N3 Complex Research Articles

The Hydrogen Bonding Properties of Cytosine: A Computational Study of Cytosine Complexed with Hydrogen Fluoride, Water, and Ammonia

Density functional theory is used to study the hydrogen bonding pattern in cytosine, which does not contain alternating proton donor and acceptor sites and therefore is unique compared with the other pyrimidines. Complexes between various small molecules (HF, H(2)O, and NH(3)) and four main binding sites in (neutral and (N1) anionic) cytosine are considered. Two complexes (O2(N1) and N3(N4)) involve neighboring cytosine proton acceptor and donor sites, which leads to cooperative interactions and bidendate hydrogen bonds. The third (less stable) complex (N4) involves a single cytosine donor. The final (O2-N3) complex involves two cytosine proton acceptors, which leads to an anticooperative hydrogen bonding pattern for H(2)O and NH(3). On the neutral surface, the anticooperative O2-N3 complex is less stable than those involving bidentate hydrogen bonds, and the H(2)O complex cannot be characterized when diffuse functions are included in the (6-31G(d,p)) basis set. On the contrary, the anionic O2-N3 structure is the most stable complex, while the HF and H(2)O N3(N4) complexes cannot be characterized with diffuse functions. B3LYP and MP2 potential energy surface scans are used to consider the relationship between the water N3(N4) and O2-N3 complexes. These calculations reveal that diffuse functions reduce the conversion barrier between the two complexes on both the neutral and anionic surfaces, where the reduction leads to a (O2-N3) energy plateau on the neutral surface and complete (N3(N4)) complex destabilization on the anionic surface. From these complexes, the effects of hydrogen bonds on the (N1) acidity of cytosine are determined, and it is found that the trends in the effects of hydrogen bonds on the (N1) acidity are similar for all pyrimidines.

Effective, Selective Coupling of Propylene Oxide and Carbon Dioxide to Poly(Propylene Carbonate) Using (Salen)CrN3 Catalysts

The copolymerization of propylene oxide and CO2 has been investigated employing Cr(salen)N3 complexes as catalysts. Unfortunately the reaction could not be studied in real time via in situ IR spectroscopy, thereby obtaining detailed kinetic data, because of the copolymer limited solubility in most solvents. Investigations employing batch reactor runs concentrating on varying the cocatalyst, the equivalents of cocatalyst, and the steric and electronic structure of the catalyst through modification of the salen ligand were undertaken. It was discovered that the optimal catalyst for copolymer selectivity vs the monomeric propylene carbonate was one that contained a salen ligand with an electron-withdrawing phenylene backbone and electron-donating tert-butyl groups in the phenolate rings. This catalyst was used to investigate the effect of altering the nature of the cocatalyst and its concentration, the three cocatalysts being tricyclohexylphosphine (PCy3), PPN+ N3(-), and PPN+ Cl-, where PPN+ is the large very weakly interacting bis(triphenylphosphoramylidene)ammonium cation. By utilization of more or less than 1 equiv of PCy3 as cocatalyst, the yield of polymer was reduced. On the other hand, the PPN+ salts showed the best activity when 0.5 equiv was employed, and produced only cyclic when using over 1 equiv.

Photoelectrochemistry at SnO 2 particulate fractal electrodes sensitized by a ruthenium complex : Solid-state solar cell assembling by incorporating a composite polymer electrolyte

Nanocrystalline tin oxide thin film electrodes were prepared and their structural and morphological properties were characterized. X-ray diffraction (XRD) confirmed the films crystallinity, whereas both scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed the presence of a porous and fractal network of interconnected nanoparticles forming uniform surface features of relatively low roughness. The SnO 2 particulate fractal electrodes were successfully sensitized by the ruthenium N3 complex and solid-state solar cells were assembled by incorporating a binary polymer/inorganic oxide electrolyte. The incorporation of the composite electrolyte consisting of poly(ethylene) oxide (PEO) filled with titanium oxide and containing LiI and I 2 as the redox couple presents a satisfying cell performance in comparison with a liquid junction photoelectrochemical cell: typical maximum incident photon to current efficiency (IPCE) as high as 46% at 510 nm, short-circuit photocurrent ( J sc) of 2.6 mA cm −2 and overall conversion efficiency ( η) of 0.14% under white light illumination were obtained. The IPCE values of the solid-state dye-sensitised solar cells based on SnO 2 are high enough and can be compared to those obtained with titania nanoporous electrodes. The relatively low light to power energy conversion efficiency is attributed to the poor fill factor (FF=0.21) and photovoltage ( V oc=0.21 V), characteristics that are related to the reduction of triodide by conduction band electrons and the intrinsic properties of tin oxide.

Synthesis and characterization of phosphorescent cyclometalated iridium complexes.

The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several different cyclometalated ligands are reported. IrCl3.nH2O cleanly cyclometalates a number of different compounds (i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole, and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, CwedgeN2Ir(mu-Cl)2IrCwedgeN2 (CwedgeNis a cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric CwedgeN2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by the nature of the cyclometalating ligand, leading to lambda(max) values from 510 to 606 nm for the complexes reported here. The strong spin-orbit coupling of iridium mixes the formally forbidden 3MLCT and 3pi-pi* transitions with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1-0.4) and room temperature lifetimes in the microsecond regime. The emission spectra of the CwedgeN2Ir(LX) complexes are surprisingly similar to the fac-IrCwedgeN3 complex of the same ligand, even though the structures of the two complexes are markedly different. The crystal structures of two of the CwedgeN2Ir(acac) complexes (i.e., CwedgeN = ppy and tpy) have been determined. Both complexes show cis-C,C', trans-N,N' disposition of the two cyclometalated ligands, similar to the structures reported for other complexes with a "CwedgeN2Ir" fragment. NMR data (1H and 13C) support a similar structure for all of the CwedgeN2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and (tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes relative to their solution spectra.

Regioselective Ring Opening of Enantiomerically Enriched Epoxides via Catalysis with Chiral (Salen)Cr(III) Complexes

Chiral (salen)chromium(III)N3 complexes are demonstrated to be catalysts for the regioselective ring opening a variety of enantiomerically enriched epoxides. Selective nucleophilic attack at either epoxide carbon atom can be achieved by selection of the appropriate enantiomer of catalyst. A highly selective synthesis of norpseudoephedrine is described using this strategy.

Umpolung of the allylpalladium reactivity: mechanism and regioselectivity of the electrophilic attack on bis-allylpalladium complexes formed in palladium-catalyzed transformations.

The structure and reactivity of various bis-allylpalladium complexes occurring as catalytic intermediates in important synthetic transformations have been studied by applying density functional theory at the B3PW91(DZ + P) level. It was found that n1,n3 coordinated bis-allylpalladium complexes are readily formed from the corresponding n3,n3 complexes, especially in the presence of pi-acceptor phosphine ligands. The theoretical calculations indicate dsigma-->pi type hyperconjugative interactions occurring in the n1-coordinated allyl moiety of the n3,n3 coordinated complexes. These hyperconjugative interactions influence the structure of the complexes and dramatically increase the reactivity of the double bond in the n1-moiety. The DFT results indicate a remarkably low activation barrier for the electrophilic attack on the n1-allyl functionality. In bridged n1,n3 complexes, the electrophilic attack occurs with a very high regioselectivity, which can be explained on the basis of d-pi type hyperconjugative interactions.

Two and three dimensional FFTs on highly parallel computers

An algorithm is described for computing two and three dimensional Fourier transforms on computers of SIMD architecture. The algorithm assumes the existence of a library routine for the calculation of a 2-d Fourier transform on a set of Np2 data points where Np2 is the number of processing elements. The paper discusses how to use this routine to calculate 2-d Fourier transforms on a set of N2 data points where NpN is a power of two, using an interleaving technique. The paper also discusses the use of the 2-d results in conjunction with base ‘r1 + r2’ FFT algorithms to calculate 3-d Fourier transforms on a set of N3 complex data points. In the final section a general program is described to calculate 3-d Fourier transforms for any values of N and Np such that NpN is a power of two. Timings are given for the algorithms run on an ICL Distributed Array Processor.

Interaction of (dien)Pd(II) with cytidine and cytidine 5'-monophosphate

The kinetics and the equilibrium of (dien)PdCl+ interaction with cytidine (C) and cytidine 5'-monophosphate (CMP) were studied by spectrophotometry and by stopped-flow methods. In both cases, the mechanism implies a (dien)Pd(H2O)2+ intermediate with a significant contribution of the solvent path at low chloride concentrations. With CMP, the rate is affected due to the addition of a mechanistic path via an intermediate formed between (dien)Pd(II) and the phosphate group of CMP. The kinetic and thermodynamic parameters have been determined and reflect the favorable electrostatic interactions due to the presence of the phosphate group of CMP. Furthermore, these parameters are in agreement with a transient (dien)Pd(II)-phosphate complex of CMP leading to the formation of the thermodynamically favored (dien)Pd(II)-N3 complex as final product.

Metallkomplexe mit Tetrapyrrol-Liganden, XXXIII [1] Darstellung von Azidochrom(III)-, Azidomangan(III)- und Azidoeisen(III)-Porphyrinen und deren Photolyse zu terminalen oder verbrückten Nitridometallporphyrinen / Metal Complexes with Tetrapyrrole Ligands XXXIII [1] Preparation of Azidochromium(III)-, Azidomanganese(III)-, and Azidoiron(III) Porphyrins and their Photolysis to Terminal or Bridged Nitridometal Porphyrins

Azidometal(III) porphyrins, e.g. M(TTP)N3 1 Aa-1 Ca (M = Cr, Mn, Fe), are transformed into nitrido complexes on irradiation with ultraviolet light. Thus, CrIII or MnIII complexes, e.g. Cr(TTP)N3 or Mn(TTP)N3, yield Crv and Mnv complexes with terminal nitride ligands, e.g. Cr(TTP)N (1Ab) or Mn(TTP)N (1Bb) with concomitant liberation of 1 mol of N2. However, the FeIII complex Fe(TTP)N3 produces the mixed-valence ,μ-nitrido-bis[iron(III,IV)] complex, [Fe(TTP)]2N (1Cg) and about 1.2 mol of N2 per mol of Fe. The azidometal(III) porphyrins are prepared from the corresponding hydroxo- or μ-oxo-metal(III) porphyrins and hydrazoic acid in benzene

The action of ligands on the association-dissociation equilibrium of river lamprey (Lampetra fluviatilis L.) methemoglobin

The dissociation‐association equilibrium of lamprey methemoglobin as a function of protein concentration, pH, and ligandation of the heme Fe3+ has been studied using sedimentation analysis.The sedimentation constant s°20,w of MetHb in the pH range 4.5 < pH < 10 amounts to 1.94 S leading to a calculated molecular weight of 17000 which corresponds to the Hb protomer.At pH 7.5 the MetHb · N3 complex is monomeric. Below pH 5.7 and at high protein concentration the dimer of 34000, s°20,w= 3.13 S, is formed, the dimerization being accompanied by an uptake of two protons per protomer: (a) 2 MetHb + 2 N3−+ 2 H+⇌ (H+· MetHb · N3)2. At high concentrations of protein and azide the association of MetHb · N3 becomes a function of pH only: (b) 2 MetHb · N3+ 2 H+⇌ (H+· MetHb · N3)2. The pK value of equilibrium (b) is found to be 6.7 pointing to a heme‐linked imidazole determining the equilibrium.As compared to the azide complex, other ligands, such as F− > OCN− > CN− > SCN−, favour the dimerization of lamprey MetHb to a lesser degree.Dimerization of the heme polypeptide chains in the MetHb‐ligand complexes and their association in DeoxyHb supposedly involves different aminoacids in the interface between the protomers.