Polymeric networks of copper(II) using succinate and aromatic N-N donor ligands: synthesis, crystal structure, magnetic behaviour and the effect of weak interactions on their crystal packing

Four succinato-bridged complexes of copper(II) have been synthesized. Complex 1, [Cu(2)(mu-OH(2))(2)L(bpy)(2)(NO(3))(2)](n) and 2, [Cu(2)(mu-OH(2))(2)L(phen)(2)(NO(3))(2)](n)(bpy = 2,2[prime or minute]-bipyridine; phen = 1,10-phenanthroline and LH(2)= succinic acid) exhibit 1D coordination polymer structures where both the nitrate ions are directly linked to the copper(ii) producing synthons in a 2D sheet. A novel 2D grid-like network, ([Cu(4)L(2)(bpy)(4)(H(2)O)(2)](ClO(4))(4)(H(2)O))n3, is obtained upon changing the nitrate by perchlorate anion in complex 1, where the channels are occupied by the anions. On changing the nitrate by tetrafluoroborate anion in complex 2, a novel octanuclear complex, [Cu(8)L(4)(phen)(12)](BF(4))(8).8H(2)O 4, is isolated. The coligand bpy and phen in these complexes show face-to-face (in 1,2,3,4) or edge-to-face (in 4 )pi-pi interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face pi-pi interactions in complex facilitates the formation of discrete octanuclear entities. Variable-temperature (300-2 K) magnetic measurements of complexes have been done. Complexes 1 and 2 show very weak antiferromagnetic (OOC-CH(2)-CH(2)-COO) and ferromagnetic coupling (mu-H(2)O). Complex 3 also shows antiferromagnetic (syn-syn mu-OCO), and ferromagnetic coupling (mu-O of the -COO group). Complex 4 with two types (syn-syn and syn-anti) of binding modes of the carboxylate group shows strong antiferromagnetic interaction.     

Prediction of heterofullerene stabilities: a combined DFT and chemometric study of C56Pt2, C57Pt2 and C81Pt2

A systematic search of the regioisomers of the heterofullerenes, C57Pt2 and C56Pt2, has been carried out by means of density functional calculations to find the most stable structures. Both heterofullerenes incorporate two metal atoms into the fullerene surface. In the case of C57Pt2, one platinum atom substitutes one carbon atom of C60 and the other platinum atom replaces a C--C bond, whereas in C56Pt2 each platinum atom replaces one C--C bond. Several geometric factors were studied, three of which have particularly important effects on the relative stabilities of the regioisomers: the Pt--Pt separation, the number of C--C bonds remaining after substitution, and the type of C--C bond that is substituted. All these factors indicate that the deformation of the carbon framework is a general factor that governs the relative stabilities of the regioisomers. Because a high number of factors affect the stability of the heterofullerenes we also used chemometric techniques in this study. Partial least-squares (PLS) regression was used to establish the structure-energy relationships of C57Pt2 and C56Pt2 heterofullerenes. The understanding gained of the factors that affect the relative isomers stabilities has allowed us to predict the stabilities of larger disubstituted carbon cages, for example, C81Pt2 heterofullerene.     

Interlaboratory study of the bioluminescence inhibition tests for rapid wastewater toxicity assessment

Several toxicity procedures are currently being used for the wastewater toxicity assessment. We have undertaken an interlaboratory comparison of the use of different bioluminescence inhibition toxicity tests based on Vibrio fischeri, in order to evaluate their reproducibility for the rapid wastewater toxicity assessment. Twenty-two laboratories took part in this study organized by the Institut Català de Tecnologia (ICT) and the Consejo Superior de Investigaciones Cientificas (CSIC). During the exercise, six series of six samples were analyzed along 5 months. Every batch of samples was composed by three real samples and three standard solutions. The real samples were: an untreated effluent of a paper industry, a sample from a first settlement of a wastewater treatment plant (WWTP) and the final effluent of the WWTP. The goals of the interlaboratory study were to evaluate the repeatability (r) and reproducibility (R) when different laboratories conduct the test, the influence of different matrix samples, the variability between different tests based on the same principle: the bioluminescence inhibition of V. fischeri, but involving different commercial devices and to determine the rate at which participating laboratories successfully completed tests initiated. The maximum number of outlier values was corresponding to a non-treated effluent from a paper industry. This also was the most complex and toxic sample analyzed. An increase on the non-convergent values obtained for the participants was observed at higher matrix complexity and at lower toxicity level. In comparison with other editions of this interlaboratory study the matrixes of real samples analyzed were more complex, nevertheless the final variability coefficient for the exercise was nearby to the average value for the past editions. Due to the high complexity of some samples involved in this intercalibration the stability of real samples were also followed during the test. On the other hand, no relation was found between final results and the different devices, as show the cluster analysis.     

Cupric sulfate–hydrazine system as an initiator of vinyl polymerization. II. Polymerization of methyl methacrylate in aqueous solution in the absence of oxygen

The cupric sulfate–hydrazine system has been used to initiate the aqueous solution polymerization of methyl methacrylate at pH 9.25 in the absence of oxygen. There is no decomposition of hydrazine on the surface of the reduced cupric hydroxide until a flocculant precipitate is formed (cupric sulfate concentration of about 10^?3 mole/1). Below this concentration, the initiating reaction occurs solely in solution, the rate of polymerization decreasing when the reaction mixture becomes depleted in cupric ions. When a suitable surface area of the precipitated polymer is attained, adsorption and decomposition of hydrazine occurs on its surface, causing further initiation of polymerization.     

Inverted colloidal crystals as three-dimensional cell scaffolds

A new type of three-dimensional scaffold with inverted colloidal crystal geometry for the investigation of topological effects in cell cultures is introduced in this publication. The scaffolds are made by infiltration of the hexagonal crystal lattice of polystyrene spheres with sol-gel formulation and subsequent annealing. It possesses a relatively high degree of order among existing cell scaffolds and affords tight control over the scaffold porosity and tissue organization. The prepared scaffolds can be a convenient system for the investigation of cell-cell and cell-matrix interactions. Their biocompatibility is demonstrated for human hepatocellular carcinoma HEP G2 and human bone marrow HS-5 cell cultures. A preliminary effect of the scaffold topology on cell proliferation is observed. HEP G2 hepatocytes form a large number of 10-15 cell colonies on scaffolds made from 75-microm spheres, while their number diminishes for scaffolds from 10- and 160-microm spheres. Under similar conditions, HS-5 forms smaller colonies consisting of three to four cells in 90-microm cavities.     

Benzomorphan related compounds. XVII . Oxidative cyclization of N-arylethyl-6, 7-benzomorphans

The synthesis of two new bridged polycyclic systems (I and II), possessing a rigid N-arylethylbenzomorphan structure, by mercuric acetate cyclization of the corresponding seco derivatives (IV and VI, respectively) is described. The relative configuration of these compounds and the preferred indolo[2, 3-a]- or benzo[a]quin-olizidine conformation is assigned.     

Mössbauer studies of complexes of diorganotin diisothiocyanates with tridentate ligands

Mössbauer and infrared spectra have been obtained for terpyridylcomplexes of dimethyl-, di-n-butyl- and diphenyltindiisothiocyanates and the corresponding[R₂Sn(NCS)·terpyridyl]⁺ [BPh₄]- compounds, and for the8-(2-pyridylmethylene-amino)quinoline, PMAQ, complexes withdi-n-butyl- and diphenyltin diisothiocyanates. Infrared spectra ofthe neutral complexes indicate seven-coordination for tin and theMössbauer parameters indicate axial C Sn bondshaving a greater tin s-character than in trans octahedralcomplexes. The largest quadrupole splitting, 4.73 mm/sec, wasobtained for the terpyridyl complex with di-n-butyltindiisothiocyanate.     

Stimulatory and inhibitory effects of alkyl bromide surfactants on beta-amyloid fibrillogenesis

Beta-amyloid peptide (Abeta), in fibrillar form, is the primary constituent of senile plaques, a defining feature of Alzheimer's disease. In solution assays, fibril formation exhibits a lag time, interpreted as a nucleation/condensation-dependent process. The kinetics of fibrillogenesis is controlled by two key parameters: nucleation and elongation rate constants. We characterized the time course of Abeta fibril formation by measuring the scattering caused by peptide aggregates. We report here the interaction of Abeta with three alkylammonium bromides (dodecyl, tetradecyl, and hexadecyl) at supra- and submicellar concentrations and their influence on the kinetic constants. We observed a dual behavior: surfactants promoted or retarded fibril formation in a concentration-dependent manner. Below a determined surfactant concentration (close to the corresponding critical micellar concentration in medium without peptide), surfactants favor aggregation, presumably by means of electrostatic interactions that destabilize the native conformation. Beyond such concentration, the stabilizing effects of the monomer predominate. As a general rule, surfactants delay but do not completely inhibit aggregation.     

Copper(II) mediated anion dependent formation of Schiff base complexes

A tetranuclear mixed ligand copper(II) complex of a pyrazole containing Schiff base and a hydroxyhexahydropyrimidylpyrazole and copper(II) and nickel(II) complexes of the Schiff base having N-donor atoms have been investigated. A 2 equiv amount of 5-methyl-3-formylpyrazole (MPA) and 2 equiv of 1,3-diamino-2-propanol (1,3-DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand complex [Cu4(L1)2(L2)2(NO3)2] (1), where H2L1 = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl-3-(5-hydroxyhexahydro-2-pyrimidyl)pyrazole. In contrast, a similar reaction with nickel(II) nitrate leads to the formation of a hygroscopic intractable material. On the other hand, the reaction involving 2 equiv of MPA and 1 equiv each of 1,3-DAP and various copper(II) salts gives rise to two types of products, viz. [Cu(T3-porphyrinogen)(H2O)]X2 (X = ClO4, NO3, BF4 (2)) (T3-porphyrinogen = 1,6,11,16-tetraza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X]X x H2O (X = Cl (3), Br (4)). The same reaction carried out with nickel(II) salts also produces two types of compounds [Ni(H2L1)(H2O)2]X2 [X = ClO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X2] x H2O [X = Cl (8), Br (9)]. Among the above species 1, 3, and 5 are crystallographically characterized. In 1, all four copper atoms are in distorted square pyramidal geometry with N4O chromophore around two terminal copper atoms and N5 chromophore around two inner copper atoms. In 3, the copper atom is also in distorted square pyramidal geometry with N4Cl chromophore. The nickel atom in 5 is in a distorted octahedral geometry with N4O2 chromophore, where the metal atom is slightly pulled toward one of the axial coordinated water molecules. Variable-temperature (300 to 2 K) magnetic susceptibility measurements have been carried out for complex 1. The separations between the metal centers, viz., Cu(1)...Cu(2), Cu(2)...Cu(2)A, and Cu(2)A...Cu(1)A are 3.858, 3.89, and 3.858 A, respectively. The overall magnetic behavior is consistent with strong antiferromagnetic interactions between the spin centers. The exchange coupling constants between Cu(1)...Cu(2) and Cu(2)...Cu(2A) centers have turned out to be -305.3 and -400.7 cm(-1), respectively, resulting in a S = 1/2 ground state. The complexes are further characterized by UV-vis, IR, electron paramagnetic resonance, and electrochemical studies.