You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

How is (68)Ga labeling of macrocyclic chelators influenced by metal ion contaminants in (68)Ge/(68)Ga generator eluates? To assess the influence of Zn(2+) , Cu(2+) , Fe(3+) , Al(3+) , Ti(IV) , and Sn(IV) on incorporation of (68) Ga(3+) into pendant-arm macrocyclic chelators, the (68) Ga labeling of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-1,4,7-tris[methyl(2-carboxyethyl)phosphinic acid]) (TRAP), and 1,4,7-triazacyclononane-1-[methyl(2-carboxyethyl)phosphinic acid]-4,7-bis[methyl(2-hydroxymethyl)phosphinic acid] (NOPO), as well as their peptide conjugates, was investigated in the presence of varying concentrations of these metal ions. The (68) Ga labeling yield for carboxylate-type chelators NOTA and DOTA is decreased at lower metal ion contaminant concentrations compared with phosphinate-type chelators TRAP and NOPO. The latter are able to rapidly exchange coordinated Zn(II) with (68) Ga(3+) , as confirmed by mass spectrometry and (31) P NMR spectroscopy. (68) Ga labeling of Zn(II) complexes of TRAP and NOPO proceeds as efficient as labeling of neat NOTA; this applies also to the corresponding peptide conjugates of these chelators. This behavior results in substantially improved selectivity for Ga(3+) and, therefore, in more robust and reliable (68) Ga labeling procedures. In addition, none of the investigated chelators binds (68) Ge, rendering post-labeling purification protocols, for example, solid-phase extraction, a reliable means of removal of (68) Ge contamination from (68) Ga radiopharmaceuticals.
{"Chemical": ["1,4,7-triazacyclononane-1,4,7-tris[methyl(2-carboxyethyl)phosphinic acid])", "(68)Ga", "Zn(2+)", "(68) Ge", "(68)Ge", "DOTA", "Zn(II)", "Ti(IV)", "1,4,7-triazacyclononane-1-[methyl(2-carboxyethyl)phosphinic acid]-4,7-bis[methyl(2-hydroxymethyl)phosphinic acid]", "Ga(3+)", "Sn(IV)", "phosphinate", "TRAP", "Fe(3+)", "carboxylate", "Al(3+)", "NOTA", "(31) P", "1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid", "(68) Ga(3+)", "Cu(2+)", "(68) Ga", "1,4,7-triazacyclononane-1,4,7-triacetic acid", "NOPO"]}