Since tyrosine's solubility in different solvents is limited and because there is a need to perform the carbodiimide reaction in the lowest amounts of DMSO, various solvent mixtures were tested for dissolving the amino acid. The final solvent mixture consisted of 90 % DMSO, 8.33 % HCl and 1.67 % double distilled water. Hence, a maximum concentration of tyrosine of 100 mg/mL was achieved following the dissolution at room temperature for few minutes. This reached 400 mg/mL with heating in a water bath. The pH of the final solution was 1.44, and minute quantities were used for the conjugation reaction. In contrast to H-Tyra, the yield of H-Tyros was 70 % due to the two step reaction. NMR spectroscopy confirmed the structure of H-Tyros conjugate, with the presence of key signals at 9.44 and 10.3 corresponding to the -OH hydrogen atoms beside hydrogens of the main porphyrin ring (Fig. ).