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The transition point from a two-dimensional (2D) to a three-dimensional (3D) structure in a series of small gold clusters remains a topic of continuing debate. In the present study, coupled-cluster CCSD(T) and DFT calculations are performed to re-examine the relative energies of several low-lying isomers of Au12, aiming to shed new light on this issue. At odds with many previous reports on the preference of a planar di-capped elongated-hexagon structure, the Au12 size is found to energetically prefer a globular cup-like form with C2v symmetry. While DFT results are not able to assign the most stable form of Au12 as the relative energies between the lowest-lying isomers are strongly functional-dependent, coupled-cluster theory calculations point out the preference of a 3D structure for having a D3h symmetry. Such a prediction is further supported by a comparison of the vibrational spectra computed using the revTPSS density functional with the available experimental infrared ones that were previously recorded from the far-IR multiple photon dissociation (FIR-MPD) experiment. [ABSTRACT FROM AUTHOR]

The Au17 gold cluster was experimentally produced in the gas phase and characterized by its vibrational spectrum recorded using far-IR multiple photon dissociation (FIR-MPD) of Au17Kr. DFT and coupled-cluster theory PNO-LCCSD(T)-F12 computations reveal that, at odds with most previous reports, Au17 prefers two star-like forms derived from a pentaprism added by two extra Au atoms on both top and bottom surfaces of the pentaprism, along with five other Au atoms each attached on a lateral face. A good agreement between calculated and FIR-MPD spectra indicates a predominant presence of these star-like isomers. Stabilization of a star form arises from strong orbital interactions of an Au12 core with a five-Au-atom string. [ABSTRACT FROM AUTHOR]

Quantum chemical computations were used to reinvestigate the geometries, spectroscopic, and energetic properties of the gold clusters Au27q in three charge states (q = 1, 0, −1). Density functional theory (DFT) and the domain‐based local pair natural orbital modification of the coupled‐cluster theory DLPNO‐CCSD(T) calculations revealed that, at variance with earlier reports in the literature, while the anion Au27− tends to exist in a tube‐like form, both the lowest‐energy Au27 and Au27+ isomers exhibit a pyramidal shape. However, several isomers were found to lie very close in energy, thus rendering a structural transition and their coexistence easy to occur. More specifically, the equilibrium geometry of the neutral Au27 is a core‐shell pyramid‐like structure with one gold atom located inside. We also identified a novel ground state for the anion Au27− and located for the first time the global minimum of the cation Au27+. The vertical detachment energies of the neutral and anionic states were also computed and used to assign the available experimental photoelectron spectra. Although many Au27 isomers were predicted to be energetically quasi‐degenerate, the corresponding distinctive vibrational signatures can be used as fingerprints for the identification of cluster geometrical features. [ABSTRACT FROM AUTHOR]

Density functional theory methods were employed to clarify the adsorption/desorption behaviors of the thione‐containing mercaptopurine and thioguanine drugs on the gold surface using both small Au6 and Au8 clusters as model reactants. Structural features, thermodynamic parameters, bonding characteristics, and electronic properties of the resulting complexes were investigated using the Perdew–Burke–Ernzerhof (PBE) and LC‐BLYP functionals along with correlation‐consistent basis sets, namely cc‐pVDZ‐PP for gold and cc‐pVTZ for non‐metals. Computed results show that the drug molecules tend to anchor on the gold cluster at the S atom with binding energies around −34 to −40 kcal/mol (in vacuum) and − 28 to −32 kcal/mol (in aqueous solution). As compared to Au8, Au6 undergoes a shorter recovery time and a larger change of energy gap that could be converted to an electrical signal for selective detection of the drugs. Furthermore, interactions between the drugs and gold clusters are reversible processes and a drug release mechanism was also proposed. Accordingly, the drugs are able to separate from the gold surface due to either a slight change of pH in tumor cells or the presence of cysteine residues in protein matrices. [ABSTRACT FROM AUTHOR]

We would like to make a few comments on the results reported in a recent paper in this journal by Tsuneda, J. Comput. Chem, 2019, 40, 206. The structures of some pure silver clusters were not correctly assigned. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Geometric, energetic and electronic properties of Aun clusters, n = 2–20 are determined using DFT calculations (BB95/cc-pVTZ-PP). Global equilibrium structures were confirmed or found, and the growth mechanism was established. Au-clusters prefer 2D-geometries up to Au 11 and are generated from the lowest-lying isomer of the smaller size by adding an extra gold atom. Transition from an oblate form to a pyramid is observed at Au 17 . Au n containing 17–20 atoms favor tetrahedral evolution by adding atoms to the Frank-Kasper 16-vertex. Binding energy per atom, second-order difference of energy, and one-step fragmentation energy show that Au 6 and Au 20 have high thermodynamic stability. Their valence electrons of generate magic numbers that can be understood using the phenomenological shell model. Due to Jahn-Teller effect, Au 16 is characterized by oblate structure whereas the anion Au 16 -exhibits Frank-Kasper form. [ABSTRACT FROM AUTHOR]

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]

Computational approaches are employed to elucidate the binding mechanism and the SERS phenomenon of 6-mercaptopurine (6MP) adsorbed on the tetrahedral Au20 cluster as a simple model for a nanostructured gold surface. Computations are carried out in both vacuum and aqueous environments using a continuum model. In the gaseous phase and neutral conditions, interaction of 6MP with the gold cluster is mostly dominated by a covalent Au−S bond and partially stabilized by the Au⋅⋅⋅H−N coupling. However, in acidic solution, the nonconventional Au⋅⋅⋅H−S hydrogen-bond becomes the most favorable binding mode. The 6MP affinity for gold clusters decreases in the order of vacuum > neutral solution > acidic medium. During the adsorption, the energy gap of Au20 substantially declines, leading to an increase in its electrical conductivity, which can be converted to an electrical noise. Moreover, such interaction is likely a reversible process and triggered by either the low pH in sick tissues or the presence of cysteine residues in protein matrices. While N−H bending and stretching vibrations play major roles in the SERS phenomenon of 6MP on gold surfaces in neutral solution, the strongest enhancement in acidic environment is mostly due to an Au⋅⋅⋅H−S coupling, rather than an aromatic ring-gold surface π overlap as previously proposed. [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 (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]

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]

Sulfathiazole is an antibiotic used to prevent diseases and promote animal growth, and may pose health risks to humans when consumed excessively. Herein, we prepared a nanosubstrate for trace determination using the surface-enhanced Raman scattering (SERS) technique by synthesizing spinous gold nanoparticles (SGNPs) through a rapid and straightforward seed-mediated method. Prior to detection, SGNPs with long tips were effectively synthesized by varying the seed solutions and the volume of ascorbic acid. These spinous nanostructures with long tips could improve the SERS detection of sulfathiazole (STZ) by creating more hot spots in the vicinity of particles. Furthermore, the SERS nano-substrate is facile to prepare with high sensitivity, and the testing sample does not undergo a complicated pretreatment procedure. The results show that nano-substrates can detect STZ at low concentrations ranging from 0.01 to 50 μg mL−1, with an excellent linear correlation between the concentration and intensity (R2 = 0.99). The limit of detection (LOD) reaches 0.22 μg mL−1, and the limit of quantification is 0.73 μg mL−1. In addition, the SERS nanosubstrate can exhibit good reproducibility with an RSD of 6.26%, as evaluated with STZ solution at a low concentration of 40 μg mL−1. The assignments of STZ Raman bands were performed using density-functional theory (DFT) quantum chemical calculations. The strong interaction affinity between Au atoms and STZ compounds was also described by calculating the binding energy of isolated species and Au20-STZ complexes. The STZ could be anchored on the Au surface through thiazole nitrogen. Furthermore, the calculated SERS spectrum of Au-STZ could be assigned to the experimental ones with the most enhanced signal near 1430 and 1540 cm−1. Potential applications that benefit from this SERS nanosubstrate are measurements for a variety of antibiotics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of biogenic silver nanoparticles (AgNPs) using Quisqualis indica Linn flowers extract with an average particle size of 10–30 nm. • AgNPs were characterized by UV–Vis, TGA, XRD, FTIR, and FESEM. • The quantum chemistry properties of compounds present in the flowers of Quisqualis indica Linn was calculated by using density functional theory (DFT) method. • Docking studies have a better interaction with the target protein 2MLM and 1KZN. The present study reports a one-step, eco-friendly, and green synthesis route of silver nanoparticles (AgNPs) from the flower extract of Quisqualis indica Linn. Analytical techniques like Ultraviole-visible (UV–Vis), Field emission scanning electron microscope (FESEM), and X-ray diffraction (XRD) were used to investigate different physicochemical characteristics of AgNPs. The UV–Vis spectrum revealed the maximum absorption at 455 nm and FESEM images confirmed that the synthesis produces stable, polydisperse with a spherical, rod-shaped, triangular, and hexagon shape. XRD analysis at 2θ degrees of 38.1o, 44.3o, 64.7o, and 77.7o corresponding to the (1 1 1), (2 0 0), (2 2 0), and (3 1 1) planes, respectively, Bragg's reflections of the face-centered cubic crystalline structure. Fourier transform infrared spectroscopy (FTIR) analysis suggested that the carbonyl and alcoholic groups of the different compounds of the extract of Quisqualis indica Linn flowers were majorly responsible for being the stabilizer and a capping agent of AgNPs. Furthermore, the quantum chemical parameters of β-Sitosterol (1), Brinzolamide (2), Gallic Acid (3), L-Asparagine (4), L-Proline (5), Quisqualic Acid (6), Quinoline-4-Carbonitrile (7), Quercetin (8), and Rutin (9) compounds present in the flowers of Quisqualis indica Linn are also calculated based on density functional theory (DFT). In silico study, a method such as molecular docking was carried out to determine the binding affinity of compounds (1–9) with presentations of Gram-positive bacteria (PDB ID: 2MLM) and Gram-negative bacteria (PDB ID-1KZN). Compounds (1), (2), (7) and (8) had a better score of binding toward the selected proteins. Overall, our findings shed light on the green synthesis of silver nanoparticles and it could be a potential candidate for the pharmaceutical industry against topical pathogens. [ABSTRACT FROM AUTHOR]