Nature of the Interaction between Natural and Size-Expanded Guanine with Gold Clusters: A Density Functional Theory Study

In this paper, we study the interaction of natural and size-expanded guanine molecules with small gold clusters, to shed light on the nature of the N/O–Au bonds and of the unconventional NH···Au hydrogen bonds, as well as on the dependence of these bonds on the charge state of the systems. Based on density functional theory results, it is found that the nature of the N/O–Au bonds between both guanine and its size-expanded form and three- and four-atom Au clusters is covalent in the neutral systems. In the −1 charged systems, the binding energy decreases by almost 50% with a significant change of geometry. Although the NH site in the spacer ring of size-expanded guanine may supply a new acceptor opportunity for forming an additional NH···Au hydrogen bond, this hardly emerges because of the nonplanarity and the large steric effect. The introduction of a spacer ring in guanine decreases the highest occupied molecular orbital–lowest unoccupied molecular orbital gap and expands the spatial distribution of electron wave functions, which make size-expanded guanine appealing for charge transfer performance. At the same time, it increases the steric hindrance, making the adsorption process more orderly, which is also good in view of molecular electronic devices

Reactivity of the ZnS(101̅0) Surface to Small Organic Ligands by Density Functional Theory

The adsorption process of small organic molecules that represent reactive groups in amino acids (H₂O, H₂S, NH₃, and HCOOH) on the nonpolar ZnS(101̅0) surface was investigated by van der Waals corrected density functional theory calculations. At the accomplished interfaces, the oxygen, sulfur and nitrogen atoms of the adsorbates point toward the zinc atoms of the substrate, realizing electronic hybridization of their <i>p</i> lone pairs with the <i>s</i> and <i>d</i> bands of Zn. This electronic hybridization that involves surface cations is accompanied by H-bond formation that involves surface anions: this concerted mechanism enhances the interface strength and stability. On the basis of our results, we distinguish two classes of adsorption modes: molecular adsorption pertains to H₂O, NH₃, and HCOOH independently of the coverage and to H₂S at low coverage, while concurrent adsorption/dissociation pertains to H₂S at saturation coverage as a compromise between steric repulsion and H-bond-like interactions. Our results shed light on the passivation and modification of ZnS substrates (quantum dots and flat surfaces) in the prospect of technological and biomedical applications

α<i>-</i>Helix C-Terminus Acting as a Relay to Mediate Long-Range Hole Migration in Proteins

Ab initio calculations suggest that the C-terminus of an α-helix can serve as a novel relay element for long-range charge migration in proteins, as an addition or alternative to the known relay properties of aromatic and S-containing amino acids. The relay ability of an α-helical C-terminus varies with helix length, capping, proximal group competition, and helix twisting/bending. The vertical ionization potential (IP_V) is a suitable indicator of hole relay ability and correlates positively with the HOMO energies and inversely with helix length and dipole moment. Different capping groups can yield different effects on the IP_V but hardly change the IP_V−helix length dependence. A series of recent experimental observations regarding charge migrations by hopping along helices or across different helices and the distance dependence of the charge-transfer rates through helices could be viewed as strong evidence for this prediction that also provides the impetus for further experimental tests and continued theoretical exploration

Discovering Partially Charged Single-Atom Pt for Enhanced Anti-Markovnikov Alkene Hydrosilylation

The hydrosilylation reaction is one of the largest-scale application of homogeneous catalysis and is widely used to enable the commercial manufacture of silicon products. However, considerable issues including disposable platinum consumption, undesired side reactions and unacceptable catalyst residues still remain. Here, we synthesize a heterogeneous partially charged single-atom platinum supported on anatase TiO₂ (Pt₁^δ+/TiO₂) catalyst via an electrostatic-induction ion exchange and two-dimensional confinement strategy, which can catalyze hydrosilylation reaction with almost complete conversion and produce exclusive adduct. Density functional theory calculations reveal that unexpected property of Pt₁^δ+/TiO₂ originates from atomic dispersion of active species and unique partially positive charge Pt^δ+ electronic structure that conventional nanocatalysts do not possess. The fabrication of single-atom Pt₁^δ+/TiO₂ catalyst accomplishes a reasonable use of Pt through recycling and maximum atom-utilized efficiency, indicating the potential to achieve a green hydrosilylation industry