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:

Novel tacrine-related drugs as potential candidates for the treatment of Alzheimer's disease. A summary of the recently published efforts on tacrine derivatives as a renewed potential therapeutic approach for the treatment of Alzheimer's disease is presented.
{"Chemical": ["tacrine"]}