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The high catalytic activity of Pt is accompanied by a high affinity for CO, making it extremely susceptible to poisoning. Such CO poisoning limits the use of proton exchange membrane fuel cells. In this work, using global minima search techniques and exhaustive electronic structure characterization, the dopant concentration is pinpointed as a crucial factor to improve the CO tolerance of Pt catalysts. By investigating the PtGe nanoclusters of different sizes and compositions, we found that, for those clusters with roughly the same amount of Pt and Ge, the binding to CO is weakened significantly. The uniqueness of the PtGe equimolar clusters is traced down to the electronic effects. The strong covalency and electrostatic stabilization arising from the advantageous Pt–Ge mixing make the equimolar clusters highly resistant toward CO poisoning and therefore more durable. Importantly, the novel catalysts not only are more resistant to deactivation but also remain catalytically active toward hydrogen oxidation. Representative clusters are additionally deposited on graphene with a pentagon–octagon–pentagon (5-8-5) reconstructed divacancy. The remarkable results of free-standing clusters hold true for surface mounted clusters, in which the interaction with CO is dramatically weakened for those compounds with a Pt:Ge ratio of 1:1. Our results demonstrate that Ge can be a promising alloying agent to mitigate the deactivation of Pt and that the dopant concentration is a critical factor in the design of advanced catalysts. [ABSTRACT FROM AUTHOR]

Control of CO emissions raises serious environmental concerns in the current chemical industry, as well as in nascent technologies based on hydrogen such as electrolyzers and fuel cells. As for now, Pt remains one of the state‐of‐the‐art catalysts for the CO oxidation reaction, but unfortunately, it suffers from CO self‐poisoning. Recently, Pt−Ge alloys were proposed to be an excellent alternative to reduce CO poisoning. This work investigates the impact of Ge content on the CO oxidation kinetics of Pt4Gen subnanoclusters supported on MgO. A Ge concentration dependence of the reaction kinetics is found due to a strong synergy between Pt and Ge. Pt−Ge nanoalloys act as a bifunctional catalyst by displaying dual adsorption sites; i. e., CO is adsorbed on Pt whereas oxygen binds to Ge, forming an alternative oxygen source GeOx. Besides, Ge alloying modifies the electronic structure of Pt (ligand effects) and reduces the affinity to CO. In this way, the competition between CO and O2 adsorption and the overbinding of CO is alleviated, achieving a CO poisoning‐free kinetic regime. Our calculations suggest that Pt4Ge3 is the optimal catalyst, evidencing that alloying composition is a parameter of extreme importance in nanocatalyst design. The work relies on global optimization search techniques to determine the accessibility of multiple structures at different conditions, mechanistic studies and microkinetic modeling. [ABSTRACT FROM AUTHOR]

Transition metals directly contribute to the neurotoxicity of the aggregates of the amyloid-forming Aβ peptide. The understanding and rationalization of the coordination modes of metals to Aβ amyloid is, therefore, of paramount importance to understand the capacity of a given metal to promote peptide aggregation. Experimentally, multiple Aβ–metal structures have been resolved, which exhibit different modes of coordination in both the monomeric and oligomeric forms of Aβ. Although Zn(II) metalloproteins are very abundant and often involve cysteine residues in the first coordination shell, in the case of Aβ–Zn(II), though, Zn(II) is coordinated by glutamic/aspartic acid and/or histidine residues exclusively, making for an interesting case study. Here we present a systematic analysis of the underlying chemistry on Aβ–Zn(II) coordination, where relative stabilities of different coordination arrangements indicate that a mixture of Glu/Asp and His residues is favored. A detailed comparison between different coordination shell geometries shows that tetrahedral coordination is generally favored in the aqueous phase. Our calculations show an interplay between dative covalent interactions and electrostatics which explains the observed trends. Multiple structures deposited in the Protein Data Bank support our findings, suggesting that the trends found in our work may be transferable to other Zn(II) metalloproteins with this type of coordination. [ABSTRACT FROM AUTHOR]

In this work, we have computed and implemented one‐body integrals concerning Gaussian confinement potentials over Gaussian basis functions. Then, we have set an equivalence between Gaussian and Hooke atoms and we have observed that, according to singlet and triplet state energies, both systems are equivalent for large confinement depth for a series of even number of electrons n = 2, 4, 6, 8 and 10. Unlike with harmonic potentials, Gaussian confinement potentials are dissociative for small enough depth parameter; this feature is crucial in order to model phenomena such as ionization. In this case, in addition to corresponding Taylor‐series expansions, the first diagonal and sub‐diagonal Padé approximant were also obtained, useful to compute the upper and lower limits for the dissociation depth. Hence, this method introduces new advantages compared to others. [ABSTRACT FROM AUTHOR]

Density functional theory is used in combination with dielectric continuum methods to estimate the pK(sub a) values for a series of twisted amides. Mechanistic implications of the change in basicity of the nitrogen as a function of the twist of the amide bond for the activation of C-N bond hydrolysis are discussed.

The time-dependent density-functional theory (TDDFT) is required to know the excitation energies of the universally minutest of miniature ZniOi clusters. However, this could be a realistic process for approximating the excitation energies of huge ZniOi clusters.

A study of the aluminum (III) and amino acid chain interactions with the sulfur containing amino acid chains of cysteine (CYs) and methionine (Met) and the analysis of the interactions with the toxic aluminum (III) and the nontoxic magnesium (II) cations is presented. The results show that Mg (II) binds to all of the neutral ligands with binding energies of 79, 97, 109 and 120 Kcal/mol for SH2, HSCH3, CH3SCH3, and CH3SCH2CH3, while aluminum (III) binds only to the largest ligands and then in a bidentate form with a bond to both S and the terminal C.

The gas-phase proton and alkali metal transfer equilibria is examined with a focus on the lithium cation.

Aluminum(III) and magnesium(II) interactions with the asparagine and glutamine amino acid chains are examined by the density functional approach. In conclusion, the binding energies of these complexes are significantly smaller than those of the aluminum(III)/magnesium(II) interactions with the acidic amino acid chains.

The structural and optical properties of both the naked and passivated bimetallic Al5Au5 nanoclusters have been analyzed based on data obtained from ab initio density functional theory and quantum molecular dynamics simulations. It has been found that the Al5Au5 nanocluster possesses a hollow shaped minimum energy structure with segregated Al and Au layered domains, the former representing the electrophilic domain and the latter the nucleophilic domain. In particular, it has been shown that alkali metal cations attach in the nucleophilic domain and hop from one Au site to the next one in the picoseconds time scale, while anions are bound tightly to the Al atoms of the electrophilic domain. Simulating annealing studies are very suggestive of the proneness of the nanocluster towards coalescence into large cluster units, when the cluster is left unprotected by appropriate ligands. Further passivation studies with NaF salt suggest, nonetheless, the possibility of the isolation of the Al5Au5 cluster in molten salts or ionic liquids. [ABSTRACT FROM AUTHOR]

Density functional theory methodology and natural bond orbital theories were applied to the ab initio analysis of aluminum(III) cation with the aspartic and glutamic amino acid residues defined as the carboxylate group. Results show that aluminum(III) exhibited tighter binding strength to the ligands than the nontoxic metal cation, magnesium(II). Methyl groups further enhanced bonding, although the original group's effect is stronger than succeeding groups.

Metal sandwich complexes made of metallic [Al.sub.3][R.sub.3] aromatic three-membered rings are characterized and their structural and electronic properties are analyzed by using density functional theory. The studies have shown that the perfluorocyclotrilane ligand has sandwiched metals and metal dimers while retaining its aromaticity upon complexation.

An ab initio study of the acid hydrolysis of a highly twisted amide and a planar amide analogue is used to investigate the effect that the twist of the amide bond has on the reaction barriers and mechanism of acid hydrolysis. The results would help in understanding the kinetic data of the rate acceleration of amides upon twisting and the relation of the observed rate acceleration with intrinsic differential reactivity upon loss of amide bond resonance.

Five different aspects of the lymphocyte function-associated antigen-1(LFA-1)/intercellular adhesion molecule-1 (ICAM-1) interaction are studied by Density Functional Theory (DFT) calculations. The analysis demonstrates that affinities are always favored by low-dielectric environments, which describes the propensity of MIDAS motifs to be surrounded by hydrophobic residues in integrins and highlights the importance of including hydrophobic groups in the inhibitors.

A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal [Li(super +), Na(super +), K(super +), Rb(super +), Cs(super +)] salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2](super 2-) catallize from dimethoxymethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an gamma(super 5) manner.

Several structure families of the clusters Cd(sub i)X(sub i), i = 1-16, X = S, Se, Te are found to undergo a ring-to-three-dimensional structural transition. This trend is credited to the stability of obtuse X-Cd-X angles in lowest lying structures and to the stability gained from the higher coordination in larger structures.

The all metal aromatic Al42- molecule is the first of the series of recently synthesized compounds that constitute a new paradigm in chemistry. The molecules are normally prepared as singly charges anions because doubly charges species are expected to be rather unstable in the gas phase due to large intermolecular Coulomb repulsion, however, it was possible to calculate stable sandwich-type structures which have a structure similar to that of metallocenes.

The ground states of Cd (sub i)O(sub i) clusters (i = 1-9, 12, 15) are studied. Ring like structures were found to be the global minima for clusters as large as i = 7, and three-dimensional structures were observed to be the global minima for larger ones (i = 8, 9, 12, 15).