Attachment of an electron-withdrawing fluorophore to a cryptand for modulation of fluorescence signaling

The laterally nonsymmetric aza cryptand synthesized by condensing tris(2-aminoethyl)amine (tren) with tris[2-[(3-(oxomethyl)phenyl)oxy]ethyl]mine readily forms mononuclear inclusion complexes with both transition- and main-group-metal ions. The fluorophore 7-nitrobenz-2-oxa-1,3-diazole is attached to one of the secondary amines, to give an integrated fluorophore-receptor configuration. The fluorophoric system does not show any appreciable emission when excited due to an efficient photoinduced intramolecular electron transfer (PET) from the nitrogen lone pair. When a metal ion enters the cavity, the PET is blocked, causing recovery of fluorescence; Cd(II) gives the highest quantum yield. The fluorophore, with pi-accepting ability, drastically alters the binding property of the cryptand. With perchlorate or tetrafluoroborate salts of Cd(II), the metal ion enters the cavity, causing recovery of fluorescence. However, in the presence of coordinating ions such as Cl-, N3-, and SCN-, the metal ion comes out of the cavity, causing PET to take place once again, and the fluorescence is lost. Thus, translocation of Cd(II) between the inside and outside of the cryptand cavity can lead to a reversible fluorescence on/off situation.     

Silver (I)-promoted asymmetric halohydrin reaction of chiral N-enoyl-2-oxazolidinones: scope and limitations

The halohydrin reaction of chiral N-enoyl-2-oxazolidinones 1 by halogen (Br₂/I₂) and water were efficiently carried out in aqueous organic solvent promoted by silver(I) with high anti- and regioselectivity and moderate to good diastereoselectivities. The alkenoyl, cinnamoyl and electron-deficient cinnamoyl substrates smoothly underwent bromohydrin reaction in aqueous acetone but no iodohydrin reaction, where as electron-rich cinnamoyl substrates preferred to undergo iodohydrin reaction in aqueous acetone with moderate diastereoselectivity and enhanced diastereoselectivity was observed in aqueous THF.     

Metal-organic framework H-bonded like a polycatenane: coexistence of acyclic water trimer and nonamer

Pyridine-2,6-dicarboxylic acid and 1,2-di-4-pyridylethylene react hydrothermally with nickel(II) nitrate, forming a metal-organic framework that forms a polycatenane-like structure through H-bonding interactions between water molecules and carboxylate O atoms with void spaces. Discrete acyclic trimeric and nonameric water clusters occupy the voids in the structures. X-ray powder diffraction and X-ray structure analysis have been used to characterize this compound. Crystal data for 1 {(3dpeH(2))[Ni(pdc)(2)](3).15H(2)O}: monoclinic space group P2(1)/c, a = 24.730(5) Angstroms, b = 19.895(2) Angstroms, c = 17.257(4) Angstroms, beta = 104.832(5) degrees, V = 8208(4) Angstroms(3), Z = 4, R1 = 0.0429, wR2 = 0.1072, and S = 1.051.     

Stereoselective syntheses of (−)-chloramphenicol and (+)-thiamphenicol

Chloramphenicol and thiamphenicol have been enantioselectively synthesized using an asymmetric halohydrin reaction as a key step. In particular, halomethoxylation reaction was used, where O-methyl functions as a hydroxyl protecting group and eliminates an additional protection step.     

Autofluorescence characterization of advanced glycation end products of hemoglobin

This article describes the analysis of autofluorescence of advanced glycation end products of hemoglobin (Hb-AGE). Formed as a result of slow, spontaneous and non-enzymatic glycation reactions, Hb-AGE possesses a characteristic autofluorescence at 308/345 nm (lambda(ex)/lambda(em)). Even in the presence of heme as a quenching molecule, the surface presence of the glycated adduct gave rise to autofluorescence with the quantum yield of 0.19. The specificity of monoclonal antibody developed against common AGE structure with Hb-AGE was demonstrated using reduction in fluorescence polarization value due to increased molecular volume while binding. The formation of fluorescent adduct in hemoglobin in the advanced stage of glycation and the non-fluorescent HbA(1c) will be of major use in distinguishing and to know the past status of diabetes mellitus. While autofluorescence correlated highly with HbA(1c) value under in vivo condition (r = 0.85), it was moderate in the clinical samples (r = 0.55). The results suggest a non-linear relation between glycemia and glycation, indicating the application of Hb-AGE as a measure of susceptibility to glycation rather than glycation itself.     

Metal complexes of sulphur-nitrogen chelating agents. Part 14. Nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) complexes of the tetradentate schiff bases having ONNS donor sites

Summary Complexes of nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) with methyl-2-(-salicylaldiminoethyl)-cyclopent-1-en-dithiocarboxylate (H₂L¹) and methyl-2-(-salicylaldiminoisopropyl)cyclopent-1-en-dithiocarboxylate (H₂L²) have been prepared. They contain the donor sites ONNS. The metal(II) ions from neutral, monomeric square planar chelate complexes. The cobalt(III) complexes [CoL¹-(H₂O)₂]X (X=Cl or ClO₄) appear to betrans-diaqua-species. All compounds have been characterized by a number of physico-chemical methods.     

Microwave Assisted Rupture of Furoxans to Nitrile Oxides and Intermolecular Capture by Dipolarophiles

3,4-Diaroylfuroxans 1 react with various dipolarophiles 3 under microwave activation to afford the cycloadduct 4 instead of the expected isoxazole 5 in good yields in the absence of solvent.