skip to main content

Search for: All records

Award ID contains: 1809116

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. null (Ed.)
    A dimeric yttrium phenoxide complex supported by a ferrocene Schiff base ligand, [(salfen)Y(OPh)] 2 (salfen = ( N,N ′-bis(2,4-di- tert -butylphenoxy)-1,1′-ferrocenediimine), was synthesized and characterized. According to electrochemical studies and 1 H NMR spectroscopy, [(salfen)Y(OPh)] 2 can be oxidized in a stepwise fashion to access three oxidation states. The catalytic activity of the three states toward the ring opening polymerization of cyclic esters and epoxides was investigated. The activity toward cyclic esters decreases upon oxidation while the opposite trend was observed in epoxide polymerization. Block copolymer syntheses using a redox switch were also performed.
  2. Three new organotin( iv ) carboxylate compounds were synthesized and structurally characterized by elemental analysis and FT-IR and multinuclear NMR ( 1 H, 13 C, 119 Sn) spectroscopy. Single X-ray crystallography reveals that compound C2 has a monoclinic crystal system with space group P 2 1 / c having distorted bipyramidal geometry defined by C 3 SnO 2 . The synthesized compounds were screened for drug-DNA interactions via UV-Vis spectroscopy and cyclic voltammetry showing good activity with high binding constants. Theoretical investigations also support the reactivity of the compounds as depicted from natural bond orbital (NBO) analysis using Gaussian 09. Synthesized compounds were initially evaluated on two cancer (HeLa and MCF-7) cell lines and cytotoxicity to normal cells was evaluated using a non-cancerous (BHK-21) cell line. All the compounds were found to be active, with IC 50 values less than that of the standard drug i.e. cisplatin. The cytotoxic effect of the most potent compound C2 was confirmed by LDH cytotoxicity assay and fluorescence imaging after PI staining. Apoptotic features in compound C2 treated cancer cells were visualized after DAPI staining while regulation of apoptosis was observed by reactive oxygen species generation, binding of C2 with DNA, a change inmore »mitochondrial membrane potential and expression of activated caspase-9 and caspase-3 in cancer cells. Results are indicative of activation of the intrinsic pathway of apoptosis in C2 treated cancer cells.« less
  3. Inverse-sandwich samarium and ytterbium biphenyl complexes were synthesized by the reduction of their trivalent halide precursors with potassium graphite in the presence of biphenyl. While the samarium complex had a similar structure as previously reported rare earth metal biphenyl complexes, with the two samarium ions bound to the same phenyl ring, the ytterbium counterpart adopted a different structure, with the two ytterbium ions bound to different phenyl rings. Upon the addition of crown ether to encapsulate the potassium ions, the inverse-sandwich samarium biphenyl structure remained intact; however, the ytterbium biphenyl structure fell apart with the concomitant formation of a divalent ytterbium crown ether complex and potassium biphenylide. Spectroscopic and computational studies were performed to gain insight into the electronic structures and bonding interactions of these samarium and ytterbium biphenyl complexes. While the ytterbium ions were found to be divalent with a 4f 14 electron configuration and form a primarily ionic bonding interaction with biphenyl dianion, the samarium ions were in the trivalent state with a 4f 5 electron configuration and mainly utilized the 5d orbitals to form a δ-type bonding interaction with the π* orbitals of the biphenyl tetraanion, showing covalent character.
  4. Redox-switchable polymerization has drawn increasing attention, in particular for the ring-opening polymerization (ROP) of biomass-derived monomers. However, an understanding of how the switch determines the observed changes is still limited. In this study, DFT calculations were employed to understand the redox-switchable ROP mechanism of ε-caprolactone catalyzed by group 4 metal complexes bearing [OSSO]-type ferrocene ligands. Our results suggest that two oxidized forms show higher reactivity because of the higher Lewis acidity of their catalytic metal centers in comparison with that of the corresponding reduced states. In one case, however, a lower activity of the oxidized species was observed that is likely due to the increased stability of the substrate-catalyst intermediate leading to a high activation barrier. In addition, other analogous metal complexes were computationally modelled by changing the metal center or modifying the ancillary ligand with different bridging-heteroatoms, and the results provide useful information on the development of new redox-switchable polymerization catalysts.
  5. DFT calculations were used to capture the properties of redox-switchable metal complexes relevant to the ring-opening polymerisation of cyclic esters by varying the metals, donors, linkers, and substituents in both accessible ferrocene oxidation states. A map of this chemical space highlights that modifying the ligand architecture and the metal has a larger impact on structural changes than changing the oxidation state of the ferrocene backbone.