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:

Ligand Based Approach to L-Type Calcium Channel by Imidazo[2,1-b]thiazole-1,4-Dihydropyridines: from Heart Activity to Brain Affinity. The synthesis, characterization, and functional in vitro assay in cardiac and smooth muscle (vascular and nonvascular) of a series of 4-imidazo[2,1-b]thiazole-1,4-dihydropyridines are reported. To define the calcium blocker nature of the imidazo[2,1-b]thiazole-1,4-DHPs and their selectivity on Cav1.2 and Cav1.3 isoforms we performed binding studies on guinea pig atrial and ventricular membranes, on intact cells expressing the cloned Cav1.2a subunit and on rat brain cortex. To get major insights into the reasons for the affinity for Cav1.2 and/or Cav1.3 molecular modelling studies were also undertaken. Some physicochemical and pharmacokinetic properties of selected compounds were calculated and compared. All the biological data collected and reported herein allowed us to rationalize the structure-activity relationship of the 4-imidazo[2,1-b]thiazole-1,4-DHPs and to identify which of these enhanced the activity at the central level.
{"Chemical": ["4-imidazo[2,1-b]thiazole-1,4-dihydropyridines", "calcium", "imidazo[2,1-b]thiazole-1,4-DHPs", "Imidazo[2,1-b]thiazole-1,4-Dihydropyridines", "Calcium", "4-imidazo[2,1-b]thiazole-1,4-DHPs"]}