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:

Promiscuous catalysis of asymmetric Michael-type additions of linear aldehydes to β-nitrostyrene by the proline-based enzyme 4-oxalocrotonate tautomerase. Exploiting catalytic promiscuity: The proline-based enzyme 4-oxalocrotonate tautomerase (4-OT) promiscuously catalyzes asymmetric Michael-type additions of linear aldehydes--ranging from acetaldehyde to octanal--to trans-β-nitrostyrene in aqueous solvent. The presence of 1.4 mol% of 4-OT effected formation of the anticipated γ-nitroaldehydes in fair to good yields with dr values of up to 93:7 and ee values of up to 81 %.
{"Chemical": ["proline", "trans-\u03b2-nitrostyrene", "\u03b3-nitroaldehydes", "acetaldehyde", "octanal", "4-OT", "4-oxalocrotonate", "\u03b2-nitrostyrene", "aldehydes"]}