M. Paula Robalo

Hyper-Rayleigh scattering study of η5-monocyclopentadienyl–metal complexes for second order non-linear optical materials

A series of ionic η5-monocyclopentadienyl–metal compounds possessing p-substituted benzonitrile ligands has been studied by hyper-Rayleigh scattering at the fundamental wavelength of 1.064 µm. Upon systematic variation of the metal ion, the first hyperpolarizability β was found to increase along the sequence Co, Ni, Ru, Fe, with about a three-fold increase from Ru to Fe. This yields very high values for the iron complexes, e.g., β=410×10–30 esu for [Fe(η5-C5H5)(dppe)( p-NCC6H4NO2)]+ [PF6 ]– dissolved in methanol. The high β values are attributed to π back-donation resulting in an extension of the conjugated π-system from the FeII organometallic fragment, acting as a good donor group, via the nitrile to the acceptor group NO2 . Complexes with single phenyl rings as conjugated chains perform better than their biphenyl analogues, which is explained in terms of non-planarity of the coordinated biphenyl ligands in solution. By comparing complexes with electron donor and acceptor substituted ligands it is demonstrated that the organometallic moiety can be used as an extremely effective donor group but not as a good acceptor group.

Methyl syringate: an efficient phenolic mediator for bacterial and fungal laccases.

The aim of the present work is to provide insight into the mechanism of laccase reactions using syringyl-type mediators. We studied the pH dependence and the kinetics of oxidation of syringyl-type phenolics using the low CotA and the high redox potential TvL laccases. Additionally, the efficiency of these compounds as redox mediators for the oxidation of non-phenolic lignin units was tested at different pH values and increasing mediator/non-phenolic ratios. Finally, the intermediates and products of reactions were identified by LC-MS and (1)H NMR. These approaches allow concluding on the (1) mechanism involved in the oxidation of phenolics by bacterial laccases, (2) importance of the chemical nature and properties of phenolic mediators, (3) apparent independence of the enzymes properties on the yields of non-phenolics conversion, (4) competitive routes involved in the catalytic cycle of the laccase-mediator system with several new C-O coupling type structures being proposed.

Organometallic compounds for non-linear optics: Synthesis, reactivity and electrochemistry of chiral η5-monocyclopentadienyl(nitrile)iron complexes

Abstract A new family of compounds of general formula [FeCp ((+)-DIOP)(p-NCC6H4R′)][PF6] (R′ = donor or acceptor group) was synthesized and characterized for non-linear optical properties. Spectroscopic (IR and 1H 13C and 31P NMR) and electrochemical (cyclic voltammetry) studies are consistent with charge-transfer from FeII to coordinated benzonitrile via d-π* back donation. One compound of this family, [FeCp((+)-DIOP)(p-NCC6H4NO2)][PF6] has an SHG value 38 times greater than that of urea.

Towards the rational biosynthesis of substituted phenazines and phenoxazinones by laccases

Laccases are multi-copper oxidases that oxidise a wide range of substrates including phenol and aniline derivatives, which could be further involved in coupling reactions leading to the formation of dimeric and trimeric structures. This paper describes the enzyme-mediated dimerisation of several ortho and meta,para-disubstituted aromatic amines into phenazine (“head-to-tail” dimers) and phenoxazinone chromophores. The redox properties of substituted aromatic amines were studied by cyclic voltammetry and the kinetic constants of CotA and Trametes versicolor laccases were measured for selected aromatic amines. The structure of novel enzymatically synthesised phenazine and phenoxazinone dyes using CotA laccase was assessed by NMR and MS. Overall our data show that this enzymatic green process is an efficient alternative to the classic chemical oxidation of aromatic amines and phenols, with an impact on the broad field of applications of these heterocyclic compounds.

Second harmonic generation of η5-monocyclopentadienyl ruthenium p-benzonitrile derivatives by Kurtz powder technique. Crystal and molecular structure determinations of [Ru(η5-C5H5)((+)-DIOP)(p-NCC6H4NO2)][X], X=PF6−, CF3SO3− and [Ru(η5-C5H5)((+)-DIOP)(NCCH3)][PF6]

Abstract A new series of salts [RuCp(PP)( p -NC(CHCH) n C 6 H 4 R)][X] (PP=((+)-DIOP, DPPE; n =0, 1; R=CH 3 , Br, OCH 3 , NH 2 , N(CH 3 ) 2 , C 6 H 5 and NO 2 ; X=PF 6 − , CF 3 SO 3 − ) were synthesised and the second harmonic generation (SHG) efficiencies were measured by Kurtz powder technique in order to better understand the relationship between structural features and solid state packing with SHG properties. A structural study of [RuCp((+)-DIOP)( p -NCC 6 H 4 NO 2 )][X], X=PF 6 − , CF 3 SO 3 − by X-ray diffraction showed crystallisation on accentric groups. The PF 6 − salt crystallised in a triclinic space group P 1 showing perfect parallel alignment of the molecular dipoles. The CF 3 SO 3 − salt crystallised in a monoclinic space group P 2 1 and shows an angle of 73.8° between the molecular dipoles in the unit cell. Complex [RuCp((+)-DIOP)( p -NCCH 3 )][PF 6 ], studied for comparison, crystallises in the C 222 1 space group and shows eight molecules per unit cell randomly orientated. Comparison of the RuN and NC distances between the three compounds are in agreement with metal–nitrile bonding suggested by the spectroscopic data.

Studies of the Antiproliferative Activity of Ruthenium (II) Cyclopentadienyl-Derived Complexes with Nitrogen Coordinated Ligands

Four cationic ruthenium(II) complexes with the formula [Ru(η 5-C5H5)(PPh3)2]+, with L = 5-phenyl-1H-tetrazole (TzH) 1, imidazole (ImH) 2, benzo[1,2-b;4,3-b′] dithio-phen-2-carbonitrile (Bzt) 3, and [5-(2-thiophen-2-yl)-vinyl]-thiophene-2-carbonitrile] (Tvt) 4 were prepared and characterized in view to evaluate their potentialities as antitumor agents. Studies by Circular Dichroism indicated changes in the secondary structure of ct-DNA. Changes in the tertiary structure of pBR322 plasmid DNA were also observed in gel electrophoresis experiment and the images obtained by atomic force microscopy (AFM) suggest strong interaction with pBR322 plasmid DNA; the observed decreasing of the viscosity with time indicates that the complexes do not intercalate between DNA base pairs. Compounds 1, 2, and 3 showed much higher cytotoxicity than the cisplatin against human leukaemia cancer cells (HL-60 cells).

High first hyperpolarizability and perfectly aligned crystal packing for an organometallic compound [Fe(η5-C5H5)((R)–PROPHOS)(p-NCC6H4NO2)][PF6]·CH2Cl2

Abstract The molecular first hyperpolarizability, β, and the X-ray crystal structure of the complex [Fe(η5-C5H5)((R)–PROPHOS)(p-NCC6H4NO2)][PF6] ((R)–PROPHOS=(R)–(+)-bis-(1,2-diphenylphosphino)propane) were determined. A near-resonant enhanced β value as high as 545×10−30 esu was obtained from hyper-Rayleigh scattering measurements. In addition, the compound crystallizes in the space group P1 with a perfect alignment of the dipolar molecules (only a single chromophore per unit cell), thus maximizing the macroscopic nonlinearity for electro-optic or parametric frequency conversion applications. The molecular packing in the crystal is analyzed in order to understand the factors leading to the perfect alignment.

Syntheses and reactivity of p-substituted benzonitrile complexes derived from dicyclopentadienyl-molybdenum and -tungsten. Oxidative electrochemistry. The crystal structure of [Mo(η5-C5H5)2(SC6H5)(p-(CH3)2NC6H4CN)][PF6]

Abstract New cationic complexes of the type [MCp 2 (SPh)( p -NCC 6 H 4 R)][PF 6 ] (M = Mo IV , W IV ; R = H, CH 3 , OCH 3 , NH 2 , N(CH 3 ) 2 , C 6 H 5 ) have been prepared by chemical oxidation of the parent bisthiolate in the presence of the corresponding benzonitrile derivative. Electrochemical studies, involving cyclic voltammetry carried out in dichloromethane and acetonitrile, showed a reversible or quasi-reversible oxidation for all the compounds. The molecular structure of [MoCp 2 (SPh)( p -NCC 6 H 4 N(CH 3 ) 2 )][PF 6 ] has been determined.

The key role of coligands in novel ruthenium(II)-cyclopentadienyl bipyridine derivatives: Ranging from non-cytotoxic to highly cytotoxic compounds.

A new family of eight ruthenium(II)-cyclopentadienyl bipyridine derivatives, bearing nitrogen, sulfur, phosphorous and carbonyl sigma bonded coligands, has been synthesized. Compounds bearing nitrogen bonded coligands were found to be unstable in aqueous solution, while the others presented appropriate stabilities for the biologic assays and pursued for determination of IC50 values in ovarian (A2780) and breast (MCF7 and MDAMB231) human cancer cell lines. These studies were also carried out for the [5: HSA] and [6: HSA] adducts (HSA=human serum albumin) and a better performance was found for the first case. Spectroscopic, electrochemical studies by cyclic voltammetry and density functional theory calculations allowed us to get some understanding on the electronic flow directions within the molecules and to find a possible clue concerning the structural features of coligands that can activate bipyridyl ligands toward an increased cytotoxic effect. X-ray structure analysis of compound [Ru(η(5)-C5H5)(bipy)(PPh3)][PF6] (7; bipy=bipyridine) showed crystallization on C2/c space group with two enantiomers of the [Ru(η(5)-C5H5)(bipy)(PPh3)](+) cation complex in the racemic crystal packing.

Synthesis of new donor/acceptor η5-cyclopentadienyl and η5-indenyliron(II) complexes with p-benzonitrile derivatives. Crystal structures of [Fe(η5-C5H5)(CO)(P(OC6H5)3)(p-NCC6H4NO2)][BF4]·CH2Cl2 and [Fe(η5-C9H7)(CO)(P(OC6H5)3)(p-NCC6H4NO2)][BF4]

Abstract New complexes of the type [Fe(η5-Cp or Ind)(L)(L′)(p-NCR)][BF4] (L, L′=CO, P(OC6H5)3, P(C6H5)3; R=C6H4N(CH3)2, C6H4NO2, (E)-C(H)C(H)C6H4NO2, (E)-C(H)C(H)C6H4N(CH3)2) have been synthesised and characterised. Spectroscopic data were analysed in order to evaluate the tuning of the electronic density at the metal centre and the extension of the π-delocalisation on the molecule, due to the presence of coligands with different acceptor/donor abilities. The structures of two complexes [Fe(η5-C5H5)(CO)(P(OC6H5)3)(p-NCC6H4NO2)][BF4] and [Fe(η5-C9H7)(CO)(P(OC6H5)3)(p-NCC6H4NO2)][BF4] were determined by X-ray crystallographic analysis. The compounds crystallised in the centrosymmetric space groups P1 and P21/n, respectively. Bond distances within the nitrile ligand are discussed in order to evaluate the nature of iron–nitrile bonding in these complexes.