Structure and reactivity studies of the first tungsten cyanoalkylidene complex

Alkylidene complex W(CHCMe2Ph)(NAr)[OCMe(CF3)2]2 (Ar = 2, 6 diisopropylphenyl) (4) reacts with one equivalent of acrylonitrile in methylene chloride to afford the tetrameric, cyanoalkylidene complex [W(CHCN)(NAr)[OCMe(CF3)2]2]4 (5) which reacts with excess acetonitrile to give the tetrameric complex [W(N(H)C(CH3)C(CN)C(CH3)N)(NAr)[OCMe(CF3)2]2]4 (6).     

Structure of a terbium(III)-quinizarine complex: the first crystallographic model for metalloanthracyclines

The crystal structure of a complex of terbium(III) with quinizarine 2-sulfonate has been solved by single-crystal X-ray diffraction methods. The metal cation is coordinated by two adjacent phenolate and quinone oxygens of the anthraquinone moiety of a quinizarine sulfonate anion and by six water molecules. To our knowledge, this is the first structure of a metal complex of the 1,4-dihydroxy anthraquinone ligand. On the basis of strict similarities in the spectroscopic features of the terbium adducts with either doxorubicin or quinizarine 2-sulfonate, the present structure is proposed as a model for the metal complexes of anthracyclines.     

Synthesis of the first 1,2,3,4-azatriphospholene complex

Synthesis of the first 1,2,3,4-azatriphospholene complex was achieved by heating a solution of a P-phenyl-substituted 7-phosphanorbornadiene tungsten complex and triphenylphosphonio cyanomethylide, whereby CH-insertion products were formed in a competing reaction; these results also provide first evidence for the ability of electrophilic terminal phosphanediyl complexes to react at the ylide carbon atom and at the carbonitrile nitrogen atom of Wittig-ylides having a nitrile functional group; the structures of both complexes were established through X-ray single-crystal diffraction studies.     

Ligand-induced formation of Hoogsteen-paired parallel DNA

zIntroduction: Based on molecular modeling studies, a model has been proposed for intercalation of triple-helixspecific ligands (benzopyridoindole (BPI) derivatives) into triple helices, in which the intercalating compounds interact mainly with the Hoogsteen-paired strands of the triple helix. We set out to test this model experimentally using DNA duplexes capable of forming parallel Hoogsteen base-paired structures.Results: We have investigated the possible formation of a parallel DNA structure involving Hoogsteen hydrogen bonds by thermal denaturation, FTIR spectroscopy and gel-shift experiments. We show that BPI derivatives bind to Hoogsteen base-paired duplexes and stabilize them. The compounds induce a reorganization from a non-perfectly matched antiparallel Watson-Crick duplex into a perfectly matched parallel Hoogsteen-paired duplex.Conclusions: These results suggest that preferential intercalation of BPI derivatives in triple helices is due to their ability to interact specifically with the Hoogsteen-paired bases. The results are consistent with a model proposed on the basis of molecular modeling studies using energy minimization, and they open a new field of investigations regarding the biological relevance of Hoogsteen base-pairing.     

Structure of the complex monolayer of gemini surfactant and DNA at the air/water interface

The properties of the complex monolayers composed of cationic gemini surfactants, [C(18)H(37)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(18)H(37)],2Br(-) (18-s-18 with s = 3, 4, 6, 8, 10 and 12), and ds-DNA or ss-DNA at the air/water interface were in situ studied by the surface pressure-area per molecule (π-A) isotherm measurement and the infrared reflection absorption spectroscopy (IRRAS). The corresponding Langmuir-Blodgett (LB) films were also investigated by the atomic force microscopy (AFM), the Fourier transform infrared spectroscopy (FT-IR), and the circular dichroism spectroscopy (CD). The π-A isotherms and AFM images reveal that the spacer of gemini surfactant has a significant effect on the surface properties of the complex monolayers. As s ≤ 6, the gemini/ds-DNA complex monolayers can both laterally and normally aggregate to form fibril structures with heights of 2.0-7.0 nm and widths of from several tens to ~300 nm. As s > 6, they can laterally condense to form the platform structure with about 1.4 nm height. Nevertheless, FT-IR, IRRAS, and CD spectra, as well as AFM images, suggest that DNA retains its double-stranded character when complexed. This is very important and meaningful for gene therapy because it is crucial to maintain the extracellular genes undamaged to obtain a high transfection efficiency. In addition, when s ≤ 6, the gemini/ds-DNA complex monolayers can experience a transition of DNA molecule from the double-stranded helical structure to a typical ψ-phase with a supramolecular chiral order.     

The first cyclopentadienyl complex of uranyl

The U(IV) linear pentacyano metallocene [U(C(5)Me(5))(2)(CN)(5)][NEt(4)](3) reacted with 2 molar equivalents of pyridine N-oxide in THF or acetonitrile to give the U(VI) complex [UO(2)(C(5)Me(5))(CN)(3)][NEt(4)](2), the first uranyl species containing the cyclopentadienyl ligand; the crystal structure revealed that the steric effects of the (C(5)Me(5)) ligand force the {UO(2)}2+ ion to deviate from linearity.     

Structure and reactivity of a novel parallel thiosulfito (SSO2-S:S') rhodium dinuclear complex

The parallel thiosulfite ligand (SSO2) in a rhodium complex, which is formed by oxygenation of a bridging disulfide, is converted to a bridging hydrocarbyl thiolate ligand and sulfur dioxide gas by the reaction with hydrocarbyl halides.     

Solid-phase synthesis, characterization and DNA binding properties of the first chloro(polypyridyl)ruthenium conjugated peptide complex

A general method for the synthesis of chloro(polypyridyl)ruthenium conjugated peptide complexes via a solid-phase strategy is described. The method is applied to synthesize two positional isomers of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6). Even though the separation of the isomers was only partially achieved chromatographically, the isomers were unambiguously assigned by NMR spectroscopy. The interactions of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6) with CT-DNA and plasmid DNA, have been studied with various spectroscopic techniques, showing that (i) the complexes coordinatively bind to DNA preferring the bases guanine and cytosine over the bases thymine and adenine after hydrolysis of the coordinated chloride, (ii) electrostatic interactions between the complex cation and the polyanionic DNA chain assist this binding (iii) only in the case of one isomer the peptide does interact further with DNA as evidenced from 31P NMR spectroscopy, (iv) DNA unwinding occurs in all cases with high binding ratio (Ru/base) values (r > 0.3).     

Synthesis of the first 2,3-dihydro-1,2,3-azadiphosphete complex

Synthesis of the first 2,3-dihydro-1,2,3-azadiphosphete complex was achieved via thermal reaction of a 2H-azaphosphirene complex in o-xylene, whereby a 2,5-dihydro-1,3-diaza-2,5-diphosphinine complex and a further unidentified byproduct were formed; the structure of the title compound was established through an X-ray single-crystal diffraction study.     

The first slipped pseudo-quadruple-decker complex of phthalocyanines

The first slipped pseudo-quadruple-decker complex of phthalocyanines was formed unexpectedly upon treatment of the protonated double-decker SmIIIH(Pc)[Pc(alpha-OC4H9)8] with NaOH. The supramolecular structure contains two double-decker units linked by two sodium ions by an extremely rare coordination mode of phthalocyanines in which an aza nitrogen atom and two oxygen atoms from neighboring alkoxy substituents form a tridentate ligand.     

The first phosphite complex of a metalloporphyrin

(Di­phenyl phosphite‐κO)(5,10,15,20‐tetra­phenyl­porphyrinato‐κ⁴N)­manganese(III) hexa­fluoro­antimonate(V), [Mn(C₄₄H₂₈N₄)(C₁₂H₁₁O₃P)](SbF₆), is the first example of a structurally characterized di­aryl or di­alkyl phosphite complex of a metal–porphyrin ion. The axial phosphite ligand binds to the Mn^III ion via the P=O O atom, affording a nominally five‐coordinate complex with an Mn—O distance of 2.120 (4) Å. The mean porphyrin Mn—N distance is 2.000 (4) Å and the Mn^III ion is displaced from the 24‐atom porphyrin mean plane by 0.1548 (13) Å towards the axial O atom. The porphyrin adopts a marked saddle conformation, with a small domed component. The saddle distortion of the porphyrin ligand reflects the tight back‐to‐back dimers formed in the lattice by pairs of neighboring cations. The `non‐covalent' dimers in the lattice exhibit an unusual (weak) η²‐type coordination of a pyrrole C=C bond from a neighboring mol­ecule, with Mn^III⃛C distances of 3.697 (5) and 3.537 (5) Å.     

Isolation of the first Li/halogen phosphinidenoid transition-metal complex

Isolation and characterisation of the first Li/halogen phosphinidenoid transition-metal complex as well as low-temperature solution NMR, MAS-NMR experiments, DFT structures and calculated NMR chemical shifts are reported.     

DNA双螺旋结构的发现

两位年轻的科学家沃森和克里克根据前人的经验,图片资料和B型DNA的X射线衍射图,充分应用查盖夫的碱基规律及DNA的电位滴定行为,从多次失败中悟出了DNA是由两条反向平行的多核苷酸围绕着同一中心轴构成的双螺旋结构,通过分子模型的制作得到证实。它圆满地解释了DNA如何自我复制并将遗传信息传给子代。沃一克俩人力挫群雄,终于攀登上科学的高峰。     

Atomic force microscopy of parallel DNA branched junction arrays

BACKGROUND: The four arms of the Holliday junction are known to stack in pairs forming two helical domains whose orientations are antiparallel, but twisted positively by about 60 degrees, based on electrophoretic, FRET and AFM measurements. Recent gel retardation studies suggest that a bowtie junction (containing 5',5' and 3',3' linkages in its crossover strands) may adopt a parallel conformation. RESULTS: An AFM study of two-dimensional arrays produced by parallelograms of bowtie junctions shows that the angle between helical domains is in the range of -68+/-2 degrees. We demonstrate by AFM that the domains are parallel by constructing V-shaped structures whose arms are separated by approximately 68 degrees and approximately 112 degrees. CONCLUSIONS: The arms of the bowtie junction are parallel rather than antiparallel. The parallel or antiparallel nature of the junction apparently is determined by the local structure of the junction, but the sign of the angle appears to be a consequence of interarm electrostatic interactions.     

The first heteronuclear liquid crystal metal complex

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2462–2463, October, 1990.     

Diarylethynyl amides that recognize the parallel conformation of genomic promoter DNA G-quadruplexes

We report bis-phenylethynyl amide derivatives as a potent G-quadruplex binding small molecule scaffold. The amide derivatives were efficiently prepared in 3 steps by employing Sonogashira coupling, ester hydrolysis and a chemoselective amide coupling. Ligand-quadruplex recognition has been evaluated using a fluorescence resonance energy transfer (FRET) melting assay, surface plasmon resonance (SPR), circular dichroism (CD) and (1)H nuclear magnetic resonance (NMR) spectroscopy. While most of the G-quadruplex ligands reported so far comprise a planar, aromatic core designed to stack on the terminal tetrads of a G-quadruplex, these compounds are neither polycyclic, nor macrocyclic and have free rotation around the triple bond enabling conformational flexibility. Such molecules show very good binding affinity, excellent quadruplex:duplex selectivity and also promising discrimination between intramolecular promoter quadruplexes. Our results indicate that the recognition of the c-kit2 quadruplex by these ligands is achieved through groove binding, which favors the formation of a parallel conformation.