Self-assembly and mineralization of full-length human amelogenin and its functional fragments in vitro.

OBJECTIVES: To investigate the dynamic process of the self-assembly behaviors of a full-length human amelogenin (AM) and its functional fragments tyrosine-rich amelogenin peptide (TRAP) and leucine-rich amelogenin peptide(LRAP) in vitro and its role in hydroxyapatite (HA) crystal formation. METHODS: The full-length human AM and its functional fragments, TRAP and LRAP, were reassembled and purified in vitro. The protein solution of 100 µg‧mL-1, pH=8, was prepared in Tris-HCl and incubated at room temperature for 1-15 min. Their self-assembly behaviors were observed and compared under a transmission electron microscope (TEM). The full-length AM was added to artificial saliva and incubated for 3 days. A scanning electron microscope (SEM) was used in observing the morphology of the induced new crystals. Then, TARP and LRAP were added. The resulting solution was incubated for 3 days and then observed again. RESULTS: When pH=8, the full-length human AM and TRAP assembly started spontaneously and formed "nanospheres" after 15 min.The nanospheres formed by TRAP existed independently, with a uniform size but without obvious internal structures. The full-length AM was assembled hierarchically, which formed "nanospheres" and further extended in all directions, formed a chain structure, and then aggregated into a net. The self-assembly behavior of LRAP was not obvious. Proteins mostly existed in the form of monomers without "nanosphere" formation. Only few oligomers were observed. The full-length AM was induced independently for 3 days to form rod-shaped HA crystals. TRAP and LRAP proteins were added, after 3 days the crystal elongation was obvious in the c axis, but the growth in plane A and plane B was poor. CONCLUSIONS: The self-assembly and mineralization behaviors of full-length human AM, TRAP, and LRAP were consistent with the directional growth mechanism of HA crystals in vivo, providing a theoretical basis for the role of the fragments in the growth and maturation of HA crystals.

Copper-Catalyzed Inter/Intramolecular N-Alkenylation of Benzimidazoles via Tandem Processes Involving Selectively Mild Iodination of sp3 C-H Bond at α-Position of Ester.

Inter/intramolecular approaches to sp2 C-N bond formation of N-alkenyl benzimidazoles have been accomplished in the presence of an iodide anion associated with a copper catalyst. Both intermolecular and intramolecular reactions included tandem processes, in which selective iodination of sp3 C-H bond at the α-position of ester under mild conditions was demonstrated for the first time. Tandem reactions involving sp3 C-H activation via α-iodo ester intermediate under copper catalysis efficiently provided more than 20 novel azole compounds, and free radicals were not involved in this transformation.

Sequential Michael addition/retro-Claisen condensation of aromatic ß-diketones with α,ß-unsaturated esters: an approach to obtain 1,5-ketoesters.

A K2CO3-catalyzed one-pot protocol involving sequential C-C bond formation and cleavage of aromatic ß-diketones with α,ß-unsaturated esters is developed to obtain 1,5-ketoesters. The sequential reaction via Michael addition and retro-Claisen condensation proceeds smoothly under mild conditions in up to 98% isolated yield. The mechanism study disclosed that the cascade process involved C-C bond cleavage of aromatic ß-diketone as a phenacyl donor under alcoholic alkalescent conditions.