Synthesis, Spectroscopic, Molecular Structure, and Antibacterial Studies of Dibutyltin(IV) Schiff Base Complexes Derived from Phenylalanine, Isoleucine, and Glycine

Extracellular biosynthesis, OVAT/statistical optimization, and characterization of silver nanoparticles (AgNPs) using Leclercia adecarboxylata THHM and its antimicrobial activity

BACKGROUND

The biosynthesis of silver nanoparticles (AgNPs) is an area of interest for researchers due to its eco-friendly approach. The use of biological approaches provides a clean and promising alternative process for the synthesis of AgNPs. We used for the first time the supernatant of Leclercia adecarboxylata THHM under optimal conditions to produce AgNPs with an acceptable antimicrobial activity against important clinical pathogens.

RESULTS

In this study, soil bacteria from different locations were isolated and screened for their potential to form AgNPs. The selected isolate, which was found to have the ability to biosynthesize AgNPs, was identified by molecular methods as Leclercia adecarboxylata THHM and its 16S rRNA gene was deposited in GenBank under the accession number OK605882. Different conditions were screened for the maximum production of AgNPs by the selected bacteria. Five independent variables were investigated through optimizations using one variable at a time (OVAT) and the Plackett-Burman experimental design (PBD). The overall optimal parameters for enhancing the biosynthesis of AgNPs using the supernatant of Leclercia adecarboxylata THHM as a novel organism were at an incubation time of 72.0 h, a concentration of 1.5 mM silver nitrate, a temperature of 40.0 °C, a pH of 7.0, and a supernatant concentration of 30% (v/v) under illumination conditions. The biosynthesized AgNPs have been characterized by UV-visible spectroscopy (UV-Vis), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The biosynthesized AgNPs showed an absorption peak at 423 nm, spherical shape, and an average particle size of 17.43 nm. FTIR shows the bands at 3321.50, 2160.15, and 1636.33 cm^-1 corresponding to the binding vibrations of amine, alkyne nitrile, and primary amine bands, respectively. The biosynthesized AgNPs showed antimicrobial activity against a variety of microbial pathogens of medical importance. Using resazurin-based microtiter dilution, the minimum inhibitory concentration (MIC) values for AgNPs were 500 µg/mL for all microbial pathogens except for Klebsiella pneumoniae ATCC13883, which has a higher MIC value of 1000 µg/mL.

CONCLUSIONS

The obtained data revealed the successful green production of AgNPs using the supernatant of Leclercia adecarboxylata THHM that can be effectively used as an antimicrobial agent against most human pathogenic microbes.

Coordination Chemistry, Antibacterial Screening, and In Silico ADME Study of Mononuclear NiII and CuII Complexes of Asymmetric Schiff Base of Streptomycin and Aniline

Two novel metal complexes, that is, Ni (StmAn)2(4) and Cu (StmAn)2(5), were synthesized from unsymmetrical Schiff base ligand StmAn (3). The ligand was prepared by refluxing streptomycin (2) and aniline (1). They were characterized by elemental microanalysis, conductivity measurements, and spectroscopic techniques such as 1H NMR, FT-IR, ESI-mass, and electronic absorption spectral study. Interestingly, the study revealed metal coordination through azomethine nitrogen and N-atom of NH-CH3 of N-methyl-L-glucosamine unit of streptomycin. The electronic absorption spectral study supported an octahedral geometry for complex 4 and a tetrahedral geometry for complex 5. Particle size calculation by Scherrer’s formula indicated their nanocrystalline nature. The geometry optimization of the complexes was achieved by running an MM2 job in Gaussian supported Cs-ChemOffice ultra-12.0.1 and ArgusLab 4.0.1 version software. Based on SwissADME predictions, a theoretical drug profile was generated by analyzing absorption, distribution, metabolism, excretion, and toxicity (ADMET) scores of the compounds. They were screened for in vitro antibacterial activity study against four clinical pathogens such as E. coli, S. pneumoniae, P. vulgaris, and S. aureus. Minimum inhibitory concentration (MIC) study demonstrated greater inhibitory potency of complex (4) (0.024 g/L) for S. aureus relative to ligand (3) and complex (5). Studies show that metal complexes are more toxic to bacteria.

Synthesis, spectroscopy, and density functional theory of organotin and organosilicon complexes of bioactive ligands containing nitrogen, sulfur donor atoms as antimicrobial agents: in vitro and in silico studies

Recently inorganic-based metallodrugs provide an effective mechanism for the drugs on the choice of metal and its properties. Medicinal complex compounds provide an efficient platform for various pharmacological and therapeutic applications. Six new organotin and organosilicon complexes containing sulphur and nitrogen donor atoms were synthesised. These complexes of (E)-2-((4-methoxybenzylidene)amino)benzenethiol were characterized by elemental analyses, molecular weights, conductance measurements, infrared, electronic, and NMR spectroscopy. The data analysis indicated that the Schiff base contains bidentate nitrogen sulfur (NS) domains and was coordinated to silicon (Si) and tin (Sn) moieties via the imine-N and thiolic-S atoms, resulting in penta- and hexa-coordinated complexes in 1 : 1 and 1 : 2 ratios, respectively. The geometries around the Sn and Si atoms in complexes 1, 3, and 5 were five-coordinated and 2, 4, and 6 were six-coordinated octahedra, respectively. Density functional theory (DFT) was used to determine the optimal structural parameters. The antimicrobial activities of the ligand and its complexes were determined. These data indicate that metal complexes are more effective against bacteria and fungi in comparison to the free ligand. Molecular docking was performed to interpret the interaction of protein and various complexes and it was observed that compound 6 showed the highest binding affinity.

Characterization of Talaromyces islandicus-mediated silver nanoparticles and evaluation of their antibacterial and anticancer potential

The biosynthesized silver nanoparticles (AgNPs) have been reported to possess several therapeutic applications. Silver is one of the important metals known for its bioactive properties not only as macromolecule but also as nanoparticle (NP). The current research focused on the eco-friendly synthesis of Talaromyces islandicus VSGF1(Lab code) -mediated AgNPs. The aqueous culture filtrate of T. islandicus VSGF1 was used as a reducing agent. The formation of AgNPs was confirmed by observing the color change from colorless to colloidal earthy-colored and a sharp absorption peak of ultraviolet-visible (UV-vis) spectroscopy at 400 nm. Fourier-transform infrared spectroscopy revealed the involvement of various functional groups for the formation and stabilization of AgNPs. The structure, size, and shape of mycosynthesized AgNPs were identified by X-ray diffraction (XRD), scanning electron microscopy, and atomic force microscopy (AFM) analysis. The XRD analysis exhibited crystalline nature of NPs whereas AFM analysis revealed the spherical shape of AgNP with average size range between 13 and 66 nm. The antibacterial activity of AgNPs (50 μg/ml) investigated against gram-positive and gram-negative bacteria revealed maximum zone of inhibition (ZOI) against drug-resistant Enterococcus faecalis MTCC439 (18.66 ± 0.57 mm) and Pseudomonas aeruginosa MTCC96 (16 ± 0 mm) followed by Staphylococcus aureus MTCC96 (15.33 ± 0.57 mm), Bacillus subtilis MTCC441 (14.66 ± 0.57 mm), and Escherichia coli MTCC45 (14.66 ± 0.57 mm). Further, the AgNPs evaluated for antitumor activity against human hepatocellular carcinoma (HepG2) cell line exhibited promising result with half-maximal inhibitory concentration (MIC) value at 38.17 μg/ml concentration through MTT (methylthiazolyl tetrazolium assay) assay. Apparently, this is the first report from T. islandicus to the best of our knowledge.

Substituted Organotin Complexes of 4-Methoxybenzoic Acid for Reduction of Poly(vinyl Chloride) Photodegradation

Poly(vinyl chloride) suffers from degradation through oxidation and decomposition when exposed to radiation and high temperatures. Stabilizers are added to polymeric materials to inhibit their degradation and enable their use for a longer duration in harsh environments. The design of new additives to stabilize poly(vinyl chloride) is therefore desirable. The current study includes the synthesis of new tin complexes of 4-methoxybenzoic acid and investigates their potential as photostabilizers for poly(vinyl chloride). The reaction of 4-methoxybenzoic acid and substituted tin chlorides gave the corresponding substituted tin complexes in good yields. The structures of the complexes were confirmed using analytical and spectroscopic methods. Poly(vinyl chloride) was doped with a small quantity (0.5%) of the tin complexes and homogenous thin films were made. The effects of the additives on the stability of the polymeric material on irradiation with ultraviolet light were assessed using different methods. Weight loss, production of small polymeric fragments, and drops in molecular weight were lower in the presence of the additives. The surface of poly(vinyl chloride), after irradiation, showed less damage in the films containing additives. The additives, in particular those containing aromatic (phenyl groups) substitutes, inhibited the photodegradation of polymeric films significantly. Such additives act as efficient ultraviolet absorbers, peroxide quenchers, and hydrogen chloride scavengers.

Elemental Silver Nanoparticles: Biosynthesis and Bio Applications

The data on the specifics of synthesis of elemental silver nanoparticles (Ag-NP) having various geometric shapes (pseudo spherical, prismatic, cubic, trigonal-pyramidal, etc.), obtained by using various biological methods, and their use in biology and medicine have been systematized and generalized. The review covers mainly publications published in the current 21st century. Bibliography: 262 references.

Long-Term Effect of Ultraviolet Irradiation on Poly(vinyl chloride) Films Containing Naproxen Diorganotin(IV) Complexes

As poly(vinyl chloride) (PVC) photodegrades with long-term exposure to ultraviolet radiation, it is desirable to develop methods that enhance the photostability of PVC. In this study, new aromatic-rich diorganotin(IV) complexes were tested as photostabilizers in PVC films. The diorganotin(IV) complexes were synthesized in 79-86% yields by reacting excess naproxen with tin(IV) chlorides. PVC films containing 0.5 wt % diorganotin(IV) complexes were irradiated with ultraviolet light for up to 300 h, and changes within the films were monitored using the weight loss and the formation of specific functional groups (hydroxyl, carbonyl, and polyene). In addition, changes in the surface morphologies of the films were investigated. The diorganotin(IV) complexes enhanced the photostability of PVC, as the weight loss and surface roughness were much lower in the films with additives than in the blank film. Notably, the dimethyltin(IV) complex was the most efficient photostabilizer. The polymeric film containing this complex exhibited a morphology of regularly distributed hexagonal pores, with a honeycomb-like structure-possibly due to cross-linking and interactions between the additive and the polymeric chains. Various mechanisms, including direct absorption of ultraviolet irradiation, radical or hydrogen chloride scavenging, and polymer chain coordination, could explain how the diorganotin(IV) complexes stabilize PVC against photodegradation.

Characterization and antimicrobial activity of silver nanoparticles mycosynthesized by Aspergillus brasiliensis

AIMS

Since mycosynthesis of metal nanoparticles (NPs) is advertised as a promising and ecofriendly approach. Thus, this study aims to investigate the capability of Aspergillus brasiliensis ATCC 16404 for mycosynthesis of silver NPs (AgNPs).

METHODS AND RESULTS

One-factor-at-a-time-technique was used to study the effect of different physicochemical parameters: the reaction time, pH, temperature, different stirring rates, illumination, and finally, the different concentrations of silver nitrate and fungal biomass on the mycosynthesis of AgNPs. The visual observation showed the characteristic brown colour formation due to the bioreduction of Ag⁺ ions to Ag⁰ by the mycelial cell-free filtrate (MCFF). The UV/visible spectrophotometric technique displayed a characteristic sharp peak at ʎ₄₄₀ confirming the mycosynthesis of AgNPs. The zeta potential value -16·7 mV assured the long-term stability of AgNPs and the dynamic light scattering analysis revealed good dispersion and average particle size 77 nm. The energy dispersive X-ray spectroscopy displayed a maximum elemental distribution of silver elements. The X-ray diffraction spectroscopy demonstrated the crystallinity of the mycosynthesized AgNPs. The field emission scanning electron microscope and high-resolution transmission electron microscope revealed monodispersed spherical shaped AgNPs with average particle size of 6-21 nm. The FTIR analysis showed the major peaks of proteins providing the possible role of MCFF in the synthesis and stabilization of the AgNPs. The mycosynthesized AgNPs expressed good biocidal activity against different pathogenic micro-organisms causing some water-related diseases and health problems to local residents.

CONCLUSIONS

This study proved that A. brasiliensis ATCC 16404 MCFF has good potential for mycosynthesis of AgNPs, which exhibited good antimicrobial effect on different pathogenic micro-organisms; thus, it can be applied for water disinfection.

SIGNIFICANCE AND IMPACT OF THE STUDY

This research provides a helpful insight into the development of a new mycosynthesized antimicrobial agent.

Biomimetic synthesis of AgNPs from Penicillium chrysogenum strain FGCC/BLS1 by optimising physico-cultural conditions and assessment of their antimicrobial potential

Biomimetic synthesis of metal nanoparticles (NPs) is safe and eco-friendly; therefore, find diverse applications. Considering this, the soil fungi Penicillium chrysogenum strain Fungal germplasm collection centre/ BLS1 was isolated, characterized and explored to synthesize extracellular silver NPs (AgNPs) under optimised conditions. The synthesis of AgNPs was investigated using ultraviolet (UV)-visible spectroscopy, Fourier-transform infra-red spectroscopy (FTIR), transmission electron microscope (TEM) and dynamic light scattering (DLS) analysis. Process optimisation exhibited AgNPs synthesis within 8 h using 2 mM AgNO3 at pH 11 and temperature 70°C. TEM analysis revealed polydispersed ellipsoidal shaped AgNPs with average particle size 96.8 nm as measured by DLS. AgNPs showed negative zeta potential that confers surface stability in solution. FTIR spectra confirmed the presence of protein bound to AgNPs. Antibacterial activity against Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus by the AgNPs (100 ppm) was demonstrated by counting colony forming unit , disc diffusion, and growth kinetics assay. Additionally radial assay revealed antifungal activity of AgNPs (100 ppm) against phytopathogenic fungi Sclerotinia sclerotiorum Microbial type culture collection 8785. Furthermore, AgNPs (100 ppm) did not show any cytotoxic effects on human Red blood cells. Therefore, this novel fungal strain can be utilised for biofabrication of AgNPs under optimised conditions and have shown strong antimicrobial property.

Efficacy of biogenic silver nanoparticles against clinical isolates of fungi causing mycotic keratitis in humans

Mycotic keratitis is mainly responsible for vision loss caused by various fungi. Sometimes, proper treatment of such infection is not possible due to unavailability of effective antifungal agents and development of resistance of such fungi to antimycotic drugs. Hence, it is necessary to search for potential antifungal agents, which can effectively eradicate fungal infection of eyes. Nanoparticles‐based antifungal drugs overcome this problem by increasing permeability and properties of drug molecules. In the present study, silver nanoparticles were synthesised by using Helminthosporium sp. and Chaetomium sp. following sequential reduction technique. The synthesised silver nanoparticles were detected primarily by UV‐visible spectrophotometer showing absorption spectra at 424 and 433 nm, respectively. Nanoparticles tracking analysis confirmed the mean particle size of silver nanoparticles as 45 and 55 nm. The synthesised AgNPs showed significant antifungal activity against fungi causing mycotic keratitis, when used alone and in combination with ketoconazole and amphotericin B in the range of 30–70 microgram per millilitre of minimum inhibitory concentration. Thus, the synthesised AgNPs can be used to enhance the activities of ketoconazole and amphotericin B.

Rapid synthesis of silver nanoparticles by Pseudomonas stutzeri isolated from textile soil under optimised conditions and evaluation of their antimicrobial and cytotoxicity properties

Present study utilised textile soil isolated bacterium Pseudomonas stutzeri to synthesise extracellular silver nanoparticles (AgNPs) under optimised conditions. The synthesised AgNPs were characterised using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Optimisation showed AgNPs synthesis within 8 h using 2mM Ag nitrate at pH9, temperature 80°C and maximum absorbance toward 400 nm. TEM analysis revealed spherical shape AgNPs and reduction in size upto 8 nm was observed under optimised conditions. FTIR spectra confirmed presence of proteins bound to AgNPs act as reducing agent. AgNPs showed strong antibacterial activity against multi-drug resistant (MDR) Escherichia coli and Klebsiella pneumoniae as demonstrated by disc diffusion and colony forming unit assays. Zone of inhibition increased with increasing concentration of AgNPs with maximum of 19 mm against E. coli and 17 mm against K. pneumoniae at concentration of 2 μg/disc. Furthermore, AgNPs did not show any cytotoxic effects on human epithelial cells as demonstrated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay even at 2 μg/ml concentration of AgNPs. The results of the present study suggest that AgNPs can be synthesised rapidly under optimised conditions and show strong antimicrobial property against MDR pathogens without having toxicity effect on human epithelial cells.

Mycoendophytes as efficient synthesizers of bionanoparticles: nanoantimicrobials, mechanism, and cytotoxicity

Mycoendophytes are the fungi that occur inside the plant tissues without exerting any negative impact on the host plant. They are most frequently isolated endophytes from the leaf, stem, and root tissues of various plants. Among all fungi, the mycoendophytes as biosynthesizer of noble metal nanoparticles (NPs) are less known. However, some reports showing efficient synthesis of metal nanoparticles, mainly silver nanoparticles and its remarkable antimicrobial activity against bacterial and fungal pathogens of humans and plants. The nanoparticles synthesized from mycoendophytes present stability, polydispersity, and biocompatibility. These are non-toxic to humans and environment, can be gained in an easy and cost-effective manner, have wide applicability and could be explored as promising candidates for a variety of biomedical, pharmaceutical, and agricultural applications. Mycogenic silver nanoparticles have also demonstrated cytotoxic activity against cancer cell lines and may prove to be a promising anticancer agent. The present review focuses on the biological synthesis of metal nanoparticles from mycoendophytes and their application in medicine. In addition, different mechanisms of biosynthesis and activity of nanoparticles on microbial cells, as well as toxicity of these mycogenic metal nanoparticles, have also been discussed.

Photostabilizing Efficiency of Poly(vinyl chloride) in the Presence of Organotin(IV) Complexes as Photostabilizers

Three organotin complexes containing furosemide as a ligand (L), Ph₃SnL, Me₂SnL₂ and Bu₂SnL₂, were synthesized and characterized. Octahedral geometry was proposed for the Me₂SnL₂ and Bu₂SnL₂, while the Ph₃SnL complex has trigonal bipyramid geometry. The synthesized organotin complexes (0.5% by weight) were used as additives to improve the photostability of poly(vinyl chloride), PVC, (40 μm thickness) upon irradiation. The changes imposed on functional groups, weight loss and viscosity average molecular weight of PVC films were monitored. The experimental results show that the rate of photodegradation was reduced in the presence of the organotin additives. The quantum yield of the chain scission was found to be low (9.8 × 10(-7)) when Ph₃SnL was used as a PVC photostabilizer compared to controlled PVC (5.18 × 10(-6)). In addition, the atomic force microscope images for the PVC films containing Ph₃SnL₂ after irradiation shows a smooth surface compared to the controlled films. The rate of PVC photostabilization was found to be highest for Ph₃SnL followed by Bu₂SnL₂ and Me₂SnL₂. It has been suggested that the organotin complexes could act as hydrogen chloride scavengers, ultraviolet absorbers, peroxide decomposers and/or radical scavengers.

Toxicity of fungal-generated silver nanoparticles to soil-inhabiting Pseudomonas putida KT2440, a rhizospheric bacterium responsible for plant protection and bioremediation

Silver nanoparticles have attracted considerable attention due to their beneficial properties. But toxicity issues associated with them are also rising. The reports in the past suggested health hazards of silver nanoparticles at the cellular, molecular, or whole organismal level in eukaryotes. Whereas, there is also need to examine the exposure effects of silver nanoparticle to the microbes, which are beneficial to humans as well as environment. The available literature suggests the harmful effects of physically and chemically synthesised silver nanoparticles. The toxicity of biogenically synthesized nanoparticles has been less studied than physically and chemically synthesised nanoparticles. Hence, there is a greater need to study the toxic effects of biologically synthesised silver nanoparticles in general and mycosynthesized nanoparticles in particular. In the present study, attempts have been made to assess the risk associated with the exposure of mycosynthesized silver nanoparticles on a beneficial soil microbe Pseudomonas putida. KT2440. The study demonstrates mycosynthesis of silver nanoparticles and their characterisation by UV-vis spectrophotometry, FTIR, X-ray diffraction, nanosight LM20--a particle size distribution analyzer and TEM. Silver nanoparticles obtained herein were found to exert the hazardous effect at the concentration of 0.4 μg/ml, which warrants further detailed investigations concerning toxicity.

An α1-adrenergic receptor ligand repurposed as a potent antiproliferative agent for head and neck squamous cell carcinoma

In this study we report the anticancer properties of RN5-Me, an α₁-adrenergic receptor ligand.