No abstract

No abstract

No abstract

No abstract

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.

The synthesis of ethyl butyrate catalyzed by lipases A (CALA) or B (CALB) from Candida antarctica immobilized onto magnetic nanoparticles (MNP), CALA-MNP and CALB-MNP, respectively, is hereby reported. MNPs were prepared by co-precipitation, functionalized with 3-aminopropyltriethoxysilane, activated with glutaraldehyde, and then used as support to immobilize either CALA or CALB (immobilization yield: 100 ± 1.2% and 57.6 ± 3.8%; biocatalysts activities: 198.3 ± 2.7 Up-NPB/g and 52.9 ± 1.7 Up-NPB/g for CALA-MNP and CALB-MNP, respectively). X-ray diffraction and Raman spectroscopy analysis indicated the production of a magnetic nanomaterial with a diameter of 13.0 nm, whereas Fourier-transform infrared spectroscopy indicated functionalization, activation and enzyme immobilization. To determine the optimum conditions for the synthesis, a four-variable Central Composite Design (CCD) (biocatalyst content, molar ratio, temperature and time) was performed. Under optimized conditions (1:1, 45 °C and 6 h), it was possible to achieve 99.2 ± 0.3% of conversion for CALA-MNP (10 mg) and 97.5 ± 0.8% for CALB-MNP (12.5 mg), which retained approximately 80% of their activity after 10 consecutive cycles of esterification. Under ultrasonic irradiation, similar conversions were achieved but at 4 h of incubation, demonstrating the efficiency of ultrasound technology in the enzymatic synthesis of esters.

The study of ceramic materials has attracted the attention of many researchers due to the possibility of their use in nanotechnology. The spinel ferrites form a large group of materials with a broad range of applications. Some examples include electronic devices such as high-frequency transformer cores, antenna rods, induction-tuners, among many others. However, when the ferritic materials display superparamagnetic behavior, their potential for biological applications like drug delivery, hyperthermia, resonance magnetic imaging and magnetic separation, become amazingly high. Therefore, the superparamagnetism is a characteristic strongly desired for spinel ferrites. Since this phenomenon is size-dependent, the methodologies to synthesize these materials has emerged as a crucial step in order to obtain the desired properties. In this regarding, several synthetic processes have been developed. For example, co-precipitation is a fast and cheap method to synthesize superparamagnetic spinel ferrites. However, methodologies involving microwave, ultrasound or polymers frequently result in these kind of materials. Therefore, this review brings a brief historic introduction about spinel ferrites as well as essential concepts to understand their structure and magnetic properties. In addition to this, recent advances in synthesis and applications of the superparamagnetic spinel ferrites are mentioned. Contents of Paper

No abstract