Few everyday experiences can compete with a good hot drink, especially on a cold winter's day or when the rain is lashing against the window. For many, the favourite is coffee, and even those of us who don't like the taste, can't help but agree that coffee has a distinctly enticing aroma when just brewed, which can drag sleepers from their cosy beds and commuters and shoppers into cafes. But underlying this seemingly commonplace beverage is a profound chemical complexity and it is this very complexity that researchers from the Università degli Studi di Roma Tre came to ISIS to understand.
Caffeine, trigonelline and nicotinic acid (vitamin B₃) are three important bioactive elements of coffee. Trigonelline is the most substantial of these three elements that contributes to coffee's bitter taste. It is found in various plants and seeds and presents in amounts like those in caffeine. It crystallizes and its structure has so far been determined by X-ray diffraction. It is also highly water soluble and previous studies have reported its many beneficial properties, from anti-bacterial to anti-migraine and also improving memory retention. However, trigonelline's interactions with water are largely unknown, and whether this molecule interacts better with water through hydrogen bonding or prefers to bind together with other trigonelline molecules through electrostatic interactions.
Therefore, the study was to investigate trigonelline-water interactions at the atomistic level using neutron diffraction with our instrument SANDALS, augmented with a computer simulation. These have implications relevant to other bioactive molecules and can also provide basic information on the extraction efficiency and on the solubility of important molecules in coffee.
The results revealed a short-range interaction between the trigonelline and the water solvent and some clustering of trigonelline molecules. The solution contained both positive and negative charges and resulted in hydronium ion-formation. The observed structures were compatible with a Zundel-like cation, which along with the Eigen cation, play an important role as intermediate structures for proton transfer processes in liquid water. The role of a Zundel-like cation, along with its interaction with the chloride ion, might be related to the extraction and solubility of important molecules in coffee, to define the best water composition resulting in the best coffee.
“This first study can be extended by looking, for instance, at the trigonelline-water interactions in presence of added ions, such as magnesium and calcium, possibly under more realistic coffee-making conditions, which suggests a new research route for us with the help of SANDALS," explains co-author Professor Fabio Bruni. “We are also very excited about the upgrades at ISIS, as in a few years' time, SANDALS-II will be available and will not only be faster but will also provide extra capability for higher Q-space resolution. This will be useful to detect even the smallest fraction of crystallinity in the samples, which will turn any such new research routes into a successful and far-reaching science project."
Read the paper in full here: Science in a cup of coffee: A structural study of a trigonelline aqueous solution - ScienceDirect
