Carboxylate Oxygen Atoms Research Articles

GLPGPSGEEGKR: Fe2+ chelating characterization and potential transport pathways for improving Fe2+ bioavailability in Caco-2 cells

We investigated the Fe2+ chelating properties and the mechanism of improving Fe2+ bioavailability of the Fe2+ chelating peptide (GLPGPSGEEGKR, peptide-G-R). Fe2+ was chelated with the carboxyl oxygen atom of the Glu-Glu residue in the form of monodentate and bidentate chelating mode. After chelation, peptide-G-R was folded and aggregated to form spherical particles with increasing particle size. Peptide-G-R could increase the Fe2+ transport/retention/uptake rate and the relative expression levels of divalent metal transporter 1 (DMT1) in the Caco-2 cells monolayer model. Peptide-G-R could reverse the inhibition of phytic acid on the Fe2+ utilization in the Caco-2 cells monolayer model. Molecular dynamics simulation showed that peptide-G-R interacted with DMT1 in the form of intermolecular hydrogen bonds. The transport mechanism of the peptide-G-R-Fe2+ complex included endocytosis (main pathway), paracellular pathway (auxiliary way), and DMT1 (potential pathway). Thus, peptide-G-R derived from tilapia skin collagen could be used as a dietary iron supplement.

High Stabilization of Low Valency in a Homoleptic ortho-Hydroxybenzoate-bridged Paddlewheel Diruthenium(II,II) Complex

Abstract A paddlewheel-type homoleptic diruthenium(II,II) complex ([Ru2II,II]), [Ru2(o-OHPhCO2)4(THF)2] (o-OH), bridged by ortho-hydroxybenzoate (o-OHPhCO2−) and tetrahydrofuran (THF) coordinated at the axial position (Lax) was isolated. The use of meta- and para-substituted hydroxybenzoate (x-OHPhCO2−; x = m and p) produced the corresponding [Ru2II,III] species neutralized by deprotonation of one of the x-OHPhCO2− ligands. In the o-OH complex, the formation of intramolecular hydrogen bonds between the o-OH group and carboxylate oxygen atom stabilized the [Ru2II,II] species significantly.

Synthesis, structural elucidation, molecular modeling, and antimicrobial studies of some nanoparticles mixed ligands complexes of cetirizine in presence of 2,2′‐bipyridine

A four mixed ligand metal complexes derived from the interaction of Cu(II), Zn(II), Zr(IV), and Cd(II) with antihistamine cetirizine.2HCl (Cetz) in the presence of 2,2′‐bipyridine (Bipy) were synthesized and characterized by using elemental analyses, Fourier transform infrared (FT‐IR), UV–visible (UV–Vis), 1H NMR, thermal analysis (thermogravimetric–differential thermogravimetry [TG–DTG]), X‐ray diffraction (XRD) analysis, molar conductance, and magnetic moment. The infrared data confirmed that Cetz interacted with metal ion as monodentate ligand through carboxylate oxygen atom, and Bipy chelated through nitrogen atoms. The decomposition mechanism (TG and DTG) for Cetz, Bipy, and their complexes were accomplished, and thermodynamic parameters (Ea, ΔH*, ΔS*, and ΔG*) were determined using Horowitz–Metzger (HM) and Coats–Redfern (CR) methods. The powder XRD analysis of all compounds was carried out to determine the average crystalline size (d) and the nature of the compounds (crystalline or amorphous). The density functional theory (DFT) was achieved to comprehend the optimized geometry for the compounds. All complexes regarded as soft in relation to Cetz, with values ranging from 12.987 to 22.727 eV and equal to 12.658 eV for Cetz. The compounds biological activity was examined against number of bacterial and fungal strains. The data revealed that the investigated complexes have a significant efficiency and may be used as better bactericides.

Synthesis, structures and properties of two lead halide coordination polymers based on pyridinedicarboxylate ligand

Two new lead halide coordination polymers, [Pb2(pydc)I2]n (1), [Pb2(pydc)ClI]n (2), (H2pydc ​= ​2,5-pyridinedicarboxylic acid) have been synthesized under hydrothermal condition, and structurally characterized by single-crystal X-ray diffraction. The results of X-ray crystallographic analysis reveal that both compounds are three-dimensional (3D) frameworks. For 1, 1D inorganic cation [Pb2I2]n2n ​+ ​ribbons are fused by the carboxylate oxygen atoms to generate 2D layers. Then the 2D layers are sustained by pydc2− ligands and result in a 3D pillared framework. Remarkably, a novel 2D mixed-halide cation [Pb2ClI]n2n ​+ ​layer is found in 2. The mixed-halide cation layers are further connected by pydc2− ligands and create a 3D network. In addition, solid-state properties of thermal stability and fluorescence for these crystalline materials are also presented. Time-dependent density functional theory (TDDFT) calculations reveal that the mechanism of the fluorescence emissions dominantly results from the ligand-to-metal charge transfer (LMCT) and partial the intraligand π→π∗ and/or n→π∗ transitions for 1 and 2, which is in good agreement with their fluorescence spectra and crystal structures.

A strongly hydrophobic ethane-selective metal-organic framework for efficient ethane/ethylene separation

The removal of ethane (C2H6) from ethylene (C2H4) is of great importance to afford polymer-grade C2H4 with purity greater than 99.95% as feedstock to produce polyethylene. Adsorptive separation with C2H6-selective metal-organic frameworks (MOFs) can directly produce high-purity C2H4, which has shown bright prospects for replacing the energy-intensive cryogenic distillation. Herein, we demonstrate a robust zirconium MOF possessing hydrophobic pores and oxygen-rich groups, namely MOF-841, can preferentially adsorb C2H6 over C2H4. Experimental adsorption isotherms and breakthrough show high separation performance for the gas mixture of C2H6 and C2H4 due to ultrahigh C2H6 uptake capacity (4.7 mmol/g) and distinctive C2H6/C2H4 uptake ratio (1.35) of MOF-841 at 298 K and 100 kPa. Computational studies reveal that aromatic rings and carboxylate oxygen atoms pointing towards the pore ascribed to trapping C2H6 through synergistic effects arising from multiple van der Waals interactions including C-H∙∙∙π and C-H···O, which are more potent than C2H4-framework interactions.

Solvo-thermal synthesis of a unique cluster-based nano-porous zinc(II) luminescent metal-organic framework for highly sensitive detection of anthrax biomarker and dichromate

In this work a flexible multi-dentate 4,4′-(1H-1,2,4-triazole-1-yl) methylene-bis(benzonic acid) (H2L) ligand has been employed, a unique cluster-based nano-porous luminescent zinc(II) metal-organic framework {[Zn(μ6-L)]·(DMAC)2}n (1) (DMAC = Dimethylacetamide) has been isolated under solvo-thermal conditions. The H2L ligand adopts hexa-dentate coordination modes via one triazole nitrogen atom and four aromatic carboxylate oxygen atoms, which bridge the neighboring six-coordinated ZnII centers, leading to a three-dimensional (3D) nano-porous metal organic framework. A PLATON program analysis suggests the total potential solvent area volume is 2028.9 Å3, which occupy 62.5% percent of the unit cell volume (3248.4 Å3). PXRD Patterns of the as-synthesized samples 1 have been determined confirming the purity of the bulky samples. Photo-luminescent properties indicate strong fluorescent emissions of 1 at the room temperature. Further photo-luminescent measurements show that 1 can exhibit highly sensitive real-time luminescence sensing of anthrax biomarker dipicolinic acid (DPA) with high quenching efficiency (KSV = 1.48 × 105 M−1) and low detection limit (0.298 μM (S/N = 3)). Meanwhile 1 also exhibits highly selective and sensitive luminescence sensing for Cr2O72- ions in aqueous solutions with high quenching efficiency KSV = 1.22 × 104 L·mol−1 and low detection limit (0.023 μM (S/N = 3)). Therefore 1 can be used a unique multi-functional 3D cluster-based metal organic material in sensitive detection and effective detection of environment pollutants and biomarker molecules.

Preparation, characterization, and properties of wampee seed antioxidant peptides‐iron chelate

The chelation process of antioxidant peptides with iron was optimized by response surface methodology with iron chelation percentage as a response. The optimum process was chelation time of 38 min, chelation temperature of 31°C, chelation pH of 5.2, and peptides-to-iron mass ratio of 3.4:1. Scanning electron microscopy observation showed the chelate was a smooth and dense granular aggregate morphology. Fourier transform infrared spectroscopy analysis indicated the chelate's characteristic peaks shifted significantly compared with the antioxidant peptides. The α-helix and random coil contents decreased from the peptides of 60.86% to the chelate of 43.74%. However, the β-structure contents increased from the peptides of 39.14% to the chelate of 56.26%. The in vitro digestion test suggested the chelate had 97.37% bioaccessibility and 58.53% DPPH radical scavenging effect in gastric digestion. But those in intestinal digestion remained 50.02% and 41.02%, respectively. The chelate can be used as a new iron supplement. Novelty impact statement The preparation process of wampee seed antioxidant peptides-iron chelate was optimized by response surface methodology. Iron ions binding to the peptides was through carboxyl oxygen and amino nitrogen atoms. Chelate showed good antioxidant activity and bioaccessibility during gastrointestinal digestion.

Synthesis, crystal structure and thermal properties of Na2Ti(CF3COO)6(CF3COOH)2

The compound Na2Ti(CF3COO)6(CF3COOH)2 was synthesized as colorless crystals, extremely unstable in air, by the reaction of TiCl4 with trifluoroacetic acid and sodium trifluoroacetate. Crystallographic studies have shown that this sodium trifluoroacetatotitanate is the first example of a tetravalent titanium carboxylate [Ti(RCOO)6]2– containing titanium in an octahedral environment of oxygen atoms of carboxylate groups. Thermal decomposition of Na2Ti(CF3COO)6(CF3COOH)2 in an argon atmosphere results in the complex fluoride Na2TiF6.

Exploration of iron-binding mode, digestion Kinetics, and iron absorption behavior of Antarctic Krill–derived heptapeptide–iron complex

A novel heptapeptide LVDDHFL derived from Antarctic krill was used to assemble an iron complex, of which the iron-binding mode, in vitro digestion kinetics, and iron absorption behavior were explored. Fe2+ bound to one carboxyl oxygen atom of Asp at position 4 and the imidazole group of His at position 5 on the LVDDHFL peptide at a stoichiometric ratio of 1:2, which induced the folding of LVDDHFL to form a more orderly structure. LVDDHFL–iron significantly enhanced the solubility of iron as compared to FeSO4 in the gastroduodenal tract (P < 0.05), making it up to 80.92 ± 3.02% at the end of gastroduodenal digestion. Moreover, iron complexation can enhance the digestive stability of LVDDHFL with the peptide retention rate as 62.26 ± 2.60% and approximately 27.54% of LVDDHFL were degraded to hexapeptide LVDDHF. Nevertheless, the enhancement of LVDDHF − iron on iron absorption was comparable to that of LVDDHFL − iron, but better than that of FeSO4.

New Cd(II) complex derived from (1-methylimidazol-2-yl) methanol: Synthesis, crystal structure, spectroscopic study, DFT and TD-DFT calculations, antimicrobial activity and free-radical scavenging capacity

A combined experimental and theoretical study of new complex with a formula of [Cd(Hmim)2(OAc)2], where Hmim stands for (1-methyl-1H-imidazol-2-yl) methanol has been reported. The complex was characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR and UV-vis spectroscopy. The crystal structure of the complex shows that two Hmim and two carboxylate groups are coordinated to the Cd(II) ion in monodentate fashion through the nitrogen and carboxylic oxygen atoms displaying a distorted tetrahedral geometry. Detailed theoretical studies were performed using DFT and TD-DFT calculations, other properties such as chemical bonding analysis (QTAIM, RDG, DOS) have been also carried out and are in agreement with the experimental results. The ligand and its Cd(II) complex have been screened in vitro and evaluated for their potential as DPPH radical scavengers as well as antimicrobial agents against five pathogenic microorganisms such as Gram-positive and Gram-negative bacteria, a yeast and a fungus using the agar diffusion method. The SAR study showed that the free ligand exerts no inhibitory activity, except a moderate activity against the yeast, while the complex exhibits an antimicrobial activity more potent or similar to that of standard drugs against all selected microorganisms, and a moderate to interesting antioxidant potential compared to Vitamin C as control.

Oxidation Enhances Binding of Extrahelical 5-Methyl-Cytosines by Thymine DNA Glycosylase.

The DNA repair protein thymine DNA glycosylase (TDG) removes mispaired or damaged bases, such as oxidized methyl-cytosine, from DNA by cleavage of the glycosidic bond between the sugar and the target base flipped into the enzyme's active site. The enzyme is active against formyl-cytosine and carboxyl-cytosine, whereas the lower oxidized hydroxymethyl-cytosine and methyl-cytosine itself are not processed by the enzyme. Molecular dynamics simulations with thermodynamic integration of TDG complexed to DNA carrying one of four different (oxidized) methyl-cytosine bases in extrahelcial conformation, methyl-cytosine (mC), hydroxymethyl-cytosine (hmC), formyl-cytosine (fC), or carboxyl-cytosine (caC), show a more favorable binding affinity of the higher oxidized forms, fC and caC, than the nonsubstrate bases hmC and mC. Despite rather comparable, reaction-competent conformations of the flipped bases in the active site of the enzyme, more and stronger interactions with active site residues account for the preferred binding of the higher oxidized bases. Binding of the negatively charged caC and the neutral fC are strengthened by interactions with positively charged His151. Our calculated proton affinities find this protonation state of His151 the preferred one in the presence of caC and conceivable in the presence of fC as well as increasing the binding affinity toward the two bases. Discrimination of the substrate bases is further achieved by the backbone of Tyr152 that forms a strong hydrogen bond to the carboxyl and formyl oxygen atoms of caC and fC, respectively, a contact that is completely lacking in mC and much weaker in hmC. Overall, our computational results indicate that the enzyme discriminates the different oxidation forms of methyl-cytosine already at the formation of the extrahelical complexes.

Novel three-dimensional coordination polymer of 2-(1,3,5-tri-aza-7-phospho-niatri-cyclo-[3.3.1.13,7]decan-7-yl)ethanoic acid with silver(I) tetra-fluoro-borate.

An AgI-based coordination polymer (CP), namely, poly[[[μ3-2-(1,3,5-tri-aza-7-phospho-niatri-cyclo-[3.3.1.13,7]decan-7-yl)ethano-ate-κ4 N:N':O,O']silver(I)] tetra-fluoro-borate], {[Ag(C9H16N3O2P)]BF4} n , was synthesized in an aqueous solution of zwitterionic 2-(1,3,5-tri-aza-7-phospho-niatri-cyclo-[3.3.1.13,7]decan-7-yl)ethan-o-ate (L) and AgBF4 with exclusion of light at room temperature. The colourless and light-insensitive CP crystallized in the monoclinic space group Cc. The asymmetric unit consists of an AgI cation, the zwitterionic L ligand and a BF4 - counter-ion. Each AgI ion is coordinated by two carboxyl-ate oxygen atoms in a chelating coordination mode, as well as one of the nitro-gen atoms of two neighbouring L ligands. The crystal structure of the CP was classified as a unique three-dimensional arrangement. The CP was also characterized in aqueous solutions by multinuclear NMR and HRMS spectroscopies and elemental analysis.

Application of a Mytilus edulis-derived promoting calcium absorption peptide in calcium phosphate cements for bone

The IEELEEELEAER peptide (PIE) identified from the protein hydrolysate of Mytilus edulis is reported to enhance osteoblast growth and differentiation, which also possesses a superior bone formation ability both in vitro and in vivo. Moreover, PIE bound to calcium spontaneously at the stoichiometry of 1:1, and there were amino nitrogen and carboxyl oxygen atoms in 2 glutamic acid residues at the calcium-binding sites in the PIE. The PIE–calcium complex facilitated calcium uptake through the Caco-2 cell monolayers. Incorporation of PIE into calcium phosphate cements enhanced calcium ion uptake and proliferation of osteoblasts and inhibit bacteria. This study suggest that calcium phosphate cements supplemented with PIE can serve as a potentially efficient material for bone graft used during spinal surgery.

Food-Borne Nanocarriers for Calcium Delivery: A New Choice for Nutrient Supplements.

Calcium is considered as an important nutrient element for the maintenance of human health, and food-borne nanoparticles (FNs) produced during food processing may have potential as nanocarriers for calcium ion delivery. Beef is an important source of animal protein that has high protein and low fat content and is rich in a variety of amino acids; thus, beef may be a suitable material for the development of calcium nanocarriers. In this paper, FNs were synthesized from beef by one-step hydrothermal synthesis. The FNs had a spherical shape with a size of about 3.0 nm and emitted a bright blue fluorescence under 365 nm ultraviolet irradiation. The amino nitrogen atom and carboxyl oxygen atom of the functional groups on the surface of the FNs were the main binding sites for the chelation of Ca(II). The size of the FNs-Ca(II) complex was about 4.75 nm, and the specific signal peak of calcium at 3.7 keV was observed in its energy dispersive X-ray spectroscopy spectrum. The viability of cells treated with FNs-Ca(II) was more than 65%, while viability was only 60% after treatment with CaCl2. The results showed that the FNs from beef have great potential in calcium delivery for the development of a calcium supplement.

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C 2 H 2 /CO 2 Separation

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C ₂ H ₂ /CO ₂ Separation

Crystallographic and computational investigations of structural properties in phenyl and methoxy‑phenyl substituted 1,4 dihydropyridine derivatives

Single crystal preparation of two 1,4-dihydropyridine (1,4-DHP) derivative molecules, namely, (i) 2,6-dimethyl-4-phenyl-1, 4-dihydro-pyridine-3, 5-dicarboxylic acid diethyl ester and (ii) 4-(4‑methoxy-phenyl)-2,6-dimethyl-1, 4-dihydro-pyridine-3, 5-dicarboxylic acid diethyl ester was done. Crystal structure solution and refinement of final R values converged to 0.0478 and 0.0466. Hirshfeld surface analysis mapped dnorm surfaces, shape index, curvedness and hydrogen bonding present in the molecules. These calculations established the relative contributions of the various intermolecular contacts to the total Hirshfeld surface area. Both the molecular structures were optimized and confirmed by Density Functional Theory (DFT) simulations in an implicit aqueous solvation environment. The molecular electrostatic potential (MEP) analysis elucidated the electrophilic and nucleophilic regions in the molecules to be the hydrogen attached to the nitrogen and the carboxyl oxygen atoms. Frontier molecular orbital analysis indicated the stability of these molecules while they appeared to be electrophilic in nature from the reactivity descriptors analysis.

Two coordination polymers induced by transition metal Zn(II) and Co(II) ions based on 3-nitrobenzene-1,2-dicarboxylic acid and 3,5-bis(1-imidazolyl)pyridine ligands

Two new coordination polymers, {[Zn(3-Nbdc)(bip)]·2H2O}n (1) and {[Co(3-Nbdc)(bip)(H2O)]0.25H2O}n (2) (H23-Nbdc = 3-nitrobenzene-1,2-dicarboxylic acid, bip = 3,5-bis(1-imida­zolyl)pyridine) were synthesized under the hydrothermal conditions and characterized by single crystal X-ray diffraction and elemental analysis. In 1, the Zn(II) ion forms a slightly distorted [ZnO2N2] tetrahedron by two carboxylate oxygen atoms and two nitrogen atoms. Adjacent Zn(II) neighbors are linked by 3-Nbdc dianions adopting monodentate coordination mode to form 1D Zn-carboxylate chain, which is further extended by bip molecules to produce a two-dimensional thick layer. For complex 2, two six-coordinated Co(II) ions with different coordination environments are alternately connected by 3-Nbdc dianions and bip ligands along different directions to generate a two-dimensional grid layer. Furthermore, Powder X-ray diffractions, FTIR spectra and thermogravimetric analyses are also investigated.

NUCLEAR MAGNETIC RESONANCE (1HNMR) STUDY OF CHROMIUM (III) SALICYLATE AND BENZOATE COMPLEXES

Chromium (III) salicylate and Chromium (III) benzoate complexes were prepared using Chromium trioxide and different molar concentrations of salicylic and benzoic acid. Tertiary amyl alcohol and ethanol are used as a solvent. 1HNMR spectra of solid samples were recorded. 1HNMR spectra of metal complexes suggest that deprotonation of – COOH group took place, and the complex formed was not through the –OH of the acid. It confirms the coordination of the ligand to the metal ion through the carboxylic oxygen atom.

The structure and spectroscopic characterization of coordination compounds with -phenyl-N-methylnitrone in solution and in solid state

New coordination compounds of a-phenyl-N-methylnitrone with Cu2+, Mn2+, Ni2+, and UO22+ were synthesized. Complexes were studied by means of IR, NMR and UV-Vis spectroscopies. The crystal and molecular structure of uranyl complex with a-phenyl-N-methylnitrone was determined by X-ray diffraction study. The monodentate nitrone ligands are coordinated to the metal ion via oxygen atom. The coordination polyhedron of uranium is a distorted hexagonal bipyramide. It was shown that there is dynamic process in the acetone solution in the temperature range of 203–297 K. The ligand exists as a trans-isomer for both present forms of organic ligand by the NOE difference. Dimeric copper(II) benzoate was obtained via recrystallization of the copper complex with a-phenyl-N-methylnitrone from methanol solution. According to X-ray diffraction analysis, the environment of each of the copper atoms is octahedral. The coordination sphere is formed by six oxygen atoms. Three anions of benzoic acid are coordinated bidentate-bridged through oxygen atoms of the carboxyl group, while one molecule of benzoic acid is coordinated monodentatically through the carboxyl oxygen atom.

Nanochannel-based {BaZn}-organic framework for catalytic activity on the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation.

Herein, the rare combination of BaII (5s) and ZnII (3d) in the presence of the structure-oriented TDP6- ligand generated the nanochannel-based hybrid material {[(CH3)2NH2]2[BaZn(TDP)(H2O)]·DMF·5H2O}n (NUC-51, H6TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine), which possesses excellent physicochemical characteristics such as nanoscopic channels, high porosity, large specific surface area, and high heat/water-resistance. To the best of our knowledge, this is the first 3D [BaIIZnII(CO2)6(H2O)]-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 4-coordinated Zn2+ ions, 7-coordinated Ba2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Catalytic experiments exhibited that activated NUC-51a possesses a high catalytic activity on the cycloaddition reactions of epoxides with CO2 at 55 °C, which can be ascribed to its structural advantages of nanoscale channels and rich bifunctional active sites. Moreover, NUC-51a could significantly accelerate the deacetalization-Knoevenagel condensation reaction in DMSO solvent at 70 °C.