Interlamellar space

Hydrophobic interactions and trapping of molecules in a molecular sieve formed by humic materials have been hypothesized as retention mechanisms for prometryn. It has been shown that fluridone, fluazifop, and bipyridyhum herbicides penetrate into interlamellar spaces of smectites and can become trapped. 

Dimerization of unsaturated fatty acids, to. so-called dimer acids, is widely practised in industry, where acid-treated clays are invariably used as a catalyst. In the case of oleic acid the major products are dimers, trimers, and isosteric acid. Koster et al. (1998) have investigated the relative importance of the various acid sites as well as structural and textural parameters of montmorrilonite. The interlamellar space dominates the oleic acid dimerization and the active site is the tetrahedrol substitution site. 

The crystal structure of zinc phenylphosphonate was solved and demonstrated the anticipated layer structure with the phenyl rings occupying the interlamellar space.409 The structure of zinc ethylphosphonate and (2-aminoethyl)phosphonate both show four-coordinate zinc centers in contrast to the coordination number of six in the phenylphosphonate compound.410... 

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

When organic cations (e.g., cationic tensides) are employed, clay organo-complexes are formed, which can be used in organic solvents. A Pd-hexadecy-lammonium montmorillonite catalyst was prepared by the reduction of Pd(OAc)2 by ethanol in the interlamellar space. At small ethanol concentrations in toluene, selective interlamellar sorption of ethanol was established consequently, the reduction also occurred only in the interlamellar space.160 The catalyst was used for the hydrogenation of alkenes.161... 

Sonawane et al. [90] investigated the affect of ultrasound and nanoclay for the adsorption of phenol. Three types of nanoclay tetrabutyl ammonium chloride (TBAC), N-acetyl-N,N,N trimethyl ammonium bromide (CTAB) and hexadecyl trimethyl ammonium chloride (HDTMA), modified under sonication, were synthesized which showed healthier adsorption of phenol within only 10 min in waste water. The interlamellar spacing of all the three clay increased due to incorporation of long chain quaternary salts under cavitational effect. 

Figure 9b, Real-space image of a new type of graphite intercalate (with FeCl2), There are two sheets of guest material accommodated in an expanded interlamellar space. Inset shows computed...

To overcome the problem of diffusion of cumbersome molecules (such as polymers) into the constrained interlamellar space of LDH, several methods have been employed, which are presented in Fig. 7. According to the general classification established by Schbllhorn et al. [35], there are three principal options to obtain a polymer intercalated inorganic host ... 

In situ polymerization is generally a highly suitable method for the ob-tention of LDH/polymer nanocomposites. Various monomers can be intercalated and polymerized within the interlamellar space of LDH and this spatial confinement is believed to increase the degree of polymerization. Yet, the process is limited by two factors [43] ... 

As can easily be understood, the in situ polymerization process is favored when distances between monomers in the interlamellar space are close to the monomeric repeat distance displayed by the polymer. Such a compatibility of distances was first demonstrated for the polymerization of aniline in V2O5 and FeOCl hosts with an exact matching between NH functions for PANl and the (1-30) crystallographic direction for V2O5 or the (201) direction for FeOCl [63]. 

Fig. 17 a One-dimensional electron density distribution of Ca2Al/VBS along the c axis b Gaussian deconvolution of the hydroxide layer c Gaussian deconvolution of the interlayer space and the resulting conformation of VBS molecules in C2/c space group, VBS molecules are related by an helicoidal axis 2 located midway in the interlamellar space... 

For the less ordered hydrotalcite type sample, a syndiotactic polymer is also probable. The amount of intercalated species and likely location within the interlamellar space is determined by the amount of trivalent cations within the... 

The molecular size and the cross-sectional area of coumarine 1 were calculated to be 3.2x10.4x7.5 (A) and 78 A, respectively. From the data of observed d-spacings and the calculated molecular size, three possibilities for the conformation of coumarine molecules could be proposed. In the dl-type [shown in Fig. 5(a)], since the thickness of one aluminosilicate layer was about 9.6 A, the full clearance space was estimated to be about 3.6 A. This value was almost equal to the thickness of the planar coumarine molecule. Therefore, it was considered that coumarine molecules were "flat" on the silicate surfaces and covered each exchangeable cation site without any overlap. In the dh-type [shown in Fig. 5(b,c)], the measured d-spacing was 18.5 A, so that the interlamellar spacing was evaluated to be about 8.9 A, in which the coumarine... 

Figure 1 A generalized diagram of the structure of the cetostearyl alcohol gel found in topical and vaginal creams. The bilayers are formed principally of cetostearyl alcohol. The hydrophilic poly(oxyethylene) chains attached to the 5-carbon sorbitan rings in Polysorbate 60 retard water drainage from the interlamellar space and keep the lamellae from collapsing into a dense crystalline structure.

An internal aluminum standard was used to calibrate the spacings, which were measured with a photo-microdensitometer. The peak intensity of the main arcs corresponds to an interlamellar spacing of 3.47 A. 0.02 A. (compare graphite, 3.35 A., with second and third orders at appropriate spacings). Other peaks present were at 2.07 A. 0.02 A. and 1.20 A. 0.02 A. These appear to represent (10) and (11) spacings, respectively. Only an extremely diffuse pattern, without evidence of preferred orientation, was obtained from the pitch surrounding the spheres. 

Al3+-exchanged synthetic hectorite is a good catalyst for these conversions, and the 13C NMR spectrum obtained in the interlamellar, proton-catalyzed addition of water to 2-methylpropene is indistinguishable (Fig. 79) from that of f-butanol. Doubtless studies of this kind, where natural-abundance, 3C NMR signals are used to probe the chemical identity and motional freedom of reactant and product species situated in the interlamellar spaces of clays or pillared clays (see below), will become increasingly popular. Using l3C NMR linewidths and spin-lattice relaxation studies, Matsumoto et al. (466) have succeeded in discriminating between the internal and external surfaces of pillared montmorillonites. 

More recently, crown ether pillared and functionalized a-zirconium phosphonates have been synthesized [34], Incorporation of crown ethers was achieved by first converting them to their respective phosphonic acids. X-ray diffraction studies showed that the interlamellar spacing was about 15 A when a biphospho-nic acid was used. Both a- and y-type zirconium phosphonates could be synthesized using this methodology. Preliminary results showed that these layered materials have good selectivity toward binding transition metal ions and that the interlamellar fluoride ions could be replaced by anion exchange. 

LDHs, which belong to the clay family, present several and various applications in different fields, such as catalysis or medicine. The general formula for these compounds is [Mi xnMxni(OH)2]+.Ax, nH20 (labelled [M11-Mm-A]) where the Ms are divalent and trivalent cations and A is an anion. LDH is composed of infinite sheets of positively charged brucite-type Mg(OH)2, where trivalent cations have replaced a fraction x of divalent cations in octahedral coordination. The interlamellar space is occupied by anions, keeping the electroneutrality of the structure, and completed by water molecules. 

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