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Context: Mercaptopurine is an effective anticancer medicine yet known with serious adverse reactions, thus requiring further attempts to enhance its biological targeting. Small gold clusters Aun (n = 2–10) were used as model reactants to simulate the surface of gold nanoparticles. The computed results show that the drug molecules tend to anchor on the gold clusters at the S atom with the associated binding energies varying from −50 to −34 kcal mol−1 (in vacuum) and from −42 to −28 kcal mol−1 (in aqueous solution). Furthermore, the adsorption of the drug onto the gold surface is considered as a reversible process, and the mechanism of drug releasing was found to be triggerable by internal factors, such as a pH change or the concentrated presence of thiol amino acids in cancerous protein structures. Method: Calculations based on density functional theory (DFT) were performed to probe the nature of interactions between the drug and gold nanoparticles. Structural features, thermodynamic parameters, bonding characteristics, and electronic properties of the resulting complexes were investigated at the PBE//cc-pVTZ/cc-pVDZ-PP level. [ABSTRACT FROM AUTHOR]

Gold and gold-based clusters are still receiving special attention owing to their diverse applicability. Density functional theory (DFT) calculations were employed to investigate the structures, the lone-pair affinity of some small Aun clusters (n = 16, 17, and the effects of chromium dopant on their properties. Regarding Au16, the boat-like Cs conformation and the hollow Td form are found to be energetically quasi-degenerate and strongly competing as the ground state. In terms of Au17, a star-like cage is computed to be more stable than the putative global minimum reported in preceding studies. Given Au16Cr isomer, a novel structure for the lowest energy is proposed. Binding energies of these species with CO, NH3, and PH3 ligands are also provided as an in-depth reference to the literature. Present results altogether encourage further theoretical implementations, e.g., CCSD(T) and experimental probes, e.g., the infrared, to validate the findings, thus harnessing the potentiality of the complexes. [ABSTRACT FROM AUTHOR]

Density functional theory approaches are employed to elucidate the structural features and electronic properties of cis-dioxidomolybdenum(VI) complexes with water, 8-hydroxyquinoline and 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one. Geometrical parameters are optimized using B3PW91, B3LYP functionals in conjunction with def2-TZVP, LanL2DZ and 6-311 + G basis sets. Computed results show that the complex energetically prefers a pseudo-pentagonal bipyramidal shape in the ground state. The nature of intramolecular interactions between Mo(VI) and ligands is evaluated by analyzing the natural bond orbital and quantum theory of atoms in molecules. The Mo–OH2 interaction is rather weak with an average distance of 2.445 Å and a very low Mayer bond order of 0.235. The vibrational signatures and vertical electronic transitions of some excitations are examined and compared to available experimental data. The most favorable sites for electrophilic, nucleophilic attack or protonation were also identified using the noncovalent interaction method. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations are employed to examine the adsorption behaviors of cysteine on the gold surface using Au6 and Au8 species as model reactants. Computed results show that cysteine molecules prefer to bind with gold clusters via the S-atom of the thiol group in vacuum and thiolate group in water. The gas-phase adsorption energies are around 20.2 kcal/mol for Au6 and 24.4 kcal/mol for Au8. In water environment, such values are slightly reduced for Au6 (19.6 kcal/mol), but increased a little more for Au8 (25.6 kcal/mol). As a result, if a visible light with a frequency of ν ≈ 6 × 1014 Hz (500 nm) is applied, the time for the recovery of Au6 and Au8 from the most stable complexes will be about 0.38 and 9.3 × 103 s, respectively, at 298 K in water. The Au6 is in addition found to benefit from a larger change of energy gap that could be converted to an electrical signal for detection of cysteine. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations were carried out to explore the geometric, spectroscopic, and electronic properties of three magic silver clusters Agn (n = 8, 18, and 20) in detail. The computed results show that the global minima of these clusters are compact, near-spherical structures, while other low-lying isomers exhibit oblate or prolate shapes. Vertical ionization energies for the low-lying isomers were also computed and assigned with respect to available experimental values. Although several isomers were predicted to have similar energies, their electronic and vibrational signatures were quite distinctive, meaning that they could be used as fingerprint signals to distinguish between isomers. In addition, the electronic structures of these systems were explored using the phenomenological shell model. Calculations for the coinage metal clusters M20 (M = Cu, Ag, Au) indicated that the structures and properties of the Ag cluster are similar to those of the Cu cluster in that both Cu20 and Ag20 prefer a compact structure whereas Au20 prefers to adopt a tetrahedral form.Shell Orbitals of Ag8 Cluster [ABSTRACT FROM AUTHOR]