Neutral rhenium(I) tricarbonyl complexes with sulfur-donor ligands: anti-proliferative activity and cellular localization.

Rhenium(I) tricarbonyl complexes are widely studied for their cell imaging properties and anti-cancer and anti-microbial activities, but the complexes with S-donor ligands remain relatively unexplored. A series of six fac-[Re(NN)(CO)3(SR)] complexes, where (NN) is 2,2'-bipyridyl (bipy) or 1,10-phenanthroline (phen), and RSH is a series of thiocarboxylic acid methyl esters, have been synthesized and characterized. Cellular uptake and anti-proliferative activities of these complexes in human breast cancer cell lines (MDA-MB-231 and MCF-7) were generally lower than those of the previously described fac-[Re(NN)(CO)3(OH2)]+ complexes; however, one of the complexes, fac-[Re(CO)3(phen)(SC(Ph)CH2C(O)OMe)] (3b), was active (IC50 ∼ 10 µM at 72 h treatment) in thiol-depleted MDA-MB-231 cells. Moreover, unlike fac-[Re(CO)3(phen)(OH2)]+, this complex did not lose activity in the presence of extracellular glutathione. Taken together these properties show promise for further development of 3b and its analogues as potential anti-cancer drugs for co-treatment with thiol-depleting agents. Conversely, the stable and non-toxic complex, fac-[Re(bipy)(CO)3(SC(Me)C(O)OMe)] (1a), predominantly localized in the lysosomes of MDA-MB-231 cells, as shown by live cell confocal microscopy (λex = 405 nm, λem = 470-570 nm). It is strongly localized in a subset of lysosomes (25 µM Re, 4 h treatment), as shown by co-localization with a Lysotracker dye. Longer treatment times with 1a (25 µM Re for 48 h) resulted in partial migration of the probe into the mitochondria, as shown by co-localization with a Mitotracker dye. These properties make complex 1a an attractive target for further development as an organelle probe for multimodal imaging, including phosphorescence, carbonyl tag for vibrational spectroscopy, and Re tag for X-ray fluorescence microscopy.

Fusing Bismuth and Mercaptocarboranes: Design and Biological Evaluation of Low-Toxicity Antimicrobial Thiolato Complexes.

This study proposes an innovative strategy to enhance the pharmacophore model of antimicrobial bismuth thiolato complex drugs by substituting hydrocarbon ligand structures with boron clusters, particularly icosahedral closo-dicarbadodecaborane (C2 B10 H12 , carboranes). The hetero- and homoleptic mercaptocarborane complexes BiPh2 L (1) and BiL3 (2) (L=9-S-1,2-C2 B10 H11 ) were prepared from 9-mercaptocarborane (HL) and triphenylbismuth. Comprehensive characterization using NMR, IR, MS, and XRD techniques confirmed their successful synthesis. Evaluation of antimicrobial activity in a liquid broth microdilution assay demonstrated micromolar to submicromolar minimum inhibitory concentrations (MIC) suggesting high effectiveness against S. aureus and limited efficacy against E. coli. This study highlights the potential of boron-containing bismuth complexes as promising antimicrobial agents, especially targeting Gram-positive bacteria, thus contributing to the advancement of novel therapeutic approaches.

Sulfoproteomics Workflow with Precursor Ion Accurate Mass Shift Analysis Reveals Novel Tyrosine Sulfoproteins in the Golgi.

Tyrosine sulfation in the Golgi of secreted and membrane proteins is an important post-translational modification (PTM). However, its labile nature has limited analysis by mass spectrometry (MS), a major reason why no sulfoproteome studies have been previously reported. Here, we show that a phosphoproteomics experimental workflow, which includes serial enrichment followed by high resolution, high mass accuracy MS, and tandem MS (MS/MS) analysis, enables sulfopeptide coenrichment and identification via accurate precursor ion mass shift open MSFragger database search. This approach, supported by manual validation, allows the confident identification of sulfotyrosine-containing peptides in the presence of high levels of phosphorylated peptides, thus enabling these two sterically and ionically similar isobaric PTMs to be distinguished and annotated in a single proteomic analysis. We applied this approach to isolated interphase and mitotic rat liver Golgi membranes and identified 67 tyrosine sulfopeptides, corresponding to 26 different proteins. This work discovered 23 new sulfoproteins with functions related to, for example, Ca2+-binding, glycan biosynthesis, and exocytosis. In addition, we report the first preliminary evidence for crosstalk between sulfation and phosphorylation in the Golgi, with implications for functional control.

Structure-activity effects in the anti-leishmanial activity of di-alkyl gallium quinolin-8-olates.

Six (G1-G6) novel organogallium complexes of the general formula [Ga(R)2quin] (where R = Et, iPr, nBu, tBu, sBu and hexyl; quin = quinolin-8-olate, C9H6NO) have been synthesised and fully characterised. Single crystal X-ray diffraction shows the complexes adopt a five-coordinate geometry through dimerisation. Complexes G1-G5 were analytically pure and could undergo further biological analysis. [Ga(hex)2quin] G6 could not be satisfactorily purified and was excluded from biological assays. 1H NMR spectroscopy indicated the complexes are stable to hydrolysis over 24 hours in 'wet' d6-DMSO. Complexes G1-G5 were assessed for their anti-leishmanial activity towards three separate strains: L. major, L. amazonensis and L. donovani, with varied results toward the promastigote form. G1 and G2 were found to be the most selective with little to no toxicity towards mammalian cell lines. Amastigote invasion assays on the three strains showed that [Ga(nBu)2quin] G3 and [Ga(tBu)2quin] G4 gave the best all round anti-parasitic activity with percentage infection ranges of 1.50-3.00% and 3.25-7.50% respectively, with G3 out-performing the drug control amphotericin B in all three assays. The activity was found to correlate with lipophilicity and water solubility, with the most effective G3 proving the most lipophilic and least water soluble.

Enhanced antibacterial activity of dimethyl gallium quinolinolates toward drug-resistant Klebsiella pneumoniae in low iron environments.

A series of dimethylgallium quinolinolate [GaMe2L] (L = 5-chloroquinolinolate, 5, 7-dichloroquinolinolate, 5, 7-dibromoquinolinolate or 5, 7-doiodoquinolinolate) complexes, shown previously to be active toward the Leishmania parasite, have been studied for their antibacterial activity toward a reference and drug resistant strain of Klebsiella pneumoniae (KP). The assays were conducted in standard iron-rich LB media and in the iron depleted RPMI and RPMI-HS media to better understand the effect of Fe concentration on the activity of the Ga complexes. In LB broth the parent quinolinols and the gallium complexes were inactive up to the highest concentration tested, 100 µM. In the more physiologically relevant 'iron-poor' RPMI-HS media the quinolonols remained inactive, however, the gallium complexes showed exceptional activity in the range 48-195 nM. Only in RPMI without any added HS did both the quinolinols and the gallium complexes show good activity. The significant differences in activity across the various media types suggest that the unnaturally high iron content of conventional LB media may provide false negative results for potentially potent Ga therapeutics. A protein binding assay on the organometallic gallium complexes showed a much slower uptake of Ga by Fe-binding proteins than is typically observed for gallium salts. This indicates that their greater lipophilicity and greater hydrolytic stability could account for their increased biological activity in RPMI-HS media.

Gallium reactivates first and second generation quinolone antibiotics towards drug-resistant Klebsiella pneumoniae.

Herein, we report on a series of homoleptic [GaL3] and heteroleptic organometallic [GaMe2L] complexes of inactive quinolone antibiotics; nalidixic acid, oxolinic acid and norfloxacin with their antibacterial activity (MIC 0.024-0.781 µM) towards four multi-drug resistant strains of Klebsiella pneumoniae through complexation to gallium.

Synthesis and the photophysical and biological properties of tricarbonyl Re(I) diimine complexes bound to thiotetrazolato ligands.

Twelve Re(I) tricarbonyl diimine (2,2'-bipyridine and 1,10-phenanthroline) complexes with thiotetrazolato ligands have been synthesised and fully characterised. Structural characterisation revealed the capacity of the tetrazolato ligand to bind to the Re(I) centre through either the S atom or the N atom with crystallography revealing most complexes being bound to the N atom. However, an example where the Re(I) centre is linked via the S atom has been identified. In solution, the complexes exist as an equilibrating mixture of linkage isomers, as suggested by comparison of their NMR spectra at room temperature and 373 K, as well as 2D exchange spectroscopy. The complexes are photoluminescent in fluid solution at room temperature, with emission either at 625 or 640 nm from the metal-to-ligand charge transfer excited states of triplet multiplicity, which seems to be exclusively dependent on the nature of the diimine ligand. The oxygen-sensitive excited state lifetime decay ranges between 12.5 and 27.5 ns for the complexes bound to 2,2'-bipyrdine, or between 130.6 and 155.2 ns for those bound to 1.10-phenanthroline. Quantum yields were measured within 0.4 and 1.5%. The complexes were incubated with human lung (A549), brain (T98g), and breast (MDA-MB-231) cancer cells, as well as with normal human skin fibroblasts (HFF-1), revealing low to moderate cytotoxicity, which for some compounds exceeded that of a standard anti-cancer drug, cisplatin. Low cytotoxicity combined with significant cellular uptake and photoluminescence properties provides potential for their use as cellular imaging agents. Furthermore, the complexes were assessed in disc diffusion and broth microdilution assays against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Escherichia coli (E. coli), and Pseudomonas aeruginosa (P. aeruginosa) bacterial strains, which revealed negligible antibacterial activity in the dark or after irradiation.

Synchrotron-Infrared Microspectroscopy of Live Leishmania major Infected Macrophages and Isolated Promastigotes and Amastigotes.

The prevalence of neglected tropical diseases (NTDs) is advancing at an alarming rate. The NTD leishmaniasis is now endemic in over 90 tropical and sub-tropical low socioeconomic countries. Current diagnosis for this disease involves serological assessment of infected tissue by either light microscopy, antibody tests, or culturing with in vitro or in vivo animal inoculation. Furthermore, co-infection by other pathogens can make it difficult to accurately determine Leishmania infection with light microscopy. Herein, for the first time, we demonstrate the potential of combining synchrotron Fourier-transform infrared (FTIR) microspectroscopy with powerful discrimination tools, such as partial least squares-discriminant analysis (PLS-DA), support vector machine-discriminant analysis (SVM-DA), and k-nearest neighbors (KNN), to characterize the parasitic forms of Leishmania major both isolated and within infected macrophages. For measurements performed on functional infected and uninfected macrophages in physiological solutions, the sensitivities from PLS-DA, SVM-DA, and KNN classification methods were found to be 0.923, 0.981, and 0.989, while the specificities were 0.897, 1.00, and 0.975, respectively. Cross-validated PLS-DA models on live amastigotes and promastigotes showed a sensitivity and specificity of 0.98 in the lipid region, while a specificity and sensitivity of 1.00 was achieved in the fingerprint region. The study demonstrates the potential of the FTIR technique to identify unique diagnostic bands and utilize them to generate machine learning models to predict Leishmania infection. For the first time, we examine the potential of infrared spectroscopy to study the molecular structure of parasitic forms in their native aqueous functional state, laying the groundwork for future clinical studies using more portable devices.

Aryl bismuth phosphinates [BiAr2(O(O)PRR')]: structure-activity relationships for antibacterial activity and cytotoxicity.

To study and evaluate the structure-activity relationships in di-aryl bismuth phosphinates on antibacterial activity and cytotoxicity a series of complexes containing ortho-methoxyphenyl, meta-methoxyphenyl, meta-tolyl and para-tolyl aryl groups; [Bi(o-MeOPh)2(O(O)P(H)Ph)]n1, [Bi(o-MeOPh)2(O(O)PPh2)]n2, [Bi(o-MeOPh)2(O(O)P(p-MeOPh)2)]n3, [Bi(m-MeOPh)2(O(O)P(H)Ph)]n4, [Bi(m-MeOPh)2(O(O)PPh2)]n5, [Bi(m-MeOPh)2(O(O)P(p-MeOPh)2)]n6, [Bi(m-tol)2(O(O)P(H)Ph)]n7, [Bi(m-tol)2(O(O)PPh2)]n8, [Bi(m-tol)2(O(O)P(p-MeOPh)2)]n9, [Bi(p-tol)2(O(O)P(H)Ph)]n10, [Bi(p-tol)2(O(O)PPh2)]n11 and [Bi(p-tol)2(O(O)P(p-MeOPh)2)]n12, were synthesised and characterised. Complexes 4, 7, 8, 10 and 11 were structurally authenticated by X-ray crystallography. Evaluation of their antibacterial activity towards methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) showed that the bismuth bound aryl group has a profound influence on activity, with the o-MeOPh complexes 1-3 showing very little activity while the m-MeOPh complexes have the greatest activity towards MRSA and VRE in the range of 0.63 to 1.25 µM. Viability studies with Cos-7 cells showed that the di-aryl bismuth complexes 1-12 are less cytotoxic than their di-phenyl bismuth analogues, with a general trend of toxicity observed as p-tolyl > m-tolyl > m-methoxyphenyl > o-methoxyphenyl. The large difference in Cos-7 viability for complexes 1 (IC50 > 80 µM) and 4 (IC50 14.0 µM) was further investigated through bismuth uptake studies, where there was no obvious difference in Cos-7 bismuth uptake at 5 µM. This suggests that the bismuth-bound aryl group has a significant impact on biological activity, which is then further mediated by other ligands.

Modulating aryl substitution: Does it play a role in the anti-leishmanial activity of a series of tetra-aryl Sb(V) fluorinated carboxylates?

Eight tetra-arylantimony carboxylates of the general formula Ar4SbOC(O)R with Ar = Ph (a), p-Tol (b), R = C6F5 (1), CH2CF3 (2), CF2Br (3), CF2CF2CF3 (4) have been synthesised and characterised. Two of them (2b, 3b) are structurally novel. All structures were analytically characterised by FT-IR, 1H, 13C NMR spectroscopy. Previously synthesised structures were also analysed by X-ray diffraction and their solid-state structures authenticated. The solid-state structures exhibited a typical trigonal-bipyramidal geometry at the antimony centre, with the carboxylic oxygen and one of the aryl group carbons occupying axial positions with the remaining three aryl groups in the equatorial plane. All complexes were screened for their anti-leishmanial activity and cytotoxicity towards mammalian macrophages. No anti-leishmanial testing on tetra-arylantimony carboxylates have been previously performed. It was observed that the tetra-phenylantimony analogues are far more effective in comparison to the tetra-(p-tolyl)antimony complexes, with IC50 values in the ranges of 2.90-7.75 µM and 64.97-124.71 µM, respectively, for the promastigote assay, and 70.87-76.28 µM, 9.08-10.18 µM for the macrophages. Interestingly, the dose-response curve for tetra-phenylantimony carboxylates is a standard sigmoid curve, while for all tetra-(p-tolyl)antimony complexes it has an unusual inverted U-shape, indicating they are effective only at a low dose. All tetra-phenylantimony carboxylates were assessed for their anti-amastigote activity and showed promising results: 1.00% ± 1.44 (1a), 5,25% ± 1.72 (2a), 20.75% ± 8.46 (3a), 5.75% ± 1.62 (4a) at 10 µM.

Medicinal chemistry and biomedical applications of bismuth-based compounds and nanoparticles.

Bismuth as a relatively non-toxic and inexpensive metal with exceptional properties has numerous biomedical applications. Bismuth-based compounds are used extensively as medicines for the treatment of gastrointestinal disorders including dyspepsia, gastric ulcers and H. pylori infections. Recently, its medicinal application was further extended to potential treatments of viral infection, multidrug resistant microbial infections, cancer and also imaging, drug delivery and biosensing. In this review we have highlighted the unique chemistry and biological chemistry of bismuth-209 as a prelude to sections covering the unique antibacterial activity of bismuth including a description of research undertaken to date to elucidate key molecular mechanisms of action against H. pylori, the development of novel compounds to treat infection from microbes beyond H. pylori and the significant role bismuth compounds can play as resistance breakers. Furthermore we have provided an account of the potential therapeutic application of bismuth-213 in targeted alpha therapy as well as a summary of the biomedical applications of bismuth-based nanoparticles and composites. Ultimately this review aims to provide the state of the art, highlight the untapped biomedical potential of bismuth and encourage original contributions to this exciting and important field.

Structures of rhodopsin in complex with G-protein-coupled receptor kinase 1.

G-protein-coupled receptor (GPCR) kinases (GRKs) selectively phosphorylate activated GPCRs, thereby priming them for desensitization1. Although it is unclear how GRKs recognize these receptors2-4, a conserved region at the GRK N terminus is essential for this process5-8. Here we report a series of cryo-electron microscopy single-particle reconstructions of light-activated rhodopsin (Rho*) bound to rhodopsin kinase (GRK1), wherein the N terminus of GRK1 forms a helix that docks into the open cytoplasmic cleft of Rho*. The helix also packs against the GRK1 kinase domain and stabilizes it in an active configuration. The complex is further stabilized by electrostatic interactions between basic residues that are conserved in most GPCRs and acidic residues that are conserved in GRKs. We did not observe any density for the regulator of G-protein signalling homology domain of GRK1 or the C terminus of rhodopsin. Crosslinking with mass spectrometry analysis confirmed these results and revealed dynamic behaviour in receptor-bound GRK1 that would allow the phosphorylation of multiple sites in the receptor tail. We have identified GRK1 residues whose mutation augments kinase activity and crosslinking with Rho*, as well as residues that are involved in activation by acidic phospholipids. From these data, we present a general model for how a small family of protein kinases can recognize and be activated by hundreds of different GPCRs.

The thiol-based reduction of Bi(V) and Sb(V) anti-leishmanial complexes.

Low molecular weight thiols including trypanothione and glutathione play an important function in the cellular growth, maintenance and reduction of oxidative stress in Leishmania species. In particular, parasite specific trypanothione has been established as a prime target for new anti-leishmania drugs. Previous studies into the interaction of the front-line Sb(V) based anti-leishmanial drug meglumine antimoniate with glutathione, have demonstrated that a reduction pathway may be responsible for its effective and selective nature. The new suite of organometallic complexes, of general formula [MAr3(O2CR)2] (M = Sb or Bi) have been shown to have potential as new selective drug candidates. However, their behaviour towards the critical thiols glutathione and trypanothione is still largely unknown. Using NMR spectroscopy and mass spectrometry we have examined the interaction of the analogous Sb(V) and Bi(V) organometallic complexes, [SbPh3(O2CCH2(C6H4CH3))2] S1 and [BiPh3(O2CCH2(C6H4CH3))2] B1, with the trifluoroacetate (TFA) salt of trypanothione and L-glutathione. In the presence of trypanothione or glutathione at the clinically relevant pH of 4-5 for Leishmania amastigotes, both complexes undergo facile and rapid reduction, with no discernible difference. However, at a higher pH (6-7), the complexes behave quite differently towards glutathione. The Bi(V) complex is again reduced rapidly but the Sb(V) complex undergoes slow reduction over 8 h (t1/2 = 54 min.) These results give the first insights into why the highly oxidising Bi(V) complexes display low selectivity in their cytotoxicity towards leishmanial and mammalian cells, while the Sb(V) complexes show good selectivity.

Development of new combination anti-leishmanial complexes: Triphenyl Sb(V) mono-hydroxy mono-quinolinolates.

In seeking to develop single entity combination anti-Leishmanial complexes six heteropletic organometallic Sb(V) hydroxido quinolinolate complexes of general formula [SbPh3(C9H4NORR')(OH)] have been synthesised and characterised, derived from a series of halide substituted quinolinols (8-hydroxyquinolines). Single crystal X-ray diffraction on all the complexes show a common distorted six-coordinate octahedral environment at the Sb(V) centre, with the aryl groups and nitrogen atom of quinolinolate ligand bonding in the equatorial planes, with the two oxygen atoms (hydroxyl and quinolinolate) occupying the axial plane in an almost linear configuration. Each complex was tested for their anti-promastigote activity and mammalian cytotoxicity and a selectivity indices established. The complexes displayed excellent anti-promastigote activity (IC50: 2.03-3.39 µM) and varied mammalian cytotoxicity (IC50: 12.7-46.9 µM), leading to a selectivity index range of 4.52-16.7. All complexes displayed excellent anti-amastigote activity with a percentage infection range of 2.25%-9.00%. All complexes performed substantially better than the parent quinolinols and comparable carboxylate complexes [SbPh3(O2CRR')2] indicating the synergistic role of the Sb(V) and quinolinol moieties in increasing parasite mortality. Two of the complexes [SbPh3(C9H4NOBr2)(OH)] 4, [SbPh3(C9H4NOI2)(OH)] 5, provide an ideal combination of high selective and good activity towards the leishmanial amastigotes and offer the potential as good lead compounds.

Interactions of Non-steroidal Anti-inflammatory Drugs and Their Bismuth Analogues (BiNSAIDs) with Biological Membrane Mimics at Physiological pH.

Previous studies have demonstrated the potential for non-steroidal anti-inflammatory drugs (NSAIDs), in particular aspirin, to be used as chemopreventives for colorectal cancer; however, a range of unwanted gastrointestinal side effects limit their effectiveness. Due to the role of bismuth in the treatment of gastrointestinal disorders, it is hypothesized that bismuth-coordinated NSAIDs (BiNSAIDs) could be used to combat the gastrointestinal side effects of NSAIDs while still maintaining their chemopreventive potential. To further understand the biological activity of these compounds, the present study examined four NSAIDs, namely, tolfenamic acid (tolfH), aspirin (aspH), indomethacin (indoH), and mefenamic acid (mefH) and their analogous homoleptic BiNSAIDs ([Bi(L)3]n), to determine how these compounds interact with biological membrane mimics composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or a mixture of POPC and cholesterol. Electrical impedance spectroscopy studies revealed that each of the NSAIDs and BiNSAIDs influenced membrane conductance, suggesting that temporary pore formation may play a key role in the previously observed cytotoxicity of tolfH and Bi(tolf)3. Quartz crystal microbalance with dissipation monitoring showed that all the compounds were able to interact with membrane mimics composed of solely POPC or POPC/cholesterol. Finally, neutron reflectometry studies showed changes in membrane thickness and composition. The location of the compounds within the bilayer could not be determined with certainty; however, a complex interplay of interactions governs the location of small molecules, such as NSAIDs, within lipid membranes. The charged nature of the parent NSAIDs means that interactions with the polar headgroup region are most likely with larger hydrophobic sections, potentially leading to deeper penetration.

Main Group Metal-Mediated Transformations of Imines.

Main-group-metal-mediated transformations of imines have earned a valued place in the synthetic chemist's toolbox. Their versatility allows the simple preparation of various nitrogen containing compounds. This review will outline the early discoveries including metallation, addition/cyclisation and metathesis pathways, followed by the modern-day use of imines in synthetic methodology. Recent advances in imine C-F activation protocols are discussed, alongside revisiting "classic" imine reactivity from a sustainable perspective. Developments in catalytic methods for hydroelementation of imines have been reviewed, highlighting the importance of s-block metals in the catalytic arena. Whilst stoichiometric transformations in alternative reaction media such as deep eutectic solvents or water have been summarised. The incorporation of imines into flow chemistry has received recent attention and is summarised within.

Antimicrobial innovation: a current update and perspective on the antibiotic drug development pipeline.

As bacteria continue to develop resistance to our existing treatment options, antibiotic innovation remains overlooked. If current trends continue, then we could face the stark reality of a postantibiotic era, whereby routine bacterial infections could once again become deadly. In light of a warning signaled by the WHO, a number of new initiatives have been established in the hope of reinvigorating the antibiotic drug development pipeline. In this perspective, we aim to summarize some of these initiatives and funding options, as well as providing an insight into the predicament that we face. Using clinical trials data, company website information and the most recent press releases, a current update of the antibiotic drug development pipeline is also included.

Hyperphosphorylation Renders Tau Prone to Aggregate and to Cause Cell Death.

Alzheimer's disease (AD) is a neurodegenerative disorder without a cure or prevention to date. Hyperphosphorylated tau forms the neurofibrillary tangles (NFTs) that correlate well with the progression of cognitive impairments. Animal studies demonstrated the pathogenic role of hyperphosphorylated tau. Understanding how abnormal phosphorylation renders a normal tau prone to form toxic fibrils is key to delineating molecular pathology and to developing efficacious drugs for AD. Production of a tau bearing the disease-relevant hyperphosphorylation and molecular characters is a pivotal step. Here, we report the preparation and characterization of a recombinant hyperphosphorylated tau (p-tau) with strong relevance to disease. P-tau generated by the PIMAX approach resulted in phosphorylation at multiple epitopes linked to the progression of AD neuropathology. In stark contrast to unmodified tau that required an aggregation inducer, and which had minimal effects on cell functions, p-tau formed inducer-free fibrils that triggered a spike of mitochondrial superoxide, induced apoptosis, and caused cell death at sub-micromolar concentrations. P-tau-induced apoptosis was suppressed by inhibitors for reactive oxygen species. Hyperphosphorylation apparently caused rapid formation of a disease-related conformation. In both aggregation and cytotoxicity, p-tau exhibited seeding activities that converted the unmodified tau into a cytotoxic species with an increased propensity for fibrillization. These characters of p-tau are consistent with the emerging view that hyperphosphorylation causes tau to become an aggregation-prone and cytotoxic species that underlies diffusible pathology in AD and other tauopathies. Our results further suggest that p-tau affords a feasible tool for Alzheimer's disease mechanistic and drug discovery studies.

Isomers of Alkali Metal (Methylbenzyl)allylamides: A Theoretical Perspective.

Recent studies of alkali metal N-(α-methylbenzyl)allylamides containing lithium, sodium, and potassium have shown unique rearrangements in NMR experiments. It was found that lithium isomers favored the formation of aza-allyl and aza-enolate complexes that could exist in a solution for a substantial amount of time. As the radius of the metal ion increases going from lithium to potassium, so does the preference for the formation of the imine structure. For sodium, the aza-allyl complex could still be isolated, whereas the imine structure was only found to be stable on the scale of several hours for potassium. In this work, ab initio calculations were used to shed light on this phenomenon. Decomposition of intermolecular interaction energies of the aza-allyl, aza-enolate, and imine complexes showed that for lithium, the formation of aza-allyl and aza-enolate complexes was driven by electrostatic interactions. For potassium, the dispersion component of the metal interaction with the ligand proved to be more important for the stability of the imine structure. The presence of the imine formation in potassium and partially in sodium was found to be due to the reduced electrostatic nature of these larger metals. The assignment of the experimental NMR spectra was further confirmed with the natural bond order (NBO) analysis as well as the partial charge calculations. Analysis of orbital energies, specifically those of the highest occupied molecular orbitals (HOMOs), as well as the deformation energies of each of the ligands, were also considered. Through these procedures, an understanding of the tendency for each metal to have a unique isomerization pathway was gained.