Hydrophobic Dodecyl Research Articles

Hyperbranched Polymers via RAFT Copolymerization of an Acryloyl Trithiocarbonate

Hyperbranched copolymers of N-isopropylacrylamide (NIPAM) and styrene were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of a novel acryloyl trithiocarbonate, namely 1-[3-(2-methyl-2-dodecylsulfanylthiocarbonylsulfanylpropionyloxy)propyl]-1H-[1,2,3]triazol-4-ylmethyl acrylate. By employing an example of ‘click chemistry’, we were able to prepare the vinyl RAFT chain transfer agent (CTA) by copper-catalyzed 1,3-dipolar cycloaddition of an azido-functionalized trithiocarbonate and propargyl acrylate. The resulting CTA facilitated the preparation of highly branched poly(N-isopropylacrylamide) (PNIPAM) and polystyrene. Interestingly, the branched PNIPAM demonstrated a reduced lower critical solution temperature (LCST) of 25°C as opposed to the conventional value of 32°C expected for linear PNIPAM, an effect attributed to increased contribution of hydrophobic dodecyl trithiocarbonate end groups.

Surface properties and enzymatic degradation of end-capped poly( l-lactide)

Surface properties and enzymatic degradation of poly( l-lactide) (PLLA) end-capped with hydrophobic dodecyl and dodecanoyl groups were investigated by means of advancing contact angle ( θ a) measurement, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The θ a values of end-capped PLLA films were larger than those of non-end-capped PLLA films, suggesting that the hydrophobic dodecyl and dodecanoyl groups were segregated on the film surface. The weight changes of end-capped PLLA thin films during enzymatic degradation in the presence of proteinase K were monitored by using a QCM technique. The relatively fast weight loss of PLLA film occurred during first few hours of degradation, followed by a decrease in the erosion rate. The erosion rate of PLLA films at the initial stage of degradation was dependent on the chain-end structure of PLLA molecules, and the value decreased with an increase in the amount of hydrophobic functional groups. The surface morphologies of PLLA thin films before and after degradation were characterized by AFM. After the enzymatic degradation, the surface of non-end-capped PLLA films was blemished homogeneously. In contrast, the end-capped PLLA thin films were degraded heterogeneously by the enzyme, and many hollows were formed on the film surface. From these results, it has been concluded that the introduction of hydrophobic functional groups at the chain-ends of PLLA molecules depressed the erosion rate at the initial stage of enzymatic degradation.

Thermally Cleavable Surfactants Based on Furan−Maleimide Diels−Alder Adducts

Two new surfactant molecules are reported that contain thermally labile Diels-Alder adducts connecting the hydrophilic and hydrophobic sections of each molecule. The two surfactants possess identical hydrophobic dodecyl tail segments but have phenol and carboxylic acid hydrophilic headgroups, respectively. Deprotonation with potassium hydroxide affords the formation of water-soluble surfactants. Room temperature aqueous solutions of both surfactants exhibit classical surface-active agent behavior similar to common analagous alkylaryl surfactant molecules. Critical micelle concentrations have been determined for each surfactant through dynamic surface tension and dye solubilization techniques. Small-angle neutron scattering measurements of the aqueous surfactant solutions indicate the presence of spherical micelles with radii of 16.5 angstroms for the carboxylate and 18.8 angstroms for the phenolate. When these surfactants are exposed to elevated temperatures (>50 degrees C), the retro Diels-Alder reaction occurs, yielding hydrophilic and hydrophobic fragments. Aqueous solutions of each surfactant subsequently exhibit a loss of all surface-active behavior and the micellar aggregates are no longer detectable.

New micrometer-sized monodispersed self-assembled amphiphilic polystyrene/poly( n-butyl methacrylate) composite particles of hemispherical morphology: synthesis and characterization

Uniform micron-sized polystyrene template particles surface grafted with polyvinylpyrrolidone were prepared by dispersion polymerization of styrene in alcoholic solvents in the presence of polyvinylpyrrolidone as stabilizer. Poly(acrylic acid, sodium salt) derivatized polystyrene/ poly( n-butyl methacrylate) micron-sized composite particles of hemispherical morphology and narrow size distribution were formed by a single-step swelling of the uniform polystyrene template microspheres dispersed in water with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide. n-Butyl methacrylate was then polymerized at 73 °C within the template microspheres in the presence of the water-soluble monomer acrylic acid, sodium salt. The sodium ions of the poly(acrylic acid) derivatized composite particles were then replaced with dodecylammonium ions by interacting these composite particles with excess dodecylamine hydrochloride. As a result of this process the surface of the hemispherical composite particles composed of hydrophilic polyvinylpyrrolidone chains on the polystyrene phase and hydrophobic dodecyl groups on the poly(acrylic acid) derivatized poly( n-butyl methacrylate) phase. These newly formed micron-sized composite particles show amphiphilic characteristics and aggregate to form micelle-like spherical clusters. The ability to control the template polystyrene microspheres’ dimensions and various polymerization parameters may open a wide variety of self-assembled spherical and other structures composed of micron-sized particles for various fundamental and practical applications such as self-assembly processes and the formation of photonic bandgap crystals.

Antioxidant activity of dodecyl gallate.

Dodecyl (C12) gallate exhibits both potent chain-breaking and preventive antioxidant activity. The pyrogallol moiety is responsible for both activities. Dodecyl (lauryl) gallate prevents generation of superoxide radicals by xanthine oxidase, and this activity comes from its ability to inhibit the enzyme. The inhibition kinetics analyzed by Lineweaver-Burk plots found that dodecylgallate is a noncompetitive inhibitor for the generation of superoxide anion. Dodecyl gallate also inhibits formation of uric acid. The inhibition kinetics analyzed by Lineweaver-Burk plots found that dodecyl gallate is a competitive inhibitor for this oxidation. Mitochondrial lipid peroxidation induced by Fe(III)-adenosine 5'-diphosphate/reduced nicotinamide adenine dinucleotide was inhibited by dodecyl gallate while its parent compound, gallic acid, did not show this inhibitory activity. Dodecyl gallate protected mitochondrial functions and human red blood cells against oxidative stresses, but gallic acid showed little effect. The hydrophobic dodecyl group is largely associated with the preventive antioxidative activity.

Hydrophobic Alkyl Chains−Pectin Conjugates. Comparative Study of Some Physicochemical Properties in Relation to Covalent Coupling vs Ionic Association

Various amphiphilic conjugates in which pectin (a polyanionic polysaccharide) is associated with hydrophobic dodecyl chains were prepared. The syntheses were carried out according to two different pathways, one affording covalent immobilization via ester bond formation, the other where a long chain alkylamine (dodecylamine) is reacted with the polysaccharide carboxyl groups, to yield the corresponding dodecylammonium salts. The present article focus on the comparative study of some physicochemical properties of these C12 derivatives. Surface tension measurements on dilute solutions evidenced opposite behaviors of the two types of conjugates. Rheological properties in the semidilute regime were also investigated, and the similarities and differences observed are tentatively interpreted in connection with the mode of association, covalent vs ionic, of the hydrophobic dodecyl chains on the polysaccharide.

Self-Assembled Supramolecular Structures of Charged Polymers at the Graphite/Liquid Interface

The self-assembly of two anionic polymers on graphite was studied in situ using an atomic force microscope (AFM). One polymer (P4-Na) had a hydrophobic phenylene backbone with hydrophilic sulfonate groups and hydrophobic dodecyl side chains. The other (diblock-P-Na) was a diblock copolymer: one block had the same structure as P4-Na and the other block had anthracene groups on the phenylene backbones. AFM revealed regular supramolecular “ribbon” structures of P4-Na and of diblock-P-Na on graphite in a mixed solvent of water and tetrahydrofuran (THF). The polymers adsorbed in two layers. The first layer adsorbed quickly, and was composed of features two molecules wide and several to hundreds of molecules long, which were arranged in domains. The second layer adsorbed more slowly and was composed of ribbon structures with a similar substructure to the first layer. The diblock-P-Na ribbons were much longer than the P4-Na ribbons. Solvent properties had a strong effect on the supramolecular structures of the two polymers.

Viscosity- and Inertia-Limited Rupture of Dextran-Supported Black Lipid Membranes

We study the rupture of polymer-supported black lipid membranes (BLMs). The irreversible rupture of membranes is triggered by application of short transmembrane voltage pulses. The rapid membrane discharge during rupture permits the evaluation of the kinetics of defect widening. The linear increase of the membrane conductance in time during the rupture process indicates that the widening is determined by the inertia of the BLMs. Defects in polymer-free BLMs increase in size with about 20 cm/s. To decrease the rupture velocity of the membranes we attach high-molecular-weight dextran derivatives via hydrophobic dodecyl anchor groups to the BLMs. The density of the hydrophobic anchor groups along the polymer chains is found to be of considerable influence: While dextran with a low anchor-group density slows down the inertia-driven rupture process of BLMs, dextran with higher anchor-group density alters the kinetics and causes an exponential increase of the membrane conductance, suggesting a viscosity-determined rupture process. Dextran derivatives of medium anchor-group density show a transition from a viscosity- to an inertia-limited rupture.

The origin of kinetic cooperativity in prebiotic catalysts.

A polyallylamine carrying long hydrophobic dodecyl groups and adenine residues as side chains (PALAD C12) may be able to catalyze the hydrolysis of N-carbobenzoxy-l-alanine p-nitrophenyl ester (N-Cbz-Ala) as well as p-nitrophenyl acetate (pNPA). The progress curve of hydrolysis of the former displays a long lag and apparently no steady state. After this transient the rate falls off due to the accumulation of the products. Conversely, the hydrolysis of p-nitrophenyl acetate displays classical burst kinetics followed by a slow decline of the reaction rate.Theoretical considerations show that a steady state may be expected to occur only if the concentration of the free catalyst is very small during the reaction. This condition is sufficient to allow the rate of disappearance of the substrate to be equal to the rate of appearance of the products, which is precisely a condition for the existence of a steady state. If the catalyst is poorly active and has a loose affinity for its substrate and product, the measurement of a significant reaction rate will require a much larger concentration of the catalyst. Therefore, under these conditions, one cannot expect a steady state to occur. The mathematical expression of the error made in the steady-state assumption has been derived. This error increases with the catalyst concentration and decreases if the affinity of the substrate for the catalyst is high. Therefore the lack of steady state is associated with the affinity (or the dissociation) of the substrate and the product for the catalyst. When this affinity is low, the free concentration of the catalyst during the reaction is high and one cannot expect a steady state to occur. This is precisely what takes place with N-Cbz-Ala.A mathematical expression of the rate of hydrolysis of N-Cbz-Ala and of any reactant that displays this type of kinetics may be derived at the end of the transient when the rate is close to its maximum value. Under these conditions the rate cannot follow classical Michaelis-Menten kinetics and displays positive cooperativity. It may therefore be speculated that primordial template-like catalysts that were displaying a poor affinity for their substrates and products were already exhibiting apparent positive cooperativity in the kinetic reactions they were able to catalyze.

Synthesis and catalytic activity of adenine containing polyamines

AbstractN6‐Ribosyladenine has been obtained as a major product in the condensation of adenine and ribose under presumably prebiotic conditions. This abnormal nucleoside exhibits a pronounced catalytic activity as compared to histidine, in the hydrolysis of p‐nitrophenyl acetate. The N6‐substituted adenine ring could be considered as a substitute for the imidazole moiety, which could have played a catalytic role in primitive enzymes. To study in more details the catalytic properties of such a group when placed in a favourable microenvironment, it was linked to poly(allylamine). The presence of one adenine ring in ten residues accelerated the p‐nitrophenyl butyrate hydrolysis at pH 8. The rate was increased two‐fold compared to the starting polymer and 100‐fold compared to free adenine. A remarkable, more than 400‐fold acceleration compared to free adenine was measured when long hydrophobic dodecyl side chains were attached as substrate binding sites on the polyamine containing adenine rings. Under mild basic conditions, the catalytic activity of the polymers in the hydrolysis of p‐nitrophenyl esters strongly increases with pH. A cooperative effect between the unprotonated aliphatic amino groups and adenine rings in proton transfers could explain these results. The imidazole ring of N6‐substituted adenine derivatives could act in catalysis with water as a proton‐relay system through a tautomeric equilibrium as the imidazole residue in actual enzymes.

Thermodynamic quantities of adsorption of polyethylene glycol dodecyl ethers to the saturated adsorption surfaces

The equilibrium surface tension of aqueous solutions of C 12 H 25 (OC 2 H 4 ) n OH (n = 2, 3, 4, and 5) was measured with the Wilhelmy plate method. The measurements were carried out at 298 K, 303 K and 308 K for solutions of several different concentrations in the saturated adsorption region. The partial molar area of the surfactant, and the standard chemical potential, entropy and enthalpy of adsorption were estimated. From these thermodynamic data, a model of molecular state in saturated adsorption surface is deduced: this includes the vortical orientation of the hydrophobic dodecyl group, a molecular arrangement similar to that in the solid crystal, and helical conformation of the hydrophilic polyoxyothyiene chains. [1]