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Structural studies of metal complexes of five ditopic hexaazamacrocycles containing two pyridine rings ([n] py(2)N(4) n = 18, 20, 22, 24 and 26) have been carried out. The synthesis of macrocycles [22]- to [26]- py(2)N(4) are also reported. The protonation constants of the last three compounds and the stability constants of their complexes with Ni2+, Cu2+, Zn2+, and Pb2+ were determined at 25 degreesC in 0.10 mol dm(-3) KNO3 in aqueous solution. Our results with [22] py(2)N(4) show significant differences from those described previously, while [24] py(2)N(4) has not been studied before and [ 26] py2N4 is a new compound. Mononuclear and dinuclear complexes of the divalent metal ions studied with [ 22]- to [26]- py(2)N(4) were found in solution. The stability constants for the ML complexes of the three ligands follow the Irving - Williams order: NiL2+ CuL2+ ZnL2+ PbL2+, however for the dinuclear complexes the values for Pb2+ complexes are higher than the corresponding values for the Ni2+ and the Zn2+ complexes. The X-ray single crystal structures of the supramolecular aggregates [Cu-2([20] py(2)N(4))(H2O)(4)][Cu(H2O)(6)](SO4)(3) . 3H(2)O ( 1) and [Cu-2([20] py(2)N(4))(CH3CN)(4)][Ni([20] py(2)N(4))](2)(ClO4)(8) . H2O (2), which are composed of homodinuclear [Cu-2([20] py(2)N(4)])(H2O)(4)](4+) ( 1a) and [Cu-2([20] py(2)N(4)])(CH3CN))(4)](4+) (2a), and mononuclear species, [Cu(H2O)(6)](2+) (1b) and [Ni([20] py(2)N(4))](2+) ( 2b), respectively, assembled by an extensive network of hydrogen bonds, are also reported. In both homodinuclear complexes the copper centres are located at the end of the macrocycle and display distorted square pyramidal coordination environments with the basal plane defined by three consecutive nitrogen donors and one solvent molecule, water in 1a and acetonitrile in 2a. The macrocycle adopts a concertina-type conformation leading to the formation of macrocyclic cavities with the two copper centres separated by intramolecular distances of 5.526(1) and 5.508(7) Angstrom in 1a and 2a, respectively. The mononuclear complex [Ni([20] py(2)N(4)])](2+) displays a distorted octahedral co-ordination environment with the macrocycle wrapping the metal centre in a helical shape. EPR spectroscopy of the copper complexes indicated the presence of mono- and dinuclear species.

A new tetraazamacrocycle containing two 5-chloro-8-hydroxyquinoline side arms, L 1 , was synthesized. The protonationconstants of L 1 and the stability constants of its complexes with Cu 2 ,Zn 2 ,Cd and Pb were determined by potentiometric orspectrophotometric methods, at 20 8C in methanol:water (5:1, v/v) and ionic strength 0.10 mol dm 3 in tetrabutylammonium nitrate(TBAN). Compound L 1 has three high protonation constants, the most basic centres being both phenolates of the arms. Mono- anddinuclear complexes were found in solution for all the metal ions, the complexes of copper are thermodynamically very stable, andthe dinuclear complexes of lead(II) are the predominant species even in 1:1 mixtures. UV / Vis spectra of some complexes and EPRof the copper ones confirmed the presence of dinuclear complexes.# 2003 Elsevier B.V. All rights reserved. Keywords: Tetraazamacrocycle; Stability constants; Dinuclear complexes; EPR copper complexes; 8-Hydroxyquinolinyl groups 1. IntroductionMacrocycles containing quinoline side arms havefound many applications as analytical reagents inabsorption spectrophotometry, fluorometry, solvent ex-traction, and partition chromatography [1,2]. Thesecompounds are also used as pesticides [2].The 8-hydroxyquinoline (HQ) forms a stable five-membered chelate ring with metal centres and verystable complexes with divalent transition and post-transition metal ions of the type M(HQ) , M(HQ)

The hexaaza macrocycles 3,6,14,17,23,24-hexaazatricyclo[ 17.3.1.1(8,12)]tetracosa-1(23), 8,10,12(24), 19,21-hexaene ([18]py(2)N(4)) and 3,7,15,19,25,26-hexaazatricyclo[19.3.1.1(9,13)]hexacosa-1(25), 9,11,13(26), 21,23-hexaene ([20]py(2)N(4)) were synthesised. The protonation constants of both compounds and the stability constants of their complexes with a wide range of metal ions (Mn2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+, Mg2+, Ca2+, Ba2+, La3+ and Gd3+) were determined at 25degreesC with ionic strengths of 0.10 mol dm(-3) in KNO3. The overall basicity of [20] py(2)N(4) is 3.20 log units larger than that of [18]py(2)N(4) due to the weaker repulsion between the contiguous protonated ammonium sites, which are separated by propyl chains in [20]py(2)N(4) rather than ethyl chains in [18]py(2)N(4). The stability constants of complexes of each metal decrease as the cavity size of the macrocycle is increased, taking into account the difference in basicity of the ligands; the values for the Cu2+, Ni2+ and Zn2+ complexes of both ligands are exceptionally high. Single crystal structures of complexes [Ni([18]py(2)N(4))](ClO4)(2).2CH(3)CN (1), [Cu([18]py(2)N(4))](ClO4)(2).2CH(3)CN (2), [Co([20]py(2)N(4))]-[Co(H2O)(6)](0.5)(SO4)(2).CH3OH.4H(2)O (3), [Ni([20]py(2)N(4))](ClO4)(2)(4) and [Cu([20]py(2)N(4))](ClO4)(2) (5) were determined. In all complexes, the metal centre exhibit a hexaco-ordinate environment and the macrocycle adopts a twisted helical topology. The effect of the cage sizes of [18]py(2)N(4) and [20]py(2)N(4) on the molecular dimensions of metal complexes of both macrocycles is evaluated and a significant decrease in the helicity is observed in complexes of the 18-membered macrocycle compared to complexes of the 20-membered ring. The X-ray structural results, together with molecular mechanics calculations and NMR studies performed for metal complexes of both macrocycles, indicate that both ligands have enough flexibility to encapsulate smaller and larger metal ions, although it is clear that [20]py(2)N(4) is more flexible than [18]py(2)N(4).

The single crystal structures of complexes [(CuLBr)-Br-1]ClO4 1, [(CuLBr)-Br-2]PF6 2, and [NiL2][ClO4](2) 3 were determined (L-1 is 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene and L-2 is 3,6,10,16-tetraazabicyclo[10.3.1]hexadeca-1(16),12,14-triene). The asymmetric unit of 1 contains two [(CuLBr)-Br-1](+) cations having different five-co-ordinated environments. One (A) exhibits a distorted square pyramidal arrangement, with the basal plane defined by three nitrogen atoms of the macrocycle and the bromine, and the apical position occupied by the nitrogen opposite to the pyridine ring. In the other (B) the donor atoms are distorted from this geometry towards a trigonal bipyramid with the equatorial plane formed by two nitrogen atoms of the macrocycle and Br, and the axial positions occupied by the nitrogen atoms contiguous to the pyridine ring. The complex cation [(CuLBr)-Br-2](+) 2 exhibits a distorted square pyramidal environment with the basal plane defined by the four nitrogen atoms of the macrocycle and the apical co-ordination by the bromine atom. In [NiL2](2+) 3 the four nitrogen atoms of the macrocycle form a distorted square planar environment around the nickel centre. Molecular mechanics calculations are used to determine the best-fit sizes for metal ions accommodated into L-1 and L-2 by evaluation of all sterically allowed conformers for five-co-ordination geometry. The results obtained, together with those of L-3 (3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene), published previously, clearly establish the effect of macrocyclic cavity size on metal ion selectivity. These macrocycles prefer a planar conformation to accommodate small metal ions but folded conformations are preferred for longer M-N distances. The increase of the macrocyclic cavity size leads to an increase of the M-N(sp(3)) distances at which the folded conformer(s) become the most stable form: 1.90, 2.14 and 2.18 Angstrom for 12-, 13- and 14-membered macrocycles, respectively.

Two N-(2-pyridylmethyl) derivatives of a 14-membered tetraaza macrocycle containing pyridine have been synthesized, L-1 and L-2. The protonation constants of these compounds and the stability constants of complexes of both ligands with Co2+ to Zn2+, Cd2+, Pb2+, Fe3+ and In3+ were determined by potentiometric methods at 25 degrees C and ionic strength 0.10 mol dm(-3) in KNO3. The values of the protonation constants for L-1 and L-2 are quite different. The metal complexes of both ligands present lower values of stability constants than expected. The only exception is the case of the Cd2+ complex with L-2 which exhibits a particularly high stability constant, indicating that this ligand has a remarkable selectivity for this metal ion relative to zinc. The Cd2+ complex seems to be the only one to bond to all the donor atoms of the ligand or at least to more than the other metal ions studied. The pM values determined at physiological pH, which take into account the competition of the protons for the ligand, have shown that L-2 is the most selective compound for cadmium relative to zinc. The single crystal structure of [CuL2][ClO4](2) determined by X-ray diffraction has shown that the co-ordination geometry around the copper atom can be described approximately as a distorted square pyramid. To achieve this geometric arrangement the macrocycle adopts a folded conformation. Furthermore the nitrogen atom of one free pyridylmethyl pendant arm is directed towards the copper centre leading to a distance between these two atoms of 3.304(11) Angstrom, which suggests a weak bonding interaction consistent with a [5+1] co-ordination.

Aydın, Asuman (Balikesir Author), The Monte Carlo code, which has been used previously to simulate the transport of positrons in aluminium and copper, was modified for simulating the positron transport in silver, tin, gold and lead with incident positron energies in the range of 159-960 keV. The calculated results have been compared with available experimental data and predictions from other calculations. Usually good agreement is observed except in cases of backscattering. (C) 1997 Elsevier Science Ltd.

We develop an algorithm, based on the acceptance-rejection method, with a simple envelope rejection function for sampling the angular distribution in Compton scattering from Klein-Nishina differential scattering cross section. The algorithm enhances the sampling efficiency for high-energy photons increasingly with increasing photon energies, The sampling efficiency is 79.6, 89.5, 92.3, 95.9, 96.6% for photon energies 1, 5, 10, 50, 100 MeV respectively. We compare the speed of our algorithm with some methods currently used and find that our method is faster than the others in most cases.

A method to obtain mass-attenuation coefficients of β particles is described. This method is based upon the simulation of β emission by means of the β energy spectrum. The range of the β particle is chosen as random incidence by means of range distribution of monoenergetic electrons which have the same energy as the β particle. Thus, the range distributions of the β particles are found. The mass-attenuation coefficient is obtained as the slope of the semi-log plot of integral range distribution. This method is applied to obtain the mass-attenuation coefficients of 204Tl and RaE β particles in Al, Cu, Ag and Pb.

Addition of the aluminum(I) reagent [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) to a series of cyclic and acyclic 1,2-, 1,3-, and 1,5-dienes is reported. In the case of 1,3-dienes, the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene-containing products. This mechanism has been examined by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4 + 1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4 + 1) cycloaddition includes styene, 1,1-diphenylethylene, and anthracene. In these cases, the diene motif is either in part, or entirely, contained within an aromatic ring and reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2-cyclononadiene or 1,5-cyclooctadiene, complementary reactivity is observed; the orthogonal nature of the C═C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavor a (4 + 1) cycloaddition. Rather, reaction pathways are determined by an initial (2 + 1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C═C π-bond, leading to complex organometallic products that incorporate fused hydrocarbon rings.

1,2-ethanedioic acid-bis(phenylglyoxylidene hydrazide), EDGH4, has been synthesized and various Cu(II), Ni(I1) and Co(I1) complexes of this compound have been isolated. Dissociation and formation constants of these complexes have been determined by spectrophotometric methods and spectrophotometric trace analyses of the Ni(I1) and Cu(I1) complexes have been performed. The structures of all isolated compounds were proposed on the basis of analyses, i.r., u.v.-visible and n.m.r. data.

The single crystal structures of complexes [CoL1]Br-0.5.[NO3](0.5). 5H(2)O 1, [Ni(HL1)]Br . 4H(2)O 2, Ca[CuL3]NO3. CH3CN . 2H(2)O 3 and [CoL3]. 2H(2)O 4 were determined, where H2L1 is 3,11-bis(carboxymethyl)-7-methyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene and H3L3 is 3,7,11-tris(carboxymethyl)-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene. In all these complexes the metal centre is encapsulated by the macrocycle in a distorted octahedral environment, the four nitrogen atoms of the tetraaza ring defining the equatorial planes. In the complexes of H2L1 the axial positions are occupied by the two carboxymethyl groups which are adjacent to the pyridine ring, while in the complexes of H3L3 one of these positions is occupied by one of the carboxymethyl arms adjacent to the pyridine ring and the other by the group opposite to the pyridine moiety. The remaining carboxymethyl arm adjacent to the pyridine ring is further away from the metal centre and plays an important role in the crystal structures of both complexes. Crystals of 3 display a three-dimensional polymeric structure derived from the Ca-O bonds. In the lattice the Ca2+ ions are surrounded by eight oxygen atoms, with two calcium ions bridged by two oxygen atoms of carboxylate groups bonded to the copper centres. This large spherical molecule has a centrosymmetric structure with the centre of the core, Ca2O2, localised on a crystallographic inversion centre. Additionally, the complexes of H3L3 (3 and 4) have interesting superstructures based on several C=O ... HO hydrogen interactions between the carboxylate pendant arms and water molecules. The Fe3+ complexes of H2L2 (3,11-bis(carboxymethyl)-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene) and of H3L3 were characterised by EPR and Mossbauer spectroscopy. Both techniques revealed that the complexes of the bis(carboxymethyl) derivative appear as an equilibrium of high- and low-spin state species, the relative amount of the latter increasing with decrease of temperature, and that the complex of the tris(carboxymethyl) derivative appears practically as a high-spin state species. Molecular mechanics studies have provided data to explain the different behaviour of the iron(III) complexes of both ligands.

Development of catalysts for the selective hydrolysis of proteins is challenging, yet important for many applications in biotechnology and proteomics. The hydrolysis of hydrophobic proteins is particularly challenging, as due to their poor solubility, the use of surfactants is often required. In this study, the proteolytic potential of catalyst systems based on the Zr(IV)-substituted Keggin polyoxometalate (Et2NH2)10[Zr(PW11O39)2] (Zr-K 1:2) and three different surfactants (ionic SDS (sodium dodecyl sulfate), zwitterionic Zw3-12 (n-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate), and CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate)), which differ in structure and polarity, has been investigated. Hydrolysis of ovalbumin (OVA) was examined in the presence of Zr-K 1:2 and surfactants by sodium dodecyl sulfate poly(acrylamide) gel electrophoresis (SDS-PAGE), which showed the appearance of new polypeptide fragments at lower molecular weight, indicating that selective hydrolysis of OVA took place for all three catalyst systems. The same fragmentation pattern was observed, showing that the selectivity was not affected by surfactants. However, the surfactants influenced the performance of the catalyst. Hence, the interactions of OVA with surfactants and Zr-K 1:2 were investigated using different techniques such as tryptophan fluorescence, Circular Dichroism, and Dynamic Light Scattering. The speciation of the catalyst in surfactant solutions was also followed by 31P Nuclear Magnetic Resonance spectroscopy providing insight into its stability under reaction conditions.