Green-Synthesized Silver Nanoparticles and Their Potential for Antibacterial Applications

The prevalence of infectious diseases is becoming a worldwide problem, and antimicrobial drugs have long been used for prophylactic and therapeutic purposes, but bacterial resistance has creating serious treatment problems. The development of antibiotic resistance makes scientists around the world to seek new drugs that would be more effective. The use and search for drugs obtained from plants and other natural products have increased in recent years. It is well known that silver and its compounds have strong antibacterial activity. Silver, compared to the other metals, shows higher toxicity to microorganisms, while it exhibits lower toxicity to mammalian cells. The progress in the field of nanotechnology has helped scientists to look for new ways in the development of antibacterial drugs. Silver nanoparticles (AgNPs) are interesting for their wide range of applications, e.g. in pharmaceutical sciences, which include treatment of skin diseases (e.g. acne and dermatitis) and other infectious diseases (e.g. post-surgical infections). Various antibacterial aids, such as antiseptic sprays, have also been developed from AgNPs. In this chapter, we have focused on various synthesis methodologies of AgNPs, antibacterial properties, and the mechanism of action

Design, Synthesis, and Evaluation of Novel Indole Hybrid Chalcones and Their Antiproliferative and Antioxidant Activity

The synthesis, anticancer, and antioxidant activities of a series of indole-derived hybrid chalcones are reported here. First, using the well-known Claisen–Schmidt condensation method, a set of 29 chalcones has been designed, synthesized, and consequently characterized. Subsequently, screening for the antiproliferative activity of the synthesized hybrid chalcones was performed on five cancer cell lines (HCT116, HeLa, Jurkat, MDA-MB-231, and MCF7) and two non-cancer cell lines (MCF-10A and Bj-5ta). Chalcone 18c, bearing 1-methoxyindole and catechol structural features, exhibited selective activity against cancer cell lines with IC50 values of 8.0 ± 1.4 µM (Jurkat) and 18.2 ± 2.9 µM (HCT116) and showed no toxicity to non-cancer cells. Furthermore, antioxidant activity was evaluated using three different methods. The in vitro studies of radical scavenging activity utilizing DPPH radicals as well as the FRAP method demonstrated the strong activity of catechol derivatives 18a–c. According to the ABTS radical scavenging assay, the 3-methoxy-4-hydroxy-substituted chalcones 19a–c were slightly more favorable. In general, a series of 3,4-dihydroxychalcone derivatives showed properties as a lead compound for both antioxidant and antiproliferative activity

In Situ Gel with Silver Nanoparticles Prepared Using <i>Agrimonia eupatoria</i> L. Shows Antibacterial Activity

Silver nanoparticles (Ag NPs) with antibacterial activity can be prepared in different ways. In our case, we used ecological green synthesis with Agrimonia eupatoria L. The plant extract was used with Ag NPs for the first time to prepare termosensitive in situ gels (ISGs). Such gels are used to heal human or animal skin and mucous membranes, as they can change from a liquid to solid state after application. Ag NPs were characterized with various techniques (FTIR, TEM, size distribution, zeta potential) and their antibacterial activity was tested against Staphylococcus aureus and Escherichia coli. In accordance with the TEM data, we prepared monodispersed spherical Ag NPs with an average size of about 20 nm. Organic active compounds from Agrimonia eupatoria L. were found on their surfaces using FTIR spectroscopy. Surprisingly, only the in situ gel with Ag NPs showed antibacterial activity against Escherichia coli, while Ag NPs alone did not. Ag NPs prepared via green synthesis using plants with medicinal properties and incorporated into ISGs have great potential for wound healing due to the antibacterial activity of Ag NPs and the dermatological activity of organic substances from plants

Mechanochemistry as an Alternative Method of Green Synthesis of Silver Nanoparticles with Antibacterial Activity: A Comparative Study

This study shows mechanochemical synthesis as an alternative method to the traditional green synthesis of silver nanoparticles in a comparative manner by comparing the products obtained using both methodologies and different characterization methods. As a silver precursor, the most commonly used silver nitrate was applied and the easily accessible lavender (Lavandula angustofolia L.) plant was used as a reducing agent. Both syntheses were performed using 7 different lavender:AgNO3 mass ratios. The synthesis time was limited to 8 and 15 min in the case of green and mechanochemical synthesis, respectively, although a significant amount of unreacted silver nitrate was detected in both crude reaction mixtures at low lavender:AgNO3 ratios. This finding is of particular interest mainly for green synthesis, as the potential presence of silver nitrate in the produced nanosuspension is often overlooked. Unreacted AgNO3 has been removed from the mechanochemically synthesized samples by washing. The nanocrystalline character of the products has been confirmed by both X-ray diffraction (Rietveld refinement) and transmission electron microscopy. The latter has shown bimodal size distribution with larger particles in tens of nanometers and the smaller ones below 10 nm in size. In the case of green synthesis, the used lavender:AgNO3 ratio was found to have a decisive role on the crystallite size. Silver chloride has been detected as a side-product, mainly at high lavender:AgNO3 ratios. Both products have shown a strong antibacterial activity, being higher in the case of green synthesis, but this can be ascribed to the presence of unreacted AgNO3. Thus, one-step mechanochemical synthesis (without the need to prepare extract and performing the synthesis as separate steps) can be applied as a sustainable alternative to the traditional green synthesis of Ag nanoparticles using plants