Complex-Formation of Ethidium Bromide with Poly[d(A-T)]·Poly[d(A-T)]

Abstract

The interaction of Ethidium Bromide (EtBr) with double-stranded (ds-) and single-stranded (ss-) poly[d(A-T)] was studied in different ionic strengths solutions. Optical spectroscopy and Scatchard analysis results indicate that the ligand interacts to both helix and coiled structures of the polynucleotide by “strong” and “weak” binding modes. The association parameters (binding constant—K—and the number of nucleotides corresponding to a binding site—n) of the strong type of interaction were found to be independent of Na+ concentration. Weak interaction occurs at low ionic strength and/or high EtBr concentration. Estimated binding parameters of EtBr with ss- and ds-polynucleotide are in good agreement with those for EtBr-B-DNA complexes. Data obtained provided an evidence for a stacking interaction of EtBr with single stranded poly[d(A-T)].     

The effect of protonation on [Mn(IV)(μ2-O)]2 complexes

The series of complexes [Mn(IV)(X-SALPN)(₂-O)]₂, 1: X=5-OCH₃; 2: X=H; 3: X=5-Cl; 4: X=3,5-diCl; 5: X=5-NO₂, contain [Mn₂O₂]⁴⁺ cores with Mn-Mn separations of 2.7 . These molecules can be protonated to form [Mn(IV)(X-SALPN)(₂-O,OH)]₂ ⁺ in which a bridging oxide is protonated. The pK_a values for the series of [Mn(IV)(X-SALPN)(₂-O,OH)]₂ ⁺ track linearly versus the shift in redox potential with a slope of 84 mV/pKa. This observation suggests that the [Mn₂O₂]⁴⁺ core can be considered as a unit in which the free energy of protonation is directly related to the ability to reduce the Mn(IV) ion. The marked sensitivity of the reduction potential to the presence of protons presents a mechanism in which an enzyme can control the oxidizing capacity of an oxo manganese cluster by the degree and timing of oxo bridge protonation.Abbreviations AnH⁺CF₃SO₃ ^- anilinium triflate - DMA N,N-dimethyl acetamide - H₂SALPN 1,3-bis(salicylideneiminato)propane - H₂(5-Cl-SALPN) 1,3-bis(5-chlorosalicylideneiminato)propane; - H₂(3,5-diCl-SALPN) 1,3-bis(3,5-dichlorosalicylideneiminato)propane - H₂(5-NO₂-SALPN) 1,3-bis(5-nitorosalicylideneiminato)propane - H₂(5-OMe-SALPN) 1,3-bis(5-methoxysalicylideneiminato)propane - LuH⁺CF₃SO₃ ^- 2,4-lutidinium triflate - ME₃NH⁺Ph₄B^- trimethylammonium tetraphenylborate - OEC oxygen evolving complex - PyH⁺ClO₄ ^- pyridinium perchlorate - SCE saturated calomel electrode     

A kinetic model for the B–Z transition of poly[d(G-C)]·poly[d(G-C)] and poly[d(G-m5C)]·poly[d(G-m5C)]

The analysis of the kinetic data of the B-Z conformational changes induced by salt in sized double-stranded poly[d(G-C)].poly[d(G-C)] and poly[d(G-m5C)].poly[d(G-m5C)] polymers indicated that there exists a salt threshold which reveals some largely, as yet, unrecognised characteristics of the transition. It was observed that there is a direct correlation between the length of the polymer and the rate of the B-Z transition when the salt concentration in the polymer solution is lower than the salt threshold. The correlation is inverse when the salt concentration is higher than the salt threshold. Thus, the molecular mechanism of the B- to Z-DNA transition varies depending on whether the salt concentration is higher or lower than the threshold. In this context, we have found that the contrasting results reported in the literature describing the rate of the B-Z transition are not contradictory but complementary. The finding of a salt threshold leads to the establishment of a relationship between the cooperativity index of the B-Z transition and the polymer chain length. That relationship is dependent on the chemical structure of the polymer but is temperature independent.     

Binuclear copper(II) complexes of tetradentate (Ne) diazine ligands. Crystal structures of [μ-1,4-Bis(4,6-dimethyl-2-pyridylamino)phthalazine-N,μ-N3,μN3,N]-(μ-Dichloro)dichlorodicopper(II), [μ-3,6-Bis(2-pyridylthio)pyridazine-N,μ-N1,μ-N2,N] (μ-dichloro)dichlorodicopper(II) ethanol,and 3,6-Bis(2-pyridylthio)-pyridazine

The X-ray structures of two binuclear copper(II) chloride complexes of the tetradentate ligands 1,4- bis(4,6-dimethyl-2-pyridylamino)phthalazine (PAP46Me) and 3,6-bis(2-pyridylthio)pyridazine are reported. [Cu₂(PAP46Me)Cl₄] (1) and [Cu₂(PTP)Cl₄]· CH₃CH₂OH (2) contain triply bridged binuclear centres involving a diazine (NN) and two chlorobridges with copper-copper separations in the fange 3.19–3.25 Å and distorted square pyramidal copper stereochemistry. The reduced room temperature magnetic moments indicate antiferromagnetically coupled binuclear copper(II) centres.Complex 1 forms green crystals with a= 15.795(3), b=10.661(3), c=16.155(4) Å, β= 113.82(3)°, C2/c, Z = 4, R_f=0.031. Complex (2) forms green crystals with a=33.9022(8), b= 9.1626(5), c= 15.7885(5) Å,β= 114.853(2)°, C2/c, Z=8, R_f=0.047. The structure of the ligand PTP is also reported and compared with that of 2.     

The mechanism of antimalarial action of the ruthenium(II)–chloroquine complex [RuCl2(CQ)]2

The mechanism of antimalarial action of the ruthenium-chloroquine complex [RuCl(2)(CQ)](2) (1), previously shown by us to be active in vitro against CQ-resistant strains of Plasmodium falciparum and in vivo against P. berghei, has been investigated. The complex is rapidly hydrolyzed in aqueous solution to [RuCl(OH(2))(3)(CQ)](2)[Cl](2), which is probably the active species. This compound binds to hematin in solution and inhibits aggregation to beta-hematin at pH approximately 5 to a slightly lower extent than chloroquine diphosphate; more importantly, the heme aggregation inhibition activity of complex 1 is significantly higher than that of CQ when measured at the interface of n-octanol-aqueous acetate buffer mixtures under acidic conditions modeling the food vacuole of the parasite. Partition coefficient measurements confirmed that complex 1 is considerably more lipophilic than CQ in n-octanol-water mixtures at pH approximately 5. This suggests that the principal target of complex 1 is the heme aggregation process, which has recently been reported to be fast and spontaneous at or near water-lipid interfaces. The enhanced antimalarial activity of complex 1 is thus probably due to a higher effective concentration of the drug at or near the interface compared with that of CQ, which accumulates strongly in the aqueous regions of the vacuole under those conditions. Furthermore, the activity of complex 1 against CQ-resistant strains of P. falciparum is probably related to its greater lipophilicity, in line with previous reports indicating a lowered ability of the mutated transmembrane transporter PfCRT to promote the efflux of highly lipophilic drugs. The metal complex also interacts with DNA by intercalation, to a comparable extent and in a similar manner to uncomplexed CQ and therefore DNA binding does not appear to be an important part of the mechanism of antimalarial action in this case.     

Synthesis and characterisation of [[μ-(1,7,11,17-tetraaza-2,6,12,16-tetraoxacycloeicosane)][(μ-(aquo)]bis[(acac)(ethanol)nickel(II)]] [BPh4]2

The pale blue title compound, 4, was obtained from the reaction between 1,7,11,17-tetraaza-2,6,12,16-tetraoxacycloeicosane, Ni(acac)₂ and NaBPh₄ in aqueous acetone. X-ray structure determination at 120 K revealed that the dication of the ionic complex, 4, contains two independent octahedral Ni^II centres with trans-Ni₂N₂O₄ chromophores. The macrocyclic ligand and an aqua ligand act as bridges to the two nickel centres: the Ni-O(aquo)-N bond angle is 137.65(17)°. Each Ni centre is bonded to two nitrogens of the macrocycle, to a chelating acac unit, to an ethanol molecule as well as the bridging oxygen of the aqua group. The two nickel atoms sit outside the macrocycle cavity, such that the macrocyclic ligand acts as a canopy for the remainder of the dication. While none of the macrocycle oxygens are involved in the coordination to Ni, they are involved in internal hydrogen bonding with the aqua and ethanol ligands. Magnetic measurements show a paramagnetic behaviour down to 2 K, with an effective moment of 2.8 Bohr magnetons at room temperature.     

Four- versus five-coordination in platinum(II) complexes of α-diimines and the crystal structure of [PtClMe(i-PrNCHCHNi-Pr)]

The complex [PtCIMe(i-PrNCHCHNi-Pr)] and its unstable five-coordinate ethylene adduct have been prepared and characterized by ¹H NMR. The crystal and molecular structure of the former has been determined. The complex crystallizes in the orthorhombic space group Pca2 ₁, with a = 12.138(6), b = 9.601(6), c = 10.586(6)Å, Z = 4. Refinement converged to a final R index of 0.059. The geometrical parameters of the structure are compared with those of a related complex and discussed in relation to the stability of the five-coordinate olefin adducts.     

Synthesis and structure of μ-3,3′-[ 1,2-ethanediyl-bis(nitrilomethylidyne)-bis(2-hydroxybenzoato)] aquadicopper(II) hydrate

The complex μ-3,3′-[1,2-ethanediyl-bis(nitrilome- thylidyne)-bis(2-hydroxybenzoato)] aquadicopper(II) hydrate, C₁₈H₁₆N₂O₈Cu₂, was isolated from an attempted preparation of a copper lanthanum binuclear complex. The dark purple crystals are monoclinic, space group P2₁/n, with 4 molecules per unit cell; dimensions a = 13.961(5), b = tl.787(3), c = 11.622(3) Å and β = 113.09(2)°. The final R was 0.046 for the 2062 reflections used in the analysis. The Cu atom in the N₂O₂ cavity is five coordinate with CuN distances of 1.879 and 1.880 Å and CuO distances of 1.898 and 1.900 Å. A water molecule at 2.557 Å completes the square pyramidal arrangement. The second Cu in the O₄ cavity is square planar, with CuO distances to the bridging oxygens of 1.914 and 1.909 Å and to the carboxy oxygens of 1.871 and 1.882 Å. A survey of copper complexes in a square planar N₂O₂ arrangement has led to the equation δCu from the N₂O₂ plane = 0.822 – 0.275 (CuO axial distance) with a correlation coefficient of 0.98 for the 12 structures in which the Cu atom is bonded to a fifth oxygen atom. A model for the transition from square planar to square pyramidal geometry is proposed.     

Ligand substitution reactions of bis(μ-acetato)dichlorodicarbonyldiiridium(II)

Seven diiridium(II) complexes were synthesized by ligand substitution reactions of [Ir₂(μ-O₂CMe)₂Cl₂(CO)₂] (1) and [Ir₂(μ-O₂CMe)₂Cl₂(CO)₂(py)₂] (2).The reaction of 2 with the silver salt of a less coordinating anion, AgSbF₆, gave a cationic complex [Ir₂(μ-O₂CMe)₂Cl(CO)₂(py)₃]SbF₆ (3).A tricarbonyl cationic complex [Ir₂(μ-O₂CMe)₂(CO)₃Cl(py)₂]SbF₆ (4) was obtained under a CO atmosphere.Complex 2 reacted with AgO₂CCF₃ to give [Ir₂(μ-O₂CMe)₂Cl(O₂CCF₃)(CO)₂(py)₂] (5) in toluene.[Ir₂(μ-hiq)₂(CO)₂Cl₂] (Hhiq = 1-hydroxyisoquinoline, 6) was synthesized by the bridging-ligand substitution of 1 with Hhiq.Its axial adducts [Ir₂(μ-hiq)₂Cl₂(CO)₂L₂] (L = Mepy (4-methylpyridine), 7 or PPh₃, 8) were synthesized by addition of the ligands to a suspension of 6.In the structures of 7 and 8, two iridium atoms are bridged by two hiq ligands in a head-to-tail arrangement.The reaction of 1 with Hmhp (2-hydroxy-4-methylpyridine) led to triply bridged [Ir₂(μ-mhp)₃(CO)₂Cl(Hmhp)] (9).In complex 9, all the mhp ligands bridge between the Ir atoms in a head-to-head manner.The Ir-Ir distances of 3, 4, 5, 7 and 8 are 2.6047(7), 2.6216(9), 2.5899(9), 2.5933(5) and 2.634(2) Å, respectively, which are similar to those observed in[Ir₂(μ-O₂CMe)₂Cl₂(CO)₂L₂]. The Ir-Ir distance of 2.5512(4) Å in 9 is shorter than in the other complexes.     

EPR and magnetic properties of [Mn(μ-Cl)2(bpy)]n: An unusual ferromagnetic interaction in a Mn(II) chloro-bridged polymer

The study of the magnetic properties and EPR spectra of the one-dimensional bis(μ-chloro) Mn(II) polymer [Mn(μ-Cl)₂(bpy)]_n (1) (bpy = 2,2′-bipyridine) is reported. Magnetic susceptibility measurements reveal a weak ferromagnetic interaction between the Mn(II) ions (J = +0.19 cm⁻¹). This is the first polymer of six-coordinated Mn(II) ions with a [Mn₂(μ-Cl)₂]²⁺ magnetic repeating unit, showing a ferromagnetic interaction. The coordination octahedra are elongated in the Cl?Cl direction and the elongation axes are parallel along the chain. Extended Hückel calculations show that the octahedra share an equatorial-apical edge, with the equatorial plane being parallel, and perpendicular to the Mn₂(μ-Cl)₂. Due to this disposition, the overlap through the chloride bridges is small, so the antiferromagnetic contribution must also be small and, therefore, a ferromagnetic behaviour is observed. The EPR spectra of a polycrystalline sample of 1 at different temperatures are also reported. A variation of the bandwidth with temperature is observed, which could be because this ferromagnetic interaction is weak: above 150 K the dipolar interaction is the predominant effect, while below 150 K the magnetic exchange interaction dominates.     

Bh-DNA: Variations of the Poly[d(A)] · Poly[d(T)] Structure within the Framework of the Fibre Diffraction Studies

Abstract

A refinement of the recent results for poly[d(A)] · poly[d(T)] (Alexeev et al., J. Biomol. Struct. Dyn. 4, 989 (1987)) involving additional parameters of the base-pair structure and of the sugar- phosphate backbone expands the conformational potential of this polynucleotide of the B type to include the possibility of bifurcated hydrogen bonds of the kind recently discovered in crystalline deoxyoligonucleotide with lone d(A)_n · d(T)_n stretch (Nelson et al., Nature 330, 221 (1987)).

Still, analysis of the available data and energy calculations do not seem to indicate that the bifurcated H-bonds are a crucial factor responsible for the anomalous structure of the d(A)_n · d(T)_n sequence. The unique structural properties of poly [d(A)] · poly[d(T)] can hardly be explained without taking into account its interactions with the double-layer hydration spine in the minor groove. In view of the hydration mechanism stabilizing poly [d(A)] · poly [d(T)] and of the polynucleotide's heteronomous prehistory (Arnott et al., Nucleic Acids Res. 11, 4141 (1983)) we suggest that this B-type structure be called B_h.     

海鳗[Muraenesox cinereus(Forsk(?)l)]骨骼的研究

鱼类的骨骼是鱼体的基本结构之一,它有支持鱼体的作用;在分类学上,它是鱼类分类的重要依据;此外,许多鱼类的年龄和生长,必须依靠骨骼的年昼(或稻为年轮)作为鉴定的材料,所以,鱼类骨骼的研究,不但在理论上值得探讨,而且在渔业实践上也具有一定的意义。     

Reactivity of [PdCl(μ-med)]2 with monodentate or bidentate ligands. Structure of the dinuclear complexes [Pd(μ-med)(PPh3)]2(BF4)2 and [Pd(μ-med)(bpy)]2(BF4)2. [Hmed=N-(2-mercaptoethyl)-3,5-dimethylpyrazole]

Treatment of the ligand N-(2-mercaptoethyl)-3,5-dimethylpyrazole with [Pd(CH₃COO)₂]₃ and reaction of [PdCl(μ-med)]₂ with pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ produced the following complexes: [Pd(CH₃COO)(μ-med)]₂, [Pd(μ-med)(py)]₂(BF₄)₂ and [Pd(μ-med)(PPh₃)]₂(BF₄)₂. Similar reactions carried out with 2,2^′-bipyridine (bpy) or 1,3-bis(diphenylphosphino)propane (dppp) produced [Pd(μ-med)(bpy)]_x(BF₄)_x (x=1 or 2) and [Pd(μ-med)(dppp)]_x(BF₄)_x (x=1 or 2). Treatment of [Pd(μ-med)(bpy)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced [Pd₃Cl₂(μ-med)₂(bpy)₂](BF₄)₂. Treatment of [Pd(μ-med)(dppp)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced a mixture of [Pd(μ-Cl)(dppp)]₂(BF₄)₂ and [Pd(μ-med)₂(dppp)]²⁺. X-ray crystal structures of [Pd(μ-med)(PPh₃)]₂(BF₄)₂ · 2CH₃CN and [Pd(μ-med)(bpy)]₂(BF₄)₂ · 0.5CH₃OH are presented.     

Synthesis and structure of the complex tetra-μ-prolinatodirhodium(II)

The dinuclear Rh^IIRh^II complex with proline [Rh₂(pro₄][NEt₄]₂ was synthesized and its structure studied by means of spectroscopic (IR, EPR and ESCA) and magnetochemical methods. It was shown that two proline molecules serve as bridging ligands, while the other two are only axially coordinated through their N atoms.