Computer evaluation of water sorption on ion exchangers

Water sorption on an ion exchanger can be described by formation of several hydrates. The general least squares program WSLET based on the "pit-mapping" approach has been written for evaluating such equilibria. It is written in FORTRAN 77 for use on personal computers. Besides finding the best values for the equilibrium constants of the various hydrates the program also searches for best values of the stoichiometric indices by using the so-called ESI-method. The program is provided with least-squares procedures and blocks for statistical analysis of the residuals as well as for data simulation. It has been tested with data on the strong base resin Dowex 1 as well as on simulated data. In the present paper an illustrative example is given together with data simulation. It is found that in most cases WSLET helps to find a better fit than earlier models quite efficiently, showing the advantage of the ESI method in combination with least-squares methods.     

Strong acidic ion exchangers structure by inverse steric exclusion chromatography

A number of strongly acidic ion exchangers, both of the standard gel and of the macroreticular type, were investigated by inverse steric exclusion chromatography in an aqueous medium, using D₂O, sugars, and dextrans as standard solutes. Their structure was characterized as an assembly of isoporous fractions by using Ogston's model of the porous medium. The data thus obtained were correlated with those on the catalytic activity of ion exchangers for the hydrolysis of saccharose.     

The structure of the ion: An ion kinetic energy spectrometry study

The kinetic energy release (T) values for the loss of CO from ions from five compounds have been obtained and are consistent with at least two different structures for the ion. This result is supported by the T value obtained for the decomposition of the molecular ions.     

Liquid ion exchangers in reversed-phase systems for chromatography of steroidal glucosiduronic acids

Steroidal glucosiduronic acids were chromatographed on paper by the reversed-phase technique using five different liquid ion exchangers as stationary phase and aqueous KCl as mobile phase. The relationship of mobility of the acids (R_M) to both the amount of exchanger on the paper and the concentration of KCl in the mobile phase is discussed: the relationships may be expressed as R_M = n·log [exchanger] + const. and R_M = −n·log [KCl] + const., respectively. Migration of the acids in the presence of different exchangers is correlated by use of the equation R_M (exchanger Y) = a·R_M (exchanger X) + b. The lack of appreciable correlation between migration of the acids in a reversed-phase system and a corresponding straight-phase system is discussed and expressed by means of regression equations. The correlation coefficients and standard errors of estimate from these equations provide useful indices for selecting two solvent systems that are to be used sequentially to obtain maximal resolution of a group of compounds. ΔR_M values obtained for various functional groups with reversed-phase and straight-phase techniques are compared.     

除Cs用无机离子交换剂的筛选

本文对用于酸性高放废液除Ｃｓｗ的五大类,２０余种无机离子交换剂的Ｃｓ性能进行了研究和比较,确定凝胶－溶胶法制备的亚铁氰化钾钛为我国酸性高放废液除Ｃｓ的首选无机离子交换剂。     

Microanalysis with the aid of ion exchangers

The resin spot test is modified by the use of a high molecular weight amine, Amberlite LA-1, in carbon tetrachloride; 0.2 μg of cobalt(II) can be detected rapidly by shaking an acidic solution containing thiocyanate with a 5% amine solution. Amine-impregnated papers can also be used.     

Comparison of nonporous silica-based ion exchangers and monolithic ion exchangers in separations of inorganic anions

Low capacity anion exchangers for IC have been prepared by modification of nonporous uniformed silica MICRA microbeads and by modification of the organic polymeric monolithic matrixes prepared in situ in quarz capillary. Due to the small particle size (1.5 microm) high-performance adsorbents were prepared allowing to obtain up to 190,000 tp/m. However, the column possesses a very high back-pressure and can be used in a short length up to 50 mm only to meet the requirements of conventional chromatographic equipment. An analysis of a test mixture of seven anions was completed within 3 min with a back column pressure of about 350 bar (HETP of about 5.5 microm, where HETP is the height equivalent to the theoretical plate). Monolithic capillary columns provide lower efficiency per column unit length than MICRA columns; however, they can be used at a longer length because of their low flow resistance. Monolithic column of ca. 40 cm length has workable pressure below 10 bar and allows separation of a five anions test mixture within less than 10 min. A better efficiency of monolithic column (HETP approximately 75 microm) can be achieved at reduced flow rates when the analysis time is not a critical parameter.     

Calculation of the equilibrium in systems containing ion exchangers in the formation of difficultly soluble precipitates

Summary Equations were derived for calculating the amounts of cation-exchange or anion-exchange resin needed as precipitants in order to purify a solution to a given degree of purity. Based on an analysis of the obtained equations it was shown that it is expedient to use a cation-exchange resin for an efficient purification of the solution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1689–1691, September, 1965     

Multiscale modeling of molecular structure and optical properties of complex supramolecular aggregates

Supramolecular aggregates of synthetic dye molecules offer great perspectives to prepare biomimetic functional materials for light-harvesting and energy transport. The design is complicated by the fact that structure–property relationships are hard to establish, because the molecular packing results from a delicate balance of interactions and the excitonic properties that dictate the optics and excited state dynamics, in turn sensitively depend on this packing. Here we show how an iterative multiscale approach combining molecular dynamics and quantum mechanical exciton modeling can be used to obtain accurate insight into the packing of thousands of cyanine dye molecules in a complex double-walled tubular aggregate in close interaction with its solvent environment. Our approach allows us to answer open questions not only on the structure of these prototypical aggregates, but also about their molecular-scale structural and energetic heterogeneity, as well as on the microscopic origin of their photophysical properties. This opens the route to accurate predictions of energy transport and other functional properties.

Multiscale modeling resolves the molecular structure of a synthetic light-harvesting complex, unraveling the microscopic origin of its photophysical properties.

Supramolecular structures may self-assemble from a variety of building blocks, resulting in a wide range of advanced materials with attractive biomimetic, sensing, catalytic, optoelectronic and photonic functionalities.^1–10 The close-packed nanoscale organization of the individual molecules within a supramolecular system, held together via noncovalent interactions, gives rise to the aggregate''s (collective) properties. Assemblies consisting of dye molecules often exhibit unique collective optical properties and are of interest for opto-electronic applications as well as artificial light-harvesting complexes that mimic natural antenna systems of photosynthetic bacteria and plants.^11–13 For example, chlorosomal antenna complexes of photosynthetic green sulfur bacteria are self-assembled into multilayer tubular structures having bacteriochlorophyll pigments as building blocks.^14–16 The structure of these antenna complexes and the underlying molecular arrangement ensures that the process of light-harvesting and excitation energy transport is very efficient, even under extremely low light conditions.^17,18 The quest to recreate such efficiency under laboratory conditions has sparked numerous studies of synthetic self-assembled systems mimicking natural chlorosomes, e.g. using porphyrins,¹⁹ zinc chlorin,²⁰ and cyanine dyes.²¹ Of particular interest are the tubular aggregates of 3,3′-bis(2-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3).^22–25 Cryo-TEM reveals a hierarchy of supramolecular architectures, including double-walled nanotubes; under certain conditions, bundles of nanotubes arise.²⁶ Thus, this system allows for the occurrence of electronic excitation energy transport at various levels: within one wall, between walls of one tube, and between different tubes, similar to the situation in natural systems.^27,28To understand how such supramolecular systems work, as well as propose design rules for new materials, it is essential to determine the relationship between molecular structure and optical properties. Current experimental techniques, however, are unable to resolve the structure at the molecular level. This, in combination with the sensitivity of spectral properties to the details of the molecular packing, leads to a crucial role for theoretical modeling.²⁹ For example, molecular dynamics (MD) simulations have been used to predict the molecular packing within a variety of supramolecular assemblies.^30–34 However, synthetic amphiphiles with aromatic groups, such as cyanine dyes—often used to prepare aggregates with optical functionality—tend to fall into kinetic traps during spontaneous self-assembly simulations and the packing of the aromatic chromophores remains highly disordered on the accessible time scale, leading to predicted (optical) spectra that are not consistent with experimental data.³⁵ This problem can be overcome by building assemblies based upon proposed architectures and assessing their stability in relatively short MD simulations.^36–38 The drawback of this approach is the requirement of a thorough understanding of what to use as a starting point and how to validate the structure. In any case, proper validation requires the modeling of the optical spectra of the obtained structure, and finally, comparing it to the experiment. The demanding character of such methods explains why an important role is played by phenomenological modeling, in which a molecular packing is guessed and the optics is obtained from parametrizing an exciton model that describes the collective excited states of the assembly with interactions dictated by the guessed packing. By comparing the calculated spectra to experimental ones, the structure and exciton model may be fine-tuned. While this method has been successful in describing spectra,^23,39 it is limited in its predictive power and also lacks access to essential microscopic parameters, such as tuning of the optical excitation energies imposed by the environment, disorder in these energies and structural heterogeneity.In this work, we use an advanced multiscale approach to determine structure–optical property relationships for the C8S3 double-walled nanotubes, guided by comparison to experiments. The optical spectrum of these aggregates, in which multiple exciton peaks may be discerned, suggests a rather complex underlying molecular packing. This fact, combined with their sheer size going up to many thousands of molecules, makes these systems exceptionally challenging to resolve and leaves important questions concerning structure–function relationships unanswered or under debate, for instance the origin of the splitting between the two lowest-energy spectral bands.^23,38 Here, we answer these questions by iteratively combining MD simulations to capture the details of molecular packing and structural disorder, an exciton Hamiltonian approach to calculate optical signatures, and explicit microelectrostatic calculations to estimate energetic disorder and solvent shifts. Previous attempts to reveal the structure of cyanine-based nanotubes were limited to small-scale system sizes,^37,38 modeling optical features phenomenologically rather than using atomistic information³⁸ or featuring simpler, single-walled systems.³⁷ In addition to answering important questions for the C8S3 double-walled nanotubes, our study opens the way to explain and predict at an unprecedented level of detail the functional properties of other highly complex molecular materials.     

Inverse gas chromatographic study of supramolecular organization in microheterogeneous systems for the example of polyblock copolymers

The potentialities of inverse gas chromatography for studying microheterogeneous polymer systems are analyzed. For the first time this method is applied to examination of the microstructure of multiblock copolymers obtained by condensation. A procedure for evaluation of the partial contribution of the dissolution to the total retention volume is suggested.     

Sorption properties of nitrogen-containing ion exchangers

Sorption capacity of ion exchangers based on glycidyl derivatives of aromatic compounds and polyamines was studied in relation to pH of solution. The mechanism of sorption of polyvalent metal ions was examined.     

Computer modeling of the structure of large molecules: II. Cluster C1500

The structure of a C₁₅₀₀ cluster modeling a “planar” polymeric buckminsterfullerene(VIII) is determined by the PM3 quantum-chemical method. The cluster consists of 25 oblate octa-, hexa-, and tetra-valent C₆₀ polyhedra and has D _2h symmetry. The calculated parameters of a rectangular unit cell are as follows: 9.016 Å along the bridging bonds in the polymer plane and 9.084 Å along the bridging bonds over and under the polymer plane. Hybrid σ orbitals of three-coordinate atoms are directed at an angle of 9.7°–9.8° to the polyhedron edges and those of four-coordinate atoms, at an angle of 8.3°–8.6° to the rectangular bridge edges. The s contribution into π orbitals is negligibly small. The GAMESS program with a new algorithm for diagonalization of large dense symmetrical matrices and a new VALENCY program were used for calculations.     

Hydrolysis of oligosaccharides by sulphonic ion exchangers

The hydrolysis of oligosaccharides by sulphonic ion exchangers has been performed in batch and in column experiments. The rate constants and selectivity are compared with the values obtained in homogeneous phase with H₂SO₄ and polystyrene sulphonic acid. The rate constants are lower in the presence of ion exchangers for dimers and the efficiency decreases as the degree of polymerization of the oligosaccharides increases, because of control by intraparticle diffusion. It is concluded that the ion exchanger process is rather inefficient for higher molecular weight solutes when compared with the corresponding polyelectrolyte or low molecular weight acid.     

First example of an ice-like water hexamer boat tape structure in a supramolecular organic host

A T6(2) tape of hydrogen bonded water molecules in boat cyclohexane conformation resides in the channel structure of a dibromophloroglucinol (DBPG) host; water escapes at 40-90 degrees C but is readily re-absorbed by the sponge-like apohost.     

Synchronization of ion exchangers by an oscillating electric field: theory

Can we physically manipulate functions of membrane proteins, such as ion exchangers, especially the active transporters? This is a fascinating question which has attracted many scientists. Recently, we developed a new technique that we call synchronization modulation with which we realized significant (many-folds) activation of Na/K pumps by a well-designed oscillating electric field. In this technique, we consider activation of the pump molecules as a dynamic entrainment procedure, where individual pumps are first entrained to run at the same pumping rate and phase as the oscillating electric field and then the two transports are electrically facilitated separately and alternately by gradually increasing the field oscillating frequency. The procedure consists of two steps: synchronization and modulation. In this paper, we discuss the underlying mechanism involved in the first step: synchronization of the pump molecules.     

Thermodynamic description of superequivalent sorption by ion exchangers: Theoretical background

A thermodynamic approach to describing ion exchange and superequivalent absorption that occur simultaneously is proposed, based on the stoichiometry of both processes. This approach allows us to calculate the activity coefficients of components of the sorbent phase and the thermodynamic constants of ion exchange and superequivalent absorption.     

Investigation of silica gel supported inorganic ion exchangers

Microcrystalline zirconium phosphate (-ZrP), hydrous manganese dioxide (HMnO), ammonium molybdophosphate (AMP) and silica gel supported forms of these materials as well as silica gel (SG) itself were investigated by thermoanalytical, electron microscopic, X-ray diffraction and infrared spectrometric methods. Chemical composition, structure and some related properties of the inorganic ion exchangers mentioned above are reported.