Dataset Information

Influence of Hydrogen-Bonding Interactions on Nuclearity and Structure of Palladium Tiara-like Complexes.

ABSTRACT: The role of intramolecular hydrogen-bonding interactions upon the nuclearity of palladium tiara-like complexes is reported herein. The synthesis of three palladium tiaras is described with three related thiolate ligands that vary in their hydrogen-bonding capability, amide vs ester for N-acetylcysteamine (tiara 1) vs 2-mercaptoethyl acetate (tiara 2) or ethyl thioglycolate (tiara 3), and in the relative position of the ester group, 2-mercaptoethyl acetate (2) or ethyl thioglycolate (3). Mass spectrometry indicates that, in the absence of protic solvents, N-acetylcysteamine reacts to form exclusively a six-membered tiara, [Pd(SCH₂CH₂NHCOCH₃)₂]₆, 1, whereas the ester containing analogues form both six- and eight-membered tiaras. Single-crystal X-ray diffraction studies indicate the significance of intramolecular N-H···O hydrogen bonds in determining the nuclearity of the amide-containing tiara 1. NMR studies indicate that 1 is not in equilibrium with larger tiaras in solution, and that the smaller size of the aggregate inhibits the fluxional behavior of the pendant thiolate ligands, typically observed for larger tiaras. Electrochemical investigations of 1 reveal reductive processes that exhibit an increase in current upon addition of acid, along with the formation of palladium nanoparticles.

SUBMITTER: Martin HJ

PROVIDER: S-EPMC6644359 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Influence of Hydrogen-Bonding Interactions on Nuclearity and Structure of Palladium Tiara-like Complexes.

Martin Harry J HJ Pfeiffer Constance R CR Stephen Davies E E Davis Adrienne L AL Lewis William W Champness Neil R NR

ACS omega 20180808 8

The role of intramolecular hydrogen-bonding interactions upon the nuclearity of palladium tiara-like complexes is reported herein. The synthesis of three palladium tiaras is described with three related thiolate ligands that vary in their hydrogen-bonding capability, amide vs ester for N-acetylcysteamine (tiara 1) vs 2-mercaptoethyl acetate (tiara 2) or ethyl thioglycolate (tiara 3), and in the relative position of the ester group, 2-mercaptoethyl acetate (2) o ...[more]

PMID: 31459009

Similar Datasets

Project description:Synthetic peroxo-bridged high-spin (HS) heme-(μ-η2:η1-O22-)-Cu(L) complexes incorporating (as part of the copper ligand) intramolecular hydrogen-bond (H-bond) capabilities and/or steric effects are herein demonstrated to affect the complex's electronic and geometric structure, notably impacting the spin state. An H-bonding interaction with the peroxo core favors a low-spin (LS) heme-(μ-η1:η1-O22-)-Cu(L) structure, resulting in a reversible temperature-dependent interconversion of spin state (5 coordinate HS to 6 coordinate LS). The LS state dominates at low temperatures, even in the absence of a strong trans-axial heme ligand. Lewis base addition inhibits the H-bond facilitated spin interconversion by competition for the H-bond donor, illustrating the precise H-bonding interaction required to induce spin-crossover (SCO). Resonance Raman spectroscopy (rR) shows that the H-bonding pendant interacts with the bridging peroxide ligand to stabilize the LS but not the HS state. The H-bond (to the Cu-bound O atom) acts to weaken the O-O bond and strengthen the Fe-O bond, exhibiting ν(M-O) and ν(O-O) values comparable to analogous known LS complexes with a strong donating trans-axial ligand, 1,5-dicyclohexylimidazole, (DCHIm)heme-(μ-η1:η1-O22-)-Cu(L). Variable-temperature (-90 to -130 °C) UV-vis and 2H NMR spectroscopies confirm the SCO process and implicate the involvement of solvent binding. Examining a case of solvent binding without SCO, thermodynamic parameters were obtained from a van't Hoff analysis, accounting for its contribution in SCO. Taken together, these data provide evidence for the H-bond group facilitating a core geometry change and allowing solvent to bind, stabilizing a LS state. The rR data, complemented by DFT analysis, reveal a stronger H-bonding interaction with the peroxo core in the LS compared to the HS complexes, which enthalpically favors the LS state. These insights enhance our fundamental understanding of secondary coordination sphere influences in metalloenzymes.

Project description:Dioxygen reduction by heme-copper oxidases is a critical biochemical process, wherein hydrogen bonding is hypothesized to participate in the critical step involving the active-site reductive cleavage of the O-O bond. Sixteen novel synthetic heme-(μ-O2 2-)-Cu(XTMPA) complexes, whose design is inspired by the cytochrome c oxidase active site structure, were generated in an attempt to form the first intramolecular H-bonded complexes. Derivatives of the "parent" ligand (XTMPA, TMPA = (tris((2-pyridyl)methyl)amine)) possessing one or two amine pendants preferentially form an H-bond with the copper-bound O-atom of the peroxide bridge. This is evidenced by a characteristic blue shift in the ligand-to-metal charge transfer (LMCT) bands observed in UV-vis spectroscopy (consistent with lowering of the peroxo π* relative to the iron orbitals) and a weakening of the O-O bond determined by resonance Raman spectroscopy (rR), with support from Density Functional Theory (DFT) calculations. Remarkably, with the TMPA-based infrastructure (versus similar heme-peroxo-copper complexes with different copper ligands), the typically undetected Cu-O stretch for these complexes was observed via rR, affording critical insights into the nature of the O-O peroxo core for the complexes studied. While amido functionalities have been shown to have greater H-bonding capabilities than their amino counterparts, in these heme-peroxo-copper complexes amido substituents distort the local geometry such that H-bonding with the peroxo core only imparts a weak electronic effect; optimal H-bonding interactions are observed by employing two amino groups on the copper ligand. The amino-substituted systems presented in this work reveal a key orientational anisotropy in H-bonding to the peroxo core for activating the O-O bond, offering critical insights into effective O-O cleavage chemistry. These findings indirectly support computational and protein structural studies suggesting the presence of an interstitial H-bonding water molecule in the CcO active site, which is critical for the desired reactivity. The results are evaluated with appropriate controls and discussed with respect to potential O2-reduction capabilities.

Dataset Information

Influence of Hydrogen-Bonding Interactions on Nuclearity and Structure of Palladium Tiara-like Complexes.

Publications

Influence of Hydrogen-Bonding Interactions on Nuclearity and Structure of Palladium Tiara-like Complexes.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets