Experimental and theoretical studies of pH-responsive iridium(III) complexes of azole and N-heterocyclic carbene ligands

A series of nine luminescent iridium(III) complexes with pH-responsive imidazole and benzimidazole ligands have been prepared and characterized. The first series of complexes were of the form [Ir(ppy)2(N^N)]+ or [Ir(ppy)2(C^N)]+ (where ppy is 2-phenylpyridine and N^N is 2-(2-pyridyl)imidazole or 2-(2-pyridyl)benzimidazole and C^N represents a pyridyl-triazolylidene-based N-heterocyclic carbene ligand). For these complexes, the benzimidazole group was either unsubstituted or substituted with electron-withdrawing (Cl) or electron-donating (Me) groups. The second series of complexes were of the form [Ir(phbim)2(N^N)]+ or [Ir(phbim)2(C^N)]+ (where phbim is 2-phenylbenzimidazole and N^N is either 2,2'-bipyridine or 1,10-phenanthroline and C^N is either a pyridyl-imidazolylidene or pyridyl-triazolylidene N-heterocyclic carbene ligand). UV-visible and photoluminescence pH titration studies showed that changing the protonation state of these complexes results in significant changes in the photoluminescence emission properties. The pKa values of prepared complexes were estimated from the spectroscopic pH titration data and these values show that the nature of the pH-sensitive ligands (either main or ancillary ligands) resulted in a significant capacity to modulate the pKa values for these compounds with values ranging from 5.19-11.22. Theoretical investigations into the nature of the electronic transitions for the different protonation states of compounds were performed and the results were consistent with the experimental results.

A common allele of HLA is associated with asymptomatic SARS-CoV-2 infection

Studies have demonstrated that at least 20% of individuals infected with SARS-CoV-2 remain asymptomatic1-4. Although most global efforts have focused on severe illness in COVID-19, examining asymptomatic infection provides a unique opportunity to consider early immunological features that promote rapid viral clearance. Here, postulating that variation in the human leukocyte antigen (HLA) loci may underly processes mediating asymptomatic infection, we enrolled 29,947 individuals, for whom high-resolution HLA genotyping data were available, in a smartphone-based study designed to track COVID-19 symptoms and outcomes. Our discovery cohort (n = 1,428) comprised unvaccinated individuals who reported a positive test result for SARS-CoV-2. We tested for association of five HLA loci with disease course and identified a strong association between HLA-B*15:01 and asymptomatic infection, observed in two independent cohorts. Suggesting that this genetic association is due to pre-existing T cell immunity, we show that T cells from pre-pandemic samples from individuals carrying HLA-B*15:01 were reactive to the immunodominant SARS-CoV-2 S-derived peptide NQKLIANQF. The majority of the reactive T cells displayed a memory phenotype, were highly polyfunctional and were cross-reactive to a peptide derived from seasonal coronaviruses. The crystal structure of HLA-B*15:01-peptide complexes demonstrates that the peptides NQKLIANQF and NQKLIANAF (from OC43-CoV and HKU1-CoV) share a similar ability to be stabilized and presented by HLA-B*15:01. Finally, we show that the structural similarity of the peptides underpins T cell cross-reactivity of high-affinity public T cell receptors, providing the molecular basis for HLA-B*15:01-mediated pre-existing immunity.

Ablation of CD8+ T cell recognition of an immunodominant epitope in SARS-CoV-2 Omicron variants BA.1, BA.2 and BA.3

The emergence of the SARS-CoV-2 Omicron variant has raised concerns of escape from vaccine-induced immunity. A number of studies have demonstrated a reduction in antibody-mediated neutralization of the Omicron variant in vaccinated individuals. Preliminary observations have suggested that T cells are less likely to be affected by changes in Omicron. However, the complexity of human leukocyte antigen genetics and its impact upon immunodominant T cell epitope selection suggests that the maintenance of T cell immunity may not be universal. In this study, we describe the impact that changes in Omicron BA.1, BA.2 and BA.3 have on recognition by spike-specific T cells. These T cells constitute the immunodominant CD8⁺ T cell response in HLA-A*29:02⁺ COVID-19 convalescent and vaccinated individuals; however, they fail to recognize the Omicron-encoded sequence. These observations demonstrate that in addition to evasion of antibody-mediated immunity, changes in Omicron variants can also lead to evasion of recognition by immunodominant T cell responses.

Antibacterial silver and gold complexes of imidazole and 1,2,4-triazole derived N-heterocyclic carbenes

A series of gold(I) (4a-4h, 5a-5b) and silver(I) (3a-3h) complexes of 1,2,4-triazolylidene and imidazolylidene based N-heterocyclic carbene ligands were prepared and the antibacterial activities of these complexes have been evaluated. The complexes were characterised using ¹H-NMR, ¹³C-NMR, HRMS and in the cases of 3a, 3c, 4b and 5b by X-ray crystallography. The gold(I) complexes with phenyl substituents (4a-4d) were found to have potent antibacterial activity against Gram-positive bacteria, with the complexes of the 1,2,4-triazolylidene ligands being more active (4c, MIC = 4-8 μg mL^-1 against Enterococcus faecium and 2 μg mL^-1 against Staphylococcus aureus) than the analogous imidazolylidene complexes 4a and 4b (4a, MIC = 64 μg mL^-1 against E. faecium and 2-4 μg mL^-1 against S. aureus). Two of the silver(I) complexes have promising antibacterial activity against Acinetobacter baumannii (3f, MIC = 2-4 μg mL^-1 and 3g, MIC = 2 μg mL^-1). Silver(I) complex 3f and gold(I) complex 4c were tested against multi-drug resistant bacterial strains and high levels of antibacterial activity were observed. The potential for antibacterial resistance to develop against these metal containing complexes was investigated and significantly, no resistance was observed upon continuous treatment, whilst resistance was developed against the widely used broad-spectrum antibiotic ciprofloxacin in the same bacterial strains, under the conditions tested. The solution and gas phase stabilities of the complexes have been investigated using a combination of ¹H-NMR, HRMS and detailed computational mechanistic studies were undertaken to gain insights into the possible decomposition reactions for silver complexes in aqueous solution.

Charge neutral rhenium tricarbonyl complexes of tridentate N-heterocyclic carbene ligands that bind to amyloid plaques of Alzheimer's disease

Two tridentate ligand systems bearing N-heterocyclic carbene (NHC), amine and carboxylate donor groups coupled to benzothiazole- or stilbene-based amyloid binding moieties were synthesised. Reaction of the imidazolium salt containing pro-ligands with Re(CO)5Cl yielded the corresponding rhenium metal complexes which were characterised by NMR, and X-ray crystallography. These ligands are of interest for the potential preparation of technetium-99m imaging agents for Alzheimer's disease and the capacity of these rhenium complexes bind to amyloid fibrils composed of amyloid-β peptide and amyloid plaques in human frontal cortex brain tissue was evaluated using fluorescence microscopy. These studies show that the complexes bound efficiently to amyloid-β fibrils and some evidence of binding to amyloid-β plaques.

Increased glutaminyl cyclase activity in brains of Alzheimer's disease individuals

Glutaminyl cyclases (QC) catalyze the formation of neurotoxic pGlu-modified amyloid-β peptides found in the brains of people with Alzheimer's disease (AD). Reports of several-fold increases in soluble QC (sQC) expression in the brain and peripheral circulation of AD individuals has prompted the development of QC inhibitors as potential AD therapeutics. There is, however, a lack of standardized quantitative data on QC expression in human tissues, precluding inter-laboratory comparison and validation. We tested the hypothesis that QC is elevated in AD tissues by quantifying levels of sQC protein and activity in post-mortem brain tissues from AD and age-matched control individuals. We found a modest but statistically significant increase in sQC protein, which paralleled a similar increase in enzyme activity. In plasma samples sourced from the Australian Imaging, Biomarker and Lifestyle study we determined that QC activity was not different between the AD and control group, though a modest increase was observed in female AD individuals compared to controls. Plasma QC activity was further correlated with levels of circulating monocytes in AD individuals. These data provide quantitative evidence that alterations in QC expression are associated with AD pathology.

A luminescent lipid mimetic iridium(III) N-heterocyclic carbene complex for membrane labelling

Labelling phospholipid membranes with luminophores without altering the biophysical characteristics of the system is particularly challenging due to the small size of the phospholipid molecules and the sensitivity of membrane properties to the presence of fused heterocyclic molecules. Here the design and synthesis of a luminescent lipid mimetic Ir(III) N-heterocyclic carbene complex of the form [Ir(ppy)₂(C^N)] (where ppy = 2-(phenyl)-pyridine and C^N is a N-heterocyclic carbene ligand) conjugated to stearic acid is described. This complex was synthesised by the reaction of an acetate functionalised Ir(III) precursor complex with tert-butyl N-(2-aminoethyl)carbamate (mono-BOC protected ethylene diamine) and after deprotection of the amine group this complex was coupled to stearic acid using the peptide coupling reagent 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The photophysical properties of the synthesised complexes were evaluated and they showed blue-green luminescence in the range of 514-520 nm. Fluorescence microscopy studies showed that the lipid mimetic complex successfully incorporated into liposomes composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), while dynamic light scattering (DLS) and differential scanning calorimetry (DSC) studies showed that the complex had negligible influence on the biophysical properties of the liposomes.

Near-Infrared Electrochemiluminescence from Bistridentate Ruthenium(II) Di(quinoline-8-yl)pyridine Complexes in Aqueous Media

We report the synthesis, photophysics, electrochemistry and electrochemiluminescence (ECL) of two dqp (dqp=2,6-di(quinoline-8-yl)pyridine) based ruthenium(II) complexes, bearing either a n-butyl ester (1) or the corresponding carboxylic acid functionality (2). The complexes were prepared from [Ru(dqp)(MeCN)₃ ][PF₆ ]₂ by reaction with the dqp precursor using microwave irradiation. In both cases, photoluminescence spectra present strong ³ MLCT-based red/near-infrared (NIR) emissions centred at about 710 nm. The photoluminescence quantum yields were 6.1 % and 1.8 % for 1 and 2 respectively while the excited state lifetimes were 3.60 μs and 2.37 μs. Both complexes are ECL active, although ECL efficiency (Φ_ECL ) of 1 was substantially higher than 2, due to its more favourable electrochemical properties. Importantly, 1 also gave strong ECL in aqueous media, which is rare for near-infrared emitters. The results suggest the possibility of very interesting ECL sensing applications for this class of emitter in biological media.

Synthesis, conformational analysis and antibacterial activity of Au(i)–Ag(i) and Au(i)–Hg(ii) heterobimetallic N-heterocyclic carbene complexes

A family heterobimetallic Au(i)–Ag(i) and Au(i)–Hg(ii) complexes of bis-N-heterocyclic carbene ligands been prepared and their antibacterial properties evaluated.

Luminescent iridium(iii)–boronic acid complexes for carbohydrate sensing

A family of four Ir(iii) complexes with either pyridyl-1,2,4-triazole or pyridyl-1,3,4-oxadiazole ligands bearing boronic acid groups have been prepared as potential luminescent sensors for carbohydrates.

Stepwise Synthesis of Tetra-imidazolium Macrocycles and Their N-Heterocyclic Carbene Metal Complexes

A modular stepwise synthetic method has been developed for the preperation of tetra-imidazolium macrocycles. Initially a series of three bis(imidazolylmethyl)benzene precursors were alkylated with 1,2-dibromoethane to produce the corresponding bis-bromoethylimidazolium bromide salts. In the second step the bis-bromoethylimidazolium bromide salts were reacted with selected bis(imidazolylmethyl)benzene molecules to produce a series of two symmetrical and three asymmetrical tetra-imidazolium macrocycles. These tetra-imidazolium salts act receptors for anions and 1H-NMR titration studies were used to determine the association constants between two of the macrocycles and the halide anions chloride, bromide and iodide. The tetra-imidazolium salts are precursors for N-heterocyclic carbene (NHC) ligands and the corresponding silver(I), gold(I), and palladium(II) NHC complexes have been prepared. Varied structures were obtained, which depend on the chosen macrocyclic ligand and metal ion and in the case of the coinage metals Ag(I) and Au(I), mono, di, and hexanuclear complexes were formed.

Tuning the electrochemiluminescent properties of iridium complexes of N-heterocyclic carbene ligands

A series of five heteroleptic Ir(iii) complexes of the general form Ir(dfppy)2(C^C) have been prepared (where dfppy represents 2-(2,4-difluorophenyl)pyridine and C^C represents a bidentate cyclometalated phenyl substituted imidazolylidene ligand). The cyclometalated phenyl ring of the imidazolylidene ligand was either unsubstituted or substituted with electron donating (OMe and Me) or electron withdrawing (Cl and F) groups in the 2 and 4 positions. The synthesised Ir(iii) complexes have been characterised by elemental analysis, NMR spectroscopy, cyclic voltammetry and electronic absorption and emission spectroscopy. The molecular structures for four Ir(iii) complexes were determined by single crystal X-ray diffraction. Each of the Ir(iii) complexes exhibited intense photoluminescence in acetonitrile solution at room temperature with quantum yields (ΦPL) ranging from 58% to 86%. Cyclic voltammetry experiments revealed one oxidation process (formally ascribed to the metal centre), and two ligand-based reductions for each complex. Complexes 1-5 gave moderate to intense annihilation and co-reactant electrochemiluminescence (ECL). Consideration of the electrochemical, spectroscopic and theoretical investigations provide insights into the electrochemiluminescence behaviour.

Luminescent iridium(iii) complexes of N-heterocyclic carbene ligands prepared using the ‘click reaction’

Luminescent and electrochemiluminescent N-heterocyclic carbene-combined 1,2,3-triazole and 1,2,3-triazolylidene Ir(iii) complexes have been prepared and their potential as luminescent probes in cell imaging has been evaluated.

Unusually Strong Electrochemiluminescence from Iridium-Based Redox Polymers Immobilized As Thin Layers or Polymer Nanoparticles

A new class of redox metallopolymer based on cyclometalated iridium(III) centers is described, with unusually intense luminescence properties in aqueous media. We report the facile synthesis, photophysical and electrochemical characterization, supported by DFT calculations and their electrochemiluminescence (ECL) properties which, under some circumstances, are significantly greater than the analogous ruthenium-based materials. The photoluminescence (PL) and ECL of these materials are further dramatically enhanced when dispersed or immobilized as polymeric nanoparticles (PNPs). This aggregation-induced emission (AIE and AIECL) operates by providing important protection for the cyclometalated iridium(III) centers against the types of quenching processes which commonly afflict iridium-based luminophores in aqueous media. The results suggest interesting new avenues of research for the application of such materials in and PL and ECL-based detection and imaging as well as light-emitting devices.

Dinuclear Au(i) N-heterocyclic carbene complexes derived from unsymmetrical azolium cyclophane salts: potential probes for live cell imaging applications

We have synthesized a new series of azolium cyclophanes and used them as precursors of inherently luminescent dinuclear Au(i)-N-heterocyclic carbene (NHC) complexes. The azolium cyclophanes contained two azolium groups (either imidazolium or benzimidazolium), an o-xylyl group, and an alkyl linker chain (either C2, C3 or C4). All of the azolium cyclophanes were characterised by X-ray diffraction studies and VT NMR studies, and all were fluxional in solution on the NMR timescale. The C3- and C4-linked azolium cyclophanes served as precursors of Au2L2(2+) complexes (L is a cyclophane bis(NHC) ligand). Due to the unsymmetrical nature of the azolium cyclophanes, the Au2L2(2+) complexes each existed as cis and trans isomers. X-ray diffraction studies showed that the Au2L2(2+) complexes had short intramolecular AuAu distances, in the range 2.9-3.3 Å, suggestive of an aurophilic attraction, presumably as a consequence of the geometrical constraints imposed by the cyclophane bis(NHC) ligands. The complexes having the shortest AuAu distances (i.e., those based on C3-linked cyclophanes) exhibited intense luminescence in solution. The uptake of one of the dinuclear Au-NHC complexes by tumorigenic cells, and its subsequent distribution and toxicity in the cells, was monitored by luminescence microscopy over 6 h and proliferation measurements, respectively.

Rhenium(i) complexes of N-heterocyclic carbene ligands that bind to amyloid plaques of Alzheimer's disease

Rhenium(i) complexes of tridentate N-heterocyclic carbene ligands that bind to amyloid plaques in human brain tissue are reported.

Access to the Parent Tetrakis(pyridine)gold(III) Trication, Facile Formation of Rare Au(III) Terminal Hydroxides, and Preliminary Studies of Biological Properties

In this paper we report on the use of [NO][BF4] to access tricationic tetrakis(pyridine)gold(III) from Au powder, a species inaccessible using the more traditional (tetrahydrothiophene)AuCl route. It is then demonstrated that this family of compounds can be used to access new terminal Au(III) hydroxides, a challenging class of compounds, and the first crystallographically characterized examples employing bidentate ligands. Finally, preliminary biological studies indicate good activity for derivatives featuring polydentate ligands against the HeLa and PC3 cell lines but also strong inhibition of primary HUVEC cells.

Metal complexes with di(N-heterocyclic carbene) ligands bearing a rigid ortho-, meta or para-phenylene bridge

Ag(i) complexes with diNHC ligands are efficient transmetalating agents towards transition metals.

The fate of NHC-stabilized dicarbon

The attempted synthesis of NHC-stabilized dicarbon (NHC=C=C=NHC) through deprotonation of a doubly protonated precursor ([NHC-CH=CH-NHC](2+) ) is reported. Rather than deprotonation, a clean reduction to NHC=CH-CH=NHC is observed with a variety of bases. The apparent resistance towards deprotonation to the target compound led to a reinvestigation of the electronic structure of NHC→CC←NHC, which showed that the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) gap is likely too small to allow for isolation of this species. This is in contrast to the recent isolation of the cyclic alkylaminocarbene analogue (cAAC=C=C=cAAC), which has a large HOMO-LUMO gap. A detailed theoretical study illuminates the differences in electronic structures between these molecules, highlighting another case of the potential advantages of using cAAC rather than NHC as a ligand. The bonding analysis suggests that the dicarbon compounds are well represented in terms of donor-acceptor interactions L→C2 ←L (L=NHC, cAAC).

Rhenium complexes of bidentate, bis-bidentate and tridentate N-heterocyclic carbene ligands

Rhenium(i) tricarbonyl complexes of a range of bidentate, bis-bidentate and tridentate NHC ligands have been prepared. These NHC ligands are of interest for possible applications in the development of Tc-99m or Re-186/188 radiopharmaceuticals and the stability of two complexes were evaluated in ligand challenge experiments using the metal binding amino acids l-histidine or l-cysteine.

Iridium(iii) N-heterocyclic carbene complexes: an experimental and theoretical study of structural, spectroscopic, electrochemical and electrogenerated chemiluminescence properties

Theoretical and experimental studies of a series of iridium N-heterocyclic carbene complexes.

Rhenium and technetium tricarbonyl complexes of N-heterocyclic carbene ligands

A strategy for the conjugation of N-heterocyclic carbene (NHC) ligands to biomolecules via amide bond formation is described. Both 1-(2-pyridyl)imidazolium or 1-(2-pyridyl)benzimidazolium salts functionalized with a pendant carboxylic acid group were prepared and coupled to glycine benzyl ester using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. A series of 10 rhenium(I) tricarbonyl complexes of the form [ReX(CO)3(ĈN)] (ĈN is a bidentate NHC ligand, and X is a monodentate anionic ligand: Cl(-), RCO2(-)) were synthesized via a Ag2O transmetalation protocol from the Re(I) precursor compound Re(CO)5Cl. The synthesized azolium salts and Re(I) complexes were characterized by elemental analysis and by (1)H and (13)C NMR spectroscopy, and the molecular structures for one imidazolium salt and seven Re(I) complexes were determined by single-crystal X-ray diffraction. (1)H NMR and mass spectrometry studies for an acetonitrile-d3 solution of [ReCl(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)] show that the monodentate chloride ligand is labile and exchanges with this solvent yielding a cationic acetonitrile adduct. For the first time the labeling of an NHC ligand with technetium-99m is reported. Rapid Tc-99m labeling was achieved by heating the imidazolium salt 1-(2-pyridyl)-3-methylimidazolium iodide and Ag2O in methanol, followed by the addition of fac-[(99m)Tc(OH2)3(CO)3](+). To confirm the structure of the (99m)Tc-labeled complex, the equivalent (99)Tc complex was prepared, and mass spectrometric studies showed that the formed Tc complexes are of the form [(99m/99)Tc(CH3CN)(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)](+) with an acetonitrile molecule coordinated to the metal center.

Triamidetriamine bearing macrobicyclic and macrotricyclic ligands: potential applications in the development of copper-64 radiopharmaceuticals

A versatile and straightforward synthetic approach is described for the preparation of triamide bearing analogues of sarcophagine hexaazamacrobicyclic cage ligands without the need for a templating metal ion. Reaction of 1,1,1-tris(aminoethyl)ethane (tame) with 3 equiv of 2-chloroacetyl chloride, yields the tris(α-chloroamide) synthetic intermediate 6, which when treated with either 1,1,1-tris(aminoethyl)ethane or 1,4,7-triazacyclononane furnished two novel triamidetriamine cryptand ligands (7 and 8 respectively). The Co(III) and Cu(II) complexes of cryptand 7 were prepared; however, cryptand 8 could not be metalated. The cryptands and the Co(III) complex 9 have been characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, and X-ray crystallography. These studies confirm that the Co(III) complex 9 adopts an octahedral geometry with three facial deprotonated amido-donors and three facial amine donor groups. The Cu(II) complex 10 was characterized by elemental analysis, single crystal X-ray crystallography, cyclic voltammetry, and UV-visible absorption spectroscopy. In contrast to the Co(III) complex (9), the Cu(II) center adopts a square planar coordination geometry, with two amine and two deprotonated amido donor groups. Compound 10 exhibited a quasi-reversible, one-electron oxidation, which is assigned to the Cu(2+/3+) redox couple. These cryptands represent interesting ligands for radiopharmaceutical applications, and 7 has been labeled with (64)Cu to give (64)Cu-10. This complex showed good stability when subjected to L-cysteine challenge whereas low levels of decomplexation were evident in the presence of L-histidine.

Diverse reactions of PhI(OTf)2 with common 2-electron ligands: complex formation, oxidation, and oxidative coupling

The crystal structures of bis-pyridine stabilized iodine dications [PhI(pyr)(2)](2+) are reported as triflate salts, representing the first ligand supported iodine dications to be structurally characterized. The pyridine complexes are susceptible to ligand exchange in reaction with stronger N-based donors such as 4-dimethylaminopyridine. Attempts to extend this reactivity to N-heterocyclic carbene and phosphine ligands, as has been accomplished in the earlier p-block groups, resulted in redox chemistry, with oxidation of the ligands rather than coordination.

Macrocyclic diamide ligand systems: potential chelators for 64Cu- and 68Ga-based positron emission tomography imaging agents

The N(4)-macrocyclic ligand 2,10-dioxo-1,4,8,11-tetraazabicyclo[11.4.0]1,12-heptadeca-1(12),14,16-triene H(2)L has been synthesized by the [1 + 1] condensation reaction between N,N'-bis(chloroacetyl)-1,2-phenylenediamine and 1,3-propylenediamine. The coordination chemistry of this ligand has been investigated with the metal ions Cu(II), Ni(II), Zn(II), and Ga(III) (complexes 1, 2, 3 and 4, respectively). H(2)L and its metal complexes have been fully characterized by the use of NMR, UV/vis, electron paramagnetic resonance, and elemental analysis where appropriate. The four metal complexes 1-4 have been structurally characterized by X-ray crystallography which confirmed that in all cases the amide nitrogen atoms are deprotonated and coordinated to the metal center. Complexes 3 and 4 are five-coordinate with a water molecule and chloride ion occupying the apical site, respectively. Cyclic voltammetric measurements on complex 1 show that this complex is oxidized reversibly with a half-wave potential, E(1/2) = 0.47 V, and reduced irreversibly at E(P) = -1.84 V. Density functional theory calculations reproduce the geometries of the four complexes. The one-electron reduction and oxidation potentials for 1 were calculated by using two solvent models, DMF and H(2)O. The calculations indicated that the one electron oxidation of 1 may involve removal of an electron from the ligand as opposed to the metal center, producing a diradical. The diamide macrocyle is of interest for the development of new positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging agents, and a radiolabeled complex has been synthesized with the positron emitting isotope (64)Cu. In vivo biodistribution studies for the (64)Cu labeled complex, (64)Cu-1, in male Lewis rats, showed that the activity is cleared rapidly from the blood within 1-2 h post-administration.

Cognitive processing in bipolar disorder conceptualized using the Interactive Cognitive Subsystems (ICS) model

BACKGROUND

There are few theoretical proposals that attempt to account for the variation in affective processing across different affective states of bipolar disorder (BD). The Interacting Cognitive Subsystems (ICS) framework has been recently extended to account for manic states. Within the framework, positive mood state is hypothesized to tap into an implicational level of processing, which is proposed to be more extreme in states of mania.

METHOD

Thirty individuals with BD and 30 individuals with no history of affective disorder were tested in euthymic mood state and then in induced positive mood state using the Question-Answer task to examine the mode of processing of schemas. The task was designed to test whether individuals would detect discrepancies within the prevailing schemas of the sentences.

RESULTS

Although the present study did not support the hypothesis that the groups differ in their ability to detect discrepancies within schemas, we did find that the BD group was significantly more likely than the control group to answer questions that were consistent with the prevailing schemas, both before and after mood induction.

CONCLUSIONS

These results may reflect a general cognitive bias, that individuals with BD have a tendency to operate at a more abstract level of representation. This may leave an individual prone to affective disturbance, although further research is required to replicate this finding.

In vitro and in vivo evaluations of a hydrophilic 64Cu-bis(thiosemicarbazonato)-glucose conjugate for hypoxia imaging

A water-soluble glucose conjugate of the hypoxia tracer 64Cu-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM) was synthesized and radiolabeled (64Cu-ATSE/A-G). Here we report our initial biological experiments with 64Cu-ATSE/A-G and compare the results with those obtained for 64Cu-ATSM and 18F-FDG.

METHODS

The uptake of 64Cu-ATSE/A-G and 64Cu-ATSM into HeLa cells in vitro was investigated at a range of dissolved oxygen concentrations representing normoxia, hypoxia, and anoxia. Small-animal PET with 64Cu-ATSE/A-G was performed in male BDIX rats implanted with P22 syngeneic carcinosarcomas. Images of 64Cu-ATSM and 18F-FDG were obtained in the same model for comparison.

RESULTS

64CuATSE/A-G showed oxygen concentration-dependent uptake in vitro and, under anoxic conditions, showed slightly lower levels of cellular uptake than 64Cu-ATSM; uptake levels under hypoxic conditions were also lower. Whereas the normoxic uptake of 64Cu-ATSM increased linearly over time, 64Cu-ATSE/A-G uptake remained at low levels over the entire time course. In the PET study, 64CuATSE/A-G showed good tumor uptake and a biodistribution pattern substantially different from that of each of the controls. In marked contrast to the findings for 64Cu-ATSM, renal clearance and accumulation in the bladder were observed. 64Cu-ATSE/A-G did not display the characteristic brain and heart uptake of 18F-FDG.

CONCLUSION

The in vitro cell uptake studies demonstrated that 64Cu-ATSE/A-G retained hypoxia selectivity and had improved characteristics when compared with 64Cu-ATSM. The in vivo PET results indicated a difference in the excretion pathways, with a shift from primarily hepatointestinal for 64Cu-ATSM to partially renal with 64Cu-ATSE/A-G. This finding is consistent with the hydrophilic nature of the glucose conjugate. A comparison with 18F-FDG PET results revealed that 64Cu-ATSE/A-G was not a surrogate for glucose metabolism. We have demonstrated that our method for the modification of Cu-bis(thiosemicarbazonato) complexes allows their biodistribution to be modified without negating their hypoxia selectivity or tumor uptake properties.

Spectroelectrochemical and computational studies on the mechanism of hypoxia selectivity of copper radiopharmaceuticals

Detailed chemical, spectroelectrochemical and computational studies have been used to investigate the mechanism of hypoxia selectivity of a range of copper radiopharmaceuticals. A revised mechanism involving a delicate balance between cellular uptake, intracellular reduction, reoxidation, protonation and ligand dissociation is proposed. This mechanism accounts for observed differences in the reported cellular uptake and washout of related copper bis(thiosemicarbazonato) complexes. Three copper and zinc complexes have been characterised by X-ray crystallography and the redox chemistry of a series of copper complexes has been investigated by using electronic absorption and EPR spectroelectrochemistry. Time-dependent density functional theory (TD-DFT) calculations have also been used to probe the electronic structures of intermediate species and assign the electronic absorption spectra. DFT calculations also show that one-electron oxidation is ligand-based, leading to the formation of cationic triplet species. In the absence of protons, metal-centred one-electron reduction gives the reduced anionic copper(I) species, [CuIATSM](-), and for the first time it is shown that molecular oxygen can reoxidise this anion to give the neutral, lipophilic parent complexes, which can wash out of cells. The electrochemistry is pH dependent and in the presence of stronger acids both chemical and electrochemical reduction leads to quantitative and rapid dissociation of copper(I) ions from the mono- or diprotonated complexes, [CuIATSMH] and [Cu(I)ATSMH2]+. In addition, a range of protonated intermediate species have been identified at lower acid concentrations. The one-electron reduction potential, rate of reoxidation of the copper(I) anionic species and ease of protonation are dependent on the structure of the ligand, which also governs their observed behaviour in vivo.

In vitro assays for assessing the potential for copper complexes to function as radiopharmaceutical agents

A series of chemical in vitro assays are described to provide a rapid initial assessment of the in vivo stability and biological behaviour of potential new copper(II) based radiopharmaceutical agents. Chemical challenges using an excess of cysteine, glutathione (GSH) and histidine, which are models of S- and N-donor molecules found in vivo, are used to provide a measure of the potential for loss of the copper(II) ion from the radiopharmaceutical as a result of ligand dissociation. In addition, thiol containing molecules such as cysteine and GSH provide a redox challenge, whereby the copper(II) complex may be reduced to give a copper(I) species. The stability of the copper(I) species toward oxidation, protonation, and ligand dissociation may be crucial in determining the biodistribution, the biological half-life and excretion mechanisms of a potential radiopharmaceutical. Further evaluation of the redox stability is assessed using the ubiquitous biological reductant ascorbic acid. The relative stability of a complex with respect to ligand dissociation in human serum provides one of the most important experiments assessing the potential of a complex to be used in vivo. Further challenge experiments with serum proteins such as thioredoxin and serum albumin can be used to provide more detailed information on the probable fate of the complex in serum. Evaluation of complex stability and speciation over a range of pH values may also be used to obtain information on potential biodistribution.

(2-Hydroxy-phenyl-imido-κN)(methano-lato-κO)[2-(2-oxidobenzyl-ideneamino)phenolato-κO,N,O'](triphenyl-phosphine-κP)rhenium(V)

In the neutral title compound, [Re(C(6)H(5)NO)(C(13)H(9)NO(2))(CH(3)O)(C(18)H(15)P)], an 18-valence-electron complex, the Re(V) ion lies in an octa-hedral coordination geometry with the tridentate dianionic Schiff base 2-(2-oxidobenzyl-idene-amino)phenolate ligand occupying three equatorial coordination sites, and with the triphenyl-phosphine ligand situated trans to the imine N atom. The Re(V) coordination is completed with a methano-late ligand and a 2-hydroxy-phenyl-imido(2-) ligand. There are two molecules in the asymmetric unit. The crystal structure involves O-H⋯O and C-H⋯O hydrogen bonds. One N and one C atom are disordered over two positions; the site occupancy factors are ca 0.7 and 0.3.

Bioenergetic differences selectively sensitize tumorigenic liver progenitor cells to a new gold(I) compound

A hallmark of cancer cells is their ability to evade apoptosis and mitochondria play a critical role in this process. Delineating mitochondrial differences between normal and cancer cells has proven challenging due to the lack of matched cell lines. Here, we compare two matched liver progenitor cell (LPC) lines, one non-tumorigenic [p53-immortalized liver (PIL) 4] and the other tumorigenic (PIL2). Analysis of these cell lines and a p53 wild-type non-tumorigenic cell line [bipotential murine oval liver (BMOL)] revealed an increase in expression of genes encoding the antiapoptotic proteins cellular inhibitor of apoptosis protein (cIAP) 1 and yes associate protein in the PIL2 cells, which resulted in an increase in the protein encoded by these genes. PIL2 cells have higher mitochondrial membrane potential (Deltapsi(m)) compared with PIL4 and BMOL and had greater levels of reactive oxygen species, despite the fact that the mitochondrial antioxidant enzyme, manganese superoxide disumutase, was elevated at transcript and protein levels. Taken together, these results may account for the observed resistance of PIL2 cells to apoptotic stimuli compared with PIL4. We tested a new gold compound to show that hyperpolarized Deltapsi(m) led to its increased accumulation in mitochondria of PIL2 cells. This compound selectively induces apoptosis in PIL2 cells but not in PIL4 or BMOL. The gold compound depolarized the Deltapsi(m), depleted the adenosine triphosphate pool and activated caspase-3 and caspase-9, suggesting that apoptosis was mediated via mitochondria. This investigation shows that the non-tumorigenic and tumorigenic LPCs are useful models to delineate the role of mitochondrial dysfunction in tumorigenesis and for the future development of mitochondria-targeted chemotherapeutics that selectively target tumor cells.