Friday, 11 May 2018

An ancient hemlock poison

Figure 1: Conium maculatum, commonly known as poison hemlock, produces a toxic alkaloid called coniine, which was supposedly the downfall of Socrates himself.

Have you seen a plant lurking in alleyways (or in some backyards!) whose leaves look a bit like those of carrot but a bit bushier? There is a good chance that such a plant is actually Conium maculatum - a poisoner that has been used by humans for centuries: poison hemlock. This plant produces a compound called coniine, an alkaloid (a nitrogen-containing molecule) that causes respiratory paralysis in many mammals. Poison hemlock contains substantial amounts of coniine in its leaves - a handful of leaves are enough to kill. This is particularly problematic for farmers who's livestock can unwittingly eat hemlock if it is in their grazing area. Coniine also seems to have played an important role in history - it was apparently used to kill condemned prisoners in ancient Greece, and seems to have been responsible for the death of Socrates himself - an event reported by Plato that has since been the subject of a famous oil painting. It is amazing that such a simple, small molecule has such a rich history.

Friday, 4 May 2018

Citronellal - natural bug repellant

Have you ever burned a citronella candle to ward off annoying insects? Where do those come from and how do they work? These candles are often made using citronella oil - the essential oil from citronella grass, or Cymbopogon nardus. This oil is used extensively in soaps, perfumes, cosmetics, and of course candles. Interestingly, citronella grass is a cousin (same genus, different species) to lemongrass Cymbopogon citratus, used in teas and some recipes.

Inside citronella oil are several different chemical compounds, the most common of which is an aldehyde called citronellal (Fig. 1). This compound is a major contributor to the anti-insect and anti-fungal properties of citronella oil. When candles contain this oil, the heat from the flame helps the citronellal evaporate into the air - creating a bug-repelling zone all around the candle.
Figure 1: The grass Cymbopogon nardus, also known as citronella grass, produces oil that contains citronellal, a natural insect repelling compound.