Davide Maffeo

Bio: Davide Maffeo is an academic researcher from Durham University. The author has contributed to research in topics: Europium & Ligand. The author has an hindex of 6, co-authored 6 publications receiving 293 citations.

Intramolecular sensitisation of lanthanide(III) luminescence by acetophenone-containing ligands: the critical effect of para-substituents and solvent

Abstract: Tetraazamacrocyclic ligands have been prepared in which three of the four nitrogen atoms are functionalised with carboxylate donors and the fourth is alkylated with a para-substituted acetophenone group {–CH2C(O)C6H4–X, where X = H, OMe, NMe2}. The europium(III), gadolinium(III) and (for X = H) terbium(III) complexes of these potentially octadentate ligands have been prepared. The unsubstituted and methoxy-substituted ligands sensitise the europium(III) emissive state with high efficiency in aqueous solution. Calculation of the pure radiative lifetime, based on the contribution of the 5D0 → 7F1 transition to the total integrated emission intensity, has allowed an estimate of the efficiency of energy transfer to be made. Sensitisation of europium luminescence also occurs in the complex of the dimethylamino-substituted ligand but the process is highly solvent-dependent: very efficient sensitisation is observed in dichloromethane and DMSO, but the complex is non-emissive in water and only slightly emissive in acetonitrile. UV-Visible absorption spectra indicate that in all the solvents investigated, the carbonyl oxygen of the ligand is directly coordinated to the metal ion. The intensity of the hypersensitive 5D0 → 7F2 transition in the three complexes mirrors the degree of polarisation of the ketone CO bond.

The efficient intramolecular sensitisation of terbium(III) and europium(III) by benzophenone-containing ligands

Abstract: The europium and terbium complexes of an octadentate macrocyclic ligand incorporating benzophenone have been prepared; excitation of the ketone, which has a triplet quantum yield of unity, results in very efficient sensitisation of the emissive states of the bound metal ions.

Copper(II) complexes of the isomeric tetraazamacrocyclic ligands 1,11- and 1,8-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane and of the 1,4,8,11-tetraazacyclotetradecane-5,12-dione analogue at neutral and basic pH

Abstract: The regioselective synthesis of the new N,N′-dialkylated tetraazamacrocycle 1,11-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane, L1, has been achieved. The copper(II) complexes of L1 and of the isomeric ligand 1,8-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane, L2, have been isolated and their crystal structures determined. The structure of [CuL2]2+(CH3CO2−)2, reveals planar N4 co-ordination of the copper by the macrocycle, which adopts the trans-III configuration, and with the pendant pyridine nitrogens occupying the elongated axial sites. In contrast, in [CuL1]2+(ClO4−)2, the copper is 5-co-ordinated by the four nitrogen atoms of the macrocycle, which adopts the trans-I configuration, and one pendant pyridine nitrogen, forming a distorted square pyramid with the pyridine nitrogen at the apex. The new macrocyclic dioxotetraamine 1,8-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane-5,12-dione, L3, has also been prepared. The crystals obtained upon reaction of L3 with copper(II) perchlorate under neutral conditions have been shown by X-ray diffraction analysis to contain two distinct macrocyclic units containing copper ions. In the first a single copper centre is co-ordinated by the two trans-orientated amino nitrogens of the macrocycle, the two pyridine nitrogens and one deprotonated amide nitrogen, forming a distorted trigonal bipyramid. The second has a 2∶1 metal:ligand stoichiometry and, in the unit cell, bridges two complexes of the first type. In contrast, crystallisation under basic conditions leads to a 1∶1 complex in which the two amides are deprotonated and the copper ion is bound within the macrocycle, weakly co-ordinated by the two pyridine nitrogens in elongated axial sites. The behaviour of the three complexes in solution has been studied by ESR, UV-visible absorption spectroscopy and by cyclic voltammetry.

Sensitization of europium(III) luminescence by benzophenone-containing ligands: regioisomers, rearrangements and chelate ring size, and their influence on quantum yields.

Abstract: A series of europium(III) complexes based on the macrocyclic azacarboxylate structure, DO3A, have been investigated, incorporating benzophenone appended at N10 of the macrocycle via linkers containing amide bonds (H3DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-tris-acetic acid). Complexes [EuL(1-3)] incorporate N10-CH2CONH-BP linkers (BP = benzophenone), which allow formation of a five-membered chelate ring containing the metal ion upon chelation of the amide oxygen; these three isomeric complexes differ from one another in the substitution position of the BP unit, namely para, meta, and ortho for L1, L2, and L3 respectively. The quantum yields of europium luminescence sensitized via the chromophore are found to be highly dependent upon the position of substitution, being 20 times smaller for the ortho compared to the para-substituted complex. A related para-substituted BP complex [EuL(4)], prepared by an unusual Michael reaction of the azamacrocycle with a BP-containing acrylamide, incorporates an additional methylene unit in the linker, namely N10-CH2CH2CONH-BP. Despite the longer linker, this complex equals the luminescence quantum yield achieved with [EuL(1)] (Phi(lum) = 0.097 and 0.095, respectively, in H2O at 298 K). Analysis of the pertinent kinetics reveals that the decreased energy transfer efficiency in this complex, arising from the longer donor-acceptor distance, is compensated by an increased radiative rate constant. Under basic conditions, the ortho-substituted complex [EuL(3)] undergoes an intramolecular rearrangement to generate an unprecedented complex [EuL(5)] incorporating a 4-phenyl-2-hydroxyquinoline unit directly bound to the ring nitrogen. Although this complex is a poor emitter, an analogous complex obtained from 2-amino-acetophenone, which generates 4-methyl-2-hydroxyquinoline during the corresponding rearrangement, is an order of magnitude more emissive while still benefiting from relatively long-wavelength absorption. The emission from this complex is pH sensitive, being dramatically quenched under mildly basic conditions.

Lanthanide probes for bioresponsive imaging.

Abstract: The chemistry of the less familiar elements is a fascinating topic especially for the inorganic minded. The lanthanides, or rare earths, comprise the 5d block of the periodic table and represent a huge array of applications from catalysis to lasers, and of course, imaging agents.1 Recent advances in luminescence and magnetic resonance microscopy have, in part, been stimulated by extraordinary success in the development of new lanthanide probes. The unique properties of the lanthanides provide for a deep tool chest for the chemist, biologist and the imaging scientist to exploit, and that exploitation is in full swing. In this review we focus on two classes of lanthanide probes that are subsets of the larger area of metalloimaging: luminescent and magnetic lanthanides. In Section 2 we discuss the general design and photophysical properties of lanthanides and how these parameters are tuned to develop bioresponsive probes for optical imaging. In Section 3 we provide a brief description of how MR images are acquired and the how MRI contrast agents are engineered to respond to biological events of interest. These guiding principles have driven research that has produced a truly diverse number of new agents that are target specific and bioresponsive (or bioactivatable). While other imaging modalities utilize lanthanide-based probes, these topics are beyond the scope of this review. We direct the reader to explore some excellent reviews in the important areas of radiometals and multimodal imaging.2–5

From antenna to assay: lessons learned in lanthanide luminescence.

Abstract: Ligand-sensitized, luminescent lanthanide(III) complexes are of considerable importance because their unique photophysical properties (microsecond to millisecond lifetimes, characteristic and narrow emission bands, and large Stokes shifts) make them well suited as labels in fluorescence-based bioassays. The long-lived emission of lanthanide(III) cations can be temporally resolved from scattered light and background fluorescence to vastly enhance measurement sensitivity. One challenge in this field is the design of sensitizing ligands that provide highly emissive complexes with sufficient stability and aqueous solubility for practical applications. In this Account, we give an overview of some of the general properties of the trivalent lanthanides and follow with a summary of advances made in our laboratory in the development of highly luminescent Tb(III) and Eu(III) complexes for applications in biotechnology. A focus of our research has been the optimization of these compounds as potential commercial agents for use in homogeneous time-resolved fluorescence (HTRF) technology. Our approach involves developing high-stability octadentate Tb(III) and Eu(III) complexes that rely on all-oxygen donor atoms and using multichromophore chelates to increase molar absorptivity; earlier examples utilized a single pendant chromophore (that is, a single "antenna"). Ligands based on 2-hydroxyisophthalamide (IAM) provide exceptionally emissive Tb(III) complexes with quantum yield values up to approximately 60% that are stable at the nanomolar concentrations required for commercial assays. Through synthetic modification of the IAM chromophore and time-dependent density functional theory (TD-DFT) calculations, we have developed a method to predict absorption and emission properties of these chromophores as a tool to guide ligand design. Additionally, we have investigated chiral IAM ligands that yield Tb(III) complexes possessing both high quantum yield values and strong circularly polarized luminescence (CPL) activity. To efficiently sensitize Eu(III) emission, we have used the 1-hydroxypyridin-2-one (1,2-HOPO) chelate to create remarkable ligands that combine excellent photophysical properties and exceptional aqueous stabilities. A more complete understanding of this chromophore has been achieved by combining low-temperature phosphorescence measurements with the same TD-DFT approach used with the IAM system. Eu(III) complexes with strong CPL activity have also been obtained with chiral 1,2-HOPO ligands. We have also undertaken kinetic analysis of radiative and nonradiative decay pathways for a series of Eu(III) complexes; the importance of the metal ion symmetry on the ensuing photophysical properties is clear. Lastly, we describe a Tb(III)-IAM compound--now carried through to commercial availability--that offers improved performance in the common HTRF platform and has the potential to vastly improve sensitivity.

The art of fluorescence imaging with chemical sensors.

Abstract: Fluorescence imaging techniques involving chemical sensors are essential tools in many fields of science and technology because they enable the visualization of parameters which exhibit no intrinsic color or fluorescence, for example, oxygen, pH value, CO(2), H(2)O(2), Ca(2+), or temperature, to name just a few. This Review aims to highlight the state of the art of fluorescence sensing and imaging, starting from a comprehensive overview of the basic functional principles of fluorescent probes (or indicators) and the design of sensor materials. The focus is directed towards the progress made in the development of multiple sensors and methods for their signal read out. Imaging methods involving optical sensors are applied in quite diverse scientific areas, such as medical research, aerodynamics, and marine research.