A functionalized noncovalent macrocyclic multiporphyrin assembly from a dizinc(II) bis-porphyrin receptor and a free-base dipyridylporphyrin

The bis-porphyrin system ZnP(2), in which two zinc porphyrins are connected by a phenanthroline linker in an oblique fashion, acts as a bifunctional receptor towards the complexation of free-base meso-5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cis DPyP). In solution, NMR spectroscopy evidenced quantitative formation of the tris-porphyrin macrocyclic assembly ZnP(2)(4'-cis DPyP), in which the two fragments are held together by two axial 4'-N(pyridyl)-Zn interactions. The remarkable stability of the edifice (an association constant of about 6x10(8) M(-1) was determined by UV/Vis absorption and emission titration experiments in toluene) is due to the almost perfect geometrical match between the two interacting units. The macrocycle was crystallized and studied by X-ray diffraction, which confirmed the excellent complementarity of the two components. Photoinduced energy transfer from the singlet excited state of the zinc porphyrin chromophores to the free-base porphyrin occurs with an efficiency of 98 % (k(en)=2x10(10) s(-1) in toluene, ambient temperature) with a mechanism consistent with a dipole-dipole process with a low orientation factor.     

Pentanuclear Ba(II) complex of a macrocyclic ligand

We report here the first pentanuclear Ba(II) complex of a new tri-aza, tri-oxa macrocycle with two carboxymethyl "arms" pending from two N atoms, H2L2. The crystal structure corresponds to the formula [Ba5(H0.375L2)4(ClO4)(CH3CH2OH)(H2O)2](ClO4)2.5 x 9.5H2O and reveals the presence of four molecules of the ligand surrounding five Ba(II) ions, giving rise to an unusual structure with the metal ions inside a spherical organic cavity.     

Magnetic studied of a binuclear Cu(II) complex constructed from Cu(II) macrocyclic complex

A new binuclear copper(II) compound [(CuL)₂(Tpha)](ClO₄)₂ · 4H₂O (I), where L = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane, Tpha = terephthalate dianion, has been constructed and structurally characterized by X-ray crystallography. Crystal analysis denotes that complex I crystallizes in the monoclinic system, space group P2₁/c with a = 11.115(2), b = 13.185(3), c = 16.184(3) Å and β = 105.68(3)°. Magnetic measurements confirm that I present an antiferromagnetic interaction between the paramagnetic ions.     

Structural basis for bifunctional zinc(II) macrocyclic complex recognition of thymine bulges in DNA

The zinc(II) complex of 1-(4-quinoylyl)methyl-1,4,7,10-tetraazacyclododecane (cy4q) binds selectively to thymine bulges in DNA and to a uracil bulge in RNA. Binding constants are in the low-micromolar range for thymine bulges in the stems of hairpins, for a thymine bulge in a DNA duplex, and for a uracil bulge in an RNA hairpin. Binding studies of Zn(cy4q) to a series of hairpins containing thymine bulges with different flanking bases showed that the complex had a moderate selectivity for thymine bulges with neighboring purines. The dissociation constants of the most strongly bound Zn(cy4q)-DNA thymine bulge adducts were 100-fold tighter than similar sequences with fully complementary stems or than bulges containing cytosine, guanine, or adenine. In order to probe the role of the pendent group, three additional zinc(II) complexes containing 1,4,7,10-tetraazacyclododecane (cyclen) with aromatic pendent groups were studied for binding to DNA including 1-(2-quinolyl)methyl-1,4,7,10-tetraazacyclododecane (cy2q), 1-(4-biphenyl)methyl-1,4,7,10-tetraazacyclododecane (cybp), and 5-(1,4,7,10-tetraazacyclododecan-1-ylsulfonyl)-N,N-dimethylnaphthalen-1-amine (dsc). The Zn(cybp) complex binds with moderate affinity but little selectivity to DNA hairpins with thymine bulges and to DNA lacking bulges. Similarly, Zn(dsc) binds weakly both to thymine bulges and hairpins with fully complementary stems. The zinc(II) complex of cy2q has the 2-quinolyl moiety bound to the Zn(II) center, as shown by (1)H NMR spectroscopy and pH-potentiometric titrations. As a consequence, only weak (500 μM) binding is observed to DNA with no appreciable selectivity. An NMR structure of a thymine-bulge-containing hairpin shows that the thymine is extrahelical but rotated toward the major groove. NMR data for Zn(cy4q) bound to DNA containing a thymine bulge is consistent with binding of the zinc(II) complex to the thymine N3(-) and stacking of the quinoline on top of the thymine. The thymine-bulge bound zinc(II) complex is pointed into the major groove, and there are interactions with the guanine positioned 5' to the thymine bulge.     

Amphiphilic macrocyclic nickel(II) complex in a liquid-crystalline matrix: Specific effects of conductivity and self-organization

A study was made of the influence of an amphiphilic macrocyclic nickel(II) complex on the electrical and electro-optic properties of liquid-crystalline systems based on ZhK-440I. It was shown that addition of this complex leads to a decrease in the electrohydrodynamic instability threshold and formation of unusual tetragonal ordered structures in the systems studied.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 6, pp. 522–526, November–December, 1993.The authors wish to express their gratitude to the Fundamental Research Fund of the General Committee of Science and Technology of the Ukraine for financial support of this investigation (Projects 3/114 and 46/3-2).     

Fixation of atmospheric carbon dioxide by a cadmium(II) macrocyclic complex

A crystal structure showing an unusual trinuclear Cd(II) cluster bridged in mu3 fashion by a carbonate ligand is reported. The carbonate ion is formed by fixation of atmospheric carbon dioxide from the corresponding cadmium mononuclear complex containing an aza crown ether.     

Remarkably selective recognition of iodobenzene derivatives by a macrocyclic bis-Pt(II) metallohost

We designed and synthesized self‐assembled bis‐Pt^II dimer 1? 4 BF₄ with quino[8,7‐b][1,10]phenanthroline as an extended π‐face contact area, which acts as the first artificial receptor with high affinity toward iodinated aromatic compounds significantly based on noncovalent iodine ??? aromatic‐plane interactions in a “side‐on” fashion. Despite their structural similarity to a previously reported metallohost 2 ⁴⁺ that bears 2,2′:6′,2′′‐terpyridine units, a dramatic change in selectivity toward substituted benzene derivatives was observed for 1 ⁴⁺. ¹H NMR spectroscopic titration revealed a high affinity of 1 ⁴⁺ towards haloarenes, with exceptionally large association constants for 2‐iodophenol (K_a=16 000 M ^?1) and 1,2‐diiodobenzene (K_a=21 000 M ^?1), which are 93‐ and 140‐fold higher, respectively, than the values obtained for 2 ⁴⁺. In addition, 1 ⁴⁺ showed a remarkably high affinity and selectivity toward 2,6‐diiodophenol (K_a=35 000 M ^?1), which is an important substructure of the thyroid hormone T₄. X‐ray crystallography and theoretical calculations strongly suggest that “side‐on” iodine ??? aromatic‐plane interactions and π–π stacking contribute to the strong 1,2‐diiodobenzene and 2,6‐diiodophenol binding. The results obtained here give unique and valuable insight into the nature of halogen atom interactions in their “side‐on” region with an electropositive aromatic plane, which may provide useful guidance for designing artificial receptors for iodinated biomolecules.     

Selective hydrogenation by a novel palladium(II) complex

A novel insoluble green complex of palladium(II) and salicylidene ethylene diamine (salen) has been prepared and found to be an active and selective heterogeneous hydrogenation catalyst especially for the reduction of alkynes in the presence of alkenes and of alkenes in the presence of other functional groups.     

Catalytic transesterification of dialkyl phosphates by a bioinspired dicopper(II) macrocyclic complex

For a number of phosphoryltransfer enzymes, including the exonuclease subunit of DNA polymerase I, a mechanism involving two-metal ions and double Lewis-acid activation of the substrate, combined with leaving group stabilization, has been proposed. Inspired by the active site structure of this enzyme, we have designed as a synthetic phosphoryl transfer catalyst the dicopper(II) macrocyclic complex LCu(2). Crystal structures of complexes [(L)Cu(2)(mu-NO(3))(NO(3))](NO(3))(2) (1), [(L)Cu(2)(mu-CO(3))(CH(3)OH)](BF(4))(2) (2), and [(L)Cu(2)(mu-O(2)P(OCH(3))(2))(NO(3))](NO(3))(2) (3) illustrate various possibilities for the interaction of oxoanions with the dicopper(II) site. 1 efficiently promotes the transesterification of dimethyl phosphate (DMP) in CD(3)OD, k(cat) = 2 x 10(-)(4) s(-)(1) at 55 degrees C. 1 is the only available catalyst for the smooth transesterification of highly inert simple dialkyl phosphates. From photometric titrations and the pH dependence of reactivity, we conclude that a complex [(L)Cu(2)(DMP)(OCH(3))](2+) is the reactive species. Steric bulk at the -OR substituents of phosphodiester substrates O(2)P(OR)(2)(-) drastically reduces the reactivity of 1. This is explained with -OR leaving group stabilization by Cu coordination, an interaction which is sensitive to steric crowding at the alpha-C-atom of substituent R. A proposed reaction mechanism related to that of the exonuclease unit of DNA polymerase I is supported by DFT calculations on reaction intermediates. The complex [(L)Cu(3)(mu(3)-OH)(mu-CH(3)O)(2)(CH(3)CN)(2)](ClO(4))(3) (4) incorporates a [Cu(OH)(OCH(3))(2)(CH(3)CN)(2)](-) complex anion, which might be considered as an analogue of the [PO(2)(OCH(3))(2)(OCD(3))](2)(-) transition state (or intermediate) of DMP transesterification catalyzed by LCu(2).     

Synthesis and crystal structure of a dinitrogen ruthenium(II) macrocyclic tertiary amine complex

Treatment of trans-[Ru^III(16-TMC)Cl₂]Cl (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane) with zinc metal in aqueous solution under nitrogen resulted in the formation of trans-[Ru^II(16-TMC)(N₂)Cl]PF₆ (1) which has been characterized by X-ray crystal analysis. The Ru---N₂ and N---N bond distances in 1 are 1.921(6) and 1.005(10) Å, respectively.     

Recognition of thymine in DNA bulges by a Zn(II) macrocyclic complex

A Zn(II) macrocyclic complex with appended quinoline is a bifunctional recognition agent that uses both the Zn(II) center and the pendent aromatic group to bind to thymine in bulges with good selectivity over DNA containing G, C or A bulges. Spectroscopic studies show that the stem containing the bulge stays largely intact in a DNA hairpin with the Zn(II) complex bound to the thymine bulge.     

含新型亲核体大环多胺锌(II)配合物对水解酶的模拟研究

本文探讨苯酚功能化的大环多胺配体6-(2'-羟基-3', 5'-二溴)-苄基-1, 4, 8, 11-四氮杂环十四烷(L)锌(II)配合物作为水解酶模拟物催化4-硝基苯酚醋酸酯(NA)水解的动力学。研究表明催化水解速率对NA及配合物浓度皆呈一级反应。水解速率遵循速率方程V=(kcat[Zn]+kOH[OH^-]+k0)[NA]。其二级反应速率常数kcat在一定范围内随着pH值的增加而增加, kcat的最大值(k)和kOH分别为0.12, 8.55mol^-^1.L.s^-^1。k0为NA的溶剂解速率常数, 其值为1.122×10^-^5s^-^1(298K, I=0.10,0.02mol.L^-^1tris缓冲溶液)。kcat值较以前报道的配合物更大, 催化活性更高。显示配位酚羟基可作为一种新型亲核体有效地催化NA的水解。配合物对NA水解的催化作用受酸碱平衡控制。根据实验结果提出了催化反应的机理。     

Reactions of a ruthenium(II) arene antitumor complex with cysteine and methionine

The Ru(II) organometallic antitumor complex [(eta(6)-biphenyl)RuCl(en)][PF(6)] (1) reacts slowly with the amino acid L-cysteine (L-CysH(2)) in aqueous solution at 310 K. Reactions were followed over periods of up to 48 h using HPLC, electronic absorption spectroscopy, LC-ESI-MS, and 1D or 2D (1)H and (15)N NMR spectroscopy. Reactions at a 1 mM/2 mM (Ru/L-CysH(2)) ratio were multiphasic in acidic solutions (pH 5.1) and appeared to involve aquation as the first step. Initially, 1:1 adducts involving substitution of Cl by S-bound or O-bound L-CysH(2), [(eta(6)-biphenyl)Ru(S-L-CysH)(en)](+) (4a) and [(eta(6)-biphenyl)Ru(O-L-CysH(2))(en)](2+) (4b) formed, followed by the cystine adduct [(eta(6)-biphenyl)Ru(O-Cys(2)H(2))(en)](2+) (3), and two dinuclear complexes from which half or all of the chelated ethylenediamine had been displaced, [(eta(6)-biphenyl)Ru(H(2)O)(microS,N-L-Cys)Ru(eta(6)-biphenyl)(en)](2+) (5) containing one bridging cysteine, and [(eta(6)-biphenyl)Ru(O,N-L-Cys-S)(S-L-Cys-N)Ru(eta(6)-biphenyl)(H(2)O)] (6) containing two bridging cysteines. The unusual cluster species [(biphenyl)Ru](8) (7a) was also detected by MS and was more prevalent in reactions at higher L-CysH(2) concentrations. Complex 5 was the dominant product at pH 2-5, but overall, only ca. 50% of 1 reacted with L-CysH(2) in these conditions. The reaction between 1 and L-CysH(2) was suppressed in 50 mM triethylammonium acetate solution at pH > 5 or in 100 mM NaCl. Only 27% of complex 1 reacted with L-methionine (L-MetH) at an initial pH of 5.7 after 48 h at 310 K and gave rise to only one adduct [(eta(6)-biphenyl)Ru(S-L-MetH)(en)](2+) (8).     

A potent ruthenium(II) antitumor complex bearing a lipophilic levonorgestrel group

The novel steroidal conjugate 17-α-[2-phenylpyridyl-4-ethynyl]-19-nortestosterone (LEV-ppy) (1) and the steroid-C,N-chelate ruthenium(II) conjugate [Ru(η(6)-p-cymene)(LEV-ppy)Cl] (2) have been prepared. At 48 h incubation time, complex 2 is more active than cisplatin (about 8-fold) in T47D (breast cancer) and also shows an improved efficiency when compared to its nonsteroidal analogue [Ru(η(6)-p-cymene)(ppy)Cl] (ppy = phenylpyridine) (3) in the same cell line. The act of conjugating a levonorgestrel group to a ruthenium(II) complex resulted in synergistic effects between the metallic center and the steroidal ligand, creating highly potent ruthenium(II) complexes from the inactive components. The interaction of 2 with DNA was followed by electrophoretic mobility. Theoretical density functional theory calculations on complex 2 show the metal center far away from the lipophilic steroidal moiety and a labile Ru-Cl bond that allows easy replacement of Cl by N-nucleophiles such as 9-EtG, thus forming a stronger Ru-N bond. We also found a minimum energy location for the chloride counteranion (4(+)·Cl(-)) inside the pseudocavity formed by the α side of the steroid moiety, the phenylpyridine chelating subsystem, and the guanine ligand, i.e., a host-guest species with a rich variety of nonbonding interactions that include nonclassical C-H···anion bonds, as supported by electrospray ionization mass spectra.     

Synthesis,crystal structure and magnetic properties of a new binuclear copper(II)-copper(II) complex of a macrocyclic oxamide

The binuclear metal complex [Cu(μ-exoO₂)cyclamCu(bpy)](ClO₄)₂·H₂O (bpy?=?2,2′-bipyridine and (exoO₂)cyclam?=?1,4,8,11-tetraazacyclotradecanne-2,3-dione) has been synthesized and characterized by single-crystal X-ray analysis and spectroscopic and magnetic measurements. The structure consists of homobinuclear [Cu(μ-exoO₂)cyclamCu(bpy)]²⁺ cations, a weakly coordinated water molecule and perchlorate ions. In each binuclear unit, Cu1, coordinated by four nitrogen atoms of the macrocyclic organic ligand is connected to Cu2 via the exo-cis oxygen atoms of the macrocyclic ligand with Cu···Cu separations of 5.151?Å; Cu2 assumes square-pyramidal geometry. Magnetic properties measured at 2–300?K show antiferromagnetic exchange between adjacent copper(II) ions.     

DNA cleavage by the photocontrolled cooperation of Zn(II) centers in an azobenzene-linked dizinc complex

We synthesized a new photoactive dinuclear zinc(II) complex by linking two zinc centers with a ligand containing an azobenzene chromophore and investigated the DNA cleavage activities of its trans and cis forms. The trans structure of the dinuclear zinc complex was determined by X-ray crystallography, where each zinc center is situated in an octahedral coordination environment comprised of three nitrogen atoms from the ligand and three oxygen atoms from two nitrate ions. The dinuclear zinc complex containing the azobenzene chromophore was photoisomerizable between the trans and cis forms. The binding affinities of the trans and cis complexes with calf thymus (CT)-DNA were similar. Although the DNA cleavage activity of the trans complex was negligible, the cis complex was able to cleave DNA. We attribute the efficient activity of the cis complex to the cooperation of the two closely located zinc centers and the inactivity of the trans complex to the two metal centers positioned far away from each other. The DNA cleavage activity of the cis complex exhibited a pH-dependent bell-shaped profile, which has been observed in the hydrolytic cleavage of DNA by zinc complexes. The DNA cleavage activity was not inhibited by a major groove binder, methyl green, but decreased significantly by a minor groove binder, 4',6-diamidino-2-phenylindole, indicating that the dinuclear zinc complex binds to the minor groove of DNA. The present work shows the importance of the cooperation of two zinc ions for hydrolytic DNA cleavage, which can be photoregulated by linking the two metal centers with a photoisomerizable spacer, such as an azobenzene chromophore.     

Stereoselective recognition of vicinal diamines with a Zn(II) complex

Zn(II) complex of L (N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane) binds chiral vicinal diamines (1,2-diphenylethylenediamine (dpen) and 1,2-diaminocyclohexane (dach)) stereoselectively. Crystallographic studies reveal that the ternary complex has the C2 symmetric cis-alpha topology. 1H NMR shows that the R,R form of the tetradentate zinc complex binds rapidly and reversibly to the R,R form of the diamine over the S,S form with a stereoselectivity of about 5:1. Although the diamine exchange rate is rapid it is slower than the NMR time scale, and distinct signals for the diastereomeric complexes are observed when racemic mixtures of the host and guest molecules are mixed. Origin of stereoselectivity is discussed in terms of steric effects.     

Preparation and electrochemical study of an iron(II) complex of a pentadentate planar macrocyclic ligand

The macrocycle L, prepared by template condensation of bis-6,6-(-methylhydrazino)-4-phenyl-2,2:6,2-terpyridine with glyoxal, forms a stable crystalline complex of Fe^II, [Fe(L)(H₂O)₂][PF₆]₂, which has been used as a starting material for electrochemical studies on a series of seven coordinate Fe^II complexes [Fe(L)X₂]²⁺ (X=pyridine, 4-cyanopyridine, 4-aminopyridine, 4-dimethylaminopyridine, thiophene, imidazole, 2-methylimidazole or 1,2-dimethylimidazole). Cyclic voltammetry of the aquo complex in MeCN shows three reversible one electron redox waves in the range –0.35–1.70V versus Ag/AgBF₄ reference electrode.     

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.