Imidazole N-atom Research Articles

ZIF-8 in-situ growth on amidoximerized polyacrylonitrile beads for uranium sequestration in wastewater and seawater

With the vigorous development of nuclear power and the shortage of terrestrial uranium resources, the extraction uranium from seawater is extremely attractive for human development. Herein, we first report ZIF-8 in-situ growth on amidoximerized polyacrylonitrile (PAO) porous materials. The porous material is a small sphere with certain mechanical strength synthesized by solvent-induced phase separation method. Because ZIF-8 nanocrystals are well-formed and evenly distributed within the PAO beads, ZIF-8/PAO has a high specific surface area (386 m2 g-1) and rich pore structure. At adsorption experiment, the highest adsorption capacity of ZIF-8/PAO reached 803 mg g-1 at pH = 4. Furthermore, competitive adsorption experiment and simulated seawater test was studied. The selectivity for uranium was excellent (Kd = 1.7 × 105 mL g-1) and uranium adsorption rate reached 99% at 3 ug L-1. XPS analysis shows that U(VI) is chelated by imidazole-N atoms and amidoxime groups in ZIF-8/PAO. Therefore, ZIF-8/PAO can be considered a highly promising adsorbent for uranium extraction from wastewater and seawater.

High and Tunable Proton Conduction in Six 3D-Substituted Imidazole Dicarboxylate-Based Lanthanide-Organic Frameworks.

Six isostructural three-dimensional (3D) Ln(III)-organic frameworks, {[Ln2(HMIDC)2(μ4-C2O4)(H2O)3]·4H2O}n [LnIII = GdIII (1), EuIII (2), SmIII (3), NdIII (4), PrIII (5), and CeIII (6)], have been fabricated by using a multifunctional ligand of 2-methyl-1H-imidazole-4,5-dicarboxylic acid (H3MIDC). Ln-metal-organic frameworks (MOFs) 1-6 present 3D structures and possess abundant H-bonded networks between imidazole-N atoms and coordinated and free water molecules. All the six Ln-MOFs demonstrate humidity- and temperature-dependent proton conductivity (σ) having the optimal values of 2.01 × 10-3, 1.40 × 10-3, 0.93 × 10-3, 2.25 × 10-4, 1.11 × 10-4, and 0.96 × 10-4 S·cm-1 for 1-6, respectively, at 100 °C/98% relative humidity, in the order of CeIII (6) < PrIII (5) < NdIII (4) < SmIII (3) < EuIII (2) < GdIII (1). In particular, the σ for 1 is 1 order of magnitude higher than that for 6, and it enhances systematically according to the decreasing order of the ionic radius, indicating that the lanthanide-contraction tactics can effectively regulate the proton conductivity while retaining the proton conduction routes. This will offer valuable guidance for the acquisition of new proton-conducting materials. In addition, the outstanding water stability and electrochemical stability of such Ln-MOFs will afford a solid material basis for future applications.

5-Amino-1-(2',3'-O-iso-propyl-idene-d-ribit-yl)-1H-imidazole-4-carboxamide: a crystal structure with Z' = 4.

The title compound, C12H20N4O5, crystallizes in the monoclinic space group P21, with four crystallographically independent mol-ecules in the asymmetric unit. The four mol-ecules have a very similar conformation that is basically determined by the formation of two intra-molecular hydrogen bonds between the amino NH2 donors and the carbonyl and ring O-atom acceptors, forming, respectively, R(6) and R(7) ring motifs.. In the crystal, inter-molecular hydrogen bonding leads to the formation of R22(10) ring patterns, involving one amide CONH2 donor and an imidazole N-atom acceptor. The cluster of the four independent mol-ecules has approximate non-crystallographic C2 point symmetry. The structural analysis also shows that during the synthesis of the title compound, the reductive cleavage of the d-ribose ring of the inosine precursor proceeds stereoselectively, with retention of configuration.

Selective and sensitive colorimetric detection of Hg(II) in aqueous solution by quinone-diimidazole ensemble with mimicking YES-OR-INHIBIT logic gate operation

A quinone-diimidazole ensemble (R1) has been prepared and characterized. The receptor exhibits a striking colour change from brown to blue instantaneously with Hg(II) ion in DMF:Water (1:9v/v) selectively and sensitively. Electronic, fluorescence and 1H NMR titration experiments show that the mechanism of sensing involves the formation of [Hg(R1)2Cl2] complex having binding constant 6.31×105M−1. The product of the reaction is characterized using LCMS and FT-IR spectroscopy which suggests the coordination of R1 to Hg(II) ion through imidazole N-atom. The addition of Hg(II) to R1 leads to fluorescence quenching with limits of detection 10nM. The concatenation of YES-OR-INHIBIT combinational logic circuit has also been simulated and its truth table is verified successfully.

3,3′-({4-[(4,5-Dicyano-1H-imidazol-2-yl)diazenyl]phenyl}imino)dipropionic acid

The title compound, C17H15N7O4, is a push–pull non-linear optical chromophore containing a di­alkyl­amino donor group and the di­cyano­imidazolyl acceptor separated by a π-conjugated path. The benzene and imidazole rings are not coplanar, making a dihedral angle of 10.0 (2)°. In the crystal, mol­ecules are linked by an extended set of hydrogen bonds and several motifs are recognized. Pairs of mol­ecules are held together by hydrogen bonding between carb­oxy O—H donor groups and diazenyl N-atom acceptors, forming R 2 2(24) ring patterns across inversion centres. Four-mol­ecule R 4 4(28) ring motifs are formed, again across inversion centres, through hydrogen bonding involving carb­oxy O—H donor groups and diazenyl and imidazole N-atom acceptors. Four-mol­ecule R 4 4(42) patterns are formed among mol­ecules related by translation and involve carb­oxy O—H and imidazole N—H donor groups with carbonyl O-atom and imidazole N-atom acceptors.

Synthesis and Crystal Structure of a Cyanido-Bridged Bimetallic Copper(II)–Silver(I) Complex of Imidazole and [Ag(CN)2]−: [Cu(Imidazole)4{Ag(CN)2}2

A cyanido-bridged Cu(II)–Ag(I) bimetallic complex, [Cu(Imidazole)4{Ag(CN)2}2] has been prepared and structurally characterized. The compound crystallizes in the orthorhombic space group Pmna. The crystal structure of the complex consists of trinuclear molecules made up of one [Cu(Imidazole)4]+2 and two [Ag(CN)2]− units. The trinuclear molecules are interlinked to each other through N–H–N and C–H–N hydrogen bonds. The Cu(II) ions are located on mirrors and assume distorted octahedral geometry with the basal plane consisting of four imidazole N-atoms.

A novel 18-membered metallocycle in {2,5-bis[3-(1H-1,3-imidazol-1-ylmethyl)phenyl]-1,3,4-oxadiazole}dichloridocobalt(II)

The title molecular complex, [CoCl(2)(C(22)H(18)N(6)O)], features a novel 18-membered Co-containing metallocycle. The Co(II) atom lies in a fairly regular tetrahedral geometry defined by two imidazole N-atom donors from one 2,5-bis[3-(1H-1,3-imidazol-1-ylmethyl)phenyl]-1,3,4-oxadiazole (L) ligand and two chloride anions. The coordinating orientation of the L ligand plays an important role in constructing the metallocycle complex. The complexes form a three-dimensional supramolecular assembly via nonclassical C-H...Cl and C-H...N hydrogen bonds and pi-pi interactions.

Chiral imidazole metalloenzyme models: Synthesis and enantioselective hydrolysis for α-amino acid esters

Chiral imidazole hydrolytic metalloenzyme models with characteristics of chiral centers directly link to imidazole N-atoms and varieties in both alkyl chain length and number of alkyl chains, have been synthesised and investigated for enantioselective hydrolysis of Boc-α-amino acid esters. The result indicates that both hydrolysis rates and enantioselectivities are increased with increases in the alkyl chain length and the number of the alkyl chains in the lipophilic chiral imidazole-type surfactants in many cases. The lipophilic chiral imidazole 4d (( S)-1-hexadecoxy-2-(1-imidazolyl)-propane), which has one long alkyl chain, shows higher hydrolysis rate and enantioselectivity ( k D = 132.5 × 10 −5, k D/ k L = 5.38), 5d (( S)-1,5-dihexadecoxy-2-(1-imidazolyl)-pentane), which has two long alkyl chains, shows the highest hydrolysis rate and enantioselectivity ( k D = 201.5 × 10 −5, k D/ k L = 11.72). Additionally, the effects of the metals, the additives, the solvents and the substrates on the hydrolysis rates and enantioselectivities are examined.

β-Peptidic Secondary Structures Fortified and Enforced by Zn2+ Complexation – On the Way toβ-Peptidic Zinc Fingers?

The correlation between β2-, β3-, and β2,3-amino acid-residue configuration and stability of helix and hairpin-turn secondary structures of peptides consisting of homologated proteinogenic amino acids is analyzed (Figs. 1–3). To test the power of Zn2+ ions in fortifying and/or enforcing secondary structures of β-peptides, a β-decapeptide, 1, four β-octapeptides, 2–5, and a β-hexadecapeptide, 10, have been devised and synthesized. The design was such that the peptides would a) fold to a 14-helix (1 and 3) or a hairpin turn (2 and 4), or form neither of these two secondary structures (i.e., 5), and b) carry the side chains of cysteine and histidine in positions, which will allow Zn2+ ions to use their extraordinary affinity for RS− and the imidazole N-atoms for stabilizing or destabilizing the intrinsic secondary structures of the peptides. The β-hexadecapeptide 10 was designed to a) fold to a turn, to which a 14-helical structure is attached through a β-dipeptide spacer, and b) contain two cysteine and two histidine side chains for Zn complexation, in order to possibly mimic a Zn-finger motif. While CD spectra (Figs. 6–8 and 17) and ESI mass spectra (Figs. 9 and 18) are compatible with the expected effects of Zn2+ ions in all cases, it was shown by detailed NMR analyses of three of the peptides, i.e., 2, 3, 5, in the absence and presence of ZnCl2, that i) β-peptide 2 forms a hairpin turn in H2O, even without Zn complexation to the terminal β3hHis and β3hCys side chains (Fig. 11), ii) β-peptide 3, which is present as a 14-helix in MeOH, is forced to a hairpin-turn structure by Zn complexation in H2O (Fig. 12), and iii) β-peptide 5 is poorly ordered in CD3OH (Fig. 13) and in H2O (Fig. 14), with far-remote β3hCys and β3hHis residues, and has a distorted turn structure in the presence of Zn2+ ions in H2O, with proximate terminal Cys and His side chains (Fig. 15).

Pseudo-merohedrally twinned tetrakis(1H-imidazole-κN3)bis(N-nitrocyanamidato-κN)copper(II)

Crystals of the title complex, [Cu(CN3O2)2(C3H4N2)4], the structure of which has been determined by single-crystal X-ray diffraction at 304 K, appear to be pseudo-merohedrally twinned. Transformation to a monoclinic C-centred cell was necessary in order to derive the twin law. Twin refinement in a triclinic unit cell significantly reduced the R value. The asymmetric unit of the triclinic cell consists of one mol­ecule in a general position and two half entities with the Cu atom on a centre of inversion. The coordination of the Cu atom is quasi-octa­hedral, with four imidazole N-atom donors in the equatorial plane and two cyano N atoms from the N-nitro­cyanamidate anion in axial positions. Owing to symmetry in the centrosymmetric mol­ecules, the trans imidazole ligands are parallel, while those in the non-centrosymmetric mol­ecule make angles of 22.8 (2) and 77.9 (2)°.

Dinickel Complexes Bridged by Unusual (N,O,O )-Coordinated α-Amino Acids: Syntheses, Structural Characterization and Magnetic Properties

Four novel dinickel complexes, coordinated by mixed ligands of tren and racemic amino acids, namely [Ni2(tren)2(dl-alaninato)(H2O)]I3·2H2O (1), [Ni2(tren)2(dl-leucinato)(H2O)]I3·2.5H2O (2), [Ni2(tren)2(dl-phenylalaninato)(H2O)]I3·H2O (3), and {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}n(4), have been synthesized and structurally characterized by X-ray crystallography, FTIR, u.v. and e.s. spectra. They represent the first series of dinickel(II) complexes bridged by the unusual (N,O,O′)-coordinated α-amino acids. In complexes (1–3), one of the nickel(II) centers is coordinated by four N-atoms of the tren ligand, one O-atom of the carboxylate group of the amino acidato ligand and one H2O molecule. The other nickel(II) center is also coordinated by the four N-atoms of the tren ligand, one carboxylic O-atom and the amino N-atom of the amino acidato ligand, resulting in an asymmetric dinuclear core with chromophores of NiN4O2 and NiN5O. In the polymeric {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}n(4), the imidazole N-atom is also involved in ligation with nickel(II) and both nickel(II) centers have the same chromophore described as NiN5O. The Ni...Ni distances are in the 5.5199(10)–5.5807(15)A range. Analyses of the magnetic properties of complexes (1), (3) and (4) show that a weak ferromagnetic interaction exists between the two nickel(II) centers.

Copper(I)–azoimidazoles: a comparative account on the structure and electronic properties of copper(I) complexes of 1-methyl-2-(phenylazo)imidazole and 1-alkyl-2-(naphthyl-(α/β)-azo)imidazoles

Bis-[1-alkyl-2-(naphthyl-(α/β)azo)imidazole]copper(I) perchlorate derivatives, [Cu(α-NaiR) 2(ClO 4)] and Cu(β-NaiR) 2](ClO 4), have been characterised by spectral and electrochemical studies. The single crystal X-ray structure of bis-[1-ethyl-2-(naphthyl-α-azo)imidazole]copper(I) perchlorate shows strong bonding with two imidazole-N atoms, two azo-N donors interact weakly and the structure is described as having a [2+2] distorted linear geometry. A structural comparison has been done with the X-ray structure of bis-[1-methyl-2-(phenylazo)imidazole]copper(I) perchlorate which is T d symmetric. Solution electronic spectra and redox properties are compared and have been correlated with EHMO calculation.

Bis[2-hydroxy-3-(1H-imidazol-4-yl)propionato]nickel(II)

In the title compound, [Ni(C6H7N2O3)2], the NiII ion has a slightly distorted octahedral coordination geometry and lies on a twofold rotation axis. 2-Hydro­xy-3-(1H-imidazol-4-yl)­propionic acid ligates in a tridentate manner. Two carboxyl­ate-O atoms and two hydroxyl-O atoms are coordinated in cis positions with respect to each other and form the equatorial plane, and two imidazole-N atoms are coordinated in axial positions. The mol­ecules are held together by an intermolecular hydrogen-bonding network involving the carboxyl­ate, imino and hydroxyl groups.