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:

Examination of the effect of increasing the number of intra-disulfide amino functional groups on the performance of small molecule cyclic polyamine disulfide vectors. Establishing structure-activity relationships is vital if the efficacy of non-viral vectors is to match that of their viral counter-parts. Recently, we reported on the ability of a series of small molecule, cyclic polyamine disulfides to condense and cage plasmid DNA (pDNA) by a process of thermodynamically controlled template polymerization, leading to a series of corresponding pDNA-polyplex nanoparticles able to mediate high levels of transfection with no associated cytotoxicities. The leading cyclic polyamine disulfide was shown to be the spermine tetra-amine disulfide (TetraN-3,4,3). Herein we report on the significantly more challenging syntheses of cyclic disulfides with longer polyamine motifs. Two new cyclic polyamine disulfides, based on hexa- and octa-amine inserts, were prepared and their transfection efficacies and cytotoxicities compared with our previously reported cyclic tri- and tetra-amine disulfides. The new cyclic hexa- and octa-amine disulfides prove more effective at transfection in vitro, especially of lung epithelial A549 cell line. By contrast, our original cyclic tetra-amine disulfide remains the most efficient agent for the transfection of lung epithelial cells in vivo following intra-nasal administration. Hypothetical mechanistic reasons are presented to explain this outcome. Our data in toto support the concept of shorter cyclic polyamine disulfides as preferred agents for polycation-mediated controlled condensation and functional delivery of pDNA to lung epithelial cells in vivo.
{"Chemical": ["cyclic disulfides", "cyclic polyamine disulfides", "cyclic polyamine disulfide", "spermine tetra-amine disulfide", "polyamine disulfide", "TetraN-3,4,3", "cyclic tri- and tetra-amine disulfides", "cyclic tetra-amine disulfide", "cyclic hexa- and octa-amine disulfides", "hexa- and octa-amine", "disulfide amino"]}