Search

Electron-withdrawing nitro-substituents were installed onto terpyridine- and phenanthroline-based metallosurfactants with 4d6 ruthenium(II), which were deposited as Langmuir–Blodgett monolayers aiming to study the feasibility of charge transport in Au‖LB‖Au junctions. The nitro groups are intended to modulate the energy of the frontier molecular orbitals to near to, or match that of Fermi levels in the gold electrodes. A series of heteroleptic metallosurfactants [RuII(C18OPh-terpy)(X-terpy)](PF6)2 and [RuII(C18OPh-terpy)(X-phen)Cl]PF6 were synthesized, where C18OPh-terpy is the 4′-[4-(octadecyloxy)phenyl]-2,2′:6′,2′′-terpyridine amphiphile common to all species, X-terpy is a terpyridine with—H (1) or—phenyl-NO2 (2) and X-phen is a phenanthroline with—H (3) or—NO2 (4) groups. These metallosurfactants were characterized by experimental and computational methods, and the presence of nitro groups affect more affordable reductions at less negative potentials, as well as slightly more positive oxidations, these changes are less pronounced in species 2 than in 4. Species 1 and 2 showed limited Pockels-Langmuir and Langmuir–Blodgett film formation with lower collapse pressure of 27 mN m−1. In contrast, metallosurfactants 3 and 4 showed enhanced hydrophilicity indicated by higher collapse pressures of ca. 36 mN m−1. The LB monolayers of 3 and 4 were deposited on gold electrodes to form Au‖LB‖Au junctions and electron transport was measured as I/V curves. The NO2-bearing species 4 showed asymmetric curves associated with directional electron transport with amplitudes up to −2.0 nA and rectification ratios from 5 to 26 between −1 to +1 V and from 3 to 14 between −3 to +3 V. [ABSTRACT FROM AUTHOR]

Blood–brain barrier (BBB) endothelial cell (EC) function depends on flow conditions and on supportive cells, like pericytes and astrocytes, which have been shown to be both beneficial and detrimental for brain EC function. Most studies investigating BBB EC function lack physiological relevance, using sub-physiological shear stress magnitudes and/or omitting pericytes and astrocytes. In this study, we developed a millifluidic device compatible with standard transwell inserts to investigate BBB function. In contrast to standard polydimethylsiloxane (PDMS) microfluidic devices, this model allows for easy, reproducible shear stress exposure without common limitations of PDMS devices such as inadequate nutrient diffusion and air bubble formation. In no-flow conditions, we first used the device to examine the impact of primary human pericytes and astrocytes on human brain microvascular EC (HBMEC) barrier integrity. Astrocytes, pericytes, and a 1-to-1 ratio of both cell types increased HBMEC barrier integrity via reduced 3 and 40 kDa fluorescent dextran permeability and increased claudin-5 expression. There were differing levels of low 3 kDa permeability in HBMEC–pericyte, HBMEC–astrocyte, and HBMEC–astrocyte–pericyte co-cultures, while levels of low 40 kDa permeability were consistent across co-cultures. The 3 kDa findings suggest that pericytes provide more barrier support to the BBB model compared to astrocytes, although both supportive cell types are permeability reducers. Incorporation of 24-hour 12 dynes per cm2 flow significantly reduced dextran permeability in HBMEC monolayers, but not in the tri-culture model. These results indicate that tri-culture may exert more pronounced impact on overall BBB permeability than flow exposure. In both cases, monolayer and tri-culture, flow exposure interestingly reduced HBMEC expression of both claudin-5 and occludin. ZO-1 expression, and localization at cell–cell junctions increased in the tri-culture but exhibited no apparent change in the HBMEC monolayer. Under flow conditions, we also observed HBMEC alignment in the tri-culture but not in HBMEC monolayers, indicating supportive cells and flow are both essential to observe brain EC alignment in vitro. Collectively, these results support the necessity of physiologically relevant, multicellular BBB models when investigating BBB EC function. Consideration of the roles of shear stress and supportive cells within the BBB is critical for elucidating the physiology of the neurovascular unit. [ABSTRACT FROM AUTHOR]

The von Hippel-Lindau (VHL) Cullin RING E3 ligase is an essential enzyme in the ubiquitin-proteasome system that recruits substrates such as the hypoxia inducible factor for ubiquitination and subsequent proteasomal degradation. The ubiquitin-proteasome pathway can be hijacked toward non-native neo-substrate proteins using proteolysis targeting chimeras (PROTACs), bifunctional molecules designed to simultaneously bind to an E3 ligase and a target protein to induce target ubiquitination and degradation. The availability of high-quality small-molecule ligands with good binding affinity for E3 ligases is fundamental for PROTAC development. Lack of good E3 ligase ligands as starting points to develop PROTAC degraders was initially a stumbling block to the development of the field. Herein, the journey towards the design of small-molecule ligands binding to VHL is presented. We cover the structure-based design of VHL ligands, their application as inhibitors in their own right, and their implementation into rationally designed, potent PROTAC degraders of various target proteins. We highlight the key findings and learnings that have provided strong foundations for the remarkable development of targeted protein degradation, and that offer a blueprint for designing new ligands for E3 ligases beyond VHL. [ABSTRACT FROM AUTHOR]

Aiming to develop a new class of metallosurfactants with unidirectional electron transfer properties, a (terpyridine) ruthenium complex containing a semiquinone derivative L2, namely [RuIII(Lterpy)(L2)Cl]PF6 (1), was synthesized and structurally characterized as a solid and in solution. The electronic and redox behaviour of 1 was studied experimentally as well as by means of DFT methods, and is indicative of significant orbital mixing and overlap between metal and ligands. The complex forms stable Pockels–Langmuir films at the air-water interface and allows for the formation of thin films onto gold electrodes to prepare nanoscale Au‖LB 1‖Au junctions for current–voltage (I/V) analysis. Complex 1 shows asymmetric electron transfer with a maximum rectification ratio of 32 based on tunnelling through MOs of the aminocatechol derivative. [ABSTRACT FROM AUTHOR]

The first diiron(III , IV)-μ2-oxo tetracarbene complex is isolated and characterized by SC-XRD, UV/Vis, EPR, Evans' NMR and elemental analysis. CV indicates the presence of a transient high-valent diiron(IV)-μ2-oxo species. Its formation and decay is investigated via UV/Vis kinetics and NMR. [ABSTRACT FROM AUTHOR]

A series of highly emissive π-conjugated A-alt-B type copolymers (P1–P3) appended with a 1,2,3-triazole moiety was synthesized via Suzuki polymerization. The well-defined and soluble π-conjugated copolymers were characterized via multinuclear NMR spectroscopy and tetradetector GPC studies, showing a molecular weight (Mn) in the range of 16.4–20.1 kDa with a polydispersity index in the range of 1.25–1.42. The synthesized emissive π-conjugated polymer probes were explored as fluorescent chemosensors for nitroaromatic compounds (NACs) in solution, vapor and contact mode. Detailed photophysical and sensing studies were performed to understand the polymer–NAC interaction, inducing the selective fluorescence quenching of the π-conjugated polymer probes through the photoinduced electron transfer (PET) mechanism. All the polymeric probes (P1–P3) were highly reversible in nature with NACs, and thus could be reused multiple times. The limit of detection of the probes towards nitroaromatics was found to be in the range of 120–200 ppb with a high association constant in the order of 104 M−1. Furthermore, test paper kits were also fabricated, which allowed the trace detection of picric acid by the naked eye, making it a practical means for the quick, easy and inexpensive on-site detection of NAC-based explosives. [ABSTRACT FROM AUTHOR]

New and highly emissive 2,6-diacetynyl and 2,6-bis-(phenylacetynyl) functionalized pentamethyldifluoroboron-dipyrromethane (BODIPY) derivatives (FBDP1–2) with perfluorinated pendant groups at the boron center have been synthesized successfully by the combination of two strategies: extending the π-conjugation and functionalization at the boron centre. The newly synthesized dyes have been characterized unambiguously by using various analytical tools such as multinuclear NMR, MALDI-TOF, and single crystal XRD analysis. The dyes (FBDP1–2) exhibit excellent photophysical properties in the yellow to red spectral region (λabs = 530 nm and 555 nm, and λem = 555 nm and 596 nm, respectively) with relatively good Stokes shifts (849 cm−1 and 1240 cm−1), high quantum efficiency (φF = 0.72 and 0.61) and excellent brightness (2.95 × 104 and 2.38 × 104 M−1 cm−1). Most importantly, under a transverse pumping condition at 532 nm, the dyes show efficient and stable laser action, having a good tunable range (20 nm and 13 nm) with a maximum lasing efficiency of 45% and 38% for FBDP1 and FBDP2, respectively. Moreover, the random lasing behavior of FBDP1 has been investigated in a dye-circulated polydimethylsiloxane (PDMS) based disordered microfluidic device. The appearance of randomly positioned sharp spikes with a full width at half maximum (FWHM) of less than 0.3 nm around 555 nm indicates the random laser (RL) emission. The relationship between input pump energy and output random lasing intensity has also been demonstrated, with the random lasing threshold of 0.5 mJ. [ABSTRACT FROM AUTHOR]

Quantum chemistry calculations showed that the first reduction, as experimentally observed by cyclic voltammetry for a series of neutral and cationic functionalised bis(cyclopentadienyl) titanium(iv) derivatives, is metal based, involving the chemically and electrochemically reversible TiIV/TiIII redox couple. The second reduction peak observed is chemically and electrochemically irreversible. For the neutral [Cp2TiIV(ligand)n] (n = 1 or 2) complexes (Cp = cyclopentadienyl), the second irreversible reduction peak is metal-based, while for the cationic [Cp2TiIV(ligand)]+ complexes, the second irreversible reduction peak involves ligand reduction, leading to a TiIII species coupled to a ligand radical. The electronic properties of the substituents directly influence electron density at the reduction centre when π-interactions between the electro-active centre and the substituent groups exist in the lowest unoccupied molecular orbital (LUMO) of the complexes. In this case, a number of relationships between the electronic properties of the substituents and the reduction potentials have been affirmed, yielding linear relationship between experimentally measured reduction potentials and DFT calculated energies (energy of the LUMO, electron affinity, Mulliken electronegativity and global electrophilicity index). However, the substituent effect is ill defined when the LUMO is highly localised without π-interaction between the electro-active centre and the substituents. [ABSTRACT FROM AUTHOR]

Positron emission tomography (PET) is an important driver for present day healthcare. Fluorine-18 is the most widely used radioisotope for PET imaging and a thorough overview of the available radiochemistry methodology is a prerequisite for selection of a synthetic approach for new fluorine-18 labelled PET tracers. These PET tracers can be synthesised either by late-stage radiofluorination, introducing fluorine-18 in the last step of the synthesis, or by a building block approach (also called modular build-up approach), introducing fluorine-18 in a fast and efficient manner in a building block, which is reacted further in one or multiple reaction steps to form the PET tracer. This review presents a comprehensive overview of the synthesis and application of fluorine-18 labelled building blocks since 2010. [ABSTRACT FROM AUTHOR]

Thione- and selone-containing compounds and their metal complexes show promise as antioxidants, as antithyroid drugs, and for applications in lasers and blue light-emitting diodes. Although Cu(i/ii), Co(ii), Ag(i), and Zn(ii) coordination to thione and selone ligands has been broadly studied and Fe(ii) plays an important role in oxidative damage, very few iron–thione complexes and no iron–selone complexes are reported. Novel Fe(ii)-containing thione and selone complexes of the formulae FeL2Cl2, [FeL2(CH3CN)2]2+, and [FeL4]2+, and {FeL′Cl2}n, (L = N,N′-dimethylimidazole selone (dmise), and thione (dmit); L′ = bis(thioimidazolyl)ethane (ebit) and bis(selenoimidazolyl)ethane (ebis)) have been synthesized and characterized. Structures of Fe(dmise)2Cl2, Fe(dmit)2Cl2, [Fe(dmit)4][BF4]2, [Fe(dmise)4][BF4]2, and {Fe(ebit)Cl2}n were determined by X-ray crystallography. All Fe(ii) centers adopt a distorted tetrahedral coordination geometry with Fe–S distances ranging from 2.339(1) to 2.397(1) Å and F–Se distances ranging from 2.453(1) to 2.514(1) Å. Density functional theory optimized structures of FeL2Cl2, [FeL2(CH3CN)2]2+, and [FeL4]2+ are consistent with experimental results and suggest that thiones and selones are π-donor ligands that coordinate through their zwitterionic resonance structures. Thione and selone coordination to Fe(ii) lowers the Fe(ii/iii) reduction potential, with a greater decrease for Fe(ii)-bound dmise than Fe(ii)-bound dmit. Dmit and dmise ligand-based oxidation potentials also significantly increase upon Fe(ii) binding compared, indicating that bound thione and selone ligands will undergo oxidation prior to Fe(ii). The synthesis of these complexes suggests that iron coordination by thione and selone ligands may occur in vivo and may contribute to the protective antioxidant properties of sulfur and selenium. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and structures of a series of homoleptic and heteroleptic copper(i) complexes supported by N-heterocyclic chalcogenone ligands is reported herein. The quasi-reversible Cu(ii/i) reduction potentials of these copper complexes with monodentate (dmit or dmise) and/or bidentate (BmmMe, BsemMe, BmeMe, BseeMe) chalcogenone ligands are highly dependent upon the nature and number of the donor groups and can be tuned over a 470 mV range (−369 to 102 mV). Copper–selone complexes have more negative Cu(ii/i) reduction potentials relative to their thione analogs by an average of 137 mV, and increasing the number of methylene units linking the heterocyclic rings in the bidentate ligands results in more negative reduction potentials for their copper complexes. This ability to tune the copper reduction potentials over a wide range has potential applications in synthetic and industrial catalysis as well as the understanding of important biological processes such as electron transfer in blue copper proteins and respiration. [ABSTRACT FROM AUTHOR]

We propose and evaluate the use of metallocene compounds as reducing agents for the chemical vapour deposition (and specifically atomic layer deposition, ALD) of the transition metal Cu from metalorganic precursors. Ten different transition metal cyclopentadienyl compounds are screened for their utility in the reduction of Cu from five different Cu precursors by evaluating model reaction energies with density functional theory (DFT) and solution phase chemistry. [ABSTRACT FROM AUTHOR]

Solution-processable polyazomethines containing thiophenes were synthesized and used as the donor material in bulk heterojunction solar cells. The blue polymers exhibited similar electrochemical properties to the benchmark P3HT with the advantage of absorbing more of the visible spectrum. The resulting photovoltaic devices using polyazomethines in the photoactive layer with PC60BM as the acceptor showed power conversion efficiencies up to 0.22% under simulated 100 mW cirT2 AM 1.5G irradiation. The low efficiencies are ascribed to poor charge generation because of too coarse bulk heterojunction morphology formation. [ABSTRACT FROM AUTHOR]

The electrochemistry of the Dawson-like sulfite polyoxometalate anion α-[Mo18O54(SO3)2]6−, derived from the TEAH6{α-[Mo18O54(SO3)2]} salt (TEAH+ is the triethanolammonium cation; pKa = 7.8), has been investigated in aqueous media using cyclic and rotated disk voltammetry at glassy carbon electrodes and bulk electrolysis, with a focus on the pH-dependence for oxidation to α-[Mo18O54(SO3)2]4−. In buffered media at pH ≥ 4, the cyclic voltammetric response for α-[Mo18O54(SO3)2]6− reveals two partially resolved one-electron oxidation processes corresponding to the sequential generation of α-[Mo18O54(SO3)2]5− and α-[Mo18O54(SO3)2]4−. At lower pH, using electrolytes containing sulfuric acid, the two waves coalesce but the individual apparent E0′ reversible formal potential values for the two processes can be extracted down to pH 2 by assuming that reversible protonation accompanies fast electron transfer. The results for 2 ≤ pH ≤ 8 are well described by the double-square scheme mechanism:where A, B and C correspond to species α-[Mo18O54(SO3)2]4−, α-[Mo18O54(SO3)2]5− and α-[Mo18O54(SO3)2]6− respectively. The following thermodynamic values could be deduced: E0/A/B = −0.009 V vs. Fc+/Fc; E0/B/C = −0.125 V vs. Fc+/Fc and KC = 1.5 × 10−5 M; values for KA, KB, E0/AH/BH and E0/BH/CH could not be determined. Protonated α-[HMo18O54(SO3)2]5−, deduced to be the major species present at pH < 4, is highly stable in aqueous media. In contrast, α-[Mo18O54(SO3)2]6−, which is dominant at higher pH values, slowly decomposes. Data considered in the context of acid–base properties of both the TEAH+ cation and α-[HMo18O54(SO3)2]5− anion imply that the TEAH+ cation is important in the isolation of (TEAH)6{α-[Mo18O54(SO3)2]}. Cyclic and rotating disk electrode voltammetries demonstrate that at least 8 electrons also can be easily added to the [Mo18O54(SO3)2]4− framework in acidic media. The existence of the electron transfer series α-[Mo18O54(SO3)2]4−/5−/6−/7−/8− was confirmed by cyclic voltammetric studies of water insoluble [Pn4N]4{α-[Mo18O54(SO3)2]} adhered to a glassy carbon electrode in contact with an aqueous 0.1 M Et4NCl electrolyte. [ABSTRACT FROM AUTHOR]

The synthesis, optical, electrochemical and physical characterization of 2,7-bis(pentafluorophenylethynyl)hexafluoroheterofluorenes is described along with a preliminary evaluation of their performance in photovoltaic applications. [ABSTRACT FROM AUTHOR]