Zoe Pikramenou

Photoactive metallocyclodextrins: sophisticated supramolecular arrays for the construction of light activated miniature devices

The introduction of photoactive metal centres onto cyclodextrin receptors opens up new possibilities for the design of sensors, wires and energy conversion systems. This tutorial review focuses on strategies involving such metallocyclodextrins for the construction of supramolecular arrays with light-activated functions. The assembly procedures for building such arrays are presented, together with the features required for their functions both as sensors for ion or small molecule detection and as wires for photoinduced long-range energy or electron transport. Systems for metal ion sensing are described where the cyclodextrin plays a mediating role in influencing the luminescence properties of an organic probe, responsive to metal binding. Small molecule sensing by the cyclodextrin cavity is realised using luminescent lanthanide or transition metal functionalised cyclodextrins. The light signal of the photoactive metal is switched on or off upon binding an analyte in the cyclodextrin cavity. The metallocyclodextrin systems that function as wires are distinguished by the controlled assembly of transition metal polypyridine and metalloporphyrin units. These units have inherent photoactivity that defines the vectorial direction of energy or electron transfer processes through the wire.

Hyper-Rayleigh scattering investigation of nitrobenzyl pyridine model compounds for optical modulation of the hyperpolarisability

Abstract Hyper-Rayleigh scattering (HRS) is used to determine the molecular hyperpolarisability (β) of model compounds for the two tautomeric forms of nitrobenzyl pyridine (NBP) derivatives. For each derivative large differences (a factor of 10 to 200) are found between the two forms which indicates that the NBP system can be used to optically modulate second-harmonic generation through a photoinduced proton transfer process.

pH-controlled delivery of luminescent europium coated nanoparticles into platelets

Water soluble, luminescent gold nanoparticles are delivered into human platelets via a rapid, pH-controlled mechanism using a pH low insertion peptide, pHLIP. The approach introduces cocoating of gold nanoparticles with a europium luminescent complex, EuL and the pHLIP peptide to give pHLIP•EuL•Au. The 13-nm diameter gold nanoparticles act as a scaffold for the attachment of both the luminescent probe and the peptide to target delivery. Their size allows delivery of approximately 640 lanthanide probes per nanoparticle to be internalized in human platelets, which are not susceptible to transfection or microinjection. The internalization of pHLIP•EuL•Au in platelets, which takes just minutes, was studied with a variety of imaging modalities including luminescence, confocal reflection, and transmission electron microscopy. The results show that pHLIP•EuL•Au only enters the platelets in low pH conditions, pH 6.5, mediated by the pHLIP translocation across the membrane, and not at pH 7.4. Luminescence microscopy images of the treated platelets show clearly the red luminescence signal from the europium probe and confocal reflection microscopy confirms the presence of the gold particles. Furthermore, transmission electron microscopy gives a detailed insight of the internalization and spatial localization of the gold nanoparticles in the platelets. Thus, we demonstrate the potential of the design to translocate multimodal nanoparticle probes into cells in a pH dependent manner.

Immobilization of π-Assembled Metallo-Supramolecular Arrays in Thin Films: From Crystal-Engineered Structures to Processable Materials

Layer-by-layer deposition of π-assembled arrays of discrete metallo units with aryl tails and polystyrenesulfonate gives structurally well-defined thin films. The formation of these films, which is controlled by π-π interactions, metal-ion coordination, and electrostatic interactions, bridges the gap between supramolecular crystal engineering and design of layered materials.

Diastereoselective formation of luminescent dinuclear lanthanide(III) helicates with enantiomerically puretartaric acid derived bis(β-diketonate) ligands

The chiral tartaric acid derived bis(β-diketonate) ligands 1–3-H2 diastereoselectively form dinuclear triple-stranded helicates with a series of lanthanide(III) ions (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb), which bind water molecules as additional co-ligands. In the cases of europium(III) and terbium(III) ions, bright red or green luminescence is observed, respectively. Hereby the energy transfer from the ligand to the metal is most effective with the bromophenyl-substituted ligand 3-H2. Reaction of 3-H2 with europium(III) in a 4 : 2 ratio results in a highly luminescent quadruple-stranded dinuclear complex [34Eu2]2–.

Luminescence from supramolecules triggered by the molecular recognition of substrates

Abstract Supramolecules containing a photoluminescent center (PLC) exhibit prompt and intense luminescence upon the molecular recognition of substrates. Luminescence from supramolecular assemblies is triggered by substrates that are light-harvesting and able to coordinate metal ion PLCs, light-harvesting and non-coordinating to PLCs, and non-absorbing and non-coordinating. Our efforts to elaborate the photophysical schemes for these three classes of substrates are described herein.

Luminescent nanobeads: attachment of surface reactive Eu(III) complexes to gold nanoparticles.

Gold nanoparticles were used as a scaffold to assemble multiple tailor-made europium(III) complexes yielding water-soluble gold nanoparticles that display red, Eu(III), luminescence.

Intracellular synchrotron nanoimaging and DNA damage/genotoxicity screening of novel lanthanide-coated nanovectors

AIMS In cancer therapy, research has focused on the development of nanocarriers that can aid diagnosis, deliver therapeutic agents and monitor treatment progress. This study introduces high-resolution synchrotron x-ray fluorescence microscopy (SR-XFM) to investigate intracellular localization of novel lanthanide-coated nanoparticles in human cells and their genotoxicity screening after internalization. MATERIALS & METHODS Noble metal nanoparticles coated with cerium and luminescent europium complexes have been developed as platforms for bioimaging and potential biodelivery applications. The intracellular distribution after internalization has been analyzed by ultrasensitive SR-XFM and genotoxicity evaluated using γ-H2AX DNA damage foci phosphorylation assay. RESULTS We demonstrate the unprecedented capability of SR-XFM for extremely sensitive nanoimaging and intracellular elemental distribution analysis of noble metal nanoparticles in cells. Furthermore, we show that, depending on the charge of the coating complex and the presence of the DNA cargo, the internalization of functionalized nanoparticles by human fibroblasts can cause elevated levels of DNA damage detected by histone H2AX phosphorylation. CONCLUSION The variable genotoxic impact of newly designed nanovectors emphasizes the need for careful and comprehensive testing of biological responses of all new nanoconstructs intended for future clinical applications. This can be greatly facilitated by SR-XFM nanoimaging of nanoparticles in cells at very low concentrations.

Platelet actin nodules are podosome-like structures dependent on Wiskott–Aldrich syndrome protein and ARP2/3 complex

The actin nodule is a novel F-actin structure present in platelets during early spreading. However, only limited detail is known regarding nodule organization and function. Here we use electron microscopy, SIM and dSTORM super-resolution, and live-cell TIRF microscopy to characterize the structural organization and signalling pathways associated with nodule formation. Nodules are composed of up to four actin-rich structures linked together by actin bundles. They are enriched in the adhesion-related proteins talin and vinculin, have a central core of tyrosine phosphorylated proteins and are depleted of integrins at the plasma membrane. Nodule formation is dependent on Wiskott–Aldrich syndrome protein (WASp) and the ARP2/3 complex. WASp−/− mouse blood displays impaired platelet aggregate formation at arteriolar shear rates. We propose actin nodules are platelet podosome-related structures required for platelet–platelet interaction and their absence contributes to the bleeding diathesis of Wiskott–Aldrich syndrome.

De Novo Design of Ln(III) Coiled Coils for Imaging Applications

A new peptide sequence (MB1) has been designed which, in the presence of a trivalent lanthanide ion, has been programmed to self-assemble to form a three stranded metallo-coiled coil, Ln(III)(MB1)3. The binding site has been incorporated into the hydrophobic core using natural amino acids, restricting water access to the lanthanide. The resulting terbium coiled coil displays luminescent properties consistent with a lack of first coordination sphere water molecules. Despite this the gadolinium coiled coil, the first to be reported, displays promising magnetic resonance contrast capabilities.