The present invention is directed generally to protecting cells, tissues and organs against the damaging effects of ionizing or other damaging agents associated with radiation or chemotherapy, or degenerative diseases or processes of various organs that elicit the production of free radicals or oxidants such as peroxides, superoxide anions, hydroxyl radicals or nitric oxides, or heavy metal cations. More particularly, the present invention is concerned with methoxypolyethylene glycol thioester chelate methyl esters that are useful as protectors against tissue damage by penetrating the cell membrane to remove electrons from free radical oxidants and remove heavy metals that may react with peroxides to produce the reactive hydroxyl radical, or remove Ca.sup.++ that may be released from organelles. These chelate esters will also have utility in reducing intraocular pressure in glaucoma patients.