Thermodynamic surprises of Cu(II)–amylin analogue complexes in membrane mimicking solutions

Membrane environment often has an important effect on the structure, and therefore also on the coordination mode of biologically relevant metal ions. This is also true in the case of Cu(II) coordination to amylin analogues—rat amylin, amylin1–19, pramlintide and Ac-pramlintide, which offer N-terminal amine groups and/or histidine imidazoles as copper(II) anchoring sites. Complex stabilities are comparable, with the exception of the very stable Cu(II)–amylin1–19, which proves that the presence of the amylin C-terminus lowers its affinity for copper(II); although not directly involved, its appropriate arrangement sterically prevents early metal binding. Most interestingly, in membrane-mimicking solution, the Cu(II) affinities of amylin analogues are lower than the ones in water, probably due to the crowding effect of the membrane solution and the fact that amide coordination occurs at higher pH, which happens most likely because the α-helical structure, imposed by the membrane-mimicking solvent, prevents the amides from binding at lower pH, requiring a local unwinding of the α-helix.

Bridging coordination of acenaphthylene to a Pd3 chain or a Pd4 sheet cluster

The μ3–η2:η2:η2-π-coordination mode or μ4–η5:η2:η3:η2-oxidative π-addition mode of acenaphthylene to a Pd3 chain or a Pd4 sheet cluster was revealed.

Bis(η5-cyclopentadienyl)(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κ3 O,N,O′)terbium

The air- and moisture-sensitive title compound, [Tb(C5H5)2(C14H12NO2)], was synthesized from tris(cyclopentadienyl)(tetrahydrofuran)terbium and 2-{[(2-methoxyphenyl)imino]methyl}phenol. Each Tb atom is coordinated by two cyclopentadienyl ligands in an η5-coordination mode and by one N and two O atoms of the organic ligand in a tridentate κ3 O,N,O′-mode.

Thermodynamic Surprises of Cu(II)-Amylin Complexes in Membrane Mimicking Solutions

Membrane environment often has an important effect on the structure, and therefore also on the coordination mode of biologically relevant metal ions.This is also true in the case of Cu(II) coordination to amylin analogues – rat amylin, amylin1-19, pramlintide and Ac-pramlintide, which offer N-terminal amine groups and/or histidine imidazoles as copper(II) anchoring sites. Complex stabilities are comparable, with the exception of the very stable Cu(II)-amylin1-19, which proves that the presence of the amylin C-terminus lowers its affinity for copper(II); although not directly involved, its appropriate arrangement sterically prevents early metal binding.Most interestingly, in membrane-mimicking solution, the Cu(II) affinities of amylin analogues are lower than the ones in water, probably due to the crowding effect of the membrane solution and the fact that amide coordination occurs at higher pH, which happens most likely because the α-helical structure, imposed by the membrane-mimicking solvent, prevents the amides from binding at lower pH, requiring a local unwinding of the α-helix.

Novel Coordination Mode in the Potassium Mefenamate Trihydrate Polymeric Structure

As a result of the synthesis of mefenamic acid with potassium hydroxide, a salt with a polymeric structure is formed. The one-dimensional polymeric structure was studied by single crystal X-ray diffraction. The potassium cation is coordinated to one oxygen atom of the carboxylate group and six water oxygen atoms. Potassium ions are bridged by oxygen atoms of water molecules. The crystal structure was used as an input to QTAIM and NCI approaches to investigate the K-O interactions linking the cation with the water oxygen and carboxylate groups. The weak K-O interactions of the potassium cation and water oxygen atoms were strong enough to form a polymeric structure. The flexibility of the weak interactions is responsible for a novel coordination mode in the potassium mefenamate trihydrate.

Synthesis, Characterization, and Reaction Studies of Pd(II) Tripeptide Complexes

The aqueous synthesis of Pd(II) complexes with alkylated tripeptides led to the hydrolysis of the peptides at low pH values and mixtures of complexed peptides were formed. A non-aqueous synthetic route allowed the formation and isolation of single products and their characterization. Pd(II) complexes with α-Asp(OR)AlaGly(OR), β-Asp(OR)AlaGly(OR), and TrpAlaGly(OR) (R = H or alkyl) as tri and tetradentate chelates were characterized. The tridentate coordination mode was accompanied by a fourth monodentate ligand that was shown to participate in both ligand exchange reactions and a direct removal to form the tetradentate coordination mode. The tetradentate coordination revealed a rare a hemi labile carbonyl goup coordination mode to Pd(II). Reactivity with small molecules such as ethylene, acids, formate, and episulfide was investigated. Under acidic conditions and in the presence of ethylene; acetaldehyde was formed. The Pd(II) is a soft Lewis acid and thiophilic and the complexes abstract sulfur from episulfide at apparent modest catalytic rates. The complexes adopt a square planar geometry according to a spectroscopic analysis and DFT calculations that were employed to evaluate the most energetically favorable coordination geometry and compared with the observed infrared and NMR data.