New unsymmetrical μ -phenoxo bridged binuclear copper(II) complexes

A series of binuclear Cu II complexes [Cu 2 XL] n + having two copper(II) ions bridged by different motifs (X = OH − , MeCO 2 − , or Cl − ) have been prepared using the ligands: H 2 L 1 = 4-methyl-2-[ N -(2-{dimethylamino}ethyl- N ′-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H 2 L 2 = 4-nitro-2-[ N -(2-{dimethylamino}ethyl- N ′-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H 2 L 3 = 4-methyl-2-[ N -(2-{diethylamino}ethyl- N ′-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol and H 2 L 4 = 4-nitro-2-[ N -(2-{diethylamino}ethyl- N ′-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol. The complexes have been characterized by spectroscopic, analytical, magnetic and electrochemical measurements. Cryomagnetic investigations (80–300 K) revealed anti-ferromagnetic exchange between the Cu II ions (−2 J in the range −50 to −182 cm −1 ). The strength of anti-ferromagnetic coupling lies in the order: OAc > OH > Cl. Cyclic voltammetry revealed the presence of two redox couples, assigned to Cu II /Cu II /Cu II /Cu I /Cu I /Cu I . The first reduction potential is sensitive to electronic effects from the aromatic ring substituents and steric effect on the donor nitrogens (side arm) of the ligand systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43853/1/11243_2004_Article_5102817.pd

Synthesis of flexible ligands for assembling two metals in close proximity. Magnetic, electrochemical and spectral properties of binuclear copper (II) complexes with different exogenous bridging motifs

Binuclear Cu II complexes having new flexible heptadentate ligands 2,6-bis{[bis(3,3′- N , N -dimethylaminopropyl)amino]methyl}-4-bromophenol [HL 1 ], 2,6-bis(3,3′- N , N -dimethylaminopropyl)amino]methyl}-4-methylphenol [HL 2 ], and 2,6-bis{[bis(3,3′- N , N -dimethylaminopropyl)amino]methyl}-4-methoxyphenol [HL 3 ], capable of assembling two copper ions in close proximity have been synthesized. Comparisons of the charge-transfer (CT) features, observed in electronic spectra of these complexes, are correlated with the electronic effect on the aromatic ring of the ligand systems. Cyclic voltammetry has revealed the existence of two reduction couples, The first is sensitive to the electronic effects of aromatic ring substituents of the ligand system, shifting to more positive potentials when more electrophilic groups replace the existing substituents. The conproportionation constants ( k con ) for the mixed valent Cu I Cu II complexes have been determined electrochemically. The magnetic susceptibilities of the complexes have been measured over the 70–300 K range and the exchange coupling parameter (−2 J ) determined by a least squares fit of the data which indicates an antiferromagnetic spin exchange (−2 J = 94–172 cm −1 ) between the Cu II ions with bridging units in the order: N 3 ≈ NO 2 > OAc > OH.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43852/1/11243_2004_Article_5095478.pd

Complementary substrate specificity and distinct quaternary assembly of the Escherichia coli aerobic and anaerobic beta-oxidation trifunctional enzyme complexes

The trifunctional enzyme (TFE) catalyzes the last three steps of the fatty acid beta-oxidation cycle. Two TFEs are present in Escherichia coli, EcTFE and anEcTFE. EcTFE is expressed only under aerobic conditions, whereas anEcTFE is expressed also under anaerobic conditions, with nitrate or fumarate as the ultimate electron acceptor. The anEcTFE subunits have higher sequence identity with the human mitochondrial TFE (HsTFE) than with the soluble EcTFE. Like HsTFE, here it is found that anEcTFE is a membrane-bound complex. Systematic enzyme kinetic studies show that anEcTFE has a preference for medium- and long-chain enoyl-CoAs, similar to HsTFE, whereas EcTFE prefers short chain enoyl-CoA substrates. The biophysical characterization of anEcTFE and EcTFE shows that EcTFE is heterotetrameric, whereas anEcTFE is purified as a complex of two heterotetrameric units, like HsTFE. The tetrameric assembly of anEcTFE resembles the HsTFE tetramer, although the arrangement of the two anEcTFE tetramers in the octamer is different from the HsTFE octamer. These studies demonstrate that EcTFE and anEcTFE have complementary substrate specificities, allowing for complete degradation of long-chain enoyl-CoAs under aerobic conditions. The new data agree with the notion that anEcTFE and HsTFE are evolutionary closely related, whereas EcTFE belongs to a separate subfamily.Peer reviewe

A novel discrete dinuclear copper(II)–gadolinium(III) complex derived from a Schiff base ligand [Cu(salbn)Gd(NO 3 ) 3 ·H 2 O] (salbn): N , N ′-butylenebis(salicylideaminato)

The synthesis, X-ray and e.p.r. spectral studies of a 3d–4f couple are described here. The crystal structure of [Cu(salbn)Gd(NO 3 ) 3 ·H 2 O], (2) , salbn = N , N ′-butylenebis(salicylideaminato), has been determined by X-ray crystallography. Compound (2) crystallizes in the monoclinic system, space group p21/n, with a = 9.025(1), b = 22.912(1), c = 12.790(1) Å, β = 99.36(1), Z = 4. The deviations of the four coordinating atoms (O(1)O(2)N(1) and N(2) of salbn and the copper atom is displaced from the plane in spite of the lack of any apical ligand. The gadolinium(III) ion is nine-coordinated by the two oxygen atoms of the salbn moiety, three bidentate nitrate ions and one water molecule. The geometry of Gd III can be described as a square antiprism, in which compound Cu II and Gd III are bridged by the two phenolic oxygens of salbn. The Cu II –Gd III distance is 3.269(1) Å. The bridging core CuO2Gd is a butterfly shape. Significant distortion was observed for the complex having the larger diamino string. The title compound exhibits seven e.s.r. transitions with | D | = 0.0467 cm −1 , which demonstrates the existence of zero field splitting. This outcome indicates that compound (2) consists of a perfectly isolated dinuclear Cu–Gd core and steric bulk alters the dihedral angle in the Cu–O–Gd bridge.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43854/1/11243_2004_Article_5115383.pd

'Click' assembly of glycoclusters and discovery of a trehalose analogue that retards A(beta)40 aggregation and inhibits A(beta)40-induced neurotoxicity

Osmolytes have been proposed as treatments for neurodegenerative proteinopathies including Alzheimer's disease. However, for osmolytes to reach the clinic their efficacy must be improved. In this work, copper(I)-catalyzed azide-alkyne cycloaddition chemistry was used to synthesize glycoclusters bearing six copies of trehalose, lactose, galactose or glucose, with the aim of improving the potency of these osmolytes via multivalency. A trehalose glycocluster was found to be superior to monomeric trehalose in its ability to retard the formation of amyloid-beta peptide 40 (Aβ40) fibrils and protect neurons from Aβ40-induced cell death

Synthesis, spectral, electrochemical and magnetic properties of new asymmetric dicopper(II) complexes bearing chemically distinct coordination sites

Two new unsymmetrical binucleating ligands, 2-[bis(3- N, N -dimethylaminopropyl)-aminomethyl]-6-[prolin-1-yl)methyl]-4-bromophenol [H 2 L 1 ] and 2-[bis(3- N, N -dimethylaminopropyl)aminomethyl]-6-[prolin-1-yl)methyl]-4-methylphenol [H 2 L 2 ], and their dicopper(II) complexes with different exogenous bridging motifs (OAc, Br and Cl) have been prepared and characterized by spectral, electrochemical, magnetic and e.p.r. studies. Electrochemical studies indicate the presence of two irreversible reduction peaks in the cathodic region. Variable temperature magnetic susceptibility studies of the complexes show that the extent of antiferromagnetic coupling increases in the order: OAc − < Cl − < Br − . Broad isotropic or axial symmetric spectral features are observed in powder e.p.r. spectra of the complexes at 77 K. A comparison of the electrochemical and magnetic behaviour of the complexes derived from the ligands is discussed on the basis of an exogenous bridge as well as the substituent at the para position of the phenolic ring.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43855/1/11243_2004_Article_5272793.pd

Multicomponent polysaccharide alginate-based bioinks

3D-Bioprinting has seen a rapid expansion in the last few years, with an increasing number of reported bioinks. Alginate is a natural biopolymer that forms hydrogels by ionic cross-linking with calcium ions. Due to its biocompatibility and ease of gelation, it is an ideal ingredient for bioinks. This review focuses on recent advances on bioink formulations based on the combination of alginate with other polysaccharides. In particular, the molecular weight of the alginate and its loading level has an impact on materials performance, as well as the loading of the divalent metal salt and its solubility, which affects the cross-linking of the gel. Alginate is often combined with other polysaccharides that can sigificantly modify the properties of the gel, and can optimise alginate for use in different biological applications. It is also possible to combine alginate with sacrificial polymers, which can temporarily reinforce the 3D printed construct, but then be removed at a later stage. Other additives can be formulated into the gels to enhance performance, including nanomaterials that tune rheological properties, peptides to encourage cell adhesion, or growth factors to direct stem cell differentiation. The ease of formulating multiple components into alginate gels gives them considerable potential for further development. In summary, this review will facilitate the identification of different alginate-polysaccharide bioink formulations and their optimal applications, and help inform the design of second generation bioinks, allowing this relatively simple gel system to achieve more sophisticated control over biological processes

A study on the formation of luminescent zinc silicate

A study to understand the mechanism of formation of zinc ortho silicate green phosphor has been attempted. Samples with different mole ratios of ZnO and Si02 ranging from 2:l to 0.25:l in steps of 0.25 respectively have been prepared. Characterisation of the samples were done by ernission and excitation spectra and XRD analysis