Coordinated Hydroxyl Groups Research Articles

(001) plan manipulation of α-Fe2O3 nanostructures for enhanced electrochemical Cr(VI) sensing

Two types of α-Fe2O3 nanostructures were synthesized under hydrothermal conditions in the presence of glycerol. Urchin-like α-Fe2O3 with limited (001) plane exposure and flower-like α-Fe2O3 with a high degree of (001) plane exposure were used to modify the surfaces of screen-printed electrodes (SPEs), which were then employed in electrochemical Cr(VI) detection. Linear sweep voltammetric results indicate that the high exposure of the (001) plane could result in a high current response toward Cr(VI) reduction due to the high adsorption capacity induced by doubly and triply coordinated hydroxyl groups on the surface of α-Fe2O3. The modified SPE had a linear response to Cr(VI) in the 5–3000μg/L concentration range with a detection limit of 1.17μg/L.

Structural characterization of the P1+ intermediate state of the P-cluster of nitrogenase

Nitrogenase is the enzyme that reduces atmospheric dinitrogen (N2) to ammonia (NH3) in biological systems. It catalyzes a series of single-electron transfers from the donor iron protein (Fe protein) to the molybdenum-iron protein (MoFe protein) that contains the iron-molybdenum cofactor (FeMo-co) sites where N2 is reduced to NH3 The P-cluster in the MoFe protein functions in nitrogenase catalysis as an intermediate electron carrier between the external electron donor, the Fe protein, and the FeMo-co sites of the MoFe protein. Previous work has revealed that the P-cluster undergoes redox-dependent structural changes and that the transition from the all-ferrous resting (PN) state to the two-electron oxidized P2+ state is accompanied by protein serine hydroxyl and backbone amide ligation to iron. In this work, the MoFe protein was poised at defined potentials with redox mediators in an electrochemical cell, and the three distinct structural states of the P-cluster (P2+, P1+, and PN) were characterized by X-ray crystallography and confirmed by computational analysis. These analyses revealed that the three oxidation states differ in coordination, implicating that the P1+ state retains the serine hydroxyl coordination but lacks the backbone amide coordination observed in the P2+ states. These results provide a complete picture of the redox-dependent ligand rearrangements of the three P-cluster redox states.

The adsorption behavior and mechanism of Cr(VI) on 3D hierarchical α-Fe2O3 structures exposed by (0 0 1) and non-(0 0 1) planes

Two kinds of 3D hierarchical α-Fe2O3 nanoparticles, flower-like structure with the (001) plane predominantly exposed on petals and urchin-like structure with nanorods grown along [001] direction, have been synthesized under the influence of glycerol by a facile hydrothermal method. It is proposed that the Fe(III)–glycerol micro-reaction units that selectively adsorb to (001) or other planes result in different morphologies. The adsorption of Cr(VI) from aqueous solution onto these α-Fe2O3 nanoparticles showed that the removal efficiency up to 98.5% and 88.8% in 25mg/L Cr(VI) solution, and the adsorption capacity reaches to 34.4mg/g and 26.0mg/g without pH adjustment. The adsorption kinetic is well described by the pseudo-second-order model and the Cr(VI) adsorption on the adsorbent agrees well with the Langmuir model. Lower surface areas and more excellent adsorption property associates with the chemisorption of Cr(VI) onto α-Fe2O3 (001), which is achieved by coordination between Cr(VI) and doubly or triply coordinated hydroxyl groups on α-Fe2O3 surface.

Activated Ag ions and enhanced gas transport by incorporation of KIT-6 for facilitated olefin transport membranes

Facilitated olefin transport membranes consisting of polymer/Ag salt/Al(NO3)3 have shown long-term stability, increasing the possibility of being used in practical applications. However, even though they show excellent separation performance over a long duration, the need for significant amounts of Ag salts acts as an obstacle, owing to relatively high cost of Ag. Thus, reduction in the amount of Ag salts in the membranes is required for practical applications in the industry. However, since the separation performance is directly related to the amount of Ag salts, it has been difficult to reduce the amount of Ag salts. In this study, we succeeded in preparing polymer/Ag salts/Al(NO3)3 membranes with 30% reduction in the amount of Ag salts by utilizing KIT-6, which is a porous material. When KIT-6 was incorporated into the polymer/Ag salts/Al(NO3)3 membrane, the separation performance for propylene/propane mixed gas increased with a propylene over propane selectivity of 20 and mixed gas permeance of 10 GPU. These values of selectivity and permeance amounted to 154% and 133% enhancement, respectively, compared to the performance without KIT-6. The enhanced separation performance is attributed to both the coordination of hydroxyl groups in KIT-6 with Ag ions and the porous properties of KIT-6, which leads to increased diffusivity. The coordination behavior of polymer/Ag salts/Al(NO3)3 containing KIT-6 was investigated by FT-IR, FT-Raman, and XPS analyses.

Preparation of α-Fe2O3 hollow spheres, nanotubes, nanoplates and nanorings as highly efficient Cr(vi) adsorbents

α-Fe2O3 nanoparticles like hollow spheres, nanotubes, nanoplates and nanorings have been synthesized. As highly efficient Cr(vi) adsorbents, the adsorption mechanism may be due to chemical adsorption by the doubly and triply coordinated hydroxyl groups.

수용액 중에서 생리학적 완충제 아미노 알코올과 Zn(II) 이온과의 착물 형성

The complex formation from Zn(II) ion and 2-(2-hydroxyethylamino)-2-(hydroxymethyl)-1,3-propanediol (Monotris), Bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane(Bistris) in aqueous solution at and at an ionic strength of 0.10 M have been studied potentiometrically. For the Zn(II)-Monotris system, in the Monotris (L) complex , one of the hydroxyl oxygen atoms as well as the amine nitrogen of the ligand are coordinated. In basic media, the coordinated hydroxyl group is deprotonated. For the Zn(II)-Bistris system, in the Bistris(L) complex , two of the hydroxyl oxygen atoms as well as the amine nitrogen of the ligand are coordinated. In basic media, one of the coordinated hydroxyl groups is deprotonated. In very high basic media, an additional hydroxyl group undergoes deprotonation. The equilibrium constants for the formation of , , , and have been determined.

Molecular docking studies and 2D analyses of DPP-4 inhibitors as candidates in the treatment of diabetes.

Dipeptidyl peptidase-4 (DPP-4) is an important biological target related to the treatment of diabetes as DPP-4 inhibitors can lead to an increase in the insulin levels and a prolonged activity of glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP), being effective in glycemic control. Thus, this study analyses the main molecular interactions between DPP-4 and a series of bioactive ligands. The methodology used here employed molecular modeling methods, such as HQSAR (Hologram Quantitative Structure-Activity) analyses and molecular docking, with the aim of understanding the main structural features of the compound series that are essential for the biological activity. Analyses of the main interactions in the active site of DPP-4, in particular, the contribution of the hydroxyl coordination between Tyr547 and Ser630 by the water molecule, which is described in the literature as important for the coordinated interactions in the active site, were performed. Significant correlation coefficients of the best 2D model (r(2) = 0.942 and q(2) = 0.836) were obtained, indicating the predictive power of this model for untested compounds. Therefore, the final model constructed in this study, along with the information from the contribution maps, could be useful in the design of novel DPP-4 ligands with improved activity.

Fluoroalkyl phosphoric acid derivatives — Model compounds to study the adsorption of electrolyte species on polycrystalline platinum

The slow oxygen reduction reaction (ORR) in concentrated phosphoric acid remains a major technological challenge for future development of phosphoric acid fuel cells (PAFCs) as well as its congener the high-temperature proton exchange membrane fuel cells (HT-PEMFCs). It is generally accepted that adsorption of molecular or anionic species from the concentrated phosphoric acid electrolyte hinders ORR by blocking active sites on the catalyst surface. Aiming to better understand the adsorption mechanisms, we conducted a systematic study employing various types of perfluoroalkylated derivatives of phosphoric acid, in which one or two hydroxyl groups of phosphoric acid were substituted by perfluoroalkyl chains of different lengths. We evaluated these model electrolytes for their adsorption behavior and influence on ORR on a polycrystalline platinum surface by dosing small amounts of these acids to a 0.5M perchloric acid solution. By means of cyclic voltammetry (CV), significant changes in the characteristic features of the pristine Pt voltammogram were observed. ORR kinetic currents measured by rotating disk electrode (RDE) were found to be strongly dependent on the molecular structure, particularly on the number of hydroxyl coordination sites and negative charge-density of the bis(perfluoroalkyl)-phosphinic or perfluoroalkyl-phosphonic acids added to the electrolyte.

Reactivity study of a hydroxyl coordinated osmium vinyl complex OsCl2(PPh3)2[CH=C(PPh3)CHPh(OH)

We studied the reactivity of an osmium vinyl complex containing a coordinated hydroxyl group OsCl2(PPh3)2[CH=C(PPh3)-CHPh(OH)] (1) toward bidentate ligand 1,4-bis(diphenylphosphino)butane (DPPB), π acid ligand (CO), base (Cs2CO3) and heat. Two osmium vinyl complexes OsCl2(dppb)[CH=C(PPh3)CHPh(OH)] (2) and OsCl2(CO)2(PPh3)[CH=C(PPh3)CHPh(OH)] (3), as well as two relatively rare phosphonium-containing osmafuran complexes Os(η2-OCOO)(PPh3)2[CHC(PPh3)CPhO] (4) and OsCl2(PPh3)2[CHC(PPh3)CPhO] (5), were obtained in high yields from these reactions. All products were characterized by NMR spectroscopy, elemental analysis, and their structures were further confirmed by single crystal X-ray diffraction.

Surface complexation modelling of arsenate and copper adsorbed at the goethite/water interface

The co-adsorption of Cu(II) and arsenate onto the surface of goethite has been studied by performing adsorption experiments and potentiometric titrations, and a surface complexation model has been developed to describe the experimental results. Models for the binary systems, Cu–goethite and arsenate–goethite, were acquired separately and the model parameters were then included in the ternary system, together with the solubility products of solid Cu(II) arsenates reported in the literature. The adsorption of Cu(II) was described applying a model in which Cu(II) forms bidentate bridging mono- and binuclear surface complexes. According to recent interpretations of ATR-FTIR and EXAFS data the arsenate ions are assumed to be coordinated in a monodentate fashion to singly coordinated hydroxyl groups at the surface, and hydrogen-bonded to neighbouring triply coordinated surface oxide sites. In the case of co-adsorption of Cu(II) and arsenate, the adsorption could not be predicted by applying the combined model from the two binary systems. Two ternary Cu(II)–arsenate–goethite surface complexes must be included, one complex in which an arsenate ion is coordinating to surface Fe(III) (FeOAsO3Cu0.5−) and one complex in which arsenate is bound to the surface by coordinating to an adsorbed Cu(II) ion ((Fe3OFeOH)Cu2(OH)2HAsO41-). No solid Cu(II) arsenate phases were formed under the experimental conditions in the present study. From constructed predominance area diagrams, the significance of adsorption and precipitation processes are discussed. Furthermore, calculated solubility of Cu(II) and As(V) is used to indicate optimum conditions for the cleaning of contaminated natural waters.

Surface phase diagram of hematite pseudocubes in hydrous environments

Hematite nanoparticles often display the pseudocubic morphology enclosed exclusively by the (012) surface. The surface chemistry on these facets is important to understand the formation and properties of these nanoparticles in varying chemical environments. The surface is typically terminated by hydroxyl groups in water or humid atmospheres, and the various terminations differ largely in composition, structure, thermodynamic stability, and chemical reactivity. When we compare a large variety of chemical configurations, we find that three specific terminations are thermodynamically stable under aerobic conditions. The termination by singly and triply coordinated hydroxyl groups (S-,T-OH) is stable at low temperatures and in hydrous environments, the stoichiometric clean termination is stable at high temperatures and in dry environments, and the termination by doubly coordinated hydroxyl groups (D-OH) is stable under intermediate conditions. The S-,T-OH termination can convert topologically to the clean surface by dissociative adsorption of water, whereas the conversion from these two terminations to the D-OH termination requires re-organization of several atomic layers at the surface. Therefore, the surface may reversibly change between S-,T-OH and the clean surface depending on the temperature and humidity. Based on these findings we have constructed surface phase diagrams to predict the termination types in different hydrous and humid environments.

Surface Structure and Environment-Dependent Hydroxylation of the Nonpolar Hematite (100) from Density Functional Theory Modeling

Hematite (α-Fe2O3) nanoparticles are typically synthesized, stored, or used in hydrous environments, and the mineral/water interfaces are important for the surface stability and reactivity of these nanoparticles. Under such conditions the exposed facets are often passivated by hydroxyl groups. The configurations of surface hydroxylation vary with environmental conditions and affect the morphology and surface chemistry. Among the low-index hematite surfaces, the {100} are the only nonpolar surfaces and are often present on nanorods or nanotubes elongated along the [001] direction. In this paper we explore the relaxation and hydroxylation of this surface using first principles thermodynamics. Our results reveal that depending on the supersaturation of water and oxygen, various extents of hydroxylation may appear. In humid or hydrous environments, undercoordinated subsurface oxygen atoms are hydrogenated. In water singly and doubly coordinated hydroxyl groups coexist with chemisorbed water molecules at the s...

Template Synthesis, Crystal Structure, and Magnetic Properties of a Dinuclear Copper(II) Complex with Cooperative Hydrogen Bonding

The dinuclear complex 1 with cooperative hydrogen bonds can be prepared by the metal-directed reaction of Eq. (2). This work shows that the coordinated hydroxyl group trans to the secondary amino group is deprotonated more readily than that trans to the tertiary amino group and acts as the hydrogen-bond accepter. The lattice water molecules in 1 act as bridges between the two mononuclear units through hydrogen bonds. The complex is quite stable as the dimeric form even in various polar solvents. The complex exhibits a weak antiferromagnetic interaction between the metal ions in spite of relatively long Cu<TEX>$\cdots$</TEX>Cu distance. This strongly supports the suggestion that the antiferromagnetic behavior is closely related to the cooperative hydrogen bonds.

Synthesis and characterization of francoisite-(Nd): Nd[(UO2)3O(OH)(PO4)2]{middle dot}6H2O

In this report, synthesis and characterization data for francoisite-(Nd), Nd[(UO2)3O(OH)(PO4)2]·6H2O are presented. Experimental studies including chemical digestion, thermogravimetric analysis (TG), attenuated total reflection infrared spectroscopy (ATR-IR), Raman spectroscopy, and X-ray powder diffraction (XRD) were conducted. The local bonding environments of uranyl and water were investigated with ATR-IR and Raman spectroscopy. The average axial uranium-oxygen bond lengths [R(U=O)] and the oxygen-oxygen hydrogen bond distances [R(O···O)] in water were calculated from the vibrational frequencies of the stretching modes of uranyl and water, respectively. The IR spectra of protiated and deuterated francoisite-(Nd) appear to confirm a coordinated hydroxyl group bridging vicinal uranyl groups in the structural unit. These studies provide the basis for further thermodynamic (e.g., calorimetry, solubility, and sorption) and geochemical modeling investigations of hydrated uranyl phosphate compounds.

Acetonitrile{3-[bis(2-pyridylmethyl-κN)amino-κN]propanol-κO}(perchlorato-κO)copper(II) perchlorate

In the title compound, [Cu(ClO4)(C2H3N)(C15H19N3O)]ClO4, the CuII ion is coordinated by three N atoms and a hydroxyl-O atom of the tetra­dentate ligand, an O atom of a perchlorate ion and an N atom of an acetonitrile ligand giving a tetra­gonally distorted octa­hedral environment around the copper(II) atom. There is an offset inter-complex face-to-face π–π inter­action [centroid–centroid distance = 3.718 (2) Å] involving one of the pyridine rings of the ligand as well as an intra-complex O—H⋯O hydrogen-bonding inter­action between the coordinated hydroxyl group of the ligand and the perchlorate counter-ion.

Bis(triethano-lamine)nickel(II) sulfate.

The title compound, [Ni(C6H15NO3)2]SO4, contains two triethano­lamine (TEA) ligands bound to an Ni2+ metal centre, which lies on a crystallographic inversion centre, and one sulfate anion located on a twofold rotation axis such that the asymmetric unit contains one-half molecule of the cation and of the anion. The triethano­lamine ligands coordinate via each axial N atom and two of the three O atoms, while the third arm of the ligand has the hydroxyl group pointing away from the metal centre. The sulfate anions are hydrogen bonded to the coordinated hydroxyl groups and also to the free arm, forming a two-dimensional supra­molecular hydrogen-bonded network expanding parallel to (010).

The structure of N,N′-bis(2-hydroxyethyl)ethane-1,2-diamine and its complexes with Zn(ii) and Cd(ii)

The crystal structure of the nitrate salt of N,N'-bis(2-hydroxyethyl)-ethane-1,2-diamine (BHEEN), and its complex with Zn(II) and Cd(II) are reported. (H(2)BHEEN)(NO(3))(2) packs in a layered structure with a herringbone pattern within each layer arising from H-bonding between amino and alcohol protons and NO(3)(-) counterions. In [Zn(BHEEN)(2)]Cl(2), each ligand coordinates to Zn(II) through its two N-donors producing a distorted tetrahedral geometry at the metal centre. The two hydroxyethyl arms of each ligand are trans to each other and the crystals obtained contained a racemic mixture of the bis-trans-R,R and the bis-trans-S,S isomers. All four hydroxyl groups are H-bonded to chloride counter ions, creating a layered structure. Whilst distant from the metal ion (average 3.00 A), the four O atoms of the pendent hydroxylamino groups appear positioned to interact with the metal. The orientation of the arms is preserved in a B3LYP gas phase calculation of the structure. An analysis using Bader's Atoms in Molecules indicates that the Zn-N bonds are predominantly ionic with some covalent character and that there is a weak interaction between the metal and the hydroxyl groups. Several other weak interactions including four O...HN, five O...HC and a H-H dihydrogen bond were identified. The Cd(II) complex of BHEEN crystallised as a dimer [(mu-Cl)(2)(Cd(BHEEN)Cl)(2))] with two asymmetrically-bound bridging Cl(-) ligands and a terminally-coordinated Cl(-) on each metal ion. One hydroxyl group of each ligand is coordinated to the metal and the uncoordinated hydroxyl group is H-bonded to the H atom of the coordinated hydroxyl group of the second ligand in the complex. The ESI-MS spectrum shows the presence of di-cadmium complexes, but the most intense peaks are due to mono-cadmium complexes. The gas phase B3LYP structure of the dimer energy-minimises into two monomers and the longer bond between Cd(II) and bridging Cl(-) breaks. Hence, dimerisation may be a consequence of the crystallisation process and the dimer may not be the predominant species in solution.

Structural basis for VO2+-inhibition of nitrogenase activity: (B) pH-sensitive inner-sphere rearrangements in the 1H-environment of the metal coordination site of the nitrogenase Fe–protein identified by ENDOR spectroscopy

The nitrogenase Fe-protein is the specific ATP-activated electron donor to the active site-containing nitrogenase MoFe-protein. It has been previously demonstrated that different VO(2+)-nucleotide coordination environments exist for the Fe-protein that depend on pH and are distinguishable by EPR spectroscopy. After having studied the nitrogenase 31P and 23Na superhyperfine structure for this system by electron nuclear double resonance (ENDOR) spectroscopy (Petersen et al. 2008 in J Biol Inorg Chem. doi:10.1007/s00775-008-0360-0), we here report on the 1H-interactions with the nucleotide-bound metal center after substitution of the natural diamagnetic metal Mg2+ with paramagnetic oxo-vanadium(IV). ENDOR spectra show a number of resonances arising from interactions of the VO2+ ion with protons. In the presence of reduced Fe-protein and VO2+ ADP, at least three sets of nonexchangeable protons are detected. At low pH the superhyperfine couplings of most of these are consistent with proton interactions originating from the nucleotide. There is no indication of 1H-resonances that exchange in D2O at neutral pH and could be assigned to inner-sphere hydroxyl coordination. Exchangeable hydroxyl protons in the inner coordination sphere with reduced Fe-protein are only found in the low pH form; based on their hyperfine tensor components these have been assigned to an axially coordinated hydroxyl water molecule. The pH-dependent alterations of the proton couplings that exchange in D2O suggest that they are partially caused by a rearrangement in the local hydroxyl coordination environment of the metal center. These rearrangements especially affect the apical metal position, where an axially coordinated water present at low pH is absent at neutral pH. Oxidation of the Fe-protein induced substantial changes in the electron-nucleus interactions. This indicates that the oxidation state of the iron-sulfur cluster has an important effect on the metal coordination environment at the nucleotide binding site of the Fe-protein. The distinct VO(2+)-nucleotide coordination structures with ADP and ATP and the redox state of the [4Fe-4S] cluster imply that VO2+ has a critical influence on the switch regions of the regulatory protein, and, taken together, this provides a plausible explanation for the inhibitory action of VO2+.

Study of raw and thermally treated sepiolite from the Mantoudi area, Euboea, Greece

Raw and thermally treated sepiolites from the Mantoudi area, Euboea, Greece, were investigated by means of X-ray diffraction (XRD) in combination with thermo-gravimetric analysis (TG/DTG) and differential thermal analysis (DTA), as well as Fourier transform (FTIR) spectroscopy, in order to study the collapse of the sepiolite structure with increasing temperature. The main mineral constituent (>95%) is a well crystallized sepiolite. Quartz and dolomite occur in minor amounts. Calcination of the samples was carried out up to 350, 720 and 820°C, for 2 h, and ‘sepiolite dihydrite’, ‘sepiolite anhydrite’ and ‘enstatite’ were formed, respectively, as magnesium co-ordinated water and octahedrically co-ordinated hydroxyl groups, are removed and the dehydroxylated phase recrystallize to enstatite (MgSiO3). These structural and textural changes play an important role to the properties and uses of the studied sepiolites.

Bis[1,3-dihydroxy-2-hydroxymethyl-2-(5-nitro-2-oxidobenzylideneamino)propane-κ3N,O,O′]nickel(II) pyridine solvate

The NiII atom in the title complex, [Ni(C11H13N2O6)2]·C5H5N, is chelated by a terdentate Schiff base anion in a slightly octa­hedral geometry. One of the coordinated hydroxyl groups forms a hydrogen bond with the pyridine solvent mol­ecule. In the crystal structure, other hydroxyl groups are involved in inter­molecular hydrogen bonding, forming a two-dimensional layer.