RESUMEN
Starting from the dinickel(II) dihydride complex [ML(Ni-H)2] (1M), where L3- is a bis(tridentate) pyrazolate-bridged bis(ß-diketiminato) ligand and M+ is Na+ or K+, a series of complexes [KLNi2(S2)] (2K), [MLNi2S] (3M), [LNi2(SMe)] (4), and [LNi2(SH)] (5) has been prepared. The µ-sulfido complexes 3M can be reversibly oxidized at E1/2 = -1.17 V (in THF; vs Fc+/Fc) to give [LNi2(Sâ¢)] (6) featuring a bridging S-radical. 6 has been comprehensively characterized, including by X-ray diffraction, SQUID magnetometry, EPR and XAS/XES spectroscopies, and DFT calculations. The pKa of the µ-hydrosulfido complex 5 in THF is 30.8 ± 0.4, which defines a S-H bond dissociation free energy (BDFE) of 75.1 ± 1.0 kcal mol-1. 6 reacts with H atom donors such as TEMPO-H and xanthene to give 5, while 5 reacts with 2,4,6-tri(tert-butyl)phenoxy radical in a reverse H atom transfer to generate 6. These findings provide the first full characterization of a genuine M-(µ-Sâ¢-)-M complex and provide insights into its proton-coupled electron transfer (PCET) reactivity, which is of interest in view of the prominence of M-(µ-SH/µ-S)-M units in biological systems and heterogeneous catalysis.
RESUMEN
Polyoxometalates (POMs) and peptides can be conjugated to yield novel bio-hybrids with potential application as nanodrugs. However, the observed POM-induced folding of the peptide prevents its availability towards biological targets. An Anderson-Evans POM was functionalized with a bombesin analog peptide and engineered by adding a tailored hydrophilic and anionic spacer between the two moieties, to make the targeting sequence more accessible and enable an unprecedented cancer cell recognition capability.