Aqueous adsorption of bisphenol A over a porphyrinic porous organic polymer.

A new porphyrinic porous organic polymer (PPOP) with high stability and excellent textural properties (929 m2/g surface area with 0.73 cm3/g pore volume) was made via the Friedel-Crafts reaction and applied for bisphenol A (BPA) adsorption in water. The material was examined by X-ray diffraction, N2 adsorption-desorption isotherms, scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state 13C CP-MAS nuclear magnetic resonance spectroscopy. PPOP was proven highly effective for capturing BPA among the many adsorbent materials investigated. The Langmuir model could closely match the adsorption isotherm data with a high adsorption amount of ca. 653 mg/g at 25 °C. Approximately 95% of BPA was adsorbed in 50 min, and the pseudo-second-order kinetic model satisfactorily described the adsorption behavior. This adsorption process was exothermic (ΔH° = -39.10 kJ/mol), and the capacity gradually decreased with increasing pH. Spectroscopic analyses indicated that the BPA adsorption on PPOP was affected by (1) π-π interaction between BPA and the aromatic constituents of PPOP, (2) hydrogen bonding between the N sites of porphyrin units in PPOP and the hydroxyl group of BPA and, and (3) hydrophobic interactions. PPOP was easily regenerated after acetone washing, and >98% efficiency was observed throughout the five repeated adsorption-desorption cycles.

Structural analysis of the manganese transport regulator MntR from Bacillus halodurans in apo and manganese bound forms.

The manganese transport regulator MntR is a metal-ion activated transcriptional repressor of manganese transporter genes to maintain manganese ion homeostasis. MntR, a member of the diphtheria toxin repressor (DtxR) family of metalloregulators, selectively responds to Mn2+ and Cd2+ over Fe2+, Co2+ and Zn2+. The DtxR/MntR family members are well conserved transcriptional repressors that regulate the expression of metal ion uptake genes by sensing the metal ion concentration. MntR functions as a homo-dimer with one metal ion binding site per subunit. Each MntR subunit contains two domains: an N-terminal DNA binding domain, and a C-terminal dimerization domain. However, it lacks the C-terminal SH3-like domain of DtxR/IdeR. The metal ion binding site of MntR is located at the interface of the two domains, whereas the DtxR/IdeR subunit contains two metal ion binding sites, the primary and ancillary sites, separated by 9 Å. In this paper, we reported the crystal structures of the apo and Mn2+-bound forms of MntR from Bacillus halodurans, and analyze the structural basis of the metal ion binding site. The crystal structure of the Mn2+-bound form is almost identical to the apo form of MntR. In the Mn2+-bound structure, one subunit contains a binuclear cluster of manganese ions, the A and C sites, but the other subunit forms a mononuclear complex. Structural data about MntR from B. halodurans supports the previous hypothesizes about manganese-specific activation mechanism of MntR homologues.