On The Physicochemical Properties Of Sodium Alginate And Preparation Of Its Special Specimens

Sodium alginate,a natural biomolecule,shows special physicochemical properties due to steric structure characterity.Being biodegradable,biocompliance and bioadhesive,alginate has being widely used in the biological and pharmaceutical fields.For better application of alginate,it is necessary that we study its sol-gel mechanism with thermodynamic and spectral methods from the physicochemical properties.Simultaneously,alginate composition showed be determined and preparation of its special samples be studied.Thermodynamics of the interaction of calcium and zinc ions with sodium alginate has been studied by isothermal titration Calorimetry.The results showed that there are two sites when calcium ion complexates with alginate, with K₁=1.21E7(L·mol^-1) ,ΔS₁=141.84(J·mol^-1·K^-1) ,ΔH₁=1.89(kJ·mol^-1) ; K₂=2.90E4(L·mol^-1),ΔS₂=79.08(J·mol^-1·K^-1),ΔH₂=^-1.84(kJ·mol^-1).There is only one site when zinc ion interacts with alginate,with the binding affinity K=9472(L·mol^-1),entropyΔS=128.95(J·mol^-1·K^-1),enthalpyΔH=15.8(kJ·mol^-1).The binding affinity of calcium ion complexating with alginate are greater than zinc ion.The scanning electron microscopy(SEM) micrograph showed that there are more linking points ,smaller cavities,and more septa between the cavities in Zn-alginate gel than in Ca-alginate gel.The steadystate interaction research of calcium and zinc ions with alginate during the sol-gel thransition by circular dichroism,show this process includes the former and latter two phases.During the first linear change scale, the structure of the gel-conjugate of alginate-metal ions is homological before the critical point.The rate and mechanism have the similar change.The research of selectivity,recognition and interactions of calcium and zinc ions with alginate, shows that the interactions of calcium ion with guluronic and mannuronic units are more different than that of zinc ion.The selectivity and recogonition of zinc ion for guluronic and mannuronic units are less than calcium ion.The circular dichroism spectra with temperature of four different composition alginate,combined with X-ray diffraction and 13C-NMR spectra technology,showed that there are functional microdomains in alginate. The functional microdomains formed by guluronate units (G),show order-disorder transitions with temperature.Swelling and shrinking,when alginate gels with divalent cations.For cupric,calcium and zinc ions,the swelling and shrinking degree are related to the cationic properties,such as the ionic radius and bond orbits.Furthermore,swelling and shrinking are reversible.The primary ITC binding sites for alginate interaction with calcium ion correspond to the first linear scale in the CD spectra of intensity variation with calcium-ion concentration.The calcium ions inlay in the"egg-box"cavities,similar with the intramolecular linkage,leading a little decrease for the viscosity.The formation process of the half-egg-box structure and dihelix aggrations ,correspond to the second ITC binding sites.The slope ratio for the second phase are smaller than the first.During this process,the intermolecular linkage are dominating,and the relative viscosity hoiks.Calcium,zinc,cupric ions interact with alginate,their enthalpies and ehtropies show isokinetic relationship,confirming that their interaction mechanisms are the same.Seven oligosaccharides were gained from poly-G-blocks hydrolyzed by guluronate lyase,with yields of 39.5%,22.1%,21.3%,2.2%,2.4%,8.3% and 1.2%,respectively.Structural elucidation showed that only one disaccharide(ΔG,39.5%) and two trisaccharides(ΔGG,22.1%;ΔMG,21.3%) were separated from the mixture.Based on the fact that noΔM,ΔMM orΔGM fractions were separated,we postulated that the hydrolysis mainly occurred between two guluronic acids(-G-G-) making one guluronic acid(G) residue on the reducing end and an unsaturated guluronic acid(Δ) in the nonreducing end.These results proved that the G-lyase was a guluronic acid specific lyase.Furthermore,a very low yield of pentasaccharide(3%) and no trace amount of hexasaccharide indicated that the minimal recognition oligosaccharides of G-lyase should be pentasaccharide.The structure composition of sodium alginate LVCR was analyzed by ¹³C-NMR with Markov(Bernoullian) statistics,the result showed that the amount of G units in alginate LVCR is 39.77%.