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:

In vitro and in vivo evaluation of superparamagnetic iron oxide nanoparticles coated by bisphosphonates: The effects of electrical charge and molecule length. Physicochemical coating properties are often considered to be determining factors for in vivo characteristics of superparamagnetic iron oxide nanoparticles, used as contrast agent in Magnetic Resonance Imaging (MRI). To investigate the electrical charge (modified by zero, one or two ammonium groups) and the molecule length (3, 5 or 7 methylene chains) effects of bisphosphonate-type coatings, we assessed the complement activation, in vivo plasma and tissue relaxation time alterations of intravenously injected small iron oxide nanoparticles (<25nm) on male healthy Wistar rats. The presence of ammonium groups induces a weak activation of the complement whatever the size and the concentration of particles, whereas hydroxyethylenebisphosphonate (HEBP)-coated particles are poor complement activators only at the lowest concentration. In vivo, HEBP-coated nanoparticles have the greatest prolonged relaxation time effects, despite their higher negative electrical charge, contrary to two ammonium bearing coatings. No significant differences were observed between mono-ammonium molecular coatings.
{"Chemical": ["hydroxyethylenebisphosphonate", "HEBP", "iron oxide", "bisphosphonates", "ammonium", "methylene", "bisphosphonate", "mono-ammonium"]}