A new fluorescent sensor based on rhodamine B for Pb2+ was synthesized. The new fluorescent sensor showed an extreme selectivity for Pb2+ over other metal ions examined in acetonitrile. Upon the addition of Pb2+, an overall emission change of 100-fold was observed, and the selectivity was calculated to be 200 times that of Zn2+. The signal transduction occurs via of reversible CHEF (chelation-enhanced fluorescence) with this inherent quenching metal ion.

Slow diffusion of AgNO3 with Me2Si(4-Py)2 yields an interwoven 2-nm-thick sheet consisting of the building block [Ag3(Me2Si(4-Py)2)4](NO3)3.H2O. The interweaving induces unique nanotunnels with a 16 x 18 A2 cross section with a 7 x 8 A2 square pore. The anion NO3- of the skeletal sheet can be reversibly exchanged with appropriately sized anions without the collapse of its structural integrity. The compound has a melting point (140 degrees C) and exists as the first 2D ionic liquid up to 193 degrees C.

L-Amino acids dominate the natural world almost to the exclusion of D-amino acids. However, some important D-amino acids 1 have been found in biology, notably as neurotransmitters (D-serine) 2 and as building blocks (D-alanine) for bacterial cell wall synthesis. 3 There has been considerable interest in understanding the mechanism of the so-called "L to D conversion" of amino acids 4 since enzymes involved in these processes are often targeted for development of therapeutic agents (e.g., antibiotics and antidepressants). In nature, L-amino acids are converted to D-amino acids by pyridoxal phosphate dependent enzymes that racemize amino acids (Scheme 1a). 4 The first step of the racemization reaction involves the formation of a special type of imines with internal resonanceassisted H-bonds (RAHB). 5 We developed a chiral analogue (1) of pyridoxal that binds amino acids by formation of imines with RAHBs. The strong H-bonds can be used to activate the bound amino acids and convert L-amino acids (L-aa) to D-amino acids (Daa) by epimerization of the imines (1-L-aa) formed between 1 and L-aa (Scheme 1b).Receptor 1 was prepared as previously described. 6 Stereoselective recognition of amino acids by 1 can be studied in two different ways. In the first procedure, at least 2-fold excess of a racemic mixture of amino acid is added to 1 and allowed to equilibrate by imine exchange. 6 In the second procedure, 1 equiv of an amino acid (racemic or either enantiomer) is added to 1 and the mixture is allowed to equilibrate by triethylamine catalyzed epimerization (Scheme 1b). Without the base, epimerization is not significant even after weeks.Epimerization of the imines (1-L-aa) formed between 1 and L-amino acids (Scheme 1b) were monitored by 1 H NMR. In a typical experiment, L-serine (10 mM) and 1 (10 mM) were mixed in a DMSO d6 solution to give the corresponding imine (1-L-Ser) within minutes. Triethylamine (50 mM) was then added to the reaction mixture and the epimerization reaction was monitored for 2 days. Figure 1 shows the time dependent change in the 1 H NMR spectrum due to the epimerization of three imines ((a) 1-L-Ser to 1-D-Ser; (b) 1-L-Ala to 1-D-Ala, (c) 1-L-His to 1-D-His).In all cases (Figure 1), the signals due to the two urea N-H and the imine C-H can be conveniently monitored free from other signals. A clear pattern in the 1 H NMR for the epimerization reaction emerges regardless of the amino acid used. The two urea N-H signals shift dramatically downfield and the imine C-H signal shifts upfield with the epimerization reaction. Figure 1 shows that the reactions are remarkably clean and complete for all amino acids. The epimerization reaction takes place by proton exchange at the R position of the amino acid as evidenced by deuteration at this position (solvent: 90/10 v/v DMSO-d6 /D 2 O). (In principle, epimerization could also take place by rotation about the single bond

A mononuclear nonheme oxoiron(IV) complex bearing a pentadentate N5 ligand was prepared in aqueous solution; the pH dependence of its stability and reactivities was reported along with the mechanistic details of sulfide oxidation by the oxoiron(IV) species.