Tetrahedral (T) closed-shell cluster of 29 silver atoms & 12 lipoate ligands, [Ag29(R-a-LA)12](3-): antibacterial and antifungal activity

Accepted author manuscriptHere we report on the identification and applications of an aqueous 29-atom silver cluster stabilized with 12 lipoate ligands, i.e. Ag29(R-α–LA)12 or (29,12), wherein R-α–LA = R-α-lipoic acid, a natural dithiolate. Its uniformity is checked by HPLC-ESI-MS and analytical ultracentrifugation, which confirms its small dimension (∼3 nm hydrodynamic diameter). For the first time, this cluster has been detected intact via electrospray ionization mass spectrometry, allowing one to confirm its composition, its [3-] charge-state, and the 8-electron shell configuration of its metallic silver core. Its electronic structure and bonding, including T-symmetry and profound chirality in the outer shell, have been analyzed by DFT quantum-chemical calculations, starting from the known structure of a nonaqueous homologue. The cluster is effective against Methicillin-Resistant Staphylococcus aureus bacteria (MRSA) at a minimum inhibitory concentration (MIC) of 0.6 mg-Ag/mL. A preformed Candida albicans fungal biofilm, impermeable to other antifungal agents, was also inhibited by aqueous solutions of this cluster, in a dose–response manner, with a half-maximal inhibitory concentration (IC50) of 0.94 mg-Ag/mL. Scanning electron micrographs showed the post-treatment ultrastructural changes on both MRSA and C. albicans that are characteristic of those displayed after treatment by larger silver nanoparticles.Ye

Metallic Particles Supported in Several Synthetic Zeolitic Materials

AbstractHigh resolution electron microscopy observations were carried out in several zeolitic systems with different supported metallic phases in order to determine besides distributions of metallic particles, possible preferential orientations of metallic phases during impregnation processes and to detect some crystallographic relations between metallic particles and support.</jats:p

Large scale synthesis of V-shaped rutile twinned nanorods

V-shaped rutile twinned nanorods (VRTNs) with different aspect ratios were synthesized on large scale using a one-pot organic solvothermal method. Although several different types of VRTNs were produced, (101) twinned nanorods were the major product with minor amounts of (301) twins and straight nanorods. STEM, TEM and XRD characterizations show that [001] is the growth direction of VRTNs, with surfaces dominated by {110} facets. Intermediate formation of both brookite and anatase nanorods provides dual pathways to VRTNs’ growth: one path in which anatase seeds trigger and promote brookite nanorod growth; and a second path in which anatase nanorods are formed by oriented attachment. Subsequent dissolution of both brookite and anatase nanorods provides titania to support VRTNs growth

Direct observation of the mechanical properties of single-walled carbon nanotubes and their junctions at the atomic level

Starting from an amorphous C film, single-walled carbon nanotubes were obtained in situ in a high-resolution electron microscope by the combined effect of irradiation and axial strain. Ductile nanotubes developed either a junction or a linear chain of C atoms before failure. These facts have been put in direct evidence for the first time. Tight-binding calculations indicate that the bonding in the linear chain is of a cumulene type.This work was supported by the CONYCYT, Argentina, by special funds from Texas Materials Institute and the Center for Nano and Molecular Technology (UT-Austin), CONACYT, México, the University of the Basque Country, DGES, and by the EU research training network NANOPHASE (HPRN-CT-2000-00167).Peer reviewe

On the breaking of carbon nanotubes under tension

Molecular dynamics simulations and high resolution TEM experiments are performed to assess the fracture of nanotubes under high stretching conditions. Brittle or plastic response is controlled by the rate of applied strain to the tube as well as by the number of defects (in particular vacancies). Simulations predict that under high temperatures and presence of defects (as induced under the high-energy electron beam of the TEM) the tubes exhibit mainly plastic deformation, with the appearance of medium size carbon chains as the latest stage before fracture. These results are in agreement with in-situ TEM observation. Carbon exhibits a very rich dynamics of bond-breaking and bond-reconstruction that allows transformations from fullerenes to tubes to chains.This work was supported by the ECRTNs NANOPHASE (HPRN-CT-2000-00167), COMELCAN (HPRN-CT-2000-00128), EXC!TiNG (HPRN-CT- 2002-00317), by Spanish MCyT(MAT2001-0946) and University of the Basque Country (9/UPV 00206.215-13639/2001).Peer reviewe

A viable way to tailor carbon nanomaterials by irradiation-induced transformations

Since the discovery of carbon nanotubes (CNT), transmission electron microscopy (TEM) has been the most important tool in their investigation. It is possible to use electron irradiation in a TEM to construct a single-walled carbon nanotube (SWCNT) from an amorphous carbon film. Here we show that such a synthesis method creates a large number of carbon ad-atoms, which after some critical amount of radiation act to restore the system by reconstructing the carbon film. The behavior of the ad-atoms can be controlled by adjusting the current density in the microscope, suggesting that carbon nanomaterials can be tailored by electron irradiation.R.C. thanks the University of Texas at Austin for their fellowship support.Peer reviewe