Water-Soluble 2-Hydroxyisophthalamides for Sensitization of Lanthanide Luminescence

Abstract

A series of octadentate ligands featuring the 2-hydroxyisophthalamide (IAM) antenna chromophore (to sensitize Tb(III) and Eu(III) luminescence) has been prepared and characterized. The length of the alkyl amine scaffold that links the four IAM moieties has been varied in order to investigate the effect of the ligand backbone on the stability and photophysical properties of the Ln(III) complexes. The amine backbones utilized in this study are N,N,N',N'-tetrakis-(2-aminoethyl)-ethane-1,2-diamine [H(2,2)-], N,N,N',N'-tetrakis-(2-aminoethyl)-propane-1,3-diamine [H(3,2)-] and N,N,N',N'-tetrakis-(2-aminoethyl)-butane-1,4-diamine [H(4,2)-]. These ligands also incorporate methoxyethylene [MOE] groups on each of the IAM chromophores to increase their water solubility. The aqueous ligand protonation constants and Tb(III) and Eu(III) formation constants were determined from solution thermodynamic studies. The resulting values indicate that at physiological pH, the Eu(III) and Tb(III) complexes of H(2,2)-IAM-MOE and H(4,2)-IAM-MOE are sufficiently stable to prevent dissociation at nanomolar concentrations. The photophysical measurements for the Tb(III) complexes gave overall quantum yield values of 0.56, 0.39, and 0.52 respectively for the complexes with H(2,2)-IAM-MOE, H(3,2)-IAM-MOE and H(4,2)-IAM-MOE, while the corresponding Eu(III) complexes displayed significantly weaker luminescence, with quantum yield values of 0.0014, 0.0015, and 0.0058, respectively. Analysis of the steady state Eu(III) emission spectra provides insight into the solution symmetries of the complexes. The combined solubility, stability and photophysical performance of the Tb(III) complexes in particular make them well suited to serve as the luminescent reporter group in high sensitivity time-resolved fluoroimmunoassays.

Strong Circularly Polarized Luminescence from Highly Emissive Terbium Complexes in Aqueous Solution

“…[9,17] As with other Tb-IAM complexes, the broad absorption bands of cyLI-Tb and dpenLI-Tb allow for excitation with wavelengths up to ca. 390 nm, which is more favorable for practical biological applications compared to many other high quantum yield Tb III complexes that require more damaging higher energy excitation wave-lengths.…”

“…The cyLI-Tb value is consistent with the high quantum yield values observed for Tb III complexes with octadentate IAM ligands. [9,11,17]…”

Optical emission studies of new europium and terbium dinuclear complexes with trifluoroacetylacetone and bridging bipyrimidine. Fast radiation and high emission quantum yield

“…The luminescence quantum yield, U overall , of the [Eu(tfaa) 3 ] 2 bpm and [Tb(tfaa) 3 ] 2 bpm complexes in CHCl 3 solution is 34% and 48%. The quantum yield of the present Eu complex is Table 2 Radiative (A RAD ) and non-radiative (A NR ) decay rates, 5 D 0 lifetime (s obs ), intrinsic quantum yield (U Eu ), energy transfer efficiency (g sen ) and overall quantum yield (U overall ) for the complexes [Eu(tfaa) 3 [29]. However, there are reports of U overall = 40% and s obs = 0.46 ms for Tb(III)-dipivaloylmethanato complexes [28].…”

Octadentate Cages of Tb(III) 2-Hydroxyisophthalamides: A New Standard for Luminescent Lanthanide Labels

“…16–20 The quantum yields reported for the Tb(III) complexes of these IAM based ligands are over 50% in aqueous solutions at physiologically relevant pH and visualization of their emission does not require the addition of augmenting agents such as micelles or fluoride. 21 The IAM-based structures display good thermodynamic stability in aqueous solution, with high molar extinction coefficients and quantum yields, and retain all of the benefits of conventional lanthanide reporters (long fluorescence lifetimes, large effective Stokes shifts and narrow emission lines).…”