A convenient access to beta-(1-->4)-linked 2-amino-2-deoxy-D-glucopyranosyl fluoride oligosaccharides and beta-(1-->4)-linked 2-amino-2-deoxy-D-glucopyranosyl oligosaccharides by fluorolysis and fluorohydrolysis of chitosan

Progress and challenges in the synthesis of sequence controlled polysaccharides

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure-properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

Insight on Solution Plasma in Aqueous Solution and Their Application in Modification of Chitin and Chitosan

Sustainability and environmental concerns have persuaded researchers to explore renewable materials, such as nature-derived polysaccharides, and add value by changing chemical structures with the aim to possess specific properties, like biological properties. Meanwhile, finding methods and strategies that can lower hazardous chemicals, simplify production steps, reduce time consumption, and acquire high-purified products is an important task that requires attention. To break through these issues, electrical discharging in aqueous solutions at atmospheric pressure and room temperature, referred to as the "solution plasma process", has been introduced as a novel process for modification of nature-derived polysaccharides like chitin and chitosan. This review reveals insight into the electrical discharge in aqueous solutions and scientific progress on their application in a modification of chitin and chitosan, including degradation and deacetylation. The influencing parameters in the plasma process are intensively explained in order to provide a guideline for the modification of not only chitin and chitosan but also other nature-derived polysaccharides, aiming to address economic aspects and environmental concerns.

The Effect of Molecular Weight on the Antibacterial Activity of N,N,N-Trimethyl Chitosan (TMC)

N,N,N-trimethyl chitosan (TMC) with 93% degree of trimethylation was synthesized. TMC and the chitosan starting material were subjected to acidic hydrolysis to produce 49 different samples with a reduced average molecular weight (Mw) ranging from 2 to 144 kDa. This was done to allow the investigation of the relationship between antibacterial activity and Mw over a wide Mw range. NMR investigation showed that hydrolysis did not affect the degree of trimethylation (DSTRI) or the structure of the polymer backbone. The activity of TMC against Staphylococcus aureus (S. aureus) increased sharply with Mw until a certain Mw value (critical Mw for high activity, CMW) was reached. After the CMW, the activity was not affected by a further increase in the Mw. A similar pattern of activity was observed for chitosan. The CMW was determined to be 20 kDa for TMC and 50 kDa for chitosan.

Metabolic engineering for the production of chitooligosaccharides: advances and perspectives

Chitin oligosaccharides (CTOs) and its related compounds chitosan oligosaccharides (CSOs), collectively known as chitooligosaccharides (COs), exhibit numerous biological activities in applications in the nutraceutical, cosmetics, agriculture, and pharmaceutical industries. COs are currently produced by acid hydrolysis of chitin or chitosan, or enzymatic techniques with uncontrollable polymerization. Microbial fermentation by recombinant Escherichia coli, as an alternative method for the production of COs, shows new potential because it can produce a well-defined COs mixture and is an environmentally friendly process. In addition, Bacillus subtilis, a nonpathogenic, endotoxin-free, GRAS status bacterium, presents a new opportunity as a platform to produce COs. Here, we review the applications of COs and differences between CTOs and CSOs, summarize the current preparation approaches of COs, and discuss the future research potentials and challenges in the production of well-defined COs in B. subtilis by metabolic engineering.

Extraction of chitosan and its oligomers from shrimp shell waste, their characterization and antimicrobial effect

Aim:

The present study was performed to utilize the shrimp shell waste for chitin and chitosan production, characterization by Fourier transform infrared (FT-IR) technique and to evaluate the antimicrobial effects of chitosan oligomers produced by depolymerization of chitosan by nitrous acid.

Materials and Methods:

Chitosan was extracted from the shrimp shell waste by the chemical method and characterized by FT-IR. Chitooligomers were produced by depolymerising chitosan using nitrous acid, and the chitooligomers were tested for antimicrobial effect against four gut pathogenic organisms, i.e., Enterobacter aerogen (National Collection of Dairy Culture [NCDC] 106), Enterococcus faecalis (NCDC 119), Escherichia coli (NCDC 134), and Staphylococcus aureus (NCDC 109) by well diffusion method using Muller-Hinton agar. A pure culture of pathogenic organisms was collected from NCDC, ICAR-National Dairy Research Institute, Karnal.

Results:

Extracted chitosan characterized by FT-IR and chitooligomers demonstrated antimicrobial effect against four gut pathogenic organisms used in this study. Zone of inhibitions (mm) were observed in E. faecalis (13±0.20), E. coli (11.5±0.4), S. aureus (10.7±0.2), and E. aerogen (10.7±0.3). E. faecalis showed larger inhibition zone as compared to all other organisms and inhibitions zones of E. aerogen and S. aureus were comparable to each other.

Conclusion:

Shrimp waste can be utilized for chitosan production, and the chitooligomers can be used as feed additive for gut health enhancement and have potential to replace antibiotics from the feed. Along with value addition pollutant load could be reduced by waste utilization.

Biotechnological approaches for field applications of chitooligosaccharides (COS) to induce innate immunity in plants

Plants have evolved mechanisms to recognize a wide range of pathogen-derived molecules and to express induced resistance against pathogen attack. Exploitation of induced resistance, by application of novel bioactive elicitors, is an attractive alternative for crop protection. Chitooligosaccharide (COS) elicitors, released during plant fungal interactions, induce plant defenses upon recognition. Detailed analyses of structure/function relationships of bioactive chitosans as well as recent progress towards understanding the mechanism of COS sensing in plants through the identification and characterization of their cognate receptors have generated fresh impetus for approaches that would induce innate immunity in plants. These progresses combined with the application of chitin/chitosan/COS in disease management are reviewed here. In considering the field application of COS, however, efficient and large-scale production of desired COS is a challenging task. The available methods, including chemical or enzymatic hydrolysis and chemical or biotechnological synthesis to produce COS, are also reviewed.

Chemical preparation and structural characterization of a homogeneous series of chitin/chitosan oligomers

The preparation of a homogeneous series of chitin/chitosan oligomers (chito-oligomers) with the same distribution of degrees of polymerization (DP) ranging from 2 to 12, but with various average degrees of N-acetylation (DA) from 0 to 90% is described. This DA-series was obtained according to a two-step chemical process involving (i) the production of a well-defined mixture of glucosamine (GlcN) oligomers obtained by acid hydrolysis of a fully N-deacetylated chitosan and after selective precipitations of the hydrolysis products, and (ii) the partial N-acetylation of the GlcN units of these oligomers from a hydro-alcoholic solution of acetic anhydride in a controlled manner. The characterization of this series of samples with different DAs by proton nuclear magnetic resonance (1H NMR) spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) allowed us to determine their average DA and identify the main oligomer structures constituting each mixture. Furthermore, MALDI-TOF MS was particularly helpful to study the distribution evolution of the diverse oligomers as a function of DA for the main DPs from 3 to 7. The modeling of these distributions by means of a binomial law displayed that the chemical N-acetylation of low DP GlcN oligomers, produced in a homogeneous medium, occurs randomly along the oligosaccharide chains in accordance with a statistical (Bernoullian) arrangement. In this case, the relative proportion of each chito-oligomer present in the mixture can be estimated precisely as a function of DA considering oligomers of same DP.

Antioxidant and Cancer Cell Proliferation Inhibition Effect of Citrus Pectin-Oligosaccharide Prepared by Irradiation

Pectin was dissolved in deionized distilled water (2%, vol/vol) and irradiated at 20 kGy using a Co-60 gamma ray irradiator. The resulting solution was dialyzed and lyophilized. The samples were separated into three groups to estimate their antioxidant and cancer cell proliferation effects: non-irradiated (0 kGy), irradiated (20 kGy), and dialyzed (20 kGy-F, mol wt <10,000) samples. Antioxidant properties of each treatment was tested by a beta-carotene-linoleic acid bleaching assay and electron donating ability and compared for antioxidant index, which indicated that the activity was higher in the order of 20 kGy-F > 20 kGy > 0 kGy. Spleen cell survival effect of the irradiated pectin (20 kGy) and dialyzed (20 kGy-F) samples was higher than the non-irradiated control (0 kGy). The pectins inhibited growth of the cancer cell in the order of 20 kGy- F > 20 kGy > 0 kGy. The Ames test revealed that none of the fractions was mutagenic, and there was no indication of a dose-dependent response for any of the samples. These results suggest that a functional pectin oligosaccharide can be produced by irradiation for the food industry without any chemical treatment.

Effect of chitooligosaccharides on calcium bioavailability and bone strength in ovariectomized rats

Chitosan polymer with deacetylation degree of 93% was hydrolyzed with an endo-type chitosanase (35,000 U/g protein) with substrate to enzyme ratio of 1 to 1.5 for 18 h in a batch reactor, and then the resultant hydrolysates were fractionated into four different molecular weights using an ultrafiltration (UF) membrane reactor system. An in vitro study elucidated that four kinds of chitooligosaccharides (COSs) could efficiently inhibit the formation of insoluble calcium salts in the neutral pH. In vivo effects of COSs on Ca bioavailability were further studied in the osteoporosis modeling rats induced by ovariectomy and concurrent low calcium intake. During the experimental period corresponding to the menopause with the osteoporosis disease, calcium retention was increased and bone turnover was decreased by COS IV supplementation in the ovariectomized (OVX) rats. After the low Ca diet, COS IV diet including both normal level of calcium and vitamin D significantly decreased calcium loss in feces and increased calcium retention compared to the control diet. The levels of femoral total calcium, bone mineral density (BMD), and femoral strength were also significantly increased by the COS IV diet in a similar level to those of CPP diet group. In the present study, the results proved the beneficial effects of low molecular chitooligosaccharide (COS IV) in preventing negative mineral balance.

Depolymerized products of chitosan as potent inhibitors of tumor-induced angiogenesis

Water-soluble low-molecular weight chitosan (LMWC) and chitooligosaccharides (COs) were obtained from chitosan (16% N-acetylation) by depolymerization induced by potassium persulfate under nitrogen atmosphere for 2 h. They were characterized by IR, X-ray, HPLC and (13)C-NMR. Splitting of C3/C5 signals in the latter indicated a newer conformation, and also showed prominence of acetyl groups in LMWC, may be due to cleavage between two consecutive deacetylated residues. Molecular weight of LMWC, determined by HPSEC, showed a single peak of approximately 37 kDa. HPLC analysis of the solvent-extracted fraction revealed COs enriched with pentamer, hexamer and higher oligomers. The effect of LMWC and COs on the growth of Ehrlich ascites tumor (EAT) cells and tumor-induced neovascularization was studied. COs (50 microg) were more effective compared to LMWC (100 microg) and proved to be potent angioinhibitory and antitumor compounds, as shown by inhibition of angiogenesis and inducing apoptosis as a function of DNA fragmentation.

Kinetics and products of the degradation of chitosan by hydrogen peroxide

Low concentrations of hydrogen peroxide induced random degradation of partially deacetylated chitin and chitosan. Average molecular weight decreased in accordance with first-order kinetics. The degradation rate was much faster than that of the ultrasonic degradation, and it was comparable to that of the enzymatic hydrolysis of chitosan. Chain-end scissions occurred after chitosan was degraded severely and produced significant amounts of oligosaccharides at temperatures > or =80 degrees C. Universal calibration moderated the change in molecular weight more closely than that calculated by the usual calibration using pullulan standards. Trace amounts of transition metal ions and the amino groups in chitosan were critical to the breakdown of the beta-1,4 glycosidic linkages. HPLC results of glucosamine and chito-oligosaccharides could be characterized by correlating the logarithmic values of retention time with the degrees of polymerization. The formation of glucosamine and chito-oligosaccharides depended on the concentration of H(2)O(2), temperature, and the physicochemical property of chitin/chitosan.

Difructose dianhydrides from sucrose and fructo-oligosaccharides and their use as building blocks for the preparation of amphiphiles, liquid crystals, and polymers

Controlled selective protonic activation of the fructosyl moiety in sucrose and fructo-oligosaccharides, with pyridinium poly (hydrogen fluoride) at 20 degrees C, yielded either the kinetic product alpha-D-fructofuranose beta-D-fructofuranose 1,2':2,1'-dianhydride (1), or its thermodynamically more stable isomer alpha-D-fructofuranose beta-D-fructopyranose 1,2':2,1'-dianhydride (2), depending on the hydrogen fluoride-pyridine ratio. A similar reaction was performed with 6,6'-dichloro-6,6'-dideoxysucrose, or 6,6'-dideoxy-6,6'-diiodosucrose, using a slightly higher ratio of HF, resulting in the corresponding 6-deoxy-6-halo-alpha-D-fructofuranose 6'-deoxy-6'-halo-beta-D-fructofuranose 1,2':2,1'-dianhydride derivatives. Both 6,6'-dihalides were converted, upon action of the appropriate nucleophile, into the difructofuranose dianhydride derivatives bearing the 6,6'-di-S-heptyl-6,6'-dithio, 6,6'-diazido-6,6'-dideoxy and then 6,6'-diamino-6,6'-dideoxy functionalities. 6-Chloro-6-deoxy and 6-deoxy-6-iodo derivatives of 2 were also prepared by direct halogenation, and further converted into the 6-S-heptyl-6-thio, 6-azido-6-deoxy and then 6-amino-6-deoxy derivatives of 2. Reaction of chloromethyloxirane with 1 or 2 yielded hydrophilic polymers. The 6,6'-di-S-heptyl-6,6'-dithio derivative of 1 displayed liquid crystal properties. The 6,6'-dideoxy-6,6'-diiodosucrose precursor was prepared by the reaction of Garegg's iodine-imidazole-triphenylphosphine reagent with sucrose in N,N-dimethylformamide solution.