Synthesis and Catalytic Properties of Silver Nanoparticle–Linear Polyethylene Imine Colloidal Systems

The excellent catalytic properties of colloidal metal nanoparticles (M-NPs), such as good selectivity, efficiency, and recyclability, have attracted great interest in academic and industrial research. However, new M-NP stabilizers/supports still need to be developed and their performance needs to be better understood. Herein, we report an approach for effectively combining a high-throughput method using linear polyethylene imine (LPEI) with <i>in situ</i> screening and multivariate optimization of the synthesis conditions to produce highly catalytically stable Ag-NPs. Selected Ag-NP/stabilizers were able to efficiently catalyze the <i>p</i>-nitrophenol (Nip) reduction by NaBH₄ in water with a rate constant normalized to the surface area of the nanoparticles per unit volume (<i>k</i>₁) up to 1.66 s^–1 m^–2 L. A full kinetic analysis based on the Langmuir model indicates that the Nip molecules have a much stronger adsorption affinity than BH₄^– ions for the Ag-NP surface and all species are likely adsorbed and accommodated on the surface before they take part in any reaction

Mechanism of a Suzuki-Type Homocoupling Reaction Catalyzed by Palladium Nanocubes

The <i>trans</i>-2-phenylvinylboronic acid homocoupling reaction catalyzed by palladium nanocubes (Pd-NCs) was investigated by kinetics, spectroscopy, and poisoning experiments. The reaction was evidenced to be sensitive to the presence of the base, which acts synergistically with the substrate molecules and assists the leaching of Pd oxide (PdO_<i>x</i>) species to the reaction medium. This species catalyzes the homocoupling reaction through the formation of Pd–O_<i>x</i>–B­(OH)₂R pretransmetalation intermediates, via coordination with the vinylboronic acid molecules, involving an <i>oxo-palladium</i>-type interaction. The reaction rate was not enhanced by the saturation of the reaction medium with O₂, which is due to the oxidized nature of the Pd-NC surface

Screening the Formation of Silver Nanoparticles Using a New Reaction Kinetics Multivariate Analysis and Assessing Their Catalytic Activity in the Reduction of Nitroaromatic Compounds

On the basis of <i>in situ</i> selection utilizing a reaction kinetics parameter, a new and straightforward method for screening the formation of catalytically active silver-PVP nanoparticles is reported. The method utilizes a multivariate analysis for the optimization of the reactant concentrations in the synthesis of nanoparticles with an analytical response based on the ability of the nanoparticles formed to catalyze the reduction of <i>p</i>-nitrofenol <i>in situ</i>. The best synthetic conditions were selected, the nanoparticles fully characterized, and their catalytic properties with regard to the reduction of five nitroaromatic compounds, possessing different substituents at the <i>para</i> position, were determined. The kinetics analysis was based on the Langmuir–Hinshelwood semi-heterogeneous model. The results showed the greater ability of substrates to adsorb onto the nanoparticle surface compared with that of borohydride ions and that the substrates possessing an electron-withdrawing substituent are more catalytically favored. These differences are discussed in terms of substrate adsorption and of a linear free-energy relationship based on the Hammett plot

Second-Coordination-Sphere Effects Increase the Catalytic Efficiency of an Extended Model for Fe^IIIM^II Purple Acid Phosphatases

Herein we describe the synthesis of a new heterodinuclear Fe^IIICu^II model complex for the active site of purple acid phosphatases and its binding to a polyamine chain, a model for the amino acid residues around the active site. The properties of these systems and their catalytic activity in the hydrolysis of bis­(2,4-dinitrophenyl)­phosphate are compared, and conclusions regarding the effects of the second coordination sphere are drawn. The positive effect of the polymeric chain on DNA hydrolysis is also described and discussed

Second-Coordination-Sphere Effects Increase the Catalytic Efficiency of an Extended Model for Fe^IIIM^II Purple Acid Phosphatases

Herein we describe the synthesis of a new heterodinuclear Fe^IIICu^II model complex for the active site of purple acid phosphatases and its binding to a polyamine chain, a model for the amino acid residues around the active site. The properties of these systems and their catalytic activity in the hydrolysis of bis­(2,4-dinitrophenyl)­phosphate are compared, and conclusions regarding the effects of the second coordination sphere are drawn. The positive effect of the polymeric chain on DNA hydrolysis is also described and discussed

Theoretical and Experimental Investigation of Acidity of the Glutamate Receptor Antagonist 6,7-Dinitro-1,4-dihydroquinoxaline-2,3-dione and Its Possible Implication in GluA2 Binding

The acidity of organic compounds is highly relevant to understanding several biological processes. Although the relevance and challenges in estimating p<i>K</i>_a values of organic acids is recognized by several reported works in the literature, there is a lack in determining the acidity of amides. This paper presents an experimental/theoretical combined investigation on the acid dissociation of the compound 6,7-dinitro-1,4-dihydroquinoxaline-2,3-dione (DNQX), a well-established antagonist of ionotropic glutamate receptor GluA2. DNQX was synthesized, and its two acidic constants were determined by UV–vis spectroscopy. The experimental p<i>K</i>_a of 6.99 ± 0.02 and 10.57 ± 0.01 indicate that DNQX mainly exists as an anionic form (DNQXA1) in physiological media, which was also confirmed by ¹H NMR analysis. Five computational methods were applied for estimating the theoretical p<i>K</i>_a values of DNQX, including B3LYP, M06-2X, ωB97XD, and CBS-QB3, which were able to provide reasonable estimates for p<i>K</i>_a associated with DNQX. Molecular dynamics studies have demonstrated that DNQXA1′ binds more effectively to the pocket of the GluA2 than neutral DNQX, and this fact is coherent to the interactions between amidic oxygens and Arg845 being the main interactions of this host–guest system. Moreover, interaction of GluA2 with endogenous glutamate is stronger than that with DNQXA1, which is in agreement with literature. To the best of our knowledge, we report herein an unprecedented approach involving acidity of the antagonist DNQX, as well as the possible implications in binding to GluA2