Hideo Hashizume

Solid-state intercalation of 4,4′-bipyridine and 1,2-di(4-pyridine)ethylene into the interlayer spaces of Co(II)-, Ni(II)- and Cu(II)-montmorillonites

Abstract Intercalation of two diimines, 4,4′-bipyridine (4BPY) and 1,2-di(4-pyridine)ethylene (DPE), into the interlayer spaces of cobalt(II)-, nickel(II)- and copper(II)-montmorillonites by solid–solid reactions was investigated. The successful intercalation of these compounds through coordination to the interlayer exchangeable cations was confirmed by powder X-ray diffraction, infrared spectroscopy, elemental (CHN) analysis, and thermal analysis of the products. The presented solid-state intercalation of bidentate bridging ligands and in situ complex formation in the interlayer spaces of montmorillonite is a feasible way to prepare clay-coordination polymer-intercalation compounds, which cannot be obtained in conventional ion exchange reactions.

ADENINE, ADENOSINE, RIBOSE AND 5′-AMP ADSORPTION TO ALLOPHANE

We have investigated the adsorption of adenine, adenosine, ribose, and adenosine-5′-phosphate (5′-AMP) by allophane at pH 4, 6 and 8. Adenine, adenosine and ribose gave similar isotherms, i.e. adsorption increased regularly with solution concentration and decreased in the order: pH 8 > pH 6 > pH 4. Allophane had a greater affinity for 5′-AMP than for adenine, adenosine or ribose. Further, the extent of adsorption for 5′-AMP increased in the order: pH 8 ≪ pH 6 ≈ pH 4. The adsorption of 5′-AMP at pH 4 and pH 6 was about 60 times greater than at pH 8. The strong adsorption of 5′-AMP accords with the well known high phosphate-retention capacity of allophane and allophane-rich soils. The experimental data may be rationalized in terms of the pH-dependent charge characteristics of the organic solutes and allophane. The large propensity of allophane to retain 5′-AMP is ascribed to ligand exchange between the phosphate of 5′-AMP and the hydroxyl of (HO)Al(OH2) groups, exposed at perforations on the wall of allophane spherules, giving rise to a surface (chelation) complex. The high affinity of nucleotides for allophane has implications for the possible role of allophane in the abiotic formation of RNA-type polynucleotides although nucleotide ‘immobilization’ by surface complexation might hinder RNA oligomerization.

Adsorption of adenine, cytosine, uracil, ribose, and phosphate by Mg-exchanged montmorillonite

Abstract We have determined the adsorption of RNA components (adenine, cytosine, uracil, ribose and phosphate) by Mg2+-exchanged montmorillonite. The isotherms for adenine, cytosine and uracil were of the C-type, the amount adsorbed increasing linearly with the equilibrium solute concentration. All three nucleic acid bases were apparently adsorbed by coordination to Mg2+ ions through a water bridge. Very little ribose was adsorbed by Mg-exchanged montmorillonite. The isotherm for phosphate was of the L-type. The plateau value of about 0.012 mmol g-1 indicated that phosphate adsorbed on the edge surface of montmorillonite. At comparable solute concentrations, adsorption decreased in the order adenine > cytosine > uracil. This observation reflects differences in basicity, size, and aqueous solubility among the three compounds.

FORMATION OF SMECTITE CRYSTALS AT HIGH PRESSURES AND TEMPERATURES

Smectite single crystals of superior quality were synthesized at high pressures and temperatures using a modified belt type high pressure apparatus. Pressure-temperature conditions were established for smectite formation by quenching experiments in the pressure range from 2–5.5 GPa and temperatures of 700°–1000°C. Smectite crystals with extraordinary quality were formed beyond 3 GPa and 1000°C with coexisting phases of coesite, kyanite, jadeite, and in some cases with mica and glass. Smectite was confirmed from the XRD taken after intercalation of ethylene glycol. The smectite crystals were considered to be quenched crystals metastably from the hydrous silicate melts formed at high pressures and temperatures.

Solid state intercalation of 4,4'-bipyridine into the interlayer space of montmorillonites

Abstract Intercalation of 4,4′-bipyridine into the interlayer spaces of cobalt(II), nickel(II) and copper(II)-montmorillonites by solid-solid reactions was investigated. The successful intercalation of 4,4′-bipyridine and the complex formation in the interlayer spaces of montmorillonites was confirmed by powder XRD (the change in the basal spacings) as well as IR and the thermal analysis of the products.

Adsorption of some aromatic compounds by a synthetic mesoporous silicate.

Abstract Water pollution by toxic organic compounds is of concern and demands for effective adsorbents for removal of the toxic compounds are increasing. Here we synthesized a mesoporous material, FSM-16, and investigated its ability to take up model compounds (benzene, toluene, phenol, and benzoic acid) from aqueous solutions by batch experiments. The adsorption isotherms were linear and adsorption capacities were small. Benzene and toluene have very similar adsorption isotherms, suggesting the side chain of toluene, i.e., alkyl chain, did not have significant effect on its adsorption. The amount of adsorption and isotherm slope were in the order of toluene ≈ benzene > benzoic acid > phenol. The occupation ratios of those organic compounds on the surfaces of FSM-16 were estimated less than 1%. Solubility of the compounds seems the major factor determining their adsorption by FSM-16. Phenol has the highest solubility and thus was least adsorbed by FSM-16. In contrast, toluene and benzene have very low solubilities and are the most adsorbed ones.

Adsorption of Nucleic Acid Bases, Ribose, and Phosphate by Some Clay Minerals

Besides having a large capacity for taking up organic molecules, clay minerals can catalyze a variety of organic reactions. Derived from rock weathering, clay minerals would have been abundant in the early Earth. As such, they might be expected to play a role in chemical evolution. The interactions of clay minerals with biopolymers, including RNA, have been the subject of many investigations. The behavior of RNA components at clay mineral surfaces needs to be assessed if we are to appreciate how clays might catalyze the formation of nucleosides, nucleotides and polynucleotides in the “RNA world”. The adsorption of purines, pyrimidines and nucleosides from aqueous solution to clay minerals is affected by suspension pH. With montmorillonite, adsorption is also influenced by the nature of the exchangeable cations. Here, we review the interactions of some clay minerals with RNA components.

Photoinduced structural changes of cationic azo dyes confined in a two dimensional nanospace by two different mechanisms

Photoresponsive change in the basal spacing of cationic azo dye-layered silicate intercalation compounds was investigated using X-ray diffraction under controlled humidity conditions to investigate the mechanism of the photoresponse triggered by trans–cis photoisomerization. The molecular design of azo dyes was conducted and two cationic azo dyes (phenylazobenzene and phenylazonaphthalene) were used to obtain intercalation compounds with different packing and hydration. Whereas the trans-phenylazobenzene-layered silicate hardly adsorbed water vapor, the trans-phenylazonaphthalene intercalation compound strongly interacted with water. Both azo dyes photoisomerized in the interlayer space reversibly. Under the relative humidity of 95%, the basal spacing of the phenylazobenzene–silicate increased upon UV irradiation, confirming that the change in the basal spacing was caused by the photoinduced hydration. Under the relative humidity of 6.8%, the basal spacing of the phenylazonaphthalene–silicate decreased upon UV irradiation, suggesting that the packing of the phenylazonaphthalene in the interlayer space was changed to be compacted by the photochemical conversion to the cis-form.

Reassembling process of colloidal single-layers of an exfoliated titanate

Colloidal nanosheets of an exfoliated titanate start to be reassembled from a novel associated pair, accommodating an interlayer water cluster of > 100 A thickness, to produce a restacked layer structure.

Interactions of Clay Minerals with RNA Components

Because of their extensive surface area, layer structure, and surface charge characteristics, clay minerals can take up a wide range and variety of organic molecules. Further, clay minerals can shield these molecules from cosmic and ultraviolet radiation, and catalyze their polymerization. For these reasons, clay minerals might have played an important role in chemical evolution and the origins of life on Earth. The proposal that ribonucleic acid (RNA) can act as both a storehouse of genetic information and an enzyme-like catalyst in the primordial Earth, has stimulated research into the ability of clay minerals to catalyze the formation of RNA from its (activated) monomers. After outlining the probable role of clay minerals in chemical evolution and the origins of life, and summarizing clay minerals structures, we describe the interactions of clay minerals with nucleic acid bases, nucleosides, nucleotides, polynucleotides, and nucleic acids. These interactions are illustrated by selective experimental results from our laboratory and the literature.