112 research outputs found
Synthesis and characterisation of phosphorescent rhenium(I) complexes of hydroxy- and methoxy-substituted imidazo[4,5- f ]-1,10-phenanthroline ligands
No full textEight new fluorescent ligands (L1-L8) derived from the fused imidazo[4,5-f]-1,10-phenanthroline core, have been synthesised utilising a one-pot methodology. The ligands include two points of structural variety, allowing multiply-substituted aryl groups (including hydroxy and methoxy moieties) to be attached to the ligand core. The ligands L1-L8 are fluorescent (λem = 399–426 nm) and react with pentacarbonylbromorhenium to give coordination complexes of the form fac-[ReBr(CO)3(NˆN)] (where NˆN = L1-L8). The complexes were characterised using a variety of spectroscopic and analytical techniques, including single crystal X-ray diffraction studies on two examples. The rhenium complexes were all found to be luminescent, revealing classical 3MLCT emission at 579–587 nm in aerated solution with corresponding lifetimes in the range 149–166 ns
Alkyl chain functionalised Ir(iii) complexes: synthesis, properties and behaviour as emissive dopants in microemulsions
No full textSix iridium(iii) complexes of the general form [Ir(C^N)2(N^N)]X (where C^N = cyclometalating ligand; N^N = disubstituted 2,2′-bipyridine), and incorporating alkyl chains of differing lengths (C8, C10, C12), have been synthesised and characterised. The complexes have been characterised using a variety of methods including spectroscopies (NMR, IR, UV-Vis, luminescence) and analytical techniques (high resolution mass spectrometry, cyclic voltammetry, X-ray diffraction). Two dodecyl-functionalised complexes were studied for their behaviour in aqueous solutions. Although the complexes did not possess sufficient solubility to determine their critical micelle concentrations (CMC) in water, they were amenable for use as emissive dopants in a N-methyl C12 substituted imidazolium salt microemulsion carrier system with a CMC = 36.5 mM. The investigation showed that the metal doped microemulsions had increased CMCs of 40.4 and 51.3 mM and luminescent properties characterised by the dopant.</p
Fluoride anion binding by cyclic boronic esters: influence of backbone chelate on receptor integrity
No full textA systematic investigation of fluoride anion binding properties as a function of chelate backbone has been carried out for ferrocene functionalised boronic esters of the types FcB(OR)(2) and fc[B(OR)(2)](2) [Fc = ferrocenyl = (eta(5)-C5H5) Fe(eta(5)-C5H4); fc = ferrocendiyl = Fe(eta(5)-C5H4)(2)]. Cyclic boronic esters containing a saturated five- or six-membered chelate ring are readily synthesized from ferrocene, and selectively bind fluoride via Lewis acid/base chemistry in chloroform solution. The resulting complexes are characterized by relatively weak fluoride binding ( e. g. K = 35.8 +/- 9.8 M-1 for FcBO(2)C(2)H(2)Ph(2)- S, S), and by cathodic shifts in the ferrocene oxidation potential that form the basis for electrochemical or colorimetric fluoride detection. The fluoride selectivity of these systems is attributed to relatively weak Lewis acidity, resulting in weak F- binding, and essentially no binding of potentially competitive anions. By contrast, more elaborate Lewis acid frameworks based on calix[4] arene (calixH(4)), such as (FcB)(2)calix or fcB(2)calix, do not survive intact exposure to standard fluoride sources (e.g. [(Bu4N)-Bu-n] F center dot xH(2)O solutions in chloroform or acetonitrile). Instead B - O bond cleavage occurs yielding the parent calixarene; the differences between alkoxo- and aryloxo-functionalised derivatives can be rationalised, at least in part, by consideration of the differences in electron donating capabilities of RO( R = alkyl, aryl)
Aryl, bi-functionalised imidazo[4,5-f]-1,10-phenanthroline ligands and their luminescent rhenium(I) complexes
No full textFive new imidazo[4,5-f]-1,10-phenanthroline based ligands (1–5) have been synthesised and characterised. The facile synthesis of 1–5 allows two regiochemical points of structural variety allowing highly conjugated and bulky aryl groups of varying functionalities, including azobenzene, trityl and terpyridine constituents, to be attached to the ligand core. 1–5 are fluorescent (λem = 410–415 nm), and react readily with [ReBr(CO)5] in toluene to give neutral coordination complexes of the form fac-[ReBr(CO)3(1–5)]. The series of complexes was characterised using a variety of spectroscopic and analytical techniques. Two examples of this series were characterised in the solid state using single crystal X-ray diffraction which confirmed the octahedral geometry and formulation. Photophysical studies showed that fac-[ReBr(CO)3(1–5)] are phosphorescent in solution under ambient conditions, revealing visible emission (558–585 nm) in aerated solution with corresponding lifetimes in the range 149–267 ns. These attributes are consistent with a triplet metal to ligand charge transfer (3MLCT) emitting state
Multidentate Lewis acids: synthesis, structure and mode of action of a redox-based fluoride ion sensor
No full textThe mode of action of the bidentate bis( boronate) Lewis acid 2 as a fluoride ion sensor is shown to involve selective anion binding together with an electrochemical response
Synthesis of polymeric and macrocyclic Lewis acids: influence of backbone on degree of aggregation
No full textA simple, one-step synthesis of multinuclear Lewis acids can be driven with high selectivity towards either macrocyclic or polymeric arrays by appropriate choice of backbone framework
Influence of ligand backbone flexibility in group 4 metal complexes of tetradentate mixed tertiary amine/alkoxide ligands
No full textSimple epoxide ring opening chemistry using the cyclic secondary amine 1,4-diazacycloheptane or the related linear species N,N'-dimethylethylenediamine, and racemic (+/-) -3,3-dimethyl-1,2-epoxybutane gives access to the pendant alcohol functionalised ditertiary amine pro-ligands [HOCH(Bu-t)CH2N(R)CH2](2) (H2L1:R-2=CH2CH2CH2; H2L2:R-2=Me-2). The contrasting reactions of H2L1 and H2L2 towards homoleptic group 4 alkoxides highlight the crucial role of ligand backbone flexibility in complex formation. Thus, the chemistry of the more conformationally rigid system (L-1)(2-) appears to be constrained by the cyclic ligand core, such that it adopts a bridging (mu(2):eta(2), eta(2)) mode of coordination towards Ti(IV), leading to dinuclear metal systems [e.g. (LTi2)-Ti-1((OPr)-Pr-i)(6)]. By contrast, the more flexible linear system (L-2)(2-) binds to both Ti(IV) and Zr(IV) in a chelating fashion leading, for example, to the synthesis of the C-2 symmetric mononuclear complex rac-(LTi)-Ti-2((OPr)-Pr-i)(2). Thus, a simple synthesis of diastereomerically pure, C-2 symmetric, geometrically cis octahedral Ti(IV) complexes from racemic precursors is presented
Chiral Ag(i) and Pt(ii) complexes of ditopic NHC ligands: synthesis, structural and spectroscopic properties
No full textThe butyl and isopropyl derivatives (4I, 5Br) of chiral pool derived bis-imidazolium dehydrohexitol salts have been prepared. The ditopic N-heterocyclic carbenes 4 and 5 form dinuclear Ag(I) and Pt(II) complexes. All compounds were fully characterised by multinuclear NMR spectroscopy. The bis-imidazolium salt 4I and platinum complexes cis-[Pt-2(mu-2)(dmso)(2)Cl-4] and cis-[Pt-2(mu-4)(dmso)(2)Cl-4] were characterised by X-ray crystallography. In the case of the Pt(II) complexes, the carbene ring is positioned in a sterically preferred orientation, approximately perpendicular to the platinum coordination plane. The H-1, C-13, N-15 and Pt-195 NMR spectra of the platinum complexes show the presence of rotamers due to hindered rotation about the carbene-metal bond
Ligand tuneable, red‐emitting iridium(III) complexes for efficient triplet‐triplet annihilation upconversion performance
No full textA series of substituted 2‐phenylquinoxaline ligands have been explored to finely tune the visible emission properties of a corresponding set of cationic, cyclometalated iridium(III) complexes. The electronic and redox properties of the complexes were investigated using experimental (including time‐resolved luminescence and transient absorption spectroscopy) and theoretical methods. The complexes display absorption and phosphorescent emission in the visible region attributed to MLCT transitions. The different substitution patterns of the ligands induce variations in these parameters. TD‐DFT studies support these assignments and show that there is likely to be a strong spin‐forbidden contribution to the visible absorption bands at 500‐600 nm. Calculation also reliably predict the magnitude and trends in triplet emitting wavelengths for the series of complexes. The complexes were assessed as potential sensitizers in triplet‐triplet annihilation upconversion experiments using 9,10‐diphenylanthracene as the acceptor, with the methylated variants performing especially well with impressive upconversion quantum yields up to 39.3 %
Emerging Cerebrospinal Fluid Biomarkers of Disease Activity and Progression in Multiple Sclerosis
No full textImportance
Biomarkers distinguishing nonrelapsing progressive disease biology from relapsing biology in multiple sclerosis (MS) are lacking. Cerebrospinal fluid (CSF) is an accessible fluid that most closely reflects central nervous system biology.
Objective
To identify CSF biological measures associated with progressive MS pathobiology.
Design, Setting, and Participants
This cohort study assessed data from 2 prospective MS cohorts: a test cohort provided serial CSF, clinical, and imaging assessments in a multicenter study of patients with relapsing MS (RMS) or primary progressive MS (PPMS) who were initiating anti-CD20 treatment (recruitment: 2016-2018; analysis: 2020-2023). A single-site confirmation cohort was used to assess CSF at baseline and long-term (&gt;10 year) clinical follow-up (analysis: 2022-2023).
Exposures
Test-cohort participants initiated standard-of-care ocrelizumab treatment. Confirmation-cohort participants were untreated or received standard-of-care disease-modifying MS therapies.
Main Outcomes and Measures
Twenty-five CSF markers, including neurofilament light chain, neurofilament heavy chain, and glial fibrillary acid protein (GFAP); 24-week confirmed disability progression (CDP24); and brain magnetic resonance imaging measures reflecting focal injury, tissue loss, and progressive biology (slowly expanding lesions [SELs]).
Results
The test cohort (n = 131) included 100 patients with RMS (mean [SD] age, 36.6 [10.4] years; 68 [68%] female and 32 [32%] male; Expanded Disability Status Scale [EDSS] score, 0-5.5), and 31 patients with PPMS (mean [SD] age, 44.9 [7.4] years; 15 [48%] female and 16 [52%] male; EDSS score, 3.0-6.5). The confirmation cohort (n = 68) included 41 patients with RMS and 27 with PPMS enrolled at diagnosis (age, 40 years [range, 20-61 years]; 47 [69%] female and 21 [31%] male). In the test cohort, GFAP was correlated with SEL count (
r
= 0.33), greater proportion of T2 lesion volume from SELs (
r
= 0.24), and lower T1-weighted intensity within SELs (
r
= –0.33) but not with acute inflammatory measures. Neurofilament heavy chain was correlated with SEL count (
r
= 0.25) and lower T1-weighted intensity within SELs (
r
= –0.28). Immune markers correlated with measures of acute inflammation and, unlike GFAP, were impacted by anti-CD20. In the confirmation cohort, higher baseline CSF GFAP levels were associated with long-term CDP24 (hazard ratio, 2.1; 95% CI, 1.3-3.4;
P
= .002).
Conclusions and Relevance
In this study, activated glial markers (in particular GFAP) and neurofilament heavy chain were associated specifically with nonrelapsing progressive disease outcomes (independent of acute inflammatory activity). Elevated CSF GFAP was associated with long-term MS disease progression
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