Chitosan-based magnetite nanocomposites were synthesized using a versatile ultrasound assisted in situ method involving one quick step. This synthetic route approach results in the formation of spheroidal nanoparticles (Fe3O4) with average diameter between 10 and 24nm, which were found to be superparamagnetic with saturation magnetization (Ms) ranges from 32-57emug(-1), depending on the concentration. The incorporation of Fe3O4 into chitosan matrix was also confirmed by FTIR and TG techniques. This hybrid nanocomposite has the potential application as electrochemical sensors, since the electrochemical signal was excepitionally stable. In addition, the in situ strategy proposed in this work allowed us to synthesize the nanocomposite system in a short time, around 2min of time-consuming, showing great potential to replace convencional methods. Herein, the procedure will permit a further diversity of applications into nanocomposite materials engineering.

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In this communication, lipase A from Candida antarctica (CALA) was immobilized by covalent bonding on magnetic nanoparticles coated with chitosan and activated with glutaraldehyde, labelled CALA-MNP, (immobilization parameters: 84.1% ± 1.0 for immobilization yield and 208.0 ± 3.0 U/g ± 1.1 for derivative activity). CALA-MNP biocatalyst was characterized by X-ray Powder Diffraction (XRPD), Fourier Transform Infrared (FTIR) spectroscopy, Thermogravimetry (TG) and Scanning Electron Microscope (SEM), proving the incorporation of magnetite and the immobilization of CALA in the chitosan matrix. Besides, the immobilized biocatalyst showed a half-life 8–11 times higher than that of the soluble enzyme at pH 5–9. CALA showed the highest activity at pH 7, while CALA-MNP presented the highest activity at pH 10. The immobilized enzyme was more active than the free enzyme at all studied pH values, except pH 7.

Residual oil from babassu (Orbignya sp.), a low-cost raw material, was used in the enzymatic esterification for biodiesel production, using lipase B from Candida antarctica (Novozym® 435) and ethanol. For the first time in the literature, residual babassu oil and Novozym® 435 are being investigated to obtain biodiesel. In this communication, response surface methodology (RSM) and a central composite design (CCD) were used to optimize the esterification and study the effects of four factors (molar ratio (1:1–1:16, free fatty acids (FFAs) /alcohol), temperature (30–50 °C), biocatalyst content (0.05–0.15 g) and reaction time (2–6 h)) in the conversion into fatty acid ethyl esters. Under optimized conditions (1:18 molar ratio (FFAs/alcohol), 0.14 g of Novozym® 435, 48 °C and 4 h), the conversion into ethyl esters was 96.8%. It was found that after 10 consecutive cycles of esterification under optimal conditions, Novozym® 435 showed a maximum loss of activity of 5.8%, suggesting a very small change in the support/enzyme ratio proved by Fourier Transform Infrared (FTIR) spectroscopy and insignificant changes in the surface of Novozym® 435 proved by scanning electron microscopy (SEM) after the 10 consecutive cycles of esterification.

Functionalized Fe3O4 nanoparticles (NPs) have emerged as a promising contrast agent for magnetic resonance imaging (MRI). Their synthesis and functionalization methodology strongly affect their performance in vivo. The methodology most used in the literature for the synthesis of Fe3O4 NPs is thermal decomposition, which has proven to be time-consuming, expensive, and laborious, as it requires further ligand exchange strategies to transfer the as-synthesized nanoparticles from organic to aqueous solvents. This work describes a rapid and facile sonochemical methodology to synthesize and functionalize Fe3O4 NPs with excellent physicochemical properties for MRI. This sonochemistry approach was used to produce, in 12 min, Fe3O4 NPs functionalized with polysodium acrylate (PAANa), trisodium citrate (CIT), branched polyethylenimine (BPEI), and sodium oleate. X-ray diffraction and transmission electron microscopy demonstrated that the NPs were composed of a single inverse spinel phase with an average diameter of 9–11 nm and a narrow size distribution. Mössbauer spectroscopy and magnetic measurements confirmed that the obtained NPs were transitioning to the superparamagnetic regime and possessed excellent magnetization saturation values (59–77 emu/g). Fourier transform infrared spectroscopy proved that the sonochemistry approach provided conditions that induced a strong interaction between Fe3O4 and the coating agents. Furthermore, dynamic light-scattering experiments evidenced that samples coated with PAANa, CIT, and BPEI possess colloidal stability in aqueous solvents. Emphasis must be placed on PAANa-coated NPs, which also presented remarkable colloidal stability under simulated physiological conditions. Finally, the obtained NPs exhibited great potential to be applied as an MRI contrast agent. The transverse relaxivity values of the NPs synthesized in this work (277–439 mM–1 s–1) were greater than those of commercial NPs and those prepared using other methodologies. Therefore, this work represents significant progress in the preparation of Fe3O4 NPs, providing a method to prepare high-quality materials in a rapid, cost-effective, and facile manner.

In this work, chitosan/magnetite nanoparticles (ChM) were quickly synthesized according to our previous report based on co-precipitation reaction under ultrasound (US) irradiation. Besides ChM was in-depth structurally characterized, showing a crystalline phase corresponding to magnetite and presenting a spheric morphology, a “nanorod”-type morphology was also obtained after increasing reaction time for eight minutes. Successfully, both morphologies presented a nanoscale range with an average particle size of approximately 5–30 nm, providing a superparamagnetic behavior with saturation magnetization ranging from 44 to 57 emu·g−1. As ChM nanocomposites have shown great versatility considering their properties, we proposed a comparative study using three different amine-based nanoparticles, non-surface-modified and surface-modified, for removal of azo dyes from aqueous solutions. From nitrogen adsorption–desorption isotherm results, the surface-modified ChMs increased the specific surface area and pore size. Additionally, the adsorption of anionic azo dyes (reactive black 5 (RB5) and methyl orange (MO)) on nanocomposites surface was pH-dependent, where surface-modified samples presented a better response under pH 4 and non-modified one under pH 8. Indeed, adsorption capacity results also showed different adsorption mechanisms, molecular size effect and electrostatic attraction, for unmodified and modified ChMs, respectively. Herein, considering all results and nanocomposite-type structure, ChM nanoparticles seem to be a suitable potential alternative for conventional anionic dyes adsorbents, as well as both primary materials source, chitosan and magnetite, are costless and easily supplied.

Silver nanoparticles (AgNPs) have several technological applications and may be synthetized by chemical, physical and biological methods. Biosynthesis using fungi has a wide enzymatic range and it is easy to handle. However, there are few reports of yeasts with biosynthetic ability to produce stable AgNPs. The purpose of this study was to isolate and identify soil yeasts (Rhodotorula glutinis and Rhodotorula mucilaginosa). After this step, the yeasts were used to obtain AgNPs with catalytic and antifungal activity evaluation. Silver Nanoparticles were characterized by UV-Vis, DLS, FTIR, XRD, EDX, SEM, TEM and AFM. The AgNPs produced by R. glutinis and R. mucilaginosa have 15.45 ± 7.94 nm and 13.70 ± 8.21 nm (average ± SD), respectively, when analyzed by TEM. AgNPs showed high catalytic capacity in the degradation of 4-nitrophenol and methylene blue. In addition, AgNPs showed high antifungal activity against Candida parapsilosis and increase the activity of fluconazole (42.2% for R. glutinis and 29.7% for R. mucilaginosa), while the cytotoxicity of AgNPs was only observed at high concentrations. Finally, two yeasts with the ability to produce AgNPs were described and these particles showed multifunctionality and can represent a technological alternative in many different areas with potential applications.

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