The heme d 1 macrocycle of Ps. aeruginosa dissimilatory nitrite reductase is an iron porphyrin-3,8-dione with a 17-acrylate substituent. We have compared the RR properties of Cu-d 1, the copper(II) TME of extracted heme d 1, with those of models that differ only with respect to the acrylate: Cu-17-acrylate-mesoporphyrin-3,8-dione (2) and Cu-mesoporphyrin-3,8-dione (3). The RR spectrum of Cu-d 1 is very similar to that of 2, including v(C=O) at ~ 1720 cm−1. Replacement of the acrylate with propionate changes the spectrum markedly. For example, the v(C=O) mode of 3 shifts to 1712 cm−1, and peaks of Cu-d 1 and 2 at ~ 1400 and ~ 1535 cm−1 are shifted or absent from the spectrum of 3. FTIR spectra of 2 and 3 also differ in their νoxo(C=O) frequencies. The acrylate thus has a surprisingly strong influence on the electronic structural and spectral properties of heme d 1. These data provide a foundation for studies of the novel biological porphyrindione macrocycles.
