Freshly out of the shower, I walked across campus this morning with my hair still wet. In the sub-0°C air, my hair froze almost immediately. I entertained myself thinking about the hydrogen bonds I broke and allowed to re-freeze as I shaped my hair into funny designs, which stuck around as long as I was outside. Most of the time, I warmed my hair between my fingertips before shaping it so that I didn’t hear any sounds as bonds broke, but every now and then there would be a louder crack as the ice crystals snapped. I wondered, as I heard that cracking, if I was breaking a few covalent bonds as well as my good friends, the hydrogen bonds.
Since I was thinking about biochemistry, I had two other natural phenomena on my mind. The first had to do with my poor aloe plant. Unfortunately, my aloe plant now sadly droops inside my house, with visible air blisters. The other night, my friend and I forgot about it in her car and it froze. We suspect that the ice crystals tore apart the plant cell walls, since the sad thing is now unable to keep its leaves up.
The second phenomenon I thought of was diamond crystals. How funny – and unpleasant – it would be if our hair were frozen in diamonds instead of water. So I started thinking about the composition of hair, and decided to look it up. It’s predominantly made of keratin, with cysteine amino acids bonded together by disulfide bonds in a repeated, twisted structure. Though predominantly carbon, like the rest of us, it’s interesting how differently carbon structures are manifested depending on their repeating units (e.g., graphite in comparison to diamond’s crystal lattice). We have little concern that our hair carbon atoms will spontaneously form diamonds, because the Gibbs free energy is much too positive. But if our hair did freeze into diamonds, I would certainly not be able to shape and reshape it so easily!
I also found that hydrogen bonding also holds the hair protein chains in their long, repeated units. I wondered if, unlike diamond structures, these hydrogen bonds are what allow our hair to bend, and unlike my aloe plant, also to freeze and unfreeze without breaking apart. I couldn’t find any especially reliable source on the internet, but I would be interested in your thoughts!