Friday, 14 September 2018

The taste and aroma of saffron

Worth more than their weight in gold, saffron crocus (Crocus sativus, Iridaceae) stigmata produce the glycoside picrocrocin and its aglycone saffranal (products of zeaxanthin degradation?) - major contributors to the taste and aroma of the "king of spices".

Friday, 31 August 2018


This week: safrole. Though found in small amounts in anise, cinnamon, and nutmeg, it's a major component of sassafras oil. It has a characteristic "candy shop" scent, is a synthetic precursor to MDMA, and is evidently banned from use in food by the FDA.

Figure 1: Sassafras albidum - the sassafras tree - oil from which contains safrole, an interesting plant chemical.

Friday, 24 August 2018

Amorphophallus titanum and the essence of rotting fish

Have you heard of the corpse flower? Scientifically known as Amorphophallus titanum, the corpse flower gets its name because it generates a variety of malodorous compounds to attract animal pollinators. Among these is trimethylamine, or "essence of rotting fish" (Fig. 1), a biomarker used by fish freshness detectors.

An excellent short video here on these compounds and the ability of the corpse flower to generate heat!
The chemistry of the corpse flower's stink - Bytesize Science

Figure 1: The flowers of Amorphophallus titanum generate, among others, the smell compound trimethylamine, which smells like rotting fish.

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.

Friday, 27 April 2018

Monolignols - Happy Arbor Day!

Happy Arbor Day from Nebraska! Today let's have a look at monolignols, simple ring molecules that when combined together make one of the strongest and most abundant biopolymers on Earth - wood.

Do you remember learning in school that the mass of a plant doesn't come from the soil, but from the air? Perhaps this tidbit is easy to forget, but it's true! Plants can suck carbon dioxide out the air and turn it into sugar. They use this sugar as energy to grow and reproduce. In order to stand up and reach for the sun, plants need to be able to build rigid structures can can hold weight. Trees are wizards at doing this.

Figure 1: The monolignols p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. In the background, an example of a lignin polymer.

To build rigid structures, woody plants break down the sugars they obtained from capturing sunlight and reassemble the carbon pieces into monolignols - ring structures made of carbon, oxygen, and hydrogen. Some of the most common monolignols are p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol (Fig. 1). Scientists suspect that the trees then produce enzymes (small molecular-scale machines) that can assemble these monolignols use what's called (I kid you not) 'radical' chemistry. Radicals are the technical name for unpaired electrons. In an unpaired state, electrons are highly reactive and it seems that it is this energy that the tree's molecular machines use to link the monolignols together.

After radical polymerization, very large polymers are formed - see the background in Fig. 1. This process consumes an incredible amount of carbon. In fact, the Carboniferous Period (350 - 300 million years ago) is in part defined by plants' evolution of the ability to sequester carbon from the atmosphere and store it in a way that allows them to stand up tall. It is these huge, cross-linked polymers that give wood its strength, and it is these same structures that are oxidized during the burning of wood, returning the carbon to the atmosphere after potentially hundreds of years in storage.

Friday, 20 April 2018

The periwinkle's deadly secret

Figure 1: The vinca alkaloid vincristine from the periwinkle Catharanthus roseus.

Periwinkle, the common ornamental plant, is highly toxic because of the chemical compounds it contains. One of these compounds is called vincristine - a compound that can prevent mammalian cells from dividing. This compound contains nitrogen atoms, making it an alkaloid. Vincristine and its sibling alkaloid, vinblastine, both inhibit cell division which makes them effective chemotheraputics. They are used to treat several types of cancer. For the plant, these compounds constitute a defense mechanism: if eaten in quantity, periwinkle leaves are highly toxic. So, even though the periwinkle is a pretty plant to look at - it's not good to eat!