Monitoring microplastic-contaminant sorption processes in real-time using membrane introduction mass spectrometry.

Microplastics are environmentally ubiquitous and their role in the fate and distribution of trace contaminants is of emerging concern. We report the first use of membrane introduction mass spectrometry to directly monitor the rate and extent of microplastic-contaminant sorption. Target contaminant (naphthalene, anthracene, pyrene, and nonylphenol) sorption behaviours were examined at nanomolar concentrations with four plastic types: low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). Under the conditions employed here, short-term sorption kinetics were assessed using on-line mass spectrometry for up to one hour. Subsequent sorption was followed by periodically measuring contaminant concentrations for up to three weeks. Short-term sorption followed first order kinetics with rate constants that scaled with hydrophobicity for the homologous series of polycyclic aromatic hydrocarbons (PAHs). Sorption rate constants on LDPE for equimolar solutions of naphthalene, anthracene, and pyrene were 0.5, 2.0, and 2.2 h-1, respectively, while nonylphenol did not sorb to pristine plastics over this time period. Similar trends among contaminants were observed for other pristine plastics with 4- to 10-fold faster sorption rates associated with LDPE when compared to PS and PP. Sorption was largely complete after three weeks, with the percent analyte sorbed ranging from 40-100% across various microplastic-contaminant combinations. Photo-oxidative ageing of LDPE had little effect on PAH sorption. However, a marked increase in nonylphenol sorption was consistent with increased hydrogen-bonding interactions. This work provides kinetic insights into surface interactions and describes a powerful experimental platform to directly observe contaminant sorption behaviours in complex samples under a variety of environmentally relevant conditions.

Characterizing photochemical ageing processes of microplastic materials using multivariate analysis of infrared spectra.

Microplastics in the environment are an emerging concern due to impacts on human and environmental health. In addition to direct effects on biota, microplastics influence the fate and distribution of trace organic contaminants through sorption and transport. Environmental weathering may influence the rate and extent of chemical sorption. Changes in the surface characteristics of four common plastics including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS) were followed under the influence of both artificial light (UV-B) and natural sunlight for up to six months. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra were collected at regular intervals. Principal component analysis (PCA) of the full dataset of UV-B weathered samples (n >500 spectra) simultaneously discriminated plastic type and extent of photochemical weathering. The magnitude of PCA scores correlated with exposure time and the loadings were consistent with surface chemistry changes including photooxidation. Projecting sunlight and UV-C exposed samples onto this PCA model demonstrated that similar chemical changes occurred, albeit at different rates. The results were compared to the carbonyl index (CI) with similar weathering trends indicating PP weathered at a faster initial rate than LDPE and HDPE. We propose that a multivariate approach is more widely applicable than CI as illustrated by PS, which lacked a stable reference peak. Kinetic analysis of the time series indicated that outdoor weathering occurred 5-12 times slower than the artificial exposure used here, depending on the plastic and the light source employed. The results provide unique insights into weathering processes and the photochemical age of naturally weathered plastics.

Oligoether-strapped calix[4]pyrrole: an ion-pair receptor displaying cation-dependent chloride anion transport.

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1·F](-) and [1·Cl](-)) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li(+), Na(+), K(+), Cs(+), as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1·F](-), no appreciable interaction with the K(+) ion was seen. On the other hand, when this complex was treated with Li(+) or Na(+) ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li(+), Na(+), K(+), treating [1·F](-) with Cs(+) ions gave rise to a stable, host-separated ion-pair complex, [F·1·Cs], which contains the Cs(+) ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1·Cl](-). Here, no appreciable interaction was observed with Na(+) or K(+). In contrast, treating with Li(+) produces a tight ion-pair complex, [1·Li·Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1·F](-), treatment of [1·Cl](-) with Cs(+) ions gives rise to a host-separated ion-pair complex, [Cl·1·Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism.

A synergistic approach to anion antiport.

A synergistic approach to Cl(-)/HCO(3)(-) antiport has been demonstrated in POPC lipid bilayers using an ion selective electrode assay showing that, when using combinations of carriers each optimised for a particular component of the transport process, enhanced rates of transport are observed.

A dual host approach to transmembrane transport of salts.

A dual host approach for M(+)/Cl(-) co-transport has been shown to be effective in lipid bilayers consisting of POPC using fluorescence-based transport assays.

Double loading of ZnCl(2) by polytopic ligands which co-extract Zn(2+) and tetrachloridozincate.

Combining cation- and anion-binding functionalities in a salen-type extractant leads to multiple loading of ZnCl(2). Zn(ii) cations are bound by the salen N(2)O(2)(2-) donor set, and chlorozincate anions are associated with protonated pendant amine groups.

Tripodal transmembrane transporters for bicarbonate.

Easy-to-make tripodal tris-thiourea receptors based upon tris(2-aminoethyl)amine are capable of chloride/bicarbonate transport and as such represent a new class of bicarbonate transport agent.

Calix[4]pyrrole-based anion transporters with tuneable transport properties.

Three new bis-1,2,3-triazole strapped calix[4]pyrroles have been prepared via'click' chemistry and their anion complexation and lipid bilayer transport properties studied by a combination of single crystal X-ray diffraction studies, (1)H NMR titration techniques, isothermal titration calorimetry and lipid bilayer anion transport studies in POPC vesicles. Bilayer transport efficiency for transmembrane chloride transport was found to directly depend on the length of the alkyl chain present in the bis-triazole strap.

Octafluorocalix[4]pyrrole: a chloride/bicarbonate antiport agent.

meso-Octamethyloctafluorocalixpyrrole, a simple tetrapyrrolic macrocycle, has been shown to function as both a chloride/nitrate and a chloride/bicarbonate antiport agent for lipid bilayer transmembrane anion transport. This is the first example of a synthetic macrocyclic pyrrole-based receptor capable of transmembrane bicarbonate transport.

1,2,3-triazole-strapped calix[4]pyrrole: a new membrane transporter for chloride.

A new triazole-strapped calix[4]pyrrole synthesised via'click' chemistry shows high affinity for chloride and lipid bilayer chloride transport properties.

Outer-sphere amidopyridyl extractants for zinc(ii) and cobalt(ii) chlorometallates.

Protonated amidopyridyl ligands show high selectivity for the extraction of [CoCl(4)](2-) or [ZnCl(4)](2-) over chloride ion into organic media via the formation of N-H and C-H hydrogen-bond donors to the outer coordination spheres of the chlorometallates.

meso-octamethylcalix[4]pyrrole: an old yet new transmembrane ion-pair transporter.

The first example of lipid bilayer membrane transport of a salt by a calix[4]pyrrole is reported.