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Research has been conducted on the intracellular Ca (super)2+ and its regulation in living animals. The use of the MRI contrast agent where the complex relaxivity is controlled by the absence or presence of the divalent ion Ca (super)2+ is described.

Axial ligation X affects reduction potentials more than equatorial substituents B and A in a study of the electrochemical properties of cobalt(III) derivatives of acacen (H2acacen = bis(acetylacetone) ethylenediimine). The lowest pi-pi* intraligand charge-transfer transition is responsible for the absorption between 340-378 nm in CoIII(acacen) spectra. A study is presented of Co(III) interactions with nucleic acids and proteins, with some cobalt(III) Schiff base complexes known to be antiviral agents.

Mechanistic investigation of isomeric series of [beta]-galactosidase-activated magnetic resonance contrast agents is reported. In the [alpha]-isomer the carbonate ion and [beta]-isomers the galactopyranose play a role in the mechanism of water exclusion from the lanthanide centre prior to cleavage.

The synthesis and characterization of various new ruthenium and rhenium complexes are discussed. The site-selective incorporation of the complexes on DNA enables the measurement of the ground-state electron transfer (ET) rates between the donor and acceptor.

The first MRI prodrug-procontrast complex is prepared by conjugating doxorubicin to a Gd(III) chelate using an acid-ladible linker. The relaxometric properties of the adduct and pH activation are presented.

The first synthesis of metallonucleoside bound to a solid support and subsequent oligonucleotide synthesis with this precursor is reported. It was seen that despite the relatively high Ru(III/II) reduction potential, oxidative quenching of photoexcited [Ru(bpy)(sub 2)(impy)](super 2+) does not lead to oxidative damages of guanine or other DNA bases.

19 F parashift probes with paramagnetically shifted reporter nuclei provide attractive platforms to develop molecular imaging probes. These probes enable ratiometric detection of molecular disease markers using a direct detection technique. Here, we describe a series of trivalent lanthanide (Ln(III)) complexes that are structural analogues of the clinically approved MR contrast agent (CA) ProHance to obtain LnL 19 F parashift probes. We evaluated trans-gadolinium paramagnetic lanthanides compared to diamagnetic YL for 19 F chemical shift and relaxation rate enhancement. The paramagnetic contribution to chemical shift (δ PCS ) for paramagnetic LnL exhibited either shifts to lower frequency (δ PCS < 0 for TbL , DyL , and HoL ) or shifts to higher frequency (δ PCS > 0 for ErL , TmL , and YbL ) compared to YL 19 F spectroscopic signal. Zero-echo time pulse sequences achieved 56-fold sensitivity enhancement for DyL over YL , while developing probe-specific pulse sequences with fast delay times and acquisition times achieved 0.6-fold enhancement in limit of detection for DyL . DyL provides an attractive platform to develop 19 F parashift probes for ratiometric detection of enzymatic activity.

A fundamental challenge in the design of bioresponsive (or bioactivated) Gd III -based magnetic resonance (MR) imaging probes is the considerable background signal present in the "preactivated" state that arises from outer-sphere relaxation processes. When sufficient concentrations of a bioresponsive agent are present (i.e., a detectable signal in the image), the inner- and outer-sphere contributions to r 1 may be misinterpreted to conclude that the agent has been activated, when it has not. Of the several parameters that determine the observed MR signal of an agent, only the electron relaxation time ( T 1e ) impacts both the inner- and outer-sphere relaxation. Therefore, strategies to minimize this background signal must be developed to create a near zero-background (or truly "off" state) of the agent. Here, we demonstrate that intramolecular magnetic exchange coupling when Gd III is coupled to a paramagnetic transition metal provides a means to overcome the contribution of second- and outer-sphere contributions to the observed relaxivity. We have prepared a series of complexes with the general formula LMLn(μ-O 2 CCH 3 )(O 2 CCH 3 ) 2 (M = Co, Cu, Zn). Solid-state magnetic susceptibility measurements reveal significant magnetic coupling between Gd III and the transition metal ion. Nuclear magnetic relaxation dispersion (NMRD) analysis confirms that the observed differences in relaxivity are associated with the modulation of T 1e at Gd III . These results clearly demonstrate that magnetic exchange coupling between Gd III and a transition metal ion can provide a significant decrease in T 1e (and therefore the relaxivity of Gd III ). This design strategy is being exploited to prepare new generations of preclinical bioresponsive MR imaging probes with near zero-background.