This paper describes colloidal particles that are designed to induce hyper-intensity contrast (T1 relaxation) in MRI. The contrast agents consist of discrete gadolinium complexes tethered to 10 nm diameter silver nanoparticles. The gadolinium complexes (1) [Gd(DTPA-bisamido cysteine)]2− and (2) [Gd(cystine–NTA)2]3−, undergo chemisorption to particle surfaces through thiol or disulfide groups, respectively, to form two new contrast agents. The resulting nanoparticulate constructs are characterized on the basis of their syntheses, composition, spectra and contrast enhancing power. The average r1 relaxivities of the of the surface bound complexes (obtained at 9.4 T and 25 °C) are 10.7 and 9.7 s−1 mM−1, respectively, as compared to 4.7 s−1 mM−1 for the clinical agent MagnevistTM. Correspondingly, the respective whole particle relaxivities are 27927 and 13153 s−1 mM−1.Uptake of gadolinium by nitrilotriacetate tethered to the surface of a silver nanoparticle. The gadolinium containing colloid induces the relaxation of proton spins in aqueous solution.

The complexes (cnt)2[Fe(nta)Cl2], where nta = nitrilotriacetate and cnt = Et4N+ or PyH+, catalyze the air oxidation of thiols to disulfides under ambient conditions. Dithiols are converted to linear and cyclic oligomers that differ in their terminal groups as a function of the counterion, cnt. Cysteine ethyl ester was converted to the corresponding cystine diethylester in high yield.The iron(III) dichloronitrilotriacetate ion, [Fe(nta)Cl2]2−, catalyzes the air oxidation of thiols and α,ω-dithiols to disulfides and oligomeric disulfides, respectively. Oligomeric products from the oxidation of propane-, butane- and pentanedithiol have been characterized by field desorption mass spectrometry and shown to form monomeric to decameric oligomers. The identity of the oligomer terminal groups is partially dependent on the nature of the catalyst counterion. The [Fe(nta)Cl2]2− ion has been characterized by electrospray mass spectrometry.

Xanthates, like thiolates, form a variety of complexes with metals in which coordinating sulfur can serve as a hydrogen bond acceptor. Nickel tris xanthate complexes [Ni(xan)3]−, (xan = o-ethylxanthate, N-(carbamoylmethyl)ethylxanthate) have been synthesized and compared by a combination of X-ray crystallographic and spectroscopic measurements. Recent results from our studies of N–H⋯S hydrogen bonding interactions in metal–xanthate complexes shows N–S distances to be longer than those in related thiolate complexes, indicative of weaker hydrogen bonds for the xanthates. The complex (Et4N)[N-(carbamoylmethyl)ethylxanthate)] adopts an extended conformation in both the solid state and solution and lacks either intraligand or intermolecular N–H⋯S hydrogen bonds. The complex (CTA)[Ni(exa)3] exhibits N–H⋯S hydrogen bonds between the amide group of the counterion and the ligand sulfur. The amide–sulfur N–H⋯S distance is 3.567 Å.Single crystal X-ray diffraction data on the complex (CTA)[Ni(exa)3] reveals the tris O-ethylxanthate complex to act as a hydrogen bond acceptor through sulfur and oxygen. An N–H donor group resides on the counterion CTA (carbamoylmethyltrimethylammonium). The complex provides an excellent system for the study of N–H⋯S hydrogen bonds as a function of sulfur charge. A xanthate bearing a secondary amide was similarly characterized by single crystal X-ray diffraction. It shows no evidence of N–H⋯S hydrogen bonding.

The complexes [(CH3)3NCH2CONH2]2[M(S2-o-xyl)2], M=Fe (1), Co (2), and [(CH3)4N]2[Co(S2-o-xyl)2]·1/2C2H5OH (3) have been characterized by X-ray crystallography and vibrational spectroscopy. Complexes 1 and 2 exhibit linear one-dimensional concatenated hydrogen bonded structures. In complex 2 there is an increase in the average metal–ligand bond length in the hydrogen-bonded form relative to 3, which contains a non-hydrogen bonded congener.