Density Of Carboxyl Groups Research Articles

Carboxyethylester-polyrotaxanes as a new calcium chelating polymer: synthesis, calcium binding and mechanism of trypsin inhibition.

A carboxyethylester-polyrotaxane was synthesized as a novel calcium chelating polymer in the field of oral drug delivery and characterized in terms of mechanism of trypsin inhibition. Here, carboxyethylester (CEE) groups are introduced to all the primary hydroxyl groups in alpha-cyclodextrins (alpha-CDs), which are threaded onto a poly(ethylene glycol) chain capped with bulky end-groups (polyrotaxane). The solubility of the CEE-polyrotaxane in physiological conditions increased with pH, indicating ionization-related solubility similar to conventional polyacrylates. The ability of calcium (Ca2+) chelation was found to increase in the order of poly(acrylic acid) (PAA)>CEE-polyrotaxanez.Gt;CEE-alpha-CD, suggesting that the increased density of carboxyl groups enhances the Ca2+ chelating ability. The activity of trypsin was inhibited by these compounds in the same order of the calcium chelation. However, the inhibitory effect of CEE-polyrotaxane was reduced by adding excess Ca2+ without precipitation that was observed in the presence of PAA. Such the reduced inhibition and precipitation by CEE-alpha-CD was not observed. Therefore, the inhibitory effect of CEE-polyrotaxane is due to Ca2+ chelation from trypsin without non-specific interaction.

Physicochemical Properties of Polysaccharide Coatings Based on Grafted Multilayer Assemblies

Carboxymethyldextrans of different charge densities have been attached to flat silicon wafer surfaces using plasma polymer interlayers in conjunction with two different chemical grafting strategies. The resultant coatings have been analyzed by XPS, to verify the surface coverage of the coatings and to estimate their dry thicknesses. Electrokinetic streaming potential measurement has been used to ascertain the electrostatic properties of the coatings, and atomic force microscope colloid probe force measurements have been used to provide insights into the extension of the polysaccharide chains from the interface in aqueous environments. The results demonstrate that polysaccharide layer thickness in solution is maximized when a secondary, amine-rich polyelectrolyte interlayer is introduced onto the plasma polymer surface prior to polysaccharide attachment. An increased carboxyl density in the polysaccharide has also been shown to give rise to thicker polymer layers in solution, with the electrokinetic proper...

Surface Modification and Blood Compatibility of Polyacrylonitrile Membrane with Immobilized Chitosan–Heparin Conjugate

Polyacrylonitrile (PAN) membranes were hydrolyzed with sodium hydroxide to introduce carboxyl groups, and then grafted with chitooligosaccharides (COS), followed by the immobilization of heparin (HEP). The properties of heparin and chitosan-immobilized PAN membranes were characterized with infrared spectroscopy. The surface densities of carboxyl groups, COS, and HEP on the PAN membranes were determined by the uptake of dye. Blood compatibility was evaluated by the activated partial thromboplastin time (APTT). The protein affinity was determined by human plasma total protein. The results showed that the amount of immobilization of COS and HEP increased with the density of carboxyl groups. The heparinized PAN membrane showed longer APTT and decreasing adsorption of plasma proteins. Less than 10% of heparin was released within 24 h, thus demonstrating the stability of the heparinization. These results demonstrated that the blood compatibility of PAN membranes could be improved by the immobilization of chitosan–heparin conjugate. The results obtained in this study will be helpful for the development of modified PAN for clinical applications.

A High Functionality Crosslinked Resin from 3,5-Diacryloyloxybenzoic Acid and Studies of Its De-Crosslinking

The diacrylate of 3,5-dihydroxybenzoic acid was readily prepared under standard interfacial Schotten-Baumann conditions. This novel crosslinker is rather unique as it contains a carboxylic acid functionality in addition to the two polymerizable acrylate groups. The free-radical polymerization of this monomer resulted in a highly crosslinked polymer, possessing a very high density of carboxylic acid groups. These acid groups impart a high level of hydrophilicity to the matrix, especially in alkaline medium. An interesting feature of this crosslinked matrix is the facile hydrolytic de-crosslinking that occurs when it is subjected to aqueous alkali, although it is very stable under neutral and acidic conditions. The kinetics of this de-crosslinking was readily studied by following the concentration of the degradation products using UV-Visible spectroscopy. NMR investigations confirm that the de-crosslinking process is indeed hydrolytic, and that it leads to the formation of poly(acrylic acid) and 3,5-dihydroxybenzoic acid. In an effort to understand the role of the carboxylic acid groups in the degradation process, other structurally similar crosslinkers that are devoid of the acid groups, namely methyl 3,5-diacryloyloxybenzoate, 3,5-diacryloyloxyacetophenone, and 1,3-diacryloyloxybenzene, were synthesized, and the degradation of the corresponding crosslinked polymers was investigated. It is apparent from these studies that the acid-containing polymer matrix degraded at significantly faster rates when compared to the other crosslinked systems suggesting the occurrence of a reactive diffusion controlled rate enhancement.

A High Functionality Crosslinked Resin from 3,5-Diacryloyloxybenzoic Acid and Studies of Its De-Crosslinking

The diacrylate of 3,5-dihydroxybenzoic acid was readily prepared under standard interfacial Schotten-Baumann conditions. This novel crosslinker is rather unique as it contains a carboxylic acid functionality in addition to the two polymerizable acrylate groups. The free-radical polymerization of this monomer resulted in a highly crosslinked polymer, possessing a very high density of carboxylic acid groups. These acid groups impart a high level of hydrophilicity to the matrix, especially in alkaline medium. An interesting feature of this crosslinked matrix is the facile hydrolytic de-crosslinking that occurs when it is subjected to aqueous alkali, although it is very stable under neutral and acidic conditions. The kinetics of this de-crosslinking was readily studied by following the concentration of the degradation products using UV-Visible spectroscopy. NMR investigations confirm that the de-crosslinking process is indeed hydrolytic, and that it leads to the formation of poly(acrylic acid) and 3,5-dihydroxybenzoic acid. In an effort to understand the role of the carboxylic acid groups in the degradation process, other structurally similar crosslinkers that are devoid of the acid groups, namely methyl 3,5-diacryloyloxybenzoate, 3,5-diacryloyloxyacetophenone, and 1,3-diacryloyloxybenzene, were synthesized, and the degradation of the corresponding crosslinked polymers was investigated. It is apparent from these studies that the acid-containing polymer matrix degraded at significantly faster rates when compared to the other crosslinked systems suggesting the occurrence of a reactive diffusion controlled rate enhancement.

Binding and Selectivity in L-Type Calcium Channels:A Mean Spherical Approximation

L-type calcium channels are Ca 2+ binding proteins of great biological importance. They generate an essential intracellular signal of living cells by allowing Ca 2+ ions to move across the lipid membrane into the cell, thereby selecting an ion that is in low extracellular abundance. Their mechanism of selection involves four carboxylate groups, containing eight oxygen ions, that belong to the side chains of the “EEEE” locus of the channel protein, a setting similar to that found in many Ca 2+-chelating molecules. This study examines the hypothesis that selectivity in this locus is determined by mutual electrostatic screening and volume exclusion between ions and carboxylate oxygens of finite diameters. In this model, the eight half-charged oxygens of the tethered carboxylate groups of the protein are confined to a subvolume of the pore (the “filter”), but interact spontaneously with their mobile counterions as ions interact in concentrated bulk solutions. The mean spherical approximation (MSA) is used to predict ion-specific excess chemical potentials in the filter and baths. The theory is calibrated using a single experimental observation, concerning the apparent dissociation constant of Ca 2+ in the presence of a physiological concentration of NaCl. When ions are assigned their independently known crystal diameters and the carboxylate oxygens are constrained, e.g., to a volume of 0.375 nm 3 in an environment with an effective dielectric coefficient of 63.5, the hypothesized selectivity filter produces the shape of the calcium binding curves observed in experiment, and it predicts Ba 2+/Ca 2+ and Na +/Li + competition, and Cl − exclusion as observed. The selectivities for Na +, Ca 2+, Ba 2+, other alkali metal ions, and Cl − thus can be predicted by volume exclusion and electrostatic screening alone. Spontaneous coordination of ions and carboxylates can produce a wide range of Ca 2+ selectivities, depending on the volume density of carboxylate groups and the permittivity in the locus. A specific three-dimensional structure of atoms at the binding site is not needed to explain Ca 2+ selectivity.

Buffering processes in a boreal dissolved organic carbon-rich stream during experimental acidification

The role of organic acids on surface water acidity as well as their buffering during anthropogenic acidification and subsequent recovery was studied in a field experiment on a total organic carbon (TOC)-rich stream draining the Svartberget catchment in northern Sweden. H 2SO 4 was added to the stream to increase SO 4 2− concentration by 90 μeq l −1 for 30 h. About 60% of the added H + was buffered by protonation of organic acids, another 20% was buffered by base cations released from the surface of the stream channel and only ca. 20% of the added acid remained unbuffered. TOC concentrations (27 mg l −1), and site density of carboxylic groups — 8.6 μeq (mg TOC) −1 — remained stable during the experiment. Two models of organic acid dissociation (a triprotic model and a monoprotic pH-dependent pKa model) were fitted to the experimental results. These models explained the observed variations in organic anions, but the model parameters were quite different from those reported by studies in Northern America and Central Europe. This experiment had substantially more buffering effect of TOC between pH 4.4 and 5.3, which is an environmentally important pH range.

Preparation and characterization of Ca-alginate microspheres by a new emulsification method

The preparation and characterization of Ca-alginate microspheres obtained by a new procedure from alginic acid, treated with an excess of NaOH and subsequently with a very concentrated solution of CaCl 2 are described. The produced particles have a spherical shape with an average diameter of 350 μm. The particles show a relative dense and homogeneous internal structure in comparison with previously reported alginate microcapsules (the bulk density being 0.47 g/cm 3), consequently the particle matrix is characterized by a high density of charged carboxylic groups. Particles produced with a contact time of 1 h showed a degree of crosslinking of 54%. Microspheres have a good stability, and despite of very low degree of swelling, they have a good solvents regain, and an excellent ionic binding capacity of cationic drugs. After preparation the beads were loaded by ionic complexation with an antitumor aromatic tetramidine. In addition, the in vitro release of drug has been studied.

Metal- and proton-binding properties of a core-shell latex: interpretation in terms of colloid surface models

The cadmium binding properties of a core-shell latex were investigated using differential pulse polarography. The latex particles have a polystyrene core which is surrounded by a hydrophilic shell containing a low density of sulphonic and carboxylic groups. For this core-shell latex dispersion, the binding of protons and metal ions can be analyzed reasonably well using Donnan's potential model [J.T. Davies and E.K. Rideal, Interfacial Phenomenon, Academic Press, New York, 1961]. However, the correction of Ohshima and Kondo [H.O. Ohshima and T. Konda, Biophys. Chem., 39 (1991) 181] of the Donnan model for the distribution of ions in the double layer near and in the shell is a real improvement. In this way, the binding constants of cadmium(II)with the surface groups of latex were separated into their intrinsic and electrostatic parts. The intrinsic constant for binding of cadmium(II) to carboxylic groups, obtained in this way, was similar to literature values.

Competitive adsorption, displacement, and transport of organic matter on iron oxide: I. Competitive adsorption

Different organic compounds or fractions of natural organic matter (NOM) show different adsorption affinities ( K) and capacities ( qm) on mineral surfaces. We hypothesize that these different organic compounds or fractions compete for adsorption when surface adsorption sites are limited. In this study, competitive adsorption of binary mixtures of Suwannee River NOM (SR-NOM), polyacrylic acid (PAA), phthalic acid, and salicylic acid on iron oxide was investigated at a constant solid:solution ratio, temperature, and pressure, but at varying C weight fractions, pH, and solution concentrations of the mixture. Results revealed that, in general, PAA is the most competitive whereas SR-NOM is more competitive than phthalic and salicylic acids. The competitive adsorption of these organic compounds is pH-dependent. At pH < 4, PAA becomes less competitive than SR-NOM or phthalic and salicylic acids. The competition among these organic compounds may be related to their carboxyl functional groups and their molecular structure. The overall strong competitiveness of PAA at pH > 4 in comparison with other organics is attributed to its high carboxyl density and linear molecular structure, which promote strong surface complexation with iron oxide. Because of the heterogeneity or polydispersity of NOM, this research indicates that NOM partitioning and transport in the subsurface soil environment are influenced by the dynamic competitive interactions between NOM subcomponents (or fractions). This process ultimately influences the distribution, interaction, and cotransport of contaminants and mineral colloids that are associated with NOM.

Adsorption of BSA on Highly Carboxylated Microspheres—Quantitative Effects of Surface Functional Groups and Interaction Forces

In order to elucidate the relations between the amount of surface functional groups and interaction forces, BSA adsorption experiments were performed, using highly carboxylated PS/PMAA microspheres as well as conventional ones. Two kinds of interaction forces were considered in this study, hydrogen bonding and hydrophobic interactions, while ionic interactions were assumed to be small or constant. Hydrophobic interactions were dominant in the lowNc(number density of surface carboxyl groups) region, below 1 carboxyl group nm−2, and were relatively sensitive to pH, while hydrogen bonding was dominant in the highNcregion, above 2 carboxyl groups nm−2, irrespective of pH. The transition region between these two interaction forces was 1 ∼ 2 carboxyl groups nm−2on the surface of a microsphere. When comparing the two extremes of hydrophobic interaction and hydrogen bonding, the latter was stronger, which was different from earlier studies. It can be explained that the conventional carboxylated microspheres do not have enough carboxyl groups on their surfaces. Adsorption constantKdiminished asNcincreased, which means that the affinity itself is reduced by hydrogen bonding. Adsorbed layer thicknesses calculated from theCm(adsorbed amount in equilibrium) were 4.66 ∼ 7.08 nm; this means that the BSA molecules exist between the side-on and end-on mode.

Preparation of Hyperbranched Polymer Films Grafted on Self-Assembled Monolayers

In this paper we report the preparation of thin films of new highly branched polymers which are relevant to boundary layer phenomena such as adhesion, wetting, and chemical sensing. Specifically, we synthesized surface-grafted, hyperbranched poly(acrylic acid) (PAA) films on self-assembled organomercaptan monolayers. These films grow in discrete steps, but unlike most layer-by-layer approaches, film thickness increase nonlinearly as a function of the number of layers because of the branched polymer architecture. Moreover, these polymer films contain a high density of carboxylic acid groups, which can selectively bind metal ions or serve as reactive sites for subsequent derivatization. Hyperbranched polymer films thus provide new platforms for chemical sensing applications and for tailoring polymer surface properties for a wide variety of technological applications. 24 refs., 4 figs.

Effect of the Molecular Chain Length of Cellulose Trunk Polymer on the Swelling Behavior of Cellulose Graft Copolymer.

The partially hydrolyzed graft copolymers of crosslinked polyacrylamide (PAM) on water-soluble hydro-xyethylcelluloses(HECs) with different molecular chain lengths were synthesized by using of the ceric ion in-itiation method in an aqueous medium, and the effect of the molecular chain length of the HEC trunk polymer on the swelling behavior of the graft copolymer (HEC-AM-Hyd) was investigated. The synthesized HEC-AM-Hyds were similar to one another in the proportion of the HEC trunk polymer and the grafted branch polymer and in the crosslinking density and content of carboxyl groups of the partially hydrolyzed PAM branch polymer. The absorbency of HEC-AM-Hyd increased with an increase in the molecular cahin length of the HEC trunk polymer. The HEC-AM-Hyd from the HEC with longer chain length had higher resistibility against the decrease in the absorbency with an increase in the NaCl concentration than that from the HEC with shorter chain length. It is con-sidered that the HEC molecule that has high rigidity and extends largely in water acts effectively in the swelling of HEC-AM-Hyd, and that the superior swelling properties of the HEC-AM-Hyd from the HEC with longer chain length are due to the larger extension of its trunk polymer.

Mechanisms of mucoadhesion of poly(acrylic acid) hydrogels.

It has been proposed that mucoadhesives which adhere to the gastric mucus layer may be used to prolong gastric retention time of oral dosage forms. Preliminary studies, using acrylic hydrogels, have established that the density of carboxyl groups on the polymer chain is important for mucoadhesion. To understand the role(s) of the carboxyl groups in mucoadhesion, acrylic acid-acrylamide random copolymers [P(AA-co-AM)] were synthesized, and the adhesion strength of the cross-linked polymers to the gastric mucus layer was examined as a function of the pH, initial concentration of the cross-linking agent, degree of swelling, and carboxyl-group density. From the study on mucoadhesion of various P(AA-co-AM), it was found that at least 80% of the vinyl groups of the polymer must possess carboxyl groups in the protonated form. The dependence of mucoadhesion on pH and carboxyl-group density suggests that mucoadhesion occurs through hydrogen bonding. In addition, the density of the cross-linking agent significantly affects mucoadhesion. As the density of the cross-linking agent is lowered, the mucoadhesive strength increases, although the density of carboxyl groups in the test surface area is reduced. It is concluded that for mucoadhesion to occur, polymers must have functional groups that are able to form hydrogen bonds above the critical concentration (80% for vinyl polymers), and the polymer chains should be flexible enough to form as many hydrogen bonds as possible.

Antitumor Activity of Polycarboxylic Acid Polymers

Abstract We have synthesized several polyanionic polymers for biological evaluation and to probe the mechanism of macrophage activation. We have determined that, while the molecular weight of the polymers is toxicologically important, the hydrophlicity, chain rigidity, and surface charge play a significant role with respect to the degree of macrophage activation. Macrophages elicited with polyanionic polymers with hydrophobic groups were cytotoxic to Lewis lung carcinoma both in vitro and in vivo. However, macrophages stimulated by polymers with high carboxylic acid group density but little hydrophobicity did not demonstrate significant antitumor activity.

Correlation between the cellulose fibres beating and the fixation of a soluble cationic polymer

AbstractThe amount of cationic soluble polymer fixed by cellulose fibres, whose specific surface area is increased by beating, was determined by a colloidal titration method. A linear relationship between the polymer uptake and the surface density of carboxyl groups was obtained up to a beating degree of 54°SR. For higher values, the uptake was found to be independent of surface carboxyl groups. These results are interpreted in terms of two mechanisms: a fixation of polycations through an ion‐exchange mechanism and an adsorption of polymer by Van der Waals interactions and/or hydrogenbonding.

コロイド滴定におよぼす塩類の影響

The colloid titration is well known to be a simple and accurate method for analyses of polyelectrolytes. But the problem often encountered in practical usages is remarkable influence of inorganic salts. Then the influece of salts, which are included in paper making white water, was studied on 13 kinds of anionic polymers, 14 kinds of cationic polymers and 6 kinds of amphoteric polymers. The results obtained are as follows.1) In a direct titration for cationic polymers with PVSK, salts generally increased the amount of PVSK at the end point which sometimes was nearly twice as high as that of true value.2) In the back titration for anionic polymers with low density of ionic groups, salts decrease the amount of PVSK at the end point. In other words, the concentration was overestimated and sometimes went up to over twice. On the other hand, the concentration of anionic polymers with high density of carboxyl groups was underestimated and sometimes reached below one-half in the presence of salts.3) Salts also inhibited greatly the metachromasy between TB and PVSK (color change at the end point).The above phenomena occured even below the average salt concentration in white water in which the ionic strength was about 0.01.These deficient results were attributable to the higher shielding of ionization in polyions with higher ionic density, acceleration of precipitation of unstoichiometric polyion complex and/or acceleration of the substitution reaction of carboxyl groups by sulfate group in PVSK caused by salts.

Electrolyte stability of carboxylated latexes prepared by several polymerization processes

Carboxylated isoprene/styrene copolymer or polystyrene latexes have been prepared by several polymerization processes. The density of carboxyl groups chemically bound to the surface of particles (surface carboxyl groups), and the electrolyte stability of these carboxylated latexes was determined to elucidate the relationship between them. The critical coagulation concentration (CCC), which represents the electrolyte stability of latex, decreases considerably with increasing valency of the cation, as expected from theory. The CCC increases remarkably with increase in the density of surface carboxyl groups or increase in the degree of neutralization of surface carboxyl groups. The electrolyte stability of these carboxylated latexes seems to be governed substantially by the density of carboxylate ions on the surface of particles irrespective of the polymerization process or the composition of polymers in the interior of particles.

Stability of organic matter in landfill leachates

Samples of grossly polluted groundwater and of leachate collected from wells or underdrains near solid waste disposal sites were subjected to extensive organic analyses. The soluble organics were concentrated, separated and characterized by membrane ultrafiltration, gelpermeation chromatography and analysis for functional groups and specific organics. Free volatile fatty acids represented the largest group of organics, and this fraction showed a rapid decrease with increasing age of the fill. The most stable group of organics with increasing age was a fulvic-like material with a relatively high carboxyl and aromatic hydroxyl group density. Increasing stability was further noted for carbohydrates, hydrolyzable amino acids and aromatic hydroxyl compounds in that order. Only leachate from a recently generating fill can be treated successfully by microbial processes because of its large biodegradable organic content; leachate from stabilized landfills is best treated by physical-chemical processes.

The effect of carboxylic monomers on surfactant-free emulsion copolymerization

A study was made of the effect of carboxylic monomers on the surfactant-free emulsion polymerization of styrene and styrene–butadiene. Acid monomers, such as acrylic acid, methacrylic acid, and itaconic acid, were shown to play a critical role in particle formation and particle stabilization in such systems. In the emulsion polymerization of styrene, methacrylic acid forms particles more efficiently than acrylic acid. This difference is attributed to the more hydrophobic nature of the methacrylic monomer which allows it to diffuse more rapidly to the particle surface where it acts to prevent agglomeration. The ability of carboxyl groups to orient at the particle–water interface was studied by acid–base and soap titrations of carboxylated styrene–butadiene latices. The polymerization of itaconic acid onto the particle surface of a styrene–butadiene latex produces a surface carboxyl density much higher than is obtainable with classically adsorbed surfactants. This result is used to explain the greater stability of carboxylated versus noncarboxylated emulsion polymers. During the polymerization of styrene–butadiene latices, carboxyl groups dervied from methacrylic acid are shown to be buried more deeply into the particle as compared to carboxyls derived from the more hydrophilic acrylic acid which orient more at the particle–water interface.