Acetylated galactopyranosyl N-heterocyclic monocarbene complexes of Silver(I) as novel anti-proliferative agents in a rhabdomyosarcoma cell line.

Herein, four silver(I) complexes bearing acetylated d-galactopyranoside-based N-heterocyclic carbene ligands were synthesized and fully characterized by elemental analysis, NMR, and X-ray photoelectron spectroscopy. All complexes were obtained with an anomeric ß-configuration and as monocarbene species. In this study, we investigated the biological effects of the silver(I) complexes 2a-d on the human rhabdomyosarcoma cell line, RD. Our results show concentration-dependent effects on cell density, growth inhibition, and activation of key signaling pathways such as Akt 1/2, ERK 1/2, and p38-MAPK, indicating their potential as anticancer agents. Notably, at 35.5 µM, the complexes induced mitochondrial network disruption, as observed with 2b and 2c, whereas with 2a, this disruption was accompanied by nuclear content release. These results provide insight into the utility of carbohydrate incorporated NHC complexes of silver(I) as new agents in cancer therapy.

Innovative Anodic Treatment to Obtain Stable Metallic Silver Micropatches on TiO2 Nanotubes: Structural, Electrochemical, and Photochemical Properties.

Electrochemical modification of the Ti surface to obtain TiO2 nanotubes (NT-Ti) has been proposed to enhance osseointegration in medical applications. However, susceptibility to microbial adhesion, linked to biomaterial-associated infections, and the high TiO2 band gap energy, which allows light absorption almost exclusively in the ultraviolet (UV) region, limit its applications. Modifying the TiO2 semiconductor with metals such as Ag has been suggested both for antimicrobial purposes and for absorbing light in the visible region. The formation of NT-Ti with Ag micropatches (Ag-NT-Ti) is pursued with the objective of enhancing the stability of the deposits and preventing cytotoxic levels of Ag cellular uptake. The innovative process proposed here involves immersing NT-Ti in a AgNO3 solution as the initial step. Diverging from previously reported electrochemical methods, this process incorporates anodization within the TiO2 oxide formation region instead of cathodic reduction generally employed by other researchers. The final step encompasses an annealing treatment. The treatments result in the in situ Ag1+ reduction and formation of stable and active micropatches of metallic Ag on the NT-Ti surface. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman, diffuse reflectance spectroscopy (DRS), wettability assessment, and electrochemical characterizations were conducted to evaluate the modified surfaces. The well-known properties of NT-Ti surfaces were enhanced, leading to improved photocatalytic activity across both visible and UV regions, significant stability against detachment, and controlled release of Ag1+ for promising antimicrobial effects.

Shell-mediated control of surface chemistry of highly stoichiometric magnetite nanoparticles.

Magnetite (Fe3O4) nanoparticles are one of the most studied nanomaterials for different nanotechnological and biomedical applications. However, Fe3O4 nanomaterials gradually oxidize to maghemite (γ-Fe2O3) under conventional environmental conditions leading to changes in their functional properties that determine their performance in many applications. Here we propose a novel strategy to control the surface chemistry of monodisperse 12 nm magnetite nanoparticles by means of a 3 nm-thick Zn-ferrite epitaxial coating in core/shell nanostructures. We have carried out a combined Mössbauer spectroscopy, dc magnetometry, X-ray photoelectron spectroscopy and spatially resolved electron energy loss spectroscopy study on iron oxide and Fe3O4/Zn0.6Fe2.4O4 core/shell nanoparticles aged under ambient conditions for 6 months. Our results reveal that while the aged iron oxide nanoparticles consist of a mixture of γ-Fe2O3 and Fe3O4, the Zn-ferrite-coating preserves a highly stoichiometric Fe3O4 core. Therefore, the aged core/shell nanoparticles present a sharp Verwey transition, an increased saturation magnetization and the possibility of tuning the effective anisotropy through exchange-coupling at the core/shell interface. The inhibition of the oxidation of the Fe3O4 cores can be accounted for in terms of the chemical nature of the shell layer and an epitaxial crystal symmetry matching between the core and the shell.

ESIPT and FRET probes for monitoring nanoparticle polymer coating stability.

Coating strategies of inorganic nanoparticles (NPs) can provide properties unavailable to the NP core alone, such as targeting, specific sensing, and increased biocompatibility. Non-covalent amphiphilic NP capping polymers function via hydrophobic interactions with surface ligands and are extensively used to transfer NPs to aqueous media. For applications of coated NPs as actuators (sensors, markers, or for drug delivery) in a complex environment, such as biological systems, it is important to achieve a deep understanding of the factors affecting coating stability and behavior. We have designed a system that tests the coating stability of amphiphilic polymers through a simple fluorescent readout using either polarity sensing ESIPT (excited state intramolecular proton transfer) dyes or NP FRET (Förster resonance energy transfer). The stability of the coating was determined in response to changes in polarity, pH and ionic strength in the medium. Using the ESIPT system we observed linear changes in signal up to ∼20-25% v/v of co-solvent addition, constituting a break point. Based on such data, we propose a model for coating instability and the important adjustable parameters, such as the electrical charge distribution. FRET data provided confirmatory evidence for the model. The ESIPT dyes and FRET based methods represent new, simple tools for testing NP coating stability in complex environments.

Sulfidization of Au(111) from thioacetic acid: an experimental and theoretical study.

We have studied the adsorption of thioacetic acid (TAAH) on Au(111) from solution deposition. The close proximity of the SH groups to CO groups makes this molecule very attractive for exploring the effect of the functional group on the stability of the S-C and S-Au bonds. Although thioacetic acid was supposed to decompose slowly in water by hydrolysis supplying hydrogen sulfide, this behavior is not expected in nonpolar solvents such as toluene or hexane. Therefore, we have used these solvents for TAAH self-assembly on the Au(111) surface. The characterization of the adsorbates has been done by electrochemical techniques, X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). We have found that even in nonpolar solvents thioacetic acid decomposes to S. The results have been discussed on the basis that the adsorbed species suffer a cleavage on the Au surface, leaving the S attached to it. The dissociation is a spontaneous process that reaches the final state very fast once it is energetically favorable, as can be interpreted from DFT calculations. The thioacetic acid adsorption reveals the strong effect that produces a functional group and the key role of the S-H bond cleavage in the self-assembly process.

The chemistry of the sulfur-gold interface: in search of a unified model.

Over the last three decades, self-assembled molecular films on solid surfaces have attracted widespread interest as an intellectual and technological challenge to chemists, physicists, materials scientists, and biologists. A variety of technological applications of nanotechnology rely on the possibility of controlling topological, chemical, and functional features at the molecular level. Self-assembled monolayers (SAMs) composed of chemisorbed species represent fundamental building blocks for creating complex structures by a bottom-up approach. These materials take advantage of the flexibility of organic and supramolecular chemistry to generate synthetic surfaces with well-defined chemical and physical properties. These films already serve as structural or functional parts of sensors, biosensors, drug-delivery systems, molecular electronic devices, protecting capping for nanostructures, and coatings for corrosion protection and tribological applications. Thiol SAMs on gold are the most popular molecular films because the resulting oxide-free, clean, flat surfaces can be easily modified both in the gas phase and in liquid media under ambient conditions. In particular, researchers have extensively studied SAMs on Au(111) because they serve as model systems to understand the basic aspects of the self-assembly of organic molecules on well-defined metal surfaces. Also, great interest has arisen in the surface structure of thiol-capped gold nanoparticles (AuNPs) because of simple synthesis methods that produce highly monodisperse particles with controllable size and a high surface/volume ratio. These features make AuNPs very attractive for technological applications in fields ranging from medicine to heterogeneous catalysis. In many applications, the structure and chemistry of the sulfur-gold interface become crucial since they control the system properties. Therefore, many researchers have focused on understanding of the nature of this interface on both planar and nanoparticle thiol-covered surfaces. However, despite the considerable theoretical and experimental efforts made using various sophisticated techniques, the structure and chemical composition of the sulfur-gold interface at the atomic level remains elusive. In particular, the search for a unified model of the chemistry of the S-Au interface illustrates the difficulty of determining the surface chemistry at the nanoscale. This Account provides a state-of-the-art analysis of this problem and raises some questions that deserve further investigation.

The complex thiol-palladium interface: a theoretical and experimental study.

This paper presents a theoretical study of the surface structures and thermodynamic stability of different thiol and sulfide structures present on the palladium surface as a function of the chemical potential of the thiol species. It has been found that as the chemical potential of the thiol is increased, the initially clean palladium surface is covered by a (√3 × âˆš3)R30° sulfur lattice. Further increase in the thiol pressure or concentration leads to the formation of a denser (√7 × âˆš7)R19.1° sulfur lattice, which finally undergoes a phase transition to form a complex (√7 × âˆš7)R19.1° sulfur + thiol adlayer (3/7 sulfur + 2/7 thiol coverage). This transition is accompanied by a strong reconstruction of the Pd(111) surface. The formation of these surface structures has been explained in terms of the catalytic properties of the palladium surface. These results have been compared with X-ray photoelectron spectroscopy results obtained for thiols adsorbed on different palladium surfaces.

A surface effect allows HNO/NO discrimination by a cobalt porphyrin bound to gold.

Nitroxyl (HNO) is a small short-lived molecule for which it has been suggested that it could be produced, under certain cofactors conditions, by nitric oxide (NO) synthases. Biologically relevant targets of HNO are heme proteins, thiols, molecular oxygen, NO, and HNO itself. Given the overlap of the targets and reactivity between NO and HNO, it is very difficult to discriminate their physiopathological role conclusively, and accurate discrimination between them still remains critical for interpretation of the ongoing research in this field. The high reactivity and stability of cobalt(II) porphyrins toward NO and the easy and efficient way of covalently joining porphyrins to electrodes through S-Au bonds prompted us to test cobalt(II) 5,10,15,20-tetrakis[3-(p-acetylthiopropoxy)phenyl]porphyrin [Co(P)], as a possible candidate for the electrochemical discrimination of both species. For this purpose, first, we studied the reaction between NO, NO donors, and commonly used HNO donors, with Co(II)(P) and Co(III)(P). Second, we covalently attached Co(II)(P) to gold electrodes and characterized its redox and structural properties by electrochemical techniques as well as scanning tunneling microscopy, X-ray photoelectron spectroscopy, and solid-state density functional theory calculations. Finally, we studied electrochemically the NO and HNO donor reactions with the electrode-bound Co(P). Our results show that Co(P) is positioned over the gold surface in a lying-down configuration, and a surface effect is observed that decreases the Co(III)(P) (but not Co(III)(P)NO(-)) redox potential by 0.4 V. Using this information and when the potential is fixed to values that oxidize Co(III)(P)NO(-) (0.8 V vs SCE), HNO can be detected by amperometric techniques. Under these conditions, Co(P) is able to discriminate between HNO and NO donors, reacting with the former in a fast, efficient, and selective manner with concomitant formation of the Co(III)(P)NO(-) complex, while it is inert or reacts very slowly with NO donors.

Synthesis and characterization of gold at gold(i)-thiomalate core at shell nanoparticles.

In this paper, the synthesis of gold at gold(I)-thiolate core at shell nanoparticles is described for the first time. The chemical nature and structure of these nanoparticles were characterized by a multi-technique approach. The prepared particles consist of gold metallic cores, about 1 nm in size, surrounded by stable gold(I)-thiomalate shells (Au at Au(I)-TM). These nanoparticles could be useful in medicine due to the interesting properties that gold(I)-thiomalate has against rheumatoid arthritis. Furthermore, the described results give new insights in the synthesis and characterization of metallic and core at shell nanoparticles.

Enhanced stability of thiolate self-assembled monolayers (SAMs) on nanostructured gold substrates.

Degradation of thiolate self-assembled monolayers (SAMs) in ambient conditions and liquid environments seriously limits the fabrication of thiol-based devices. Here, we demonstrate that nanostructured gold exhibits higher resistance to SAM degradation and increased electrochemical stability against thiolate desorption in relation to polycrystalline preferred oriented Au(111). The increased stability can be related to the presence of a large number of defects, such as adatoms, vacancies, and steps where the thiolate binding energy is stronger than at terraces. The nanostructured Au is an interesting platform because it can be easily prepared, has surface enhanced Raman spectroscopy (SERS) activity, and exhibits a high signal/noise ratio for amperometric detection because of its large real surface area.