N-methyl mesoporphorin IX forms a dimer in aqueous solution

N-methyl mesoporphyrin IX (NMM) has rapidly become a significant tool for the characterization of quadruplex DNA (GQ-DNA) structures. These novel DNA structures are of interest due to their enrichment in protooncogene sequences and telomeres [Kosiol 2021]. As NMM becomes a standard tool in the sub-field of GQ-DNA research, it becomes increasingly important to understand its behavior. NMM’s utility is based on a shift in absorbance from a max at 379 nm to a max at 400 nm in the presence of GQ binding partners, and fluorescence enhancement upon the presence of binding partners [Yett 2019]. In this work we present preliminary results showing that NMM, in aqueous solution, without GQ-DNA present, shows a concentration dependent shift in peak absorbance from 400 nm to 379 nm with increasing concentration. This shift is consistent with NMM forming a dimer. In addition, NMM displays increasing fluorescence intensity with increasing temperature, consistent with fluorescence quenching in the dimer state.