A carbonate controlled-addition method for amorphous calcium carbonate spheres stabilized by poly(acrylic acid)s

Stable amorphous calcium carbonate (ACC) composite particle with a size-controlled monodispersed sphere was obtained by a new simple carbonate controlled-addition method by using poly(acrylic acid) (PAA) (Mw = 5000), in which an aqueous ammonium carbonate solution was added into an aqueous solution of PAA and CaCl2 with a different time period. The obtained ACC composite products consist of about 50 wt % of ACC, 30 wt % of PAA, and H2O. Average particle sizes of the ACC spheres increased from (1.8 +/- 0.4) x 102 to (5.5 +/- 1.2) x 102 nm with an increase of the complexation time of the PAA-CaCl2 solution from 3 min to 24 h, respectively. The ACC formed from the complexation time for 3 min was stable for 10 days with gentle stirring as well as 3 months under a quiescent condition in the aqueous solution. Moreover, the ACC was also stable at 400 degrees C. Stability of the amorphous phase decreased with an increase of the complexation time of the PAA-CaCl2 solution. No ACC was obtained when the lower molar mass PAAs (Mw = 1200 and 2100) were used. In the higher molar mass case (Mw = 25 000), a mixture of the amorphous phase and vaterite and calcite crystalline product was produced. The present results demonstrate that the interaction and the reaction kinetics of the PAA-Ca2+-H2O complex play an important role in the mineralization of CaCO3.

Synthesis of Optically Active P-Chiral and Optically Inactive Oligophosphines

A series of optically active P-chiral oligophosphines (S,R,R,S)-2, (S,R,S,S,R,S)-3, (S,R,S,R,R,S,R,S)-4, and (S,R,S,R,S,R,R,S,R,S,R,S)-5 with four, six, eight, and 12 chiral phosphorus atoms, respectively, were successfully synthesized by a step-by-step oxidative-coupling reaction from (S,S)-1. The corresponding optically inactive oligophosphines 1'-5' were also prepared. Their properties were characterized by DSC, XRD, and optical-rotation analyses. While optically active bisphosphine (S,S)-1 and tetraphosphine (S,R,R,S)-2 behaved as small molecules, octaphosphine (S,R,S,R,R,S,R,S)-4 and dodecaphosphine (S,R,S,R,S,R,R,S,R,S,R,S)-5 exhibited the features of a polymer. Furthermore, DSC and XRD analyses showed that hexaphosphine (S,R,S,S,R,S)-3 is an intermediate between a small molecule and a polymer. Comparison of optically active oligophosphines 1-5 with the corresponding optically inactive oligophosphines 1'-5' revealed that the optically active phosphines have higher crystallinity than the optically inactive counterparts. It is considered that the properties of oligophosphines depend on the enantiomeric purity as well as the oligomer chain length.

Water-soluble anionic POSS-core dendrimer: synthesis and copper(II) complexes in aqueous solution

A carboxylic acid-terminated polyhedral oligosilsesquioxane (POSS)-core dendrimer (POSS-CO2H) was synthesized from octa(3-ammoniumpropyl)octasilsesquioxane octachloride (POSS-NH3+) via a t-butyl ester-terminated POSS-core dendrimer that was prepared from neutralized POSS-NH3+ and t-butyl acrylate. Complexing properties of the sodium salts of POSS-CO2H (POSS-CO2Na) with Cu2+ were studied in comparison with those of the G1.5 poly(amidoamine) (PAMAM) dendrimer (G1.5-CO2Na) by spectroscopic approach and isothermal titration calorimetry. In the case of G1.5-CO2Na, Cu2+-N4 and Cu2+-N2O2 complexes are possible coordination modes, and only a Cu2+-N2O2 complex can be formed for POSS-CO2Na. In the case of POSS-CO2Na, upon increasing the concentration of Cu2+, the values of the binding constants decreased. However, the values of binding constants in the regions of the Cu2+-N2O2 coordination mode for G1.5-CO2Na increased with increasing concentration of Cu2+. This observation suggests that the uptake of Cu2+ is inhibited by increasing binding numbers of Cu2+ due to the rigid structure of the POSS-core dendrimer.

Synthesis of organic-metal hybrid nanowires by cooperative self-organization of tetrathiafulvalene and metallic gold via charge-transfer

Organic-metal hybrid nanowires were synthesized by cooperative self-organization of the one-dimensional stacking of tetrathiafulvalene (TTF) via charge-transfer interaction with metallic gold originating from the redox reaction between TTF and gold ions. The nanowires can be easily obtained as purple precipitates just by mixing TTF and HAuCl4 in a CH3CN solution at room temperature. The feed molar ratio of TTF to HAuCl4 was 4.4. The average diameter and length of the observed nanowires were 90 +/- 36 nm and 15 +/- 3 microm, respectively. The formation was facilitated by the arrangement of the neutral and oxidized TTF along the one direction in a mix-valence state, which was confirmed by a broad absorption that appeared in the region of 2000 nm and the composition of the nanowires of [(TTFCl(0.78))Au(0.12)].

Formation of stable vaterite with poly(acrylic acid) by the delayed addition method

The crystallization of CaCO3 was examined by changing the addition time of poly(acrylic acid) (PAA) to an aqueous solution of calcium carbonate by selectively interacting with the crystal at different stages during the crystal-forming process. The precipitation of CaCO3 was carried out by a double jet method to prevent heterogeneous nucleation on glass walls, and the sodium salt of PAA was added by a delayed addition method. In the initial presence of PAA in an aqueous solution of calcium carbonate, PAA acted as an inhibitor for the nucleation and growth of crystallization. However, it was found that stable vaterite particles were successfully obtained by delaying the addition of PAA from 1 to 60 min. The vaterite particles were stable in the aqueous solution for more than 30 days, and the CaCO3 particles were formed by a spherulitic growth mechanism. It is suggested that PAA strongly binds with the Ca2+ ion on the surface of CaCO3 particles to stabilize the unstable vaterite form effectively. Upon changing the addition time of PAA, we found that CaCO3 particles were formed through different formation mechanisms in selectively controlled crystallization at different stages during the crystallization process.