Some spectroscopic and transport properties of a rare-earth chelate, Tb-PCTMP Original Research Article

A polyazamacrocyclic chelate of Terbium III; 3,6,9-Tris(methyl phosphonic acid)-3,6,9,15-tetraazabicyclo[9,3,1]pentadeca-1(15),11,13-triene, Tb-PCTMP, has been shown to exhibit rich spectroscopic properties, tissue selectivity [M.P. Houlne et al., Appl. Spectrosc. 10 (1996) 225–244], millisecond fluorescence lifetimes [D.S. Hubbard, M.P. Houlne, G.E. Kiefer, H.F. Janssen, C. Hacker, D.J. Bornhop, Lasers Med. Sci. (13) (1998) 14–21], sharply spiked emission spectra (<15 nm FWHM), large Stokes shifts (>280 nm), high water solubility and good fluorescence quantum yields (∼0.24). Expanded investigations of the Tb-PCTMP chelate are presented here that further indicate Tb-PCTMP can be used for transport investigations, using endoscopy. First we elucidate the spectroscopic sensitivity of the chelate to physiological pH changes. Second we demonstrate a lack of cyctotoxicity using in-vitro studies. Finally, we show that chelate transport, through a collagen matrix, can be quantitatively monitored using fluorescence endoscopy. The results provide new insights about how solutes, having different chemical structures, move through the interstitial space and show the potential for performing such measurements minimally invasively, in-vivo.