. Thus, a well-defined vertical jet falls down when the solution is injected in an acidic aqueous solution. The neutralization of the base at the acid-base interface triggers the gelation and leads to the formation of well-defined gel filaments as well. The acid-base reaction at the interface has been visualized by colored pH indicators. With phenol red (pKa = 7.9), a pink-to-yellow V-shaped “flame” transition is clearly observed. A similar transition from colorless-to-pink is observed with the pH indicator acid fuchsin, which pKa = 13 is close to the N-heptyl-D-galactonamide pKa. The distance from the nozzle of this transition zone is directly related to the injection rate, which is well-described by a model. We also applied this method to 3D printing, by a liquid-in-liquid direct writing. It gives well-resolved patterns. The opportunity to get noodles or 3D printed patterns made of single small molecules by acid-base exchange opens new perspectives. Notably, the supramolecular fibers could be used to support and direct the formation of inorganic materials with original microstructures.

Molecular simulations of alkali metal halide hydrates

It has been known that classical molecular simulations of concentrated aqueous electrolyte solutions are limited by the ability of microscopic models (force fields) to predict the correct values of salt solubility, which also requires their ability to faithfully model crystalline salts. Previous simulation studies have often focused on the solubility of anhydrous crystalline salts, but virtually never on crystalline hydrates, except for hydrohalite, NaCl⋅2H2O, despite there are at least 23 experimentally known different hydrates that can precipitate from alkali-halide solutions. This work attempts to fill this gap in hydrate simulation studies by systematically investigating the ability of the best force fields selected to qualitatively capture the stability of the individual phases of various alkali-halide hydrates and to quantitatively predict their lattice parameters. First, we show that the nonpolarizable force fields studied often fail to model hydrates containing the Li+ cations, whereas the polarizable force fields recently refined by us are able to model all the hydrates except for LiCl⋅H2O. Second, we further refine our FFs for Li+ to yield stable LiCl⋅H2O. Third, our simulations clarify the positions of the Li+ cations in the β phases of LiBr⋅H2O and LiI⋅H2O, whose distributions were previously described only as stochastic. As a byproduct, a simple and reliable simulation methodology suitable also for complex polarizable models and nonorthorhombic crystal lattices is proposed and tested, based on simulations of finite crystals floating in vacuum.

Mass transport limitations in concentrated aqueous electrolyte solutions: Theoretical and experimental study of the hydrogen–bromine flow battery electrolyte

Modelling and simulation is a powerful tool to support the development of novel flow cells such as electrolysers and flow batteries. Electrolytes employed in such cells often consist of aqueous solutions of highly concentrated solutes at elevated temperatures. Such conditions pose numerous challenges in conventional model parametrisation because of non-ideal behaviour of the electrolytes. The aim of this work is to study mass transport of electroactive species in highly-concentrated media.We selected the hydrogen–bromine flow battery posolyte, HBr (aq) and Br2, as an exemplary flow battery electrolyte and we leveraged chronoamperometric techniques involving ultramicroelectrodes to study diffusion and migration of bromide and bromine at high concentration and temperature. We successfully simulated the current densities of HBr/Br2 redox reactions in solutions up to 8 mol L–1 using advanced mass transport theory which agreed well with the results obtained with ultramicroelectrodes.While uncharged species transport (Br2) can be credibly modelled using conventional theories such as Fick’s law, charged species (Br–) require special treatment as the diffusion coefficient vary with concentration up to 50 % with respect to the limiting value at infinite dilution. The transport of charged species without added supporting electrolyte occurs via both migration and diffusion and the contribution of migration current may be up to 50 % of the total current. At HBr concentration > 0.6 mol L–1 migration appears to be suppressed due to the “self-screening” effect of the electrolyte.Proper experimental electrolyte characterisation under operating conditions similar to the actual flow cell applications is indispensable to establish predictive models and digital twins of electrochemical devices. Straightforward transfer of concepts known in electro-analytical chemistry to flow cells modelling may lead to erroneous simulations or model overfitting.

Cluster-size distribution of ions in concentrated aqueous NaCl solutions: Molecular dynamics simulations

Recently, the properties of screening phenomena in concentrated electrolytes have attracted considerable attention. Molecular dynamics (MD) simulations were performed on an aqueous NaCl solution, and the cluster-size distribution of cations and anions was clarified. The cluster-size distribution exhibited approximately power-law decay behavior with a sufficiently high concentration. In addition, the fraction of isolated ions without pairing or clustering was also investigated. In concentrated electrolytes, the number of isolated ions does not significantly depend on the electrolyte concentration. This study clarifies the statistical physics of the cations and anions in concentrated electrolytes.

Microporous, Crystalline, and Water‐Processable Framework Materials of Organic Amphiphile Salts

AbstractPorous framework materials are of major importance for a wide range of technologies. Nevertheless, many of these materials lack processibility as they are typically synthesized under rather harsh conditions and obtained as microcrystalline powders that cannot easily be coated or deposited from solution. Herein, a new approach to water‐processable metal–organic framework materials is presented. The materials are based on amphiphilic organic building blocks consisting of polar carboxylate groups and non‐polar alkyl chains connected to a rigid aromatic core. The amphiphilic building blocks assemble to porous framework structures via bonding to kinetically labile sodium ions from concentrated aqueous solution. The obtained crystalline materials, termed amphiphile salt frameworks , are thermally and mechanically stable (some derivatives up to 365 °C and up to at least 4000 bar hydrostatic pressure), exhibit persistent microporous channels accessible to several gases (N2, CO2, propane, propylene, n‐butane), and can be reversibly assembled/disassembled by crystallization from or dissolution in water. Systematic variation of the hydrophobic side chains of the amphiphile building blocks allows extracting structure‐property relationships and first design rules for this new class of water‐processable microporous framework materials.

Searching for Life on Venus: History of the Problem and Basic Concepts

Venus has always been one of the priorities of the space research program in Russia. The history of successful investigations of Venus in the Soviet Union is primarily associated with delivering a whole series of spacecraft to it and implementing the first ever landing on its surface. In the last few years, the study of Venus in astrobiological direction has been rapidly developing. To date, a fairly large number of theoretical papers have been published, the main purpose of which is to estimate the possibility of the existence of living organisms on Venus. The most likely ecosystem, in which Earth-type organisms could develop, is considered to be a dense cloud layer of Venus. It is supposed that, in this layer, hypothetical microbial communities could exist in aerosols being a concentrated aqueous solution of sulfuric acid. Microorganisms in such a specific air habitat are to be exposed to several extreme factors at once, the main among which are very low values of pH and water activity. The principal strategies for survival under these conditions should be the availability of effective biochemical mechanisms of resistance to the impact of adverse environmental factors and the use of all possible ways of extracting energy in such an ecosystem to maintain the biomass of organisms at a level for stable reproduction.

Dynamics of Concentrated Aqueous Lithium Chloride Solutions Investigated with Optical Kerr Effect Experiments

We report the dynamics of concentrated lithium chloride aqueous solutions over a range of moderate to high concentrations. Concentrations (1-29 to 1-3.3 LiCl-water) were studied in which, at the highest concentrations, there are far too few water molecules to solvate the ions. The measurements were made with optically heterodyne-detected optical Kerr effect experiments, a non-resonant technique able to observe dynamics over a wide range of time scales and signal amplitudes. While the pure water decay is a biexponential, the LiCl-water decays are tetra-exponentials at all concentrations. The faster two decays arise from water dynamics, while the slower two decays reflect the dynamics of the ion-water network. The fastest decay (t1) is the same as pure water at all concentrations. The second decay (t2) is also the same as that of pure water at the lower concentrations, and then, it slows with increasing concentration. The slower dynamics (t3 and t4), which do not have counterparts in pure water, arise from ion-water complexes and, at the highest concentrations, an extended ion-water network. Comparisons are made between the concentration dependence of the observed dynamics and simulations of structural changes from the literature, which enable the assignment of dynamics to specific ion-water structures. The concentration dependences of the bulk viscosity and the ion-water network dynamics are directly correlated. The correlation provides an atomistic-level understanding of the viscosity.

Development of rechargeable high-energy hybrid zinc-iodine aqueous batteries exploiting reversible chlorine-based redox reaction

The chlorine-based redox reaction (ClRR) could be exploited to produce secondary high-energy aqueous batteries. However, efficient and reversible ClRR is challenging, and it is affected by parasitic reactions such as Cl2 gas evolution and electrolyte decomposition. Here, to circumvent these issues, we use iodine as positive electrode active material in a battery system comprising a Zn metal negative electrode and a concentrated (e.g., 30 molal) ZnCl2 aqueous electrolyte solution. During cell discharge, the iodine at the positive electrode interacts with the chloride ions from the electrolyte to enable interhalogen coordinating chemistry and forming ICl3-. In this way, the redox-active halogen atoms allow a reversible three-electrons transfer reaction which, at the lab-scale cell level, translates into an initial specific discharge capacity of 612.5 mAh gI2−1 at 0.5 A gI2−1 and 25 °C (corresponding to a calculated specific energy of 905 Wh kgI2−1). We also report the assembly and testing of a Zn | |Cl-I pouch cell prototype demonstrating a discharge capacity retention of about 74% after 300 cycles at 200 mA and 25 °C (final discharge capacity of about 92 mAh).

In-situ synthesis of floating ZnIn2S4/cellulose foam for facile photocatalysis

The delicate design of photocatalyst monoliths is of great significance for the practical applications of artificial photocatalysis. An in-situ synthesis to prepare ZnIn2S4/cellulose foam was developed. Cellulose is dispersed in a highly concentrated ZnCl2 aqueous solution to prepare Zn2+/cellulose foam. Zn2+ ions are pre-anchored by hydrogen bonds on cellulose and become in-situ sites for synthesizing ultra-thin ZnIn2S4 nanosheets. This synthesis method makes ZnIn2S4 nanosheets and cellulose tightly bound and prevents ZnIn2S4 nanosheets from stacking in multiple layers. As a proof of concept, the prepared ZnIn2S4/cellulose foam exhibits a favorable performance for photocatalytic reduction of Cr(VI) under visible light. By adjusting the concentration of zinc ions, the optimal ZnIn2S4/cellulose foam is capable to completely reduce Cr(VI) in 2 h and the photocatalytic activities show no decrease after 4 cycles. This work could inspire people to build floating cellulose-based photocatalysts via in-situ synthesis.

Intermolecular Interactions and Electrochemical Studies on Highly Concentrated Acetate-Based Water-in-Salt and Ionic Liquid Electrolytes

Water-in-salt electrolytes constitute a new class of materials that have distinct properties relative to lower-concentration solutions. A recent approach to further increase the salt concentration and decrease the water content includes the addition of an ionic liquid to a highly concentrated aqueous solution. However, the physicochemical and electrochemical properties of aqueous lithium acetate-1-ethyl-3-methylimidazolium acetate solutions as well as the molecular interactions between electrolyte species have not been characterized. Here, we investigate these properties by evaluation of the ionic conductivity, viscosity, and thermal properties as well as the electrochemical behavior of various electrodes in these electrolytes. The intermolecular interactions are probed by nuclear magnetic resonance and infrared spectroscopies. We find that the addition of the ionic liquid increases the solubility limit of lithium acetate and that with an increase in both acetate salt and ionic liquid concentration in the electrolyte and decrease in water concentration, a strong acetate-water network is formed. The electrochemical stability window increases upon addition of the ionic liquid and reaches a value larger than 5 V for a set of negative Al and positive Ti electrodes in the highest acetate salt/ionic liquid concentration. Preliminary electrochemical charge storage performance measurements of a symmetric device based on two porous carbon electrodes cycled at a current density of 25 mA g-1 delivered a specific capacitance of 20 F g-1 with a Coulombic efficiency higher than 99% using a 1.8 V voltage window.

OBTAINING AND RHEOLOGICAL PROPERTIES OF PECTIN ISOLATED USING MICROWAVE RADIATION

А method has been developed for extracting modified pectin from plant raw materials by using microwave radiation at the stage of washing. The rheological properties of 5.0% aqueous solutions of apple PV obtained by exposure to microwave radiation of various powers: 300, 450 and 600 W, as well as PV obtained by the traditional method at temperatures of 25, 40, 55, 70 °C were investigated. It is shown that the use of microwave radiation makes it possible to improve the method of obtaining pectins with the possibility of increasing the yield of pectin substances and regulating their structure and properties. The rheological properties of concentrated aqueous solutions of pectins obtained by exposure to microwave radiation of various powers have been studied. It is shown, that all the studied systems of PV solutions are non-Newtonian fluids with a pseudoplastic type of viscous flow anomaly, determined by the values of the microwave energy. The values of the apparent activation energies of the viscous flow of solutions, which are an indirect characteristic of the strength of the structures of the system, have been estimated. Information was obtained on the structure and changes in the structure of their concentrated solutions under the action of external forces and temperature in the course of a viscous flow. It is shown that the power values оf microwave radiation are the main factor determining the structure of molecular matrices of pectin substances and the structure of their concentrated aqueous solutions.

New Zwitterionic Oligonucleotides: Preparation and Complementary Binding

New zwitter-ionic oligonucleotide derivatives containing 1,2,3,4-tetrahydroisoquinoline-7-sulfonyl phosphoramidate group are described. Automated synthesis of these compounds was carried out according to the β-cyanoethyl phosphoramidite scheme using the Staudinger reaction between 2-trifluoroacetyl-1,2,3,4-tetrahydroisoquinoline-7-sulfonyl azide and phosphite triester within an oligonucleotide grafted to a polymer support. 1,2,3,4-Tetrahydroisoquinoline-7-sulfonyl phosphoramidate group (THIQ) proved to be stable under the conditions of standard oligonucleotide synthesis, including the removal of protective groups and cleavage of the oligonucleotide from the polymer support by treatment with a mixture of concentrated aqueous solutions of ammonia and methylamine (1 : 1) at 55oC. Oligonucleotides modified by one to five THIQ groups in various positions were obtained. The zwitter-ionic character of the obtained derivatives was reflected in their different mobility under conditions of denaturing PAGE. The thermal stability of the duplexes of oligodeoxynucleotides containing THIQ groups with complementary DNA and RNA differed only slightly from that of natural DNA:DNA and DNA:RNA duplexes. The results obtained suggest the possible use of oligonucleotides modified with zwitterionic THIQ groups as antisense therapeutic agents.