Photocatalytic degradation of acridine dyes using anatase and rutile TiO2.

The adsorption and photodegradation of acridine orange (AO) and acriflavine (AF) dyes on two mesoporous titania crystalline phases, anatase and rutile, were experimentally studied. Anatase and rutile were characterized by nitrogen adsorption, electron scanning and transmission microscopy, and X-ray diffraction. The adsorption capacity of rutile was higher than that of anatase, while the reverse is observed for photodegradation of both dyes. The adsorption of AF on both adsorbents was higher than that of AO, which was related with the smaller size of AF molecules compared with those of AO, therefore the access of AF to the adsorption sites is favored.

Structures of two natural product methyltransferases reveal the basis for substrate specificity in plant O-methyltransferases.

Chalcone O-methyltransferase (ChOMT) and isoflavone O-methyltransferase (IOMT) are S-adenosyl-l-methionine (SAM) dependent plant natural product methyltransferases involved in secondary metabolism in Medicago sativa (alfalfa). Here we report the crystal structure of ChOMT in complex with the product S-adenosyl-l-homocysteine and the substrate isoliquiritigenin (4,2',4'-trihydroxychalcone) refined to 1.8 A as well as the crystal structure of IOMT in complex with the products S-adenosyl-l-homocysteine and isoformononetin (4'-hydroxy-7-methoxyisoflavone) refined to 1.4 A. These two OMTs constitute the first plant methyltransferases to be structurally characterized and reveal a novel oligomerization domain and the molecular determinants for substrate selection. As such, this work provides a structural basis for understanding the substrate specificity of the diverse family of plant OMTs and facilitates the engineering of novel activities in this extensive class of natural product biosynthetic enzymes.