Toshihiro Seo

Sorption Behavior of Chemically Modified Chitosan Gels

The chemical modification of chitosan by acylation of the amino group with various carboxylic anhydrides was performed to introduce a new functionality. The state of water in N-acylated chitosan gels was studied by DSC technique. The amounts of two states of water, freezable and nonfreezable water, were found to depend on the chemical and physical structure of the gels. The interaction between chitosan and its acyl (octanoyl, dodecanoyl, octadecanoyl and benzoyl) derivatives and the dyes carrying the ionic, hydrophilic and hydrophobic nature was discussed in detail. The sorption isotherms were interpreted by means of a dual mechanism which comprises partition and Langmuir sorption modes. The dyes having -OH, -N(C4H9)2, and a naphthalene nucleus show a remarkable increase of the equilibrium sorption compared with that of Methyl Orange. The contribution of the electrostatic, hydrophobic and hydrogen bonding interaction in the sorption was discussed. On the other hand, the sorption of D, L-amino acids by chitosan gels with hydrophobic group was investigated under various conditions. The L-amino acis are sorbed to a greater extent than their isomers, which suggests that chemically modified chitosan gels are able to separate D, L-amino acids.

Ester hydrolysis by poly(allylamine)s having hydrophobic groups : Catalytic activity and substrate specificity

Abstract The hydrolysis of phenyl esters having anionic, hydrophobic, and stereoisomeric groups by poly(allylamine)s (I) with various hydrophobic groups was investigated. The derivatives of I with dodecyl and benzyl groups (IIc and III) form a hydrophobic microdomain near the catalytic site. For I, the hydrolysis rate of 4-acetoxy-3-nitro-benzoic acid is extremely high, indicating a significant contribution of the electrostatic effect. IIc (degree of substitution, DS ≧ 0.12) and III (DS ≧ 0.48) have a considerable large catalytic activity for the more hydrophobic substrates than p-nitrophenyl acetate. The reaction mechanism was found to be of the Michaelis-Menten type. According to kinetic and thermodynamic analysis, it was found that the lower polarity (E T ≈ 55) and compact structure lead to effective hydrophobic interaction and high substrate binding, resulting in enhancement of the catalytic activity. In the case of III (DS = 0.75), it was suggested that the substrate should be bound and fixed in the ...