Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms

We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.     

DFT description of the electronic structure and spectromagnetic properties of strongly correlated electronic systems: NiII, CuII and ZnII o-dioxolene complexes

The spectroscopic and magnetic properties of dioxolene complexes of zinc, copper and nickel were studied by DFT calculations on model complexes of formulas [(NH(3))(4)M(II)(SQ)](+) (M=Zn, Ni; SQ=semiquinonato) and [(NH(3))(2)Cu(II)(SQ)](+). Standard approaches such as time-dependent DFT (TDDFT), the Slater transition state (STS), and broken symmetry (BS) were found to be unable to completely account for the physical properties of the systems, and complete active space-configuration interaction (CAS-CI) calculations based on the Kohn-Sham (KS) orbitals was applied. The CAS-CI energies, properly corrected with multireference perturbation theory (MR-PT), were found to be in good agreement with experimental data. We present here a calculation protocol that has a low CPU cost/accuracy ratio and seems to be very promising for interpreting the properties of strongly correlated electronic systems in complexes of real chemical size.     

Photogeneration of the free radicals and singlet oxygen by chrysophanol from rheum

Chrysophanol (3-methyl-1,8-dihydroxyanthraqui-none) belongs to a family of anthraquinone pigmentsthat naturally exist in many kinds of plants, such asrheum, a Chinese herbal medicine growing abundantlyin China. Besides their biological activities, thesepigments are also well known as photosensitizers[1,2].Photosensitizers are able to photochemically producehighly reactive species, such as O2, O2 , ?OH, and 1 ??induce a series of damage to biologic…     

去甲肾上腺素的光谱电化学研究

本文用平行入射式光谱电化学方法，测定了去甲肾上腺素的热力学常数Ｅ和ｎ值，用ｎ＾２＋作为自由基稳定剂，讨论了其通过一个电子传递产生半醌自由基中间体的电极反应机理并结合其它电化学方法，证明了ＮＥ在电极上以传质扩散为主的准可逆过程。     

漆树漆酶的催化氧化作用——Ⅷ.四卤代氢醌的漆酶催化氧化

在静止条件下,对四卤代氢醌(TXQH_2,X=Cl、Br、I)的漆酶催化氧化行为进行了考察。结果证明,四卤代氢醌的酶反应具有几个明显特征:1)一级离解种是底物参与反应的必要形式;2)半醌自由基阴离子是反应的产物;3)半醌自由基经歧化转变成相应的对醌;4)整个反应过程呈现出连串反应属性。这些特征反映了漆酶催化氧化反应的共性。结果还表明,由于卤原子的吸电子作用不强,不能使自由电子有效地离域,生成的半醌自由基寿命短,衰减快;但在二甘醇存在下,可以有效地延缓半醌自由基的衰减,实现提高半醌自由基动力学稳定性的目的。