John Reglinski

Supporting conformational change at metal centres. Part 2: four and five coordinate geometry

Abstract The X-ray crystal structures of pyridino-(N,N′-bis(salicylidene)-1,2-ethylenediamine)zinc, bis-(N,N′-bis(salicylidene)-1,3-propanediamine zinc) and bis-((μ-acetato-O,O′)-(N,N′-bis(salicylidene)-1,4-butanediamine) zinc) zinc are reported. These elusive motifs complete a structure based matrix of compounds for the late transition metals zinc with the popular ligands N,N′-bis(salicylidene)-1,2-ethylenediamine, N,N′-bis(salicylidene)-1,3-propanediamine and N,N′-bis(salicylidene)-1,4-butanediamine. Coupled with the structural data from previously reported zinc complexes, it is possible to provide an in depth analysis of the behaviour of these three ligand systems within a five coordinate environment. The information is further combined with structural data on the homologous copper and nickel complexs to provide an overview of the conformational flexibility of these three ligands within a four, five or six coordinate environment. It is demonstrated that the more neglected N,N′-bis(salicylidene)-1,4-butanediamine motif may have great potential for supporting chemistry at a metal centre where significant changes in coordination number and geometry are desired.

Importance of Nanoparticle Size in Colorimetric and SERS-Based Multimodal Trace Detection of Ni(II) Ions with Functional Gold Nanoparticles

Colorimetric detection of analytes using gold nanoparticles along with surface-enhanced Raman spectroscopy (SERS) are areas of intense research activity since they both offer sensing of very low concentrations of target species. Multimodal detection promotes the simultaneous detection of a sample by a combination of different techniques; consequently, surface chemistry design in the development of multimodal nanosensors is important for rapid and sensitive evaluation of the analytes by diverse analytical methods. Herein it is shown that nanoparticle size plays an important role in the design of functional nanoparticles for colorimetric and SERS-based sensing applications, allowing controlled nanoparticle assembly and tunable sensor response. The design and preparation of robust nanoparticle systems and their assembly is reported for trace detection of Ni(II) ions as a model system in an aqueous solution. The combination of covalently attached nitrilotriacetic acid moieties along with the L-carnosine dipeptide on the nanoparticle surface represents a highly sensitive platform for rapid and selective detection of Ni(II) ions. This systematic study demonstrates that significantly lower detection limits can be achieved by finely tuning the assembly of gold nanoparticles of different core sizes. The results clearly demonstrate the feasibility and usefulness of a multimodal approach.

Supporting conformational change at metal centres. Part 1: octahedral systems

The X-ray crystal structures bis-((μ 2 -acetato- O )-μ- fac -( N,N ′-bis(salicylidene)-1,4-butane-diamine)-(methanol) nickel) nickel and bis-((μ-acetato- O , O ′)-μ- mer -( N,N ′-bis(salicylidene)-1,4-butanediamine)-(dimethylformamido) nickel) nickel are presented. These elusive motifs complete a structure based matrix of compounds for nickel with the popular Schiffs base ligands N,N ′-bis(salicylidene)-1,2-ethylenediamine, N,N ′-bis(salicylidene)-1,3-propanediamine and N,N ′-bis(salicylidene)-1,4-butanediamine. Coupled with data from previously reported structures and data derived from the additional structures of bis-((μ-acetato- O,O ′)-μ- mer -( N,N ′-bis(salicylidene)-1,3-propanediamine)-(pyridine) nickel) nickel and dichloro-(μ 2 -( N,N ′-bis(salicylidene)-1,3-propane-diamine)-bis(pyridine) nickel) lead it is possible to provide an in depth analysis of the behaviour of these three ligand systems within a six coordinate environment. Although, the geometries observed for N,N ′-bis(salicylidene)-1,2-ethylenediamine and N , N ′-bis(salicylidene)-1,3-propanediamine seem to be constrained by the chelate ring generated by the imine groups, the larger ring size of the N , N ′-bis(salicylidene)-1,4-butanediamine derived chelate would seem to confer substantial flexibility in the backbone and as such, considerable variation in the potential geometry, i.e. mer and fac conformers of the complexes formed.

The synthesis of soft tripodal ligands: restrictions on the preparation of hydrotris(thiazolyl)borate anions from borohydride melts

The syntheses of two new, soft, tripodal anions, hydrotris(mercaptothiazolyl)borate (Tz) and hydrotris(mercaptobenzothiazolyl)borate (Tbz), are reported. These species not only extend the series of thiazolylborate anions which call be generated using the protocol of Trofimenko, but analysis of the respective thione melting points and pK(a) values, enables the prediction of which thiazolylborate anions can be produced using borohydride melts. Both of the products are converted into their thallium complexes, which can be used as convenient ligand transfer reagents. The X-ray crystal structure of thaliium(I) hydrotris(2-mercapto-benzothiazolyl)borate, [Tl(Tbz)](infinity), is reported. The ligand complexes to Tl as a C-3 tridentate species, while a bridging thione links Tl(Tbz) units into zigzag one-dimensional polymeric chains.

Erythrocyte glutathione balance and membrane stability during preeclampsia

This study aimed to determine whether oxidative damage to the erythrocyte occurs in preeclampsia, and relates to disease severity. The oxidative status of intact erythrocytes from preeclamptic patients and normal pregnant women was determined using spin echo 1H-NMR, which measures both the concentration and redox state of intracellular glutathione. Previous studies of preeclampsia have only measured total glutathione levels. Membrane fragility was determined from the degree of lysis caused by incubation in hypotonic saline. Erythrocytes from moderate-severe preeclamptic patients underwent more lysis than erythrocytes from control pregnant women (p < .05) or mild preeclamptic patients. It is suggested that increased lysis results from oxidative damage to the erythrocyte membrane, causing a decrease in membrane fluidity and reducing its ability to withstand osmotic changes. Intracellular glutathione was more oxidized in erythrocytes from pregnant women compared to nonpregnant controls (p < .05), and there was a less significant trend toward more oxidized glutathione with increasing severity of preeclampsia. The moderate-severe group showed a clear division in glutathione redox status: some patients had very oxidized glutathione while others had a normal redox balance. This novel finding suggests that some patients may be unusually susceptible to erythrocyte glutathione oxidation, possibly leading to general cellular damage, in particular HELLP Syndrome.

The Preparation and Structures of Group 12 (Zn, Cd, Hg) Complexes of the Soft Tripodal Ligand Hydrotris(methimazolyl)borate (Tm)

Complexes of the hydrotris(methimazolyl)borate ligand (Tm) have been prepared with zinc, cadmium and mercury halides. Complexes of type [M(Tm)X] were obtained and characterised by NMR and mass spectrometry, X-ray crystallographic analysis of [Zn(Tm)X] (X = Cl, Br, I) reveals a symmetrical coordination mode of the ligand, but no significant change with different halides, which sit on the approximate C-3 axes of the complexes, The structures of [M(Tm)Br] (M = Cd, Hg) are isomorphous with one another, Again, the ligand is symmetrically coordinated to the metal, but the halide is now significantly displaced from the approximate C-3 axis of the M(Tm) unit, resulting in what approximates to a trigonal pyramidal geometry. Unlike in most distorted mercury structures, little bond length expansion (towards two- or three-coordinate geometries) occurs. This is ascribed to the strong affinity of the thione donors for Hg.

INTERACTION OF NITROGEN MONOXIDE WITH CYTOCHROME P-450 MONITORED BY SURFACE-ENHANCED RESONANCE RAMAN SCATTERING

The reaction of mammalian cytochrome P-450 2B4 with nitrogen monoxide and oxygen has been studied by surface-enhanced resonance Raman scattering (SERRS) to obtain sharp and definitive information in situ on the nature of the changes in the active site pocket. The initial reaction produces a six co-ordinate low spin haem-nitrogen monoxide adduct. A slower reaction leads to the irreversible formation of a five co-ordinate high-spin iron (III) haem with no nitrogen monoxide bound to it and to the nitration of an aromatic side chain, probably a tyrosine, in the proximity of the active site. In the presence of excess nitrogen monoxide, the second reaction is controlled by oxygen concentration. The sequence of events corresponds to the biphasic inhibition induced by NO in other cytochromes P-450 and peroxidases and is postulated to occur by the formation of a nitrating agent at the haem followed by diffusion to the tyrosine. The nitrated amino acid and the oxidation and spin state of the haem are observed easily by SERRS with low concentrations of protein making it a particularly suitable method for the investigation of reactions of NO in complex biological matrices.

A simple, novel method for preparing an effective water oxidation catalyst

A novel oxygen catalyst is prepared via the photodeposition of ruthenium(IV) oxide on a titania photocatalyst derived from a perruthenate precursor.

A1 H spin echo and 51V NMR study of the interaction of vanadate with intact erythrocytes

Abstract The action of vanadate on intact human erythrocytes was studied by 1H spin echo and 51V NMR spectroscopy as a model for the behaviour of vanadium(V) complexes in experimental diabetes. Vanadate is reduced by the intact erythrocyte at the expense of intracellular glutathione which rapidly depletes from the intracellular volume. Using the blocking agent 4,4′-diisothio-cyanatostilbene-2,2′-disulfonic acid (DIDS), which specifically blocks the anion transporter, vanadate reduction could be inhibited and glutathione depletion arrested. Thus, for the reaction with the intact cell to occur, vanadium(V) must cross the cell wall, possibly via the anion transporter. Nitrofurantoin was used to inhibit glutathione reductase in the erythrocyte suspensions. Under these conditions, treatment of the cells with vanadate induced glutathione oxidation prior to depletion. A study of the reaction of vanadate with haemolysate indicates that, without the influence of the membrane, rapid oxidation of glutathione to glutathione disulfide by the vanadyl cation occurs with no glutathione depletion, and that under these conditions vanadate reduction is incomplete. This study generates a model for the behaviour of vanadium complexes in vivo, providing a basis for the rational design and synthesis of new vanadium-based agents as insulin mimics. In essence, vanadium is transported across the membrane as vanadate(V), is reduced in situ by glutathione, and becomes complexed to a wide range of intracellular binding sites. Exchange reactions between glutathione and sulfhydryl groups present on haemoglobin and membrane lead to the depletion of glutathione from the cytosol.

Hydrotris(methimazolyl)borate, a soft analogue of hydrotris(pyrazolyl)borate. Preparation and crystal structure of a novel zinc complex

The synthesis of a new ligand, hydrotris(methimazolyl)borate,† a soft analogue of hydrotris(pyrazolyl)borate, is reported; to demonstrate the coordination chemistry of this novel ligand, complexes of CuI and ZnII are prepared and characterised.