Reasons for the Smell of the Sea

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Ever heard of the 'ozone' or 'iodine' smell of the sea? Well, the smell of the sea is characteristic but it has got nothing to do with ozone or iodine. It's more likely to be dicytopterene, a family of volatile cyclopropanes used by female brown algae to attract male gametes.

In order to reproduce, these female gametes of marine brown algae must attract the mobile male gametes. This they do by releasing a pheromone, long thought to be an ectocarphene. In 1995, results were published that suggested that, in fact, the pheromone was a cyclopropane and the ectocarphene was ineffective as a pheromone.

Scientists were confused. How was it that the experiments suggest that the pheromone was one compound but that compound was not biologically active?

Well, the remarkable thing is that the cyclopropyl pheromone inactivates itself, with a half life of several minutes at ambient temperature, by a [3,3] sigmatropic rearrangement to the ectocarphene, driven by the release of the strain energy from the three-membered ring. In everyday parlance, this means that cyclopropane is produced as the pheromone and degrades quickly to the ectocarphene at room temperature.

This not only confused the earlier pheromone chemists, but also provides a marvellously precise way for the algae to signal their presence and readiness for reproduction without saturating the sea with meaningless pheromones.

What a smart move by these algae! They create compounds that can be automatically deactivated when not needed.

The next time you feel the gentle sea breeze caressing your cheeks and smell its earthy scent, do take note that the smell's just some sex pheromones by brown marine algae.

Source credit: Dr Time Wallace
Information from: Organic Chemistry, pages 949 and 1066

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