Control of the phase formation process in solutions of anionic polyelectrolyte—cationic surfactant complexes in a microfluidic channel

Russian Chemical Bulletin - The process of phase formation in solutions of polyacrylic acid and cetyltrimethylammonium bromide was studied in microfluidic channels with a characteristic size of...     

Host–guest chemistry of radical-copper wheels. A supramolecular control of magnetic exchange coupling

The crystal of the hexanuclear wheel-shaped complex, [CuCl₂·(4PMNN)]₆ (1), has a channel structure in a direction perpendicular to the molecular plane (4PMNN=4-pyrimidinyl nitronyl nitroxide). Excess LiCl, NaCl, or KCl added to a methanol solution of 1 yielded the corresponding guest-included compounds, (LiCl)₆@1, (NaCl)₂@1, and (KCl)₂@1. The inclusion of the guests was confirmed by means of elemental analysis and X-ray diffraction study. The crystallographic c length and the cell volume were slightly shrunk by the guest inclusion. The ferromagnetic interaction, which is ascribed to intermolecular contacts between the nitronyl nitroxide groups, was remarkably enhanced almost in proportion to the cell shrinkage. Similar enhancement was observed for the host–guest complexes from the bromide analogue [CuBr₂·(4PMNN)]₆]. The crystallization in the presence of water gave (H₂O)_n@1. In addition to enhancement of the ferromagnetic interaction of (H₂O)_n@1, we found that the ferromagnetic interaction decreased back to a level of that of the empty 1 after removal of H₂O by evacuation.     

Dilational viscoelasticity of anionic polyelectrolyte/surfactant adsorption films at the water–octane interface

In this article, the interfacial tension and interfacial dilational viscoelasticity of polystyrene sulfonate/surfactant adsorption films at the water–octane interface have been studied by spinning drop method and oscillating barriers method respectively. The experimental results show that different interfacial behaviors can be observed in different type of polyelectrolyte/surfactant systems. Polystyrene sulfonate sodium (PSS)/cationic surfactant hexadecanetrimethyl–ammonium bromide systems show the classical behavior of oppositely charged polyelectrolyte/surfactant systems and can be explained well by electrostatic interaction. In the case of PSS/anionic surfactant sodium dodecyl sulfate (SDS) systems, the coadsorption of PSS at interface through hydrophobic interaction with alkyl chain of SDS leads to the increase of interfacial tension and the decrease of dilational elasticity. For PSS/nonionic surfactant TX100 systems, PSS may form a sub-layer contiguous to the aqueous phase with partly hydrophobic polyoxyethylene chain of TX100, which has little effect on the TX100 adsorption film and interfacial tension.     

Host–guest interaction of hemicucurbiturils with phenazine hydrochloride salt

The host–guest interactions between phenazine hydrochloride salt (PheH⁺) and hemicucurbit[n]uril (n = 6 or 12) (HemiQ[6 or 12]) have been studied by ¹H NMR, UV–vis, IR, mass spectrometry (MS) and quantum chemistry. In ¹H NMR spectra, the broadening of proton resonances of the hosts suggests the interactions of PheH⁺ with HemiQs. The quantitative stabilities of the host–guest systems have been obtained by UV–vis titration experiments, that is, the stoichiometric interactions of PheH⁺ with HemiQ[6] have been observed with an association constant of K_a = (2.5 ± 1.2) × 10⁶ L mol^? 1, while the 2:1 ratio complexes of PheH⁺ with HemiQ[12] are formed with stepwise association constants of K₁ = (9.2 ± 2.8) × 10⁴ L mol^? 1 and K₂ = (6.4 ± 0.9) × 10⁵ L mol^? 1, respectively, which induce a total association constant of K_a = 5.9 × 10¹⁰ L² mol^? 2. Both the 1:1 and 2:1 complexes have been detected by MS. Quantum chemistry calculations have been used to understand the static structures and thermodynamic stabilities of the supramolecular assemblies.     

Host–guest inclusion complex of β-cyclodextrin and benzoic acid in water–ethanol solvents: spectroscopic and thermodynamic characterization of complex formation

Journal of Thermal Analysis and Calorimetry - In this study, an inclusion complex of benzoic acid with β-cyclodextrin (BA-βCD) was obtained from water–ethanol solvents. The yield of...     

Transport properties in the nanofiltration of NaNO3–water solutions with a weak acid polyelectrolyte membrane

The nanofiltration of 0.02–1.0 mol/dm³ NaNO₃ solutions at pH 4.0 and 8.0 using a dynamically-formed zirconium hydrous oxide-polyacrylate (FIP-ZPA) membrane has been investigated at 318 K. The practical transport coefficients for hydrodynamic permeability (L_p), reflection (σ) and solute permeability (ω), were calculated from the nanofiltration results using irreversible thermodynamic equations.     

Host–guest system of Vitamin B10 in β-cyclodextrin: characterization of the interaction in solution and in solid state

Conventional drugs are usually formulated for the immediate release of the medicinal substances and for obtaining the desired therapeutic effect. The aim of this paper was to investigate the possible interactions between Vitamin B10 and β-cyclodextrin (β-CD), to determine the physical-chemical characteristics and the interactions present in the corresponding inclusion compound. The so-obtained compounds were characterized by X-ray diffraction, DSC and FTIR spectroscopy. ¹H NMR and UV–vis spectroscopic methods were employed to study the inclusion process in aqueous solution. The X-ray powder diffraction patterns demonstrate the inclusion compound formation, especially for the lyophilized product where the amorphous phase dominates. The existence of the inclusion compounds obtained by different methods was confirmed by comparing with DSC and FTIR data of the pure compounds and the (1:1) Vitamin B10:β-CD physical mixture (pm). ¹H NMR measurements on aqueous solutions of Vitamin B10 and β-CD in D₂O allowed us to establish the corresponding Vitamin B10’s and cyclodextrin’s protons implied in the complexation process. 2D NMR spectroscopy established the geometry of the inclusion complex. ¹H NMR, UV–Vis and fluorescence data were used to obtain the stoichiometry and the stability constant of the complex.     

Surface tension studies on the complexation of dodecylpyridinium chloride byβ-cyclodextrin in aqueous electrolyte solutions

Surface tension measurements have been performed at 25° C for aqueous mixtures of dodecylpyridinium chloride and -cyclodextrin in 0.1 M NaCl. Data analyses assuming 1:1 stoichiometry were applied to estimate the complexation constant of the host-guest complex formation. The technique yields consistent results for solutions with a swamping, constant concentration of a simple inorganic electrolyte.     

Medium effects on HSO 4 − formation in a mixture of isomolar solutions of hydrochloric acid and an alkali metal chloride

The strontium sulfate solubility has been studied in mixtures of isomolar MCl and HCl solutions (M = Li, Na, K, Cs) with ionic strengths of I = 0.5, 1.0, 2.0, 3.0, and 4.0 at 25°C. At I ≥ 2, the SrSO₄ solubility as a function of hydrogen ion concentration passes through a maximum in all systems but (Li,H)Cl. The position of this maximum depends only slightly on the nature and ionic strength of the medium. The presence of the maximum is unambiguous evidence that there are secondary effects of the medium associated with the substitution of H⁺ for M⁺. These effects oppose the ordinary shift of the HSO ₄ ^? formation equilibria. A method is suggested for separating these effects. The standard values of pSP⁰ and logβ⁰, determined by extrapolation to zero ionic strength, are in satisfactory agreement with the literature. The parameter α₁, which characterizes the secondary effects of the medium on one of the basic equilibrium constants (log K _S1 ^O ), increases in the order (Li,H)Cl < (Na,H)Cl < (K,H)Cl < (Cs,H)Cl.     

Electrosynthesis and biological properties of persulfate–chloride solutions

A method for electrochemical synthesis of medical solutions for oxidation of toxic substances in the human organism has been developed. The method is based on electrooxidation of sodium sulfate in the presence of chloride and NaOH microadditions (in amounts that provide рН 13) in a filter-press membrane electrolyzer. A diagram is presented for choosing the optimum ratio between the current density and the flow rate of electrolyte during the electrosynthesis of a medical solution. The use of an electrolyte of the suggested composition under the optimum electrosynthesis conditions leads to solutions with physiological рН values (7.2–7.4) and high oxidative ability with respect to Micrococcus sp. and Staphylococcus coag (–), but there was no injuring effect on blood cells.     

NMR Studies of Host–guest Complexes Between Monocarboxylic Acids and Amide-based Cyclophanes in Chloroform

Formation of host–guest complexes with acetic acid and benzoic acid was studied by NMR for amide-based octaazacyclophanes having pendant methyl ester arms; the cyclophanes were tetramethyl 2,9,18,25-tetraoxo-1,4,7,10,17,20,23,26-octaaza[10.10]paracyclophane-4,7,20,23-tetraacetate, its meta-isomer and analogues. Amide NH proton and CH₂ proton adjacent to amide C = O in every cyclophane host showed down-field NMR shifts in the presence of the guest acids in CHCl₃-d, suggesting the formation of 1:1 complexes in which the carboxyl group of an acid molecule formed two hydrogen bonds with the amide NH and C = O moieties of a host molecule. Since the complex formation competed with the dimerization of the guest acids, the monomer–dimer equilibrium was restudied by NMR and the equilibrium constant was determined to be 330 M^? 1 for acetic acid and 518 M^? 1 for benzoic acid. By using these values, the formation constants of the host–guest complexes were determined to be 8–51 M^? 1. The close contact between the host and guest molecules via hydrogen bonding was consistently confirmed by NMR shifts due to the ring current of aromatic group.     

Host–guest complexes of cucurbit[7]uril with albendazole in solid state

The inclusion complex of cucurbit[7]uril (CB7) and albendazole (ABZ) in solid state was prepared by freeze-drying. The formation of a host–guest complex was confirmed by microanalysis, ¹H-nuclear magnetic resonance spectroscopy, and fourier transformed-infrared spectroscopy (FT-IR) techniques. The shifts in the NMR peaks supported the encapsulation from the propylthio and not the carbamate site, in agreement with the previously reported results in solution. The N₂ adsorption–desorption isotherms indicated no change in the calculated surface area or the pore size distribution for the unbound and CB7-bound ABZ solid drugs. Freeze-drying produced a system with a higher degree of amorphisation as confirmed by the X-ray powder diffraction (XRD) technique. Thermal analysis of the drug-loaded CB7 by using differential scanning calorimetry and thermogravimetry demonstrated the possibility of dehydration at temperature 100 °C beyond the melting point of unbound ABZ since no melting of the samples was observed until the CB7 itself begins to decompose around 300 °C. Putting it all together, the results supported that CB7 imparts significant thermal/physical stability on the ABZ drug in the solid state.     

Competing mechanisms in polyelectrolyte multilayer formation and swelling: Polycation–polyanion pairing vs. polyelectrolyte–ion pairing

The competition of interactions between charged groups of polyanions and polycations and their interaction with small counterions strongly affect the formation and stability of polyelectrolyte multilayers. This has consequences for the properties of polyelectrolyte multilayers like mechanics, polymer mobility and swelling in water.     

The influence of mixed cationic–anionic surfactants on the three-phase contact parameters in silica–solution systems

The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C₁₄TAB) and (b) surfactant mixture of the cationic C₁₄TAB with the anionic sodium alkyl- (straight chain C₁₂–, C₁₄– and C₁₆–) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C₁₄TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.     

Review of the quantitative structure–activity relationship modelling methods on estimation of formation constants of macrocyclic compounds with different guest molecules

There is an increasing interest in the use of quantitative structure–activity relationship (QSAR) approaches as a progressive tool in modelling and prediction of many physicochemical properties in host–guest interactions of macrocyclic complexes. A review is presented on the QSAR modelling of macrocyclic compounds formation constants, which focus on two most interesting macrocycles, e.g. crown ethers and cyclodextrins (CDs), with different guest molecules. The review starts with a short overview on experimental methods of stability constant measurement, followed by a short explanation of the QSAR methodologies. In the next section, we focus on and discuss QSAR techniques that used to predict the stability (binding) constants or free energy complexation of some most interesting macrocyclic compounds, e.g. CDs and crown ethers, with different guest molecules including anionic, cationic and neutral molecules.     

Host–guest complexes of various cucurbit[n]urils with the hydrochloride salt of 2,4-diaminoazobenzene

The interaction products of normal cucurbit[n]urils (n = 7, 8; Q[7] Q[8]) and a sym- tetramethyl-substituted cucurbit[6]uril derivative (TMeQ[6]) with the hydrochloride salts of 2,4-diaminoazobenzene (g·HCl) were investigated in aqueous solution using ¹H NMR spectroscopy, electronic absorption spectroscopy, as well as single crystal X-ray diffraction. The ¹H NMR spectra analysis established a basic interaction model in which inclusion complexes with a host:guest ratio of 1:1 form for the TMeQ[6] and Q[7] cases, while they form with a host:guest ratio of 1:2 for the Q[8] case. Commonly, the hosts selectively bound to the phenyl moieties of the guests. Absorption spectrophotometric analysis in aqueous solution defined the stability of the host–guest inclusion complexes at pH 3.2. Quantitatively, at this pH, complexes with a host:guest ratio of 1:1—those with smaller hosts TMeQ[6] and Q[7]—formed with logK values between 6 and 7. That with host Q[8] and a host:guest ratio of 1:2 formed with a logK value of 10.8. Single crystal X-ray structures of the inclusion complexes TMeQ[6]–g·HCl and Q[8]–g·HCl showed the phenyl moiety of the guest inserted into the host cavity. This result supports the solution-based ¹H NMR spectroscopic study.     

Photon correlation spectroscopic and spectrophotometric studies of the formation of cadmium sulfide nanoparticles in ammonia–thiourea solutions

Nucleation of CdS in an aqueous ammonia solution of thiourea and cadmium chloride was studied by photon correlation spectroscopy (PCS), static light scattering, and spectrophotometry. The hydrodynamic diameter of nanoparticles, light scattering intensity, and optical density of the solutions increased with temperature and synthesis time. The processes of formation, growth, and coagulation of nanoparticles can be transferred from solution to the filter surface by continuously filtering the reaction mixture through a 200-nm filter.     

The formation of host–guest complexes between surfactants and cyclodextrins

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host–guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host–guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD–surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature.