Detection of highly oriented aggregation of L-glutamic acid-derived lipids in dilute organic solution

Aggregation structures in organic gels and xerogels formed from L-glutamic acid-derived lipids were investigated by scanning and transmission electron microscopies, X-ray analyses, and 1H NMR and IR spectroscopic methods. These analyses showed that the gels were produced through the formation of highly oriented aggregates based on a single layer and a remarkable development of their fibrous morphology. We also describe how the critical aggregation concentration can be observed at a concentration below the critical gel concentration by using a dye-complexation method with a cyanine dye, NK-77.     

The aggregation behavior of O-carboxymethylchitosan in dilute aqueous solution

O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.     

Functional organic gels. Enantioselective elution using chiral gels from amino acid-derived lipids

The L-glutamic acid-derived lipids form organic gels in benzene, which show enantioselective elution of N-dansyl L-phenylalanine from organic gels to aqueous phases. Differential scanning calorimetry and circular dichroism measurements demonstrate that this enantioselectivity occurred through highly-oriented structures of aggregated lipids like those of aqueous lipid membrane systems.     

A highly oriented cubic phase formed by lipids under shear

We demonstrate the formation of a macroscopically oriented inverse bicontinuous cubic (Q(II)) lipid phase from a sponge (L(3)) phase by controlled hydration during shear flow. The L(3) phase was the monoolein/butanediol/water system; the addition of water reduces the butanediol concentration, inducing the formation of a diamond (Q(II)(D)) cubic phase, which is oriented by the shear flow. The phenomenon was reproduced in both capillary and Couette geometries, indicating that this represents a robust general route for the production of highly aligned bulk Q(II) samples, with applications in nanomaterial templating and protein research.     

Fluorescence study for the electrostatic interaction and aggregation in dilute polar solution of polyelectrolytes

Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethylacryl-amide (DMAA) were observed in dilute salt-free aqueous solutions as a function of the mole fraction F_AMPS of AMPS from 0 to 0.896. Monoexponential and biexponential decays were found for the samples of F_AMPS < 0.35 and samples of FAMPS > 0.35, respectively. The fast decay component is 80% and the averaged lifetime <τ> and lifetime τ₁ of the fast decay decreased with increasing F_AMPS. Quenching efficiency of Cu²⁺, CH₃NO₂, and dinitrobenzene to the pyrene label was investigated in the framework of Stern-Volmer plot. The quenching effects of Cu²⁺ included both of dynamic and static ones, the latter was due to the condensed Cu²⁺. For the neutral quenchers, the quenching rate constant k_q increased when F_AMPS < 0.449 then decreased, showing a decline of accessibility to the pyrene label. I₁/I₃ value in salt-free dilute aqueous solution and in DMSO solution decreased obviously with an increase in F_AMPS, indicating that the labeled fluorophore experienced a decrease in polarity of its microenvironment with increasing charge density of the polymer. This I₁/I₃ decrease was enhanced with increasing the polymer concentration and adding salt NaCl up to 0.75 mol/L showed no effect on the appearance of this decrease. These results were interpreted consistently with the counterion condensation concept, where condensed counterions induced the “temporal” aggregation of less-polar in the polyelectrolyte solutions surrounding the pyrene labels.     

Investigation on critical aggregation concentration of carbosiloxane dendrimer in dilute solution probed by rhodamine B

We propose a novel method for probing aggregation of dendrimers by investigating the isomerization equilibrium between pink zwitterionic form (Z-form) and colorless lactonic form (L-form) of rhodamine B (RhB) molecules in dilute solution. Investigation using carbosiloxane dendrimers (CSiO-D) with different generations as the model dendrimer molecules showed that the equilibrium constant of isomerization of RhB increased dramatically at the critical aggregation concentration (CAC) of dendrimers. The redox potential differences between isomers of RhB indicated that aggregation of CSiO-D accelerated the isomerization of RhB and stabilized the L-form of RhB. The data on Gibbs energy and electrolytic conductivity provided further evidence for confirming the CAC of dendrimers in dilute solution and showed good agreement with our other experimental results. The proposed method is effective in estimating the CAC of dendrimers in dilute solution.     

Dynamic viscosity of dilute solutions of poly(L-glutamic acid)

The dynamic viscosity η′ of a dilute solution of poly(L-glutamic acid) (DP = 1370) in a mixed solvent made up of aqueous 0.2M NaCl and dioxane (2:1 by volume) is measured over the pH range 4.2–10 and in the frequency range 2–500 kHz. The frequency dependence of η′ in the helix region (low pH) is interpreted in terms of a model molecule consisting of n rigid helical segments connected by universal joints. The steady-flow viscosity, relaxation time, and high-frequency limiting viscosity at pH 4.75 (helical content 80%) are well explained by this model with n = 5. This value of n is consistent with that estimated from the nucleation parameter σ = 1.4 × 10^?3 obtained from the relation between reduced steady-flow viscosity and helical content. The high-frequency values of η′ in the coil region (high pH) are fitted by Peterlin's theory. The internal viscosity seems to arise in part from the polyelectrolytic character of the molecule. An additional relaxation at low frequencies in the coil region is ascribed to rotation of molecules elongated by the electrostatic interaction. The lower value of reduced steady-flow viscosity in the coil region in the mixed solvent compared with that in water is interpreted in terms of the lower degree of effective ionization and the selective solvation of water by the polypeptide. No anomaly is observed in the helix–coil transition region, indicating that the relaxation time for helix–coil equilibrium is less than 10^?6sec.     

Lattice expansion of highly oriented 2D phthalocyanine covalent organic framework films

Expanding into application: covalent organic framework (COF) films are ideally suited for vertical charge transport and serve as precursors of ordered heterojunctions. Their pores, however, were previously too small to accommodate continuous networks of complementary electron acceptors. Four phthalocyanine COFs with increased pore size well into the mesoporous regime are now described.     

Group contributions to the thermodynamic properties of non-ionic organic solutes in dilute aqueous solution

The thermodynamic properties G _h ^o,H _h ^o, and C _p,h ^oassociated with the transfer of non-ionic organic compounds from gas to dilute aqueous solution and the limiting partial molar properties C _p ^o ,2 and V₂ ² of these compounds in water are described through a simple scheme of group contributions. A distinction is made between groups made only of carbon and hydrogen, and functional groups i.e. groups containing at least one atom different from carbon and hydrogen. Each group is assigned a contribution, for each property, through a least squares procedure which utilizes only molecules containing at most one functional group. Finally, for compounds containing more than one functional group, correction parameters are evaluated as the differences between the experimental values and those calculated by means of the group contributions. The different behavior of hydrophilic compared with hydrophobic groups is discussed for the various properties. A rationale for the correction parameters, i.e. for the effects of the interactions among hydrophilic groups on the thermodynamic properties, is attempted.     

Evidence of aggregation in dilute solution of amphoteric poly(amido-amine)s by size exclusion chromatography

Evidence of aggregation of amphoteric linear poly(amido-amine)s (PAAs) was proved using a multi-angle laser light scattering detector on-line to a size exclusion chromatography (SEC) system. As a rule the PAAs chemical structure, with the presence of charged groups that are both anionic and cationic, easily generates aggregation and non-steric fractionation. A non-amphoteric, non-aggregate PAAs polymer with an elution pattern close to ideal SEC was also obtained and characterized for comparison. The influence of PAAs synthesis conditions on the extent of aggregation was also studied.     

Detection of novel gaseous states at the highly oriented pyrolytic graphite-water interface

We report a novel form of the gaseous state at the interface of water and highly oriented pyrolytic graphite (HOPG) that is induced by local supersaturation of gas. Such local supersaturation of gas next to the HOPG substrate can be achieved by (1) displacing an organic liquid with a gentle flow of water, (2) displacing cold water (approximately 0 degrees C) with a gentle flow of warm water (approximately 40 degrees C), or (3) preheating the HOPG substrate to approximately 80 degrees C before exposing it to water at room temperature. In addition to the spherical-cap-shaped nanobubbles reported by many researchers, flat (quasi-two-dimensional, pancake-like) gas layers and nanobubble-flat gas layer composites (spherical-cap-shaped nanobubbles sitting on top of the quasi-two-dimensional gas layers) were detected. These entities disappeared after the system was subjected to a moderate level of degassing (approximately 0.1 atm for 1.5 h), and they did not form when the liquids involved in the aforementioned displacing procedure (to induce local supersaturation of gas) had been predegassed (to approximately 0.1 atm). The stability and some physical properties of these newly found gaseous states are examined.     

Study of controllable aggregation morphology of ABA amphiphilic triblock copolymer in dilute solution by changing the solvent property

We have studied, both experimentally and theoretically, the aggregation morphology of the ABA amphiphilic triblock copolymer in dilute solution by changing the solvent property. Experimental results showed that the micellar morphology changed from spheres to rods and then to vesicles by changing the common solvent from N-N-dimethylformamide (DMF) to dioxane and then to tetrahydrofuran (THF). These controllable aggregates were also obtained by Monte Carlo simulation. The simulative results showed that the solvent property is a key factor that determines the copolymer aggregation morphology. The morphology changed from spheres to rods and then to vesicles by increasing the solvent solubility, corresponding to the change of stretched of the copolymer chains in the micellar cores. This result is in good agreement with the experimental one. Moreover, the simulative results revealed that the end-to-end distant of the ABA triblock copolymer in the vesicle was larger than that in the spheres and rods, indicating that the copolymer chains were more stretched in vesicles than in the spheres and rods. Furthermore, we gave the distribution of the fraction of the chain number with the end-to-end distance. The results indicated that the amount of folded chains is almost the same as that of stretched chains in the vesicle. Although most chains were folded, stretched chains could be found in the rod and sphere micelles.     

Structural studies on the hydration of L-glutamic acid in solution

A combination of neutron diffraction augmented with isotopic substitution and computer modeling using empirical potential structure refinement has been used to extract detailed structural information for L-glutamic acid dissolved in 2 M NaOH solution. This work shows that the tetrahedral hydrogen bonding network in water is severely disrupted by the addition of glutamic acid and NaOH, with the number of water-water hydrogen bonds being reduced from 1.8 bonds per water molecule in pure water to 1.4 bonds per water molecule in the present solution. In the glutamic acid molecule, each carboxylate oxygen atom forms an average of three hydrogen bonds with the surrounding water solvent with one of these hydrogens being shared between the two oxygen atoms on each carboxylate group, while each amine hydrogen forms a single hydrogen bond with the surrounding water solvent. Additionally, the average conformation of the glutamic acid molecules in these solutions is extracted.     

Birefringence of highly oriented fibers

A spectrophotometric method was developed for measuring the birefringence of highly oriented synthetic fibers. This method surmounts the low birefringence limit of the standard quartz compensator method and the difficulties in interpretation of the photographic fringe method. A highly oriented aramid fiber gave birefringence values of 0.60–0.75 by this method, compared with 0.25 for polyester and 0.06 for nylon by other conventional methods. The operating principles and excellent results of this new method provide a basis for the extension of routine birefringence characterization to highly oriented fibers.     

Self-hardening of highly oriented polyethylene

Ultra-oriented polyethylene fibers obtained by drawing to approximately 30 times their original length have a Young's modulus of approximately 800 kbar. Such fibers, if unconstrained, contract on heating to a length near the original. We have studied the forces causing this contractile behavior by monitoring the stress in the fiber while maintaining it at constant length. In the course of this we observed a complex sequence of both reversible and irreversible behavior. In the reversible case we observed first energy and then entropy elastic behavior. The most significant feature observed is that at sufficiently high temperature the fiber stress relaxes to an unmeasurably low value. A fiber allowed to relax in this way possesses a much lower room temperature tensile modulus (ca. 80 kbar) immediately after relaxation but, remarkably, this modulus increases to approach the initial high value over a period of a few hours when the fiber is stored either clamped or unclamped at room temperature. High x-ray orientation is preserved throughout the storage period but the density which dropped during the stress decay rose again in the course of the spontaneous stiffening. None of the stress relaxed fibers displays large-scale contractile behavior on subsequent heating. A phenomenological composite model is proposed which involves stiff microfibrils of short length—surrounded by a matrix present as a minority component. The softening of this matrix on heating and its subsequent stiffening on storage, involving a certain amount of melting and recrystallization, respectively, could then be responsible for the observed variations in the macroscopic tensile properties using simple fiber composite theories. The fibers are likely to be of extended-chain type produced by the initial drawing while the matrix may consist of a combination of oriented amorphous material (tie chains), randomly oriented chains, and transverse lamellar overgrowth present in varying proportions in the different stages of sample treatment. The wider implications, fundamental and practical, of this remarkable self-hardening process are indicated.     

Electrophoresis of a highly charged fluid droplet in dilute electrolyte solutions: Analytical Hückel-type solution

An analytical formula is presented here for the electrophoresis of a dielectric or perfectly conducting fluid droplet with arbitrary surface potentials suspended in a very dilute electrolyte solution. In other words, when the Debye length (κ⁻¹) is very large, or κa$\ll$1, where κ is the electrolyte strength and a stands for the droplet radius. This formula can be regarded as an extension of the famous Hückel solution valid for weakly charged rigid particles to arbitrarily charged fluid droplets. The formula reduces successfully to the ones obtained by Booth for a dielectric droplet, and Ohshima for a perfectly conducting droplet, both under Debye–Hückel approximation valid for weakly charged droplets. Moreover, the formula is valid for a gas bubble and a rigid solid particle as well. Classic results obtained by Hückel for a rigid particle are reproduced as well. We found that for a dielectric droplet, the more viscous the droplet is, the faster it moves regardless of its surface potential, contrary to the intuition based on the purely hydrodynamic consideration. For a perfectly conducting liquid droplet, on the other hand, the situation is reversed: The less viscous the droplet is, the faster it moves. The presence or absence of the spinning electric driving force tangent to the droplet surface is found to be responsible for it. As a result, an axisymmetric exterior vortex flow surrounding the droplet is always present for a dielectric liquid droplet, and never there for a conducting liquid droplet.     

Radiolysis of paracetamol in dilute aqueous solution

Using radiolytic experiments hydroxyl radical (main reactant in advanced oxidation processes) was shown to effectively destroy paracetamol molecules. The basic reaction is attachment to the ring. The hydroxy-cyclohexadienyl radical produced in the further reactions may transform to hydroxylated paracetamol derivatives or to quinone type molecules and acetamide. The initial efficiency of aromatic ring destruction in the absence of dissolved O₂ is c.a. 10%. The efficiency is 2–3 times higher in the presence of O₂ due to its reaction with intermediate hydroxy-cyclohexadienyl radical and the subsequent ring destruction reactions through peroxi radical. Upon irradiation the toxicity of solutions at low doses increases with the dose and then at higher doses it decreases. This is due to formation of compounds with higher toxicity than paracetamol (e.g. acetamide, hidroquinone). These products, however, are highly sensitive to irradiation and degrade easily.     

Behaviour of cellulose tricarbanilate in dilute solution

Cotton linters were subjected to acid hydrolysis for various times and the products fully substituted to yield cellulose tricarbanilate samples ($\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{= 0·21 × 10}{}^6\text{to 1·1 × 10}{}^6$). Intrinsic viscosities were measured in dioxan and methyl ethyl ketone over a range of temperature. and also under θ-conditions. Mark-Houwink constants were found to be temperature dependent. Unperturbed dimensions and their temperature coefficient were derived by a number of procedures. The Flory-Huggins interaction parameter _%1 increased with temperature, thus indicating negative entropies and enthalpies of dilution. The results show that the environment is well displaced from the normal θ-state and is closer to the lower critical solution temperature, which was determined from cloud point measurements to be about 234° in dioxan.     

New insights in the removal of diluted volatile organic compounds from dilute aqueous solution by pervaporation process

The present work aimed the mass transfer investigation in the removal of organic contaminants from water by the pervaporation process. The terpolymer ethene-propene-diene (EPDM) was used as the selective elastomer. Two classes of model organic solutes were chosen: chlorinated hydrocarbons (trichloroethylene, dichloromethane and trichloromethane) and aromatic ones (toluene, phenol and aniline). Pervaporation tests were carried out using dense and composite membranes with different thickness, solute concentrations and feed flow velocities at room temperature. The liquid boundary layer resistance (i.e., concentration polarization phenomenon) was observed for all solutes. The resistance-in-series model was used to determine liquid and polymer phase resistances. The results obtained indicate that the model would be better written considering the chemical potential gradient as driving force, in order to take into account affinity between water and the organic solutes, as well as their interactions with the polymer selective layer. The rational activity coefficients of the solutes in the polymer phase were determined by inverse gas chromatography (IGC) and related to the mass transfer coefficient in the polymer phase.