Anti-electron

Anti-electrons are a rare (seemingly liquid) substance with various unusual properties, such as causing Transformers to malfunction. Unicron's head possesses a supply of anti-electrons in his Cerebro chamber. Grimlock's New Brain

Despite their name, they appear to be distinct from positrons, the real-world antimatter equivalent of electrons, since Megatron was happily flinging antimatter about with no ill effects back in Roll for It.