Painful chemistry! From barbecue smoke to riot control

Abstract

AbstractPain! Most humans feel it throughout their lives. The molecular mechanisms underlying the phenomenon are still poorly understood. This is especially true of pain triggered in response to molecules of a certain shape and reactivity present in the environment. Such molecules can interact with the sensory nerve endings of the eyes, nose, throat and lungs to cause irritation that can range from mild to severe. The ability to alert to the presence of such potentially harmful substances has been termed the ‘common chemical sense’ and is thought to be distinct from the senses of smell or taste, which are presumed to have evolved later. Barbecue a burger excessively and you self-experiment. Fatty acids present in the meat break off their glycerol anchor under the thermal stress. The glycerol loses two molecules of water and forms acrolein, whose assault on the eyes is partly responsible for the tears elicited by smoke. Yet the smell and taste of the burger are different experiences. It was this eye-watering character of acrolein that prompted its use as a warfare agent during World War I. It was one of several ‘lachrymators’ deployed to harass, and the forerunner of safer chemicals, such as ‘tear gas’ CS, developed for riot control. The history of development and mechanism of action of some sensory irritants is discussed here in relation to recent advice from the Scientific Advisory Board (SAB) of the Organisation for the Prohibition of Chemical Weapons (OPCW) on chemicals that conform to the definition of a riot control agent (RCA) under the Chemical Weapons Convention.