Platinum(II)-glutamic acid dendrimer conjugates: Synthesis, characterization, DFT calculation, conformational analysis and catalytic properties

Abstract

Abstract A series of platinum(II)- l -glutamic acid dendrimer conjugates having the formula PtCl2(5,5′-Gn(OR)-2,2′-bipyridine); Gn (n = 0, 1, 2), have been synthesized by various amide bond formation methods. The dendrimer complexes were terminated as carboxylic acid (R = H) or methyloxy ester (R = Me). The complexes were characterized by mass spectrometry, elemental analysis, UV-vis, FTIR, 1H-, 13C NMR, 1H-TOCSY, HSQC. The G1(OH) complex aggregate in solution and solid state, giving rise to a rigid conformation for the glutmaic acid side chain. The G2(OH) exists in the “monomeric” form with several conformations for the glutamic acid side chains. Complexes terminated with carboxyl group (R = H) were active catalyst toward hydrogen gas (H2) production by photo-induced splitting of water. The turnover frequency (TOF) for the G1(OH) complex is 14.7 × 1015 s−1, and it exhibits a ∼ 2-fold enhancement in H2 production compared to the unmodified parent complex G0(OH) (TOF = 7×1015 s−1). While G2(OH) complex displayed a lower hydrogen activity (TOF = 3.8 × 1015 s−1) compared to G0(OH). The platinum-glutamic acid dendrimer conjugates showed a correlation between H2 evolution activity and their ability to form aggregates, which driven by the steric hindrance of the peptide residues in the vicinity of Pt-center.