Proton sensor ligands

Ligand (264) has been prepared and complexed with Ru" to give [Ru(264)(4-Metpy)] + which protonates on the cyclam N atoms to give a series of species up to [Ru(H3264)(4-Metpy)] +. In aqueous solution, the system acts as a selective luminescent sensor for ATP (with respect to phosphate, sulfate, and chloride ions). Oxaaza macrocycles attached to the 4 -position of tpy either directly or with a spacer as in (265) have been synthesized in addition, l,10-diaza-18-... 

Ruthenium complexes with mixed bipyridyl ligands, immobilized inside a Nation film, may also be used as pH-sensitive sensor layers [90]. A completely different approach for a ratiometric imaging of pH sensor foils was developed for diagenetic studies of marine sediments, using the dual fluorescence excitation ratio of the pH-sensitive fluorophore 8-hydroxypyrene-l,3,6-trisulfonic acid (HPTS) [91]. Commonly used dual fluorophors with different absorption and emission maxima in the protonated and basic form for ratiometric measurements are the naphthofluorescein and seminaphthofluorescein derivates (SNARF and SNAFL) [92], It should be noted that ammonia or carbon dioxide can also be detected by some of these pH-sensitive materials [55,93]. 

So far, lanthanide-based sensors have been successfully used for drug screening, assays and diagnostics as reviewed in Hemmila and Webb (1997). Sensors for pH, pC>2 and some anions (Cl-, CO32-,...) have been tested as examplified in Parker et al. (1998), Bazzicalupi et al. (2001). In the case where protonation/deprotonation of part of the ligand (in its excited state) is the sensor basis, the pKa of interest is that of the excited state, which may differ from that of the ground-state, as explained in sect. 5 (Parker et al., 1998 Blair et al., 2001). 

Luminescent sensors for pH, p02, halide, and hydroxide concentrations have been developed using the Eu(III) and Tb(III) complexes of ligands 46 and 56 in their N-methylated, nonmethylated, or protonated... 

The complexation reaction involves displacement of a proton from the EBT. As a result, response to Mg(ll) will be inherently pH dependent. As pH decreases, the sensor will be less sensitive because a larger Mg(ll) concentration will be required to displace the proton and form the complex. To avoid this effect, all measurements were made in an ammonia/ammonium buffer with a pH of 9.6. This buffer serves not only to control pH but also as a secondary ligand to tie up metal ions such as Cu(ll) that might otherwise interfere in the measurement. 

This has allowed us to develop a very simple method for the preparation of complexes which exhibit pH-ometric sensor ability. The protonation-deprotonation equilibrium changes the overall charge of the complex and also alters the donor character of the ligand [3]. 

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