Search

A bis(μ-oxo)diiron(IV,IV) complex as a model for intermediate Q in the methane monooxygenase reaction cycle has been prepared. The precursor complex with a [FeIIIFeIV(μ-O)2] core was fully characterized by X-ray crystallography and other spectroscopic analyses and was converted to the [FeIV2(μ-O)2] complex via electrochemical oxidation at 1000 mV (vs Ag/Ag+) in acetone at 193 K. The UV-vis spectral features, Mossbauer parameters (ΔEQ = 2.079 mm/s and δ = -0.027 mm/s), and EXAFS analysis (Fe-O/N = 1.73/1.96 A and Fe···Fe = 2.76 A) support the structure of the low-spin (S = 1, for each Fe) [FeIV2(μ-O)2] core. The rate constants of the hydrogen abstraction reaction from 9,10-dihydroanthracene at 243 K suggest the high reactivity of these synthetic bis(μ-oxo)diiron complexes supported by simple N4 tripodal ligand.

A quinoline-based hexadentate ligand, (S,S)-N,N,N′,N′-tetrakis(6-methoxy-2-quinolylmethyl)-1,2-diphenylethylenediamine ((S,S)-6-MeOTQPh2EN), exhibits fluorescence enhancement at 498 nm upon additio...

A bis(μ-oxo)diiron(IV,IV) complex as a model for intermediate Q in the methane monooxygenase reaction cycle has been prepared. The precursor complex with a [Fe

A quinoline-based hexadentate ligand, (

A quinoline-based heptadentate ligand, N,N,N′,N′-tetrakis(2-quinolylmethyl)-3-oxa-1,5-pentanediamine (TQOPEN), exhibits a fluorescence increase (ICd/I0 = 25, ϕCd = 0.017) at 428 nm upon addition of 1 equiv of Cd2+. In contrast, 1 equiv of Zn2+ induces a negligible fluorescence change due to weak interaction (IZn/I0 = 2.5, IZn/ICd = 10%). In comparison with TQOPEN, the thia and aza derivatives TQSPEN and TQNPEN exhibit improved Cd2+/Zn2+ selectivity and higher Cd2+-binding affinity, respectively. The solid-state structures of mononuclear Cd2+ and hydroxide-bridged dinuclear Zn2+ complexes of TQOPEN were elucidated by X-ray crystallography. Although the crystal structure of the TQOPEN-Cd2+ complex exhibits a six-coordinate metal center, in which one quinoline weakly interacts with the Cd center (Cd···Nquinoline = 3.303(3) A), a 1H NMR study at 233 K suggests that all quinolines interact with the Cd center to form a symmetrical seven-coordinate structure in solution. Theoretical calculations (TDDFT) support ...

The tetrakisquinoline ligand HT(6-MeO8Q)HPN (N,N,N′,N′-tetrakis(6-methoxy-8-quinolylmethyl)-2-hydroxy-1,3-propanediamine) exhibited Zn2+-induced fluorescence enhancement with high specificity and sensitivity (IZn/I0 = 57 and ICd/IZn = 6% in the presence of 2 equiv of Zn2+; LOD (limit of detection) = 15 nM). This ligand also exhibited fluorescence enhancement specific to inorganic phosphate (PO43–) in DMF–HEPES buffer (50 mM HEPES, 100 mM KCl, pH = 7.5) (1:1) in the presence of 2 equiv of Zn2+. The structure of the unprecedented tetranuclear zinc complex with a μ4-PO4 bridge was elucidated by X-ray crystallography as the key species responsible for fluorescence enhancement.

Dinuclear Zn2+ complexes with HTQHPN (N,N,N′,N′-tetrakis(2-quinolylmethyl)-2-hydroxy-1,3-propanediamine) derivatives have been prepared, and their pyrophosphate (PPi, P2O74–) sensing properties wer...

A quinoline-based heptadentate ligand, N,N,N',N'-tetrakis(2-quinolylmethyl)-3-oxa-1,5-pentanediamine (TQOPEN), exhibits a fluorescence increase (I

The tetrakisquinoline ligand HT(6-MeO8Q)HPN (N,N,N',N'-tetrakis(6-methoxy-8-quinolylmethyl)-2-hydroxy-1,3-propanediamine) exhibited Zn

Two methoxy-substituted TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) derivatives, T(MQ)EN (N,N,N',N'-tetrakis(6-methoxy-2-quinolylmethyl)ethylenediamine) and T(TMQ)EN (N,N,N',N'-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)ethylenediamine), have been prepared, and their fluorescence properties with respect to Zn2+ coordination were investigated. Introduction of a methoxy substituent at 6-position of the quinoline ring enhances the fluorescence intensity by 10-fold, and the three methoxy substituents in the 5,6,7-positions afford significant enhancement of the long-wavelength component of the fluorescence of zinc complex. The substituents did not alter the binding affinity of these compounds toward zinc ion significantly. T(MQ)EN was proved to be effective in detection of zinc ion in cells by fluorescent microscopy.

Six sugar-pendant 2,2'-dipicolylamine (DPA) ligands (L1-3 and L'1-3) have been prepared. OH-protected and unprotected D-glucose, D-mannose, and D-xylose were attached to a DPA moiety via an O-glycoside linkage. X-ray crystallography of the copper(II) complexes (1-5) with these ligands revealed that the anomeric oxygen atom is coordinated to the metal center in the solid state, generating a chiral center at the oxygen atom. The CD spectra of these copper complexes in methanol or aqueous solution exhibit Cotton effects in the d-d transition region, which indicates that the ether oxygen atoms remain coordinated to the metal center and the oxygen-atom chirality is preserved even in solution. For complexes 1 and 2, the inverted oxygen-atom chirality and chelate-ring conformation in the solid state are well correlated with the mirror-image CD spectra in methanol solution. The concomitant inversion of the asymmetric configuration around the copper center was also observed in a methanol solution of complex 3 and a pyridine solution of complex 2. The square-pyramidal/octahedral copper(II) centers also exhibited characteristic absorption and CD spectra.

Dinuclear zinc complex [Zn2(TQHPN)(AcO)](2+) exhibits characteristic fluorescence response (λex = 317 nm and λem = 455 nm) toward pyrophosphate (PPi) with maximum fluorescence upon 1:1 Zn2(TQHPN)-PPi complex formation. The crystallographic investigation utilizing P(1)P(2)-Ph2PPi revealed that the fluorescent response mechanism is due to intramolecular excimer formation of two quinoline rings.

A new heptadentate N6-O1 ligand, N,N,N',N'-tetrakis(2-quinolylmethyl)-2-hydroxy-1,3-propanediamine (Htqhpn), was synthesized and used to generate compounds with linearly ordered MnIIMnIIIMnIIIMnII tetranuclear cores. This is the lowest valent tetranuclear manganese complex that exhibits a (mu2-O)2Mn2 core in the molecule. The electron paramagnetic resonance and magnetic measurements of these tetranuclear complexes suggest moderately strong antiferromagnetic coupling for the central MnIII2 core, with weak coupling between the MnII and MnIII centers.

A pair of copper(II) complexes 1 and 2 exhibit an enantiomeric chiral center at the oxygen atom that coordinates to the metal center. The configurations of the oxygen atom chirality and the chelate ring conformation are simply controlled by protected/free hydroxyl groups of the sugar moiety, yielding mirror image CD spectra. In this system, repulsive and attractive forces are used to regulate chirality on the copper-coordinated oxygen atom both in the solid state and in solution.

Isoquinoline-based tetradentate ligands with C(3)-symmetry, tris(1- or 3-isoquinolylmethyl)amine (1- or 3-isoTQA), have been prepared and their zinc-induced fluorescence enhancement was investigated. Upon excitation at 324 nm, 1-isoTQA shows very weak fluorescence (ϕ = ∼0.003) in DMF/H(2)O (1/1) solution. In the presence of zinc ion, 1-isoTQA exhibits fluorescence increase (ϕ = 0.041) at 359 and 470 nm. This fluorescence enhancement at 470 nm is specific for zinc. However, 3-isoTQA exhibited a smaller fluorescence enhancement upon zinc complexation (ϕ = 0.017, λ(em) = 360 and 464 nm) compared with 1-isoTQA. Crystal structures of zinc complexes of isoTQAs demonstrate the diminished steric crowding and shorter Zn-N(aromatic) distances compared with isoTQENs (N,N,N',N'-tetrakis(isoquinolylmethyl)ethylenediamines) leads to a higher fluorescent response toward zinc relative to cadmium.

Three discrete carbohydrate-appended 2,2'-dipicolylamine ligands were complexed to the {M(CO)(3)}(+) (M = (99m)Tc/Re) core: 2-(bis(2-pyridinylmethyl)amino)ethyl-beta-d-glucopyranoside (L(1)()), 2-(bis(2-pyridinylmethyl)amino)ethyl-beta-D-xylopyranoside (L(2)()), and 2-(bis(2-pyridinylmethyl)amino)ethyl-alpha-d-mannopyranoside (L(3)). An ethylene spacer is used to separate the carbohydrate moiety and the dipicolylamine (DPA) function in all three ligands. The Re complexes [Re(L(1-3))(CO)(3)]Br were characterized by (1)H and (13)C 1D/2D NMR spectroscopies, which confirmed the pendant nature of the carbohydrate moieties in solution. NMR measurements also established the long-range asymmetric effect of the carbohydrate functions on the chelating portion of the ligand. One analogue, [Re(L(1))(CO)(3)]Cl, was characterized in the solid state by X-ray crystallography. Further characterization was provided by IR spectroscopy, elemental analysis, conductivity, and mass spectrometry. Radiolabeling of L(1)-L(3) with [(99m)Tc(H(2)O)(3)(CO)(3)](+) afforded high yield compounds of identical character to the Re analogues. The radiolabeled compounds were found to be stable toward ligand exchange in the presence of a large excess of either cysteine or histidine over a 24-h period.