Phase separation, chitin

Chitosan is a polymer produced from hydrolysis of natural chitin. Chitosan is not readily soluble in aqueous solutions, but can be solubilized and is thus considered with other water soluble polymers. In the hydrophobic form, chitosan has been treated in a similar manner to other hydrophobic polymers with microparticles produced by emulsion and phase separation techniques. Microparticles can be taken up by the gastrointestinal lining in a manner similar to that discussed for other hydrophobic microparticles. 

Wang AJ, Cao WL, Gong K et al (2006) Controlling morphology and porosity of 3-D chitosan scaffolds produced by thermally induced phase separation technique. Asian Chitin J 2 69-78... 

Li, J., Revol, J.F., Naranjo, E., Marchessault, R.H. Effect of electrostatic interaction on phase separation behaviour of chitin crystallite suspensions. Int. J. Biol. Macromol. 18, 177-187 (1996a)... 

EL. Mi, Y.M. Lin, Y.B. Wu, S.S. Shyu, and Y. H. Tsai, Chitin/PLGA blend microspheres as a biodegradable drug-delivery system Phase-separation, degradation and release behavior. Biomaterials, 23, 3257-3267, 2002. 

Li, J., Revol, J. F, Naranjo, E., and Marchessault, R. H. (1996]. Effect of Electrostatic Interaction on Phase Separation of Chitin Crystaiiite Suspensions, IntJ. Biol Macromol, 18,177-187. 

Nevertheless, if a gradual increase in temperature is applied, the alkali-chitin solution undergoes phase separation, yielding a dilute (solvent-rich) sol phase and a concentrated (solute-rich) gel phase (see Fig. 2). 

Fig. 2. Alkali chitin in aqueous solution at 20°C and after phase separation-gelation upon heating to 70°C...

The cloud point values thus obtained for alkali chitin solutions in the range 0.15 to 1.5%, clearly describe lower limiting phase separation behaviour, as can be observed from Fig. 4. The lower critical solution temperature (LCST) is apparently located at T = 30°C (1% concentration), where there is a minimum in the cloud point curve. It should be noted the excellent agreement between the three experimental techniques employed at this polymer concentration. 

Later, the same authors [40] investigated the performances of chitin and chitosan beds modified by different metal ions solutions [Cu(II), Co(II), Ni(II), Hg(II), Ag(I)] for the resolution of five racemic amino acids (threonine, alanine, valine, leucine, and phenylglycine). Results showed that only stationary phases of chitin modified by Cu(II) ions may be used for separation of the aforementioned racemates using both binary and ternary mobile phases. In particular, the best results were obtained with methanol/water/acetonitrile mixtures (1 1 0.1, v/v/v) for which D,L-valine showed the highest a-value (a = 12.9) and D,L-phenylglycine the lowest (a = 4.56). 

Few reports exist on the l.c. separation of such cationic carbohydrate oligomers as those resulting from partial hydrolysis of chitosan. The neutral, A -acetylated analogs from chitin hydrolyses are, however, well separated on columns of aminopropyl silica gel and reversed-phase silica gel. ... 

Chitin has been used as the stationary phase to separate mixtures of phenols, amino acids, nucleic acid derivatives, and inorganic ions by thin layer chromatography. Also chitin has been used to prepare affinity chromatography columns to isolate lectins and determine their structure. 

Rodrigues, C. A. Oliveira, A. E. Willain, F. R. Cechinel-Filho, V. Guimaraes, C. L. Yimes, R. A. Delle Monache, F., Separation of biflavonoids from Rheedia gardneriana using chitin-Fe complex as stationary phase, Die Pharmazie, 2000, 55, 699-700. 

Crosslinked chitosan stationary phases were shown to effectively separate PAH mixtures. Chitosan was prepared by deacetylation of the acetylamino groups on chitin extracted from the cell walls of crustaceans. Chitosan, 95% crosslinked with EOAD and packed into a fused-silica... 

Malinowska and Rozylo (103,104) used this method for the enantiomeric separation of amino acids with different solvent systems, e.g. methanol, ethanol, or ternary mobile phases of methanol-water-acetonitrile mixtures. Beside many interesting separations their results show some absurdities, because the nonenantiomeric glycine was also separated into two compounds Also, the authors mentioned, that separated amino acid enantiomers were detected in two spots with different colors. Normally separated enantiomers will show identical colors when detected on the plate. Nevertheless, chitin seems to be a very interesting sorbent for enantiomeric separation. 

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