Chelating agents are chemicals or chemical compounds that react with heavy metals, rearranging their chemical composition and improving their general stability and likelihood of bonding with other metals, nutrients, or substances. When this happens the metal that remains is known as a “chelate,” a word that derives from the Greek chela, meaning claw. These sorts of agents exist in nature and are an important part of many biological processes. They help transport nutrients throughout plants, for instance, and assist in digestion in people and many animals. In many places they’re also created synthetically, and have a number of important uses in both industry and medicine. These sorts of agents can be very useful any time heavy metal ions need to be broken down, isolated, or moved.
How They Work
The chemistry behind how these agents work tends to be somewhat complex, but to put it simply they bond to metal ions in such a way as to reorganize their core structure and chemical composition. Most metals have chemical structures that most closely resemble chains, but chelating agents join the ends in order to form a ring, known as a ligand. This ring structure makes the ions more stable and helps them move with greater ease through a range of different environments.
Ethylenediamine is one of the most common chelating agents, and is a good example of how these substances work. It has a chemical structure of C2H8N2. It is known chemically as a multidentate agent, or more specifically a bidentate ligand, which means that can form two bonds — each nitrogen atom can bond with the same metal ion. Depending on how many bonds the metal ion can accept, the ion may form a chelate with one, two, or three ethylenediamine molecules. The more bonds there are, the stronger and more stable the chelate is likely to be.
Role in Nature
Naturally-occurring chelates are necessary for many life-sustaining processes, and they can’t be formed without agents that can help their transformation. The vitamin B12-cobalt complex is one example. It is a dietary requirement for people and most animals, but in most cases it can’t properly be digested or absorbed until it has formed a ligand with one of the many chelating agents in the body. The hemoglobin-iron complex transports oxygen through the blood after chelation, and similarly, the chlorophyll-magnesium complex is a critical component of photosynthesis in plants. If chelating agents weren’t at work these processes would be slower, and might not even happen at all.
Use in Industry
Agents are commonly used in industrial manufacturing as detergent additives, stabilizing agents, preservatives, and flavor and color retainers. Ethylenediaminetetraacetic acid (EDTA) is one of the most popular. It is what is known as a “quadridentate” or “hexadentate” agent that is capable of forming either four or six bonds with metal ions. EDTA is widely used for enhancing the cleaning power of detergents and soaps by forming chelates with the magnesium and calcium metals in hard water. These agents are also used as color retainers for textile dyes.
EDTA is used in many places as a food additive, too. Food spoilage is typically catalyzed by enzymes that require certain transition metals in order to work, but EDTA deactivates the spoilage enzymes that would otherwise cause the food to become rancid. It also deactivates the enzymes that cause food to lose color or flavor.
Importance to Medicine
These agents are essential to many medical treatments and tests. They can be used to isolate and move calcium ions out of the blood, which helps preserve blood during surgeries or operations, for instance, and they’re also an important part of many lead poisoning and other metal poisoning treatments. When agents enter the bloodstream they can target free metal ions and chelate them and then remove them from the blood stream, often by flushing them out in urine. Dimercaprol is one of the most common examples. It removes heavy metal poisons, such as antimony, mercury, and arsenic, by forming sulfur bonds to the metal ions.