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[Gd(HP‐DO3A)] (gadoteridol) as an active compound of ProHance® is a widely employed contrast agent in clinical MRI scans in the last 30 years. Recent concerns about the long‐term retention of gadolinium‐based contrast agents (GBCAs) led to a deeper investigation of the structural features underlying the integrity of the paramagnetic metal complex. Several human and nonclinical studies have noted marked differences among the macrocyclic GBCAs, with the least retention of Gd traces and most rapid elimination consistently being reported for [Gd(HP‐DO3A)]. It was deemed of interest to assess how minor structural/electronic changes associated to the ligand structure may affect basic properties of the metal complex with several [Gd(HP‐DO3A)] analogues synthesized and characterized in the last years. We recently reported that the closest homolog of [Gd(HP‐DO3A)], i. e.: [Gd(HB‐DO3A)], in which a (±)‐2‐hydroxy‐1‐propyl pendant arm is replaced by a (±)‐2‐hydroxy‐1‐butyl moiety, showed a significantly different retention behaviour in the model interaction with collagen, despite the apparently very minor structural difference. In this paper we report a comprehensive study of the structural, thermodynamic, kinetic and relaxation properties of [Gd(HB‐DO3A)], compared to the parent [Gd(HP‐DO3A)] and to other closely related macrocyclic GBCAs to assess whether very minor structural changes can modulate the physico‐chemical properties of Gd3+ complexes. [ABSTRACT FROM AUTHOR]

The treatment of the 90 degree angular precursor trans-[Ru[Cl.sub.2][(dmso-S).sub.4]] with an equivalent amount of the linear and rigid pyrazine (pyz) linker has produced the molecular triangle [[{trans,cis-Ru[Cl.sub.2][(dmso-S).sub.2]([mu]-pyz)}.sub.3]] instead of the molecular squares. The results have shown that the entropically favored molecular triangles are preferred over the expected molecular squares with metal corner fragments that have favored [N.sub.pyz]-M-[N.sub.pyz] angles narrower than 90 degrees due to the presence of ancillary ligands.

Compounds such as Ru-, Os-, Rh-, and Ir are a rich and interesting chemistry, characterized by the presence of several geometrical and linkage isomers, and by the possibility that either the dmso's or the chlorides, or both are replaced by neutral or anionic ligands under appropriate reaction conditions.

Research has been conducted on the ruthenium(II)- and ruthenium(III)-chloride-dimethyl sulfoxide precursors and the antimetasatic drug [ImH][trans-RuCl (sub)4 (dmso-S)] (Im= imidazole, dmso= dimethyl sulfoxide). The reactivity of these compounds toward nitric oxide has been studied and the details are reported.

The 2+2 neutral metallacycles made of porphyrins and octahedral ruthenium coordination compounds of formula [trans,cis,cis-RuCl2(dmso-S)2(4'-cis-DPyP)]2, [trans,cis,cis-RuCl2(CO)2(4'-cis-DPyP]2, and [trans,cis,cis-RuCl2(dmso-S)(CO)(4'-cis-DPyP)]2 is formed after the treatment of the octahedral Ru(II)-dimethyl sulfoxide trans-RuCl2(dmso-S)4, trans-RuCl2(dmso-O)2(CO)2, and trans-RuCl2(dmso)3(CO) with a stochiometric amount of 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cis-DPyP).

Research has been conducted on the pyridylporphyrins and ruthenium complexes. The adducts between these complexes have been investigated and the results indicate that the porphyrin singlet is quenched in all the adducts.

Research has been conducted on the factors that influence the dynamic motion of planar N-donor heterocyclic ligands. The use of X-rays and NMR in investigating mixed-ligand mu-oxorhenium dimers is discussed.

The X-ray structure of (Ru(TTP)(CO)(3'MPyP)) (1) showed that, in the solid state, the two mean porphyrin planes in 1 are canted at an angle of ca. 43 degrees. Diffraction data permitted the refinement of the atomic positional parameters of 1 with the lowest calculated errors among those determined for similar porphyrin adducts. Based on NMR measurements, the solution structure of 1 was found to be very similar to that observed in the solid state though more symmetrical because of the presence of a pseudomirror plane perpendicular to 3'MPyP and going through the 3'N(py) ring.

The conformers of cis,cis,cis-RuCl2(Me2SO)2(3,5-lut)(1,2-Me2Im) (3,5-lut = 3,5-lutidine, 1,2-Me2Im = 1,2-dimethylimidazole) in fluxional equilibrium in solution were observed to be trapped and almost unaltered in the solid state. These presented a rare example in which the solid state closely reflects the solution state, both in the structure of species involved in a conformational equilibrium and in the position of that equilibrium.

A series of ruthenium complex - 4-pyridyl/phenyl porphyrins is designed, synthesized and spectrally characterized. Ruthenium complex - 4-pyridyl/phenyl porphyrins ratios of 1:1 and 1:2 for monomers, 2:1 for dimers and 4:1 for tetramers were used in the analysis. These newly described adducts have self-assembling properties and are seen as a new type of building blocks.

Exchange-NOE nuclear magnetic resonance spectroscopy data is shown to be an efficient method for determining the extent of planar N-donor heterocyclic coordinated ligands (L's) rotation about the metal-N bond, the direction of L rotation and even the halves of C2-symmetrical L's that interchange during dynamic processes. It marks the first time that preferred pathways of rotation were demonstrated.

Two octahedral complexes characterized by the restricted rotation of the nitrogen ligands about the Ru-N bond at room temperature are investigated. The first complex is a good example of topomerization while the second one provides an example of diastereotopomerization. There are two possible atropisomers for each geometric isomer of the first complex and four for the second. It is shown that the second complex is the first compound of its type to be both head-to-head in solution and in solid-state.

The synthesis and characterization of cis,cis,cis-RuX2(Me2SO)2(1,2Me2Im)L complexes and their rotamers, where L = 1,2-dimethylimidazole or 1,5,6-trimethylbenzimidazole; X = Cl or Br; Me2SO = s-bonded dimethylsulfoxide, are described. The results showed that L 'b' (trans to Me2SO) can rotate regardless of orientation of L 'a' (trans to Cl) while L 'a' can rotate only when L 'b' has the orientation with its 2-Me group directed away from L 'a.'

The neutral RhCl3(DMSO)3 mer,cis-isomer photochemically isomerizes in acetone solution to yield a new linkage isomer, trans-RhCl3(DMSO)2(DMSO) of the rhodium-chloride-dimethyl sulfoxide complex. H-NMR analysis of the linkage isomers displays two new singlets at 3.53 parts per million and 2.78 parts per million. The mer,trans-isomer is thermodynamically less stable than the mer, cis-isomer. Mer,trans-isomer stereospecifically yields monosubstituted linkage isomers of mer-cis isomer on reaction with neutral ligands.

The structure of the reaction complex between trans-RuCl(sub 2)(DMSO)(sub 4), an antitumor octahedral complex, and guanine dinucleotide was characterized using nuclear magnetic resonance and molecular modelling studies. Results show the existence of two guanines, two DMSO(sub 4) and a halogen atom in the ruthenium coordination sphere. The molecule has structural features similar to the corresponding cisplatin complex.