RESUMO
Layer-by-layer (LbL) multilayer films were prepared using phenylboronic acid-modified poly(amidoamine) dendrimers and poly(vinyl alcohol) (PVA) in order to investigate the glucose sensitivity of the films. We used dendrimer derivatives modified with 3-carboxyphenylboronic acid (3CPBA-D) and 3-carboxy-5-nitrophenylboronic acid (3C5NPBA-D) to evaluate the effect of electron-withdrawing nitro groups on glucose sensitivity. PVA/3CPBA-D and PVA/3C5NPBA-D films were prepared on the surface of a quartz slide from PVA and 3CPBA-D or 3C5NPBA-D solutions at pH 7.0, 8.0, and 9.0 through boronate ester bonds. The dendrimer-based LbL films were stable at pH 7.0-9.0, whereas they decomposed in acidic media because of the instability of the boronate ester linkages. The pH threshold of decomposition was at pH 6.0-7.0 for both films. The PVA/3C5NPBA-D film was more stable than the PVA/3CPBA-D film in this range. Both films decomposed in response to glucose under physiological conditions (pH 7.4 buffer solution containing 150 mM NaCl at 37 °C), and the decomposition depended on the glucose concentration. The PVA/3C5NPBA-D film was more sensitive to glucose than the PVA/3CPBA-D film, probably due to the higher binding affinity of 3C5NPBA-D to glucose under physiological conditions. The higher response of the PVA/3C5NPBA-D film was explained by the electron-withdrawing effect of the nitro substituent on the phenylboronic acid ring. The results suggest that dendrimer-based LbL films could be used for glucose-triggered release systems.
RESUMO
The phenylboronic acids substituted with an azo group on the ortho-position show a significant change in UV-vis spectra upon sugar binding. A new mechanism for the spectral change of the dyes is proposed based on the formation and cleavage of B-N dative bond between boronic acid group and azo group.
