The ability to spatiotemporally identify the formation of specific anionic species, or track changes in their concentration inside living systems, is of critical importance in deciphering their exact ...biological roles and effects. The development of probes (also called bioimaging agents and intracellular sensors) to achieve this goal has become a rapidly growing branch of supramolecular chemistry. In this critical review the challenges specific to the task are identified and for a select range of small anions of environmental and biological relevance (fluoride, chloride, iodide, cyanide, pyrophosphate, bicarbonate, hydrosulphide, peroxynitrite, hypochlorite and hypobromite) a comprehensive overview of the currently available in vitro and in vivo probes is provided.
This critical review focuses on the development of anion sensors, being either fluorescent and/or colorimetric, based on the use of the 1,8-naphthalimide structure; a highly versatile building unit ...that absorbs and emits at long wavelengths. The review commences with a short description of the most commonly used design principles employed in chemosensors, followed by a discussion on the photophysical properties of the 4-amino-1,8-naphthalimide structure which has been most commonly employed in both cation and anion sensing to date. This is followed by a review of the current state of the art in naphthalimide-based anion sensing, where systems using ureas, thioureas and amides as hydrogen-bonding receptors, as well as charged receptors have been used for anion sensing in both organic and aqueous solutions, or within various polymeric networks, such as hydrogels. The review concludes with some current and future perspectives including the use of the naphthalimides for sensing small biomolecules, such as amino acids, as well as probes for incorporation and binding to proteins; and for the recognition/sensing of polyanions such as DNA, and their potential use as novel therapeutic and diagnostic agents (95 references).
Antibiotic proliferation in the environment and their persistent nature is an issue of global concern as they induce antibiotic resistance threatening both human health and the ecosystem. Antibiotics ...have therefore been categorized as emerging pollutants. Fluoroquinolone (FQs) antibiotics are an emerging class of contaminants that are used extensively in human and veterinary medicine. The recalcitrant nature of fluoroquinolones has led to their presence in wastewater, effluents and water bodies. Even at a low concentration, FQs can stimulate antibacterial resistance. The main sources of FQ contamination include waste from pharmaceutical manufacturing industries, hospitals and households that ultimately reaches the wastewater treatment plants (WWTPs). The conventional WWTPs are unable to completely remove FQs due to their chemical stability. Therefore, the development and implementation of more efficient, economical, convenient treatment and removal technologies are needed to adequately address the issue. This review provides an overview of the technologies available for the removal of fluoroquinolone antibiotics from wastewater including adsorptive removal, advanced oxidation processes, removal using non-carbon based nanomaterials, microbial degradation and enzymatic degradation. Each treatment technology is discussed on its merits and limitations and a comparative view is presented on the choice of an advanced treatment process for future studies and implementation. A discussion on the commercialization potential and eco-friendliness of each technology is also included in the review. The importance of metabolite identification and their residual toxicity determination has been emphasized. The last section of the review provides an overview of the policy interventions and regulatory frameworks that aid in retrofitting antibiotics as a central key focus contaminant and thereby defining the discharge limits for antibiotics and establishing safe manufacturing practices.
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•Advanced technologies to remove antibiotic residues from environment is reviewed.•Metabolites and importance of studying their residual toxicity is emphasized.•Modelling approach to establish PNEC as ETP discharge limit has been discussed.•Policy interventions needed to control unmonitored antibiotic release is discussed.
Hydrogels retain substantial quantities of both water and nutrients within their three dimensional polymeric network. As such they have the ability to modify the local micro-environment of ...seeds/seedlings to enhance their growth outcomes. In terms of both safety and sustainability, the use of natural biopolymer based hydrogels is more advantageous. The network structure of hydrogels is typically formed by physical interaction and/or chemical crosslinking between polymer chains. The nature, strength and extent of crosslinking can be tailored to customize gel properties (such as mechanical strength, porosity and swelling behaviour) to suit a given type of application. This review highlights the use of hydrogels in agriculture where they (i) provide drought resistance to crops, (ii) act as reservoirs for critical nutrients, (iii) function as seed coating agents and (iv) improve transplantation success rate. The biodegradability and environmental compatibility of hydrogels for a range of applications in the farming sector is also discussed. Finally, the challenges of modifying hydrogels to suit specific agricultural applications are elaborated including issues that need to be overcome to exploit the full potential of these novel soft materials in sustainable farming practices of the future.
Hydrogels are a class of materials that have found many applications across society. Petrochemicals are a dominant, but unsustainable feedstock of crosslinked polymer networks that underpin ...functional hydrogels. Therefore an urgent need exists for sustainable biopolymer replacements, where agricultural by products, such as cellulose prove an ideal source of green hydrogels. These polymers are cheap and environmentally friendly, have excellent water absorption capacity and the products are inherently biodegradable and, most importantly for technical applications, can be easily functionalised. For example, 3-D cross linked hydrogel structures can be optimised by modifying the hydroxy groups of the parent structure into ether and ester derivatives that include additional functional groups. In this regard, carboxymethylcellulose (CMC) has emerged as a promising cellulose derivative as it possesses readily available carboxylic groups along the polymer chain. This property both imparts good water solubility and high chemical reactivity making it an ideal candidate for hydrogel synthesis. This review highlights recent developments in both the preparation and application of CMC based hydrogels. We discuss how the various physical and chemical properties of a range of CMC based hydrogels impinge on key parameters such as water absorption, mechanical strength and biodegradability. Finally, we will discuss key applications and the future potential of CMC hydrogels in various fields.
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Prior to the bioconversion of low cost, renewable lignocellulosic residues such as rice straw into value added bio-products, their recalcitrant structure needs to be fractionated by using various ...pretreatment methods. This study is aimed at the comparison of pretreatment protocols that will enable more efficient degradation and conversion of lignocellulosic biomass into cellulose-rich fractions. In this study, the cellulose-rich fractions of rice straw were obtained using the following pretreatment methods: alkali pretreatment using 5% (w/w) NaOH at 121 °C for 1 h, alkali treatment followed by bleaching pretreatment using acidified NaClO
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at 75 °C for 30 min, organosolvent pretreatment using formic acid: ethanol (3:1) at 160 °C for 1 h and steam explosion pretreatment at 180 °C for 5 min. The compositional analysis showed that alkali pretreatment followed by bleaching had remarkable fractionation efficiency with an increase in the relative cellulose concentration from 37.2 to 64.3%. The organosolvent and steam explosion pretreatment methods are green alternatives for the fractionation of lignocellulosic components. However, in comparison to the alkali bleaching pretreatment, these methods are less efficient with a relative increase in cellulose concentration from 37.2% in untreated rice straw to 46.5 and 43.7% in organosolvent and steam explosion pretreatment, respectively. The pretreated rice straw fractions were then investigated on the basis of various physicochemical characterization techniques such as Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). Further the economic feasibility of these pretreatment methods needs to be considered to estimate the related cost for technology transfer. This paper gives a comprehensive characteristic comparison of cellulose-rich variants obtained from the rice straw using different pretreatment methods along with the preliminary cost analyses indicating their potential economic feasibility.
This review article focuses primarily on the work carried in our laboratories over the last few years using luminescent and colorimetric sensors, where the anion recognition occurs through hydrogen ...bonding in organic or aqueous solvents. This review begins with the story of the discovery of fluorescent photoinduced electron transfer (PET) sensors for anions using charged neutral urea or thiourea receptors where both fluorescent and NMR spectroscopic methods monitored anion recognition. This work led to the development of dual luminescent and colorimetric anion sensors based on the use of the ICT based naphthalimide chromophore, where ions such as fluoride gave rise to changes in both the fluorescence and the absorption spectra of the sensors, but at different concentrations. Here, the former changes were due to hydrogen bonding interactions, whereas the latter was due to the deprotonation of acidic protons, giving rise to the formation of the bifluoride anion (HF
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−). Modification of the 4-amino-l,8-naphthalimide moiety has facilitated the formation of colorimetric anion sensors that work both in organic or aqueous solutions. Such charge neutral receptor motifs have also been incorporated into organic scaffolds with norbomyl and calixarene backbones, which have enabled us to produce anion directed self-assembled structures.
The real-time observation of chemical bond formation at the single-molecule level is one of the great challenges in the fields of organic and biomolecular chemistry. Valuable information can be ...gleaned that is not accessible using ensemble-average measurements. Although remarkably sophisticated techniques for monitoring chemical reactions have been developed, the ability to detect the specific formation of a chemical bond in situ at the single-molecule level has remained an elusive goal. Amide bonds are routinely formed from the aminolysis of N-hydroxysuccinimide (NHS) esters by primary amines, and the protocol is widely used for the synthesis, cross-linking, and labeling of peptides and proteins. Herein, a plasmonic nanocavity was applied to study aminolysis reaction for amide bond formation, which was initiated by single nanoparticle collision events between suitably functionalized free-moving gold nanoparticles and a gold nanoelectrode in an aqueous buffer. By means of simultaneous surface enhanced Raman spectroscopy (SERS) and single-entity electrochemistry (EC) measurements, we have probed the dynamic evolution of amide bond formation in the aminolysis reaction with 10 s of millisecond time resolution. Hence, we demonstrate that single-entity EC-SERS is a valuable and sensitive technique by which chemical reactions can be studied at the single-molecule level.
The synthesis of a centrally functionalized, ribbon‐shaped 6polynorbornane ligand L that self‐assembles with PdII cations into a {Pd2L4} coordination cage is reported. The shape‐persistent {Pd2L4} ...cage contains two axial cationic centers and an array of four equatorial H‐bond donors pointing directly towards the center of the cavity. This precisely defined supramolecular environment is complementary to the geometry of classic octahedral complexes M(XY)6 with six diatomic ligands. Very strong binding of Pt(CN)62− to the cage was observed, with the structure of the host–guest complex {Pt(CN)6@Pd2L4} supported by NMR spectroscopy, MS, and X‐ray data. The self‐assembled shell imprints its geometry on the encapsulated guest, and desymmetrization of the octahedral platinum species by the influence of the D4h‐symmetric second coordination sphere was evidenced by IR spectroscopy. Fe(CN)63− and square‐planar Pt(CN)42− were strongly bound. Smaller octahedral anions such as SiF62−, neutral carbonyl complexes (M(CO)6; M=Cr, Mo, W) and the linear Ag(CN)2− anion were only weakly bound, showing that both size and charge match are key factors for high‐affinity binding.
Wear what suits you: A self‐assembled {Pd2L4}4+ coordination cage featuring two axial cations and four equatorial H‐bond donors is able to bind octahedral complexes such as Fe(CN)63−, Pt(CN)62−, and M(CO)60 (M=Cr, Mo, W). As a custom‐built second coordination sphere of D4h symmetry, the cage lowers the symmetry of the guests, as indicated by IR spectroscopy.
The Hg(II) complex of rhodamine-nitronaphthalimide 1 can sense and discriminate both the oxidised and reduced forms of glutathione (GSSG and GSH).
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•The unique crystal structure of 1 ...shows coplanar chromophores—energy transfer processes such as FRET can readily occur.•The 1:Hg complex gives a unique fluorescent response for both forms of the biologically relevant glutathione (GSH and GSSG).•Cellular imaging shows that 1 readily crosses cell membranes and has potential use in evaluating biochemical redox processes.
Dual-fluorophore systems have attracted attention as they offer versatile photophysical properties and multiple mechanisms for sensing. Here we report that the Hg2+ complex of rhodamine-nitronaphthalimide conjugate 1 functions as a switch-on sensor for the simultaneous detection of reduced (GSH) and oxidised (GSSG) glutathione via a resonance Rayleigh scattering process, with detection limits of 4.3 μM and 11.9 μM, respectively. Hydroxide anion regenerates nitronanphthalimide 1 causing the fluorescence to “switch-off”, and the system is recyclable. This photophysical behaviour towards Hg2+, GSH and HO‾ forms the basis of a molecular level INHIBIT and AND logic gate.
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