Interaction of inorganic salts with polar polymers. II. Infrared studies of polymer–inorganic nitrate systems

Certain inorganic nitrate salts are quite soluble in the polymers studied, namely, cellulose acetate, poly(vinyl acetate), poly(vinyl alcohol), poly(methyl methacrylate), and poly(methyl acrylate). Large effects upon the glass-transition temperature were observed in those systems where the transition could be readily measured. Large shifts in the infrared spectra of both the inorganic nitrate salts and in the polymer carbonyl and ester ether frequencies have been observed. These observations have been interpreted in terms of complex formation between these polymers and salts in the solid state. The proposed structure of the complex explains the nature of the infrared shifts both for the nitrate salts and the polymers as well as explaining the concentration effects observed. Effects of the solvating environment upon the salt and polymer spectra remain unexplained. The large glass-transition effects are a result of the degree of solubility of the salts in the polymers and the interactions between them. However, the reason why, in some cases, the change in the transition temperature as a function of concentration goes through a maximum is unclear.     

Proton exchange and tritium enrichment in inorganic systems: Inorganic metal salts

Summary Tritium exchange and enrichment was studied for several different metal salts, e.g., AlF₃ ^. H₂O, FeO(OH), CsI, CsF, NaI, NaF and Al(OH)₃ using a cryosublimation apparatus. Experiments were performed below equilibrium vapor pressure to avoid any isotope effects. A comparable tritium enrichment factor of 1.14 to 1.43 was obtained for all systems, except for CsF, which gave an enrichment factor of 1.93. These results confirm the concept, that ³H is accumulated in weak hydrogen bonds as already observed in organic molecules.     

DSC studies of binary inorganic ammonium compound systems

The thermal behaviour of the binary systems HNH₂SO₃-NH₄NH₂SO₃ (I), HNH₂SO₃-(NH₄)₂SO₄ (II), HNH₂SO₃-NH₄HSO₄ (III), NH₄NH₂SO₃-(NH₄)₂SO₄ (IV), NH₄NH₂SO₃-NH₄HSO₄ (V), (NH₄)₂SO₄-NH₄HSO₄ (VI) was investigated with a Du Pont Thermal Analyzer supplied with a DSC module. The corresponding single compounds and freshly prepared (NH₄)₂S₂O₇ were examined under the same conditions in preliminary experiments. The ΔH _f values of HNH₂SO₃, NH₄NH₂SO₃, (NH₄)₂S₂O₇ and (NH₄)₂SO₄ · NH₄HSO₄ determined in the absence of air were 11.9, 16.8, 11.7 and 11.7 kJ/mole. Due to the moisture content of the atmosphere, an repeated heating in air the DSC curves showed more endothermic peaks than under air-free conditions. Exothermic additive reactions took place for binary systems (I) and (III), resulting in the formation of (NH₄SO₃)₂NH and (NH₄)₂S₂O₇, respectively, and for systems (II) and (VI), producing a new compound on melting.     

Non-aqueous determination of inorganic salts

The procedures suggested for the determination of salts in nonaqueous solutions have been limited almost wholly to the analysis of amine salts and salts of the alkali and alkaline earth metals. Other salts are usually assayed by a variety of specific cationic or anionic procedures. By the proposed method, salts of all types can be determined titrimetrically so long as the compound will participate in an anion-exchange reaction. The procedure simply involves acidification of the salt with an excess of a strong acid, addition of a nonaqueous solvent and a differentiating potentiometric titration. Carbonate and hydroxide impurities do not interfere in the analysis and the solubility difficulties experienced in other nonaqueous procedures are not encountered in this method.     

Enantiomer resolution in immobilized pH gradient gels via inclusion of a chiral discriminator

The separation of enantiomeric forms of dansylated amino acids by isoelectric focusing in immobilized pH gradients (IPG) is demonstrated for the first time. Separations occur in a pH 3.0-4.0 IPG interval, in presence of 7Murea, 10% methanol and 60 mM beta-cyclodextrin (CD) as chiral discriminator. It is found that the inclusion complex formed between the D-form and CD has a lower pI than the uncomplexed form (delta pI = 0.05 for DL-Phe and delta pI = 0.025 for DL-Trp); from this, it is calculated that the pK of the tertiary amino group in the dansyl moiety is lowered by 0.1 pH unit in the former case (D-Phe) and by 0.05 in the case of D-Trp (both values referring to 60 mM CD gels). For some racemates (e.g., DL-Phe) the separation mechanism is still operative with CD concentrations as low as 20 mM. In our system 60 mM CD appears to be the solubility limit of CD. As the complex is stable in the electric field for at least 15 h, this separation mechanism could be exploited for purifying large quantities of pure D and L forms from racemates in multicompartment electrolyzers with isoelectric Immobiline membranes.     

Enantiomer and diastereomer resolution of dipeptides by gas chromatography on chirasil-val

Several dipeptides have been separated into stereoisomers (enantiomers, diastereoisomers, sequential isomers) by GC on the chiral stationary phase Chirasil-Val. Sufficiently volatile N-TFA-dipeptide methyl esters have been formed by derivatization at ambient temperature, thus avoiding racemization (or epimerization, respectively), and peptide cleavage. This novel approach has proven particularly useful for the determination of stereoisomeric composition of dipeptides in biological fluids.     

Enantiomer resolution of intrinsically chiral C21-alkylated N-confused porphyrin complexes

The resolution of stereoisomers of C21‐alkylated nickel(II) complexes of N‐confused porphyrin (NCP) was performed by means of chiral‐phase HPLC with an effectiveness of above 90 % molar ratio for each isomer. The reverse signs of the Cotton effects in the circular dichroism (CD) spectra of the separated fractions are indicative of the pair of enantiomers. The application of low‐temperature 2D NMR methods to the separated diastereomers of the system comprising a chiral 2‐(S)‐methylbutyl substituent, in connection with the CD spectra and relative HPLC migration rates, allowed the assignment of the absolute configuration of the chiral C21‐substituted complexes of NCP. The assignment was confirmed by time‐dependent DFT (TDDFT) calculations of CD spectra for the C21‐methylated nickel(II) complex. The system remains chiral after removal of the metal ion from the macrocyclic crevice, despite the fact that this demetalation is connected with a change of the C21 hybridization from pyramidal to trigonal. The retention of chirality was established by means of CD spectra and confirmed by TDDFT calculations for a C21‐methylated NCP free base. Stereoisomers were also separated for three covalently linked bis(NCP) systems with bridges involving one or two C21 carbon atoms. The occurrence of a pair of enantiomers was established for nonsymmetrical dimers comprising only one stereogenic center. In the case of the 21,21′‐(o‐xylene)‐linked dimer, three stereoisomers, that is, a pair of enantiomers and an optically inactive meso‐form, were separated and analyzed by CD and ¹H NMR spectroscopy. The stereoisomers of a diastereoselectively formed nonsymmetrical chloroplatinum(II)‐linked dimer, consisting of heterochiral C21‐alkylated NCP nickel(II) subunits, after separation displayed a strong optical activity, which can be ascribed to the rigid helical structure of the complex.     

Reversed-phase liquid chromatography of alkaloids: Masking effects of inorganic salts

The addition of salts (investigated cations Na(+), NH(+)(4), K(+), KBu(+)(4) combined with the anions acetate, Br(-), SCN(-) and I(-)) can be used to eliminate peak tailing and to decrease retention of cationic species in the course of the separation of alkaloids from Chelidonium majus L. by reversed-phase chromatography on a ODS Hypersil column, using water-acetonitrile-methanol mixture as eluent. These findings are interpreted in terms of a silanol masking effect. The extended donor-acceptor concept is used to interpret the effectiveness of different salts in masking the active sites of the stationary phase.     

Aqueous biphasic systems formed by nonionic polymers I. Effects of inorganic salts on phase separation

The effect of salts KSCN, KI, KBr, KCl, KClO₄, KF, K₂SO₄ and NH₄Cl, LiCl, NaCl, KCl, CsCl on the binodials of the phase diagrams for aqueous biphasic dextranpolyvinylpyrrolidone, dextran-polyvinyl alcohol, dextran-ficoll and dextran-polyethylene glycol systems was studied. It is established that the K-salts present at the concentrations of 0.1 and 0.5 mol/kg alter the binodials of the phase diagrams for the above systems. The effect of a salt is found to be related to the lyotropy of the salt quantified by the salt molal surface tension increment. It is assumed that phase separation in an aqueous polymer biphasic system is affected by the presence of a salt mainly due to the effect of the salt on the structure and/or state of water in the system.     

Enantiomer resolution by using capillary zone electrophoresis: resolution of racemic tryptophan and determination of the enantiomer composition of commercial pharmaceutical epinephrine

The enantiomers of D- and L-tryptophan were separated by capillary electrophoresis, using alpha-cyclodextrin as a chiral active component in the background electrolyte. The separation of (-) and (+) epinephrine was achieved by supplementing the background electrolyte with Heptakis (2,6-di-O-methyl-beta-cyclodextrin). As a practical application of the method, the quantitative analysis of (-) and (+) enantiomers in commercial pharmaceutical solutions of adrenaline is shown.     

Complex formation of inorganic salts withβ-cyclodextrin

The interactions between some alkali halides, perchlorates and sulfates and-cyclodextrin (cycloheptaamylose, CD) have been investigated by solubility, spectrophotometric, thermoanalytical and preparative methods. The main conclusions are as follows. (i) The most pronounced interaction occurs with the anions; in dilute solutions this can be characterized as the formation of 1 : 1 complexes. In more concentrated solutions ternary associates and more complicated ones (involving the cations as well) are also formed. (ii) Changes in the activity coefficients or of the activity of water may also have some role in the phenomena, but it cannot be dominant: differences according to the individual properties of the anions are much more pronounced than to those of the cations or to changes of the ionic strength. (iii) Regarding the type of complex formation, real inclusion and outer sphere interactions (via hydrogen bonds) are also probable.     

Spectroscopic characterization of aqueous microdroplets containing inorganic salts

We have developed and studied methods to characterize the time-varying composition of liquid microdroplets, under controlled changes to environmental conditions, using Raman tweezers. This work has focussed on measurements of inorganic salts, such as nitrate and sulfate anions, which comprise a major fraction of the dissolved solutes in atmospheric aerosols. The experimental Raman intensities for the anions of inorganic salts in optically tweezed droplets were found to be in good agreement with theoretical estimates of photon scattering. The detection limit for sodium nitrate salt in a single particle was found to be ~4 pg. The mass of an inorganic salt in the droplet can be estimated from the Raman intensity of the anion bands using a calibration curve which is independent of droplet volume. The volume of the droplet, and concentration of solute, can be found directly from the spacing of morphology dependent resonances in the Raman band of water, or indirectly from the integrated-intensity of the Raman band for the solvent. The later strategy eliminates the uncertainty in the collection efficiency of Raman-scattered light related to varying particle sizes.     

Solubility of inorganic salts in pure ionic liquids

The solubility of different conventional salts in several room-temperature ionic liquids – containing ammonium, phosphonium or imidazolium cations combined with acetate, sulfate, sulfonate, thiocyanate, chloride, tetracyano-borate, tris(pentafluoroethyl)trifluoro-phosphate, l-lactate, bis(trifluoromethylsulfonyl)imide or trifluoromethylsulfonate anions – were screened using a visual detection method. The most promising mixtures were then re-measured using an ATR–FTIR (Attenuated Total Reflection Fourier Transform Infra Red) spectroscopy technique in order to accurately and quantitatively determine the corresponding solubility at 298.15 K.     

Aqueous biphasic systems formed by nonionic polymers II. Concentration effects of inorganic salts on phase separation

Concentration effects of KSCN, KClO₄, KI, KBr, KNO₃, KCl, KF and K₂SO₄ on the compatibility of dextran with ficoll, polyvinylpyrrolidone and poly(ethylene glycol) at fixed polymer concentration ratios were studied in aqueous solution. The results obtained are considered in terms of the Patterson theory of-effect. It is assumed that phase separation in an aqueous solution of two nonionic polymers results from the appearance of two different water structures in the vicinity of the phase polymers. The data obtained are considered in terms of the concept of salting-in-salting-out effects of neutral salts on aqueous solubility of biopolymers. The salt effects observed are attributed to two antagonistic influences of salts on the electrostatic (dipole-dipole) polymer-water interactions and on the water-water interactions in the vicinity of the phase polymers.     

Precipitation of inorganic salts inside hollow micrometer-sized polyelectrolyte shells

Hollow polymer shells formed by layer-by-layer adsorption of oppositely charged polyelectrolytes onto micrometer-sized colloidal particles with subsequent decomposition of the colloidal core were employed as a model system for the study of inorganic crystallization reactions in restricted volumes. The size-selective permeability of shells is used for spatially controlling the precipitation of inorganic salts CaCO3 and BaCO3 into the shell interior. Outside the shells the precipitation was suppressed by the polymers, which are unable to penetrate the shell wall. The precipitates were studied by scanning electron microscopy and atomic force microscopy. The fundamental and applied aspects of research on spatially confined synthesis of inorganic particles are under discussion.     

Sorption of inorganic salts on carbon nanomaterials and magnetite

Magnetic composites based on graphene oxides and functionalized carbon nanotubes containing magnetite nanoparticles are synthesized. The dispersing ability of these composites in water at different pH values is studied. It is shown that the solubility of Fe₃O₄ composites is constant in the рН range of 3.5–10, though these composites are unstable at both lower and higher pH values. Magnetic sorbents for extracting Се(NO₃)₃ and La(NO₃)₃ from solutions are tested. Dependences of the volume on the sorbent’s composition, pH value, and salt concentration in the solution are found. Maximum sorption capacity in relation to Се³⁺ and La³⁺ at рН 7.5 and 8.5 are found to be 1040 and 920 mg/g respectively.