HSA is the most abundant protein in plasma and plays an important role in the transport of hormones, fatty acids, and foreign molecules. The impact of HSA binding on the luminescence properties of lanthanide complexes can therefore provide insight into the potential utility of these probes in complex biological samples and settings. The main goal of this project is to better understand the behavior of two Tb(III) complexes in the presence of HSA. To date, two DO3A derivatives, JPEB8 and JPEB11, have been synthesized and characterized, with JPEB8 containing a tris(2-pyridylmethyl)amine (TPA) side arm, and JPEB11 with a picolyl amine side arm. The luminescence properties of their Tb(III) complexes have been investigated in the presence and absence of HSA. In the presence of 2.5 molar equivalents of HSA, a 74% and 29% decrease in luminescence intensity was observed for Tb-JPEB8 and Tb-JPEB11 respectively, suggesting that Tb-JPEB8 and Tb-JPEB11 both bound to HSA, but the interaction between Tb-JPEB8 and HSA was much stronger. Association constants revealed an order of magnitude difference in binding strength between these two complexes, and the stronger binding interaction of Tb-JPEB8 was attributed to its additional di-(2-picolyl) amine subunit. The number of bound water molecules (q) was found to remain constant (0 for Tb-JPEB8 and 0.7 for Tb-JPEB11) in the absence and presence of 2.5 equivalents of HSA; indicating that the quenching of the luminescence intensity was not due to a change in q, but rather, was due to a change in the photophysical environment of the pyridine chromophores upon interaction with HSA. Future work will include an estimation of the singlet and triplet state energies with Gd(III) complexes of these ligands, and measurement of quantum yields in the presence and absence of HSA.

Effect of human serum albumin (HSA) binding on the optical properties of terbium(III) DO3A derivatives

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