Effect of the buffer composition on the aggregation state of the zinc(II) tetra-spermine porphyrin derivative

The aggregative state of the Zn(II) tetra-spermine porphyrin derivative, ZnTCPPSpm4, has been investigated in the presence of different buffers at the same pH value: 5K (cacodylate) buffer, phosphate sodium salt buffer, and PBS. The photophysical characterizations (UV-vis, Fluorescence, and RLS) have indicated a precise self-assembly phenomenon depending on the buffered solution used. The porphyrin does not undergo a significant aggregation in 5K buffer, differently from what occurs in phosphate and PBS buffers. Here, the likely specific interaction between the phosphate molecules and spermine pendants leads to spontaneous porphyrin aggregation, as detected by the high fluorescence quenching, enhancement of the RLS signal, and a significant splitting of the porphyrin Soret band. As a result, the current paper aims to highlight the importance of the employed buffer throughout the experimental procedures performed in the presence of porphyrinoids.