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  • Conference paper
    Farnaby J, Hickson J, Long N, 2016,

    Synthetic routes to multi-metallic f-element complexes with redox-active ligands

    , Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
  • Book chapter
    Phanopoulos A, Long NJ, Miller PW, 2016,

    Triphosphine ligands: coordination chemistry and recent catalytic applications

    , The Chemical Bond III, Editors: Mingos, Publisher: Springer, Pages: 31-61

    Phosphines are a long established class of ligand that are known to form a vast array of transition metal complexes. They behave as neutral electron pair donors, or Lewis bases, that alter the solubility and stereoelectronic properties of the metal centre. A key motivation for their continued development is for homogeneous catalysis. For over five decades, transition metal–phosphine complexes have been used for catalytic reactions, mainly exploiting monodentate or bidentate phosphine ligands. Multidentate phosphines by comparison have received much less attention in part because they tend to form more stable complexes with a saturated coordination environment around the metal centre. Recent developments in the areas of catalytic reduction of carboxylic acid derivatives using molecular hydrogen and in the field of biomass up-conversion have exploited catalysts based on tridentate phosphines. This chapter highlights the use of these multidentate phosphines for synthesis of coordination complexes and discusses some of their recent applications in homogeneous catalysis.

  • Journal article
    Phanopoulos A, White AJP, Long NJ, Miller PWet al., 2016,

    Insight into the stereoelectronic parameters of N-triphos ligands via coordination to tungsten(0)

    , Dalton Transactions, Vol: 45, Pages: 5536-5548, ISSN: 1477-9226

    A series of new N-triphos tungsten complexes have been synthesised and structurally characterised. The coordination behaviour of a range of N-triphos (N(CH2PR2)3, NP3R) ligands, and a mixed-arm diphosphine-pyridyl (PPNCyh) ligand were explored. The steric and electronic parameters of five N-triphos ligands: NP3Ph, NP3iPr, NP3Cyp, NP3Cyh and NP3PhF2, and the carbon-centred triphos ligand, CH3C(CH2PPh2)3 (MeCP3Ph), were established. Steric parameters were evaluated by analysing the cone angles calculated from X-ray crystal structures, whilst the electron-donating ability of the ligands was determined from 31P–77Se NMR coupling constants of selenium derivatives and the IR carbonyl stretching frequencies across a series of tungsten–carbonyl complexes. In general, electron-rich phosphines formed bidentate complexes while less electron-rich ligands coordinated in a tridentate mode, regardless of steric bulk. An indirect interaction between the apical nitrogen of the ligand and metal centre is implicated for tridentate complexes and is supported through DFT calculations and analysis of N-protonated complexes. Complexes 1, 3, 4, 6–8 and 10 were characterised by single-crystal X-ray crystallography.

  • Journal article
    Kumar S, Johnson TW, Wood CK, Qu T, Wittenberg NJ, Otto L, Shaver J, Long NJ, Victoria RH, Edel JB, Oh SHet al., 2016,

    Template-Stripped Multifunctional Wedge and Pyramid Arrays for Magnetic Nanofocusing and Optical Sensing

    , Acs Applied Materials & Interfaces, Vol: 8, Pages: 9319-9326, ISSN: 1944-8252

    We present large-scale reproducible fabrication of multifunctional ultrasharp metallic structures on planar substrates with capabilities including magnetic field nanofocusing and plasmonic sensing. Objects with sharp tips such as wedges and pyramids made with noble metals have been extensively used for enhancing local electric fields via the lightning-rod effect or plasmonic nanofocusing. However, analogous nanofocusing of magnetic fields using sharp tips made with magnetic materials has not been widely realized. Reproducible fabrication of sharp tips with magnetic as well as noble metal layers on planar substrates can enable straightforward application of their material and shape-derived functionalities. We use a template-stripping method to produce plasmonic-shell-coated nickel wedge and pyramid arrays at the wafer-scale with tip radius of curvature close to 10 nm. Further we explore the magnetic nanofocusing capabilities of these ultra-sharp substrates deriving analytical formulas and comparing the results with computer simulations. These structures exhibit nanoscale spatial control over the trapping of magnetic microbeads and nanoparticles in solution. Additionally, enhanced optical sensing of analytes by these plasmonic-shell-coated substrates is demonstrated using surface-enhanced Raman spectroscopy. These methods can guide the design and fabrication of novel devices with applications including nanoparticle manipulation, biosensing, and magnetoplasmonics.

  • Journal article
    Inkpen MS, White AJP, Albrecht T, Long NJet al., 2016,

    Complexes comprising ‘dangling’ phosphorus arms and tri(hetero)metallic butenynyl moieties

    , Journal of Organometallic Chemistry, Vol: 812, Pages: 145-150, ISSN: 1872-8561

    Trans-RuCl2(PP3)2 (1a) (PP3 = tris[2-(diphenylphosphino)ethyl]phosphine) was prepared by reaction of RuCl2(PPh3)3 with 2 eq. PP3. Through coordination of two potentially tetradentate ligands in a bidentate arrangement, four uncoordinated phosphine moieties remain readily available for subsequent reaction. This is demonstrated through their facile oxidation with hydrogen peroxide, providing trans-RuCl2(PP[Pdouble bond; length as m-dashO]2)2 (1b) (PP[Pdouble bond; length as m-dashO]2 = bis[2-(diphenylphosphine oxide)ethyl][2-(diphenylphosphino)ethyl]phosphine). Whilst chloride abstraction reactions from 1a appear slow (typical for trans dichlorides), cis-RuCl2(PP3) is shown to react rapidly with ethynylferrocene under ‘Dixneuf’ conditions (CH2Cl2, NaPF6, NEt3), providing the tri(hetero)metallic butenynyl complex [(PP3)Ru(η3–FcC3CHFc)]PF6 (2, Fc = ferrocenyl). The pendant groups of 1a-b offer great potential for future coordination studies (for example, to prepare mixed transition metal/lanthanide materials), whereby the facile synthetic route to 2 suggests a path towards examination of complex mixed-valence systems comprising multiple redox-active centres.

  • Journal article
    Laurent D, Vinet L, Lamprianou S, Daval M, Filhoulaud G, Ktorza A, Wang H, Sewing S, Juretschke H-P, Glombik H, Meda P, Boisgard R, Nguyen DL, Stasiuk GJ, Long NJ, Montet X, Hecht P, Kramer W, Rutter GA, Hecksher-Sorensen Jet al., 2016,

    Pancreatic β-cell imaging in humans: fiction or option?

    , Diabetes Obesity & Metabolism, Vol: 18, Pages: 6-15, ISSN: 1462-8902

    Diabetes mellitus is a growing worldwide epidemic disease, currently affecting 1 in 12 adults. Treatment of disease complications typically consumes ∼10% of healthcare budgets in developed societies. Whilst immune-mediated destruction of insulin-secreting pancreatic β cells is responsible for Type 1 diabetes, both the loss and dysfunction of these cells underly the more prevalent Type 2 diabetes. The establishment of robust drug development programmes aimed at β-cell restoration is still hampered by the absence of means to measure β-cell mass prospectively in vivo, an approach which would provide new opportunities for understanding disease mechanisms and ultimately assigning personalized treatments. In the present review, we describe the progress towards this goal achieved by the Innovative Medicines Initiative in Diabetes, a collaborative public–private consortium supported by the European Commission and by dedicated resources of pharmaceutical companies. We compare several of the available imaging methods and molecular targets and provide suggestions as to the likeliest to lead to tractable approaches. Furthermore, we discuss the simultaneous development of animal models that can be used to measure subtle changes in β-cell mass, a prerequisite for validating the clinical potential of the different imaging tracers.

  • Journal article
    Inkpen MS, Du S, Hildebrand M, White AJP, Harrison NM, Albrecht T, Long NJet al., 2015,

    The unusual redox properties of fluoroferrocenes revealed through a comprehensive study of the haloferrocenes

    , Organometallics, Vol: 34, Pages: 5461-5469, ISSN: 1520-6041

    We report the synthesis and full characterization of the entire haloferrocene (FcX) and 1,1′-dihaloferrocene (fcX2) series (X = I, Br, Cl, F; Fc = ferrocenyl, fc = ferrocene-1,1′-diyl). Finalization of this simple, yet intriguing set of compounds has been delayed by synthetic challenges associated with the incorporation of fluorine substituents. Successful preparation of fluoroferrocene (FcF) and 1,1′-difluoroferrocene (fcF2) were ultimately achieved using reactions between the appropriate lithiated ferrocene species and N-fluorobenzenesulfonimide (NFSI). The crude reaction products, in addition to those resulting from analogous preparations of chloroferrocene (FcCl) and 1,1′-dichloroferrocene (fcCl2), were utilized as model systems to probe the limits of a previously reported “oxidative purification” methodology. From this investigation and careful solution voltammetry studies, we find that the fluorinated derivatives exhibit the lowest redox potentials of each of the FcX and fcX2 series. This counterintuitive result is discussed with reference to the spectroscopic, structural, and first-principles calculations of these and related materials.

  • Journal article
    Long NJ, Stasiuk G, Gallo J, Bañobre-López2 M, Keasberry N, Wood Cet al., 2015,

    Tuning the relaxation rates of dual mode T1/T2 nanoparticle contrast agents: a study into the ideal system

    , Nanoscale, Vol: 7, Pages: 16119-16128, ISSN: 2040-3372

    Magnetic resonance imaging (MRI) is an excellent imaging modality. However the low sensitivity of the technique poses a challenge to achieving an accurate image of function at the molecular level. To overcome this, contrast agents are used; typically gadolinium based agents for T1 weighted imaging, or iron oxide based agents for T2 imaging. Traditionally, only one imaging mode is used per diagnosis although several physiological situations are known to interfere with the signal induced by the contrast agents in each individual imaging mode acquisition. Recently, the combination of both T1 and T2 imaging capabilities into a single platform has emerged as a tool to reduce uncertainties in MR image analysis. To date, contradicting reports on the effect on the contrast of the coupling of a T1 and T2 agent have hampered the application of these specialised probes. Herein, we present a systematic experimental study on a range of gadolinium-labelled magnetite nanoparticles envisioned to bring some light into the mechanism of interaction between T1 and T2 components, and advance towards the design of efficient (dual) T1 and T2 MRI probes. Unexpected behaviours observed in some of the constructs will be discussed. In this study, we demonstrate that the relaxivity of such multimodal probes can be rationally tuned to obtain unmatched potentials in MR imaging, exemplified by preparation of the magnetite-based nanoparticle with the highest T2 relaxivity described to date.

  • Conference paper
    Miller P, Phanopoulos A, Long N, 2015,

    Direct conversion of levulinic acid to 2-methyltetrahydrofuran using discrete Ru and Rh N-triphos catalysts

    , Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
  • Conference paper
    Duerrbeck A, Hor A, Long N, 2015,

    New highly-emissive soluble dynamic Eu(III) coordination polymers for Ln(III) and transition metal sensing applications

    , Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
  • Journal article
    Albrecht T, Inkpen MS, Lemmer M, Fitzpatrick N, Costa-Milan D, Nichols RJ, Long NJet al., 2015,

    New insights into single-molecule junctions using a robust, unsupervised approach to data collection and analysis

    , Journal of the American Chemical Society, ISSN: 1520-5126
  • Software
    Inkpen M, Lemmer M, Fitzpatrick N, Costa-Milan D, Nichols RJ, Long NJ, Albrecht Tet al., 2015,

    Macro Scheduler code for data collection

    Supporting information associated with the publication "New insights into single-molecule junctions using a robust, unsupervised approach to data collection and analysis", J. Am. Chem. Soc., 2015, DOI: 10.1021/jacs.5b05693. This Macro Scheduler (MJT Net Ltd, UK) script is a representative example of that used to automatically measure I(s) traces from 1,8-ODT-coated and blank (uncoated) Au substrates using an Agilent 5100 Scanning Tunnelling Microscope (interfacing with PicoView 1.14, Agilent Technologies). A short 'Guide to...' document is also included to introduce the user, as are additional files (Microsoft Excel spreadsheets and images) required by the script.

  • Software
    Inkpen MS, Lemmer M, Fitzpatrick N, Costa-Milan D, Nichols RJ, Long NJ, Albrecht Tet al., 2015,

    MATLAB script for data sorting

    Supporting information associated with the publication "New insights into single-molecule junctions using a robust, unsupervised approach to data collection and analysis", J. Am. Chem. Soc., 2015, DOI: 10.1021/jacs.5b05693. This MATLAB script is a representative example of that used to objectively sort I(s) traces obtained from 1,8-ODT-coated and blank (uncoated) Au substrates. A short 'Guide to...' document is also included to introduce the user.

  • Journal article
    Phanopoulos A, Miller PW, Long NJ, 2015,

    Beyond Triphos - New hinges for a classical chelating ligand

    , Coordination Chemistry Reviews, Vol: 299, Pages: 39-60, ISSN: 1873-3840

    Branched triphosphine ligands have been less widely studied than mono- and bi-dentate analogues. The most studied ligand of this type is TriphosPh (CH3C(CH2PPh2)3). Substitution of the apical Csingle bondCH3 moiety with boron, silicon, tin, nitrogen or phosphorus fragments has generated a new family of ligands, in some cases displaying varying coordination chemistry and reactivity to the parent carbon-based system. This review includes the synthetic strategies implemented to afford these ligands, as well as derivatives by way of varying the phosphine substituents. Although not exhaustive, relevant types of reported complexes featuring these ligands are discussed, as well as their reactivity and catalytic applications. Through critical analysis, common themes and chemical trends across this family of apical heteroatomic, branched triphosphines can be identified, leading to improvements in current chemical applications, as well as new areas that remain underdeveloped.

  • Journal article
    Phanopoulos A, White AJ, Long NJ, Miller PWet al., 2015,

    Catalytic transformation of levulinic acid to 2-methyltetrahydrofuran using ruthenium–N-triphos complexes

    , ACS Catalysis, Vol: 5, Pages: 2500-2512, ISSN: 2155-5435

    A series of pre- or in situ-formed ruthenium complexes were assessed for the stepwise catalytic hydrogenation of levulinic acid (LA) to 2-methyltetrahydrofuran (2-MTHF) via γ-valerolactone (γVL) and 1,4-pentanediol (1,4-PDO). Two different catalytic systems based on the branched triphosphine ligands Triphos (CH3C(CH2PPh2)3) and N-triphos (N(CH2PPh2)3) were investigated. The most active catalyst was the preformed ruthenium species [RuH2(PPh3){N(CH2PPh2)3-κ3P}] (5), which gave near quantitative conversion of LA to 1,4-PDO when no acidic additives were present, and 87% 2-MTHF when used in conjunction with HN(Tf)2. Various acidic additives were assessed to promote the final transformation of 1,4-PDO to 2-MTHF; however, only HN(Tf)2 was found to be effective, and NH4PF6 and para-toluenesulfonic acid (p-TsOH) were found to be detrimental. Mechanistic investigations were carried out to explain the observed catalytic trends and importantly showed that PPh3 dissociation from 5 resulted in its improved catalytic reactivity. The presence of acidic additives removes catalytically necessary hydride ligands and may also compete with the substrate for binding to the catalytic metal center, explaining why only an acid with a noncoordinating conjugate base was effective. Crystals suitable for X-ray diffraction experiments were grown for two complexes: [Ru(NCMe)3{N(CH2PPh2)3-κ3P}] (14) and [Ru2(μ-Cl)3{N(CH2PPh2)3-κ3P}2][BPh4] (16).

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