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:

Revisiting the Mechanism of Neutral Hydrolysis of Esters: Water Autoionization Mechanisms with Acid or Base Initiation Pathways. The mechanism of neutral hydrolysis of ester has long been explored by theoretical studies. However, reliable theoretical calculations show that the usual bifunctional catalysis mechanism reported by different authors cannot explain the experimental kinetics. An important advance was recently reported by Gunaydin and Houk , suggesting that ions are involved in the mechanism and the process initiates by water autoionization followed by protonation of the ester (WAIA mechanism). However, this mechanism does not explain the hydrolysis of activated esters. In this work, we have used ab initio calculations, continuum solvation models and ab initio classical trajectory to support the WAIA mechanism for normal ester. In the case of activated esters, the process can also be viewed as water autoionization with formation of hydroxide ion aided by a second water moleculeacting as a general base (WAIB mechanism). This is the mechanism proposed by Jencks and Carriuolo fifty years ago. Our analysis point out that the usual method for exploring mechanisms, searching for saddle points, may not work for problems like the present one, since there are no saddle points on the reaction pathway. Rather, the formation of a pair of ions from a neutral species may have an asymptotic barrier. The approach used in this paper allows the calculation of the free energy profile and enable us to explain the mechanism and kinetics of the neutral hydrolysis of normal (methyl acetate) and activated (methyl trifluoroacetate) esters. In addition, the present study suggests that formation of a pair of ions should be always considered in reactions in aqueous solution.
{"Chemical": ["Esters", "hydroxide", "esters", "ester", "methyl acetate", "methyl trifluoroacetate"]}