Polysaccharide Scleroglucan Research Articles

A possible pH-controlled drug delivery system based on a derivative of the polysaccharide scleroglucan.

Four carboxylated derivatives of scleroglucan have been obtained by oxidation, to different extents, of the glucopyranose side chains of the natural polysaccharide. The diffusion of model molecules through aqueous solutions of these new products was measured at various pH values. The reversible pH induced sol-gel transition of some of the polyelectrolyte solutions tested effects a remarkable variation in the diffusion rate of the permeating species; in this sense the most interesting polysaccharide appears to be the product with 70% oxidized glucopyranose moieties. The behaviour of scleroglucan and its derivatives has been compared with that of carboxymethylcellulose and the mechanism involved in drug permeation and release discussed. The possible application of one of the new products in controlled release formulations for oral use is also reported.

Hydrogels from scleroglucan and ionic crosslinkers: Characterization and drug delivery

The polysaccharide scleroglucan (Sclg), exploited as a matrix suitable for modified drug delivery, was crosslinked in the presence of three ions: borate, aluminum, and iron. A rheological investigation indicated the main differences between the hydrogels in their viscoelastic linear response: the Sclg/borax system showed the highest strength when deformed by elongation, whereas the strength of the other systems broke down, in terms of viscosity, at much lower values of the imposed strain. Tablets prepared from the gels showed remarkable differences in their water uptake and dimensional swelling. On the other hand, the tablets, loaded with drugs of different steric hindrances, showed similar release behavior, regardless of the crosslinking agent. Scanning electron microscopy analysis was related to the delivery and rheological profiles. Texture analysis, carried out on tablets swollen for 5 h, showed different values of cohesion. Furthermore, when the generalized Maxwell model was applied to the relaxation data, the obtained mechanical spectra showed a more pronounced solidlike character of the Sclg/iron network in comparison with the prevailing viscous behavior of the other matrices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Scleroglucan-Borax Hydrogel: A Flexible Tool for Redox Protein Immobilization

A highly stable biological film was prepared by casting an aqueous dispersion of protein and composite hydrogel obtained from the polysaccharide Scleroglucan (Sclg) and borax as a cross-linking agent. Heme proteins, such as hemoglobin (Hb), myoglobin (Mb), and horseradish peroxidase (HRP), were chosen as model proteins to investigate the immobilized system. A pair of well-defined quasi-reversible redox peaks, characteristics of the protein heme FeII/FeIII redox couples, were obtained at the Sclg-borax/proteins films on pyrolytic graphite (PG) electrodes, as a consequence of the direct electron transfer between the protein and the PG electrode. A full characterization of the electron transfer kinetic was performed by opportunely modeling data obtained from cyclic voltammetry and square wave voltammetry experiments. The efficiency of our cross-linking approach was investigated by studying the influence of different borax groups percentage in the Sclg matrix, revealing the versatility of this hydrogel in the immobilization of redox proteins. The native conformation of the three heme proteins entrapped in the hydrogel films were proved to be unchanged, reflected by the unaltered Soret adsorption band and by the catalytic activity toward hydrogen peroxide (H2O2). The main kinetic parameters, such as the apparent Michaelis-Menten constant, for the electrocatalytic reaction were also evaluated. The peculiar characteristics of Sclg-borax matrix make it possible to find wide opportunities as proteins immobilizing agent for studies of direct electrochemistry and biosensors development.

Theoretical and Experimental Study on a Self-Assembling Polysaccharide Forming Nanochannels: Static and Dynamic Effects Induced by a Soft Confinement

It is well-known that the polysaccharide scleroglucan (Sclg) exhibits a triple-helix conformation (triplex) and it is able to form hydrogels in water solution. Furthermore, these hydrogels are influenced by the presence of borax, in terms of rheological and drug release properties. In previous works, we showed that the presence of borax stabilizes the intertriplex interactions and that the property variations, induced by borax, can be fully explained, considering that the Sclg triplexes can form nanochannel-like structures. In this paper, the stability of these aggregates has been experimentally studied by means of atomic force microscopy (AFM) and theoretically investigated by means of molecular dynamics (MD) simulations. The simulations indicate that the borax stabilizes nanochannel-like structures when seven triplexes are considered. The simultaneous presence of different Sclg triplexes in a narrow space strongly influences the properties of confined water molecules in a way similar, in many aspects, to that of water molecules located in the inner part of well-defined nanochannels (e.g., diffusion inside carbon nanotubes). As a consequence, also the conformational properties of flanking regions of Sclg triplexes are influenced. Furthermore, differential scanning calorimetry (DSC) data show that the well-known conformational transition occurring at 280 K for Sclg does not take place in the presence of borax. The MD simulations suggest that such lack of transition is a direct consequence of the presence of borax. The role of Na+ counterions in the hydrogel structure is also investigated.

Small angle x-ray scattering study of local structure and collapse transition of (1,3)-β-D-glucan-chitosan gels

Scleroglucan is a (1,3)-beta-D-glucan polysaccharide produced by the fungus Sclerotium. Dissolved in water at room temperature it adopts a linear, rigid, triple helical structure. Gelation of scleroglucan can be obtained by Schiff-base formation between partly periodate oxidized scleroglucan and the primary amine groups of chitosan. The scleraldehyde-chitosan gels exhibit a collapse transition when exposed to volume fractions of isopropanol, Wp, larger than 65%. The aim of the present study is to provide structural information concerning the local polymer distribution and the collapse transition in (1,3)-beta-D-glucan-chitosan gels. Small angle x-ray scattering was used to investigate solutions and gels of scleroglucan in water, as well as in an aqueous mixture containing 65% isopropanol. The results reveal that in aqueous solution, the polysaccharide scleroglucan chains have an approximately cylindrical cross section of external diameter close to 17 A. The gels display the same local structure, but form clusters on a longer distance scale. For the collapsed gels in the water-isopropanol mixture, partial phase separation occurs in which ordered domains of approximate size of 110 A develop. This study indicates that local ordering in liquid-crystalline-type domains is a possible molecular mechanism contributing to the collapse of gels composed of semiflexible polymers. The triple helical structure of the molecule appears not to be conserved in the majority phase in this solvent, but it is conserved in the liquid crystalline domains.

An experimental and numerical investigation of drag reduction in a turbulent boundary layer using a rigid rodlike polymer

The drag reduction in a zero pressure gradient (ZPG) turbulent boundary layer (TBL) using a rigid rodlike polymer was experimentally and numerically investigated. Using injection of the rigid polysaccharide scleroglucan, drag reductions of approximately 10–15 % were observed, with three distinct drag reduction regimes: a non-Newtonian flow region near the injector, followed by a region of nearly constant drag reduction, and finally a region of negligible drag reduction. Decreasing the effective rotary Peclét number reduced the drag reduction effectiveness. Increasing the concentration did not improve the drag reduction, but instead shifted the spatial development of the drag reduction further downstream. A complementary direct numerical simulation of the ZPG TBL using the rigid rod constitutive equation was performed at a matching inlet Reynolds number. The simulation assumed a homogeneous concentration distribution and used estimated effective parameters for the rodlike additive. Spatial evolution of the fiber stresses is rapid and develops asynchronously with the flow structure. The simulated turbulence statistics and experimental measurements at a position 23 boundary layer thicknesses downstream compare favorably, with the primary differences due to the concentration distribution assumed in the simulation.

Molecular dynamics investigations of the polysaccharide scleroglucan: first study on the triple helix structure

Explicit solvent molecular dynamics (MD) simulations on the triple helix of the polysaccharide Scleroglucan (Sclg) at two temperatures (273 and 300 K) were carried out. Owing to the complexity of the system, a united-atom force field, based on the properly modified GROMACS parameters, was adopted. To test these parameters for our system, MD simulations of the two disaccharidic units, representing the main chain and the side-chain linkages of the Sclg repeating unit, were performed and the results were compared with the literature data. The simulated triple helix of Sclg retained the main experimentally determined features of the polymer. The residence times of the solvent molecules at 273 and 300 K were analyzed. The results show that the more internal water molecules, interacting with the core of the Sclg triplex are not influenced substantially by changing the temperature, on the contrary the water molecules, interacting with the side-chain glucose residues show more significant differences. These data suggest that the more external water molecules, interacting with the side chain, play a major role in the conformational transition experimentally observed at low temperature.

Study of a novel labelled scleroglucan macromolecule

A fast and rapid chemical reaction is presented here for labelling the polysaccharide scleroglucan with iodine to simplify its detection. The conditions proposed for the chemical reaction (temperature, concentrations of reactants and pH) were selected so as to substitute only a few of the OH groups in the polymer. The quantification of the labelled macromolecule is possible by radioactivity or Total Reflection X-ray Fluorescence techniques, depending on the iodine isotope used. Both techniques were adjusted for their use in labelled (with 127I or 131I) scleroglucan solutions. A comparison of the molecular weight distribution and the viscosity between solutions of the labelled product and the original one is performed and no major differences were found.

Structural and rheological characterization of Scleroglucan/borax hydrogel for drug delivery

The polysaccharide Scleroglucan, one of the most rigid polymers found in nature, can form a chemical/physical gel, in the presence of borax. The obtained hydrogel was loaded with three different model molecules (Theophylline, Vitamin B12 and Myoglobin) and then, after freeze-drying, was used as a matrix for tablets. The release profiles of the substances from the dosage forms were evaluated; the matrix appeared capable to modulate the diffusion of the chosen molecules, and different diffusion rates were observed, according to the different radii of the tested molecules. Interestingly, in the dissolution medium the matrix undergoes an anisotropic swelling taking place only in the axial direction, while a negligible radial variation occurs. The water uptake of the matrix occurs according to a Fickian process. Samples at two different polymer concentrations (0.7 and 2.3%, w/v) were characterized in terms of rheological and mechanical parameters and the properties were interpreted in terms of the molecular structure obtained by conformational analysis. The flow curves acquired in the viscoelasticity interval, show the effect of the borate ion in improving the resistance of the gel in comparison to the polymer alone. The evaluation of the moduli indicates that the system is viscoelastic, with an appreciable liquid component that increases as the polymer concentration decreases. Also the cohesion of the gel is higher in comparison to the Scleroglucan and is strongly dependent on temperature. The combination of experimental and theoretical conformational analysis approaches, allowed us to propose a model for the structure of the macromolecular network and to give an explanation to the anomalous swelling that was observed. It came out that the polymer can built up a channel structure, mediated via borax ion interaction, that can accommodate guest molecules of different size.

Synthesis and conformational properties of cyanoethyl–Scleroglucan

Cyanoethyl derivatives were obtained as intermediates in the chemical modification of the neutral polysaccharide Scleroglucan, aimed at attaining new ionic carbohydrate polymers. The chemical and conformational properties of the cyanoethylated polymer were investigated and compared with those exhibited by the native one. In particular, capillary viscosity and small angle X-ray scattering experiments demonstrated that in aqueous solutions cyanoethyl derivatives were not able to assume the triple helix structure typical of the parent sclecroglucan.

Structure and dynamics of the branched polysaccharide scleroglucan in dilute solutions studied by 1D and 2D NMR spectroscopy

Variable temperature and magnetic field dependent 13C NMR relaxation measurements ( T 1 and NOE) were carried out for the branched polysaccharide scleroglucan in DMSO-d 6 dilute solutions. The relaxation data of the backbone carbons were analyzed quantitatively by using the bimodal time-correlation functions developed by Dejean, Lauprêtre, and Monnerie (DLM), which offered the best quantitative description of the segmental motion of the carbohydrate chains. Simple internal rotations of the free hydroxymethyl groups of the backbone rings about the exocyclic C-5–C-6 bonds superimposed on segmental motion have been described as a diffusion process of restricted amplitude. Multiple internal rotations involving the exocyclic hydroxymethyl group of the ring at the branched point and that of the side chain ring, as well as the side chain ring itself were described by employing a composite TCF for side chain motions superimposed on polymer segmental motions. These time-correlation functions and their Fourier transform pairs, the spectral densities, offered the best interpretation of the relaxation data of the exocyclic free hydroxymethyl groups, and the pendent d-glucorynosyl ring. Finally, the 1H- and 13C NMR spectra of the neutral scleroglucan in DMSO-d 6 were analyzed by employing a series of 2D NMR experiments. The 500 MHz 1H NMR spectrum of scleroglucan at 283 K show severe peak overlaps, which do not allow the complete assignment of all signals in the carbon spectrum.

Solid-state 13C NMR Study of Scleroglucan Polysaccharide. Effect of the Drying Process and Hydration on Scleroglucan Structure and Dynamics

High-resolution solid-state 13C CP/MAS NMR was used to study the evolution of a polysaccharide (scleroglucan) conformation from the anhydrous to the hydrated form. The influence of a thermo-mechanical treatment applied during the drying process of scleroglucan is analyzed both on the dried and rehydrated product. 13C NMR spectra, 13C relaxation times (T 1C) and 1H relaxation times in the rotating frame (T 1ρH) of scleroglucan dried by using instantaneous controlled pressure drop (Détente Instantanée Controlée™) were analyzed in order to explain the observed differences of rehydration capacity. Although the scleroglucan treated at 6 bar has the same conformational state (triple-helix) as the one treated at 1 bar, it shows two different relaxation times T 1C for the C-3 carbon involved in the interglycosidic linkage. The magnetization decay of the hydrated sample exhibits a decrease of two time constants with significant shortening of the spin-lattice relaxation times T 1C that accounts for the higher mobility of the chains. High-pressure treatment creates highly rigid and compact domains. Consequently, water molecules cannot readily access the inside of the triple-helix and relax the interchain hydrogen bonds.

Free-radical degradation of triple-stranded scleroglucan by hydrogen peroxide and ferrous ions

The triple-stranded polysaccharide scleroglucan was subjected to free-radical depolymerisation with Fenton's reagent (H 2O 2/Fe 2+), and partially degraded samples in the molecular weight ( M w) range from 8 200 000 to 5200 were studied. Analyses of the chemical composition of partially degraded samples by 13C nuclear magnetic resonance spectroscopy and by determination of reducing end-groups suggested that the degradation was random. The decrease in M w followed the kinetics expected for a multiple-stranded polymer. Following an apparently initial stable regime, degradation occurred with an exponential decrease (exponent (ν) ∼3.6) in M w. Partially degraded samples displayed bimodal molecular weight distributions. This was attributed to the release of single-stranded oligomers having a degree of polymerisation ( DP) too low to remain incorporated in the triplex structure ( DP< DP c; the critical lower DP for triplex formation). The weight-average molecular weight of the low- M w fraction was estimated to about 36 000 ( DP w∼56 tetrasaccharide units). Following a heat treatment at 100°C (15 min) of the partially degraded samples, a reduction in M w by a factor of 2 to 2.5 was observed. This was attributed to the formation of more perfectly matched triple-stranded molecules, without aggregation or ring formation, as shown by electron microscopy.

Imaging of individual biopolymers and supramolecular assemblies using noncontact atomic force microscopy.

A variety of biopolymers is imaged using noncontact atomic force microscopy. Samples are prepared by aerosol spray deposition of aqueous solutions on freshly cleaved mica followed by air drying. The distributions of contour lengths and chain or fibril thicknesses normal to the mica substrate can be measured for individual polymer molecules or molecular assemblies. In many cases it is possible to conclude that the structures imaged and quantitatively analyzed are representative of those present in solution and not artifacts of the deposition/dessication process. Imaging of linear and cyclic triple helices of the polysaccharide scleroglucan is demonstrated. Measurements of the triple helix thickness normal to the mica surface are analyzed, and successful measurements of the molecular weight distribution and mean molar mass are described. It is demonstrated that the extent of chain association in the polysaccharide xanthan can be modulated by the addition of low molecular weight salts. The contour length and chain thickness distributions in a xanthan fraction are presented. Increases in the extent of chain association with increasing polymer concentration are documented for the gelling polysaccharide gellan, and the formation of stiff fibrillar gellan aggregates in the presence of added low molecular salt is demonstrated. Images are presented of the polysaccharide kappa-carrageenan in its disordered, and presumably single-stranded, state. Biopolymers other than polysaccharides can be imaged by the same technique; this is demonstrated with the fibrous protein collagen. In general it is shown that aerosol spray deposition of biopolymer samples can be used in conjunction with noncontact atomic force microscopy to provide a fast, reliable, and reproducible method for assessing the size and shape distributions of individual biological macromolecules and macromolecular assemblies in solution with a minimum of time and effort devoted to sample preparation.

Tapping mode Atomic Force Microscopy of scleroglucan networks.

Tapping mode Atomic Force Microscopy (TmAFM) has been used to study the fungal polysaccharide scleroglucan deposited from aqueous solution and dimethyl sulfoxide (DMSO) onto a mica surface. The solutions from which the microscope samples were produced were prepared by first dissolving the solid scleroglucan in 0.1M NaOH, then neutralizing the solution with HCl, followed by dilution to the required concentration in either water or DMSO. It was found that from the aqueous solution described above, scleroglucan forms networks. Based on a comparison of the denatured-renatured and aqueous solution samples, network formation is due to the imperfect registration between the chains forming the triple helices. The relatively large stiffness of the scleroglucan triple helix is also assumed to contribute to the formation of the extended networks. The triple helix diameter was measured to be 0.92 +/- 0.27 nm, which is in the same range as that obtained by other researchers using similar techniques. Denatured scleroglucan, deposited from DMSO onto mica, forms a web-like layer on top of which there are sphere-like structures. These morphologies are believed to be due to triple helix denaturation yielding highly flexible single chains in DMSO, which results in coiling and web-like dense packing of scleroglucan upon deposition onto mica. Most interestingly after additional of water to the samples deposited from DMSO, some of the chains can be renatured into short, stiff rod-like structures which are similar to the structures observed by others researchers. The imaging data for aqueous solution deposition can be analyzed by plotting maximum end-to-end distance versus the perimeter of the networks deposited onto mica. This yields a Flory-like exponent of 0.67, which is almost similar in value to that obtained by other researchers for linear structures of scleroglucan but less than that expected for a polymer chain following a self-avoiding walk (upsilon = 0.75) model on a two-dimensional surface. The fractal dimension that can be used to characterize the networks was determined graphically to be 1.22 +/- 0.06.

APPARENT NON-FICKIAN RELEASE FROM A SCLEROGLUCAN GEL MATRIX

Abstract Hydrogels, and particularly biopolymeric hydrogels, have recently received tremendous interest as controlled release systems for their peculiar features such as high biocompatibility, biodegradability, bioadhesivity, chemical and thermal resistance and good mechanical properties. Among biopolymers, the exocellular microbial polysaccharide scleroglucan appears to be particularly well suited for the formulation of monolithic hydrogel matrices for controlled drug release. In this work we studied the macroscopic factors influencing the kinetics of a model drug release (theophylline) from a scleroglucan hydrogel matrix (2%w/w) and modeled the relevant experimental results. The evidences for the release experiments indicate that the kinetics of the processes follow an apparently non-Fickian behavior under different active drug concentration, temperature and stirring speed. However, by considering the peculiar nature of the hydrogel matrix and the geometrical features of the experimental setup in the fo...

Divalent cation interactions with a carboxylated derivative of scleroglucan

AbstractDivalent cation binding was investigated on a semisynthetic carboxylate derivative obtained from the fungal polysaccharide scleroglucan. Polarography, circular dichroism and isothermal microcalorimetry were used to study both the binding ability of Cu(II), Pb(II), and Zn(II) ions and the macromolecular properties of the systems under investigation. A theoretical model, proposed by Schwarz for the cooperative binding, was used to evaluate binding constants and the parameter σ related to the degree of cooperativity. All findings are discussed in terms of the differences in the binding ability of the different cations investigated. Pb(II) ions exhibit the higher affinity for oxidised scleroglucan and, in addition to this, its binding process is characterised by a cooperative behavior due to the onset of a disorder‐to‐order conformational transition of the polysaccharidic backbone. On the other hand, Cu(II) ions are less effective in the binding and unable to induce the conformational transition.

Mechanical Strength of Clay Minerals as Influenced by an Adsorbed Polysaccharide

AbstractThe water‐stabilizing action of polysaccharides on soil aggregates has been ascribed to the binding together of soil particles by polymer bridges. This study was conducted to investigate the ability of polysaccharides to increase the strength of interparticle bonds by measuring the mechanical strength of clay‐polysaccharide complexes. Kaolinite, montmorillonite, and the polysaccharide scleroglucan were used. Cores were prepared from dilute suspensions of the complexes, air dried, and manufactured either into small briquets or into spherical aggregates to measure respectively the modulus of rupture and the tensile strength. The polysaccharide increased the mechanical strength of both clay minerals. The modulus of rupture of montmorillonite increased from 265 to 580 × 105 Pa at the maximum adsorption of scleroglucan, which was 140 g kg−1 clay. In the case of kaolinite, modulus of rupture measurements indicated that particle‐orientation effects were small and could be neglected. The tensile strength of kaolinite increased from 1 to 20.6 × 105 Pa at the maximum adsorption of scleroglucan (29.9 g kg−1 clay). In this case, the mechanical properties were not due to changes in the clay microorganization, since scleroglucan affected neither the fabric nor the porosity of the kaolinite. Increases in strength were thus intercepted as the formation of polymer bridges between the clay particles and were related to the progressive coverage of the surface area of the clay by the polysaccharide. We concluded that the aggregating action of polysaccharides is predominantly due to an increased strength of interparticle bonds.

On the solid state and solution conformations of a polycarboxylate derived from the polysaccharide scleroglucan

The main conformational features of a polycarboxylate (S-1·0) derived from the polysaccharide scleroglucan have been investigated in the solid state and in aqueous solution. X-Ray diffraction experiments performed on oriented fibres indicate the presence of triple helices both at low and high relative humidity. Aqueous solution studies, carried out by means of polarimetry, potentiometry and viscosimetry indicate that S-1·0 chains in water (neutral pH) are in an essentially disordered state and can undergo salt-induced and pH-induced conformational changes. Tentative models are proposed for S-1·0 solution conformations which may account for both the solid state and solution experimental results.

Influence of the charge density on the solution behaviour of polycarboxylates derived from the polysaccharide scleroglucan

Solution properties of polycarboxylates obtained by periodate oxidation of scleroglucan, with different degrees of oxidation, have been studied as a function of pH. Viscosity, calorimetric, optical and chiro-optical measurements show that the two carboxylated samples with higher degrees of oxidation (S-1·0 and S-0·7) can assume an ordered conformation at low pH. On the contrary the sample characterized by a lower extent of oxidation (S-0·2) shows no conformational changes. Optical measurements suggest that this polymer would be in an ordered helical form in dilute aqueous solution.