Here we show that the efficacy of the chitosan interaction with diglycidyl ethers of glycols significantly depends on pH and the nature of acid used to dissolve chitosan. In solutions of hydrochloric acid, cross-linking with diglycidyl ethers of ethylene glycol (EGDGE) and polyethylene glycol (PEGDGE) at room and subzero temperatures yields mechanically stable chitosan gels and cryogels, while in acetic acid solutions only weak chitosan gels can be formed under the same conditions. A combination of elemental analysis, FT-IR spectroscopy, and solid state 13 C and 15 N NMR spectroscopy was used to elucidate possible differences in the mechanism of chitosan cross-linking in alkaline and acidic media at room and subzero temperatures. We have proved that in acidic media diglycidyl ethers of glycols interacted with chitosan mainly via hydroxyl groups at the C6 position of the glucosamine unit. Besides, not only cross-linkages but also grafts were formed at room temperature. The cryo-concentration effect facilitates cross-linkages formation at −10 °C and, despite lower modification degrees compared to those of gels obtained at room temperature, supermacroporous chitosan cryogels with Young's moduli up to 90 kPa can be fabricated in one step. Investigations of chitosan cryogels biocompatibility in a mouse model have shown that a moderate inflammatory reaction around the implants is accompanied by formation of a normal granulation tissue. No toxic, immunosuppressive, and sensitizing effects on the recipient's tissues have been observed.

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Bis(N,N-dimethylamino)methane has been shown to be a convenient reagent for the aminomethylation of chlorophyll a derivatives. Methylpheophorbide a (in enol form) and chlorin e 6 13-amides were aminomethylated with bis(N,N-dimethylamino)methane. Reactivity of methylpheophorbide a exo-ring and chlorin e 6 13-amides vinyl group were shown to be different. Selective methylpheophorbide a exo-ring aminomethylation was realized and isomerization of the exo-ring aminomethylation product with rhodochlorin 15-acrylic derivative formation was studied. The action of bis(N,N-dimethylamino)-methane in the presence of weak acid has been shown to be a simple and effective synthetic procedure to obtain a new chlorin e 6 derivative with two N,N-dimethylaminomethyl substituents in the vinyl group. The aminomethylation products' high yields, the simplicity of the procedure, the use of metal-free chlorines and the possible synthesis of new compounds, were found to be the main advantages of using bis(N,N-dimethylamino)methane as an aminomethylation reagent in chlorophyll a derivatives' chemistry.