Vanillin crosslinked chitosan films: The states of water and the effect of carriers on curcumin uptake.

In this work, chitosan chains were crosslinked with different contents of vanillin (Van), characterized and loaded with curcumin (CUR), a hydrophobic drug. Sodium dodecyl sulfate (SDS), Tween 20® (T20) and ß-cyclodextrin (ßCD) were used as curcumin carriers. Films prepared with Van 20 % yielded gel content of 70 %, swelling degree of ~23 gwater/g, bound water and capillary water, as revealed by Time-Domain Nuclear Magnetic Resonance measurements. Films prepared with higher Van contents showed small swelling degree (< 1.6 gwater/g) and hydrophobicity, making them inadequate for drug loading. UV-Vis and fluorescence spectroscopic studies indicated that Van 20 % combined with SDS and SDS/ßCD presented the highest CUR uptake (~3.0 mg/g), favored by electrostatic interactions and hydrophobic interactions. CHI and Van 20 % films did not present any cytotoxicity in human neuroblastoma SH-SY5Y cells. At pH 1.0 the films were completely soluble, pointing to their potential application as gastric delivery systems for hydrophobic drugs. Chemical compounds studied in the manuscript: Chitosan, vanillin, curcumin, ß-cyclodextrin, sodium dodecyl sulfate, polyethylene glycol sorbitan monolaurate.

Tyrosinase enzyme Langmuir monolayer: Surface chemistry and spectroscopic study.

This study investigates the surface chemistry properties of the tyrosinase enzyme Langmuir monolayer at air-aqueous interface using sodium chloride in the subphase to induce the surface activity of the enzyme. Investigation of surface packing and stability of the tyrosinase Langmuir monolayer were performed using surface chemistry experiments while spectroscopic analysis was done to study enzyme conformation. It was found that the tyrosinase enzyme forms a fluid film at air-aqueous interface with good stability as shown by compression-decompression cycles experiments and stability measurements at various surface pressures. UV-vis absorption and fluorescence measurements at different surface pressures revealed that the Langmuir monolayer has good homogeneity with no evidence of aggregates during compression. To gain insight on the conformation of tyrosinase Langmuir monolayer p-polarized infrared-reflection absorption spectroscopy was used. It was found that at high surface pressures the predominant secondary structures were ß-sheets while at lower surface pressure both α -helices and ß-sheets were present. The circular dichroism spectra were obtained by transferring the Langmuir monolayer at 10 mN.m-1 to a solid quartz support (Langmuir-Blodgett film, LB film), which showed that the major conformation present were α-helices. Images from the immobilized LB films were obtained using atomic force microscopy which showed homogenous and regular deposition with a mean thickness ranging from 3 to 4 nm.