Jorge A. López

A New Gadolinium-Based MRI Zinc Sensor

The properties of a novel Gd(3+)-based MRI zinc sensor are reported. Unlike previously reported Gd(3+)-based MRI contrast agents, this agent (GdL) differs in that the agent alone binds only weakly with human serum albumin (HSA), while the 1:2 GdL:Zn(2+) ternary complex binds strongly to HSA resulting in a substantial, 3-fold increase in water proton relaxivity. The GdL complex is shown to have a relatively strong binding affinity for Zn(2+) (K(D) = 33.6 nM), similar to the affinity of the Zn(2+) ion with HSA alone. The agent detects as little as 30 microM Zn(2+) in the presence of HSA by MRI in vitro, a value slightly more than the total Zn(2+) concentration in blood (approximately 20 microM). This combination of binding affinity constants and the high relaxivity of the agent when bound to HSA suggests that this new agent may be useful for detection of free Zn(2+) ions in vivo without disrupting other important biological processes involving Zn(2+).

Cleavage of Palladium Metallacycles by Acids: A Probe for the Study of the Cyclometalation Reaction

Useful mechanistic information about the cyclometalation reaction may be obtained by studying the reverse reaction, namely, the protonation of metallacycle 1 by acids of different coordinating anions (see scheme). Ar=3,5-(F3C)2C6H3; Tf=F3CSO2.

Reactivity of an anionic Pd(II) metallacycle with CH2X2(X = Cl, Br, I): formal insertion of methylene into a Pd–Caryl bond

Whereas the reaction of the anionic palladium metallacycle [K[Pd(CH2CMe2-o-C6H4)(kappa2-Tp)]] with CH2Cl2 leads to the isolation of the stable Pd(IV) chloromethyl complex [Pd(CH2CMe2-o-C6H4)(kappa3-Tp)(CH2Cl)], the analogous reactions with CH2Br2 and CH2I2 give rise to the six membered metallacycles [Pd(CH2CMe2-o-C6H4(CH2))(kappa3-Tp)X](X = Br or I), as a result of the formal insertion of CH2 into the Pd-C(aryl) bond.

A second generation MRI contrast agent for imaging zinc ions in vivo

A Zn2+ specific GdDOTA derivative containing two bis-(3-pyrazolyl) units was prepared and characterized. Unlike a previously reported Zn2+ binding agent, the new agent binds to human albumin both in the presence and absence of Zn2+.

Synthesis and reactivity studies on alkyl–aryloxo complexes of nickel containing chelating diphosphines: cyclometallation and carbonylation reactions

Nickel alkyl–aryloxo complexes of composition Ni(R)(OC6H32,6-Me2)(PP) (R= CH2SiMe3 ,C H 3 ,C H 2CMe2Ph; PPPPr2 (CH2)nPPr2 , n=2 (dippe) or 3 (dippp)) have been synthesized. While the (trimethylsilyl)methyl and the methyl derivatives are stable in solution at room temperature, the bis-neophyl (R = CH2CMe2Ph) complexes undergo a cyclometallation reaction that leads to the metallacycles Ni(CH2CMe2-o-C6 H4)(PP) together with 2,6-dimethylphenol. The alkyl–aryloxo complexes cleanly react with carbon monoxide giving products resulting from CO insertion and reductive elimination, i.e. Ni(CO)2(PP) and the corresponding 2,6-dimethylphenyl carboxylates quantitatively.

New seven membered palladacycles: C–Br bond activation of 2-bromo-pyridine derivative by Pd(II)

C-Br bond activation followed by a C-C coupling reaction of the 2-bromo-pyridyl unit of [1-phenyl-2-(6-bromopyridin-2-yl)-benzoimidazole] was performed by Pd(CH(2)CMe(2)-o-C(6)H(4))(η(4)-COD). Two new seven membered palladacycles were obtained. A combined experimental and theoretical DFT study elucidates the mechanism for this reaction.