Antibacterial Nanomaterials: Mechanisms, Impacts on Antimicrobial Resistance and Design Principles.

Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR-independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure-activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano-microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.

Study of the Electrochemical Behavior of N-Substituted-4-Piperidones Curcumin Analogs: A Combined Experimental and Theoretical Approach.

The electrochemical behavior of N-methyl- and N-benzyl-4-piperidone curcumin analogs were studied experimentally and theoretically. The studied compounds present different substituents at the para position in the phenyl rings (-H, -Br, -Cl, -CF3, and -OCH3). We assessed their electrochemical behavior by differential pulse and cyclic voltammetry, while we employed density functional theory (DFT) M06 and M06-2x functionals along with 6-311+G(d,p) basis set calculations to study them theoretically. The results showed that compounds suffer a two-electron irreversible oxidation in the range of 0.72 to 0.86 V, with surface concentrations ranging from 1.72 × 10-7 to 5.01 × 10-7 mol/cm2. The results also suggested that the process is diffusion-controlled for all compounds. M06 DFT calculations showed a better performance than M06-2x to obtain oxidation potentials. We found a good correlation between the experimental and theoretical oxidation potential for N-benzyl-4-piperidones (R2 = 0.9846), while the correlation was poor for N-methyl-4-piperidones (R2 = 0.3786), suggesting that the latter suffer a more complex oxidation process. Calculations of the BDEs for labile C-H bonds in the compounds suggested that neither of the two series of compounds has a different tendency for a proton-coupled electron transfer (PCET) oxidation process. It is proposed that irreversible behavior is due to possible dimerization of the compounds by Shono-type oxidation.

On the Use of Styrene-Based Nanoparticles to Mitigate the Effect of Montmorillonite in Copper Sulfide Recovery by Flotation.

Clay minerals have different negative effects on the froth flotation process such as low adsorption of collectors on valuable minerals, increased pulp viscosity, and the reduction in recovery and grade concentrates of copper sulfides. This study aims to evaluate the use of polystyrene-based nanoparticles (NPs) for the froth flotation of chalcopyrite and their ability to mitigate the negative effect of montmorillonite on the recovery of this sulfide. The experimental stage consisted of preparing a type of polystyrene-based nanoparticle (St-CTAB-VI), which was analyzed by dynamic night scattering (DLS) to establish its hydrodynamic size. Then, the effect of NPs on chalcopyrite's angle's in the presence and absence of montmorillonite (15%) was evaluated and compared with the contact angle achieved using potassium amyl xanthate (PAX) and a mixture of PAX and NPs. In addition, zeta potential measurements were carried out to investigate the interactions between the chalcopyrite and the montmorillonite or the NPs under fixed concentrations and microflotation tests were performed employing different times to evaluate the chalcopyrite recovery in the presence of montmorillonite, using NPs and mixtures with PAX. Finally, turbidity analysis as a function of time was performed to evaluate the occurrence of sedimentation and flocculation phenomena in suspensions of 15% montmorillonite in the presence and absence of chalcopyrite, nanoparticles, and mixtures of NPs and PAX. The results indicated that the mixture of NPs and PAX contributed to increasing the contact angle of chalcopyrite in the presence of montmorillonite. This can be associated with the presence of molecular and nanometric collectors that generated a higher hydrophobicity on the chalcopyrite particles, contributing to reducing the presence of clay minerals on the mineral surface. In addition, the mixture of NPs and PAX promoted the generation of nanoparticles on the sulfide mineral surface, which helps to detach the slime and facilitate the bubble/mineral attachment step during flotation.

Biopolymer-Based Composite Hydrogels Embedding Small Silver Nanoparticles for Advanced Antimicrobial Applications: Experimental and Theoretical Insights.

In this work, we report a two-step methodology for the synthesis of small silver nanoparticles embedded into hydrogels based on chitosan (CS) and hydroxypropyl methylcellulose (HPMC) biopolymers. This method uses d-glucose as an external green reducing agent and purified water as a solvent, leading to an eco-friendly, cost-effective, and biocompatible process for the synthesis of silver nanocomposite hydrogels. Their characterization comprises ultraviolet-visible spectroscopy, Fourier-transform infrared spectra, differential scanning calorimetry, scanning electron microscopy with energy-dispersive spectroscopy, and transmission electron microscopy assays. Moreover, the structural stability of the hydrogels was investigated through sequential swelling-deswelling cycles. The nanomaterials showed good mechanical properties in terms of their structural stability and revealed prominent antibacterial properties due to the reduced-size particles that promote their use as new advanced antimicrobial agents, an advantage compared to conventional particles in aqueous suspension that lose stability and effectiveness. Finally, theoretical analyses provided insights into the possible interactions, charge transfer, and stabilization process of nanoclusters mediated by the high-electron-density groups belonging to CS and HPMC, revealing their unique structural properties in the preparation of nano-scaled materials.

Recent progress, trends, and new challenges in the electrochemical production of green hydrogen coupled to selective electrooxidation of 5-hydroxymethylfurfural (HMF).

The production of clean electrical energy and the correct use of waste materials are two topics that currently concern humanity. In order to face both problems, extensive work has been done on the electrolytic production of green H2 coupled with the electrooxidative upgrading of biomass platform molecules. 5-Hydroxymethylfurfural (HMF) is obtained from forest waste biomass and can be selectively oxidized to 2,5-furandicarboxylic acid (FDCA) by electrochemical pathways. FDCA is an attractive precursor to polyethylene furanoate (PEF), with the potential to replace petroleum-based polyethylene terephthalate (PET). An integrated electrochemical system can simultaneously produce H2 and FDCA at a lower energy cost than that required for electrolytic water splitting. Here, the benefits of the electrochemical production of H2 and FDCA over other production methods are presented, as well as the innovative applications of each reaction product and the advantages of carrying out both reactions in a coupled system. The recently reported progress is disclosed, through an exploration of electrocatalyst materials used in simultaneous production, including the use of nickel foams (NF) as modification substrates, noble and non-noble metals, metal non-oxides, metal oxides, spinel oxides and the introduction of oxygen vacancies. Based on the latest trends, the next challenges associated with its large-scale production are proposed for its implementation in the industrial world. This work can offer a guideline for the detailed understanding of the electrooxidation of HMF towards FDCA with the production of H2, as well as the design of advanced electrocatalysts for the sustainable use of renewable resources.

A New Quinone-Based Inhibitor of Mitochondrial Complex I in D-Conformation, Producing Invasion Reduction and Sensitization to Venetoclax in Breast Cancer Cells.

Mitochondrial Complex I plays a crucial role in the proliferation, chemoresistance, and metastasis of breast cancer (BC) cells. This highlights it as an attractive target for anti-cancer drugs. Using submitochondrial particles, we identified FRV-1, an ortho-carbonyl quinone, which inhibits NADH:duroquinone activity in D-active conformation and reduces the 3ADP state respiration dependent on Complex I, causing mitochondrial depolarization, ATP drop, increased superoxide levels, and metabolic remodeling towards glycolysis in BC cells. Introducing methyl groups at FRV-1 structure produced analogs that acted as electron acceptors at the Complex I level or increased the inhibitory effect of FCCP-stimulated oxygen consumption rate, which correlated with their redox potential, but increased toxicity on RMF-621 human breast fibroblasts was observed. FRV-1 was inactive in the naphthoquinone oxidoreductase 1 (NOQ1)-positive BC cell line, MCF7, but the sensitivity was recovered by dicoumarol, a NOQ1 inhibitor, suggesting that FRV-1 is a NOQ1 substrate. Importantly, FRV-1 selectively inhibited the proliferation, migration, and invasion of NQO1 negative BC cell, MDA-MB-231, in an OXPHOS- and ROS-dependent manner and sensitized it to the BH3 mimetic drug venetoclax. Overall, FRV-1 is a novel Complex I inhibitor in D-active conformation, blocking possibly the re-activation to A-state, producing selective anti-cancer effects in NQO1-negative BC cell lines.

Use of Polystyrene Nanoparticles as Collectors in the Flotation of Chalcopyrite.

This study proposes the use of polymeric nanoparticles (NPs) as collectors for copper sulfide flotation. The experimental phase included the preparation of two types of polystyrene-based NPs: St-CTAB and St-CTAB-VI. These NPs were characterized by Fourier-Transform Infrared (FTIR) spectroscopy and dynamic light scattering (DLS). Then, microflotation tests with chalcopyrite under different pH conditions and nanoparticle dosages were carried out to verify their capabilities as chalcopyrite collectors. In addition, the zeta potential (ZP) measurements of chalcopyrite in the presence and absence of NPs were carried out to study their interaction. Lastly, some Atomic Force Micrographs (AFM) of NPs and Scanning Electronic Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analysis of NPs on the chalcopyrite surface were conducted to analyze the size, the morphology and their interaction. The results obtained at pH 6 and pH 8 show that the NPs under study can achieve a chalcopyrite recovery near or higher than that obtained with the conventional collector. In this study, it was possible to observe that the NPs functionalized by the imidazole group (St-CTAB-VI) achieved better performance due to the presence of this group in its composition, allowing to achieve a greater affinity with the surface of the mineral.

Genetic Diversity, Population Structure and Linkage Disequilibrium Analyses in Tropical Maize Using Genotyping by Sequencing.

Several maize breeding programs in India have developed numerous inbred lines but the lines have not been characterized using high-density molecular markers. Here, we studied the molecular diversity, population structure, and linkage disequilibrium (LD) patterns in a panel of 314 tropical normal corn, two sweet corn, and six popcorn inbred lines developed by 17 research centers in India, and 62 normal corn from the International Maize and Wheat Improvement Center (CIMMYT). The 384 inbred lines were genotyped with 60,227 polymorphic single nucleotide polymorphisms (SNPs). Most of the pair-wise relative kinship coefficients (58.5%) were equal or close to 0, which suggests the lack of redundancy in the genomic composition in the majority of inbred lines. Genetic distance among most pairs of lines (98.3%) varied from 0.20 to 0.34 as compared with just 1.7% of the pairs of lines that differed by <0.20, which suggests greater genetic variation even among sister lines. The overall average of 17% heterogeneity was observed in the panel indicated the need for further inbreeding in the high heterogeneous genotypes. The mean nucleotide diversity and frequency of polymorphic sites observed in the panel were 0.28 and 0.02, respectively. The model-based population structure, principal component analysis, and phylogenetic analysis revealed three to six groups with no clear patterns of clustering by centers-wise breeding lines, types of corn, kernel characteristics, maturity, plant height, and ear placement. However, genotypes were grouped partially based on their source germplasm from where they derived.

Hydroxypropyl methylcellulose-copper nanoparticle and its nanocomposite hydrogel films for antibacterial application.

Currently, special emphasis is being given to the design and fabrication of antibacterial nanocomposite hydrogels for wound dressing applications. Herein, we report the synthesis and characterization of hydroxypropyl methylcellulose (HPMC) reinforced with HPMC capped copper nanoparticles (HCu NPs) based nanocomposite hydrogel films (NHFs). Spherical nanostructures of HCu NPs (∼40 nm) were achieved by facile precipitation technique using ascorbic acid as a nucleating agent and subsequently made their NHFs via solution casting method. Spectral, thermal and structural characteristics of the developed materials were carried out. Antibacterial activity of the resultant NHFs showed the MIC and MBC values of 350 and 1400 µg/mL for S. aureus, and 500 and 2000 µg/mL for E. coli, respectively. These results conveyed that the HCu NPs incorporated HPMC NHFs can be used effectively in antibacterial applications.

Development of sub-tropically adapted diverse provitamin-A rich maize inbreds through marker-assisted pedigree selection, their characterization and utilization in hybrid breeding.

Malnutrition has emerged as one of the major health problems worldwide. Traditional yellow maize has low provitamin-A (proA) content and its genetic base in proA biofortification breeding program of subtropics is extremely narrow. To diversify the proA rich germplasm, 10 elite low proA inbreds were crossed with a proA rich donor (HP702-22) having mutant crtRB1 gene. The F2 populations derived from these crosses were genotyped using InDel marker specific to crtRB1. Severe marker segregation distortion was observed. Seventeen crtRB1 inbreds developed through marker-assisted pedigree breeding and seven inbreds generated using marker-assisted backcross breeding were characterized using 77 SSRs. Wide variation in gene diversity (0.08 to 0.79) and dissimilarity coefficient (0.28 to 0.84) was observed. The inbreds were grouped into three major clusters depicting the existing genetic diversity. The crtRB1-based inbreds possessed high ß-carotene (BC: 8.72µg/g), ß-cryptoxanthin (BCX: 4.58µg/g) and proA (11.01µg/g), while it was 2.35µg/g, 1.24µg/g and 2.97µg/g in checks, respectively. Based on their genetic relationships, 15 newly developed crtRB1-based inbreds were crossed with five testers (having crtRB1 gene) using line × tester mating design. 75 experimental hybrids with crtRB1 gene were evaluated over three locations. These experimental hybrids possessed higher BC (8.02µg/g), BCX (4.69µg/g), proA (10.37µg/g) compared to traditional hybrids used as check (BC: 2.36 µg/g, BCX: 1.53µg/g, proA: 3.13µg/g). Environment and genotypes × environment interaction had minor effects on proA content. Both additive and dominance gene action were significant for proA. The mean proportion of proA to total carotenoids (TC) was 44% among crtRB1-based hybrids, while 11% in traditional hybrids. BC was found to be positively correlated with BCX (r = 0.68) and proA (r = 0.98). However, no correlation was observed between proA and grain yield. Several hybrids with >10.0 t/ha grain yield with proA content >10.0 µg/g were identified. This is the first comprehensive study on development of diverse proA rich maize hybrids through marker-assisted pedigree breeding approach. The findings provides sustainable and cost-effective solution to alleviate vitamin-A deficiency.

Chitosan-pluronic based Cu nanocomposite hydrogels for prototype antimicrobial applications.

Copper nanoparticles were synthesized via precipitation technique using the pseudonatural cationic chitosan biopolymer as a stabilizing agent. The nanoparticles developed were successfully incorporated into the 1:1 ratio of blended chitosan: pluronic F127 polymer solution and made their nanocomposite hydrogels by solution casting method. The formed copper-based nanocomposite hydrogels were characterized by using Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy and transmission electron microscopy studies. The antimicrobial activity of the fabricated nanocomposite hydrogels was tested via an inhibition zone process against both E. coli (gram-negative) and S. aureus (gram-positive) bacteria. The results conveyed that the copper-embedded chitosan-pluronic\ F127 nanocomposite hydrogels can be used effectively for antimicrobial applications as well as for wound care applications.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials.

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Chitosan capped copper oxide/copper nanoparticles encapsulated microbial resistant nanocomposite films.

Chitosan (CH) capped inorganic nanomaterials have been considered as significant antibacterial materials in the clinical field. This work shows the synthesis of two new different antibacterial composite films as a result of the incorporation of CH capped copper oxide (CHCuO) and copper (CHCu) nanoparticles (NPs). Here, CHCuO and CHCu NPs were achieved by a facile chemical reduction of Cu2+ ions using sodium hydroxide and ascorbic acid. TEM analysis revealed the morphology as rod-type nanoflakes for CHCuO and a spherical shape for CHCu NPs with ~7 ±â€¯2 nm size. Antimicrobial activity of the developed materials was studied by the inhibition zone method, against both gram-negative and gram-positive bacteria. The antimicrobial activity revealed that the CHCuO NPs and CHCuO-CH film showed a higher inhibition zone than the other nanomaterials. The results suggested that the synthesized materials can be used in wound dressing applications.

Green synthesis of tea Ag nanocomposite hydrogels via mint leaf extraction for effective antibacterial activity.

In this report, we investigated the swelling behavior and antibacterial property of nanosilver composite hydrogels made from tea with polyacrylamide via a free-radical polymerization and green process technique. This is probably for the first time; tea-based nano silver composite hydrogels were developed. The composite hydrogels comprise embedded nano silver particles in the tea hydrogel matrix via a green process with mint leaf extract. The size of the nano silver particles in the hydrogel matrix was found to be < 10 nm. The nano silver composite hydrogels formed and their blank hydrogels from the mint leaf were characterized by using ultraviolet-visible spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, transmission electron microscopy, thermogravimetric analysis and X-ray diffraction studies. The nano silver composite hydrogels developed exhibit eminent antibacterial activity against Escherichia coli and Staphylococcus aureus. This clearly indicates that the nano silver composite hydrogels are potential candidates for antimicrobial applications.