Do Anionic Gold Clusters Modify Conventional Hydrogen Bonds? The Interaction of Anionic Aun (n = 2−4) with the Adenine−Uracil Base Pair

Enhancing the Stability and Catalytic Performance of Gold Subnanoclusters Mediated by Au···H-C Hydrogen Bonding and Au···π Interactions

Gold subnanoclusters (AuSNCs) exhibit remarkable catalytic activity; however, their short-lived transient existence and strong tendency for self-aggregation remain disadvantageous for practical application. Considering that weak secondary interactions, such as Au···H-C or Au···π, could enhance the stability of the subnanocluster system, we have assessed their influence on the stabilization through a combination of experimental and computational analyses. We have evaluated the stabilization ability of different functional groups toward the AuSNCs system. Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) experiments, density functional theory (DFT) calculations, and topological tools (QTAIM and NCI) provide decisive insights into the mechanism of stabilization of the short-lived AuSNCs species. Additionally, we extended the stabilization analysis to an application in catalysis. By conducting a complete NCI analysis of an optimized energy pathway, we demonstrate how an Au3 subnanocluster can be stabilized by a series of weak secondary interactions, including hydrogen bonds to gold (Au···H-C) as well as Au···π interactions in intermediates and transition states.

Directional affinity of a spherical Gold nanoparticle for the adsorption of DNA bases

In this work, the adsorption activities of different facets of a spherical gold nanoparticle (Au(111), Au(100) and Au(110)) for adenine (ADE) and cytosine (CYT) in two different environments including gas phase and in the presence of solvent (water) have been investigated, separately. It has been found that the adsorption energy (E_ad) and geometry of the DNA bases depend strongly on the kind of nanoparticle facet. The Au (110) facet showed the highest adsorption affinity for the ADE and CYT in both gas phase and water compared to Au(111) and Au(100) facets. Comparison of the E_ads of bases calculated in the gas phase with those obtained in the presence of water showed that the electrostatic field of solvent decreases the E_ads of bases, especially, for the Au (110) facet. The adsorption geometry of the CYT showed strong dependency on the kind of nanoparticle facet compared to ADE. Also, it has been shown that the direction and amount of charge transfer (CT) between the molecule and nanoparticle strongly depends on the kind of nanoparticle facet and environment. The CT is from the Au (111) facet to the ADE while the CT direction is reversed when the ADE is adsorbed on the Au (110) and Au (100) facets in the gas phase. The CT is from the CYT to three facets in the gas phase while its direction for the ADE and CYT adsorbed on Au (100) facet is reversed. The atoms in molecules (AIM) analysis has been employed to determine the bond paths (BPs) and bond critical points (BCPs) between the bases and facets. The infrared (IR) spectra of the bases adsorbed on the selected facets were calculated and compared with each other and with the spectra of the isolated bases. It was found that the symmetric and unsymmetric stretching of the NH of NH₂ group, C-H stretching of the rings and CO stretching of bases can be used for the discrimination of the selected facets.

The key role of Au-substrate interactions in catalytic gold subnanoclusters

The development of gold catalysis has allowed significant levels of activity and complexity in organic synthesis. Recently, the use of very active small gold subnanoclusters (Au_n, n < 10) has been reported. The stabilization of such nanocatalysts to prevent self-aggregation represents a true challenge that has been partially remediated, for instance, by their immobilization in polymer matrices. Here, we describe the transient stabilization of very small gold subnanoclusters (Au_n, n < 5) by alkyl chains or aromatic groups appended to the reactive π bond of simple alkynes. The superior performance toward Brønsted acid-free hydration of medium to long aliphatic alkynes (1-hexyne and 1-docecyne) and benzylacetylene with respect to phenylacetylene is demonstrated experimentally and investigated computationally. A cooperative network of dispersive Au···C–H and/or Au···π interactions, supported by quantum mechanical calculations and time-resolved luminescence experiments, is proposed to be at the origin of this stabilization.

Stabilization of gold nanoclusters in order to prevent their self-aggregation remains a great challenge. Here, the authors describe transient stabilization of very small catalytic gold subnanoclusters by alkyl chains or aromatic groups appended to the reactive π bond of simple alkynes.

Carbon dioxide interaction with isolated imidazole or attached on gold clusters and surface: competition between σ H-bond and π stacking interaction

Using first principle methodologies, we investigate the subtle competition between σ H-bond and π stacking interaction between CO2 and imidazole either isolated, adsorbed on a gold cluster or adsorbed on a gold surface. These computations are performed using MP2 as well as dispersion corrected density functional theory (DFT) techniques. Our results show that the CO2 interaction goes from π-type stacking into σ-type when CO2 interacts with isolated imidazole and Au clusters or surface. The balance between both types of interactions is found when an imidazole is attached to a Au20 gold cluster. Thus, the present study has great significance in understanding and controlling the structures of weakly-bound molecular systems and materials, where hydrogen bonding and van der Waals interactions are competing. The applications are in the fields of the control of CO2 capture and scattering, catalysis and bio- and nanotechnologies.

On the Ag+–cytosine interaction: the effect of microhydration probed by IR optical spectroscopy and density functional theory

Single water molecule hydration stabilizes two quasi-isoenergetic complexes of cytosine⋯Ag⁺.

Role of size and shape selectivity in interaction between gold nanoclusters and imidazole: a theoretical study

We present a theoretical study on the structure, stability, spectra and electronic properties of imidazole (Im) adsorbed on gold nanoclusters (Aun, n = 2, 4, 6, 8, 10, and 20). These computations were performed using various density functional theories with and without inclusion of Grimme's (D3) dispersion correction. For small clusters, we also carried out wavefunction-based ab initio (MP2 and SCS-MP2) computations for comparison. Vibrational, atoms in molecules (AIM) and natural bond orbital (NBO) analyses clearly reveal the occurrence of charge transfer (CT) through covalent (N1-Au) and noncovalent interactions that play important roles in the stability of the Im@Aun complexes with anchor assisted H-bonds (Cα-H · Au). Therefore, gold clusters can act as H-bond acceptors with biomolecules for development of new materials and applications. Our study establishes also the ability and reliability of PBE0 and M05-2X functionals compared to B3LYP and PBE for an accurate description of covalent and noncovalent interactions between Im and gold clusters since they lead to close agreement with MP2. Finally, we show that the Au8 cluster may be viewed as large enough to mimic the 3D gold surface.

The gold-hydrogen bond, Au-H, and the hydrogen bond to gold, Au∙∙∙H-X

In the first part of this review, the characteristics of Au-H bonds in gold hydrides are reviewed including the data of recently prepared stable organometallic complexes with gold(I) and gold(III) centers. In the second part, the reports are summarized where authors have tried to provide evidence for hydrogen bonds to gold of the type Au∙∙∙H-X. Such interactions have been proposed for gold atoms in the Au(-I), Au(0), Au(I), and Au(III) oxidation states as hydrogen bonding acceptors and H-X units with X = O, N, C as donors, based on both experimental and quantum chemistry studies. To complement these findings, the literature was screened for examples with similar molecular geometries, for which such bonding has not yet been considered. In the discussion of the results, the recently issued IUPAC definitions of hydrogen bonding and the currently accepted description of agostic interactions have been used as guidelines to rank the Au∙∙∙H-X interactions in this broad range of weak chemical bonding. From the available data it appears that all the intra- and intermolecular Au∙∙∙H-X contacts are associated with very low binding energies and non-specific directionality. To date, the energetics have not been estimated, because there are no thermochemical and very limited IR/Raman and temperature-dependent NMR data that can be used as reliable references. Where conspicuous structural or spectroscopic effects have been observed, explanations other than hydrogen bonding Au∙∙∙H-X can also be advanced in most cases. Although numerous examples of short Au∙∙∙H-X contacts exist in the literature, it seems, at this stage, that these probably make only very minor contributions to the energy of a given system and have only a marginal influence on molecular conformations which so far have most often attracted researchers to this topic. Further, more dedicated investigations will be necessary before well founded conclusions can be drawn.