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Abstract Marine fish precipitate carbonates in their intestines that they subsequently excrete as part of an osmoregulatory strategy. While fish carbonates are proposed to be volumetrically significant to the global carbonate budget, no study has presented direct evidence of fish carbonates in the open ocean. Here we examine sediment trap material collected by the Oceanic Flux Program (OFP) in the North Atlantic and observe the episodic occurrence of enigmatic blue particles since 1992. The blue particles are comprised of calcite with unusually high magnesium content (up to 46 mol%) with distinctively depleted δ¹³C and enriched δ¹⁸O compared with calcite produced by common marine calcifiers. Based on the mineralogical, isotopic, and textural similarities between the blue particles and fish carbonates, we propose that the blue particles are produced by pelagic fish. Our data suggest that fish modify their intestinal fluids to create a concentrated, highly supersaturated,¹³C depleted solution capable of precipitating calcite with high magnesium content and low δ¹³C. Collectively, our data imply that fish carbonate production is an open‐ocean phenomenon, opening up the possibility that fish contribute to the production, dissolution, and export of carbonates globally. 

Ion receptors are molecular hosts that bind ionic guests, often with great selectivity. The interplay of solvation and ion binding in anion host-guest complexes in solution governs the binding efficiency and selectivity of such ion receptors. To gain molecular-level insight into the intrinsic binding properties of octamethyl calix[4]pyrrole (omC4P) host molecules with halide guest ions, we performed cryogenic ion vibrational spectroscopy (CIVS) of omC4P in complexes with fluoride, chloride, and bromide ions. We interpret the spectra using density functional theory, describing the infrared spectra of these complexes with both harmonic and anharmonic second-order vibrational perturbation theory (VPT2) calculations. The NH stretching modes of the pyrrole moieties serve as sensitive probes of the ion binding properties, as their frequencies encode the ion-receptor interactions. While scaled harmonic spectra reproduce the experimental NH stretching modes of the chloride and bromide complexes in broad strokes, the high proton affinity of fluoride introduces strong anharmonic effects. As a result, the spectrum of F−·omC4P is not even qualitatively captured by harmonic calculations, but it is recovered very well by VPT2 calculations. In addition, the VPT2 calculations recover the intricate coupling of the NH stretching modes with overtones and combination bands of CH stretching and NH bending modes and with low-frequency vibrations of the omC4P macrocycle, which are apparent for all halide ion complexes investigated here. A comparison of the CIVS spectra with infrared spectra of solutions of the same ion-receptor complexes in d3-acetonitrile and d6-acetone shows how ion solvation changes the ion-receptor interactions for the different halide ions. 

We present the vibrational spectra of a series of dicationic, organometallic complexes consisting of a transition metal center (Co, Ni, or Cu) coordinated by 4,4′-di(tert-butyl)- 2,2′-bipyridine (DTBbpy) ligands and a formate adduct. Spectral features are analyzed and assigned through comparison with density functional theory calculations, and structures are reported. Natural population analysis shows that the DTBbpy ligands serve as flexible charge reservoirs in each complex. Shifts in the vibrational signatures of the formate moiety reveal that the nature of the metal center plays a crucial role in the charge distribution and formate−metal binding motif in each complex, illustrating the impact of the metal center on the structural and electronic properties of these complexes.