Fe3O4-Methylene diphenyl diisocyanate-guanidine (Fe3O4-4,4′-MDI-Gn): A novel superparamagnetic powerful basic and recyclable nanocatalyst as an efficient heterogeneous catalyst for the Knoevenagel condensation and tandem Knoevenagel-Michael-cyclocondensat

Fe3O4@C@MCM41-guanidine core-shell nanostructures as a powerful and recyclable nanocatalyst with high performance for synthesis of Knoevenagel reaction

In this study, preparation, characterization and catalytic application of a novel core-shell structured magnetic with carbon and mesoporous silica shells supported guanidine (Fe₃O₄@C@MCM41-guanidine) are developed. The Fe₃O₄@C@MCM41-guanidine was prepared via surfactant directed hydrolysis and condensation of tetraethyl orthosilicate around Fe₃O₄@C NPs followed by treatment with guanidinium chloride. This nanocomposite was characterized by using Fourier transform infrared spectroscopy, vibrating sample magnetometry, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermal gravimetric analysis, wide-angle X-ray diffraction and low-angle X-ray diffraction techniques. This nanocomposite have high thermal, chemical stability, and uniform size. Fe₃O₄@C@MCM41-guanidine catalyst demonstrated high yield (91-98%) to prepare of Knoevenagel derivatives under the solvent free conditions at room temperature in the shortest time. Also, this catalyst was recovered and reused 10 times without significant decrease in efficiency and stability. Fortunately, an excellent level of yield (98-82%) was observed in the 10 consecutive catalyst cycles.

Effect of Cucurbit[7]uril on Adsorption of Aniline Derivatives at Quartz

The adsorption behavior of small molecules at solid–liquid interfaces have become an important research topic in recent years. For example, small molecules of aniline pollutants will adsorb on solid surfaces with a massive discharge of industrial wastewater and are difficult to separate. Therefore, their adsorption and desorption on solid surfaces have become an important scientific problem. In this study, the interactions of cucurbit[7]uril (Q[7]) with 4,4′-diaminodiphenylmethane (MDA) and benzidine (AN) are studied using 1H NMR, UV-Vis spectrometry and fluorescence spectroscopy. The results show that Q[7] forms an inclusion complex with MDA and AN. According to the results of Quartz Crystal Microbalance with Dissipation (QCM-D), MDA adsorbs onto a quartz surface and forms a viscous adsorption layer on it. The AN adsorbs on the quartz surface and forms a rigid adsorption film on it. Q[7] can reduce the adsorption of MDA on the quartz surface and increases the adsorption of AN on it. Through the dynamic adsorption experiments, we find that Q[7] has a desorption effect on MDA molecules adsorbed on the quartz surface. An Atomic Force Microscope (AFM) is used to measure the morphological changes in the adsorption film before and after Q[7] makes contact with the quartz surface, and it proves that Q[7] has a desorption effect on MDA molecules adsorbed on the surface.

From Neutral Aniline to Aniline Trication: A Computational and Experimental Study

We report density functional theory computations and photoionization mass spectrometry measurements of aniline and its positively charged ions. The geometrical structures and properties of the neutral and singly, doubly, and triply positively charged aniline are computed using density functional theory with the generalized gradient approximation. At each charge, there are multiple isomers closely spaced in total energy. Whereas the lowest energy states of both neutral and cation have the same topology C₆H₅-NH₂, the dication and trication have the C₅NH₅-CH₂ topology with the nitrogen atom in the meta- and para-positions, respectively. We compute the dissociation pathways of all four charge states to NH or NH⁺ and NH₂ or NH₂⁺, depending on the initial charge of the aniline precursor. Dissociation leading to the formation of NH (from the neutral and cation) and NH⁺ (from the dication and trication) proceeds through multiple transition states. On the contrary, the dissociation of NH₂ (from the neutral and cation) and NH₂⁺ (from the dication and trication) is found to proceed without an activation energy barrier. The trication was found to be stable toward abstraction on NH⁺ and NH₂⁺ by 0.96 and 0.18 eV, respectively, whereas the proton affinity of the trication is substantially higher, 1.98 eV. The mass spectra of aniline were recorded with 1300 nm, 20 fs pulses over the peak intensity range of 1 × 10¹³ to 3 × 10¹⁴ W cm^-2. The analysis of the mass spectra suggests high stability of both dication and trication to fragmentation. The formation of the fragment NH⁺ and NH₂⁺ ions is found to proceed via Coulomb explosion.