Qingliang Liu

An unusual alternating ferro- and antiferromagnetic 1D hydrogen-bonded µ2-1,3-azide-bridged copper(II) complex: a dominant ferromagnetic couplingElectronic supplementary information (ESI) available: EPR spectra of 1 (Fig. S1) and fit of χMT data with the binuclear model (Fig. S2). See http://www.rsc.org/suppdata/nj/b1/b108511p/

A single-crystal structure analysis of [Cu2(bben)2(N3)4]n (1) [bben1,2-bis(benzylamino)ethane] revealed that the complex consists of double asymmetric μ2-1,3-azide-bridged dimeric copper(II) moieties; each copper(II) coordinates with one bben, one terminal azido, and the two bridging azido ligands. The Cu–N3–Cu torsion angle has a very large value of 47.5°. The dimeric units are assembled into 1D chains through N(bben)–H⋯N (azido) hydrogen bonds. The intra- and the interdimeric Cu⋯Cu distances in the chain are 5.281(2) and 3.662(2) A, respectively. Magnetic measurements on 1 have revealed the existence of a dominant ferromagnetic interaction with exchange coupling parameters of JF = 16.8 cm−1, and JAF = −3.6 cm−1, using an alternating ferro- and antiferromagnetic chain model for S = 1/2 local spins. The ferro- and antiferromagnetic interactions are ascribed to the μ2-1,3-azide bridges and the hydrogen bonds, respectively; the former interactions are rationalized by the large Cu–N3–Cu torsion angles.

Structural and magnetic properties of O-bridged tetranuclear and binuclear Cu(II) complexes

Abstract Two copper(II) complexes [Cu 4 (L 1 ) 4 ] ( 1 ) and [Cu 2 (phen) 2 (HL 2 ) 2 ] (ClO 4 ) 2 ( 2 ) have been synthesized from two potentially tridentate ligands N -(2-hydroxybenzyl) propanolamine (H 2 L 1 ) and N -(2-hydroxybenzyl) ethanolamine (H 2 L 2 ). X-ray analyses revealed that 1 contains a Cu 4 O 4 cubane core, with each two Cu(II) atoms bridged by a pair of alkoxides; 2 has a bis(μ 2 -phenoxo)-bridged dicopper(II) structure. Variable temperature magnetic measurements of 1 have revealed that the correlation between 2 J and the bridge angles φ for 1 shows a very strong antiferromagnetic tendency, i.e. the ferromagnetic and antiferromagnetic interactions cross at the φ of 94.5°. The relatively weak antiferromagnetic interactions (2 J =−226.8 cm −1 ) with respect to the bridge angles ( φ =100.4°) for 2 have been ascribed to the pyramidal distortions at the phenoxide oxygen atoms in addition to the unfavorable overlaps of the magnetic orbitals for the highly distorted copper coordination polyhedra.

The purification and spectral properties of polyphenol oxidase I fromNicotiana tabacum

Polyphenol oxidase plays a key role in plant defense systems. We report the first-time purification of polyphenol oxidase (PPO 1.14.18.1) from fresh leaves of tobacco (Nicotiana tabacum) using acetone powder, ammonium sulfate precipitation, and column chromatography with DEAE-Sephadex A-50, CM-Sephadex C-50, and Sephadex G-75. PPO I was purified approximately 71-fold (3200 U/mg). The MALDI-TOF-MS spectrum showed that the enzyme was purified to a pure protein with a molecular weight of 35700 Da. The optimum pH of PPO I was 7, the optimum temperature was 40°C, and the Km value was 6.8 mM using catechol as the substrate at pH 6.5 and with 0.05 M H3PO4−NaOH buffer. The maximum emission peak of PPO I was 339 nm with 16 nm of blue-shifted compared with 355 nm of free tryptophan. The UV/VIS spectra and the absence of an EPR signal are indicative of type-3 coppers, but not type-1 or type-2 coppers. PPO I and mushroom PPO have the same active center for a pair of coupled antiferromagnetic copper ions.

Crystal structure and magnetic properties of a Cu4O4 cubane complex with N-(2-hydroxybenzyl)-propanolamine

Abstract The crystal structure of [ Cu ( L 1 )] 4 ( 1 ) (H2L1=N-(2-hydroxybenzyl)-propanolamine) contains a Cu4O4 cubane core, involving four intramolecular hydrogen bonds. Magnetic studies reveal a good linear correlation between 2J and the bridge angle φ; the more antiferromagnetic trend than the literature correlations for the alkoxo-bridged complexes is ascribed to the additional superexchange pathways via the multiple hydrogen bonds.

The FT-IR spectrometric analysis of the changes of polyphenol oxidase II secondary structure

Abstract Polyphenol oxidase II is a novel protein purified from tobacco, which acts as a key role in plant defense system. From the analysis of FT-IR spectrums, Fourier self-deconvolution (FSD) spectrums and second-derivative spectrums of PPO II at different pH and peroxide PPO II adduct, the secondary structure fractions are analyzed. PPO II at low pH (pH=3.0) and peroxide PPO II adduct almost keep the same secondary structure of native PPO II. The percentages of β-turn and random coil increase rapidly and the percentages of α-helix and anti-parallel β-sheet decrease rapidly at high pH (pH=10.0) comparing with that of native PPO II. All these conclusions are proved by the secondary structure calculations of circular dichroism spectrums in different states.

Ca(II)- and Tb(III)-induced stabilization and refolding of anticoagulation factor I from the venom of Agkistrodon acutus

Anticoagulation factor I (ACF I) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X‐binding protein in a Ca2+‐dependent fashion with marked anticoagulant activity. The equilibrium unfolding/refolding of apo‐ACF I, holo‐ACF I, and Tb3+‐reconstituted ACF I in guanidine hydrochloride (GdnHCl) solutions was studied by following the fluorescence and circular dichroism. Metal ions were found to increase the structural stability of ACF I against GdnHCl and thermal denaturation and, furthermore, influence its unfolding/refolding behavior. The GdnHCl‐induced unfolding/refolding of both apo‐ACF I and Tb3+‐ACF I is a two‐state process with no detectable intermediate state(s), whereas the GdnHCl‐induced unfolding/refolding of holo‐ACF I in the presence of 1 mM Ca2+ follows a three‐step transition, with intermediate state a (Ia) and intermediate state b (Ib). Ca2+ ions play an important role in the stabilization of the Ia and Ib states. The decalcification of holo‐ACF I shifts the ending zone of unfolding/refolding curve toward lower GdnHCl concentration, whereas the reconstitution of apo‐ACF I with Tb3+ ions shifts the initial zone of denaturation curve toward higher GdnHCl concentration. Therefore, it is possible to find a denaturant concentration (2.0 M GdnHCl) at which refolding from the fully denatured state of apo‐ACF I to the Ib state of holo‐ACF I or to the native state of Tb3+‐ACF I can be initiated merely by adding the 1 mM Ca2+ ions or 10 μM Tb3+ ions to the unfolded state of apo‐ACF I, respectively, without changing the concentration of the denaturant. Using Tb3+ as a fluorescence probe of Ca2+, the kinetic results of metal ions–induced refolding provide evidence that the compact Tb3+‐binding region forms first, and subsequently, the protein undergoes further conformational rearrangements to form the native structure.

Synthesis, crystal structure and properties of the zinc complexes with unsymmetrical tridentate ligands

Abstract Two complexes of zinc (II) with mixed-ligand, [Zn2(phen)2(HL1)2] (ClO4)2 (1) and [Zn2(phen)2(HL2)2] (ClO4)2(2) (H2L1N–(2-hydroxybenzyl) ethanolamine and H2L2=N–(2-hydroxybenzyl) propanolamine), and another zinc complex ZnL1 (3) were synthesized and characterized by elemental analysis, IR spectra, thermal analysis, fluorescence and 1H NMR. The crystal structure of (1) has a centrosymmetric di-phenoxo-bridged dizinc (II) core and each zinc center is laid in a slightly distorted trigonal bipyramidal geometry. A 2D supramolecular structure is formed approximately along bc plane in terms of the action of multiple N–H⋯O and O–H⋯O hydrogen bonds between the (HL1)− ligands and the π⋯π stacking interactions between the phenanthroline ligands. Thermal behavior, studied by TG and DTA in nitrogen atmosphere, indicates that phen is eliminated at higher temperature than (HL1)− and (HL2)−. Several possible mechanisms for the fluorescence quenching of the metal complexes are proposed.

The Effect of Calcium (II) on the Binding of Anticoagulation Factor I with Activated Coagulation Factor X

Anticoagulation factor I (ACF I) from the venom of Agkistrodon acutus forms a 1:1 complex with activated coagulation factor X (FXa) in a Ca2+-dependent fashion and thereby prolongs the clotting time. In the present study, the dependence of the binding of ACF I with FXa on the concentration of Ca2+ ions was quantitatively analyzed by HPLC, and the result showed that the maximal binding of ACF I to FXa occurred at concentration of Ca2+ ions of about 1 mM. The binding of Ca2+ ions to ACF I was investigated by equilibrium dialysis and two Ca2+-binding sites with different affinities were identified. At pH 7.6, the apparent association constants K1 and K2 for these two sites were (1.8 ± 0.5) × 105 and (2.7 ± 0.6) × 104 M−1 (mean ± SE, n = 4), respectively. It was evident from the observation of Ca2+-induced changes in the intrinsic fluorescence of ACF I that ACF I underwent a conformational change upon binding of Ca2+ ions. The occupation of both Ca2+-binding sites in ACF I required a concentration of Ca2+ ions of about 1 mM, which is equal to the effective concentration of Ca2+ ions required both for maximal binding of ACF I to FXa and for the maximal enhancement of emission fluorescence of ACF I. It could be deduced from these results that the occupation of both Ca2+-binding sites in ACF I with Ca2+ ions and subsequent conformational rearrangement might be essential for the binding of ACF I to FXa.

SOLUTION STUDY AND CRYSTAL STRUCTURE OF A PENTACOORDINATE ZINC(II) COMPLEX WITH N,N″-bis-(2-HYDROXYBENZYL)-DIETHYLENETRIAMINE

Abstract The stability constants of Zn(II) complexes with N,N″-bis-(2-hydroxybenzyl)-diethylenetri-amine(H2L) were determined by potentiometric pH titration at 25°C and at 0.1 M KNO3 ionic strength. A neutral complex ZnL was synthesized. In addition to IR, and 1H NMR spectra, its structure was established by single crystal X-ray diffraction. The crystal is orthorhombic, of space group Pbca, with cell constants a = 17.865(4), b = 20.079(4), c = 9.598(2)Å, z = 8 and Dc = 1.461 g°Cm−3. The structure was solved and refined to R = 0.049 (Rw = 0.054). The coordination geometry around the zinc ion is trigonal-bipyramidal with a large distortion, exhibiting two nonequivalent phenolates.

Synthesis, structure and properties of a 4,4′-bipyridine bridged dinuclear Cu(II) complex: {Cu2(4,4′-bipy)[HOCH2CH2N(CH2CH2NH2)2]2}· (ClO4)4·1/2(4,4′-bipy)·4H2O

A new bicopper(II) complex was synthesized and characterized by X-ray crystallography. Crystals of the complex were monoclinic, space group C2 with a = 33.717(10), b = 12.078(4), c = 11.386(3) Å and β = 103.980(6)°. The two Cu(II) atoms are bridged by 4,4′-bipyridine and each Cu(II) is five-coordinate in a distorted trigonal-bipyramid geometry. Magnetic investigation shows that the complex has a weak ferromagnetic interaction between the two metal ions. A cyclic voltammogram of the complex shows two quasi-reversible peaks for the couples CuIICuII/CuICuII and CuICuII/CuICuI. Study of the antimicrobial activity showed the complex was active against Candida albican, Staphylococcus aureu, Bacillus pumilus and Eschierichia coli.