Interlamellar Water Molecules Research Articles

Isomorphic Insertion of Ce(III)/Ce(IV) Centers into Layered Double Hydroxide as a Heterogeneous Multifunctional Catalyst for Efficient Meerwein-Ponndorf-Verley Reduction.

The development of highly active acid-base catalysts for transfer hydrogenations of biomass derived carbonyl compounds is a pressing challenge. Solid frustrated Lewis pairs (FLP) catalysis is possibly a solution, but the development of this concept is still at a very early stage. Herein, stable, phase-pure, crystalline hydrotalcite-like compounds were synthesized by incorporating cerium cations into layered double hydroxide (MgAlCe-LDH). Besides the insertion of well-isolated cerium centers surrounded by hydroxyl groups, the formation of hydroxyl vacancies near the aluminum centers, which were formed by the insertion of cerium centers into the layered double hydroxides (LDH) lattice, was also identified. Depending on the initial cerium concentration, LDHs with different Ce(III)/Ce(IV) ratios were produced, which had Lewis acidic and basic characters, respectively. However, the acid-base character of these LDHs was related to the actual Ce(III)/Ce(IV) molar ratios, resulting in significant differences in their catalytic performance. The as-prepared structures enabled varying degrees of transfer hydrogenation (Meerwein-Ponndorf-Verley MPV reduction) of biomass-derived carbonyl compounds to the corresponding alcohols without the collapse of the original lamellar structure of the LDH. The catalytic markers through the test reactions were changed as a function of the amount of Ce(III) centers, indicating the active role of Ce(III)-OH units. However, the cooperative interplay between the active sites of Ce(III)-containing specimens and the hydroxyl vacancies was necessary to maximize catalytic efficiency, pointing out that Ce-containing LDH is a potentially commercial solid FLP catalysts. Furthermore, the crucial role of the surface hydroxyl groups in the MPV reactions and the negative impact of the interlamellar water molecules on the catalytic activity of MgAlCe-LDH were demonstrated. These solid FLP-like catalysts exhibited excellent catalytic performance (cyclohexanol yield of 45%; furfuryl alcohol yield of 51%), which is competitive to the benchmark Sn- and Zr-containing zeolite catalysts, under mild reaction conditions, especially at low temperature (T = 65 °C).

A novel intumescent flame-retardant to inhibit the spontaneous combustion of coal

The present paper proposes an intumescent flame-retardant, which is suitable for the entire process of spontaneous combustion of coal. Scanning electron microscopy (SEM), simultaneous thermal analysis, in situ FTIR, and temperature programmed experiment were adopted to analyze its inhibiting effect and mechanism. The results indicate that the flame-retardant can play good inhibitory effects during all stages of coal oxidation and decomposition. In the low-temperature stage of 30–120 °C, the flame-retardant carries a lot of water and the surface temperature of coal is reduced since the evaporation of water removes heat. Meanwhile, the hydroxyl groups in the flame-retardant can connect with the -COO- groups on the surface of coal through hydrogen bonds, and enhance the stability of coal. With the temperature increase, some interlamellar water molecules in Mg-Al-CO3 layered double hydroxides (LDHs) are removed, which reduces the surface temperature of coal. When the temperature is higher than 170 °C, the IFR/LDH undergoes alcholysis and expands, releasing a large amount of non-flammable gas to dilute the oxygen around coal. When the temperature reaches 300 °C, the expanded foam layer is carbonized and forms a porous char layer, thereby inhibiting the combustion. The CO release of coal sample with flame retardant reduces significantly. The temperature with the maximum weight loss rate increases by 50–70 °C, while the heat release reduces by 11.1–24.2%. After calcination at 500 °C for 30 min, the carbon residue is more than 1.6 times that of the untreated coal sample.

Self-Assembling Behavior of Glycerol Monoundecenoate in Water.

The self-assembling properties of glycerol esters in water are well known. Still, few data on glycerol monoesters of undecylenic acid are available. The aim of this study was to highlight the behavior of glycerol monoundecenoate (GM-C11:1) in different diluted and concentrated states. Its self-assembling properties in water and upon solid inorganic surfaces were investigated in the diluted state using surface tension experiments, atomic force microscopy, and cryogenic transmission electron microscopy studies. In the concentrated state, the gelling properties in the presence of water were investigated using polarized light microscopy, differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) experiments. GM-C11:1 at 100 mg/L self-assembles at the liquid/air interfaces as aggregates of approximately 20 nm in diameter, organized into concentric forms. These aggregates are spherical globules composed of several molecules of GM-C11:1. At higher concentrations (1000 and 104 mg/L), GM-C11:1 is able to uniformly coat liquid/air and liquid/solid interfaces. In bulk, GM-C11:1 forms spontaneously aggregates and vesicles. In a more concentrated state, GM-C11:1 assembles into lamellar Lβ and Lα forms in water. By cross-referencing SAXS and DSC findings, we were able to distinguish between interlamellar water molecules strongly bound to GM-C11:1 and other molecules remaining unbound and considered to be "mobile" water. The percentage of water strongly bound was proportional to the percentage of GM-C11:1 in the system. In this case, GM-C11:1 appears to be an effective molecule for surface treatments for which water retention is important.

Self-Assembly of Reduced Graphene Oxide into Three-Dimensional Architecture by Divalent Ion Linkage

Gel-like three-dimensional (3D) reduced graphene oxide (rGO) structure can be achieved upon connecting rGO sheets with divalent ions (Ca2+, Ni2+, or Co2+) and water molecules via hydrothermal treatment. In this architecture, the rGO sheets, water molecules, and divalent ions play the role of skeleton, filler, and linker, respectively. The rGO sheets in the gel-like 3D rGO structure mainly exist as single or double layers by the isolation of the interlamellar water molecules. Since a large amount of water (∼99 wt %) facilitates the introduction of polyvinyl alcohol as a strengthening agent, hereby dried 3D rGO structure with micropores could be obtained after freeze drying.

Water behavior in the conversion process of gel-to-subgel phase in dimyristoylphosphatidylethanolamine–water system as studied by DSC

The gel phase of dimyristoylethanolamine (DMPE)–water system was annealed at temperatures of −5 to +5 °C for periods of 2 weeks and was converted into a more stable state of the so-called L-subgel phase. To elucidate the role of water molecules in the conversion of the gel to the subgel phase, the ice-melting behavior for the DMPE–water samples of varying periods of the annealing was investigated by a differential scanning calorimetry (DSC). The ice-melting DSC curves were deconvoluted according to a computer program for multiple Gaussian curve analysis, and the numbers of freezable interlamellar and bulk water molecules were estimated from respective ice-melting enthalpies of the deconvoluted curves. At the annealing periods of 4 days, water molecules amounting to 3.5 H 2O/lipid were observed to be further incorporated into regions between the bilayers, giving rise to the total number of freezable interlamellar water molecules 7 H 2O/lipid which is fairly larger than that (4 H 2O/lipid) estimated for the gel phase. Finally, the conversion of the gel-to-subgel phases completed at the annealing periods of 10 days. The resultant subgel phase showed the amount of nonfreezable interlamellar water larger by 1 H 2O/lipid than that of the nonannealed gel phase. Furthermore, the present study indicated an essential role of the bulk water molecules, which fill an empty space produced at the lipid bilayer surface in the conversion process of the gel-to-subgel phases.

Estimation of interlamellar water molecules in sphingomyelin bilayer systems studied by DSC and X-ray diffraction

A study on the hydration property of lipid bilayer systems was performed with DSC and X-ray diffraction techniques for two sphingomyelins, a naturally occurring bovine brain sphingomyelin having a heterogeneous acyl chain and a semisynthetic sphingomyelin having the acyl chain of 16 saturated carbons. The number of differently bound interlamellar water molecules was estimated for the two sphingomyelin systems from a deconvolution analysis of the ice-melting DSC curves of varying water content. The estimated limiting, maximum number of freezable interlamellar water molecules for the semisynthetic sphingomyelin system was 5.5 H 2O per molecule of lipid, which is close to a value (5 H 2O/lipid) previously reported by us for a system of dipalmitoylphosphatidylcholine. However, for the brain-sphingomyelin system, a limiting hydration for this type of water was not reached even up to the water/lipid molar ratio ∼20. In this accord, the electron density profile analysis of X-ray lamellar diffraction patterns for the brain–SM system showed that the thickness of interlamellar water layer increases in proportion to the amount of added water.

Synthesis and characterization of a novel layered zinc phosphate

Abstract The syntheses and crystal structures of a novel layered zinc phosphate and its high temperature variant are described. Both structures were solved from powder diffraction data using both synchrotron and conventional X-ray radiation. The as-synthesized material (UiO-27-as) with composition [C6H17N3]2+[Zn3(HPO4)(PO4)2]2−·H2O crystallizes in the space group P21/c with a=12.67072(15), b=8.24293(8), c=18.48425(19) A, β=109.1346(7)° and V=1823.904(35) A3. The zinc phosphate layers are built from corner sharing hexameric secondary building units. In the interlamellar space there are organic cations and water molecules. A high temperature variant exists around 200°C (UiO-27-200). This compound [C6H17N3]2+[HZn3(PO4)3]2− crystallizes in the monoclinic space group P21/c with a=12.29010(23), b=8.39995(13), c=18.49914(30) A, β=114.2504(11)° and V=1741.261(51) A3. The transformation to UiO-27-200 involves removal of the interlamellar water molecules. The atomic arrangement within the zinc phosphate layers is maintained; however, the layers are brought closer which leads to inter-layer hydrogen bonding interactions.

Layered aluminophosphates III. Crystal structure and thermal properties of the novel layered aluminophosphate UiO-18

The synthesis and crystal structure of a novel layered aluminophosphate and its two high-temperature variants are described. Two of the structures were solved from powder X-ray diffraction data. The as-synthesised material (UiO-18-as) with a composition [Al 2(OH) 2(PO 4) 2(H 2O) 2] 2−[NH 3(CH 2) 3NH 3] 2+2H 2O crystallises in the orthorhombic space group Pnma with a=6.91809(8) Å, b=22.3000(4) Å, c=9.60666(12) Å, V=1482.053(36) Å 3 and Z=4. The aluminophosphate layers are composed of aluminium octahedra forming infinite chains along [1 0 0] that are cross-linked by phosphate tetrahedra. The layers are held together by hydrogen bonding interactions involving the interlamellar 1.3-propanediammonium ions and water molecules. A high-temperature variant exists around 100°C (UiO-18-100). This compound with the composition [Al 2(OH) 2(PO 4) 2] 2−[NH 3(CH 2) 3NH 3] 2+ crystallises in the monoclinic space group P2 1/ n with a=21.5516(12) Å, b=6.96437(22) Å, c=8.1635(4) Å, β=100.042(4)°, V=1206.51(11) Å 3 and Z=4. The transformation to UiO-18-100 involves removal of the interlamellar water molecules and water molecules coordinating aluminium. The inorganic sheets retain their structure with infinite chains of aluminium trigonal bipyramids cross-linked by phosphate tetrahedra. The conformation of the 1.3-propanediammonium ion changes from the straight one observed in UiO-18-as to a more staggered one. Another high-temperature variant exists around 200°C (UiO-18-200). 13C CP-MAS NMR data indicate that the 1.3-propanediammonium ion remains unaffected by the transformation to UiO-18-200, and the weight loss associated with it involves release of water molecules and probably formation of tetrahedral Al–O–Al bonding just as in UiO-15-225. Structure elucidation of this compound is, however, prevented by severe disorder.

Studies of Phospholipid Hydration by High-Resolution Magic-Angle Spinning Nuclear Magnetic Resonance

A sample preparation method using spherical glass ampoules has been used to achieve 1.5-Hz resolution in 1H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of aqueous multilamellar dispersions of 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC), serving to differentiate between slowly exchanging interlamellar and bulk water and to reveal new molecular-level information about hydration phenomena in these model biological membranes. The average numbers of interlamellar water molecules in multilamellar vesicles (MLVs) of DOPC and POPC were found to be 37.5 ± 1 and 37.2 ± 1, respectively, at a spinning speed of 3 kHz. Even at speeds as high as 9 kHz, the number of interlamellar waters remained as high as 31, arguing against dehydration effects for DOPC and POPC. Both homonuclear and heteronuclear nuclear Overhauser enhancement spectroscopy (NOESY and HOESY) were used to establish the location of water near the headgroup of a PC bilayer. 1H NMR comparisons of DOPC with a lipid that can hydrogen bond (monomethyldioleoylphosphatidylethanolamine, MeDOPE) showed the following trends: 1) the interlamellar water resonance was shifted to lower frequency for DOPC but to higher frequency for MeDOPE, 2) the chemical shift variation with temperature for interlamellar water was less than that of bulk water for MeDOPE MLVs, 3) water exchange between the two lipids was rapid on the NMR time scale if they were mixed in the same bilayer, 4) water exchange was slow if they were present in separate MLVs, and 5) exchange between bulk and interlamellar water was found by two-dimensional exchange experiments to be slow, and the exchange rate should be less than 157 Hz. These results illustrate the utility of ultra-high-resolution 1H MAS NMR for determining the nature and extent of lipid hydration as well as the arrangement of nuclei at the membrane/water interface.

Calorimetric investigation of the behavior of interlamellar water in phospholipid-water systems

The interaction of water and three phospholipids with different polar-head groups, phosphatidylethanolamine (PE), phosphatidylcholine (PC) and phosphatidylgylcerol (PG) were investigated by differential scanning calorimetry (DSC). Ice-melting DSC curves showed that two types of water molecules, nonfreezable and freezable, interacting with lipid-head groups in intra-, and inter-bilayers are present in the gel phase of three lipid-water systems of varying water content up to 40 g%. The ice-melting curves were deconvoluted according to a computer program and the number of bulk water molecules and subsequently the number of nonfreezable and freezable interlamellar water molecules was estimated from enthalpy changes of deconvoluted components. The number of nonfreezable interlamellar water molecules increased in the order of PE (2.3 H 2O/lipid, PG (4.0 H 2O/lipid) and PC (5.5 H 2O/lipid), that is, in the order of an increase in the effective area occupied by the three-head groups. However, a distinct difference was observed for the freezable interlamellar water: the number of this water molecules of PG system continuously increases up to 40 g%, in contrast with their limiting number of 3.7 and 4.5 H 2O/lipid for PE and PC systems, respectively. This difference accounted well for a difference in the multiplicity of bilayer lamellar, that is, a single lamellar for PG system and a multilamellar for PE and PC systems shown by electron microscopy.

THERMAL BEHAVIOR OF HYDROTALCITE-LIKE [Mg1−xGax(OH)2](CO3)x/2·mH2O AS A FUNCTION OF GALLIUM CONTENT

The thermal behavior of a series of Ga-substituted hydrotalcites [Mg1−xGax(OH)2] (CO3)x/2·mH2O, where x = 0.072−0.35, was examined by means of thermal gravimetric analysis, (TGA), differential thermal analysis (DTA) and x-ray diffraction (XRD) measurements. The weight loss patterns of Ga-hydrotalcites depend on the Mg/Ga molar ratios. For example, a high [CO3]2− density in the interlayer region of Ga-rich samples (i.e. Mg/Ga = 1.8) makes them more difficult to dehydrate and slower to decompose than Ga-poor samples (i.e. Mg/Ga = 12.9). Removal of interlamellar water molecules in Ga-rich hydrotalcites consumes less energy than that in Ga-poor ones. The decomposition stage, regardless of Mg/Ga ratios, takes place at a constant temperature of ≈ 410 K, but this process requires much less energy in Ga-rich (Mg/Ga = 1.8; 22 J g−1) than in Ga-poor samples (Mg/Ga = 12.9; 202 J g−1). XRD analysis indicates that the layered structure is destroyed below 573 K, and that between 623 and 973 K, Ga-hydrotalcites convert into MgO-like materials, probably substituted by Ga3+. Calcination temperatures above 1073 K yield MgO-MgGa2O4 mixtures. © 1997 Elsevier Science Ltd

Kanemite (NaHSi2O5·3H2O) and its hydrogen-exchanged form

Kanemite, NaHSi2O5·3H2O, is able to exchange metal cations directly from aqueous solution. However, the degree of extraction is dependent upon whether kanemite or its hydrogen-exchanged form is the exchanger. Zinc cations, for example, are exchanged from basic solutions but the equilibrium extraction decreases with increasing acidity (at an equilibrium pH of 11.2, Kd=1070 cm3 g–1, whereas at an equilibrium pH of 4.88, Kd=70 cm3 g–1). Kanemite acts as an effective ion exchanger but the hydrogen-exchanged form is less effective, exchanging only by surface sorption at pH 2. In order to explain these and other properties, high-resolution solid-state magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) has been used to probe the structure of kanemite and its hydrogen-exchanged form. In kanemite there are only Q3 silicon-containing groups with extensive hydrogen bonding, and the interlamellar water molecules interact strongly with the silicate layers. In the hydrogen form, there is a dominance of Q3, but there are also Q2 and Q4 silicons. There is no NMR evidence for extensive hydrogen bonding and the SiO-H group is essentially undissociated. There are Bipolar interactions between the protons and the Q3 silicon atoms with weaker interactions with the Q2 and Q4. When the H-form is heated to 400 °C, some of the Q3 groups are involved in dehydroxylation reactions, as evidenced by the formation of Q4 silicons, but there are still some Q3 silicons remaining, and hence there are OH groups in the resulting material both from interlamellar water and Si-OH groups.

Preparation and Characterization of Two Distinct Ethylene Glycol Derivatives of Kaolinite

AbstractA new, well-ordered, thermally robust ethylene glycol intercalate of kaolinite was formed by refluxing the dimethyl sulfoxide intercalate of kaolinite (Kao-DMSO) with dry ethylene glycol (EG). This new phase (Kao-EG 9.4 Å) which is characterized by a d001 of 9.4 Å is distinct from a previously reported ethylene glycol intercalated phase of kaolinite (Kao-EG 10.8 Å) which has a d001 of 10.8 Å. The characterization of these two phases was studied by XRD, NMR, FTIR, and TGA/DSC. It was found that the concentration of water in the ethylene glycol reaction media played a crucial role in governing which of the phases predominated. Water favored Kao-EG 10.8 Å formation, while anhydrous conditions favored the formation of Kao-EG 9.4 Å. It is hypothesized that Kao-EG 9.4 Å is a grafted phase resulting from the product of the condensation reaction between an aluminol group on the interlamenar surface of kaolinite and the alcohol group of ethylene glycol. Ethylene glycol units would be attached to the interlamellar surface of kaolinite via Al-O-C bonds. The Kao-EG 9.4 Å phase was found to be resistant to both thermal decomposition up to 330°C and also, once formed, in the absence of interlamellar water molecules, to decomposition by hydrolysis in refluxing water.

A 1H NMR relaxation time study of dynamic processes in zirconium phosphates of differing crystallinities and in related compounds

The temperature dependences of the 1H NMR relaxation times T 1, T 1ϱ and T 2 are reported for crystalline zirconium phospha te and for related compounds which also have the α-layered structure: zirconium phosphate (ZrP, Zr(HPO 4) 2·H 2O), zirconium phosphate phosphite (ZrPP, Zr(HPO 3) 1,2(HPO 4) 0.8·0.5H 2O), pellicular zirconium phosphate (p-ZrP, Zr(HPO 4) 2·1.2H 2O) and its ammonitated daughter compound ((NH 4) 1.8H 0.2[Zr(PO 4) 2]·0.8H 2O). Variations in the forms of the temperature dependences are directly linked with variations in structure. In the ordered crystalline materials single minima in spin-lattice relaxation time ( T 1) are assigned as arising from 180°-flips of interlamellar water molecules; in p-ZrP the disordered interlayer region results in a distribution of reorientational correlation times. Two minima in T 1 are observed for each of p-ZrP and its ammoniated daughter compound; the higher temperature minimum arises from interlamellar species (H 2O in p-ZrP and NH + 4 in the ammonium compound) and the lower temperature minimum is assigned to those same species present in defects and having a consequent distribution of correlation times.

Conductivite ionique de composes de type hydrotalcite

Lamellar compounds Zn 2Cr(OH) 6Cl· nH 2O and Zn 2Al(OH) 6Cl· nH 2O exhibit an ionic conductivity upto 1.3×10 -3 ω -1 at 21°C. The conductivity, essentially intrinsic to the material is attributable in part to protonic exchange between hydroxylated sheets and inter-lamellar water molecules, and also in part to chloride ions which are also mobile. Evolution of conductivity of both materials was followed as a function of temperature in the range -32-+98°C and of degree of hydration determined by control of atmosphere relative humidity. Interlamellar water content is a parameter of great importance in conductivity of these materials. Zn 2Al(OH) 6Cl· nH 2O is a promising system for deposition of 20–50 μm layer on alumina substrates. The enhanced conductivity in such layers is attributed to a high level of orientation of cristallites in relation to the substrate.

Interlamellar Metal Complexes in Layer Silicates III Silver(I)—Arene Complexes in Smectites

AbstractThe complexation of benzene and several methyl substituted benzenes with exchangeable silver(I) on the interlamellar surfaces of Ag(I)-montmorillonite has been studied using spectroscopic methods. There are no physically adsorbed molecules interacting with the internal silicate surfaces and the only chemisorbed species present are those which are coordinated through π electrons to the exchangeable Ag(I) ions. In each case the coordinated species are similar to the previously studied Cu(II)-montmorillonite Type I complexes where aromaticity is retained. Complete replacement of coordinated and other interlamellar water molecules was accomplished with relative ease. Stoichiometric determinations indicate a 2:1 benzene: Ag(I) complex. Similarities between the Cu(II) and Ag(I) complexes are discussed in relation to electronic configurations.

Neutron scattering studies of hydrated layer silicates

Slow-neutron scattering spectrometry has been used to investigate the dynamics of interlamellar water molecules in layered silicate clay minerals. Experiments on hydrated lithium vermiculite give information in three regions. At energy transfers between 200 and 800 cm–1, vibrational bands associated with hydrogen motions in the silicate lattice and in the water are distinguished. In the low-frequency region, ca. 15–150 cm–1, a broad band of scattering characteristic of water emerges as the water content of the clay increases. Line-broadening effects arising from small energy transfers are indicative of diffusional processes in the water layers, but improved technique is required to make this certain for the thinnest films. The data are analyzed with particular reference to the thickness of the interlamellar water layers, and indicate significant changes in the water structure for water thicknesses of ca. 1–2 molecular layers. Similar results obtain in experiments with sodium vermiculite, and with lithium and sodium montmorillonite.