1082-19-5Relevant articles and documents
Monitoring helical twists and effective molarities in dinuclear triple-stranded lanthanide helicates
Ryan, Patrick E.,Guenee, Laure,Piguet, Claude
, p. 11047 - 11055 (2013)
The replacement of terminal benzimidazole-pyridine binding units in the neutral di-tridentate segmental ligand L1 with phenanthroline in L10 reduces the number of torsional degrees of freedom by two units. Reactions of these ligands with trivalent europium or lutetium cations yield structurally similar self-assembled dinuclear triple-stranded [Ln2(Lk)3] 6+ complexes, thus demonstrating that the increased rigidity of the strand in L10 is compatible with its helical twist. With the larger lanthanum cations, the metallic coordination spheres are completed with two terminal axial triflate counter-anions to give [La2(L10)3(CF 3SO3)2]4+. Thermodynamic investigations in acetonitrile confirm the minor constraints produced by the planar phenanthroline unit in L10 leading to comparable effective molarities EMEu,L1 ≈ EMEu,L10 = 10 -3.9(4) M with mid-range EuIII cations. The striking minute effective molarities EMLn,Ln-2H ≈ 10-6-10-9 M obtained upon the replacement of terminal phenanthrolines with structurally analogous fused hydroxyquinolines in L9 can be thus unambiguously assigned to solvation effects, a new tool for controlling complexity in metal-induced self-assembly processes.
A single iron porphyrin shows ph dependent switch between "push" and "pull" effects in electrochemical oxygen reduction
Bhunia, Sarmistha,Dey, Abhishek,Dey, Somdatta Ghosh,Mukherjee, Sudipta,Nayek, Abhijit
, p. 14564 - 14576 (2020)
The "push-pull"effects associated with heme enzymes manifest themselves through highly evolved distal amino acid environments and axial ligands to the heme. These conserved residues enhance their reactivities by orders of magnitude relative to small molecules that mimic the primary coordination. An instance of a mononuclear iron porphyrin with covalently attached pendent phenanthroline groups is reported which exhibit reactivity indicating a pH dependent "push"to "pull"transition in the same molecule. The pendant phenanthroline residues provide proton transfer pathways into the iron site, ensuring selective 4e-/4H+ reduction of O2 to water. The protonation of these residues at lower pH mimics the pull effect of peroxidases, and a coordination of an axial hydroxide ligand at high pH emulates the push effect of P450 monooxygenases. Both effects enhance the rate of O2 reduction by orders of magnitude over its value at neutral pH while maintaining exclusive selectivity for 4e-/4H+ oxygen reduction reaction.
Hybrid bis-histidine phenanthroline-based ligands to lessen aβ-bound cu ros production: An illustration of cu(i) significance
Drommi, Marielle,Esmieu, Charlène,Hureau, Christelle,Rulmont, Clément
, (2021/12/24)
We here report the synthesis of three new hybrid ligands built around the phenanthroline scaffold and encompassing two histidine-like moieties: phenHH, phenHGH and H’phenH’, where H correspond to histidine and H’ to histamine. These ligands were designed to capture Cu(I/II) from the amyloid-β peptide and to prevent the formation of reactive oxygen species produced by amyloid-β bound copper in presence of physiological reductant (e.g., ascorbate) and dioxygen. The amyloid-β peptide is a well-known key player in Alzheimer’s disease, a debilitating and devasting neurological disorder the mankind has to fight against. The Cu-Aβ complex does participate in the oxidative stress observed in the disease, due to the redox ability of the Cu(I/II) ions. The complete characterization of the copper complexes made with phenHH, phenHGH and H’phenH’ is reported, along with the ability of ligands to remove Cu from Aβ, and to prevent the formation of reactive oxygen species catalyzed by Cu and Cu-Aβ, including in presence of zinc, the second metal ions important in the etiology of Alzheimer’s disease. The importance of the reduced state of copper, Cu(I), in the prevention and arrest of ROS is mechanistically described with the help of cyclic voltammetry experiments.
Tridentate Directing Groups Stabilize 6-Membered Palladacycles in Catalytic Alkene Hydrofunctionalization
O'Duill, Miriam L.,Matsuura, Rei,Wang, Yanyan,Turnbull, Joshua L.,Gurak, John A.,Gao, De-Wei,Lu, Gang,Liu, Peng,Engle, Keary M.
, p. 15576 - 15579 (2017/11/14)
Removable tridentate directing groups inspired by pincer ligands have been designed to stabilize otherwise kinetically and thermodynamically disfavored 6-membered alkyl palladacycle intermediates. This family of directing groups enables regioselective remote hydrocarbofunctionalization of several synthetically useful alkene-containing substrate classes, including 4-pentenoic acids, allylic alcohols, homoallyl amines, and bis-homoallylamines, under Pd(II) catalysis. In conjunction with previous findings, we demonstrate regiodivergent hydrofunctionalization of 3-butenoic acid derivatives to afford either Markovnikov or anti-Markovnikov addition products depending on directing group choice. Preliminary mechanistic and computational data are presented to support the proposed catalytic cycle.
