Proton and carbon-13 NMR studies on xanthan derivatives

A review of the enzymatic, physical, and chemical modification techniques of xanthan gum

Xanthan gum (XG), a bacterial polysaccharide has numerous valuable characteristics in the food, biomedical, pharmaceuticals, and agriculture sector. However, XG has also its particular limitations such as its vulnerability to microbial contamination, inadequate mechanical and thermal stability, unusable viscosity, and poor water solubility. Therefore, XG's structure and conformation need to be modified enzymatically, chemically, or physically to improve its optimistic features and decrease the formation of crystals, increase antioxidant ability, and radical scavenging activity. We have found out different means to modify XG and elaborate the importance and significance of the modified structure of XG. In this review, different enzymes are reviewed for XG degradation, which modifies their structure from different points (main chain or side chain). This article also reviews various physical methods (ultrasound, shear, pressure, sonication, annealing, and heat treatments) based on prevailing publications to alter XG conformation and produce low molecular weight (LMW) and less viscous end-product. Moreover, some chemical means are also discussed that result in modified XG through crosslinking, grafting, acetylation, pyruvation, as well as by applying different chemical agents. Overall, the current progress on XG degradation is very auspicious to develop a new molecule with considerable uses, in various industries with future assessments.

An Overview of Biopolymeric Electrospun Nanofibers Based on Polysaccharides for Wound Healing Management

Currently, despite the thoroughgoing scientific research carried out in the area of wound healing management, the treatment of skin injuries, regardless of etiology remains a big provocation for health care professionals. An optimal wound dressing should be nontoxic, non-adherent, non-allergenic, should also maintain a humid medium at the wound interfacing, and be easily removed without trauma. For the development of functional and bioactive dressings, they must meet different conditions such as: The ability to remove excess exudates, to allow gaseous interchange, to behave as a barrier to microbes and to external physical or chemical aggressions, and at the same time to have the capacity of promoting the process of healing by stimulating other intricate processes such as differentiation, cell adhesion, and proliferation. Over the past several years, various types of wound dressings including hydrogels, hydrocolloids, films, foams, sponges, and micro/nanofibers have been formulated, and among them, the electrospun nanofibrous mats received an increased interest from researchers due to the numerous advantages and their intrinsic properties. The drug-embedded nanofibers are the potential candidates for wound dressing application by virtue of: Superior surface area-to volume ratio, enormous porosity (can allow oxy-permeability) or reticular nano-porosity (can inhibit the microorganisms'adhesion), structural similitude to the skin extracellular matrix, and progressive electrospinning methodology, which promotes a prolonged drug release. The reason that we chose to review the formulation of electrospun nanofibers based on polysaccharides as dressings useful in wound healing was based on the ever-growing research in this field, research that highlighted many advantages of the nanofibrillary network, but also a marked versatility in terms of numerous active substances that can be incorporated for rapid and infection-free tissue regeneration. In this review, we have extensively discussed the recent advancements performed on electrospun nanofibers (eNFs) formulation methodology as wound dressings, and we focused as well on the entrapment of different active biomolecules that have been incorporated on polysaccharides-based nanofibers, highlighting those bioagents capable of improving the healing process. In addition, in vivo tests performed to support their increased efficacy were also listed, and the advantages of the polysaccharide nanofiber-based wound dressings compared to the traditional ones were emphasized.

Application of xanthan gum as polysaccharide in tissue engineering: A review

Xanthan gum is a microbial high molecular weight exo-polysaccharide produced by Xanthomonas bacteria (a Gram-negative bacteria genus that exhibits several different species) and it has widely been used as an additive in various industrial and biomedical applications such as food and food packaging, cosmetics, water-based paints, toiletries, petroleum, oil-recovery, construction and building materials, and drug delivery. Recently, it has shown great potential in issue engineering applications and a variety of modification methods have been employed to modify xanthan gum as polysaccharide for this purpose. However, xanthan gum-based biomaterials need further modification for several targeted applications due to some disadvantages (e.g., processing and mechanical performance of xanthan gum), where modified xanthan gum will be well suited for tissue engineering products. In this review, the current scenario of the use of xanthan gum for various tissue engineering applications, including its origin, structure, properties, modification, and processing for the preparation of the hydrogels and/or the scaffolds is precisely reviewed.

Oxidized Xanthan Gum and Chitosan as Natural Adhesives for Cork

Natural cork stopper manufacturing produces a significant amount of cork waste, which is granulated and combined with synthetic glues for use in a wide range of applications. There is a high demand for using biosourced polymers in these composite materials. In this study, xanthan gum (XG) and chitosan (CS) were investigated as possible natural binders for cork. Xanthan gum was oxidized at two different aldehyde contents as a strategy to improve its water resistance. This modification was studied in detail by ¹H and ¹³C nuclear magnetic resonance (NMR), and the degree of oxidation was determined by the hydroxylamine hydrochloride titration method. The performance of the adhesives was studied by tensile tests and total soluble matter (TSM) determinations. Xanthan gum showed no water resistance, contrary to oxidized xanthan gum and chitosan. It is hypothesized that the good performance of oxidized xanthan gum is due to the reaction of aldehyde groups—formed in the oxidation process—with hydroxyl groups on the cork surface during the high temperature drying. Combining oxidized xanthan gum with chitosan did not yield significant improvements.

A rheological study of the order-disorder conformational transition of xanthan gum

The rheological properties of a moderately concentrated solution of xanthan gum in both the ordered and the disordered state have been studied. Oscillatory shear, steady shear flow, and extensional flow experiments have been performed at different temperatures, covering the order-disorder transition determined by differential scanning calorimetry (DSC). The principle of time/temperature superposition was applied to the xanthan solutions for the different types of flow. Although a master curve covering six decades of frequency could be obtained for the storage modulus over the entire investigated temperature range, less agreement was found for the other modulus. This indicates that the order-disorder transition reflects changes on the molecular scale and slight modification of the physical network structure. To the authors' knowledge, this is the first time that this transition has been observed using these different rheological techniques.

Degradation of double-stranded xanthan by hydrogen peroxide in the presence of ferrous ions: comparison to acid hydrolysis

Conformationally ordered, double-stranded xanthan, degraded in the presence of H2O2 and Fe2+ (at 20 degrees C) or in dilute acid (0.1 M HCl at 80 degrees C), produced xanthan variants with weight-average molecular weights (Mw) ranging from 2 x 10(6) to 5.4 x 10(4). In both cases the fraction of cleaved linkages in the glucan backbone (alpha), measured as reducing ends, increased to very high values (0.05 for Mw = 2-3 x 10(4)), demonstrating that a large number of linkages in the backbone could be cleaved without a correspondingly large reduction in Mw, in accordance with the double-stranded nature of xanthan. Extensive degradation (more than 10-fold reduction in Mw) in both cases released single-stranded, conformationally disordered oligomers; this release was accompanied by an increase in the rate of acid hydrolysis of the glucan backbone and a pronounced increase in the rate of release of glucose monomer. In contrast, there was no significant change in the rate of reducing end-group formation associated with the release of oligomers upon degradation with H2O2/Fe2+. Both types of degradation were accompanied by changes in the composition of the side chains. However, in contrast to acid hydrolysis, where the terminal beta-D-mannose is preferentially hydrolyzed, the reaction with H2O2/Fe2+ resulted in removal of both mannose and glucuronic acid at approximately equal rates. This observation can be explained by a preferential attack on the inner alpha-D-mannose, with concomitant removal of the entire side chain. Removal of side chains and the release of single-stranded oligomers by H2O2/Fe2+ strongly influenced the optical rotation and also broadened the chiroptically detected conformational transition, whereas no change in the transition temperature was observed.

NMR studies of acetan and the related bacterial polysaccharide, CR1/4, produced by a mutant strain of Acetobacter xylinum

Acetan is a bacterial polysaccharide produced by Acetobacter xylinum NRRL B42. Chemical mutagenesis of A.xylinum allowed selection of a mutant strain which produced a new polysaccharide, CR1/4. 2D NMR methods have been used to assign the 1H and 13C spectra of the two polysaccharides and to determine that CR1/4 has the structure shown below. The total number of O-acetyl groups is slightly less than two per repeating unit. [formula: see text] The pentasaccharide side chain of acetan is truncated to a disaccharide unit in CR1/4, but the structures are otherwise identical. In particular, the degree of acetylation is about the same and the O-acetyl groups are located at the same position in both polysaccharides.