nH 2O Research Articles

Proton relay network in P450cam formed upon docking of putidaredoxin.

Cytochromes P450 are versatile heme-based enzymes responsible for vital life processes. Of these, P450cam (substrate camphor) has been most studied. Despite this, precise mechanisms of the key O─O cleavage step remain partly elusive to date; effects observed in various enzyme mutants remain partly unexplained. We have carried out extended (to 1000 ns) MM-MD and follow-on quantum mechanics/molecular mechanics computations, both on the well-studied FeOO state and on Cpd(0) (compound 0). Our simulations include (all camphor-bound): (a) WT (wild type), FeOO state. (b) WT, Cpd(0). (c) Pdx (Putidaredoxin, redox partner of P450)-docked-WT, FeOO state. (d) Pdx-docked WT, Cpd(0). (e) Pdx-docked T252A mutant, Cpd(0). Among our key findings: (a) Effect of Pdx docking appears to go far beyond that indicated in prior studies: it leads to specific alterations in secondary structure that create the crucial proton relay network. (b) Specific proton relay networks we identify are: FeOO(H)⋯T252⋯nH 2 O⋯D251 in WT; FeOO(H)⋯nH 2 O⋯D251 in T252A mutant; both occur with Pdx docking. (c) Direct interaction of D251 with -FeOOH is, respectively, rare/frequent in WT/T252A mutant. (d) In WT, T252 is in the proton relay network. (e) Positioning of camphor appears significant: when camphor is part of H-bonding network, second protonation appears to be facilitated.

Molecular structures of gas-phase neutral morpholine and its monohydrated complexes: experimental and theoretical approaches

Morpholine (NH(CH2CH2)2O) is a typical six-membered aliphatic heterocyclic compound.

Silicon isotope composition of diatoms as a paleoenvironmental proxy in Lake Huguangyan, South China

Silicon is essential for the growth of diatoms, which utilize dissolved silicic acid in lake water and form opaline silica (SiO 2· nH 2O). During the uptake of dissolved silicic acid, there is a preferential incorporation of light silicon isotope ( 28Si) into biogenic silica, resulting in the enrichment of heavy silicon isotope ( 30Si) in dissolved silicic acid. The silicon isotope composition of diatom silica (δ 30Si diatom) may thus record changes in the percentage utilization of dissolved silicic acid by diatoms, which can be then related to other aspects of climate/environment. With the aim of exploring the potential of δ 30Si diatom as an indicator of lacustrine environment, here we made the first measurements of δ 30Si diatom in the sediment core from Lake Huguangyan, a closed crater lake in China. The result shows that δ 30Si diatom varies from −0.6‰ to 1.1‰ and displays broad similarities to variations in contents of biogenic silica and organic carbon throughout the sediment core. δ 30Si diatom is a reliable paleotemperature proxy in Lake Huguangyan, which is supported by good correlation between δ 30Si diatom and available temperature records. Heavier δ 30Si diatom indicates greater dissolved silicic acid utilization at higher temperature while lighter δ 30Si diatom reflects decreased utilization at lower temperature. The most negative δ 30Si diatom values in the sediment core occur between AD 1580 and 1920, which suggests AD 1580–1920 was the coldest period in Lake Huguangyan over the past 2000 years, thus providing evidence for the existence of the LIA in tropical South China. There are few means by which to reconstruct the history of temperature changes in tropical terrestrial region. δ 30Si diatom, in this study, has proven to be a new promising paleotemperature proxy in lacustrine sediments, and may play important role in reconstructing past temperature changes at low latitude in the future. Detailed investigations on the silicon isotopes of diatoms in more lakes would be desirable in further research.

Nano-structured birnessite prepared by electrochemical activation of manganese(III)-based oxides for aqueous supercapacitors

Powdery Mn 3O 4 and Mn 2O 3 electrodes with carbon and binding polymer were electrochemically stimulated and activated by successive potential cycles in a mild aqueous electrolyte containing alkali sulfate. The activation of the manganese oxides is affected by the electrode material, milling treatment, potential region, and electrolyte solution. It is found that the ball-milled Mn 3O 4 electrode demonstrated the highest specific capacitance, 190 F g −1, in 1 mol dm −3 Na 2SO 4 aqueous solution due to the phase transition from Mn 3O 4 to electrochemically active birnessite, Na y MnO 2· nH 2O. The increase in capacitance originated from the formation of birnessite possessing highly porous morphology. The nano-structured birnessite demonstrated long cycle life of about 2000 cycles with acceptable capacitance retention of 190–160 F g −1. The birnessite was applied as positive electrode of the asymmetric electrochemical capacitor with activated carbon negative electrode in the mild aqueous solution.

Thermodynamic modeling of solid solutions between monosulfate and monochromate 3CaO • Al 2O 3 • Ca[(CrO 4) x(SO 4) 1-x] • nH 2O

In hydrated cement paste AFm-phases are regarded to play an important role in the binding of the toxic contaminant chromate through isomorphic substitution with sulfate. Solid solutions formation can lower the solubility of the solids, thus reducing chromate leaching concentrations. Solid solutions between monosulfate and monochromate were synthesized and characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and inductive coupled plasma optical emission spectroscopy (ICP-OES). Based on the measured ion concentrations in solution total solubility products of the solid solution series were determined. For pure monochromate a logK = − 28.4 ± 0.7 was determined. Results from solid and solution analysis showed that limited solid solutions exist. Based on XRD diffractograms a solid solution with a miscibility gap 0.15 < Crx < 0.85 with a dimensionless Guggenheim parameter of 2.43 was proposed.

Facile one-pot synthesis and luminescence of hexagonal TbPO 4· nH 2O hollow spheres

Monodisperse hexagonal TbPO 4· nH 2O hollow spheres were successfully obtained by utilizing Tb(OH)CO 3 colloidal spheres as the precursor and NH 4H 2PO 4 as the phosphorus source through the hydrothermal process. The obtained hollow spheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), respectively. They have the average diameter of 200 nm. There are a number of tiny nanorods with the length of about 60 nm on the surface of the spheres. The obtained TbPO 4 hollow spheres exhibit green color emission from 5D 4 − 7F J ( J = 6, 5, 4, 3) transitions of the Tb 3+ ions, which are expected to be applied in display applications and biological applications.

Supramolecular networks through second-sphere coordination based on 1D metal-4,4′-dipyridyldisulfide coordination polymers and hydrogenfumarate or sulfonate anions

Four hydrogen-bonded assemblies of formula [M(dpds) 2(OH 2) 2]A 2· nH 2O (A = anion) are described. These assemblies result from the second-sphere coordination interactions between the 1D coordination polymers [M(dpds) 2(OH 2) 2] 2+, M = Zn(II) and Cu(II), dpds = 4,4′-dipyridyldisulfide, and the pyridine-3-sulfonate (3pySO 3 −) or hydrogenfumarate (Hfum −) anions. Significantly, supramolecular structural variations are observed depending on the presence of water lattice molecules, which formed discrete aggregates when the Hfum − anion was used. The effects of geometrical variations in the building blocks are also evident on using Jahn–Teller-distorted divalent Cu(II) ions or regular octahedral species based on Zn(II) ions. The second-sphere effects on the stabilization of the compounds are illustrated by TGA experiments.

Thermal expansion in 3 d-metal Prussian Blue Analogs—A survey study

We present a comprehensive study of the structural properties and the thermal expansion behavior of 17 different Prussian Blue Analogs (PBAs) with compositions M II 3[( M′) III(CN) 6] 2· nH 2O and M II 2[Fe II(CN) 6]· nH 2O, where M II=Mn, Fe, Co, Ni, Cu and Zn, ( M′) III=Co, Fe and n is the number of water molecules, which range from 5 to 18 for these compounds. The PBAs were synthesized via standard chemical precipitation methods, and temperature-dependent X-ray diffraction studies were performed in the temperature range between −150 °C (123 K) and room-temperature. The vast majority of the studied PBAs were found to crystallize in cubic structures of space groups Fm3̄ m, F4̄3 m and Pm3̄ m. The temperature dependence of the lattice parameters was taken to compute an average coefficient of linear thermal expansion in the studied temperature range. Of the 17 compounds, 9 display negative values for the average coefficient of linear thermal expansion, which can be as large as 39.7× 10 −6 K −1 for Co 3[Co(CN) 6] 2·12H 2O. All of the M II 3[Co III(CN) 6] 2· nH 2O compounds show negative thermal expansion behavior, which correlates with the Irving–Williams series for metal complex stability. The thermal expansion behavior for the PBAs of the M II 3[Fe III(CN) 6] 2· nH 2O family are found to switch between positive (for M=Mn, Co, Ni) and negative ( M=Cu, Zn) behavior, depending on the choice of the metal cation ( M). On the other hand, all of the M II 2[Fe II(CN) 6]· nH 2O compounds show positive thermal expansion behavior.

Synthesis, structure and magnetism of a S-shaped multi-iron substituted arsenotungstate containing a trivacant Keggin [B- α-As VW 9O 34] 9− and a hexavacant Keggin [ α-As VW 6O 26] 11− fragments

A S-shaped multi-iron substituted arsenotungstate [enH 2] 2[( α-H 2As VW 6O 26)Fe 3(H 2O)(B- α-H 4As VW 9O 34)] 2[Fe] 2·8H 2O ( 1) (en=ethylenediamine) has been prepared by reaction of K 14[As 2 IIIW 19O 67(H 2O)]· nH 2O with Fe 2(SO 4) 3· xH 2O under hydrothermal conditions and structurally characterized by elemental analyses, IR spectra, UV spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. The skeleton of 1 consists of two asymmetric sandwich-type subunits [( α-H 2As VW 6O 26)Fe 3(H 2O)(B- α-H 4As VW 9O 34)] 5− linked by a di-Fe III cluster. Moreover, magnetic susceptibility measurements demonstrate that 1 indicates the antiferromagnetic coupling interactions within Fe III centers with the best-fitting set of parameters of J 1=−7.07 cm −1, J 2=−0.45 cm −1 and g=2.05, which are generated by the addition of the expressions of the molar susceptibilities of two tri-Fe III clusters and one di-Fe III cluster derived from for spin pairs coupled through the isotropic exchange interactions.

Synthesis of transparent aqueous sols of colloidal layered niobate nanocrystals at room temperature

Transparent aqueous sols of colloidal tetramethylammonium niobate nanocrystals were synthesized by mixing tetramethylammonium hydroxide (TMAOH), niobium ethoxide, and water at TMAOH/Nb ⩾ 0.7 at room temperature. The X-ray diffraction patterns of the thin films prepared by evaporating the colloidal solutions on a glass substrate indicated that the colloidal niobate had a layered crystalline structure. Two types of layered structures are known as a layered niobate, i.e. M 4Nb 6O 17· nH 2O and MNb 3O 8 (M = H, H 3O, or alkaline metal). Raman spectra and electron diffraction suggested that the niobate nanocrystals were similar in crystal structure to M 4Nb 6O 17· nH 2O compounds. Moreover, when niobium oxide thin films were fabricated from the niobate colloidal solutions by the sol–gel method, oriented T-Nb 2O 5 thin films, whose c-axis was parallel to the substrate surface, were obtained. The orientation of the thin films was probably attributed to the layered structure of the colloidal niobate nanocrystals.

Preparation and luminescence characterization of new carbonate (Y 2(CO 3) 3· nH 2O:Eu 3+) phosphors via the hydrothermal route

A new Eu 3+-activated Y 2(CO 3) 3· nH 2O phosphor was successfully prepared via the hydrothermal process using urea as a reaction agent. Y 2(CO 3) 3· nH 2O:Eu 3+ phosphors displayed an intense red emission at 615 nm due to the 5D 0 → 7F 2 transition of Eu 3+ ions under 254 nm excitation. The intensity of this emission was significantly increased with a rise in the hydrothermal temperatures. The study of photoluminescence properties demonstrated that Y 3+ ions were replaced by Eu 3+ ions in the host lattice at the 9-coordination sites. With an increase in heating temperatures, the morphology of Y 2(CO 3) 3· nH 2O:Eu 3+ powders changed from a spherical to a rod-like shape. Calcination at elevated temperatures resulted in thermal decomposition of Y 2(CO 3) 3· nH 2O:Eu 3+ to form Y 2O 3:Eu 3+. The formed Y 2O 3:Eu 3+ powder exhibited a rod-like morphology with an intense red emission.

Thermal and luminescence characterization of lanthanide 2,6-naphthalenedicarboxylates series

The lanthanide 2,6-naphthalenedicarboxylates series of the formulas Ln 2(ndc) 3·nH 2O, where Ln = lanthanides from La(III) to Lu(III); ndc – C 10H 6(COO) 2 2−; n = 4, 4.5 or 5 have been prepared by the precipitation method. All obtained products were examined and characterized by elemental analysis, FTIR spectroscopy, simultaneous thermal analyses TG-DSC and TG-FTIR, X-Ray diffraction patterns as well as luminescence measurements. The crystalline compounds form three isostructural groups: Ce–Sm; La and Eu–Dy; Ho–Lu. In all complexes, the ndc 2− ligand appears in the deprotonated form. Heating of the complexes resulted in the multi-steps decomposition process. The dehydration process leads to the formation of stable crystalline Ln 2ndc 3 compounds which further decompose to the corresponding lanthanide oxides (air atmosphere). In argon atmosphere they decompose with releasing of water, carbon oxides and naphthalene molecules. The luminescence properties of Eu(III), Nd(III), Tb(III) and Er(III) complexes were investigated. The complexes of Eu(III) and Tb(III) emitted red and green light when excited by ultraviolet light whereas Nd(III) and Er(III) display emissions in the NIR region.

Syntheses, structures and properties of two cadmium compounds containing neutral or in situ protonized 1,4-diazabicyclo[2.2.2]octane

Reaction of Cd(Ac) 2, 1,4-diazabicyclo[2.2.2]octane (DABCO) and biphenyl-2,2′-dicarboxylic acid or biphenyl-4,4′-dicarboxylic acid, two new cadmium complexes, namely molecular quadrangle [Cd 2(2,2′-BPDC) 2(Ac) 2(DABCOH) 2]·2H 2O ( 1) and one dimension (1-D) chain [Cd(Ac) 2(DABCO)(H 2O)] n ·2 nH 2O ( 2), have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. The solution–gel–solution transformation course to crystallize 2 was captured. Through the alternately hydrogen bonds between coordinated Ac − and lattice H 2O, both 1 and 2 give rise to a three-dimensional supramolecular structures. In room temperature, 1 displays intense blue fluorescent emission derived from ligand-to-metal change transfer (LMCT).

Self-assembled light lanthanide oxalate architecture with controlled morphology, characterization, growing mechanism and optical property

Flower-like Sm 2(C 2O 4) 3·10H 2O had been synthesized by a facile complex agent assisted precipitation method. The flower-like Sm 2(C 2O 4) 3·10H 2O was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, thermogravimetry–differential thermal analysis and photoluminescence. The possible growth mechanism of the flower-like Sm 2(C 2O 4) 3·10H 2O was proposed. To extend this method, other Ln 2(C 2O 4) 3· nH 2O (Ln = Gd, Dy, Lu, Y) with different morphologies also had been prepared by adjusting different rare earth precursors. Further studies revealed that besides the reaction conditions and the additive amount of complex agents, the morphologies of the as-synthesised lanthanide oxalates were also determined by the rare earth ions. The Sm 2(C 2O 4) 3·10H 2O and Sm 2O 3 samples exhibited different photoluminescence spectra, which was relevant to Sm 3+ energy level structure of 4f electrons. The method may be applied in the synthesis of other lanthanide compounds, and the work could explore the potential optical materials.

Permanganate oxidation of arsenic(III): Reaction stoichiometry and the characterization of solid product

Permanganate (MnO 4 −) has widely been used as an effective oxidant for drinking water treatment systems, as well as for in situ treatment of groundwater impacted by various organic contaminants. The reaction stoichiometry of As(III) oxidation by permanganate has been assumed to be 1.5, based on the formation of solid product, which is putatively considered to be MnO 2(s). This study determined the stoichiometric ratio (SR) of the oxidation reaction with varying doses of As(III) (3–300 μM) and MnO 4 − (0.5 or 300 μM) under circumneutral pH conditions (pH 4.5–7.5). We also characterized the solid product that was recovered ∼1 min after the oxidation of 2.16 mM As(III) by 0.97 mM MnO 4 − at pH 6.9 and examined the feasibility of secondary heterogeneous As(III) oxidation by the solid product. When permanganate was in excess of As(III), the SR of As(III) to Mn(VII) was 2.07 ± 0.07, regardless of the solution pH; however, it increased to 2.49 ± 0.09 when As(III) was in excess. The solid product was analogous to vernadite, a poorly crystalline manganese oxide based on XRD analysis. The average valence of structural Mn in the solid product corresponded to +III according to the splitting interval of the Mn3s peaks (5.5 eV), determined using X-ray photoelectron spectroscopy (XPS). The relative proportions of the structural Mn(IV):Mn(III):Mn(II) were quantified as 19:62:19 by fitting the Mn2p 3/2 spectrum of the solid with the five multiplet binding energy spectra for each Mn valence. Additionally, the O1s spectrum of the solid was comparable to that of Mn-oxide but not of Mn-hydroxide. These results suggest that the solid product resembled a poorly crystalline hydrous Mn-oxide such as (Mn II 0.19Mn III 0.62Mn IV 0.19) 2O 3· nH 2O, in which Mn(II) and Mn(IV) were presumably produced from the disproportionation of aqueous phase Mn(III). Thermodynamic calculations also show that the formation of Mn(III) oxide is more favorable than that of Mn(IV) oxide from As(III) oxidation by permanganate under circumneutral pH conditions. Arsenic(III), when it remained in the solution after all of the permanganate was consumed, was effectively oxidized by the solid product. This secondary heterogeneous As(III) oxidation consisted of three steps: sorption to and oxidation on the solid surface and desorption of As(V) into solution, with the first step being the rate-limiting process as observed in As(III) oxidation by various Mn (oxyhydr)oxides reported elsewhere. We also discussed a potential reaction pathway of the permanganate oxidation of As(III).

Preparation and characterization of Tb 3+ and Tb(sal) 3· nH 2O doped PC:PMMA blend

Tb doped polycarbonate:poly(methyl methacrylate) (Tb–PC:PMMA) blend was prepared with varying proportions of PC and PMMA. Thermal and spectroscopic properties of the doped polymer have been investigated employing Fourier Transform Infrared (FTIR) absorption and differential scanning calorimetric (DSC) techniques. PC:PMMA blend (with 10 wt% PC and 90 wt% PMMA) shows better miscibility. Optical properties of the dopant Tb 3+ ions have been investigated using UV–vis absorption and fluorescence excited by 355 nm radiation. It is seen that luminescence intensity of Tb 3+ ion depends on PC:PMMA ratio and on Tb 3+ ion concentration. Concentration quenching is seen for TbCl 3·6H 2O concentration larger than 4 wt%. Addition of salicylic acid to the polymer blend increases the luminescence from Tb 3+ ions. Luminescence decay curve analysis affirms the non-radiative energy transfer from salicylic acid to Tb 3+ ions, which is identified as the reason behind this enhancement.

Fluctuation kinetics of the hopping fluorescence quenching in disordered solid solutions: A theoretical model and experimental evidence

Fluctuation kinetics of the hopping fluorescence quenching in disordered solid solutions is investigated for the first time. Measurements were made in the chelated complexes of rare-earth ions [Y 1− x Tb x (pyca) 3(H 2O) 2] nH 2O used as chromophore. The Tb 3+ ions and the OH --ions of unbounded water molecules appear as fluorescent donors and randomly distributed acceptors, respectively, with the dipole–dipole interaction between them. The measured fluctuation kinetics is the kinetics of the Förster type but with larger decay amplitude. It begins almost immediately after the initial static stage of quenching, and lasts for the entire interval of measurements leaving no room at all for the well-known exponential kinetics with constant rate. Proposed theoretical explanation of the phenomenon is based on the solution of the closed many-particle integral equation for the observable kinetics of hopping fluorescence quenching. The methods for determination of the energy transfer microparameters by the measured fluorescence quenching kinetics are discussed.

Synthesis and characterization of heterobimetallic molybdenum and nickel complexes derived from polyfunctional disalicylaldehyde oxaloyldihydrazone

Heterobimetallic nickel and molybdenum complexes of the composition [Ni(L)MoO 2(A) 4]· nH 2O (A = H 2O (1), py (2), 2-pic (3), 3-pic (4), and 4-pic (5); n = 0, 2) and [Ni(L)(MoO 2)(BB) 2](BB = bpy (6) and (phen (7)) have been synthesized from the multidentate ligand disalicylaldehyde oxaloyldihydrazone (H 4L) in methanol. The composition of the complexes has been established based on data obtained from elemental analyses, thermoanalytical, mass spectral and molecular weight studies. The probable structures of the complexes have been discussed in the light of molar conductance, magnetic moment data and electronic, EPR and infrared spectral studies. In all of the complexes, the dihydrazone is present in enol form and coordinates to the metal centre as a tetrabasic hexadentate ligand. All of the complexes are normal paramagnetic to the extent of two unpaired electrons per nickel atom. The μ eff values for the complexes lying in the region 2.87–3.07 B.M. are consistent with the octahedral stereochemistry of nickel(II) in the heterobimetallic complexes. The EPR and electronic spectral data also support the distorted octahedral stereochemistry of the nickel(II) centre. Both nickel and molybdenum have octahedral geometry in the complexes.

New complexes of lanthanide Ln(III), (Ln = La, Sm, Gd, Er) with Schiff bases derived from 2-furaldehyde and phenylenediamines

Some new Schiff bases derivates from 2-furaldehyde and phenylenediamines (L 1–3) and their complexes with lanthanum (La), samarium (Sm), gadolinium (Gd) and erbium (Er) have been synthesized. These complexes with general formula [Ln(L 1–3) 2(NO 3) 2]NO 3· nH 2O (Ln = La, Sm, Gd, Er) were characterized by elemental analysis, UV–Vis, FT-IR and fluorescence spectroscopy, molar conductivity and thermal analysis. The metallic ions were found to be eight coordinated. The emission spectra of these complexes indicate the typical luminescence characteristics of the Sm(III), La(III), Er(III) and Gd(III) ions.

Internally consistent thermodynamic data for metal divalent sulphate hydrates

Divalent metal sulphate hydrates (M 2+SO 4· nH 2O) represent a characteristic mineral group for the surface environments of the Earth. Generally, they change their hydration state in response to the local temperature and humidity conditions — n decreases as the relative humidity is decreased or temperature is increased. Here, using mathematical programming (MAP) techniques, we derived standard thermodynamic values consistent both with calorimetric data taken from the literature and previously published temperature humidity brackets obtained by reversal experiments for several minerals of this group: rozenite (FeSO 4· 4H 2O), melanterite (FeSO 4· 7H 2O), bianchite (ZnSO 4· 6H 2O), goslarite (ZnSO 4· 7H 2O), retgersite (NiSO 4· 6H 2O), morenosite (NiSO 4· 7H 2O), moorhouseite (CoSO 4· 6H 2O), bieberite (CoSO 4· 7H 2O), bonattite (CuSO 4· 3H 2O), and chalcanthite (CuSO 4· 5H 2O). The most significant changes appeared in the Fe 2+ system. Therefore, the available data and the resulting phase diagrams are discussed in more detail — the recommended standard values for melanterite and rozenite are: Rozenite : Δ f H 0 298 = − 2128 . 89 kJ mol − 1 , S 0 298 = 281 . 52 J mol − 1 K − 1 Melanterite : Δ f H 0 298 = − 3 0 14 . 39 kJ mol − 1 , S 0 298 = 4 0 9 . 29 J mol − 1 K − 1 .