Hydrothermal treatment of lime-silica mixtures under saturated steam pressures below 200°C usually gives C-S-H as an initial product, which reacts further to give crystalline calcium silicate hydrates. In this paper, C-S-H was hydrothermally prepared using CaO and silicic acid at CdSi ratios of 0.3 to 2.0 and 120" to 180°C for 2 h. The C-S-H was examined mainly using 29Si NMR by the magic angle spinning gate proton decoupling and cross polarization magic angle spinning methods. XRD for all of the C-S-H showed bands at 0.304, 0.280, 0.183, and 0.166 nm. NMR results showed that all of the C-S-H contained single chains of silicate anion, which became progressively longer as the CdSi ratio decreased, i.e., as the system became richer in silica. This was independent of the preparation temperature. The 0.8 ratio preparations at 180°C contained small amounts of double-chain structure of 1.1-nm tobermorite. The reaction processing in the lime-silicic acid mixtures is also discussed.

ol-C,SH can be synthesized by hydrothermal treatment of lime and silicic acid for 2 h at 200°C. When heated to 390-490"C, a-C,SH dissociates through a two-step process to form an intermediate phase plus some y-C,S. This appears to be a new dicalcium silicate different from known dicalcium silicate-, a'", p, and y phase-and is stable until around 900°C. At 920-96OoC, all the phases are transformed to the atL phase. The intermediate phase has high crystallinity and is stable at room temperature. 29Si MAS NMR measurements indicate the possibility that it contains both protonated and unprotonated monosilicate anions. The intermediate phase that has passed through the a' phase at higher temperature yields p-C2S on cooling. The intermediate phase is highly active, and completed its hydration in 1 day ( w / s = 1.0, 25°C). Among the crystalline calcium silicate hydrates with Ca/Si = 2.0, it is hillebrandite that yields p-C,S at the lowest temperature.

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The cytotoxic activity of methanol extracts of leaves collected from 39 seashore plants in Iriomote Island, subtropical Japan was examined on human leukaemia cells (K562 cells) using a flow cytometer with two fluorescent probes, ethidium bromide and annexin V-FITC. Five extracts (10 microg/mL) from Hernandia nymphaeaefolia, Cerbera manghas, Pongamia pinnata, Morus australis var. glabra and Thespesia populnea greatly inhibited the growth of K562 cells. When the concentration was decreased to 1 microg/mL, only one extract from H. nymphaeaefolia still inhibited the cell growth. A cytotoxic compound was isolated from the leaves by bioassay-guided fractionation and was identified as (-)-deoxypodophyllotoxin (DPT). The fresh leaves of H. nymphaeaefolia contained a remarkably high amount of DPT (0.21 +/- 0.07% of fresh leaf weight), being clarified by a quantitative HPLC analysis. DPT at 70-80 pM started to inhibit the growth of K562 cells in an all-or-none fashion and at 100 pM or more it produced complete inhibition in all cases. Therefore, the slope of the dose-response curve was very steep. DPT at 100 pM or more decreased the cell viability to 50%-60% and increased the number of cells undergoing apoptosis (annexin V-positive cells). The results indicate that DPT contributes to the cytotoxic action of the extract from the leaves of H. nymphaeaefolia on K562 cells.

P-dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca,(SiO,)(OH),) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, 29Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C-S-H consisted mainly of a dimer and a single-chain polymer. Polymerization advances with increasing curing temperature and curing time. The C-S-H has an oriented fibrous structure and exhibits a 0.73-nm dreierketten in the longitudinal direction. On heating, the C-S-H dissociates to form P-C,S. The temperature at which P-C,S begins to form decreases with increasing chain length of the C-S-H or as the CdSi ratio becomes higher. The high activity of p-C,S is due to its large specific surface area and the fact that the hydration is chemical-reaction-rate-controlled until its completion. As a result, the hydration progresses in situ and C-S-H with a high CdSi ratio is formed.

A mixture of CaO and silicic acid prepared with a CdSi ratio of 2.0 was hydrothermally synthesized at 80" to 200"C, and the thermal decomposition behavior of the products (C-S-H with Ca(OH),) was analyzed using XRD, 29Si MAS NMR, and the trimethylsililation method (TMS). It was found that the main silicate anion structure of C-S-H was a mixture of a dimer and a single-chain polymer (larger than Si,O,,) and that polymerization advanced with an increase of the synthesizing temperature. On heating, the products decomposed to form p-C,S. It was found that the decomposition was gradual and that the higher the temperature of hydrothermal synthesis, the lower was the temperature of the decomposition into p-C,S. Although the decomposition proceeded to form a monomer (p-C,S) from the polymer and dimer, this dimer was resistant to heat and did not decompose unless heated to above 400°C.

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The hydration of p-C,S prepared from hillebrandite [Ca,(SiO,)(OH),] and having specific surface areas of 6.8, 5.5, and 3.1 mz/g was investigated. Different specific areas were obtained by varying the dissociation temperature of hillebrandite. In addition, the hydration of $-C,S synthesized from high-temperature solid-state reaction was also studied as a comparison. The specific surface area exerts a strong influence on the hydration rate, which increases as the surface area increases. The degree of influence changes with the reaction, becoming greater as hydration progresses. There is initially a linear relationship between specific area and the time required to complete a specific reaction. The specific surface area also affects the reaction mechanism. In the case of specific areas of 5.5 mZ/g or less, the reaction changes from a chemical reaction to a diffusion-controlled one, and the degree of reaction comes almost to a halt at 80% to 85%. The Ca/Si ratios of hydrate and the silicate anion structures were also investigated in this study.