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Various studies are conducted to examine the cleavage of the diribonucleoside and the RNA analogues, which is mediated by an active dinuclear Zn(ll) catalyst, Zn(sub 2)(H (sub 2)O) giving it a transition-state stabilization. The results show that the transition state for the reaction between the zinc complex and the dinucleoside is stabilized by the interactions between the catalyst and the oxyanion of the basic alkoxy group.

A dinuclear metal ion complex Zn2(L2O) and its mononuclear analogue Zn(L1OH) are synthesized and studied as catalysts of the cleavage of the phosphate diester 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP).

Three cyclen-based lanthanide complexes of europium namely Eu(THED)3+, Eu(s-THP)3+ and La(TCMC) were evaluated for their reactivity upon 5' cap structure of messenger RNA. The study utilized product and kinetic analyses on the reactive complexes. Results reveal that the lanthanide(III) complexes cleave the 5' cap structure of mRNA. Furthermore, metal-activated nucleophile is necessary for cleavage to occur.

The catalytic properties of the metal complex Eu(L1)3+ (L1 = hexadentate ligand) in RNA transesterification were reported. A series of lanthanide complexes of L1 were also shown to promote transesterification in simple RNA oligomers. The efficient promotion of phosphate ester hydrolysis and RNA transesterification by lanthanide complexes was attributed to their inert behavior. A presented rate data established Eu(L1)3+ as the most effective for RNA catalytic cleavage.

Eu[(S-THP).sup.3+] is the first PARACEST agent that has functioned through exchange of hydroxyl protons with water protons in aqueous solution and the CEST spectrum of this complex is strongly pH dependent. The sensitivity of the alcohol proton environment to interactions with the anions has shown that the complex has potential as a responsive PARACEST MRI contrast agent.

The cyclization of 2-(hydroxypropyl)-4-nitrophenyl phosphate (HpPNP) catalyzed by the dinuclear zinc complex of 1,3-bis(1,4,7-triazacyclonon-1-yl)-2-hydroxypropane has proceeded by a transition state that is different from that of the uncatalyzed reaction. The results have shown the potential for a catalyst by using biologically relevant metal ions to select for an altered transition state for phosphoryl transfer.

Lanthanide ion complexes with neutral ligands are shown to be very effective catalysts for the cleavage of phosphate esters and RNA. The studies have shown that macrocyclic ligands with aromatic pendent groups have formed Er(III) complexes that are among the most effective catalysts for cleavage of 2-hydroxypropyl-4-nitrophenyl phosphate (HpPNP) and for a dinucleoside, uridylyl-3'-5'-uridine (UpU), in water.

The chemical exchange saturation transfer (CEST) characteristics of europium(III) macrocyclic complexes having appended hydroxyethyl groups are investigated in order to determine avenues to improve the sensitivity of agents like CEST. The utility of this class of europium(III) complex for CEST imaging applications is limited by the small chemical shifts induced by the hydroxyl-appended ligands of this type and the resulting small DELTAomega values for the exchangeable hydroxyl protons.

The cleavage of UpPNP catalyzed by Zn(sub 2) is shown to have a normal equilibrium solvent deuterium isotope effect on the pK(sub a) of an essential Zn(super 2+) bound water with no primary kinetic solvent isotope effect so that concerted Bronsted acid-base catalysis does not contribute to the extraordinary rate acceleration observed for this catalyst.

The article focuses on the development of Ln(III) macrocyclic complexes used as contrast agents through paramagnetic chemical exchange saturation transfer (PARACEST) as responsive magnetic resonance imaging (MRI) contrast agents. The inner-sphere/outer-sphere binding dichotomy for two different ligands shows mechanism for selectively responsive CEST agent development. The binding constants suggest its viability to develop PARACEST agents for phosphate-containing metabolite detection.