Vacuolar myelinopathy is a fatal neurological disease that was initially discovered during a mysterious mass mortality of bald eagles in Arkansas in the United States. The cause of this wildlife disease has eluded scientists for decades while its occurrence has continued to spread throughout freshwater reservoirs in the southeastern United States. Recent studies have demonstrated that vacuolar myelinopathy is induced by consumption of the epiphytic cyanobacterial species Aetokthonos hydrillicola growing on aquatic vegetation, primarily the invasive Hydrilla verticillata. Here, we describe the identification, biosynthetic gene cluster, and biological activity of aetokthonotoxin, a pentabrominated biindole alkaloid that is produced by the cyanobacterium A. hydrillicola. We identify this cyanobacterial neurotoxin as the causal agent of vacuolar myelinopathy and discuss environmental factors—especially bromide availability—that promote toxin production.

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A set of N-rich salts, 3 -9, of the heavy lanthanoids (terbium, 3; dysprosium, 4; holmium 5; erbium, 6; thulium, 7; ytterbium, 8; lutetium, 9) based on the energetic 5,5'-azobis[1H-tetrazole] (H 2 ZT) was synthesized and characterized by elemental analysis, vibrational (IR and Raman) spectroscopy, and Xray structure determination. The synthesis of the lanthanoid salts 3 -9 was performed by crystallization from concentrated aqueous solutions of disodium 5,5'-azobis[1H-tetrazol-1-ide] dihydrate (Na 2 ZT · 2 H 2 O; 1) and the respective Ln(NO 3 ) 3 · 5 H 2 O and yielded large rhombic crystals of the type [Ln(H 2 O) 8 ] 2 (ZT) 3 · 6 H 2 O in ca. 70% of the theoretical yield. The compounds 3 -9 are isostructural (triclinic space group P1 ) to the previously published yttrium salt 2; they show, however, a clear lanthanoid contraction of several crystallographic parameters, e.g., the cell volume or the LnÀO bond lengths of the Ln 3þ ions and the coordinating H 2 O molecules. The lanthanoid contraction influences the strengths of the H-bonds, which can be observed as a red shift by 4 cm À1 in the characteristic IR band, in particular from 3595 cm À1 (3) to 3599 cm À1 (9). In good agreement with previous works, 2 -9 are purely salt-like compounds without a coordinative bond between the tetrazolide anion and the Ln 3þ cation.

The complexation of Cm(III) and Eu(III) with the novel i-SANEX complexing agent 2,6-bis[1-(propan-1-ol)-1,2,3-triazol-4-yl]pyridine (PTD) was studied by time-resolved laser fluorescence spectroscopy (TRLFS). The formation of 1:3, 1:2, and 1:1 metal/ligand complexes was identified upon increasing PTD concentration in 10 mol/L HClO and in 0.44 mol/L HNO solutions. For all these complexes, stability constants were determined at different acid concentrations. Though under the extraction conditions proposed for an An/Ln separation process, that is, for 0.08 mol/L PTD in 0.44 mol/L HNO, 1:3 complexes represent the major species, a significant fraction of 1:2 complexes was found. This is caused by ligand protonation, and results in lower Eu(III)/Am(III) separation factors compared to SO-Ph-BTP, until now considered the i-SANEX reference ligand. Focused extraction studies performed at lower proton concentration, where the 1:3 complex is formed exclusively, confirm this assumption.