Superoxide dismutase-like activity of cobalt(ii) complexes based on a sugar platform

Preparation of Keratin-Glycine Metal Complexes and Their Scavenging Activity for Superoxide Anion Radicals

To address the problem of limited application of natural SOD, the development of SOD mimic enzymes is of great importance for bioantioxidation. Herein, we report on a new type of biopolymer antioxidant with excellent scavenging activity for O2•-, keratin-glycine metal complexes (FK-GlyM, M = Zn, Cu, Mn, Ni). They are prepared by feather keratin firstly combined with glycine and then metal ions. Using FT-IR, TG, CD, and SEM, the performance of the obtained complexes (FK-GlyM) for scavenging O2•- is analysed and investigated. Importantly, the scavenging activity of FK-GlyCu is excellent in all FK-GlyM, and FK-GlyCu60 has the most excellent anti-O2•- activity in all FK-GlyCux, of which EC50 and degree of simulation were, respectively, up to 4.5×10-3±0.0012 μmol/L and 911.1% compared with nature Cu, Zn-SOD. Finally, its mechanism was also discussed. In summary, this method about the simulation strategies will provide a novel idea for exploiting new-type biocompatible and highly reactive antioxidants.

Mononuclear nonheme iron(iii) complexes that show superoxide dismutase-like activity and antioxidant effects against menadione-mediated oxidative stress

Iron(iii) complexes with pentadentate monocarboxylamido ligands display excellent SOD-like antioxidant activity to reduce superoxide radicals in cultured cells.

Substitution pattern reverses the fluorescence response of coumarin glycoligands upon coordination with silver (I)

Development of sugar-based fluorescence (FL) chemo-probes is of much interest since sugars are biocompatible, water-soluble and structurally rigid natural starting materials. We report here that fluorescent glycoligands with two triazolyl coumarin moieties installed onto the different positions of an identical glucosyl nucleus exert completely reversed optical response to a metal ion. C3,4-, C2,3- and C4,6-di-substituted coumarin glucosides synthesized by a click reaction similarly showed a selective FL variation in the presence of silver (I) among a range of metal cations in an aqueous solution. However, the variation was determined to be converse: the FL of the C3,4-ligand was quenched whereas that of the C2,3/C4,6-ligand tangibly enhanced. FL and NMR titrations suggested that this divergence was due to the distinct complexation modes of the conformationally constrained ligands with the ion. The optimal motifs of the ligand-ion complexation were predicted by a computational simulation. Finally, the C2,3-ligand was determined to be of low cytotoxicity and applicable in the FL imaging of silver ions internalized by live cells.

Sugars to control ligand shape in metal complexes: conformationally constrained glycoligands with a predetermination of stereochemistry and a structural control

In coordination chemistry, ligand shape can be used to tune properties, such as metal selectivity, coordination number, electronic structure, redox potential, and metal center stereochemistry including coordination helicates formation, and also to generate cavities for encapsulation. The results presented in this article indicate that two epimeric glycoligands (3 and 4) based on the conformationally restrained xylo- and ribo-1,2-O-isopropylidenefurano scaffolds are preorganized in water through pi-pi stacking due to hydrophobic interactions, as evidenced from excimer observation. The structure obtained in the solid state for one of the Cu(II) complexes (5) is chiral, with an original helical chirality arising from the coiling of the two ligands around the Cu-Cu axis. It shows an unusual double-deck type structure, with pi-pi interaction between two triazoyl-pyridyl rings and with a small cavity between the two Cu(II) ions able to host a bridging water molecule, as suggested by electron paramagnetic resonance. The Cu(II) complex from the epimeric ligand (6) shows similar properties with a mirror-image CD spectrum in the d-d region of the Cu(II). There is a predetermination of chirality at the metal center by the glycoligand induced by the C3 configuration, 6 and 5 being pseudoenantiomers. Interestingly, the stereochemistry at the metal center is here controlled by the combination of pi-stacking and chiral backbone.

Glycoligands Tuning the Magnetic Anisotropy of NiII Complexes

Two organic ligands based on a sugar-scaffold derived from galactose and possessing three O-CH(2)-pyridine pendant arms at the 3-, 4-, and 5-positions of the galactopyranose that act as chelates afford mononuclear complexes when reacted with a Ni(II) salt. The magnetization behavior in the form of M=f(H/T) plots suggests the presence of appreciable magnetic anisotropy within the two complexes. The analysis of the EPR spectra performed at two different temperatures (7 and 17 K) and at three frequencies (190, 285, and 380 GHz) leads to the conclusion that the anisotropy has a high degree of axiality (E/D=0.17 for the two complexes), but with a different sign of the D parameter. The spin hamiltonian parameters D and E were reproduced for the two complexes by using calculations based on the angular overlap model (AOM). The structural difference between the two complexes responsible of the sign of the D parameters was also determined using AOM calculations. A thorough analysis of the structures showed that the structural differences in the coordination sphere of the two complexes responsible of the different D parameter sign result from the nature of the sugar scaffolds. In complex 1, the sugar scaffold imposes an intramolecular hydrogen bond with one of the atoms linked to Ni(II); this arrangement leads to a distorted coordination sphere and positive D value, while the absence of such a hydrogen bond in complex 2 leads to a less distorted environment around the Ni center and to a negative D value.

Glycoligands and Co(ii) glycocomplexes. Investigation of the variation of the sugar-scaffold on the structure and chirality measured by circular dichroism

Glycoligands using various monosaccharide platforms functionalised by three 2-picolyl groups and coordinated to Co(II) through the bidentate 2-picolyl ether moieties are interesting ligands as they efficiently induce chirality at the cobalt with a fine control of the structure through the central sugar scaffold.