An overview of structural aspects and health beneficial effects of antioxidant oligosaccharides

Background: Non-digestible oligosaccharides are versatile sources of chemical diversity, well known for their prebiotic actions, found naturally in plants or produced by chemical or enzymatic synthesis or by hydrolysis of polysaccharides. Compared to polyphenols or even polysaccharides, the antioxidant potential of oligosaccharides is still unexplored. The aim of the present work was to provide an up-to-date, broad and critical contribution on the topic of antioxidant oligosaccharides. Methods: The search was performed by crossing the words oligosaccharides and antioxidant. Whenever possible, attempts at establishing correlations between chemical structure and antioxidant activity were undertaken. Results: The most representative in vitro and in vivo studies were compiled in two tables. Chitooligosaccharides and xylooligosaccharides and their derivatives were the most studied up to now. The antioxidant activities of oligosaccharides depend on the degree of polymerization and the method used for depolymerization. Other factors influencing the antioxidant strength are solubility, monosaccharide composition, the type of glycosidic linkages of the side chains, molecular weight, reducing sugar content, the presence of phenolic groups such as ferulic acid, and the presence of uronic acid, among others. Modification of the antioxidant capacity of oligosaccharides has been achieved by adding diverse organic groups to their structures, thus increasing also the spectrum of potentially useful molecules. Conclusion: A great amount of high-quality evidence has been accumulating during the last decade in support of a meaningful antioxidant activity of oligosaccharides and derivatives. Ingestion of antioxidant oligosaccharides can be visualized as beneficial to human and animal health.This work was funded by the Conselho Nacional de Desenvolvimento Cientffico e Tecnológico (CNPq), Brazil; grants numbers 40898/2016-5 and 307944/2015-8).info:eu-repo/semantics/publishedVersio

Di-μ-chlorido-bis­[chlorido(1,4,6-trimethyl-6-nitro-1,4-diazepine)copper(II)]

The title neutral copper complex, [Cu2Cl4(C8H17N3O2)2], shows a binuclear center with a Cu—(μ-Cl)2—Cu core, in which each copper ion is coordinated by the N,N,O donor atoms of the tridentate ligand 1,4,6-trimethyl-6-nitro-1,4-diazepine (meaaz-NO2) and three chloride exogenous ligands. Each metal ion is facially coordinated by meaaz-NO2 through N,N,O donor atoms, whereas two bridging and one terminal chloride ions occupy the other face of the highly Jahn–Teller-distorted octa­hedron. Two N atoms from tertiary amine groups of the meaaz-NO2 ligand and two exogenous Cl atoms with short Cu—N and Cu—Cl distances define the equatorial plane. The coordination around each CuII ion is completed by another Cl atom and an O atom from the NO2 group, in the axial positions. The binuclear complex exhibits a centrosymmetric structure with point symmetry

Probing the role of the divalent metal ion in uteroferrin using metal ion replacement and a comparison to isostructural biomimetics

Purple acid phosphatases (PAPs) are a group of heterovalent binuclear metalloenzymes that catalyze the hydrolysis of phosphomonoesters at acidic to neutral pH. While the metal ions are essential for catalysis, their precise roles are not fully understood. Here, the Fe(III)Ni(II) derivative of pig PAP (uteroferrin) was generated and its properties were compared with those of the native Fe(III)Fe(II) enzyme. The kcat of the Fe(III)Ni(II) derivative (approximately 60 s–1) is approximately 20% of that of native uteroferrin, and the Ni(II) uptake is considerably faster than the reconstitution of full enzymatic activity, suggesting a slow conformational change is required to attain optimal reactivity. An analysis of the pH dependence of the catalytic properties of Fe(III)Ni(II) uteroferrin indicates that the l-hydroxide is the likely nucleophile. Thus, the Ni(II) derivative employs a mechanism similar to that proposed for the Ga(III)Zn(II) derivative of uteroferrin, but different from that of the native enzyme, which uses a terminal Fe(III)-bound nucleophile to initiate catalysis. Binuclear Fe(III)Ni(II) biomimetics with coordination environments similar to the coordination environment of uteroferrin were generated to provide both experimental benchmarks (structural and spectroscopic) and further insight into the catalytic mechanism of hydrolysis. The data are consistent with a reaction mechanism employing an Fe(III)-bound terminal hydroxide as a nucleophile, similar to that proposed for native uteroferrin and various related isostructural biomimetics. Thus, only in the uteroferrin- catalyzed reaction are the precise details of the catalytic mechanism sensitive to the metal ion composition, illustrating the significance of the dynamic ligand environment in the protein active site for the optimization of the catalytic efficiency

Synthesis, characterization and photoinduced CO-release by manganese(i) complexes

Herein, we report the CO-release activity of three new photoCORMs, two with nonbonding pyridine moieties and one with a benzyl group. The compounds [MnBr(CO)3(bpa-κ2)] (2, where bpa = N-benzyl(2-pyridylmethyl)amine); [MnBr(CO)3(pmpeaκ2)] (3, where pmpea = N-(2-pyridylmethyl)-N’-(2-pyridylethyl)amine) and [MnBr(CO)3(bpea-κ2)] (4, where bpea = N-bis(2- pyridylethyl)amine) were synthesized and characterized by common spectroscopic techniques (UV-Vis, IR). Density functional theory studies were also performed to provide new insights into the M–C bond and to assume the orbitals involved in the absorption transitions. Their CO-release activities were measured both in organic and in physiological media and compared to that of a previously published compound [Mn(CO)3(dpa-κ3)]Br (1, where dpa = N-bis(2- pyridylmethyl)amine). An increase in the number of members of the chelate from five to six, influenced the release of CO, affecting both the binding mode of the ligand and the CO-release process and affecting their potential use as potentials CO release carriers as therapeutic agents

New mononuclear copper(II) complex based on a salen derivative ligand with an unusual coordination and its catecholase activity

The new mononuclear copper(II) complex [CuII(H2LDA)(ClO4)](ClO4) (1) ([H2LDA = N,N′-[bis-(2-hydroxy-3- formyl-5-methylbenzyl)(dimethyl)]-ethylenediamine])with an unusual coordination mode of a salen derivative ligand is reported. The most interesting feature of 1 is that the ligand is doubly protonated and presents significant intermolecular π-stacking interactions, contributing to the dimer structure stabilization in the solid state and in CH3CN and methanolic solutions. The complex was characterized by X-ray crystallography and shows catecholase-like activity in the oxidation of the substrate 3,5-di-tert-butylcatechol (3,5-dtbc), with the formation of H2O2, which kinetic parameters are similar to those observed in conventional dinuclear bridged CuII complexes.FAPESCCAPESINCT-Catális

A new heteropentanuclear complex containing the [Fe2 IIIZn3 II(μ-OH)3] structural motif as a model for purple acid phosphatases

Herein, we describe the synthesis and X-ray structure of a new heteropentanuclear complex (2) containing a [Fe2 IIIZn3 II(μ-OH)3] structural unit and the unsymmetrical ligand H2L2-et. The molecular structure of (2) shows that it is formed by a basic dinuclear [FeIII(μ-OH)ZnII(L2-et)] unit that is connected to a second dinuclear [FeIII(μ-OH)ZnII(L2-et)] unit through a hydroxo bridge while a third ZnII ion is coordinated by the pendant 1,2-ethanediamine groups of H2L2-et, resulting in the pentanuclear complex. Kinetic studies on the hydrolysis of the substrate 2,4-BDNPP (bis(2,4-dinitrophenyl)phosphate) reveal that (2) shows diesterase activity. While the kinetic activity is comparable to the corresponding dinuclear FeIIIZnII complex containing the same ligand, the association with 2,4-BDNPP is significantly decreased

Dinuclear copper(II) complexes with derivative triazine ligands as biomimetic models for catechol oxidases and nucleases

The research reported herein focuses on the synthesis of two new Cu(II) complexes {[Cu(2-X-4,6-bis(di-2-picolylamino)-1,3,5-triazine], with X = butane-1,4-diamine (2) or N-methylpyrenylbutane-1,4-diamine (3)}, the latter with a pyrene group as a possible DNA intercalating agent. The structure of complex (3) was determined by X-ray crystallography and shows the dinuclear {Cu(μ-OCH)Cu} unit in which the Cu···Cu distance of 3.040 Å is similar to that of 2.97 Å previously found for 1, which contains a {Cu(μ-OH)Cu} structural unit. Complexes (2) and (3) were also characterized in spectroscopic and electrochemical studies, and catecholase-like activity were performed for both complexes. The kinetic parameters obtained for the oxidation of the model substrate 3,5-di-tert-butylcatechol revealed that the insertion of the spacer butane-1,4-diamine and the pyrene group strongly contributes to increasing the catalytic efficiency of these systems. In fact, K becomes significantly higher, indicating that these groups influence the interaction between the complex and the substrate. These complexes also show DNA cleavage under mild conditions with moderate reaction times. The rate of cleavage (k) indicated that the presence of butane-1,4-diamine and pyrene increased the activity of both complexes. The reaction mechanism seems to have oxidative and hydrolytic features and the effect of DNA groove binding compounds and circular dichroism indicate that all complexes interact with plasmid DNA through the minor groove. High-resolution DNA cleavage assays provide information on the interaction mechanism and for complex (2) a specificity for the unpaired hairpin region containing thymine bases was observed, in contrast to (3)

Guanidine- and purine-functionalized ligands of FeIIIZnII complexes: effects on the hydrolysis of DNA

In this paper, the catalytic effects of aminoguanidine and aminopurine groups in the second sphere of a FeZn complex that mimics the active site of the metallohydrolase purple acid phosphatase (PAP) are investigated, with a particular view on DNA as substrate. The ligand 3-(((3-((bis(2-(pyridin-2-yl)ethyl)amino)methyl)-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino)meth-yl)-2 hydroxy-5-methylbenzaldehyde—(HLbpea) was synthesized and its complex [(OH)Fe(μ-OH)Zn(HO)(Lbpea)](ClO) was used as a base for comparison with similar complexes previously published in the literature. Subsequent modifications were conducted in the aldehyde group, where aminoguanidine (amig) and aminopurine (apur) were used as side chain derivatives. The complexes [(OH)Fe(μ-OH)Zn(HO)(Lbpea)](ClO) (1), [(OH)Fe(μ-OH)Zn(HO)(Lbpea–amig)](ClO) (2) and [(OH)Fe(μ-OH)Zn(HO)(Lbpea–apur)](ClO) (3) were characterized by spectroscopic methods (infrared, UV–Vis) and ESI-MS spectrometry. Density functional theory (DFT) was also used to better understand the structure of the complexes. The hydrolytic activity of complexes 1, 2 and 3 was analyzed using both the model substrate 2,4-BDNPP (bis-(2,4-dinitrophenyl)phosphate) and DNA. Complexes 2 and 3, containing the derivatized ligands, have a significantly higher association constant (K≅ 1/K) for the activated substrate 2,4-BDNPP compared to complex 1. The catalytic efficiency (k/K) is also higher due to hydrogen bonds and/or π-stacking interactions between the substrate and the aminoguanidine or aminopurine groups present in 2 and 3, respectively. In the DNA cleavage assays, all complexes were able to cleave DNA, with 1 and 2 having higher catalytic activity than 3. In addition, when compared to previously analyzed complexes, complex 2 is one of the most active, having a k of 0.21\ua0h. Graphical abstract: [Figure not available: see fulltext.]

An Unprecedented FeIII(μ-OH)ZnII Complex that Mimics the Structural and Functional Properties of Purple Acid Phosphatases

This communication reports the synthesis and X-ray structure of the first mixed-valence FeIIIZnII complex containing the FeIII(μ-OH)ZnII structural unit. Based on the structure, physicochemical solution studies, and the catalytic properties toward the hydrolysis of the diester 2,4-bis(dinitrophenyl)phosphate (BDNPP), it is proposed that complex 1 employs a hydrolytic mechanism similar to that proposed for red kidney bean purple acid phosphatase, including a nucleophilic attack by the terminal, FeIII-bound hydroxide and the concomitant release of 2,4-dinitrophenolate. Furthermore, it is demonstrated that the μ-hydroxo group in the {FeIII(μ-OH)(μ-ROPO3)ZnII} intermediate is unable to hydrolyze the monoester 2,4-dinitrophenylphosphate (DNPP), which suggests that the μ-hydroxo group is a significantly poorer nucleophile than the terminally FeIII-bound OH- group