Zeolite framework stabilized copper complex inspired by the 2-His-1-carboxylate facial triad motif yielding oxidation catalysts

The stabilization of a mononuclear copper(II) complex with one MIm2Pr ligand [MIm2Pr = 3,3-bis(1-methylimidazol-2-yl)propionate] in the supercages of zeolite Y was attempted, and the resulting materials were tested for their activity in oxidation catalysis. The preparation procedure yielded initially two species (labeled 1 and 2) within the pore system of the zeolite material, which differ in molecular structure and chemical composition as determined by UV/vis, ESR, IR, and XAFS spectroscopy. In species 1, the copper was found to be five-coordinated, with one MIm2Pr ligand in a facial-type NNO coordination toward copper, the other two coordination sites being occupied by oxygen atoms from either the zeolite framework and/or a water molecule. The total charge of this complex is 1+. In species 2, the copper is surrounded by two MIm2Pr ligands, both in a facial-type coordination mode, identical to the homogeneous Cu(MIm2Pr)2 complex. This neutral species 2 is easily washed out of the zeolite, whereas the mononuclear species 1 remains inside the zeolite material upon washing. The spectroscopic characteristics and activity for 3,5-di-tert-butylcatechol and benzyl alcohol oxidation of species 1 compared closely with that of the zeolite-immobilized Cu(histidine) complexes but differed from that of the homogeneous Cu(MIm2Pr)2 complex. It was therefore found that encapsulation in zeolite offers a route to stabilize a 5-fold-coordinated copper complex with novel catalytic properties. This 1:1 Cu(MIm2Pr) complex is not formed in solution.     

3-benzoyl-2-quinolinecarboxaldehyde: A novel fluorogenic reagent for the high-sensitivity chromatographic analysis of primary amines

3-Benzoyl-2-quinolinecarboxaldehyde has been synthesized and characterized for use as a precolumn fluorogenic reagent for the ultrahigh sensitivity determination of primary amines by micro-column liquid chromatography with laser-induced fluorescence detection. The reaction conditions and the spectral properties of the derivatives were investigated with standard amino-acids. The detection limits, with an HeCd laser operated at 442 nm, are in the low femtogram range. The linear dynamic range is at least three orders of magnitude. The separation of a standard amino-acid mixture and the high-sensitivity analysis of a hydrolysed protein sample are demonstrated.     

The role of synchrotron radiation in examining the self-assembly of crystalline nanoporous framework materials: from zeolites and aluminophosphates to metal organic hybrids

This tutorial review describes the role of synchrotron-based techniques in the study of the formation of Crystalline Nanoporous Framework Materials (CNFMs), such as zeolites, aluminophosphates (AlPOs) and metal organic frameworks (MOFs). Initially, a general formation process for CNFMs is described and the 'tool kit' (including synchrotron and non-synchrotron-based techniques) used to examine this complex process is presented. The need for realistic in situ conditions and the balance between this, data quality and time resolution, are also discussed with reference to commonly utilized in situ synchrotron-based experimental cells. The experimental studies into the formation of several CNFM systems are then examined and the role of the synchrotron-based experiments, in context with those obtained from other techniques, is discussed. From this the importance of the synchrotron-based technique is demonstrated, however it is also shown that, to obtain a more complete understanding of the formation process, complementary independent measurements are still often required. During these discussions some of the most common experimental techniques and analytical methods are also discussed in detail and critically assessed.     

Monitoring the coordination of aluminium during microporous oxide crystallisation by in situ soft X-ray absorption spectroscopy

An in situ cell, which is capable of obtaining time resolved soft X-ray data (200 eV < E < 3000 eV) under hydrothermal conditions has been developed and used to study the self-assembly processes occurring during microporous aluminophosphate crystallization.     

New insights into the coordination chemistry and molecular structure of copper(II) histidine complexes in aqueous solutions

Aqueous solutions of Cu2+/histidine (his) (1:2) have been analyzed in parallel with infrared, Raman, ultraviolet/visible/near-infrared, electron spin resonance, and X-ray absorption spectroscopy in the pH range from 0 to 10. Comprehensive interpretation of the data has been used to extract complementary structural information in order to determine the relative abundance of the different complexes. The formation of six different, partly coexisting species is proposed. Structural proposals from literature have been unambiguously confirmed, refined, or, in several cases, corrected. At highly acidic conditions, Cu2+ and his are present as free ions, but around pH = 2, coordination starts via the deprotonated carboxylic acid group. This results in the intermediate species Cu2+[H3his+(Oc)] and Cu2+[H3his+(Oc)]2. The coordination via Oc is attended with a drop in the pKa value of the other receptor groups resulting in a concomitant conversion to the bidentates Cu2+[H2his0(Oc,Nam)] and Cu2+[H2his0(Oc,Nam)]2, with the latter being dominant at pH = 3.5. Coordination of the imidazole ring begins around pH = 3 and leads to the formation of the mixed ligand complexes Cu2+[H2his0(Oc,Nam)][Hhis-(Oc,Nam,Nim)] and Cu2+[Hhis-(Nam,Nim)][Hhis-(Oc,Nam,Nim)] around pH = 5. It is demonstrated that coordination of the imidazole ring occurs predominantly via the N(pi) atom. At pH > 7, the double-tridentate ligand complex Cu2+[Hhis-(Oc,Nam,Nim)]2 is the major species with the N atoms in the equatorial plane and the O atoms in the axial position. This complex decomposes at pH > 10 into a copper oxide/hydroxide precipitate. The overall results provide a consistent picture of the mechanism that drives the coordination and complex formation of the Cu2+/his system.     

Detection of s-triazine pesticides in natural waters by modified large-volume direct injection HPLC

There is a need for simple and inexpensive methods to quantify potentially harmful persistent pesticides often found in our water-ways and water distribution systems. This paper presents a simple, relatively inexpensive method for the detection of a group of commonly used pesticides (atrazine, simazine and hexazinone) in natural waters using large-volume direct injection high performance liquid chromatography (HPLC) utilizing a monolithic column and a single wavelength ultraviolet-visible light (UV-vis) detector. The best results for this system were obtained with a mobile phase made up of acetonitrile and water in a 30:70 ratio, a flow rate of 2.0 mL min⁻¹, and a detector wavelength of 230 nm. Using this method, we achieved retention times of less than three minutes, and detection limits of 5.7 μg L⁻¹ for atrazine, 4.7 μg L⁻¹ for simazine and 4.0 μg L⁻¹ for hexazinone. The performance of this method was validated with an inter-laboratory trial against a National Association of Testing Authorities (NATA) accredited liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method commonly used in commercial laboratories.     

Total syntheses of the bromotyrosine-derived natural products ianthelline, 5-bromoverongamine and JBIR-44

The total syntheses of the bromotyrosine-derived natural products ianthelline, 5-bromoverongamine and JBIR-44 are described and their cytotoxic activity in a cervical cancer (HeLa) cell line and human umbilical vein endothelial cells (HUVECs) are reported.