A homologous series of macrocyclic Ni clusters: synthesis, structures, and catalytic properties.

Due to their intriguing ring structures and promising applications, nickel-thiolate clusters, such as [Nin(SR)2n] (n = 4-6), have attracted tremendous interest. However, investigation of the synthesis, structures, and properties of macrocyclic Nin clusters (n > 8) has been seriously impeded. In this work, a homologous series of macrocyclic nickel clusters, Nin(4MPT)2n (n = 9-12), was fabricated by using 4-methylphenthiophenol (4MPT) as the ligand. The structures and compositions of the clusters were determined by single-crystal X-ray diffraction (SXRD) in combination with electrospray ionization mass spectrometry (ESI-MS). Experimental results and theoretical calculations show that the electronic structures of the clusters do not change significantly with the increase of Ni atoms. The coordination interactions between Ni and S atoms in [NiS4] subunits are proved to play a crucial rule in the remarkable stability of Ni clusters. Finally, these clusters display excellent catalytic activity towards the reduction of p-nitrophenol, and a linear correlation between catalytic activity and ring size was revealed. The study provides a facile approach to macrocyclic homoleptic nickel clusters, and contributes to an in-depth understanding of the structure-property correlations of nickel clusters at the atomic level.

Au16 Cd16 (SC6 H11 )20 : A Glance at Structure-Property Relationship.

Doping Cd atom(s) into gold clusters is very promising in both theoretical study and practical applications. However, it has long been a challenge to synthesize heavily Cd-doped AuCd bimetallic clusters and thereby reveal their structure-property correlations. Herein a novel AuCd bimetallic cluster: Au16 Cd16 (SC6 H11 )20 (SC6 H11 denotes deprotonated cyclohexanethiol) with a Cd to Au atomic ratio of 1:1 is reported. The precise structure of the cluster determined by single crystal X-ray diffraction demonstrates that it has a unique hexatetrahedron Au14 core and a distinctive shell. Intriguingly, due to the special protecting motifs, the cluster exhibits high stability in various conditions studied, indicating that the geometric structure is crucial in determining the stability of the cluster. Most importantly, the photothermal property of the cluster has been investigated in comparison with those of M13 -kernel (M denotes metal atoms) clusters, and the results imply that the compactness and the Cd atom doping of the core play important roles in dictating the photothermal effect of the cluster. The authors believe that this work will provide some ideas for the rational design of clusters with high stability and excellent photothermal property.

Identifying the Real Chemistry of the Synthesis and Reversible Transformation of AuCd Bimetallic Clusters.

The capability of precisely constructing bimetallic clusters with atomic accuracy provides exciting opportunities for establishing their structure-property correlations. However, the chemistry (the charge state of precursors, the property of ligands, the amount of dopant, and so forth) dictating the fabrication of clusters with atomic-level control has been a long-standing challenge. Herein, based on the well-defined Au25(SR)18 cluster (SR = thiolates), we have systematically investigated the factors of steric hindrance and electronic effect of ligands, the charge state of Au25(SR)18, and the amount of dopant that may determine the structure of AuCd clusters. It is revealed that [Au19Cd3(SR)18]- can be obtained when a ligand of smaller steric hindrance is used, while Au24Cd(SR)18 is attained when a larger steric hindrance ligand is used. In addition, negatively charged [Au25(SR)18]- is apt to form [Au19Cd3(SR)18]- during Cd doping, while Au24Cd(SR)18 is produced when neutral Au25(SR)18 is used as a precursor. Intriguingly, the reversible transformation between [Au19Cd3(SR)18]- and Au24Cd(SR)18 is feasible by subtly manipulating ligands with different steric hindrances. Most importantly, by introducing the excess amount of dopant, a novel bimetallic cluster, Au4Cd4(SR)12 is successfully fabricated and its total structure is fully determined. The electronic structures and the chirality of Au4Cd4(SR)12 have been elucidated by density functional theory (DFT) calculations. Au4Cd4(SR)12 reported herein represents the smallest AuCd bimetallic cluster with chirality.

The Factors Dictating Properties of Atomically Precise Metal Nanocluster Electrocatalysts.

Metal nanoparticles occupy an important position in electrocatalysis. Unfortunately, by using conventional synthetic methodology, it is a great challenge to realize the monodisperse composition/structure of metal nanoparticles at the atomic level, and to establish correlations between the catalytic properties and the structure of individual catalyst particles. For the study of well-defined nanocatalysts, great advances have been made for the successful synthesis of nanoparticles with atomic precision, notably ligand-passivated metal nanoclusters. Such well-defined metal nanoclusters have become a type of model catalyst and have shown great potential in catalysis research. In this review, the authors summarize the advances in the utilization of atomically precise metal nanoclusters for electrocatalysis. In particular, the factors (e.g., size, metal doping/alloying, ligand engineering, support materials as well as charge state of clusters) affecting selectivity and activity of catalysts are highlighted. The authors aim to provide insightful guidelines for the rational design of electrocatalysts with high performance and perspectives on potential challenges and opportunities in this emerging field.

Species-dependent plasma metabolism of the ester compound daidzein 7,4'di-succinic acid mon-ester-O-ethoxy (DZ5).

Daidzein 7,4'di-succinic acid mon-ester-O-ethoxy (DZ5) is an ester-containing compound, which was recently synthesized. The objective of this study was to determine the hydrolysis rate of DZ5 in blood from the rat and the dog. The data showed that the hydrolysis rate of DZ5 in plasma was much more rapid in rats than in dogs following intravenous administration. Moreover, similar results were observed after in vitro incubation of DZ5 in the rat or dog plasma. The findings suggested that plasma esterases in the rat plasma have higher activity than in the dog and plasma metabolism of DZ5 is species-dependent.

Validation of an HPLC method for the simultaneous determination of DZ5 and its active metabolite in dog plasma and its pharmacokinetics.

A validated HPLC method is described for the simultaneous determination of daidzein 7,4'-di-succinic acid mon-ester-O-ethoxy (DZ5) and its active metabolite daidzein 7,4'-dioxy-ethoxy (DZ4) in dog plasma. DZ5 and DZ4 were determined by reversed-phase HPLC (column: Hypersil C18 5 microm silica, 200 mm x 4.6 mm i.d.; eluent: 400 ml water, 500 microl 85% phosphoric acid, 600 ml methanol) and photometric detection (250 nm), with Kaempferol as the internal standard. The calibration curve was linear over the range 0.1-50.0 microg/ml in dog plasma. The average extraction recoveries were 84.6% (DZ5), 82.7% (DZ4) and the within-day and between-day precisions were less than 10.93%. The assay was applied to the analysis of samples from a pharmacokinetic study. Following the oral administration and intravenous administration of DZ5, DZ5 was eliminated rapidly from the plasma and DZ4 was found in plasma. The absolute bioavailability of total DZ5 and DZ4 was 41.5%. The method was demonstrated to be feasible for pharmacokinetic studies of DZ5 in dogs.