Definition of "isomer" [i•so•mer]

• Chemistry Any of two or more substances that are composed of the same elements in the same proportions but differ in properties because of differences in the arrangement of atoms. (noun)
• Physics Any of two or more nuclei with the same mass number and atomic number that have different radioactive properties and can exist in any of several energy states for a measurable period of time. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "However, the trans-10 cis-12 CLA isomer alone is known to have some adverse effects, such as, fatty liver formation, insulin resistance, etc. which can be corrected by combining with the cis-9 trans-11 CLA isomer, which is known to improve insulin sensitivity as well as fatty liver formation, "wrote the researchers."
• "Because all amino acids except glycine are chiral, biosynthetic pathways must generate the correct isomer with high fidelity."
• "Chemet® (succimer) contains the stable meso isomer of dimercaptosuccinic acid which has also been known as DMSA."