Catalytic and Biological Activity of Silver and Gold Complexes Stabilized by NHC with Hydroxy Derivatives on Nitrogen Atoms

In this paper is reported the synthesis of N,N′ hydroxy derivative of NHC silver (3a–4a) and gold(I) (3b–4b) complexes of general formula [M(NHC)2]+ [MX2]−. All compounds were characterized by spectroscopic and analytic techniques. The complexes turned out to be effective in both catalytic and biological applications. They catalyzed the coupling of aldehyde, piperidine, and phenylacetylene in A3-reaction to produce propargylamines and showed antimicrobial activity. In fact, minimal inhibition concentration (MIC) tests with Gram-positive and Gram-negative bacteria demonstrated that the silver compounds are selective toward E. coli, whereas the gold analogues are active against S. aureus. Moreover, the N,N′ hydroxy derivative of NHC silver complexes 3a and 4a exhibited good anticancer activity on the HeLA cancer cells (3a-IC50 = 12.2 ± 0.1 µM, 4a-IC50 = 11.9 ± 1.2 µM), whereas gold complex 4b displayed good anticancer activity towards the MCF-7 cells (IC50 = 12.2 ± 1.2 µM).

Silver diamine fluoride for managing carious lesions: A literature review

Though the prevalence and the severity of dental caries is decreased in past few years, still children from low socioeconomical status in many industrialized or developing countries are still suffering from ill-effects of dental caries. The antimicrobial effect of silver compounds has been proven by the 100-year-old application of silver compounds. Silver diamine fluoride (SDF) has been used to arrest dental caries during 1970s in Japan, but it was not exposed much to other parts of the world. Today in many countries a 38% (44,800 ppm fluoride) SDF solution is commonly used to arrest caries and also to reduce hypersensitivity in primary and permanent teeth. Application of SDF to arrest dental caries is non-invasive procedure and is quick and simple to use. Reports of available studies showed that there is no severe pulpal damage after SDF application. However, it has some drawbacks like black discoloration of the carious teeth and an unpleasant metallic taste. But, low cost of SDF and its simplicity in application suggest that it is an appropriate agent for use in community dental health programme. Thus, SDF appears to meet the criteria of both the WHO Millennium Goals and the US Institute of Medicine’s criteria for 21st century medical care, that is, it is a safe, effective, efficient, and equitable caries preventive agent.

Minimally Invasive Techniques Used for Caries Management in Dentistry. A Review

Objective: Minimally invasive techniques that use silver compounds and glass ionomer cement are suggested for caries management due to their effectiveness, simplicity, and low cost. The aim of this review is to examine the evidence supporting the use of silver compounds and glass ionomer cement in dentistry. Study design: Literature was searched using PubMed, Elsevier, EBSCO, Google scholar, AAPD and UABC’s database from 1958 to 2018 with the keywords: “Silver nitrate”, “silver diamine fluoride”, and “glass ionomer cement”. The selected studies were then fully read to prove their relevance for this review. Results: The use of glass ionomer cement and silver compounds were shown to be effective in arresting caries. These compounds reduce cariogenic microorganisms. Their chemical properties inhibit bacterial growth while promoting remineralization. They are simpler and less time consuming than conventional restorations. They also cause less discomfort and anxiety to patients. Silver compounds were shown to stain teeth and may burn the cornea if used in high concentration. These disadvantages limit the use of silver compounds to posterior teeth and require caution when handling. Conclusions: Minimally invasive therapies are easy to apply, non-invasive and affordable. Further studies should be done to provide more evidence of these techniques for caries management.

Polystyrene Nanoplastics as Carriers of Metals. Interactions of Polystyrene Nanoparticles with Silver Nanoparticles and Silver Nitrate, and Their Effects on Human Intestinal Caco-2 Cells

Environmental plastic wastes are continuously degraded to their micro and nanoforms. Since in the environment they coexist with other pollutants, it has been suggested that they could act as vectors transporting different toxic trace elements, such as metals. To confirm this, we have assessed the potential interactions between nanopolystyrene, as a model of nanoplastic debris, and silver compounds (silver nanoparticles and silver nitrate), as models of metal contaminant. Using TEM-EDX methodological approaches, we have been able to demonstrate metal sorption by nanopolystyrene. Furthermore, using Caco-2 cells and confocal microscopy, we have observed the co-localization of nanopolystyrene/nanosilver in different cellular compartments, including the cell nucleus. Although the internalization of these complexes showed no exacerbated cytotoxic effects, compared to the effects of each compound alone, the silver/nanopolystyrene complexes modulate the cell’s uptake of silver and slightly modify some harmful cellular effects of silver, such as the ability to induce genotoxic and oxidative DNA damage.

Photochemical Printing of Plasmonically Active Silver Nanostructures

In this paper, we demonstrate plasmonic substrates prepared on demand, using a straightforward technique, based on laser-induced photochemical reduction of silver compounds on a glass substrate. Importantly, the presented technique does not impose any restrictions regarding the shape and length of the metallic pattern. Plasmonic interactions have been probed using both Stokes and anti-Stokes types of emitters that served as photoluminescence probes. For both cases, we observed a pronounced increase of the photoluminescence intensity for emitters deposited on silver patterns. By studying the absorption and emission dynamics, we identified the mechanisms responsible for emission enhancement and the position of the plasmonic resonance.