Since our discovery of the catalytic reduction of dinitrogen to ammonia at a single molybdenum center, we have embarked on a variety of studies designed to further understand this complex reaction cycle. These include studies of both individual reaction steps and of ligand variations. An important step in the reaction sequence is exchange of ammonia for dinitrogen in neutral molybdenum(III) compounds. We have found that this exchange reaction is first order in dinitrogen and relatively fast (complete in <1 h) at 1 atm of dinitrogen. Variations of the terphenyl substituents in the triamidoamine ligand demonstrate that the original ligand is not unique in its ability to yield successful catalysts. However, complexes that contain sterically less demanding ligands fail to catalyze formation of ammonia from dinitrogen; it is proposed as a consequence of a base-catalyzed decomposition of a diazenido (Mo-NANH) intermediate.

We have developed a silver-releasing biomaterial with promising potential for wound healing applications. The material is made of ultrashort peptides which can self-assemble in water to form hydrogels. Silver nanoparticles (Ag NPs) were synthesized in situ within the biomaterial, using only UV irradiation and no additional chemical reducing agents. The synthetic strategy allows precise control of the nanoparticle size, with the network of peptide fibers preventing aggregation of Ag NPs. The biomaterial shows increased mechanical strength compared to the hydrogel control. We observed a sustained release of Ag NPs over a period of 14 days. This is a crucial prerequisite for effective anti-bacterial therapy. The ability to inhibit bacterial growth was tested using different bacterial strains, namely gram-negative Escherichia coli and Pseudomonas aeruginosa and gram-positive Staphylococcus aureus. Inhibition of bacterial growth was observed for all strains. The best results were obtained for Pseudomonas aeruginosa which is known for exhibiting multidrug resistance. Biocompatibility studies on HDFa cells, using Ag NP-containing hydrogels, did not show any significant influence on cell viability. We propose this silver-releasing hydrogel as an excellent biomaterial with great potential for applications in wound healing due to its low silver content, sustained silver nanoparticle release and biocompatibility.

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The trigonally symmetric Mo(III) coordination compounds [HIPTN 3 N]MoL (L = N 2 , CO, NH 3 ; [HIPTN 3 N]Mo = [(3,5-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 3 NCH 2 CH 2 ) 3 N]Mo) are low-spin d 3 , S = 1/2) species that exhibit a doubly-degenerate 2 E ground state susceptible to a Jahn-Teller (JT) distortion. The EPR spectra of all three complexes and their temperature and solvent dependences are interpreted within a formal '2-orbital' model that reflects the ground-state configuration, describes the vibronic interactions that lead to the JT distortions, and addresses whether these complexes exhibit static or dynamic JT distortions. The electronic and vibronic properties of these complexes are then analyzed through ab initio quantum chemical computations. It is not possible to interpret the spectroscopic properties of the orbitally degenerate [Mo]L with DFT methods, so we have resorted to multireference wavefunction approaches, the entry level of which is the complete active space self-consistent field (CASSCF) method. Overall the experimental and computational studies provide new insights into the role of trigonal coordination, as enforced by the [HIPTN 3 N] 3− ligand, in activating the Mo ion for the binding and reduction of N 2 .