Interlamellar water

Montmorillonites containing interlamellar water associated with cations (Cu2+, Fe3+, Al3+) react under mild conditions with terminal alkenes to give the corresponding di-sec-alkyl ethers.26 The alkene-water reaction is a stoichiometric process, while the reaction of the second molecule of alkene with the intermediate 2-alkanol is catalytic. 

The meaning of one-, two-, and three-layer clays is best illustrated diagrammatically (see Fig. 77). Layers in this context refer to the interlamellar water, though the precise chemical nature of this entrained water is not easily established and is, in any case, a function of the parent silicate. In some sheet silicates the water is believed to take up an ice-like monolayer. Recent studies reveal that the interlamellar ion and associated water are rather mobile above room temperature. Such water is readily, but not always... 

They exhibit strong acidity, which is usually of the Bronsted type, partly because of the influence of the strong internal electrostatic fields (ca. 106 Vcm 1) exerted on the interlamellar water (which generates protons by dissociation) or, because of the additional influence of certain hydrated interlamellar cations, notably Al3+. Cation hydrolysis, just as with strongly polarizing cations in zeolites, yields free protons, thus ... 

Fig. 79. I3C NMR spectra showing that when 2-methylpropene (isobutene) is intercalated in a synthetic hectorite r-butanol is formed when the guest species reacts with the interlamellar water. The peaks labeled 1 and 2 refer to the two distinct types of carbon atom in r-butanol (453).

Boehmite is of considerable interest to the surface scientist. It was pointed out by Lippens and Steggerda (1970) that a clear distinction should be made between crystalline boehmite and the gelatinous forms of pseudoboehmite, which always contains some non-stochiometric, interlamellar water. Pseudoboehmite is the main constituent of European bauxites and can be easily prepared by the neutralization of aluminium salts, but hydrothermal conditions are required for the formation of crystalline boehmite. 

Because of the close relationship to the mineral particles in the sediment, interlamellar water is usually of types (2) and (3). A special type of water, so-called "polywater" or "superwater", which has been reviewed and considered by Kamb (1971) and Henniker (1949), is a modification of water solution, as a result of impurities in a water solution. It is an interesting phenomenon, provided such solutions occur in nature. "Polywater" has been observed to have a density of about 1.4g/cm and a viscosity about 15 times greater than normal water. Capillaries with "polywater" might be expected in a finegrained sediment (Low and White, 1970) with a considerable amount of clay mineral particles like mud. The significance of the various t3q es of water in sediments must not be underestimated, as they may influence other processes taking place in the aqueous phase. 

Another aspect of current interest associated with the lipid-water system is the hydration force problem.i -20 When certain lipid bilayers are brought closer than 20-30 A in water or other dipolar solvents, they experience large repulsive forces. This force is called solvation pressure and when the solvent is water, it is called hydration pressure. Experimentally, hydration forces are measured in an osmotic stress (OS) apparatus or surface force apparatus (SFA)2o at different hydration levels. In OS, the water in a multilamellar system is brought to thermodynamic equilibrium with water in a polymer solution of known osmotic pressure. The chemical potential of water in the polymer solution with which the water in the interlamellar water is equilibrated gives the net repulsive pressure between the bilayers. In the SEA, one measures the force between two crossed cylinders of mica coated with lipid bilayers and immersed in solvent. 

Recently, a molecular dynamics study of the phospholipid DLPE was reported by Damodaran et al. using a united atom model. The model was built from the crystal structure of DLPE reported by Elder et al. The fully hydrated DLPE bilayer has an interlamellar water layer of 5 A. The bilayer was solvated by 553 SPCE waters ( 11 water molecules/lipid) in the head group region. This lipid has a gel-to-liquid-crystalline transition temperature of... 

In contrast to the stmcture of a-V0(HP04) 2H2O, that of p-VO (HPO4) 2H2O, shown in Figure 7, exhibits no interlamellar water but rather two aqua hgands on each vanadium site, one trans to the terminal 0x0 group. The... 

The two clay samples were expanded using a SiOj-TiOj sol solution prepared by a procedure described by Yamanaka and coworkers (4). Tetraethylorthosilicate is first hydrofyzed with an excess of an HQ (IN) and ethanol mixture, and then reacted with titanium tetraisopropoxide (hydrolyzed with IN HQ). to form a sol with composition TiOj-lOSiO. The sol is then added to a slurry containing 1% clay. The resulting mixture is stirred for 90 minutes at 60 C. After filtration and washing, part of the clay is allowed to diy in air at 60 C. The remaining clay was washed with ethanol (to displace interlamellar water) and then dried with supercritical COj at 120 atm and 40°C A schematic of the clay catalyst s preparation is shown in Figure 5-1. 

In fact, the interlamellar space of anionic clays is generally cluttered by the pillars and the overall interactions of the pillars with the sheets and the interlamellar water molecules reduces the... 

In the most reactive silicic acids the layers of the air-dried samples are separated by water molecules. The intercalation of guest molecules is then a displacement of interlamellar water molecules and does not require the high energy needed for layer separation of the anhydrous acids. Therefore, compounds with dipole moments below 4 Debye are also intercalated, for instance, ethylene glycol, with 2.28 Debye, or alcohols (1.7 Debye). Nevertheless, the interplay between formation of hydrogen bonds and arrangements with optimal van der Waals energy also determines the intercalation reaction. 

It is more plausible that the seven HjO molecules per lipid constitute real nonfreezable water (which is not detected by DSC) and freezable interlamellar water (to which the above-mentioned melting peak below 0°C may be ascribed). This number is to be compared with the five nonfreezable water molecules per molecule of lipid plus five freezable interlamellar water molecules per molecule of lipid that were evaluated by Kodama and Aoki [134] for the gel phase of the DPPC-water system, using a deconvolution analysis. The 7 A (= 65 - 58) decrease in the interbilayer distance is then due to the loss of five molecules of... 

V. Ice-Melting Behavior for a Minute Amount of Freezable Interlamellar Water... 

A characteristic feature of DSC is its ability to distinguish clearly between freezable water, for which ice-melting behavior is observed, and nonfreezable interlamellar water, for which it is not observed even at temperatures low enough to form ice. As is well known, the structure of ice is characterized by networks of hydrogen bonds formed among neighboring water molecules. Therefore, the point to note is that the water molecules present as nonfreezable water cannot participate in the formation of such hydrogen bonds even when cooled to extremely low temperatures. 

FIG. 2 Comparison of ice-melting enthalpy curves of AH and AH-y for bulk water per mole of lipid. The AHs curve is an experimental one determined by DSC, and the AHj curve is a theoretical one obtained by assuming that all the water added is present as free water. In this figure, the AH curve consists of the curves a and b for limited and infinite hydration, respectively. is the water/lipid molar ratio. N (a) is the water/lipid molar ratio when the maximum amount of interlamellar water is reached in a lipid-water system. 

A//b curve intersects the abscissa and Nb at each Ny, is calculated from A/ b/1-436 (2) the enthalpy difference, AHj - AH, between the theoretical and experimental curves corresponds to 1.436 Ni, where Ni = Nn f) + lVi(f) in Eq- (3), so for each iVw Ni is calculated as equal to (AHj - A//b)/1-436. AH curve a is parallel to the theoretical curve, indicating that the total (nonfreezable plus freezable) amount of interlamellar water reaches a maximum at the N, value of the intersection point, denoted as iVw(a), and so iVw(a) just gives the maximum amount of interlamellar water above iVw(a), all the water added exists as bulk water outside the lamellae. Thus, such a parallel curve proves a limited uptake of the interlamellar water. On the other hand, AH curve b, which is not parallel to the theoretical curve, indicates an infinite uptake of the interlamellar water. Thus, some of the water added beyond the intersection point exists as bulk water, and the remainder increases the amount of interlamellar water. 

FIG. 4 Comparison of ice-melting enthalpy curves of AH and for bulk and freezable interlamellar water per mole of hpid. The AHb and AH if curves are determined from the deconvoluted ice-melting curves for the bulk and freezable interlamellar water, respectively. iVw(a) and iV (b) are water/lipid molar ratios at the maximum amounts of freezable and nonfreezable interlamellar water, respectively. The designations 1,11, and 111 represent the three regions < N (b) (i.e., in the presence of only nonfreezable interlamellar water), Al (b) N a.) (i.e., in the presence of nonfreezable and freezable interlamellar and bulk water), respectively. 

V. ICE-MELTING BEHAVIOR FOR A MINUTE AMOUNT OF FREEZABLE INTERLAMELLAR WATER... 

On the other hand, as discussed later, the freezable interlamellar water of the DPPC-water system begins to appear at 5 (Wh o H wt%) therefore, IVw(b) 5. However, as shown in Fig. 8, the ice-melting behavior (curves a-c)... 

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