ABSTRACT
In this work, first-principles calculations by using density functional theory at the GFN-xTB level, are performed to investigate the relative stability and structural, electronic, and magnetic properties of bimetallic Pt13-nNin (n = 0, 3, 6, 9, 13) nanoclusters by using corrected Hammer and Nørskov model. In addition, by employing the reaction path and the energetic span models, the energy profile and the turnover frequency are calculated to disclose the corresponding reaction mechanism of the water-gas shift reaction catalyzed by these nanoclusters. Our findings render that Ni causes an overall shrinking of the nanocluster's size and misalignment of the spin channels, increasing the magnetic nature of the nanoclusters. Pt7Ni6 nanocluster is the most stable as a result of the better coupling between the Pt and Ni d-states. Pt4Ni9 maintains its structure over the reaction cycle, with a larger turnover frequency value than Pt7Ni6. On the other hand, despite Pt10Ni3 presenting the highest value of turnover frequency, it suffers a strong structural deformation over the completion of a reaction cycle, indicating that the catalytic activity can be altered.
ABSTRACT
A systematic study of the influence of the first coordination sphere over the reactivity and structure of metallo-ß-lactamase (MßL) monozinc model complexes is reported. Three ZnII complexes with tripodal ligands forming the series [Zn(N-NNN)], [Zn(N-NNS)], and [Zn(N-NNO)] where N-NNX represents the tripodal donor atoms were investigated regarding their ability to mimic MßL. The tripodal series was inspired by MßL active sites in the respective subclasses, representing the (His, His, His) Zn1 site present in B1 and B3 subclasses, (His, His, Asp) present in the B3 subclass site and the thiolate present in B1 and B2 sites. The results were supported by electronic structure calculations. XAS analysis demonstrated that the ZnII electronic deficiency significantly changes in the order [Zn(N-NNS)] < [Zn(N-NNN)] < [Zn(N-NNO)]. This effect directly affects the reactivity over nitrocefin and amoxicillin, observed by the hydrolysis kinetics, which follows the same trend. NMR spectroscopy revealed the coordination of the carboxylic group in the substrate to the metal changes accordingly, affecting the hydrolysis kinetics. Our results also demonstrated that not only the Lewis acidity is changed by the ligand system but also the softness of the metal. [Zn(N-NNS)] is softened by the thiolate, promoting the ligand substitution reaction with solvents and favoring a secondary interaction with substrates, not observed for [Zn(N-NNO)]. XRD of the models reveals their similar geometric aspects in comparison to the crystal structure of GOB MßL. The present work demonstrates that the ZnII electronic details must be considered in the design of new MßL models that will further aid in the design of clinically useful inhibitors.