Calculation of Mark-Houwink-Sakurada (MHS) equation viscometric constants for chitosan in any solvent-temperature system using experimental reported viscometric constants data

Chitosans with high degree of polymerization and molecular weight exhibit poor aqueous solubility which is an impediment in their applicability. The low molecular weight chitosans (LMWCs) and chitooligosaccharides (COSs) can be used to avoid this hurdle. The development of an efficient process for reducing the molecular weight of chitosan, without altering its chemical structure, is of great interest to produce tailormade chitosans of varying Degree of Acetylation (DAs) and Degree of Polymerization (DPs). The production of well-defined COS-mixtures, or even pure COS, is of great interest since these oligosaccharides are thought to have several interesting bioactivities and applications. For this proper delineation of their characteristics is needed. Hence it is our attempt to provide an overview of difffernt methods and techniques of their production and characterization. Several methods viz. depolymerization under the action of reagents, enzymes, high energy impact and combinations thereof have been employed to get COS by depolymerization of high molecular weight chitosans. Acid hydrolysis (hydrochloric, nitrous, phosphoric acid, hydrogen fluoride) and oxidative reductive depolymerization (mediated by peroxide, ozone, and persulfate) are important routes for synthesis of COSs. These oligomers can be produced from chitin or chitosan as a starting material by enzymatic conversions. For this, numbers of enzymes have been used. Depolymerization under high energy impact and recombinant approaches are also being tried for production of COSs. LMWC and COS, like parent chitosan, can be used for drug delivery and gene delivery. The efficient and productive processes are needed for separation of COSs into its components or mixture of defined characters. The characterization of COS can be carried out by chromatographic and spectroscopic techniques. Importantly COSs display an array of biological activities as antimicrobial, anticancer/antimetastatic, wound healing acceleration, immunostimulation, apoptosis induction or inhibiton, antioxidant, enzyme inhibiton, antihyperlipidemic, antidiabetic, chemoprevention, and many more. A few of the biological actions are reported only sporadically where as some are persistently taken up by the scientific fraternity to substantiate the claims and propose possible mechanisms of action. However there remains the disagreement of results on COS activities. The disagreements can arise due to poor and variable reporting of the properties of COS such as used in the studies as molecular weight, degree of acetylation, molecular weight distribution, and the pattern of N-acetylation etc. With production of COS of well defined characters it might be possible to understand the modes of actions of COS in better ways.

Chitooligosaccharides: Synthesis, characterization and applications

We explore the role of crystallinity and inter- or intramolecular forces in chitosan for its solubility in water and demonstrate the expansion of its solubility to a wider pH range. Due to its semicrystalline nature, derived mainly from inter- and intramolecular hydrogen bonds, chitosan is water-soluble only at pH < 6. In acidic conditions, its amino groups can be partially protonated resulting in repulsion between positively charged macrochains, thereby allowing diffusion of water molecules and subsequent solvation of macromolecules. We show that chemical disruption of chitosan crystallinity by partial re-acetylation or physical disruption caused by the addition of urea and guanidine hydrochloride broadens the pH-solubility range for this biopolymer.

Exploring the Factors Affecting the Solubility of Chitosan in Water

Extraction of chitin from prawn shells and conversion to low molecular mass chitosan

Salt-assisted acid hydrolysis of chitosan to oligomers under microwave irradiation.

The kinetic rules for the acidic hydrolysis of chitosan have been studied and the effective rate constants and activation energy of this process have benn calculated. It has shown that in homogeneous conditions, polymer homologues with an average MM of 6000 and above may be formed. The rules for splitting the glycoside bonds of chitosan are described within the framework of a monomolecular A-1 hydrolysis mechanism.

The partial acidic hydrolysis of chitosan

A study was made of the variation of rheological properties of chitosan solutions, according to the concentration of the polymer, the composition and type of solvent, the presence of various low-molecular weight additives (electrolyte, urea, etc.). It was noted that some rheological properties of chitosan solutions in the concentration range studied depend on its polyelectrolyte nature. It was shown that the viscosity variation of chitosan solutions on keeping them over a period of time is not due to the rupture of glycoside bonds of the polymer. It was found that chitosan solutions have the highest stability over a period of time in salt media also containing a hydrogen bond acceptor.

Study of rheological properties of dilute and moderately concentrated solutions of chitosan

Halogenomethylation of styrene and divinylbenzene copolymers

1

The interaction of the iodomethylated copolymer of styrene and divinylbenzene with amides ofα-amino acids was studied, anion exchange resins were produced on the basis of these compounds, and their properties were studied




2

Amphoteric ion exchange resins were produced by hydrolysis of the amide groups on the resin




3

Optically active ion exchange-resins with L-leucinamide and L-leucine as the ionogenic groups were synthesized, and the possibility of separation of racemic amygdalic acid with their aid was demonstrated

S.V. Rogozhin

Papers

The partial acidic hydrolysis of chitosan

Study of rheological properties of dilute and moderately concentrated solutions of chitosan

Halogenomethylation of styrene and divinylbenzene copolymers

Synthesis of optically active ion exchange resins

Synthesis and properties of ion-exchange resins based on α-amino acids and halomethylated styrene-divinyl benzene copolymers☆