Preparation of magnetite and its decomposition of water

The optimum conditions were studied for the formation of magnetite by the air oxidation of Fe(OH)2 suspensions. The cation-deficient magnetite (Fe3-δO4, δ>0) was obtained by the air (200mL/min) oxidation of Fe(OH)2 suspensions for 8- 25 h at 343 -358 K and NaOH/FeSO4=2.0 (mole ratio). The oxygen-deficient magnetite (Fe3+δO4, δ>0) was prepared through CO gas reduction of the cation-deficient magnetite at 563 K and its stableness at various temperatures and atomspheres was surveyed. The activity of decomposing water into hydrogen gas with oxygen-deficient magnetite at 563 K was studied and its relations to the oxygen-deficient degree and reaction temperature were investigated, respectively. The results show that the longer the time for magnetite being reduced by carbon monoxide, the higher the oxygen-deficient degree, and the more active its dedcomposition of water is. After reaction, oxygen (O2-) was taken away from water by oxygen-deficient magnetite, which converted to the cation-deficient magnetit     

Surface oxidation and water desorption of CdS

The surface oxidation and HP desorption of powder CdS were studied by means of X-ray photoetectron spectroscopy (XPS), quadrupole mass spectrometry (QMS) and in-situ FTIR. The results show that with the changes of surface composition and the elongation of store time of CdS there are four types of H2O thermally desorbed at different temperatures. It has also been found that through high-temperature air treatment for a short time the oxidized surface layer of CdS can prevent O2 and H2O in air from further attacking the inner CdS molecules.     

Bulk properties and hydration numbers of components of water–salt,water–urea,and water–urea–salt systems

With an increase in the concentration of additives, the hydration numbers of compounds decrease. Thus, in a saturated 54.6% solution, urea loses approximately 3/4 of the initial amount of water, forming an aquacomplex of the composition (NH₂)₂CO?H₂O. In a supersaturated 44% solution, the sodium chloride aquacomplex is dehydrated by 2/3, and in a supersaturated 67% solution, sodium sulfate is dehydrated by 5/6. The density of these solutions is 1.354÷1.360 g/cm³ (44% NaCl) and 1.800÷1.849 g/cm³ (67% Na₂SO₄). In a saturated urea solution, NaNO₃, NaCl, and Na₂SO₄ complexes lose 53÷55% of hydration water. It is shown that the interactions in the binary water–urea system somewhat increase the hydration number of the salts (structural hydration). The hydration water density, a structurally important characteristic, increases in the series of solutions of urea, NaNO₃, NaCl, and Na₂SO₄. In the same series of additives, the excess volume of binary water–urea and water–salt systems becomes more negative.     

Mechanisms and solubility equations of gas dissolving in water

The two mechanisms of gas dissolving in water, interstice filling and aquation, are proposed. General equations of gas solubility have been deduced from the mechanisms and experimental observations. Dependence of Henry's coefficient on temperature, pressure, aquation equilibrium constant and gas molecular wlume is discussed. The theoretical equations were verified by experimental data, which shows that the theoretical results of the solubility of methane are in good agreement with the experimental data in the range of 20 -160℃ and under a pressure of less than 60 MPa.     

Structure and property of the hydrogen bonding complex between triazines and water

The study of the intermolecular interactions that drive the solvation of six-membered nitrogenated aromatic rings is of particular importance since they are known to constitute key building blocks of pro- teins and nucleotides[1―5]. The investigation of the 1:1 adduct of these molecules with water will be the first step in the understanding of such interactions. These molecules possess two different proton-acceptor sites: the ring π cloud and the lone pairs of electrons on the nitrogen atoms…     

Characteristics of sodium alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures

Alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures were prepared and tested. The sodium alginate membrane was water soluble and mechanically weak but it showed promising performance for the pervaporation dehydration. To control the water solubility the sodium alginate membrane was crosslinked ionically using various divalent and trivalent ions. Among them the alginate membrane crosslinked with Ca²⁺ ion showed the highest pervaporation performance in terms of the flux and separation factors.     

Partition coefficients of ω-phenylalkanols between water and liposome membranes of phospholipids

For the liposome of two types of phospholipids (zwitterionic dipalmitoyl-phosphatidylcholine (DPPC) and anionic dimyristoylphosphatidic acid (DMPA)), the partition coefficient K _X for partition of homologous -phenylalkanols (C₆H₅(CH₂) _mp OH; m _p =0–8) between bulk water and the liposome membrane was determined on the basis of the gel to liquid crystalline phase transition temperature T _m of the liposome membrane. The plot of log K _X vs. m _p gave a break at m _p =7 for both phospholipids, and a second break at m _p =4 was observed for DPPC. The local polarity of the surface region and the orderliness of phospholipid molecules in the liposome membrane were estimated from ESR spectra of two spin probes solubilized in the membrane. The results suggest that the hydration of DPPC liposome membrane is relatively restricted to its surface region, but for DMPA the hydration spreads not only along the surface but also to the inside of the membrane. The main factor controlling the partitioning of the alkanols is the local polarity. The higher alkanols (m _p =7, 8) are solubilized not only in the liquid crystalline phase but also in the gel phase, although the other lower alkanols are solubilized in the liquid phase only.     

DSC study of phase transition of anhydrous phospholipid DHPC and influence of water content

The phase transition behavior of 1,2-di-n-heptadecanoyl phosphatidylcholme (DHPC)with and without water has been studied by use of differential scanning calorimetry It was found by experiment that the glass transition occurred at first during the first heating of a sample of DHPC without water and then the sample underwent melting as an ordinary crystal.Therefore the sample of DHPC without water was a glassy crystal However,the DHPC sample crystallizing from melt was an ordinary crystal From the relationship between the total melting enthalpy Qf of freezable water and the water content h,it was concluded that the water contained in the DHPC samples might exist in three states recognizable thermodynamically.The water in the first state was an unfreezable water It was the water bound directly with the head groups of the phospholipid,i.e.the primary hydration water Every head group might bind seven such molecules of water.The water in the second state was the secondary hydration water,us melt ing point was     

Question of “bound” and “free” water

Summary The physical meaning of the correction for the binding of water by ions is clarified, and an equation is proposed for its accurate calculation.     

Validation of ELISA methods for search and quantification of β-n-methylamino-l-alanine in water and fish tissue

Water basins with low hydrodynamic activities can promote the growth and increase in algal biomass due to eutrophication, and toxic cyanobacteria species might then produce metabolites hazardous to human health. Over the last decade, a neurotoxic non-protein amino acid, (2S)-2-amino-3-(methylamino) propanoic acid, known as β-N-methylamino-L-alanine (BMAA), has become of particular interest because it has been hypothesised to be involved in progressive human neurodegenerative pathologies. This toxin can be found both in algal cells and free in water, as well as in some foods of aquatic and terrestrial origin. Analytical methods used for BMAA are often based on chromatography coupled with mass spectrometry, although these techniques involve long and expensive analysis. As the availability of a faster and cheaper screening method would be useful, we tested the only available Enzyme-Linked Immunosorbent Assay kit for BMAA evaluation and validated methods to verify their reliability for the analysis of water and fish muscle. For both matrices, we determined adequate selectivity and repeatability (relative standard deviation < 6%), with recoveries from 70% to 83% at the tested spiking levels; the methods were also robust. These data appear in contrast to a previous evaluation carried out on the same kit in 2013, although this might depend on an improvement to the kit performance. We can conclude that a preliminary determination of BMAA in water, and also in fish tissue after an adequate extraction procedure, can be performed efficiently with the tested kit, which provides for easier monitoring of this dangerous toxin.     

Temperatures of liquid–liquid separation and excess molar volumes of {N-methylpiperidine–water} and {2-methylpiperidine–water} systems

Partial miscibility in binary systems {N-methylpiperidine–water} and {2-methylpiperidine–water} was studied. The temperatures of liquid–liquid separation were determined as function of composition using both calorimetric technique and phase equilibrium cell. The densities of {amine–water} mixtures were determined in the domain of total miscibility at temperatures between 288 K and 338 K. Excess molar volumes were derived from experimental density data and fit to a Redlich–Kister polynomial.     

Bubble points of hydrogen chloride–water–isopropanol and hydrogen chloride–water–isopropanol–benzene systems and liquid–liquid equilibria of hydrogen chloride–water–benzene and hydrogen chloride–water–isopropanol–benzene systems

Bubble points of the HCl–water–isopropanol and the HCl–water–isopropanol–benzene systems and liquid–liquid equilibria (LLE) of the HCl–water–benzene and the HCl–water– isopropanol–benzene systems were measured at 25–85°C and 30–70°C, respectively. The electrolyte nonrandom two-liquid model proposed by Chen et al. [C.-C. Chen, H.I. Britt, J.F. Boston, L.B. Evans, AIChE J. 28 (1982) 588–596] can satisfactorily correlate bubble points and liquid–liquid equilibria of the present mixed-solvent electrolyte systems over the entire range of temperature and concentrations using only binary adjustable parameters.     

Partition coefficients of ω-phenylalkanols between water and sodium deoxycholate micelles

The partition coefficient of -phenylalkanols [C₆H₅(CH₂)_mpOH, m _p =3–6] between water and micelles of sodium deoxycholate (NaDC) has been determined by a differential spectroscopic method at 25°C. The linear dependence of thestandard free energy change of transfer calculated from the partition coefficient on the alkyl chain length of the alkanols (m _p 4) yields the standard free energy change per methylene group [G^o(CH₂)]. G^o(CH₂) value for the present system, –3.21 kJ-mol ^–1 is larger in magnitude than that for sodium dodecylsulfate (SDS)--phenylalkanol system, –2.40 kJ-mol ^–1 . The result indicates that the alkyl chain of -phenylalkanols has higher affinity to NaDC micelles than to SDS micelles although the molecular structure of NaDC is more rigid and bulkier than that of SDS and the aggregation number of micelles of the former is much smaller than that of micelles of the latter. On the basis of the linear relation between the effect of added -phenylalkanols on the critical micelle concentration of NaDC (–dC_cmc/dC_a) and the partition coefficient, it is found that the degree of ionization of NaDC micelles is not influenced by solubilization of -phenylalkanols into the micelles.     

A quick and regioselective access of spirooxindole-oxazoline by reaction of isatin and isocyanoacetate “on water”

A greener, rapid and regioselective “on water” synthesis of spirooxindole-oxazoline by the reaction of isatin and isocyanoacetate at room temperature is described. The developed protocol has the advantage of being atom-economical, eco-friendly, and benign reaction conditions. Broader substrate scope, experimentally simple procedures, and easy purification of products with high yield further make this method attractive. The synthesized compounds have been fully characterized with spectral analysis.     

Structures of an infinite helical water chain and discrete lattice water in metal–organic framework structures

Two supramolecular complexes Ni[(Py)₂C(OH)₂]₂·(CH₃COO)₂·4H₂O 1 and Co[(Py)₂C(OH)₂]₂·(CH₃COO)₂·2H₂O 2 have been synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR spectra, and X-ray single-crystal diffraction. The X-ray diffraction analysis indicates that the center metal (Ni²⁺ and Co²⁺) ions having the same coordination environments are chelated by two pyridyl N atoms and a hydroxyl O atom of the gem-diol ligand in an octahedral geometry. In 1, the lattice water molecules form infinite single helical chains, while in 2, two lattice water molecules are discrete. In their crystal structures, intermolecular O–H···O and C–H···O hydrogen bonds form an extensive three-dimensional network, which consolidates the crystal packing.     

Arenesulfonylation of dl-serine, l-proline, l-threonine, and dl-methionine in systems 1,4-dioxane—water and propan-2-ol—water

Kinetics of interaction of dl-serine, l-proline, l-threonine, and dl-methionine with 3-nitrobenzenesulfonyl chloride in water (40%)—1,4-dioxane and water (40%)—isopropanol mixed solvents was studied spectrophotometrically at 298 K. The main reactive form of α-amino acids is shown to be anionic. Under conditions of arenesulfonylation, the basicity of α-amino acids is crucial in determining the reaction rate. Arenesulfonylation rate constants are 20—50 times lower than the constants of N-acylation of the same α-amino acids with benzoyl chloride and 10⁴–10⁵ times higher than the rate constants of their reactions with benzoic acid 4-nitrophenyl ester.     

Poly(vinyl methyl ether) hydrogels at temperatures below the freezing point of water—molecular interactions and states of water

Water interacting with a polymer reveals a number of properties very different to bulk water. These interactions lead to the redistribution of hydrogen bonds in water. It results in modification of thermodynamic properties of water and the molecular dynamics of water. That kind of water is particularly well observable at temperatures below the freezing point of water, when the bulk water crystallizes. In this work, we determine the amount of water bound to the polymer and of the so-called pre-melting water in poly(vinyl methyl ether) hydrogels with the use of Raman spectroscopy, dielectric spectroscopy, and calorimetry. This analysis allows us to compare various physical properties of the bulk and the pre-melting water. We also postulate the molecular mechanism responsible for the pre-melting of part of water in poly(vinyl methyl ether) hydrogels. We suggest that above ?60 °C, the first segmental motions of the polymer chain are activated, which trigger the process of the pre-melting.     

Solid and liquid phase equilibria and solid-hydrate formation in binary mixtures of water with amines

Solid and liquid phase diagrams have been constructed for {water+triethylamine,or+N,N-dimethylformamide(DMF) or+N,N-dimethlacetamide (DMA)} Solid-hydrates form with the empirical formulae N(C2H5)3 3H2O,DMF 3H2O,DMF 2H2O,DMA 3H2O and (DMA)2 3H2O.All are congruently melting except the first which melts incongruently.The solid-hydrate formation is attributed to hydrogen bond.The results are compared with the references