RESUMO
Nowadays, there are several approaches reported to accomplish the green synthesis of metal nanoparticles by using bacterial and fungi supernatants or by-products generated by these microorganisms. Therefore, agars as solely reductive regents have started to be used in order to obtain metal nanoparticles. This paper shows the results of the synthesis of gold and silver nanoparticles with different morphology, mainly triangular and truncated triangular, using Eosin Methylene Blue (EMB) agar as reducing agent. To control the reaction process, the necessary activation energy for the reducer was provided by three different techniques: microwave radiation, using a domestic microwave oven, ultraviolet radiation, and heating on a conventional plate. The evolution of the reduction process and stability of the samples was performed by ultraviolet visible spectroscopy. Morphology was carefully analyzed using high-resolution transmission electron microscopy (HRTEM) and Transmission electron microscopy (TEM). A one step synthesis for gold and silver nanoparticles was optimized with an eco-friendly and economic process.
RESUMO
Gold nanoparticles (AuNPs) stabilized by imidazolium salts derived from amino acids [glycine (1), rac-alanine (2), l-phenylalanine (3), and rac-methionine (4)] were prepared. The AuNPs were stabilized the most by 4, which kept the particles dispersed in water for months at pH > 5.5. These AuNPs exhibited a well-defined absorption band at 517 nm and had an average particle size of 11.21 ± 0.07 nm. The 4-AuNPs were reversibly aggregated by controlling the pH of the solution. Chiral R,R-4-AuNPs and S,S-4-AuNPs were synthesized, and the chiral environment on the nanoparticle surface was confirmed using circular dichroism; these nanoparticles exhibited a molecular recognition of chiral substrates. Furthermore, they showed potential for separating racemic mixtures when supported on a layered double hydroxide.
RESUMO
Organoaluminium(III) thioetherbis(phenolate) complexes derived from 2,2-thiobis(4,6-diterbuthylphenolate) (Stdiol) and 2,2-thiobis(4,6-dimethylphenolate) (Smdiol) were prepared by reaction of AlMe3 with the diol proligands LH2 (SmdiolH2, StdiolH2). Monomeric complexes of general formulae [LAlR(L)] (L = Stdiol, R = Me, L = THF (1); L = Stdiol, R = Me, L = Et2O (2); L = Stdiol, R = iBu, L = THF) (3); L = Smdiol, R = Me, L = THF (4); L = Smdiol, R = iBu, L = THF (5)) and [LAlCl(THF)] (L = Stdiol (6); L = Smdiol (7)) were obtained when the reactions were performed in THF or Et2O in hexane or toluene, species of formulae [(L2Al)AlR2] (L = Stdiol, R = Me (8); L = Stdiol, R = iBu (9); L = Smdiol, R = Me (10)) were formed as evidenced by spectroscopic methods. Crystals suitable for X-ray diffraction studies were obtained for 2, 3, 4, 6, 8, 9 and 10. In these cases the sulfur atom coordinates to the aluminium center with Al-S bond lengths between 2.43-2.75 A adopting boat-boat conformations. Compounds 1, 3, 4, and 8 were tested in the catalytic Diels-Alder cycloaddition reaction between methacrolein and cyclopentadiene showing excellent regioselectivities with good conversion yields.
RESUMO
The pyrazolato complexes [(Me(2)pz)(THF)Li] (1), [((t)Bu(2)pz)Li](4) (2), [((t)Bu(2)pzH)((t)()Bu(2)pz)Li](2) (2a), [(Me(2)pz)Na] (3), [((t)Bu(2)pz)Na](4), [((t)Bu(2)pz)(6)(OH)Na(7)] (4a), [((t)Bu(2)pz)(18-crown-6)Na] (4b), and [((t)Bu(2)pz)K] (5) were synthesized by metalation reactions between R(2)pzH (R = Me, (t)()Bu) and alkyllithium, elemental sodium, or potassium. All the complexes were characterized by spectroscopic methods and microanalysis, and in addition, the crystal structures of 2, 2a, 3, 4a, 4b, and 5 were obtained by single-crystal X-ray diffraction. They show monomeric, dimeric, cluster, and 1D chain structures in the solid state. Ab initio calculations on the structure and stabilities of the monomeric pzM complexes were performed at the MP2 level of theory showing good agreement with the coordination preferences of the pyrazolato ligand to a particular alkali ion.
