Supporting ligands limit the degree of electrophilic ac-tivation for any substrate because they also reduce the Lewis acidity of the transition metal ion. Here, we tem-porarily mask the Lewis acidity of dicationic Pd(II) by using “shapeshifting” bidentate pyrimidine/olefin lig-ands L1 and L2. These ligands delocalize/relocalize charge via reversible C–N bond formation. So, although ligated dicationic Pd compounds [1]2+ and [2]2+ appear charge separated (distributed across Pd and ligand), they react comparably to a solvated Pd(II) dication. We also observe properties that are atypical of electrophilic cata-lysts (e.g. broader functional group tolerance). We pro-pose these properties originate from the more nucleo-philic (charge separated) state. More broadly, catalysts featuring reversible dynamics may be advantaged rela-tive to structurally static counterparts.

Supporting ligands reduce the Lewis acidity of transition metal ions, limiting the degree of electrophilic activation for any substrate. Here, we demonstrate that L1 and L2 mask the Lewis acidity of dicationic Pd(II) via a reversible C–N bond formation. These shapeshifting complexes catalyze electrophilic olefin isomerization, even in the presence of a polar functional group. The equilibrium between two coor-dination modes allows the system to access an electrophilic state that is comparable to a “naked” Pd(II) Lewis acid. However, because these shapeshifting systems are not sub-ject to the same rate determining step (via interconversion with a second less electrophilic state), they are also faster catalysts than the benchmark Pd(II) Lewis acid. Overall, we demonstrate that catalytic systems featuring reversible dy-namics can be advantaged relative to structurally static counterparts.

Quantification and characterization of microplastics, synthetic polymers less than 5 mm in diameter, requires extraction methods that can reduce non-plastic debris without loss or alteration of the polymers. Nitric acid has been used to extract plastic particles from zooplankton and other biota because it completely digests tissue and exoskeletons, thus reducing interferences. While the impact of acid digestion protocols on several polymers has been demonstrated, advice for quantifying microplastic and interpreting their spectra following nitric acid digestion is lacking. Fourier transform infrared (FTIR) and/or Raman spectroscopy was performed on plastics from > 50 common consumer products (including a variety of textiles) pre- and post-nitric acid treatment. The percent match and assigned polymer were tabulated to compare the accuracy of spectral identification before and after nitric acid digestion via two open spectral analysis software. Nylon-66, polyoxymethylene, polyurethane, polyisoprene, nitrile rubber, and polymethyl methacrylate had ≥ 90

Microplastics (MP) are considered emerging contaminants in the water environment, and there is an interest in understanding their entry into the food web. As a growing body of literature demonstrates the ingestion of MP by zooplankton in controlled laboratory studies, few data are available demonstrating in situ observations of MP in zooplankton. A field survey was performed to collect zooplankton in the highly urbanized Hudson-Raritan estuary. Following washing, sorting by species, and enumeration, three dominant species of copepods (Acartia tonsa, Paracalanus crassirostris and Centropages typicus) were digested. MP were filter concentrated and characterized by size, morphology, and color via microscopy and polymer type by micro-FTIR imaging and/or Raman spectroscopy. MP were observed in all extracts performed on the three copepod species with averages ranging from 0.30 to 0.82 MP individual-1. Polyethylene and polypropylene were the dominant polymer types observed and fragments and beads the most commonly observed morphologies for MP. These data were used to estimate the flux of MP through zooplankton based on gut turnover times, which we compare to estimates of MP entering this environment though the local waterways. The estimated fluxes were sufficiently large, indicating that ingestion by zooplankton is a major sink of MP in the size range subject to zooplankton feeding in surface estuarine waters.

Comprehensive approaches are needed to understand accumulation patterns and the relative importance of pathways of entry for microplastics in the marine environment. Here, a highly urbanized estuarine environment was sampled along a salinity gradient from the mouth of the Raritan River, (New Jersey, USA) and into the Raritan Bay and the coastal ocean which are further influenced by discharge from the larger Hudson River. Polymers were characterized in two size classes by FTIR and/or Raman spectroscopy. The highest concentration of 500-2000 mm microplastic particles were observed in the mouth of the Raritan during summer low flow conditions, whereas the 250-500 mm microplastic particles were more prevalent in the bay and coastal ocean samples. These results were interpreted using fragmentation and mixing models to provide insight into the sources and fate of microplastics in this estuarine/coastal region. To investigate the potential pathways of entry into the system, samples were collected from various hydraulically connected storm water outfalls and the influent and effluent of wastewater treatment plants and polymer concentrations and types were compared to the estuarine samples. The concentrations of microplastics (500-2000 mm) ranged from 400 to 600 microplastics/m(3) in storm water compared to <1-2.75 microplastics/m(3) across the estuary. Of interest for analysis is the observed linear correlation between the total concentration of particles in a sample following oxidation and density separation and its microplastic concentration. Overall, the results presented reveal potentially important sources of microplastics in the estuarine environment and have implications for understanding the behavior, transport, and fate of microplastics under varying flow conditions and from estuaries with variable flushing times. (C) 2021 Elsevier Ltd. All rights reserved.