Red Hippopotamus Sweat

Hippos have developed a very interesting form of sweat that possesses additional functionality than cooling down the body temperature. Before studied, the sweat was thought to be blood due to the red colour, but it was found to just be two pigmented molecules which have two functions for the hippo, being a sunscreen, and an antibiotic. It has been found that the main components aren't secreted as most sweat components are, but secreted in subdermal glands, making the classification of the sweat false as sweat is secreted from sweat glands, located in the epidermis.

The two molecules that are secreted are Hipposudoric acid and Norhipposudoric acid (seen below)

Hipposudoric acid

Norhipposudoric acid

These molecules are conjugated systems, meaning in layman's terms that the bonds alternate single to double, but this also means that light is absorbed into this system ranging from the 200nm - 600nm wavelength.  This property is what gives the sweat the sunscreen-like properties and the red colour where the Hipposudoric acid is red and the Norhipposudoric acid is orange.  As for the antibiotic properties, this is the job of Hipposudoric acid, which inhibits two species of pathogenic bacteria Pseudomonas aeruginosa and Klebsiella pneumoniae.

In finding this, there is an obvious potential for this to be used in consumer sunscreens as there is such a demand for natural sources in cosmetics. Now it's not like there would be a farm somewhere collecting hippo sweat, as there is a method for synthesizing Hipposudoric acid, published in 2006 in Tetrahedron Letters.

Reference

Mushroom Coral as a Sunscreen

In an episode of Man vs. Wild that I was watching, a Mushroom Coral's mucus was used as a sunscreen, so me as a chemist interested in cosmetics, I wanted to know what photoprotecting chemicals were in this mucus.  The coral Fungia fungites and a couple other species gained this ability to protect themselves because they would grow in shallow water of the Adaman Sea where a lot of UV radiation penetrates through the clear water.  First looking at this ability one would expect the coral to synthesize these molecules, but it turns out that the culprits are tiny symbiotic dinoflagellates. In a paper from 1999 by Brown¹ studying the makeup of the mucus required for photoprotection, they look at the concentration of xanthophylls in the mucus, the primary photoprotector. Their study looked at how the concentrations of xanthophylls varried throughout the day, and showed that it is best to harvest the mucus at noon when the xanthophylls are at their peak concentration.

So finally to the chemistry of all of this. The molecule shown above is called diatoxanthin, which is a type of xanthophylls, and this is the molecule mostly responsible for filtering out the harmful rays.  So how does this happen? Well molecules and atoms absorb light one way or another through absorbing the photons, resulting in electron excitation, and in this case, the molecule absorbs in the UV portion of the electromagnetic spectrum. So what happens after the diatoxanthin molecules become excited? Well biology has found a solution for that, which has been named the Xanthophyll Cycle. It's job is to convert all the used up diatoxanthin back into diatoxanthin.

References:
1. Fitt, W. K., R. P. Dunne, S. W. Gibb, D. G. Cummings, I. Ambarsari, B. E. Brown, and M. E. Warner. "Diurnal Changes in Photochemical Efficiency and Xanthophyll Concentrations in Shallow Water Reef Corals : Evidence for Photoinhibition and Photoprotection." Coral Reefs (1999): 99-105.