Synthesis, structure, and electrochemical properties of a family of 2-(arylazo)phenolate complexes of ruthenium with unusual C-C coupling and N=Ncleavage

Reaction of 2-(4'-R-phenylazo)-4-methylphenols (R = OCH3, CH3, H, Cl, and NO2) with [Ru(dmso)(4)Cl-2] affords a family of five ruthenium(III) complexes, containing a 2-(arylazo)phenolate ligand forming a six-membered chelate ring and a tetradentate ligand formed from two 2-(arylazo) phenols via an unusual C-C coupling linki.ng the two ortho carbons of the phenyl rings in the arylazo fragment. A similar reaction with 2-(2'-methylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl-2] has afforded a similar complex, in which one 2-(2'-methylphenylazo)-4-methylphenolate ligand is coordinated forming a six-membered chelate ring, and the other two ligands have undergone the C-C coupling reaction, and the coupled species is coordinated as a tetradentate ligand forming a five-membered N,O-chelate ring, a nine-membered N,N-chelate ring, and another five-membered chelate ring. Reaction of 2-(2',6'-dimethylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl-2] has afforded a complex in which two 2-(2',6'-dimethylphenylazo)-4-methylphenols are coordinated as bidentate N,O-donors forming five- and six-membered chelate rings, while the third one has undergone cleavage across the N=N bond, and the phenolate fragment, thus generated, remains coordinated to the metal center in the iminosemiquinonate form. Structures of four selected complexes have been determined by X-ray crystallography. The first six complexes are one-electron paramagnetic and show rhombic ESR spectra. The last complex is diamagnetic and shows characteristic H-1 NMR signals. All the complexes show intense charge-transfer transitions in the visible region and a Ru(III)-Ru(IV) oxidation on the positive side of SCE and a Ru(III)-Ru(II) reduction on the negative side.

Synthesis, structural analysis, and magnetic behaviour of three fumarate bridged coordination polymers: five-fold interpenetrated diamond-like net of Ni-II, sheets of Ni-II and Co-II

The hydrothermal reactions of Ni(NO3)(2).6H(2)O, disodium fumarate (fum) and 1,2-bis(4-pyridyl)ethane (bpe)/1,3-bis(4-pyridyl) propane (bpp) in aqueous-methanol medium yield one 3-D and one 2-D metal-organic hybrid material, [Ni(fum)(bpe)] (1) and [Ni(fum)(bpp)(H2O)] (2), respectively. Complex 1 possesses a novel unprecedented structure, the first example of an "unusual mode" of a five-fold distorted interpenetrated network with metal-ligand linkages where the four six-membered windows in each adamantane-type cage are different. The structural characterization of complex 2 evidences a buckled sheet where nickel ions are in a distorted octahedral geometry, with two carboxylic groups, one acting as a bis-chelate, the other as a bis-monodentate ligand. The metal ion completes the coordination sphere through one water molecule and two bpp nitrogens in cis position. Variable-temperature magnetic measurements of complexes 1 and 2 reveal the existence of very weak antiferromagnetic intramolecular interactions and/or the presence of single-ion zero field splitting (D) of isolated Ni-II ions in both the compounds. Experimentally, both the J parameters are close, comparable and very small. Considering zero-field splitting of Ni-II, the calculated D values are in agreement with values reported in the literature for Ni-II ions. Complex 3, [{Co(phen)}(2)(fum)(2)] (phen=1,10-phenanthroline) is obtained by diffusing methanolic solution of 1,10-phenanthroline on an aqueous layer of disodium fumarate and Co(NO3)(2).6H(2)O. It consists of dimeric Co-II(phen) units, doubly bridged by carboxylate groups in a distorted syn-syn fashion. These fumarate anions act as bis-chelates to form corrugated sheets. The 2D layer has a (4,4) topology, with the nodes represented by the centres of the dimers. The magnetic data were fitted ignoring the very weak coupling through the fumarate pathway and using a dimer model.

The crucial importance of agostic interactions in intermediates formed in propylene polymerization using neutral salicyladiminato palladium(II) and nickel complexes as catalysts

The structures of intermediates formed in propylene polymerisation using neutral salicyladiminato palladium(II) and nickel(II) complexes as catalysts have been investigated using density functional theory. Calculations show that all low energy intermediates contain agostic interactions either between the metal and a hydrogen from the added propylene forming four- or five-membered chelate rings, or, when a phenyl ring is present, between the metal and an aromatic C-C bond. The agostic interactions with the metal are concomitant with changes in ligand dimensions and electronic properties. In particular when a metal to hydrogen bond is formed, there is a lengthening of the C-H bond. Significant differences are found for the agostic interactions with palladium and nickel in that for Pd there is a clear preference for specific intermediates but for Ni there are several different structures with similar energies which are likely to lead to a greater variety of products on further polymerisation. (c) 2007 Elsevier B.V. All rights reserved.

Solvent-Assisted Formation of Vesicles by a Self-Assembling Ni-3-Schiff Base Complex

A linear trinuclear Ni-Schiff base complex [Ni-3(salpen)(2)(PhCH2COO)(2)(EtOH)] has been synthesized by combining Ni(ClO4)(2)center dot 6H(2)O, phenyl acetic acid (C6H5CH2COOH), and the Schiff base ligand, N,N'-bis(salicylidene)-1,3-pentanediamine (H(2)salpen). This complex is self-assembled through hydrogen bonding and C-H-g interaction in the solid state to generate a sheet-like architecture, while in organic solvent (CH2Cl2), it forms vesicles with a mean diameter of 290 nm and fused vesicles, depending upon the concentration of the solution. These vesicles act as an excellent carrier of dye molecules in CH2Cl2. The morphology of the complex has been determined by scanning electron microscopy and transmission electron microscopy experiments, and the encapsulation of dye has been examined by confocal microscopic image and electronic absorption spectra.

Facile strategies for the synthesis and crystallization of linear trinuclear nickel(II)-Schiff base, complexes with carboxylate bridges: Tuning of coordination geometry and magnetic properties

Three new linear trinuclear nickel(II) complexes, [Ni-3(salpen)(2)(OAc)(2)(H2O)(2)]center dot 4H(2)O (1) (OAc = acetate, CH3COO-), [Ni-3(salpen)(2)(OBz)(2)] (2) (OBz=benzoate, PhCOO-) and [Ni-3(salpen)(2)(OCn)(2)(CH3CN)(2)] (4) (OCn = cinnamate, PhCH=CHCOO-), H(2)salpen = tetradentate ligand, N,N'-bis(salicylidene)-1,3-pentanediamine have been synthesized and characterized structurally and magnetically. The choice of solvent for growing single crystal was made by inspecting the morphology of the initially obtained solids with the help of SEM study. The magnetic properties of a closely related complex, [Ni-3(salpen)(2)(OPh)(2)(EtOH)] (3) (OPh = phenyl acetate, PhCH2COO-) whose structure and solution properties have been reported recently, has also been studied here. The structural analyses reveal that both phenoxo and carboxylate bridging are present in all the complexes and the three Ni(II) atoms remain in linear disposition. Although the Schiff base ligand and the syn-syn bridging bidentate mode of the carboxylate group remain the same in complexes 1-4, the change of alkyl/aryl group of the carboxylates brings about systematic variations between six- and five-coordination in the geometry of the terminal Ni(II) centres of the trinuclear units. The steric demand as well as hydrophobic nature of the alkyl/aryl group of the carboxylate is found to play a crucial role in the tuning of the geometry. Variable-temperature (2-300 K) magnetic susceptibility measurements show that complexes 1-4 are antiferromagnetically coupled (J = -3.2(1), -4.6(1). -3.2(1) and -2.8(1) cm(-1) in 1-4, respectively). Calculations of the zero-field splitting parameter indicate that the values of D for complexes 1-4 are in the high range (D = +9.1(2), +14.2(2), +9.8(2) and +8.6(1) cm(-1) for 1-4, respectively). The highest D value of +14.2(2) and +9.8(2) cm(-1) for complexes 2 and 3, respectively, are consistent with the pentacoordinated geometry of the two terminal nickel(II) ions in 2 and one terminal nickel(II) ion in 3. (C) 2009 Elsevier Ltd. All rights reserved.

Cu-II acetate complexes involving N,N,O donor Schiff base ligands: Mono-atomic oxygen bridged dimers and alternating chains of the dimers and Cu-2(OAc)(4)

Two tridentate N,N,O donor Schiff bases, HL1 (4-(2-ethylamino-ethylimino)-pentan-2-one) and HL2 (3-(2-amino-propylimino)-1-phenyl-butan-1-one) on reaction with Cu-II acetate in presence of triethyl amine yielded two basal-apical, mono-atomic acetate oxygen-bridging dimeric copper(II) complexes, [Cu2L21(OAc)(2)] (1), [Cu2L22(OAc)(2)] (2). Whereas two other similar tridentate ligands HL3 (4-(2-amino-propylimino)-pentane-2-one) and HL3 (3-(2-amino-ethylimino)-1-phenyl-butan-1-one) under the same conditions produced a mixture of the corresponding dinners and a one-dimensional alternating chain of the dimer and copper acetate moiety, [Cu4L23(OAc)(6)](n) (3) and [Cu4L24(OAc)(6)](n) (4), formed by a very rare mu(3) bridging mode of the acetate ion. All four complexes (1-4) have been characterized by X-ray crystallography. The isotropic Hamiltonian, H = -JS(1)S(2) has been used to interpret the magnetic data. Magnetic measurements of 1 and 2 in the temperature range 2-300 K reveal a very weak antiferromagnetic coupling for both complexes U = -0.56 and -1.19 cm(-1) for 1 and 2, respectively). (C) 2008 Elsevier Ltd. All rights reserved.

Trinuclear Cu(II) complexes containing peripheral ketonic oxygen bridges and a mu(3)-OH core: steric influence on their structures and existence

Two tridentate Schiff bases, HL1(6-amino-3-methyl-1-phenyl-4-azahex-2-en-1-one), and HL2 (6-atnino-3,6-dimethyl-1-phenyl-4-azahex-2-en-1-one) on reaction with Cu(II) perchlorate in the presence of triethyl amine yielded two new trinuclear copper(II) complexes, [(CuL1)(3)(mu(3)-OH)](ClO4)(2) (1) and [(CuL2)(3)(mu(3)-OH)](ClO4)(2) center dot 0.75H(2)O (2), whereas another tridentate ligand HL3 (7-amino-3-methyl-1-phenyl-4-azahept-2-en-1-one) underwent hydrolysis under the same reaction conditions to result in the formation of a mononuclear complex, [Cu(bn)(pn)ClO4] (3) [where bn = 1-benzoylacetonate and pn = 1,3-propanediamine]. All three complexes have been characterized by X-ray crystallography. For both 1 and 2 the cationic part is trinuclear with a [Cu3OH] core held by three carbonyl oxygen bridges between each pair of copper(II) atoms. The structure of 3 is a monomer with a chelating 1,3-propanediamine and a benzoyl acetone moiety. Magnetic measurements of I and 2 have been performed in the 2-300 K temperature range. The experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -J(S1S2 + S2S3 + S1S3), yielding as best fit parameters: J = -25.6 cm(-1), g = 2.21 for 1 and J = 11.2 cm(-1), g = 2.10 for 2. The EPR spectra at low temperature could be indicative of spin frustration in complex 1. (C) 2006 Elsevier Ltd. All rights reserved.

Copper(II) azide complexes with mono-anionic tridentate Schiff-base ligands: monomer versus dimer

Three new copper(II) complexes [(CuLN3)-N-1](2) (1), [(CuLN3)-N-2] (2) and [(CuLN3)-N-3] (3) with three very similar tridentate Schiff base ligands [HL1=6-diethylamino-3-methyl-1-phenyl-4-azahex-3-en1- one, HL2= 6-amino-3-methyl-1-phenyl-4-azahex-3-en-1-one and HL3= 6-amino-3-methyl1- phenyl-4-azasept-3-en-1-one] have been synthesized and structurally characterized by X-ray crystallography. In complex 1 half of the molecules are basal-apical, end-on azido bridged dimers and the remaining half are square-planar monomers whereas all the molecules in complexes 2 and 3 are monomers with square-planar geometry around Cu(II). A competition between the coordinate bond and H-bond seems to be responsible for the difference in structure of the complexes.

Deprotection, tethering, and activation of a one-legged metalloporphyrin on a chemically active metal surface: NEXAFS, Synchrotron XPS, and STM study of [SAc]P-Mn(III)Cl on Ag(100)

The structural and reactive properties of the acetyl-protected "one-legged" manganese porphyrin [SAc]P-Mn(III)Cl on Ag(100) have been studied by NEXAFS, synchrotron XPS and STM Spontaneous surface-mediated deprotection occurs at 300 K accompanied by spreading of the resulting thio-tethered porphyrin across the metal surface Loss of the axial chlorine ligand occurs at 498 K, without any demetalation of the macrocycle, leaving the Mn center in a low co-ordination state At low coverages the macrocycle is markedly tilted toward the silver surface, as is the phenyl group that forms part of the tethering "leg". In the monolayer region a striking transition occurs whereby the molecule rolls over, preserving the tilt angle of the phenyl group, strongly increasing that of the macrocycle, decreasing the apparent height of the molecule and decreasing its footprint, thus enabling closer packing These findings are in marked contrast with those previously reported for the corresponding more rigidly bound four-legged porphyrin [Turner, M., Vaughan, O. P. H., Kyriakou, G., Watson, D. J., Scherer, L. J; Davidson, G J. E, Sanders, J. K. M.; Lambert, R. M J. Am. Chem Soc 2009, 131, 1910] suggesting that the physicochemical :)properties and potential applications of these versatile systems should be strongly dependent on the mode of tethering to the surface.

Redox chemistry and electronic properties of 2,3,5,6-tetrakis(2-pyridyl)pyrazine-bridged diruthenium complexes controlled by N,C,N '-biscyclometalated ligands

To investigate the consequences of cyclometalation for electronic communication in dinuclear ruthenium complexes, a series of 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) bridged diruthenium complexes was prepared and studied. These complexes have a central tppz ligand bridging via nitrogen-to-ruthenium coordination bonds, while each ruthenium atom also binds either a monoanionic, N,C,N'-terdentate 2,6-bis(2'-pyridyl)phenyl (R-N boolean AND C boolean AND N) ligand or a 2,2':6',2 ''-terpyridine (tpy) ligand. The N,C,N'-, that is, biscyclometalation, instead of the latter N,N', N ''-bonding motif significantly changes the electronic properties of the resulting complexes. Starting from well-known [{Ru(tpy)}(2)(mu-tppz)](4+) (tpy = 2,2':2 '',6-terpyridine) ([3](4+)) as a model compound, the complexes [{Ru(R-N boolean AND C boolean AND N)}(mu-tppz){Ru(tpy)}](3+) (R-N boolean AND C(H)boolean AND N = 4-R-1,3-dipyridylbenzene, R = H ([4a](3+)), CO2Me ([4b](3+))), and [{Ru(R-N boolean AND C boolean AND N)}(2)(mu-tppz)](2+), (R = H ([5a](2+)), CO2Me ([5b](2+))) were prepared with one or two N,C,N'-cyclometalated terminal ligands. The oxidation and reduction potentials of cyclometalated [4](3+) and [5](2+) are shifted negatively compared to non-cyclometalated [3](4+), the oxidation processes being affected more significantly. Compared to [3](4+), the electronic spectra of [5](2+) display large bathochromic shifts of the main MLCT transitions in the visible spectral region with low-energy absorptions tailing down to the NIR region. One-electron oxidation of [3](4+) and [5](2+) gives rise to low-energy absorption bands. The comproportionation constants and NIR band shape correspond to delocalized Robin-Day class III compounds. Complexes [4a](3+) (R = H) and [4b](3+) (R = CO2Me) also exhibit strong electronic communication, and notwithstanding the large redox-asymmetry the visible metal-to-ligand charge-transfer absorption is assigned to originate from both metal centers. The potential of the first, ruthenium-based, reversible oxidation process is strongly negatively shifted. On the contrary, the second oxidation is irreversible and cyclometalated ligand-based. Upon one-electron oxidation, a weak and low-energy absorption arises.

Flavanol monomer-induced changes to the human faecal microflora

We have investigated the bacterial-dependent metabolism of (-)-epicatechin and (+)-catechin using a pH-controlled, stirred, batch-culture fermentation system reflective of the distal region of the human large intestine. Incubation of (-)-epicatechin or (+)-catechin (150mg/l or 1000mg/l) with faecal bacteria, led to the generation of 5-(3,4'-dihydroxyphenyl)-gamma-valerolactone, 5-phenyl-gamma-valerolactone and phenylpropionic acid. However, the formation of these metabolites from (+)-catechin required its initial conversion to (+)-epicatechin. The metabolism of both flavanols occurred in the presence of favourable carbon sources, notably sucrose and the prebiotic fructo-oligosaccharides, indicating that bacterial utilisation of flavanols also occurs when preferential energy sources are available. (+)-Catechin incubation affected the growth of select microflora, resulting in a statistically significant increase in the growth of the Clostridium coccoides-Eubacterium rectale group, Bifidobacterium spp. and Escherichia coli, as well as a significant inhibitory effect on the growth of the C. histolyticum group. In contrast, the effect of (-)-epicatechin was less profound, only significantly increasing the growth of the C. coccoides-Eubacterium rectale group. These potential prebiotic effects for both (+)-catechin and (-)-epicatechin were most notable at the lower concentration of 150 mg/l. As both (-)-epicatechin and (+)-catechin were converted to the same metabolites, the more dramatic change in the growth of distinct microfloral populations produced by (+)-catechin incubation may be linked to the bacterial conversion of (+)-catechin to (+)-epicatechin. Together these data suggest that the consumption of flavanol-rich foods may support gut health through their ability to exert prebiotic actions.

Effects of calcium-chelating agents and pasteurisation on certain properties of calcium-fortified soy milk

Addition of 25 mM calcium chloride to soy milk reduced pH, increased ionic calcium and caused it to coagulate. The effects of different chelating agents were investigated on selected physicochemical properties of soy milk and on preventing coagulation. The soy milks were then pasteurised to examine how heat treatment changed some of these properties as well as to evaluate their effects on heat stability. Sediment formation and susceptibility to coagulation could be reduced by decreasing ionic calcium and increasing pH. To achieve this, the most effective chelating agents were tri-sodium citrate and disodium hydrogen phosphate. These chelating agents also reduce absolute viscosity and particle size. Sodium hexa meta phosphate was also effective, but less so; it reduced ionic calcium but had a less noticeable effect on pH. The disodium salt of ethylenediamine tetraacetic acid was not effective, as it decreased the pH of soy milk. Ionic calcium and pH are useful indicators of heat stability of calcium-fortified soy beverages. (C) 2009 Elsevier Ltd. All rights reserved.

Effects of phosphates and citrate on sediment formation in UHT goats' milk

Sediment formation was investigated during UHT treatment of goats' milk, subjected to indirect treatment at 140 degrees C for 2 s, with upstream homogenisation. Stabilisers evaluated were sodium hexametaphosphate (SHMP), trisodium citrate (TSC), disodium hydrogen orthophosphate (DSHP), and sodium dihydrogen orthophosphate (SDHP). With no added stabiliser, goats' milk produced a heavy sediment on UHT treatment. Addition of SDHP reduced pH, had little effect on ionic calcium and did not substantially reduce sediment. However, addition of SHMP, DSHP and TSC each reduced ionic calcium, increased ethanol stability and reduced sediment. Following stabiliser additions, there was a good correlation between ethanol stability and ionic calcium (R-2=0.85) but not between ethanol stability and pH (R-2=0.08). Overall, reducing ionic calcium reduced the amount of sediment formed for all these three stabilisers, although there was no single trend line between sediment formation and ionic calcium concentration. Sediment formation was not well correlated with pH for TSC or for SHMP, but it was for DSHP, making it the only stabiliser where sediment formation correlated well both with ionic calcium and pH, which might account for its effectiveness at higher ionic calcium levels. Sediment was much reduced when the temperature was reduced from 140 degrees C to 125 degrees C and 114 degrees C. There were no further changes in sediment on storage for two weeks. Analysis of the sediment showed that it was predominantly fat and protein, with a mass ratio ranging between 1.43:1 and 1.67:1. Its mineral content was usually less than 5% of dry weight. The maximum amounts of P and Ca were found to be 2.32% and 1.63%, respectively.

Proliferative and antiproliferative effects in substituted titanocene anticancer drugs

Substituted titanocenes like ansa-titanocenes, diarylmethyl-substituted and benzyl-substituted titanocenes, are known for their cytotoxic potential and they can be synthesised using 6-arylfulvenes. Nevertheless, in the case of using 6-(4-morpholin-4yl-phenyl) fulvene (5a) or 6-{[bis-(2-methoxyethyl)amino]phenyl} fulvene (5b) the synthetic possibilities seem to be limited, but the morpholino and the bis-(2-methoxyethyl)amino substituent are in terms of an improved water solubility and drug availability in the cell very interesting groups. The corresponding benzaldehydes, which are the starting material for the synthesis of these fulvenes, were not commercially available and therefore, a modified synthetic approach had to be introduced. Nevertheless, the reactivity of the obtained fulvenes was unexpected and only the ansa-titanocene bis-[{[bis-(2-methoxyethyl)amino]phenyl}cyclopentadienyl] titanium(IV) dichloride (6b) and the benzyl-substituted titanocene [1,2-di(cyclopentadienyl)-1,2-di(4-morpholin-4yl-phenyl)-ethanediyl] titanium dichloride (8a) could be obtained and characterised. When the benzyl-substituted titanocene (8a) was tested against pig kidney cells (LLC-PK) an anti-proliferative effect, resulting in an IC50 value of 25 mu M, was observed. This IC50 value is in the lower range of the cytotoxicities evaluated for titanocenes up to now. The ansa-titanocene (6b) showed surprisingly, when tested on the same cell line, a proliferative effect.

Glycol methyl ether and glycol amine substituted titanocenes as antitumor agents

6-[4-(2-Methoxyethoxy)phenyl]fulvene (3a) and 6-(4-[2-(di-methylamino)ethoxy]phenyl)fulvene (3b) were prepared as starting materials for the synthesis of three dofferent classes of titanocenes, which are ansa-titanocenes, diarylmethyl-substituted titanicenes and benzyl-substituted titanocenes and benyzyl-subtituted titanocenes. Because the synthetic possibilities seem to be limited, only ansa-titanocene {1,2-bis(cyclopentadienyl)-1,2-bis[4-(2-methoxyethoxy)phenyl]ethanediyl}titanium dichloride (4a) and benzyl-substituted titanocene bis-{[4-(2-methoxyethoxy)benzyl]cyclopentadienyl}titantium(IV) dichloride (6a) were obtained and characterised. The change in the substitution pattern f the phenyl moiety from an oxygen atom to a nitrogen atom had such a big influence on the reaction that not one compound of the threee titanocene classes could be synthesised, and it was also not possible to obtain diarylmethyl-substituted titanocenes with the use of either of the fulvenes. When benzyl-substituted titanocene 6a was tested agianst pig kidney cells (LLC-PK), an antiproliferative effect that result in an IC50 value of 43 mu m, was observed. This IC50 value is in the lower range of the cytotoxicities evaluated for titanocenes up to now. ansa-Titanocene 4a surprisingly showed, when tested on the same cell line, a proliferative effect together with a fast rate of hydrolysis.