Interactions between Adsorbed Layers of a Low Charge Density Cationic Polyelectrolyte on Mica in the Absence and Presence of Anionic Surfactant

Interactions between two negatively charged mica surfaces across aqueous solutions containing various amounts of a 10% charged cationic polyelectrolyte have been studied. It is found that the mica surface charge is neutralized when the polyelectrolyte is adsorbed from a 10–50 ppm aqueous solution. Consequently no electrostatic double-layer force is observed. Instead an attractive force acts between the surfaces in the distance regime 250–100 Å. We suggest that this attraction is caused by bridging. Additional adsorption takes place when the polyelectrolyte concentration is increased to 100 and 300 ppm, and a long-range repulsion develops. This repulsive force is both of electrostatic and steric origin. The polyelectrolyte layer adsorbed from a 50 ppm solution does not desorb when the polyelectrolyte solution is replaced with an aqueous polyelectrolyte-free solution. Injection of sodium dodecyl sulfate (SDS) into the measuring chamber to a concentration of about 0.01 CMC (8.3 × 10⁻⁵M) does not affect the adsorbed layers or the interaction forces. However, when the SDS concentration is increased to 0.02 CMC (0.166 mM) the adsorbed layer expands dramatically due to adsorption of SDS to the polyelectrolyte chains. The sudden swelling suggests a cooperative adsorption of SDS to the preadsorbed polyelectrolyte layer and that the critical aggregation concentration between the polyelectrolyte and SDS at the surface is about 0.02 CMC. The flocculation behavior of the polyelectrolyte in solution upon addition of SDS was also examined. It was found that 0.16–0.32 mol SDS/mol charged segments on the polyelectrolyte is enough to make the solution slightly turbid.     

Electroconductivity of the calcium oxide-ethylene glycol-water system

The electroconductivity of calcium oxide-ethylene glycol (EG) and calcium oxide-EG-water systems is measured in wide ranges of temperatures and compositions. With increasing temperature, the conductivity of the former system passes through a maximum, which shifts to lower temperatures with increasing electrolyte concentration. Thermodynamic characteristics of the calcium hydroxy glycolate association in EG are estimated using the Lee-Wheaton equation. The conductivity of the latter system decreases with increasing EG content. Its dependence on the limiting high-frequency conductivity of the mixed solvent is analyzed. The activation energy for conduction in both systems decreases with increasing temperature and electrolyte concentration.     

HPLC of biological macromolecules: The first decade

Summary During the past decade, HPLC has developed into a powerful new technique for the analysis of complex mixtures of biological macromolecules. Through the use of microparticulate supports of vastly improved mechanican strength, superior stationary phase chemistry, and advanced instrumentation, it is now possible to separate biological macromolecules more than 10 times faster and with greater resolution than in the classical SEC, IEC, HIC, bioaffinity, and hydroxyapetite chromatography columns. Additionally, the introduction of new separation modes such as RPC and metal chelate make it possible to carry out separations that were not possible with the classical gel-type media. It is anticipated that 1) expanded use of non-porous media, 2) development of new stationary phases for carbohydrates, 3) greater throughput and resolution in preparative separations, and 4) better understanding of retention mechanisms are a few of the areas of macromolecular separations in which advances can be expected in the next few years.     

A Novel Proton Transfer Self‐Associated Compound from Dipicolinic Acid and Guanidine and Its Cadmium(II) Complex: Synthesis,Characterization, Crystal Structure,and Solution Studies

A novel 1:2 proton transfer self‐associated compound LH₂ , (GH⁺)₂(pydc^2—), was synthesized from the reaction of dipicolinic acid, pydcH₂, (2, 6‐pyridinedicarboxylic acid), and guanidine hydrochloride, (GH⁺)(Cl^—). The characterization was performed using IR, ¹H and ¹³C NMR spectroscopy and single‐crystal X‐ray diffraction. LH₂ · H₂O crystallizes in the space group C2/c of the monoclinic system and contains eight molecules per unit cell. The unit cell dimensions are: a = 26.480(5)Å, b = 8.055(2)Å, c = 14.068(3)Å. The first coordination complex (GH)₂[Cd(pydc)₂] · 2H₂O, was prepared using LH₂ and cadmium(II) iodide, and characterized by ¹H and ¹³C NMR spectroscopy and X‐ray crystallography. The crystal system is triclinic with space group P1¯ with one molecule per unit cell. The unit cell dimensions are: a = 8.5125(7)Å, b = 11.0731(8)Å, c = 13.2404(10)Å. The cadmium(II) atom is six‐coordinated with a distorted octahedral geometry. The two pydc^2— units are almost perpendicular to each other. The protonation constants of the building blocks of the pydc‐guanidine adduct, the equilibrium constants for the reaction of pydc^2— with guanidine and the stoichiometry and stability of the Cd²⁺ complex with LH₂ in aqueous solution were accomplished by potentiometric pH titration. The solution studies strongly support a self‐association between pydc^2— and GH⁺ with a stoichiometry for the Cd^II complex similar to that observed for the isolated crystalline complex. In fact, the [Cd(pydc)₂]^2— complex was found as the most abundant species in solution (> 90 %) at a pH >5.     

Purification and characterization of a solvent stable protease from Pseudomonas aeruginosa PseA

A solvent tolerant Pseudomonas aeruginosa PseA strain was isolated from soil. It secreted a novel alkaline protease, which was stable and active in the presence of range of organic solvents, thus potentially useful for catalysis in non-aqueous media. The protease was purified 11.6-fold with 60% recovery by combination of ion exchange and hydrophobic interaction chromatography using Q-Sepharose and Phenyl Sepharose 6 Fast Flow matrix, respectively. The apparent molecular mass based on the sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was estimated to be 35,000 Da. The enzyme was stable in the pH range of 6.0-9.0, the optimum being 8.0. The Km and Vmax towards caseinolytic activity were found to be 2.7 mg/ml and 3 micromol/min, respectively. The protease was most active at 60 degrees C and characterized as a metalloprotease because of its sensitivity to EDTA and 1,10-phenanthroline. It was tested positive for elastase activity towards elastin-orcein, thus appears to be an elastase, which is known as pseudolysin in other strains of P. aeruginosa. The protease withstands range of detergents, surfactants and solvents. It is stable and active in all the solvents having log P above 3.2, at least up to 72 h. These two properties make it an ideal choice for applications in detergent formulations and enzymatic peptide synthesis.     

Vibrational Spectroscopic Study on Ion Solvation and Association of Lithium Perchlorate in 4-Methoxymethyl-ethylene Carbonate

Solvation interaction and ion association in solutions of lithium perchlorate/4-methoxymethyl-ethylene carbonate （MEC） have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li^＋ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li^＋ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO4^- band revealed the presence of contact ion pair, and free ClO4^- anion in the concentrated solutions.     

Conductance of tetraalkylammonium salts in 2-butanone from −45 to 25°C

Interactions of three types of tetraalkylammonium cations (tetrapropyltetrabutyl-and tri-isoamylbutyl- ammonium) with perchlorate and tetraphenylborate anions were studied by the conductivity method in 2-butanone from –45°C to 25°C. Conductance data obtained for diluted solutions (5×10^–5 – 2×10^–3 mol-dm^–3) were used to calculate the limiting molar conductivities and associationconstants. The conductance equation of Fuoss-Hsia including the Chen term and the chemical model assumption were applied. Limiting ion conductivities were calculated assuming equal limiting conductivities of the i-Am₃BuN⁺ and BPh ₄ ^– ions at all temperatures. Gibbs energies and entropies of ion pair formation, calculated from the dependence of association constants on temperature, are presented including the contributions due to short-range forces.     

Enhancement of the solubilities of polycyclic aromatic hydrocarbons by weak hydrogen bonds with water

Summary The thermodynamics of mobile order is applied to predict the aqueous solubility of liquid and solid aliphatic and polycyclic aromatic hydrocarbons. The solubility values are mainly determined by the magnitude of the hydrophobic effect. However, contrary to the solubilities of the alkanes, the solubilities of polycyclic aromatic hydrocarbons in water predicted in absence of solute-solvent hydrogen (H) bonds are systematically too low. This shows the contribution of weak specific interactions between the OH groups and the electrons of the aromatic substances. According to the theory, these interactions are characterized by a stability bility constant K_o which can be derived from solubility data. At 25°C, this constant amounts to 80 cm³/mol, the order of magnitude of which can be explained by the competition of these intermolecular bonds with the rather weak self-association bonds in the secondary chains of water.     

Dissociation of photochromic spiroanthrooxazine dimers in the excited state

The influence of temperature and concentration on the spectral polarization properties of the luminescence and absorption of molecules of the original form of photochromic spiroanthrooxazine (SAO) in petroleum ether and polyethylene was investigated. It was shown that the long-wave part of the absorption spectra of the molecules is formed by at least two -*-type electronic transitions, the oscillators of which are mutually orthogonal. It is suggested that the SAO molecules form dimers in nonpolar media through dipole-dipole interaction, and at high concentrations they also form higher associates. Dimers stable in the ground state dissociate when excited to the second electronic transition with a rate constant of 10¹²–10¹³ s^–1.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Department of the Institute of Solid-State Physics and Semiconductors, Academy of Sciences of Belarus, 211177 Vitebsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 99–106, January, 1992.     

Template functions of particle monolayers on hydrophobic solid substrates

The template function of cationic particle monolayers bearing quaternary ammonium groups on their surfaces towards anionic colloids was investigated in this paper. Monodispersed cationic polymer particles having quaternary ammonium groups were self-organized on octadecylated glass plates through hydrophobic interaction. The morphology of the resulting particle monolayers was changed by tuning hydrophilic–hydrophobic balance of particles to fabricate aggregated type and dispersed type of particle monolayers. Gold and silver colloids were selectively deposited onto the particle monolayers through electrostatic interaction. The deposited gold and silver colloids on particle monolayers showed plasmon absorbance. Fluorescent silica colloids were also selectively deposited on particle monolayers to permit fluorescence labeling of the particle monolayers. Cationic particle monolayers fabricated on hydrophobic solid octadecylated were found to effectively work as templates for the deposition of above mentioned inorganic colloids.