A QM/MM approach for the study of monolayer-protected gold clusters

We report the development and implementation of hybrid methods that combine quantum mechanics (QM) with molecular mechanics (MM) to theoretically characterize thiolated gold clusters. We use, as training systems, structures such as Au25(SCH2-R)18 and Au38(SCH2-R)24, which can be readily compared with recent crystallographic data. We envision that such an approach will lead to an accurate description of key structural and electronic signatures at a fraction of the cost of a full quantum chemical treatment. As an example, we demonstrate that calculations of the 1H and 13C NMR shielding constants with our proposed QM/MM model maintain the qualitative features of a full DFT calculation, with an order-of-magnitude increase in computational efficiency.Comment: Journal of Materials Science, 201

Synthesis, characterization and biological activity of novel Cu(II) complexes of 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehy de-4N-substituted thiosemicarbazones

Three new 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-thiosemicarbazones-N-4-substituted pro-ligands and their Cu(II) complexes (1, -NH2; 2, -NHMe; 3, -NHEt) have been prepared and characterized. In both the X-ray structures of 1 and 3, two crystallographically independent complex molecules were found that differ either in the nature of weakly metal-binding species (water in 1a and nitrate in 1b) or in the co-ligand (water in 3a and methanol in 3b). Electron Paramagnetic Resonance (EPR) measurements carried out on complexes 1 and 3 confirmed the presence of such different species in the solution. The electrochemical behavior of the pro-ligands and of the complexes was investigated, as well as their biological activity. Complexes 2 and 3 exhibited a high cytotoxicity against human tumor cells and 3D spheroids derived from solid tumors, related to the high cellular uptake. Complexes 2 and 3 also showed a high selectivity towards cancerous cell lines with respect to non-cancerous cell lines and were able to circumvent cisplatin resistance. Via the Transmission Electron Microscopy (TEM) imaging technique, preliminary insights into the biological activity of copper complexes were obtained

Thiophenolate clusters as potential nanosized building blocks for zinc-based nanocomposite materials: synthesis and characterization

The synthesis, the spectroscopic and structural characterization of different thiophenolate-capped zinc clusters are reported and described. In particular, different reactions of 4-chlorobenzenethiol with zinc salts yield the clusters [Me4N][Et3NH][Zn4(mu-S-C6H4-Cl)6(S-C6H4-Cl)4] (2a), [Et3NH]2[Zn4(mu-S-C6H4-Cl)6(S-C6H4-Cl)4] (2b), and [Me4N]2[Zn4(mu-S-C6H4-Cl)6(S-C6H4-Cl)4] (2c), and also the thiophenolate derivative [Et3NH]2[Zn4(mu-S-C6H5)6(S-C6H5)4] (1b) was obtained. The nanosized thiophenolate-capped clusters were investigated by 1H and 13C NMR, elemental analysis, and electrospray ionization (ESI) mass spectrometry. NMR experiments provided insights into the dynamic behaviour of the clusters. The thermal decomposition patterns of 2c were analyzed in air as well as in nitrogen, indicating the formation of zinc oxide and metallic zinc, respectively. The X-ray structure of 2a revealed that the cluster core consists of an adamantane-like framework analogous to those realized in many other M4(SR)10 metal complexes

Surface functionalization with phosphazene substrates, Part IV: Silica and Si(100) surface functionalization using cyclophosphazenes partially substituted with trialkoxysilane derivatives and PEG-750 monomethylether, 2,2,3,3-tetrafluoropropanol and 4-hydroxyazobenzene

This paper deals with the possibility of functionalizing the surface of silicon-based materials by exploiting cyclophosphazenes containing suitable substituent groups. Thus, phosphazene trimers were prepared, containing about 50% of the reactive sites substituted by gamma-amino-propyltriethoxy silane (APTES), while the residual positions in the cycle contain poly(ethylene glycol) monomethylether (MW approx. 750; PEG-750-ME), tetrafluoropropanol (TFP) and 4-hydroxyazobenzene (AzB). Using these novel materials we succeeded in surface functionalizing SiO2 beads in the coating of silicon wafers or sodalime slides and in the preparation of cyclophosphazene-based monoliths in the presence of hydrolyzed TEOS by sol-gel technique. The whole series of products has been characterized by standard spectroscopic (IR, UV-Vis, H-1-, C-13-, Si-29- and P-31-NMR, both in solution and in solid state) and thermal (DSC and DMTA) techniques. This approach to the surface functionalization of silicon-based materials containing carefully selected substituents is completely general and can be used to attach to the hydroxylated surfaces practically any type of nucleophile that can be supported on the cyclophosphazene ring

Reactivity of trans-[PtCl2(NCMe)2]) with cycloaliphatic amines: An ESI and NMR study. X-ray structure of trans-[PtCl2{Z-N(H)=C(CH3)NHCHCH2CH2}2]

The reactivity of the cyclic primary aliphatic amines cyclopropyl-, cyclopentyl-and cyclohexylamine with cis- and trans-[PtCl(2)(NCMe)(2)], under the same experimental conditions, is compared. Whereas cis-[PtCl(2)(NCMe)(2)] yields the neutral diamidine compounds, the reactions with trans-[PtCl(2)(NCMe)(2)] take place either with addition or substitution processes yielding the neutral diamidine complexes trans-[PtCl(2)(Amidine)(2)], the monocationic trans-[PtCl(Amine)(Amidine)(2)]Cl and the dicationic trans-[Pt(Amine)(2)(Amidine)(2)]Cl(2) salts. An NMR and ESI study indicate that the main species formed is the monocationic trans-[PtCl(Amine)(Amidine)(2)] Cl complex. The X-ray structure of trans-[PtCl(2){N(H)=C(CH(3))NHCHCH(2)CH(2)}(2)] is reported and its supramolecular arrangement is described. (C) 2009 Elsevier B. V. All rights reserved

A Tetranuclear Planar Hafnium Complex Containing O-Hf-S Moieties

The HfIV-oxothiocluster, [Hf4(η2-μ2-SAc)4(η2-μ2-SAc)2(η2-μ2-BuO)4(η2-BuO)2(μ3-O)2], was synthesized by reaction of hafnium butoxide with thioacetic acid. The crystal structure shows the presence of a planar tetranuclear Hf4 core, in which the metal atoms are μ3-O bridged and the thioacetate ligands coordinate the Hf ions both through a bridging and a chelating mode. The structural findings are confirmed by multinuclear NMR spectroscopic data