"Size or mass" which plays a role? An investigation on the optical and ultrasonic properties of chitosan-lanthanide composites.

In this present exploration, chitosan doped with different lanthanide oxides such as CeO2, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Dy2O3 and Ho2O3 has been prepared and its optical and thermodynamical properties were studied as a function of the ion size of the lanthanide element and its atomic masses. From the refractive index measurement, the space-filling factor and polarizability have been obtained. The propagation of ultrasonic waves like ultrasonic velocity and its derived quantities such as relaxation strength (rs), adiabatic bulk modulus (Ks), acoustic impedance (Z) and adiabatic compressibility (ß) have been obtained for different Chitosan-Lanthanide oxides (Ch-LnO). FTIR studies confirm the formation of different Ch-LnO. The variation of all the said properties with ion size is opposite to that of atomic mass due to lanthanide contraction. The results are presented and discussed in a detailed manner.

Diarylphosphate as a New Route for Design of Highly Luminescent Ln Complexes.

Organophosphate-chloride complexes [{(2,6-iPr2C6H3-O)2POO}2LnCl(CH3OH)4]·2CH3OH, Ln = Nd (1), Eu (2), Gd (3), and Tb (4) have been obtained and structurally characterized. Their reaction with 2,2':6',2″-terpyridine leads to the formation of 1:1 adducts ([{(2,6-iPr2C6H3-O)2POO}2LnCl(terpy)(H2O)2(CH3OH)], Ln = Eu (5), Gd (6), Tb (7) with exception of Nd, where tris-diisopropylphenylphosphate complex [{(2,6-iPr2C6H3-O)2POO}3Nd) (terpy)(H2O)(CH3OH)] (8) was obtained due to the ligand metathesis. A bright luminescence observed for the Eu and Tb organophosphate complexes is the first example of an application of organophosphate ligands for 4f-ions luminescence sensitization. Photophysical properties of all complexes were analyzed by optical spectroscopy and an energy transfer scheme was discussed. A combination of two types of ligands into the coordination sphere (phosphate and phenanthroline) allows designing the Eu surrounding with very high intrinsic quantum yield QEuEu (0.92) and highly luminescent Ln complexes for both visible and near-infrared (NIR) regions.

Nanostructures based on vanadium disulfide growing on UCNPs: simple synthesis, dual-mode imaging, and photothermal therapy.

It remains a great challenge to integrate effective photothermal therapeutic materials with upconversion nanoparticles (UCNPs) into one structure with small size. Herein, a new and simple method was developed to combine the luminescent UCNPs with vanadium disulfide (VS2) heterogeneously growing on the UCNPs. VS2 was grown directly on the surface of UCNPs to obtain oil-soluble nanocomposites, UCNPs@VS2. Then polyethylene glycol (mPEG) was functionalized on the surface of the nanocomposites to improve the water solubility, resulting in the integrated nanostructure UCNPs@VS2-mPEG (with an approximate size of 25 nm) for bioimaging and photothermal therapy in vitro. Importantly, cytotoxicity test results show that the final nanostructure has good biocompatibility. Furthermore, due to the excellent photothermal effects of VS2 and the unique imaging function of UCNPs, the nanostructure shows effective photothermal therapy for HeLa cells and was successfully applied in magnetic resonance imaging and upconversion luminescence imaging in vitro. Therefore, this study demonstrates a simple yet powerful method of growing VS2 on the surface of UCNPs, which provides an effective method to establish one integrated nanostructure with a nanoscale advantage for dual-model bioimaging and treatment.

Dual Emission in a Ligand and Metal Co-Doped Lanthanide-Organic Framework: Color Tuning and Temperature Dependent Luminescence.

In this study, we report the luminescence color tuning in the lanthanide metal-organic framework (LnMOF) ([La(bpdc)Cl(DMF)] (1); bpdc2- = [1,1'-biphenyl]-4,4'-dicarboxylate, DMF = N,N-dimethylformamide) by introducing dual emission properties in a La3+ MOF scaffold through doping with the blue fluorescent 2,2'-diamino-[1,1'-biphenyl]-4,4'-dicarboxylate (dabpdc2-) and the red emissive Eu3+. With a careful adjustment of the relative doping levels of the lanthanide ions and bridging ligands, the color of the luminescence was modulated, while at the same time the photophysical characteristics of the two chromophores were retained. In addition, the photophysical properties of the parent MOF (1) and its doped counterparts with various dabpdc2-/bpdc2- and Eu3+/La3+ ratios and the photoinduced energy transfer pathways that are possible within these materials are discussed. Finally, the temperature dependence study on the emission profile of a doped analogue containing 10% dabpdc2- and 2.5% Eu3+ (7) is presented, highlighting the potential of this family of materials to behave as temperature sensors.

Syntheses, characterization, DNA/HSA binding ability and antitumor activities of a family of isostructural binuclear lanthanide complexes containing hydrazine Schiff base.

Three dinuclear lanthanide complexes, [Ln2(L)2(µ3-OAc)4(H2O)2]⋅2H2O (Ln = La (1), Eu (2) and Dy (3), HL = N'-(2-hydroxybenzylidene) nicotinohydrazide), have been synthesized and characterized by IR, elemental analysis and X-ray single-crystal diffraction. Crystallographic study revealed that the representative complex 1 displays a discrete dinuclear structure with a distorted tricapped trigonal prismatic geometry around La(III) ion. The interaction of complexes 1-3 with CT-DNA was investigated by absorption spectra, fluorescence quenching and viscosity, which reveals that the complexes bind to CT-DNA with a moderate intercalative mode. The complexes exhibited obvious DNA cleavage activities in the presence of H2O2. All complexes could bind to human serum albumin (HSA) with medium affinity through static mode; thus, HSA could effectively transport complexes. Furthermore, three complexes exhibited specific cytotoxicity to A549 cancer cells in micromole magnitude than other cancer cells tested and less toxicity than cisplatin for normal human cells HUVEC, in which massive cell apoptosis was induced by complexes through producing DNA damage and suppressing DNA synthesis.Communicated by Ramaswamy H. Sarma.

Synthesis and Near Infrared Luminescence Properties of a Series of Lanthanide Complexes with POSS Modified Ligands.

A polyhedral oligomeric silsesquioxanes (POSS) modified 8-hydroxyquinoline derivative (denoted as Q-POSS) was synthesized and used as a ligand to coordinate with lanthanide ions to obtain a series of lanthanide complexes Ln(Q-POSS)3 (Ln = Er3+, Yb3+, Nd3+). The as-prepared lanthanide complexes have been characterized by FT-IR, UV⁻Vis, and elemental analysis. All these complexes showed the characteristic near-infrared (NIR) luminescence originated from the corresponding lanthanide ions under excitation. Compared with the unmodified counterparts LnQ3 (HQ = 8-hydroxyquinoline), the Ln(Q-POSS)3 complexes showed obviously increased emission intensity, which was ascribed mainly to the steric-hindrance effects of the POSS moiety in the ligands. It is believed that the POSS group could suppress undesired excimer formation and intermolecular aggregation, thus decreasing the concentration quenching effect of the corresponding lanthanide complexes.

Lanthanide-Doped Photoluminescence Hollow Structures: Recent Advances and Applications.

Lanthanide-doped nanomaterials have attracted significant attention for their preeminent properties and widespread applications. Due to the unique characteristic, the lanthanide-doped photoluminescence materials with hollow structures may provide advantages including enhanced light harvesting, intensified electric field density, improved luminescent property, and larger drug loading capacity. Herein, the synthesis, properties, and applications of lanthanide-doped photoluminescence hollow structures (LPHSs) are comprehensively reviewed. First, different strategies for the engineered synthesis of LPHSs are described in detail, which contain hard, soft, self-templating methods and other techniques. Thereafter, the relationship between their structure features and photoluminescence properties is discussed. Then, niche applications including biomedicines, bioimaging, therapy, and energy storage/conversion are focused on and superiorities of LPHSs for these applications are particularly highlighted. Finally, keen insights into the challenges and personal prospects for the future development of the LPHSs are provided.

Synthesis, photophysical and cellular characterisation of folate and methotrexate labelled luminescent lanthanide complexes.

In this work we have developed a series of highly emissive europium(III) and terbium(III) complexes tethered to either folic acid (FA) or methotrexate (MTX), with the aim of developing visual probes that enable the imaging of folate receptors in cancer cells. The synthesis, photophysical properties and cellular behaviour are reported for four new lanthanide Ln(III) complexes, where either FA or MTX are tethered to 1,4,7-tris(carbonylmethyl)-10-(4'-quinolineacetic acid, (7'-acetamido)-1',2'-dihydro-2'-oxo)-1,4,7,10-tetraazacyclododecane Ln(III) complex, and Ln(III)=Eu(III) or Tb(III); herein referred to as Eu-FA, Eu-MTX, Tb-FA or Tb-MTX. All four complexes were found to be sensitive to the presence of the folate receptor in a range of cell lines. The MTX conjugates showed different cellular specificity in an oral adenosquamous carcinoma cell line (CAL-27) compared with the analogous FA conjugates. This suggests that it is viable to explore differences in folate receptors using folate vs. anti-folate probes, with labels that have different emissive properties (e.g. Eu-FA vs. Tb-MTX). The MTX complexes were found to be the most cytotoxic, with Eu-MTX showing greater cytotoxicity than free MTX or the isostructural Tb-MTX. This suggested that there could be a synergistic effect on toxicity for the Eu(III) chelate and the MTX components of the complex.

Ultrasensitive optical imaging with lanthanide lumiphores.

In principle, the millisecond emission lifetimes of lanthanide chelates should enable their ultrasensitive detection in biological systems by time-resolved optical microscopy. In practice, however, lanthanide imaging techniques have provided no better sensitivity than conventional fluorescence microscopy. Here, we identified three fundamental problems that have impeded lanthanide microscopy: low photon flux, inefficient excitation, and optics-derived background luminescence. We overcame these limitations with a new lanthanide imaging modality, transreflected illumination with luminescence resonance energy transfer (trLRET), which increases the time-integrated signal intensities of lanthanide lumiphores by 170-fold and the signal-to-background ratios by 75-fold. We demonstrate that trLRET provides at least an order-of-magnitude increase in detection sensitivity over that of conventional epifluorescence microscopy when used to visualize endogenous protein expression in zebrafish embryos. We also show that trLRET can be used to optically detect molecular interactions in vivo. trLRET promises to unlock the full potential of lanthanide lumiphores for ultrasensitive, autofluorescence-free biological imaging.

Synthesis of Core-shell Lanthanide-doped Upconversion Nanocrystals for Cellular Applications.

Lanthanide-doped upconversion nanocrystals (UCNs) have attracted much attention in recent years based on their promising and controllable optical properties, which allow for the absorption of near-infrared (NIR) light and can subsequently convert it into multiplexed emissions that span over a broad range of regions from the UV to the visible to the NIR. This article presents detailed experimental procedures for high-temperature co-precipitation synthesis of core-shell UCNs that incorporate different lanthanide ions into nanocrystals for efficiently converting deep-tissue penetrable NIR excitation (808 nm) into a strong blue emission at 480 nm. By controlling the surface modification with biocompatible polymer (polyacrylic acid, PAA), the as-prepared UCNs acquires great solubility in buffer solutions. The hydrophilic nanocrystals are further functionalized with specific ligands (dibenzyl cyclooctyne, DBCO) for localization on the cell membrane. Upon NIR light (808 nm) irradiation, the upconverted blue emission can effectively activate the light-gated channel protein on the cell membrane and specifically regulate the cation (e.g., Ca2+) influx in the cytoplasm. This protocol provides a feasible methodology for the synthesis of core-shell lanthanide-doped UCNs and subsequent biocompatible surface modification for further cellular applications.

Synthesis and Structural Investigation of New Bio-Relevant Complexes of Lanthanides with 5-Hydroxyflavone: DNA Binding and Protein Interaction Studies.

In the present work, we attempted to develop new metal coordination complexes of the natural flavonoid 5-hydroxyflavone with Sm(III), Eu(III), Gd(III), Tb(III). The resultant hydroxo complexes have been characterized by a variety of spectroscopic techniques, including fluorescence, FT-IR, UV-Vis, EPR and mass spectral studies. The general chemical formula of the complexes is [Ln(C15H9O3)3(OH)2(H2O)x]·nH2O, where Ln is the lanthanide cation and x = 0 for Sm(III), x = 1 for Eu(III), Gd(III), Tb(III) and n = 0 for Sm(III), Gd(III), Tb(III), n = 1 for Eu(III), respectively. The proposed structures of the complexes were optimized by DFT calculations. Theoretical calculations and experimental determinations sustain the proposed structures of the hydroxo complexes, with two molecules of 5-hydroxyflavone acting as monoanionic bidentate chelate ligands. The interaction of the complexes with calf thymus DNA has been explored by fluorescence titration and UV-Vis absorption binding studies, and revealed that the synthesized complexes interact with DNA with binding constants (Kb) ~ 104. Human serum albumin (HSA) and transferrin (Tf) binding studies have also been performed by fluorescence titration techniques (fluorescence quenching studies, synchronous fluorescence spectra). The apparent association constants (Ka) and thermodynamic parameters have been calculated from the fluorescence quenching experiment at 299 K, 308 K, and 318 K. The quenching curves indicate that the complexes bind to HSA with smaller affinity than the ligand, but to Tf with higher binding affinities than the ligand.

De Novo Designed Imaging Agents Based on Lanthanide Peptides Complexes.

Herein are discussed a selection of lanthanide peptide/protein complexes in view of their potential applications as imaging agents, both in terms of luminescence detection and magnetic resonance imaging. Though this chapter covers a range of different peptides and protein, if focuses specifically on the opportunities afforded by the de novo design of coiled coils, miniature protein scaffolds, and the development on lanthanide-binding sites into these architectures. The requirements for lanthanide coordination and the challenges that need to be addressed when preparing lanthanide peptides with a view to their potential adoption as clinical imaging applications, will be highlighted.

A new luminescent lanthanide supramolecular network possessing free Lewis base sites for highly selective and sensitive Cu(2+) sensing.

A series of new lanthanide complexes, formulated as [Ln2(DCSAL)3(H2O)11]·3DCSAL·4H2O [Ln = Eu (1), Gd (2) and Tb (3); DCSAL = 3,5-dichlorosalicylate], have been synthesized and characterized by single crystal X-ray analysis. They are dinuclear clusters and form a 3D supramolecular network viaπ-π stacking and halogen bonding interactions. 3 exhibits strong Tb characteristic emission, whose quantum yield is as high as 38%. Due to binding with Cu(2+) ions via its Lewis acid-base interactions, 3 displayed a high selectivity and sensitivity for Cu(2+) detection based on Tb(3+) emission quenching. The possible quenching mechanism was further proved to be a static quenching mechanism by Stern-Volmer plots and UV-vis spectrum. More importantly, the binding constant between 3 and Cu(2+) is also calculated by the Benesi-Hildebrand method, which is helpful for quantitative analysis.

Lanthanide-Connecting and Lone-Electron-Pair Active Trigonal-Pyramidal-AsO3 Inducing Nanosized Poly(polyoxotungstate) Aggregates and Their Anticancer Activities.

By virtue of the stereochemical effect of the lone-electron pair located on the trigonal-pyramidal-AsO3 groups and the one-pot self-assembly strategy in the conventional aqueous solution, a series of novel lanthanide-bridging and lone-electron-pair active trigonal-pyramidal-AsO3 inducing nanosized poly(polyoxotungstate) aggregates [H2N(CH3)2]6 Na24H16{[Ln10W16(H2O)30O50](B-α-AsW9O33)8}·97H2O [Ln = Eu(III) (1), Sm(III) (2), Gd(III) (3), Tb(III) (4), Dy(III) (5), Ho(III) (6), Er(III) (7), Tm(III) (8)] were prepared and further characterized by elemental analyses, IR spectra, UV spectra, thermogravimetric (TG) analyses and single-crystal X-ray diffraction. The most remarkable structural feature is that the polyanionic skeleton of {[Ln10W16(H2O)30O50](B-α-AsW9O33)8}(46-) is constructed from eight trivacant Keggin [B-α-AsW9O33](9-) fragments through ten Ln centers and sixteen bridging W atoms in the participation of fifty extraneous oxygen atoms. Notably, 4 and 8 can be stable in the aqueous solution not only for eight days but also in the range of pH = 3.9-7.5. Moreover, the cytotoxicity tests of 4 and 8 toward human cervical cancer (HeLa) cells, human breast cancer (MCF-7) cells and mouse fibroblast (L929) cells were performed by the 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and the cell apoptosis processes were characterized by calcein AM/PI staining experiments, annexin V-FITC/PI staining experiments and morphological changes.

Synthesis of novel lanthanide acylpyrazolonato ligands with long aliphatic chains and immobilization of the Tb complex on the surface of silica pre-modified via hydrophobic interactions.

Five new complexes Ln(Q(C17))3(H2O)(Solv) (Ln = Y, Solv = H2O, Ln = Tb, Dy, Sm or Eu, Solv = EtOH) were synthesized with the acylpyrazolonato ligand Q(C17) bearing a long aliphatic C17H35 chain in the acyl moiety, and the crystal structure of Y(Q(C17))3(H2O)2 shows the three aliphatic chains from the coordinated ligands positioned in the same direction, affording plane layers built by Y(Q(C17))3(H2O)2 molecules connected through H-bonding interactions. The layers are stitched to each other like in "hook & loop" tapes. Luminescence of complexes was determined and the complex Tb(Q(C17))3(H2O)(EtOH) was immobilized on the surface of silica preprocessed using a C17H35CONH(CH2)3Si(OEt)3 reagent via hydrophobic interactions of long aliphatic chains. Luminescent properties and micromorphology of the obtained hybrid particles and hybrid films were investigated. Intensive green emission of the complex retains after grafting onto the silica surface. Inclusion of the complex on the surface of silica materials occurs as separate molecules, after the disruption of the H-bonding network present in the crystalline phase of the pure terbium sample.

Construction of Identical [2 + 2] Schiff-Base Macrocyclic Ligands by Ln(III) and Zn(II) Template Ions Including Efficient Yb(III) Near-Infrared Sensitizers.

Identical 34-membered [2 + 2] pendent-armed Schiff-base macrocyclic ligands (H4La and H4Lb) can be constructed via the condensation reactions between rigid o-phenylenediamine and extended dialdehydes (H2hpdd/H2pdd) in the presence of either Ln(III) or Zn(II) template with remarkable distinction on the ion radii and charge. X-ray single-crystal diffraction analyses reveal the formation of mononuclear Ln(III) complexes (1-4 and 7) and dinuclear Zn(II) complexes (5 and 6). It is noted that Ln(III) macrocyclic complexes have eight-coordinate sandwich-like mononuclear structures fully surrounded by flexible and large-sized macrocyclic ligands. Photophysical studies have demonstrated that both H4La and H4Lb can serve as effective sensitizers for the Yb(III) ion (2 and 7) exhibiting near-infrared emission at 974 nm with high quantum yields in solution (C2H5OH and CH3OH, ∼1%). Moreover, the quantum yields of two Yb(III) complexes 2 and 7 could be increased ∼15% in CH3OH under weak alkaline condition (pH = 8-9), while no significant changes are observed in C2H5OH by contrast. We think the unique sandwich-like macrocyclic structures of Yb(III) complexes 2 and 7 play important roles in simultaneously guaranteeing the effective match of the energy levels of Yb(III) centers as well as shielding from the solvent molecules and counterions.

Photofunctional hybrids of lanthanide functionalized bio-MOF-1 for fluorescence tuning and sensing.

A series of luminescent Ln(3+)@bio-MOF-1 (Ln=Eu, Tb, bio-MOF-1=Zn8(ad)4(BPDC)6O⋅2Me2NH2 (ad=adeninate, BPDC=biphenyldicarboxylate)) are synthesized via postsynthetic cation exchange by encapsulating lanthanide ions into an anionic metal-organic framework (MOF), and their photophysical properties are studied. After loading 2-thenoyltrifluroacetone (TTA) as sensitized ligand by a gas diffusion ("ship-in-bottle") method, it is found that the luminescent intensity of Eu(3+) is enhanced. Especially, when loading two different lanthanide cations into bio-MOF-1, the luminescent color can be tuned to close white (light pink) light output. Additionally, bio-MOF-1 and Eu(3+)@bio-MOF-1 are selected as representative samples for sensing metal ions. When bio-MOF-1 is immersed in the aqueous solutions of different metal ions, it shows highly sensitive sensing for Fe(3+) as well as Eu(3+)@bio-MOF-1 immersed in the DMF solutions of different metal ion. The results are benefit for the further application of functionalized bio-MOFs in practical fields.

Lanthanide complexes of azidophenacyl-DO3A as new synthons for click chemistry and the synthesis of heterometallic lanthanide arrays.

Lanthanide complexes of azidophenacyl DO3A are effective substrates for click reactions with ethyne derivatives, giving rise to aryl triazole appended lanthanide complexes, in which the aryl triazole acts as an effective sensitising chromophore for lanthanide luminescence. They also undergo click chemistry with propargylDO3A derivatives, giving rise to heterometallic complexes.

Synthesis, characterization and luminescent properties of lanthanide complexes with a novel multipodal ligand.

Solid complexes of lanthanide nitrates with an novel multipodal ligand, 1,2,4,5-tetramethyl-3,6-bis{N,N-bis[((2'-furfurylaminoformyl)phenoxyl)ethyl]-aminomethyl}-benzene (L) have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Sm(III), Eu(III), Tb(III) and Dy(III) nitrate complexes in solid state were investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of central metal ions. The lowest triplet state energy level of the ligand indicates that the triplet state energy level (T1) of the ligand matches better the resonance level of Tb(III) than other lanthanide ions.

Three novel lanthanide metal-organic frameworks (Ln-MOFs) constructed by unsymmetrical aromatic dicarboxylatic tectonics: synthesis, crystal structures and luminescent properties.

Three novel Ln(III)-based coordination polymers, {[Ln2 (2,4-bpda)3 (H2O)x]·yH2O}n (Ln = La (III) (1), x = 2, y = 0, Ce (III) (2), Pr (III) (3), x = 4, y = 1) (2,4-H2bpda = benzophenone-2,4-dicarboxylic acid) have been prepared via a solvothermal method and characterized by elemental analysis, IR, and single-crystal X-ray diffraction techniques. Complex 1 exhibits a 3D complicated framework with a new 2-nodal (3,7)-connected (42·5) (44·51·66·8) topology. Complexes 2 and 3 are isomorphous, and feature a 3D 4-connected (65·8)-CdSO4 network. Moreover, solid-state properties such as thermal stabilities and luminescent properties of 1 and 2 were also investigated. Complex 1 crystallized in a monoclinic space group P21/c with a = 14.800 (3), b = 14.500 (3), c = 18.800 (4) Å, ß = 91.00 (3), V = 4033.9 (14) Å3 and Z = 4. Complex 2 crystallized in a monoclinic space group Cc with a = 13.5432 (4), b = 12.9981 (4), c = 25.7567 (11) Å, ß = 104.028 (4), V = 1374.16 (7) Å3 and Z = 4.