Modulating the oxygen affinity of porphyrins with metals, ligands, and functional groups: A DFT study.

The interaction between different metals (M), axial ligands (L), and ring substituents (R) in porphyrins was investigated using density functional theory. Different combinations of iron and cobalt as metal centers; imidazole, chlorine, and an n-heterocyclic carbene (NHC) as axial ligands, and unsubstituted, octaethyl-, and tetraphenyl-porphyrins were explored in their low, intermediate, and high-spin states, alongside oxygen affinity. Remarkably, the n-heterocyclic carbene enhanced the affinity of cobalt porphyrins to oxygen, with binding energies on average 4.

Repeated evolution of underwater rebreathing in diving Anolis lizards.

Air-based respiration limits the use of aquatic environments by ancestrally terrestrial animals. To overcome this challenge, diving arthropods have evolved to respire without resurfacing using air held between their cuticle and surrounding water. Inspired by natural history observations in Haiti (unpublished data) and Costa Rica, we conducted experiments documenting routine air-based underwater respiration in several distantly related semi-aquatic Anolis lizard species.