Synthesis of diblock copolymers with cellulose derivatives. 3. Cellulose derivatives carrying a single pyrene group at the reducing-end and fluorescent studies of their self-assembly systems in aqueous NaOH solutions

Novel cellobiose and cellulose (DPn=ca. 30) derivatives, N-(1-pyrenebutyloyl)-4-O-(beta-D-glucopyranosyl)beta-D-glucopyranosylamine (6), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-4-O-(beta-D-glueopyranosyl)-beta-D-glucopyranosylamine (7), N-(1-pyrenebutyloyl)-beta-cellulosylamine (13), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-beta-cellulosylamine (14) carrying a pyrene group as a single fluorescent probe at the reducing end, were prepared in order to investigate their self-assembly systems in solutions. The relative intensity of the excimer emission at ca. 480 nm due to dimerized pyrenes (intensity I-E) to the monomer emission at ca. 380 nm due to isolated pyrene (intensity I-M), i.e., I-E/I-M, was monitored in various solutions. In water/dimethyl sulfoxide (DMSO) mixed solvent (0-98%, v/v), the ratio I-E/I-M remained low (0.04) for compound 6 over the range of water concentrations, indicating that pyrenes at C-1 position of compound 6 were diffused. On the other hand, the ratio I-E/I-M increased (0.04-4.96) for compound 7 with the increase in water concentration, indicating that pyrenes at C-1 position were associated. In aqueous NaOH solutions (4.4-17.5%, w/w), compound 14 showed a large increase in the ratio I-E/I-M (0.84-8.14) with the increase in NaOH concentration, compared to compound 13 (0.06-0.41). It was found that the association of hydrophobic groups at the I reducing-end of cellulose could be controlled by the hydrophilic-hydrophobic balance of compounds and the solvent polarity.