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Two series of new chitosan derivatives were synthesized by reaction of deacetylated chitosan (CH) with propyl (CH-Propyl) and pentyl (CH-Pentyl) trimethylammonium bromides to obtain derivatives with increasing degrees of substitution (DS). The derivatives were characterized by (1)H NMR and potentiometric titration techniques and their antifungal activities on the mycelial growth of Aspergillus flavus were investigated in vitro. The antifungal activities increase with DS and the more substituted derivatives of both series, CH-Propyl and CH-Pentyl, exhibited antifungal activities respectively three and six times higher than those obtained with commercial and deacetylated chitosan. The minimum inhibitory concentrations (MIC) were evaluated at 24, 48 and 72 h by varying the polymer concentration from 0.5 to 16 g/L and the results showed that the quaternary derivatives inhibited the fungus growth at polymer concentrations four times lower than that obtained with deacetylated chitosan (CH). The chitosans modified with pentyltrimethylammonium bromide exhibited higher activity and results are discussed taking into account the degree of substitution (DS).

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Electrochemical sensing depends on the immobilization of biorecognition elements and charge transfer to the electrode, which can be tuned and sometimes controlled using self-assembled monolayers (SAMs) as matrices. In this study, we show that an efficient immobilization of an ssDNA probe to detect the prostate cancer antigen 3 biomarker is achieved even for less organized SAMs provided that the terminal groups were ionized. These conclusions were reached by comparing the biosensors made with 11mercaptoundecanoic acid (11-MUA) prepared in ethanol and thioglycolic acid (mercaptoacetic acid: MAA) prepared in ethanolic and aqueous solvents. The highest sensitivity with electrochemical impedance spectroscopy was observed for sensors assembled over MAA monolayers on gold prepared in ethanol and water (at pH 12.5), with limits of detection of 1.2 × 10 −9 and 1.7 × 10 −9 mol L −1 , respectively. The biosensors made on MAA films prepared in water at pH 7.0 and 2.5 were not efficient because they are mostly terminated by protonated carboxylic acid groups, according to sum-frequency generation vibrational and polarization modulationinfrared reflection-absorption (PM-IRRAS) spectroscopies, which prevent an adequate attachment of the biomarker. Well-organized SAMs of 11-MUA also showed good detection performance, but the limit of detection was not as low, 2.1 × 10 −9 mol L −1 , probably due to its long chains that decrease the charge transfer. Therefore, the matrix fabrication method can control the molecular assembly of biosensors and hence their performance.

Amphiphilic chitosans, which may self-assemble in aqueous solution to form nanoaggregates with different conformations depending to the environmental pH, can be used as drug transport and delivery agents, when the target pH differs from the delivery medium pH. In this study, quercetin, a bioactive flavonoid, was encapsulated in a pH-responsive system based on amphiphilic chitosan. The hydrophilic reagent 2-chloro-N,N-diethylethylamine hydrochloride (DEAE), also known to inhibit the proliferation of cancer cells, was used as a grafting agent. Drug loading experiments (DL ∼5%) showed a quercetin entrapment efficiency of 73 and 78% for the aggregates. The sizes of blank aggregates measured by dynamic light scattering (DLS) varied from 169 to 263nm and increased to ∼410nm when loaded with quercetin. The critical aggregation concentration, zeta potential and morphology of the aggregates were determined. pH had a dominant role in the release process and Fickian diffusion was the controlling factor in drug release according to the Korsmeyer-Peppas mathematical model. In vitro studies indicated that the DEAE-modified chitosan nanoaggregates showed a synergistic effect with quercetin on the control of the viability of MCF-7 cells. Therefore, DEAE-modified chitosan nanoaggregates with pH-sensibility can be used as optimized nanocarriers in cancer therapy.

Low molecular weight amphiphilic derivatives of chitosan were synthesized, characterized and their antifungal activities against Aspergillus flavus and Aspergillus parasiticus were tested. The derivatives were synthesized using as starting material a deacetylated chitosan sample in a two step process: the reaction with propyltrimethyl-ammonium bromide (Pr), followed by reductive amination with dodecyl aldehyde. Aiming to evaluate the effect of the hydrophobic modification of the derivatives on the antifungal activity against the pathogens, the degree of substitution (DS1) by Pr groups was kept constant and the proportion of dodecyl (Dod) groups was varied from 7 to 29% (DS2). The derivatives were characterized by 1H-NMR and FTIR and their antifungal activities against the pathogens were tested by the radial growth of the colony and minimum inhibitory concentration (MIC) methods. The derivatives substituted with only Pr groups exhibited modest inhibition against A. flavus and A. parasiticus, like that obtained with deacetylated chitosan. Results revealed that the amphiphilic derivatives grafted with Dod groups exhibited increasing inhibition indexes, depending on polymer concentration and hydrophobic content. At 0.6 g/L, all amphiphilic derivatives having from 7.0 to 29% of Dod groups completely inhibited fungal growth and the MIC values were found to decrease from 4.0 g/L for deacetylated chitosan to 0.25–0.50 g/L for the derivatives. These new derivatives open up the possibility of new applications and avenues to develop effective biofungicides based on chitosan.