Bilayer-coated capsule membranes. IV. : Control of NaCl permeability by phase transition of synthetic bilayer coatings,depending on their hydrophilic head groups

Ultrathin nylon capsule membranes coated with synthetic bilayers, the hydrophilic head groups of which had cationic, anionic, zwitterionic and nonionic charges, were prepared. Permeation of NaCl trapped in the inner aqueous phase was reduced by a factor of 10-1000 relative to that of the uncoated, semipermeable capsules, and drastically changed at the phase transition temperature, T_c, of the coating bilayers, depending on the charge of their hydrophilic head group. In the case of capsules coated with positively or negatively charged bilayers, NaCl permeation was enhanced at temperatures above the T_c of the coating bilayers, as expected. On the other hand, NaCl release of capsules coated with neutral charged (nonionic and zwitterionic) bilayers was largely reduced at temperatures above the T_c. From activation energy data of Arrhenius plots, the permeation mechanism of NaCl, depending on the membrane surface charge, below and above the T_c was discussed.     

Phase Behavior of Tetradecyldimethylaminoxide in the Presence of Perfluorooctanol and HCl

The ternary phase diagrams of zwitterionic single-chain hydrocarbon surfactant (tetradecyldimethylaminoxide, C₁₄DMAO)—a perfluoro cosurfactant (1,1-H-dihydroperfluorooctanol, C₇F₁₅CH₂OH)-H₂O, and C₁₄DMAO-C₇F₁₅CH₂OH-H₂O-HCl have been studied at 25°C. The identification of the phases was done by means of electrical conductivity, optical polarizing microscopy, and ²H-NMR techniques. In this system the originally uncharged zwitterionic surfactant was increasingly charged by protonation through addition of HCl. The sequence of the phases observed is similar to that observed for hydrocarbon surfactant–cosurfactant mixtures, namely, L₁, L₁/L_α, L_α and L₂, as relative volume fraction of apolar compound increases over that of polar compound. The absence of sponge phase (L₃) is a result of the high bending constant of the mixed bilayers in this perfluoro system.     

Effect of electrostatic interaction on hydrolytic activity of phospholipase A2 at the polarized oil-water interface

The hydrolytic activity of phospholipase A₂ (PLA₂) against the dipalmitoylphosphatidylcholine monolayer formed at the nitrobenzene-water interface has been studied under the control of the potential drop across the monolayer. The activities of both porcine pancreatic and Naja naja PLA₂S was the highest when the potential of the nitrobenzene phase was 60 mV negative with respect to that of the aqueous phase. The local electrostatic interaction between the positively charged domain, the recognition site, of PLA₂ molecules with the negatively charged substrate side of the interface, where zwitterionic substrate molecules and negatively charged product molecules were adsorbed, is an important factor in determining the interfacial enzymatic activity. Irreversible adsorption of PLA₂ molecules on the substrate monolayer is confirmed, giving unequivocal evidence for the scooting mode of hydrolysis by PLA₂.     

Directional Potassium Transport through a Unimolecular Peptide Channel

Three unimolecular peptide channels have been designed and prepared by using the β‐helical conformation of gramicidin A (gA). The new peptides bear one to three NH₃⁺ groups at the N‐end and one to three CO₂^? groups at the C‐end. These zwitterionic peptides were inserted into lipid bilayers in an orientation‐selective manner. Conductance experiments on planar lipid bilayers showed that this orientation bias could lead to observable directional K⁺ transport under multi‐channel conditions. This directional transport behavior can further cause the generation of a current across a planar bilayer without applying a voltage. More importantly, in vesicles with identical external and internal KCl concentrations, the channels can pump K⁺ across the lipid bilayer and cause a membrane potential.     

Effect of Anions from the Hofmeister Series and Urea on the Binding of the Charged and Uncharged Forms of the Local Anesthetic Tetracaine to Zwitterionic Micelles*

It is widely known that ions in the aqueous phase affect the binding of charged solutes to membranes. Here we report the effect of ions and urea on the interaction of both the charged and uncharged forms of the local anesthetic tetracaine (TTC, an aminoester derivative of ben-zoic acid) to zwitterionic micelles. Binding was monitored by the increase in TTC fluorescence. Shifts in the emission wavelength maximum (δ_max) indicated that the anesthetic was located in an environment of lower polarity. The neutral form of TTC bound to micelles to a larger extent than the protonated form, in agreement with results found for lipid bilayers (Boulanger, Leitch, Schreier and Smith, Can. J. Biochem. 58 , 986–995, 1980). When ions from the Hofmeister series and urea were compared in their ability to affect the partitioning of the anesthetic, binding of both the charged and uncharged forms was found to increase upon addition of SO₄^2– and CI^? but was seen to decrease in the presence of SCN^?, CIO₄^?_- and urea. Solubility measurements revealed that the solubility of uncharged TTC increases in solutions containing the additives in the following order: SO₄^2– < CI^? < CIO₄^?_- < dilute buffer < SCN^? < urea. Spin label EPR spectra indicated that, except for CIO₄^?_-, the ions had little effect on micellar structure. Static light scattering measurements corroborated this result indicating a large increase in micellar molecular weight in the presence of CIO₄^?_- and lesser increases for CI^.- and SCN^?. The results show that, besides affecting the binding of ionic species through an electrostatic mechanism, ions also act by altering water structure and, as a consequence, the water solubility and the tendency to partition into the less polar micellar environment of polar charged or uncharged small organic solutes such as the benzoic acid ester derivative. Moreover, evidence suggests that the ions bind directly to the zwitterionic polar groups of the micelles, leading to changes in structure and size.     

Bilayer swelling of nonionic surfactant and sodium dodecylsulfate mixed system by refractive-index matching

Bilayer swelling behavior of nonionic and anionic surfactant mixed aqueous solution induced by adding glycerin was studied. The phenomenon were performed on a system, polyethylene glycol ether of tridecyl alcohol with the average number of ethylene oxide of 5 (CH₃(CH₂)₁₂(OCH₂CH₂)₅OH; abbreviation IT5) and SDS mixed aqueous solution, with white cream of the upper phase and micelles (L₁) of the lower phase. White cream containing densely packed multilamellar vesicles was revealed by freeze-fracture transmission electron microscopy and polarized microscope observations. Phase transition from white cream/L₁, two-phase, to clear unique vesicle phase can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by refractive-index matching between solvent and bilayers.     

Physical immobilization of laccase on an electrode by means of poly(ethyleneimine) microcapsules

Microcapsules of poly(ethyleneimine) were used to immobilize laccase on the surface of an electrode and its mediated electron transfer was studied with the redox mediator p-phenylenediamine (PPD). The microcapsules consisted of a cross-linked PEI wall generated from an emulsion of an aqueous phase containing the enzyme. The reaction of encapsulated laccase with PPD was studied by spectrophotometry and oxygen consumption. We found that the encapsulation resulted in a small shift for the optimum pH and a lower K_m value when compared to free laccase. These differences are attributed to the charged micro-environment offered by the microcapsules. The microcapsules were then deposited on a glassy carbon electrode and chronoamperometry was used to evaluate the mediated electron transfer between the enzyme and the electrode. No significant differences in term of optimum pH and K_m occurred upon capsules deposition on the electrode. The response time of the electrode for PPD oxidation was higher than those found in the literature, which suggests that the PEI capsule wall offers some resistance to mediator permeation, an hypothesis that was verified by RDE measurements. The charged nature of the PEI membrane appeared to affect several parameters of the laccase-mediator reaction and the effect of pH and mediator charge on this reaction are reported. The immobilization platform under study can be applied to different enzyme-mediator systems than the laccase-PPD used here and is relevant to the development of bioelectrocatalytic systems.     

Bis(glycinium) oxalate: evidence of strong hydrogen bonding

In the title 2:1 salt, 2C₂H₆NO₂⁺·C₂O₄²⁻, the glycine mol­ecule is in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The doubly charged oxalate anion lies across a crystallographic inversion centre. One of the reasons why the 1:1 glycinium oxalate salt has a higher melting point than the title compound may be the difference in their hydrogen‐bonding patterns. A database search for salts formed between amino acids or substituted amino acids and oxalic acid revealed that, in most of the structures, the conformation about the O=C—OH bond is synplanar. d ‐Tryptophan oxalate is the only example where the OH group of a semi‐oxalate adopts an anti­planar conformation. The 2:1 stoichiometry seen in the present salt is observed only in the salts of dl ‐serine, dl ‐aspartic acid and betaine with oxalic acid.     

Radiolysis of aqueous solutions of poly(vinyl alcohol) at 77 K

Paramagnetic products of low-temperature X-ray radiolysis of aqueous poly(vinyl alcohol) solutions (2.5 and 5% by weight) were studied by ESR spectroscopy. Experimental spectra were ascribed to a superposition of signals from hydroxyl radicals and –CH₂?^?C(OH)–CH₂? macroradicals (C_α-macroradicals), respectively. No ESR signals corresponding to trapped electrons were observed that was attributed to the peculiarities of microheterogenous structure of the frozen aqueous polymer solutions. Annealing at 115 K resulted in partial conversion of OH radicals to C_α-macroradicals. It was suggested that main part of hydroxyl radicals was stabilized in phase of polycrystalline ice while macroradicals were formed in “mixed” water–polymer phase. The radiation–chemical yields of paramagnetic species stabilized in the systems under study were determined.     

Anionization of volatile molecules on the surface of electrolytic solutions exposed to high electric fields

The anionization of molecules supplied from the gas phase onto a negatively charged [Cl]^? or [NO₃]^? ion donating surface has been investigated. The charged surface was prepared by exposing an aqueous solution of LiCl (or LiNO₃) and polyethylene oxide to a high external field as is done in negative ion field desorption mass spectrometry. The ionization of some monosaccharides and adenosine by [Cl]^? and [NO₃]^? attachment and of some acids by proton abstraction is reported.     

Products of aqueous vitamin B5 (pantothenic acid) formed by free radical reactions

The radiolysis of aqueous vitamin B5 (pantothenic acid) has been investigated under various experimental conditions. The highest vitamin degradation (G=3.22) was observed in solutions saturated with N₂O, where 90% OH radicals are operating. As final products, the following were established: aldehydes, carboxylic acids and ammonia. Their yield strongly depends on the presence/absence of air as well as on N₂O (used to convert e_aq⁻ into OH) and was determined as a function of absorbed radiation dose. HPLC-analysis showed that in all media, a main product is formed, having the highest yield in aerated solutions.Based on the chemical analysis, it appears that the OH radicals are most involved in the degradation process. A precise sequence of the reaction steps could not be given presently, because of the implication of many simultaneous reactions.     

Determination of inorganic acids by ion chromatography with n-tetradecylphosphocholine (zwitterionic surfactant) as the stationary phase and pure water as the mobile phase

A new ion chromatographic (IC) system, in which n-tetradecylphosphocholine (TDPC, a phosphobetaine type of zwitterionic surfactant) was used as the stationary phase, pure water as the mobile phase, and conductivity as the method of detection, has been developed for the determination of inorganic acids. Five model acids, HCl, HNO₃, HClO₄, H₂SO₄, and H₃PO₄, were separated to baseline and eluted in the order H₃PO₄ > HCl > HNO₃ > H₂SO₄ > HClO₄. When peak areas were plotted against the concentrations of the acids in samples, linear calibration curves were obtained. Ultimate determination limits were approximately 1 mmol L^–1, but the discrimination of the method between solutions of different concentration was better than 10 μmol L^–1 for those model analytes. Salts of divalent cations could also be separated, but they were eluted faster than the acids. No separation was observed for the salts of monovalent cations. This newly proposed approach is applicable to the simultaneous determination of the inorganic acids (produced by reactions of NO_x, SO_x, and HCl with water) in aerosols.     

Partial Molar Volumes of Some of α-Amino Acids in Binary Aqueous Solutions of MgSO4·7H2O at 298.15 K

The apparent molar volume, V ^o _{φ, 2}, of glycine, alanine, α-amino-n-butyric acid, valine and leucine have been determined in aqueous solutions of 0.25, 0.5 and 1.0 mol⋅dm⁻³ magnesium sulfate, and the partial specific volume from density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volume, V ^o _2,m , group contribution of amino acids and partial molar volume of transfer, Δ_tr V _2,m ^o, from water to aqueous magnesium sulfate solutions. The linear correlation of V _2,m ^o for a homologous series of amino acids has been utilized to calculate the contributions of charged end groups (NH₃ ⁺, COO⁻), CH₂ - groups and other alkyl chains of amino acids to V _2,m ^o. The results for Δ_tr V _2,m ^o of amino acids from water to aqueous magnesium sulfate solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic and hydrophobic-hydrophobic group interactions. The values of the standard partial molar volume of transfer for the amino acids with different hydrophobic contents, from water to aqueous MgSO₄ are in general positive, indicating the predominance of the interactions of zwitterionic/hydrophilic groups of amino acids with ions of the salt. The hydration number decreases with increasing concentration of salt. The number of water molecules hydrated to amino acids decreases, further strengthening the predominance of ionic/hydrophilic interactions in this system.     

Simulation of the Raman spectra of zwitterionic glycine + nH2O (n = 1, 2, …, 5) by means of DFT calculations and comparison to the experimentally observed Raman spectra of glycine in aqueous medium

Raman spectra of an aqueous solution of glycine (Gly) have been recorded in the range of 400-2000 cm⁻¹. In aqueous solution, glycine molecules exist in their zwitterionic form, having two opposite charged poles, COO⁻ and NH₃⁺. The zwitterionic structure of glycine (ZGly) is stabilized by the hydrogen bond interaction of water (W) molecules. In the present report, we have optimized the ground state geometries of different hydrogen bonded complexes of [ZGly + (W)_n=1-5] in aqueous medium using DFT calculations at the B3LYP/6-311++G(d) level of theory. A comparative discussion on the structural details and binding energies (BEs) of each conformer has been also done. The theoretical Raman spectra were calculated corresponding to the most stable [ZGly + (W)_n=1-5] conformers. The theoretically simulated Raman spectra of each stable conformer were compared with experimentally observed Raman spectra to explore the number of water molecules needed for stabilizing the structure of ZGly. The theoretically simulated Raman spectra corresponding to the most stable conformer of [ZGly + (W)₅] having a BE of −22.8 kcal/mol, are matching nicely with the experimentally observed Raman spectra. Thus, on the basis of the above observations, we conclude that the conformer, [ZGly + (W)₅] is the most probable conformer in the aqueous medium. We also believe that in the conformer, [ZGly + (W)₅] the five water molecules are arranged around the ZGly in such a way that the effect of steric hindrance is less compared to the other conformers. The dipole-dipole interaction potential (DDP) is also calculated corresponding to the strongest hydrogen bond for each [ZGly + (W)_n=1-5] conformer.     

Solvent extraction of certain rare earth metal ions with 1-(2-pyridylazo)-2-naphthol (PAN)

The solvent extraction of Yb(III) by 1-(2-pyridylazo)-2-naphthol (PAN or HL) in carbon tetrachloride from aqueous—ethanol phase has been investigated as a function of thepH ^X of the polar phase and the concentrations ofPAN or ethanol (EtOH) in the organic phase. It was confirmed that the addition of ethanol to the aqueous phase causes an increase of the Yb(III) distribution coefficient. The equation for the extraction reaction has been suggested as: $$Yb(H_2 O)_{m(^p )}^{3 + } + 3H L_{(o)} + t Et OH_{(o)} \rightleftharpoons Yb L_3 \left( {EtOH} \right)_{t(o)} + 3H_{(^p )}^ + + mH_2 O$$ wheret changes from 0 to 3. The extraction equilibrium constant (K _ex ) and two-phase stability constants (β ₃ ^× ) for the YbL ₃ (EtOH)₃ complex have been evaluated. The formation of solvates YbL ₃ (EtOH) _t is probably the main reason of the synergistic effect which was observed.     

Extraction of triply charged metal cations in aqueous phase-separating system antipyrine–sulfosalicylic acid–water

Extraction of macro amounts of triply charged metal cations (0.01–0.05 mol L^?1) in aqueous phase-separating system antipyrine–sulfosalicylic acid–water containing no organic solvent is studied. Optimum conditions for phase separation are established and the influence of the concentrations of the major components, inorganic acids (H₂SO₄, HCl), salting-out agents, and the volume of the aqueous phase on the process in question is determined. It was found that the optimum antipyrine/sulfosalicylic acid ratio in the system was (1.5–2.0): 1.0. The introduction of inorganic salting-out agents causes the volume of the organic phase (0.8–1.8 mL) to increase to 2 mL and more. The extractability series of triply charged metal ions is as follows: Tl > Fe > Sc > In > Ga. It was shown that inorganic salts and hexamine influence the degree of extraction of metal cations and that inorganic acids and water affect the distribution mechanism and the composition of the complexes. The half-extraction pH values (pH₁/₂) of the cations are calculated and correlations between the pH₁/₂ values, the ionic radii of the cations, and the polarization ability of the metal ions are established.

     

Flow-through sensors for enhancing sensitivity and selectivity of FTIR spectroscopy in aqueous media

The principle of novel flow-through sensor systems with FTIR spectroscopic detection is presented on the example of the determination of organic acids in aqueous solution. The constructed flow-through sensor system is based on trapping of derivatized porous polymer beads in a conventional IR transmission cell and integration of the flow cell into a sequential injection (SI) manifold. By the SI-manifold sample pre-conditioning, sample-sensor interaction and sensor regeneration were performed in an automated and highly reproducible way. The polymer beads used in this study contained anion exchanger groups so that negatively charged molecules such as organic acids present in the anionic form could selectively interact with the polymer beads. Upon pumping a sample through the sensor cell organic acids were retained on the polymer beads whereas non-ionic matrix molecules passed hence allowing to separate the target analytes form the matrix. Apart from that the organic acids were also concentrated onto the polymer beads so that absolute analyte amounts in the low μg range could easily be detected. Linear calibration curves from 0 to 1 mmol l⁻¹ were recorded for acetic and malic acid using a sample volume of 500 μl (s_x0: 0.032 mmol l⁻¹ acetic acid and 0.031 mmol l⁻¹ malic acid). Mixtures of both acids were analyzed as well and it could be shown that by application of multivariate data evaluation procedures (PLS) simultaneous quantification of both acids could be performed successfully using the developed flow-through sensor system.     

New Zwitterionic Spirocyclic λ5Si-Silicates with Two Ethane-1,2-diolato(2–), Oxalato(2–), or Benzene-1,2-diolato(2–) Ligands – Synthesis,Structure, and Dynamic Behavior

The syntheses of the zwitterionic spirocyclic λ⁵Si-silicates 6–9 are described. These chiral zwitterions contain a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom. Compounds 6 · ¹/₂ HO(CH₂)₂OH, 7 , 8 · CH₃CN, and 9 were studied by solution-state (¹H, ¹³C, ²⁹Si) and solid-state (²⁹Si CP/MAS) NMR experiments. In addition, all compounds were structurally characterized by single-crystal X-ray diffraction. The dynamic behavior (Berry-type enantiomerization) of 7–9 in solution was studied by VT ¹H NMR experiments. These experimental studies were completed by ab initio investigations of the related anionic model species 10–12 .     

Equilibria in aqueous solution between Be(II) and iminodiacetic,N-methyliminodiacetic,N-ethyliminodiacetic and N-propyliminodiacetic acids

The complex species formed in aqueous solution between Be(II) and iminodiacetic, N-methyliminodiacetic, N-ethyliminodiacetic and N -propyliminodiacetic acids were studied at 25°C and ionic strength 0.5 M in Na ClO₄. The application of the least-squares computer program LETAGROP to the experimental potentiometric data, taking into account hydrolysis of the Be(II) ion, indicates that, upon varying the ligand-metal relationship, only the monohydroxide complex [Be(OH)C]⁻ (H₂C ligand) is formed in significant amounts for the four systems studied. The formation constants β_pr (11, − 11 and −21) of the protonated species of the ligands, β_pq(− 12 and − 33) of the hydrolytic species of Be(II), and β_pqr(− 311) of the complex [Be(OH)C]⁻ were determined.