Gold nanomaterials have widespread applications across multiple areas of science and technology. Sulfur-containing ligands (thiols and thioethers) have been traditionally used as ligands to protect and functionalize these materials. N-Heterocyclic carbenes (NHCs) have recently emerged as organic alternatives to thiols in stabilizing gold nanoparticles (AuNPs) and flat surfaces. In fact, gold-containing materials decorated with NHCs have been shown to withstand a variety of harsh conditions. However, such materials still suffer from limited stability in the presence of thiols, such as the biologically relevant glutathione, in aqueous media. Here, we report the synthesis and application of polymeric mesoionic NHC–Au(I) complexes as precursors to polyNHC-stabilized AuNPs. Using copper-catalyzed alkyne–azide cycloaddition polymerization of diazide- and dialkyne-containing monomers, we directly install 1,2,3-triazole groups, as precursors to mesoionic carbenes, on the backbone of the resulting polymers. This effectively eliminates the need to presynthesize NHC–Au(I)-containing monomers to access this class of polymers. Using these polymers as the substrate, the resulting robust AuNPs, protected by a catenated network of NHCs, demonstrate exceptional stabilities in aqueous media under various conditions, particularly against high concentrations of glutathione (up to 6 mM) for extended periods of time (up to 10 days). Moreover, the use of the macromolecular substrate, compared to small NHC–Au complexes used thus far yielding relatively small AuNPs (∼5 nm), results in the formation of larger AuNPs (∼12 nm). Such enhanced stabilities in aqueous media together with their larger diameters make these materials promising for potential applications in nanomedicine. To highlight their multifunctionality, we also demonstrate their catalytic activity in the reduction of 4-nitrophenol.
There is urgent need for effective bactericidal agents for use in real commercial formulations since many old disinfectants, such as halogenated compounds, are now banned. Cationic polymers may have good bactericidal properties in pure water or buffer, but typically become ineffective in the presence of anionic surfactants that are widely used in many commercial formulations. Here, we discover that polyion complex (PIC) nanoparticles formed by cationic polymers of Poly(3-AcrylaMidoPropyl) TriMethylAmmonium chloride (PAMPTMA) in the presence of anionic surfactants display promising fast-bactericidal effect (> 99.99 % killing within 10-min treatment) on Gram-negative Escherichia coli (E. coli, ATCC ® 8739™). To examine the influence of hydrophobicity on bactericidal property, we synthesize PAMPTMA-b-Poly(Butyl MethAcrylate) and discover that increasing hydrophobicity has little influence on bactericidal property of PIC nanoparticles. Mechanism study shows that cationic PIC nanoparticles rapidly cause significant pores both in the outer-and inner-membranes because of their large size and high local concentration of positive charges. The rapid membrane pore formation results in fast cell death. The discovery --certain cationic polymers when formulated with anionic surfactants are even more bactericidal than neat cationic polymers alone --paves the way for potential applications of synthetic cationic polymers in commercial formulations.
Deltas are among the most productive and diverse global ecosystems. However, these regions are highly vulnerable to natural disasters and climate change. Nature-based solutions (Nbs) have been increasingly adopted in many deltas to improve their resilience. Among decision support tools, assessment of ecosystem services (ES) through spatially explicit modelling plays an important role in advocating for Nbs. This study explores the use of the Land Utilisation and Capability Indicator (LUCI) model, a high-resolution model originally developed in temperate hill country regions, to map changes in multiple ecosystem services (ES), along with their synergies and trade-offs, between 2010 and 2018 in the Vietnamese Mekong Delta (VMD). In so doing, this study contributes to the current knowledge in at least two aspects: high-resolution ES modelling in the VMD, and the combination of ES biophysical and economic values within the VMD to support Nbs implementation. To date, this is the highest resolution (5 by 5 m) ES modelling study ever conducted in the VMD, with ~1500 million elements generated per ES. In the process of trialling implementations of LUCI within the VMD’s unique environmental conditions and data contexts, we identify and suggest potential model enhancements to make the LUCI model more applicable to the VMD as well as other tropical deltaic regions. LUCI generated informative results in much of the VMD for the selected ES (flood mitigation, agriculture/aquaculture productivity, and climate regulation), but challenges arose around its application to a new agro-hydrological regime. To address these challenges, parameterising LUCI and reconceptualising some of the model’s mechanisms to specifically account for the productivity and flood mitigation capability of water-tolerant crops as well as flooding processes of deltaic regions will improve future ES modelling in tropical deltaic areas. The ES maps showed the spatial heterogeneity of ES across the VMD. Next, to at least somewhat account for the economic drivers which need to be considered alongside biophysical valuations for practical implementations of ES maps for nature-based solutions (Nbs) in the upstream VMD, economic values were assigned to different parcels using a benefit transfer approach. The spatially explicit ES economic value maps can inform the design of financing incentives for Nbs. The results and related work can be used to support the establishment of Nbs that ultimately contribute to the security of local farmers’ livelihoods and the sustainability of the VMD.
In recent years, N-heterocyclic carbenes (NHCs) have garnered significant attention as promising alternatives to thiols to stabilize metallic nanoparticles and planar surfaces. While most studies thus far have focused on NHC-functionalized gold nanoparticles (AuNPs), as an ideal platform to investigate the role of NHCs in stabilizing such nanoparticles, their ability to protect more unstable coinage metal nanoparticles, such as silver nanoparticles (AgNPs), has been largely overlooked. This is despite the fact that AgNPs possess a much more sensitive optical response that, upon their enhanced stability, can broaden their scope of application in various fields, including nanomedicine and catalysis. In this study, the synthesis and use of monomeric and polymeric mesoionic NHC–Ag(I) complexes as precursors to mono- and multidentate NHC-tethered AgNPs are reported. The polymeric analog was obtained by first synthesizing a polymer, containing 1,2,3-triazole repeat units, employing the copper-catalyzed alkyne–azide cycloaddition click polymerization of monomers containing diazide- and dialkyne functional groups. Subsequent quaternization of the triazole moieties and Ag insertion yielded the target NHC–Ag-containing polymer. Using this polymer as well as its monomeric analog as substrates, AgNPs with either catenated networks of NHCs or monomeric NHCs were fabricated by their reduction using borane–tert-butylamine complex. Our stability studies demonstrate that while monomeric NHCs impart some degree of stability to AgNPs, particularly at elevated temperatures in aqueous as well as organic medium, their polymeric analogs further enhance their stability in acidic environment (pH = 2) and against glutathione (3 mM), as an example of a biologically relevant thiol, in aqueous media. To highlight the application of these NHC-functionalized AgNPs in catalysis, we explore the aqueous phase reduction of methyl orange and 4-nitrophenol.
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