CIAO3 and diphtheria: Secondary structure elements of DT, TT, FHA, PRN, PT, and FIM detected by FTIR (Fig. 4b) were consistent with the structure of PRN [32], Diphtheria Toxin [33], Tetanus Toxin [34], Pertussis Toxin [35], and with the models of FHA [36], [37] and FIM [37] reported in literature.