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Research has been conducted on the ruthenium salen nitrosyl and ruthenium salophen nitrosyl complexes. The synthesis, characterization and photochemical reactions of these complexes have been investigated and the photochemical applications of the nitric oxide delivery to biological targets are discussed.

The synthesis, characterization and photophysical properties are described for many Ln(III) complexes of a tetradentate chelate (5LIOMAM), derived from the common flavor enhancer 'maltol'. A very poor metal-centered quantum yield with Eu(III) and sensitized emission from the Yb(III) and Nd(III) cations are observed, which emit in the near infrared.

The synthesis, X-ray structure, stability and photophysical properties of many trivalent lanthanide complexes formed from two differing bis-dentate ligands incorporating either alkyl or alkyl ether linkages and featuring the 1-hydroxy-2-pyridinone (1,2-HOPO) chelate group in complex with Eu(III), Sm(III) and Gd(III) are described. The comparison of the high resolution Eu(III) emission spectra in solution and from single crystals have shown a more symmetric coordination geometry about the metal ion in solution due to dynamic rotation of the solid state structure.

The studies about the 1,2-hydroxypyridinones (1,2-HOPO) which forms very stable lanthanide complexes that might be useful as contrast agents for magnetic resonance imaging (MRI) is presented.

The relaxometry and solution thermodynamic measurements of Gd(H(2,2)-1,2-HOPO) showed it to be a good candidate as a contrast agent for magnetic resonance imaging (MRI-CA).

The stability and photophysics of 1,2-hydroxypyridinonate chromophore as a tetradentate derivative, 5LIO-1,2-HOPO, which forms an [ML.sub.2] complex with Eu(III) are reported. 1,2-HOPO-based chelators are proving helpful for applications in highly sensitive biological assays on account of their high luminescent properties with Eu(III) and excellent thermodynamic stability.

A new class of pyrone-derived tripodal chelators that form stable and soluble Gd(super 3+) complexes with high relaxivity for use as magnetic resonance imaging contrast agents (MRI-CAs) is described. The compounds are among the most soluble with a q=2 value, and one of them can be readily and economically synthesized from the food additive maltol.

1 ,2-Hydroxypyridinones (1,2-HOPO) form very stable lanthanide complexes that may be useful as contrast agents for magnetic resonance imaging (MRI). X-ray diffraction of single crystals established that the solid-state structures of the Eu(IIIand the previously reported [Inorg. Chem. 2004, 43, 5452] Gd(III) complex are identical. The recently discovered sensitizing properties of 1,2-HOPO chelates for Eu(III) luminescence [J. Am. Chem. Soc. 2006, 128, 10067] allow for direct measurement of the number of water molecules coordinated to the metal center. Fluorescence measurements of the Eu(III) complex corroborate that, in solution, two water molecules coordinate the lanthanide (q = 2) as proposed from the analysis of NMRD profiles. In addition, fluorescence measurements have verified the anion binding interactions of lanthanide TREN-1,2-HOPO complexes in solution, studied by relaxivity, revealing only very weak oxalate binding (KA 82.7 ± 6.5 M-1). Solution thermodynamic studies of the metal complex and free ligand have been carried out using potentiometry, spectrophotometry, and fluorescence spectroscopy. The metal ion selectivity of TREN-1,2-HOPO supports the feasibility of using 1,2-HOPO ligands for selective lanthanide binding [pGd = 19.3 (2), pZn = 15.2 (2), pCa = 8.8 (3)]. [ABSTRACT FROM AUTHOR]

Relaxometry and solution thermodynamic measurements show that Gd(H(2,2)-1 ,2-HOPO) is a good candidate as a contrast agent for magnetic resonance imaging (MRI-CA). Acidic, octadentate H(2,2)-1,2-HOPO forms a very stable Gd(III) complex [pGd = 21 .2(2)1. The coordination sphere at the Gd(III) center is completed by one water molecule that is not replaced by common physiological anions. In addition, this ligand is highly selective for Gd(III) binding in the presence of Zn(II) or Ca(II). The symmetric charge distribution of the 1,2-HOPO chelates is associated with favorably long electronic relaxation time T1,2e comparable to those of GdDOTA. This, in addition to the fast water exchange rate typical of HOPO chelates, improves the relaxivity to r1p = 8.2 mM-1 s-1 (0.47 T). This remarkably high value is unprecedented for small-molecule, q = 1 MRI-CA. [ABSTRACT FROM AUTHOR]

The desire to improve and expand the scope of clinical magnetic resonance imaging (MRI) has prompted the search for contrast agents of higher efficiency. The development of better agents requires consideration of the fundamental coordination chemistry of the gadolinium(III) ion and the parameters that affect its efficacy as a proton relaxation agent. In optimizing each parameter, other practical issues, such as solubility and in vivo toxicity, must also be addressed, making the attainment of safe, high-relaxivity agents a challenging goal. This Minireview presents recent advances in the field, with an emphasis on gadolinium(III) hydroxypyridinone chelate complexes.