Abstract
Musk odorants represent a class of fragrances which exhibit a warm, sensual, animalistic and natural scent, and were introduced into the perfume industry at the beginning of the 20th century. Structurally, musk odorants are remarkably diverse, including macrocyclic molecules, polycyclic benzene derivatives, nitro arenes, and linear aliphatic compounds, and therefore there is lack of knowledge of the molecular determinants that lead to musk odour. Moreover, some classes of musks such as nitro musks have been proved to be toxic, while others such as polycyclic musks resulted in bioaccumulation and biomagnification through the food chain. Macrocyclic musks, which are biodegradable and exhibit strong olfactory and fixative properties, have an expensive and complex synthesis. The alicyclic class was discovered most recently and so far constitutes the most suitable replacement for macrocyclic musks at commercial scale. There is interest in the perfume industry to develop new musks, but these molecules are conformationally rich and there is very limited knowledge of their active conformations.In this project, we have investigated the conformational landscapes of several musk odorants from alicyclic and macrocyclic classes using broadband rotational spectroscopy. Rotational spectroscopy is a high-resolution technique directly dependent on molecular mass distribution, and therefore able to distinguish minute structural changes. Together with theoretical computations, rotational spectroscopy allows unambiguous identification of co-existing conformers in molecular jets. As part of this project, two alicyclic musks, romandolide and helvetolide, both widely used in the perfume industry, have been investigated. From the macrocyclic musk class the spectra of muscone, civetone and exaltolide have been analysed. Their conformational landscapes have been found to be extraordinarily rich and complex. To understand conformational changes as ring size increases, smaller cyclic ketones of 8-, 11- and 12-membered rings have also been analysed. A clear trend emerges that with the increase in the ring size the number of low energy conformers increases considerably. From the comparison between the observed conformations of all musks, information on conformational preferences, intramolecular interactions, and the structural features responsible for the musky scent has been obtained. The results have been compared to previous work on musks, including the musk olfactophore models, and are essential for understanding odorant identification and for a rational design of new musk odorants.
| Date of Award | 1 Aug 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Maria Sanz (Supervisor) |