Distribution Of Free Carboxyl Groups Research Articles

An Integrally Formed Janus Hydrogel for Robust Wet-tissue Adhesive and Anti-postoperative Adhesion.

Facile fabrication of asymmetrically adhesive hydrogel with robust wet tissue adhesion simultaneously with effective anti-postoperative adhesion still remains a great challenge. In this work, an integrally formed Janus hydrogel is facilely fabricated in one step by controlling the interfacial distribution of free carboxyl groups on the two sides of hydrogels. At a lower stirring speed, the generated bigger sized emulsion droplets mainly occupy the top surface of hydrogel, which effectively hinders the exposition of carboxyl groups on the top surface, driving them to be more distributed on the bottom surface, ultimately resulting in the poor adhesion of top surface but robust adhesion of bottom surface to various wet tissue even underwater. The difference in adhesive strength achieves as high as 20 times between the two surfaces. In vivo rabbit experiment outcomes clearly validate that the bottom surface of hydrogel firmly adheres to the stomach defect, and the other opposite surface can efficiently address the postoperative adhesion problem. Besides, this hydrogel exhibits superior mechanical toughness and conductivity which has been used as a highly adhesive strain sensor to real-time monitor the beating heart in vivo. This simple yet effective strategy provides a much more feasible approach for creating Janus hydrogels bio-adhesives. This article is protected by copyright. All rights reserved.

Influence of enzymatic and acidic demethoxylation on structure formation in sugar containing citrus pectin gels

Aim of the present study was to investigate the impact of different demethoxylation methods and the co-occuring side effects on the molecular properties and structure formation in pectin gels.A high-methoxylated citrus pectin (HMP) was demethoxylated using either hydrochloric acid or pectin methylesterases of plant (pPME) or fungal (fPME) origin. pPME treatment causes a more block-wise distribution of free carboxyl groups, fPME or acidic treatment a random distribution. Twelve pectin samples with four different degrees of methoxylation (DM) between 62% and 41% were prepared. The gelation process was studied by oscillatory measurements.In pectin samples from pPME treatment structure formation started at higher temperature and the final gels were more elastic in comparison to pectin from the two other modifications. The impact of the block-wise distribution of the free carboxyl groups became more evident with decreasing DM. The gelling process of pectin samples with random distribution was similar independent of DM.Side effects of all demethoxylation reactions were an altered sodium ion content (high in enzymatically treated pectin, close to zero in acidic treated) and a decrease of the molecular weight with increasing degree of demethoxylation. These side effects additionally altered the gelation process and the final gel properties in different ways.

Modification and physico-chemical properties of citrus pectin – Influence of enzymatic and acidic demethoxylation

Aim of the present study was to investigate the effect of the method of demethoxylation on the particle structure and techno-functional properties of pectins with different degree of methoxylation and distribution of free carboxyl groups. Two groups of model pectins, one with 57% and one with 42% degree of methoxylation have been prepared from one single commercial pectin. Modifications were performed by an acidic and two enzymatic methods using fungal and plant-derived pectin methyl esterases. Thermal stability was investigated by thermal analysis and water uptake was determined by a sorption and a capillary sucking method.The enzyme-treated pectins were thermally less stable than the acid-treated. The water uptake of enzyme-treated pectins was higher than in acid-treated samples in the sorption method and lower in the capillary sucking tests. The different behaviour is explained by differences in pH during demethoxylation and a co-occurring variation in sodium content. Both parameters affected intermolecular interactions of the pectin macromolecules in solution, which resulted in differences in the particle morphology. The effect of the distribution of free carboxyl groups (statistical or block-wise) on the techno-functional properties was more pronounced in high-methoxylated pectins than in low-methoxylated pectins.

Complexation of Ferric Oxide Particles with Pectins of Ordered and Random Distribution of Charged Units

Complexation between ferric oxide particles and pectins with degree of methylation 50% but having ordered or random arrangement of free carboxyl groups is investigated by electric light scattering and electrophoresis. The influence of charge distribution in pectin chain on the electrical properties of oppositely charged oxide particles and stability of their suspensions is examined as a function of pectin concentration. Although the difference in charge density of pectin samples is ~5%, we found small but measurable difference in the behavior of both oxide/pectin complexes. This is attributed to condensation of counterions near the chains of pectin with ordered distribution of charges, leading to a decrease in the effective charge density and to a corresponding decrease in the contour length of the adsorbing pectin chains. Two parameters are sensitive to the conformation of the adsorbed chains in suspensions, stabilized by pectin adsorption (at particle charge reversal). The electro-optical effect is higher for the complex with less charged pectin, which is explained with larger amount of chains, adsorbed in more coiled conformation than the chains of pectin with random distribution of free carboxyl groups. The addition of small amounts of CaCl(2) has no significant influence on the thickness of the layer from the less charged pectin, in agreement with a more compact conformation of the chains in this adsorbed layer. In contrast, the thickness of the layer from pectin with random distribution of charged groups decreases with increasing concentration of CaCl(2), indicating a more loose structure of this layer.

Interchain Heterogeneity of Enzymatically Deesterified Lime Pectins

Two series of pectins with different levels and patterns of methyl esterification were produced by treatment of a very highly methylated lime pectin with a fungus- or plant-pectin methylesterase. The interchain distribution of free carboxyl groups was investigated by size exclusion and ion exchange chromatography. "Homogeneous" populations with respect to molar mass or charge density were thereby obtained, and their composition, molar mass, and calcium binding properties were investigated. The composition varies from one size exclusion chromatography fraction to another, the highest molar mass fraction being richer in rhamnogalacturonic sequences and exhibiting a slightly higher degree of methylation (DM). Separation of pectins by ion exchange chromatography revealed a narrow charge density distribution for pectins deesterified by fungus-pectin methylesterase, in agreement with a multichain mechanism. Conversely, pectins deesterified by plant-pectin methylesterase exhibited a very large charge density distribution suggesting a processive mechanism. The interchain polydispersity with regard to DM was however shown to have no impact on calcium binding properties of the different fractions. The progressive dimerization through calcium ions with decreasing DM of pectins deesterified by plant-pectin methylesterase seems to be the result of a peculiar intrachain pattern of methyl esterification that can be attributed to a multiple attack mechanism.

Chromatographic study of highly methoxylated lime pectins deesterified by different pectin methyl-esterases

The inter-molecular distribution of free carboxyl groups of two highly methoxylated pectins enzymatically deesterified by plant and fungus pectin methyl-esterases were investigated by size-exclusion (SEC) and ion-exchange chromatography (IEC). “Homogeneous” populations with respect to molar mass or charge density were thereby obtained and their chemical composition and physico-chemical properties (transport parameter for monovalent cations and calcium, calcium activity coefficient) were studied. Chemical analysis showed that the composition varies from one SEC fraction to another, the highest molar mass fraction being richer in rhamnose and galactose and exhibiting a slightly higher degree of methylation. Separation of pectins by IEC revealed a quite homogeneous charge density distribution for F58 contrary to P60 which exhibited a large distribution of methoxyl groups. The free carboxyl groups distributions and calcium binding behaviours of SEC and IEC fractions were shown to differ widely for highly methoxylated pectins deesterified by plant and fungus pectin methyl-esterases.

Interactions between food components and drugs. Part 4: Influence of pectins and bile salts on propranolol absorption

Influence of dietary fiber components on drug absorption was studied in vitro using artificial membranes and mucosa preparations from guinea pig in 2-compartment model systems (permeation model and equilibrium dialysis). Well defined pectin preparations with different structural properties were used as food components and propranolol (P) as basic model drug. The retardation of drug was increased with decreased degree of esterification (DE) of pectin. Pectins with a blockwise distribution of free carboxyl groups possessed a more intensive effect than pectins with a random arrangement. It was found that P transport across the artificial lipid membrane was significantly decreased by pectins with a blockwise (DE <- 54%) or statistical (DE = 36%) distribution of free COOH. Pectins with lower molecular weight giving low viscosities in the medium showed only a small effect on permeation of the drug. Furthermore, the influence of bile acids without and with pectins on P absorption was studied. The bile salts did only influence P transport when they were applied above the critical micellar concentration (CMC). P transport across the lipid membranes increased slightly when pectins were additionally used to the bile salts above the CMC. Transport of P across the guinea pig mucosa was less than the permeation through the artificial lipid membranes. However, the transport of P across the mucosa was significantly reduced by glycocholic acid (GC), by pectin BL-3 as well as by BL-3 and GC in the same way as found using the artificial lipid membranes.

Structure and properties of apple and sugar-beet pectins extracted by chelating agents

Pectins were extracted from apple or sugar-beet cell walls (alcohol-insoluble solids) at pH 4.5 and 20°C and at pH 6.5 and 80°C in acetate and phosphate buffer solutions, respectively, and in the same buffers containing cyclohexanediaminetetraacetic acid or ethylenediaminetetraacetic acid. The yields were very different between the two pH and temperature conditions, but variations with the nature of the extractant were small at pH 4.5 and 20°C, and no differences were observed at pH 6.5 and 80°C. The pectins extracted at pH 6.5 and 80°C were richer in neutral sugars and acetic acid. Degradation of the pectins extracted at high pH and temperature was shown by the decrease of the intrinsic viscosity and by the shift of the uronic acid peak toward the total volume in gel-filtration chromatography. These pectins contained a high molecular weight population rich in neutral sugars and a low molecular weight acid population, in contrast to the pectins extracted at low temperature and pH, for which neutral and acidic sugars had similar elution profiles. At pH 6.5 and 80°C, rather extensive degradation of the pectins occurred. Calcium-binding experiments (potentiometry with specific electrode and conductimetry) indicated a statistical distribution of free carboxyl groups. These results do not support the hypothesis that chelating-agent extractable pectins are held in the cell wall by calcium cross-links involving the formation of “egg-boxes”.

Studies on the intermolecular distribution of industrial pectins by means of preparative ion-exchange chromatography

Three industrial high methoxyl pectins have been fractionated by ion-exchange chromatography on a preparative scale. Chemical analysis of the resulting fractions revealed that pectin molecules varying in charge, also differ in composition. Neutral sugars, phenolic and proteinaceous compounds were found to coelute with pectin molecules. The nonuronide material appeared to be associated with all pectin molecules, but mainly attached to those requiring a high ionic strength to be released from the ion exchanger. Moreover, despite large quantitative differences, the distribution of individual neutral sugars among the molecules was found to be very similar for pectins from lemon and apple, indicating a great similarity in structural features. Separation of pectin molecules by ion-exchange chromatography was found to depend on many different chemical parameters such as degree of methoxylation, but, probably also the intramolecular distribution of free carboxyl groups and the presence of phenolics. This renders the interpretation of ion-exchange elution profiles difficult and uncertain.

Evaluation of a method for determining the free carboxyl group distribution in pectins

The distribution of free carboxyl groups in pectins has been investigated by a method that involves blocking the free carboxyl groups by glycolation, and hydrolysis of the methylesterified regions with a mixture of pectic enzymes. The hydrolysis products are separated from the glycolated regions on an ion exchange column and after deglycolation the oligomer size distribution is obtained by Sephacryl S-200 chromatography. The method was applied to five pectins with degrees of esterification in the range 5–70%. For two of the samples (an enzyme and an alkali de-esterified low methoxyl pectin) the degree of hydrolysis was significantly lower than would be predicted from the initial degree of esterification and thus for these materials the values obtained for the carboxyl group block sizes were considered to be a maximum rather than an accurate estimate. All the samples investigated had a significant proportion of free carboxyl regions with a degree of polymerisation greater than 10. With the possible exception of the pectate (degree of esterification 5%) none of the samples had a random distribution of carboxyl groups. This was considered to be a reflection of the distribution in the native pectin rather than indicating that chemical de-esterification was non-random. The large free carboxyl group block sizes was consistent with the egg-box model for low methoxyl pectin gelation. Larger blocks were found in the enzyme de-esterified pectin compared with the alkali and acid de-esterified material.

Distribution of free carboxyl groups in the molecule of pectin after esterification of pectic and pectinic acid by methanol

Distribution of free carboxyl groups in the molecule of pectin after esterification of pectic and pectinic acid by methanol

Distribution of free carboxyl groups in the pectin molecule after treatment with pectin esterase

Distribution of free carboxyl groups in the pectin molecule after treatment with pectin esterase