G. G. Allan

Molecular weight manipulation of chitosan. I: Kinetics of depolymerization by nitrous acid.

The kinetics of the depolymerization of chitosan in dilute aqueous HCl solutions by nitrous acid were studied. The rate of depolymerization is independent of the molecular weight of chitosan, first order with respect to the concentrations of both nitrous acid and glucosamine moieties, not catalysed by either hydrogen or chloride ions, and Arrhenius temperature dependent. Chitosan exhibits significantly decreased reactivity as the degree of deacetylation of the polymer increases. These results are consistent with a depolymerization reaction mechanism in which the rate-limiting step is nitrosation of the unprotonated amine by nitrous acidium ion.

BIOMEDICAL APPLICATIONS OF CHITIN AND CHITOSAN

A strategy for the commercialization of chitin and chitosan is outlined starting from the concept that the development of low-volume, high-value speciality applications should precede the creation of high-volume, low-value commodity markets.

Molecular weight manipulation of chitosan II: prediction and control of extent of depolymerization by nitrous acid

Abstract The molecular size of chitosan can be precisely modified by depolymerization with nitrous acid. The stoichiometry and specificity of the reaction, together with the simplicity of the reaction kinetics, provide the basis for derivation of a theoretical expression that relates the number-average molecular weight (Mn) of chitosan before and after depolymerization to the mass ratio of nitrous acid added to chitosan originally present. The simplicity of the expression and the lack of limiting assumptions in its derivation permits its use for the determination of the amount of nitrous acid required to degrade chitosan to a specified molecular weight or for the estimation of the Mn of high molecular weight chitosan. Optimized experimental conditions are identified for quantitative application of the method.

Marine Polymers. IV Diatom Polysaccharides

Introduction The composition and properties äs well äs the commercial Uti l i ty of many of the anionic carbohydrate components of marine algae, such äs carrageenan, alginic acid, and agar are well known (PERCIVAL and McDowELL, 1967; LEVRING et al,5 1969). However, this type of Information is notably lacking for diatoms, a prolific group of the phytoplankton which are easily cultured. A preliminary examination of the polysaccharide constituents of a number of diatom species has therefore been carried out äs part of a program designed to investigate the properties and utillzation of marinederived polymers. The objective of the aspect of the program now reported was to identify and characterize those carbohydrate components which could be secured in high yield äs a prelude to mass culture of potentially suitable diatoms. These macromolecules were arbitrarilv̂ fractionated into three categories: (1) the extracellular water-soluble polymers, (2) the hot water-soluble polyrners lixiviated from alcohol-extracted whole diatoms, and (3) the polymers remaining in water-extracted diatoms.

New bromoperoxidase of marine origin. Partial purification and characterization

Abstract Enzymes capable of catalyzing the bromination of p- hydroxybenzyl alcohol by Br− have been shown to be present in crude homogenates of the alga Rhodomela larix (Rhodophyta). There are also indications of such activity in the marine invertebrates Thelepus setosus and Ptychodera flava laysanica. Detailed analysis of R. larix samples indicated that the activity in this species is greatest in the late spring and summer. After partial purification the enzyme had a pH optimum of approx. 4.4, a temperature optimum around 32°C and was inhibited by NaN3. This algal bromoperoxidase requires the presence of H2O2 and can brominate monochlorodimedon and oxidize iodide, but it cannot oxidize chloride. The enzyme appears to be particulate.

Marine plant polymers : Part III. A kinetic analysis of the alkaline degradation of polysaccharides with specific reference to (1→3)-β-D-glucans

Abstract A general kinetic expression is presented for the rate of alkaline degradation of linear polysaccharides in terms of mono- and di-anionic species formed from the reducing end-groups. Specific rate constants have been determined for the end-wise depolymerization of the (1→3)-β- D -glucans, laminaran, laricinan, and pachyman, and compared with similar data for amylose degradation. The rate constants of degradative chain-propagation via the mono- and di-anion intermediates have been shown to be essentially equal. The effect of the type and concentration of base on the mechanism of end-wise degradation is described for both (1→3)-linked and (1→4)-linked polysaccharides. Inhibition of alkaline degradation is discussed in terms of chain branching and blockage of reducing end-groups.

The stereochemistry of the boswellic acids

Abstract The configuration of the substituents at C(3), C(4), C(5), C(8), C(10), C(13) and C(17) in α- and β-boswellic acids have been shown to be identical by an ursane-oleanane interconversion. Synthetic and dehydration studies of the C(3) epimeric alcohols have confirmed the axial configuration of the hydroxyl group in the boswellic acids and indicated that coplanarity of participating groups need not be an essential requirement for ring contraction. Cyclization reactions of C(3) and C(24) dihydroxy derivatives of the boswellic acids have shown that ring A can readily change from a chair to a boat form to permit cyclic acetalization of trans diaxial hydroxy groups.

Sugar-cellulose composites V. The mechanism of fiber strengthening by cell wall incorporation of sugars

The incorporation of sucrose or some other disaccharides (cellobiose, α-lactose or trehalose) into the cell wall of pulp fibers increases the tearing resistance of the resultant sugar-containing paper relative to that of its sugar-free counterpart, but only when the fiber is well-refined. Maltose and β-lactose do not exhibit this effect. By the use of a high cellulose pulp the increase is shown not to be due to the presence of hemicelluloses. Differential scanning calorimetry indicates that the interaction between the sucrose molecules and the cellulosic fibers changes and becomes more uniform as the fibers are refined. Although the azo dye Congo red bonds strongly with cellulose the analogous reaction with disaccharides and cyclodextrins, established spectrophotometrically, could not be used to predict the physical outcome of the interactions with added disaccharides or cyclodextrins. From a consideration of the stereochemistry of the impregnant disaccharides the augmentation of the fiber strength is attributed to the interlamellar hydrogen bonding of impregnant molecules having hydroxy endgroups in the cis conformation and separated by about 10Å. The incorporation of cyclodextrins further demonstrates that the conformation and the separation distance between the OH groups located in the interlamellar sugar molecule play an important role in strengthening the sugar-impregnated fiber and in augmenting the tearing resistance of sugar-containing papers.

The Mechanism of Adhesion of Phenol-Formaldehyde Resins to Cellulosic and Lignocellulosic Substrates

Abstract The mechanism of adhesion of phenolic resins to cellulosic and lignocellulosic fibers has been explored using a nonpolymerizable bromine-labelled benzyl alcohol as a model for the adhesive. Bromine analysis by neutron activation techniques is sufficiently sensitive to show that reaction occurs much more extensively with the lignified fibers. This is attributed to the formation of covalent linkages between the model adhesive and the guaiacyl units in the lignin. The excellent general performance of phenolic adhesives on cellulose and lignocellulosic substrates can therefore be in part ascribed to the existence of high enthalpy covalent chemical bonds between adherend and adhesive.

Physical Entrapment of Polyelectrolytes within Microporous Solids: the “Jack-in-the-Box” Effect

CATIONIC polymers are strongly adsorbed onto cellulose fibres by mechanisms which are regarded as primarily electrostatic1–5. Unexpectedly, however, the adsorption of polyethyleneimine (PEI) is apparently not completely reversible and this has been attributed to an intimate chain entanglement with polysaccharide molecules which inhibits its elution4,6. We now present evidence for a new general type of physical combination of polymers with microporous solids which is responsible for this apparent irreversible retention of PEI.