Cyclen lanthanide-based micellar structures for application as luminescent [Eu(iii)] and magnetic [Gd(iii)] resonance imaging (MRI) contrast agents

A Tumor Microenvironment-Responsive Theranostic Agent for Synergetic Therapy of Disulfiram-Based Chemotherapy and Chemodynamic Therapy

Despite the fact that chemotherapy has been widely used in the clinical treatment of breast cancer, the toxicity of chemotherapeutics to normal tissues cannot be ignored due to the low specificity. Therefore, due to the non-negligible toxicity of chemotherapeutic agents to normal tissues, tumor microenvironment (TME)-responsive cancer therapy has attracted a great deal of attention. Here, we report a TME-responsive theranostic nanoagent MnOx@PAA@HKUST-1-DSF@BSA fabricated via a layer-by-layer synthesis method. Once endocytosed by tumor cells, the nanoagent can be degraded into Mn²⁺ for magnetic resonance imaging and Cu²⁺ for Fenton-like reaction and chelating with released disulfiram in situ, achieving enhanced chemotherapy. Both in vitro and in vivo experiments demonstrate that the TME-targeted nanoagent can efficiently kill tumor cells. This work provides an alternative option for effective imaging and treatment of breast cancer without collateral damage to normal tissues.

Structural Characterization, Magnetic and Luminescent Properties of Praseodymium(III)-4,4,4-Trifluoro-1-(2-Naphthyl)Butane-1,3-Dionato(1-) Complexes

Four new Pr(III) mononuclear complexes of formula [Pr(ntfa)3(MeOH)2] (1), [Pr(ntfa)3(bipy)2] (2), [Pr(ntfa)3(4,4′-Mt2bipy)] (3) and [Pr(ntfa)3(5,5′-Me2bipy)] (4), where ntfa = 4,4,4-trifuoro-1-(naphthalen-2-yl)butane-1,3-dionato(1-), 5,5′-Me2bipy = 5,5′-dimethyl-2,2′-dipyridine, 4,4′-Mt2bipy = 4,4′-dimethoxy-2,2′-dipyridine, have been synthesized and structurally characterized. The complexes display the coordination numbers 8 for 1, 3 and 4, and 10 for 2. Magnetic measurements of complexes 1–4 were consistent with a magnetically uncoupled Pr3+ ion in the 3H4 ground state. The solid state luminescence studies showed that the ancillary chelating bipyridyl ligands in the 2–4 complexes greatly enhance the luminescence emission in the visible and NIR regions through efficient energy transfer from the ligands to the central Pr3+ ion; behaving as “antenna” ligands.

Design and Synthesis of Luminescent Lanthanide-Based Bimodal Nanoprobes for Dual Magnetic Resonance (MR) and Optical Imaging

Current biomedical imaging techniques are crucial for the diagnosis of various diseases. Each imaging technique uses specific probes that, although each one has its own merits, do not encompass all the functionalities required for comprehensive imaging (sensitivity, non-invasiveness, etc.). Bimodal imaging methods are therefore rapidly becoming an important topic in advanced healthcare. This bimodality can be achieved by successive image acquisitions involving different and independent probes, one for each mode, with the risk of artifacts. It can be also achieved simultaneously by using a single probe combining a complete set of physical and chemical characteristics, in order to record complementary views of the same biological object at the same time. In this scenario, and focusing on bimodal magnetic resonance imaging (MRI) and optical imaging (OI), probes can be engineered by the attachment, more or less covalently, of a contrast agent (CA) to an organic or inorganic dye, or by designing single objects containing both the optical emitter and MRI-active dipole. If in the first type of system, there is frequent concern that at some point the dye may dissociate from the magnetic dipole, it may not in the second type. This review aims to present a summary of current activity relating to this kind of dual probes, with a special emphasis on lanthanide-based luminescent nano-objects.

Polymerizable Gd(iii) building blocks for the synthesis of high relaxivity macromolecular MRI contrast agents

A new synthetic strategy for the preparation of macromolecular MRI contrast agents (CAs) is reported. Four gadolinium(iii) complexes bearing either one or two polymerizable methacrylamide groups were synthesized, serving as monomers or crosslinkers for the preparation of water-soluble, polymeric CAs using Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization. Using this approach, macromolecular CAs were synthesized with different architectures, including linear, hyperbranched polymers and gels. The relaxivities of the polymeric CAs were determined by NMR relaxometry, revealing an up to 5-fold increase in relaxivity (60 MHz, 310 K) for the linear polymers compared with the clinically used CA, Gd-DOTA. Moreover, hyperbranched polymers obtained from Gd(iii) crosslinkers, displayed even higher relaxivities up to 22.8 mM⁻¹ s⁻¹, approximately 8 times higher than that of Gd-DOTA (60 MHz, 310 K). A detailed NMRD study revealed that the enhanced relaxivities of the hyperbranched polymers were obtained by limiting the local motion of the crosslinked Gd(iii) chelate. The versatility of RAFT polymerization of Gd(iii) monomers and crosslinkers opens the doors to more advanced polymeric CAs capable of multimodal, bioresponsive or targeting properties.

A new synthetic strategy for the preparation of efficient macromolecular MRI contrast agents is reported.

Chiral luminescent lanthanide complexes possessing strong (samarium, SmIII) circularly polarised luminescence (CPL), and their self-assembly into Langmuir-Blodgett films

The lanthanide directed self-assembly of chiral amphiphilic 2,6-pyridinedicarboxylic acid based ligands 1 and 2 with various Ln(CF₃SO₃)₃ (Ln = Tb^III, Sm^III, Lu^III, Dy^III) salts was studied in CH₃CN and evaluated with the expected 1 : 3 and 1 : 1 Ln : Ligand species forming in solution. Ligand chirality was retained and transferred, as depicted by circular dichroism (CD) and circularly polarised luminescence (CPL) measurements (for Tb^III and Sm^III), to the lanthanide centre upon complexation with high dissymmetry factor values for the Sm^III complexes obtained (g_lum = -0.44 and 0.29 and 0.45 and -0.23 for the ⁴G_5/2→⁶H_5/2 and the ⁴G_5/2→⁶H_7/2 transitions of Sm·1₃ and Sm·2₃, respectively). The ability of the complexes to form stable Langmuir monolayers at the air-water interface was also established while Langmuir-Blodgett films of Tb·L₃ and Sm·L₃ exhibited lanthanide luminescent emission.

Effects of europium spectral probe interchange in Ln-dyads with cyclen and phen moieties

Antenna-lanthanide energy transfer is investigated via a bimetallic complex with one silent and one probe lanthanide ion, when their positions are interchanged in the complex.

The effect of the linker size in C2-symmetrical chiral ligands on the self-assembly formation of luminescent triple-stranded di-metallic Eu(iii) helicates in solution

Chiral lanthanide-based supramolecular structures have gained significant importance in view of their application in imaging, sensing and other functional purposes. We have designed chiral C2-symmetrical ligands (L) based on the use of two 2,6-pyridine-dicarboxylic-amide moieties (pda), that differ from one another by the nature of the diamine spacer groups (from 1,3-phenylenedimethanamine (1(S,S), 2(R,R)) and benzene-1,3-diamine (3(S,S), 4(R,R)) to much bulkier 4,4'-(cyclohexane-1,1-diyl)bis(2,6-dimethylaniline) (5(S,S), 6(R,R))) between these two pda units. The self-assembly between L and Eu(iii) ions were investigated in CH3CN solution at low concentration whereby the changes in the absorbance, fluorescence and Eu(iii)-centred emission spectra allowed us to model the binding equilibria occurring in the solution to the presence of [Eu:L2], [Eu2:L2], [Eu2:L3] assemblies and reveal their high binding constant values. The self-assembly in solution were also studied at higher concentration by following the changes in the 1H NMR spectra of the ligands upon Eu(iii) addition, as well as by using MALDI-MS of the isolated solid state complexes. The chiroptical properties of the ligands were used in order to study the structural changes upon self-assembly between the ligands and Eu(iii) ions using circular dichroism (CD) and circularly polarised luminescence (CPL) spectroscopies. The photophysical properties of [Eu2:L3] complexes were evaluated in solution and showed a decrease of luminescence quantum yield when going from the ligand with smaller (1(S,S)) to bulkier (5(S,S)) linker from ∼5.8% to ∼2.6%. While mass-spectrometry revealed the possible formation of trinucler assemblies such as [Eu3:L3] and [Eu3:L2].

Developing the family of picolinate ligands for Mn2+ complexation

We have reported here a series of ligands containing pentadentate 6,6'-(azanediylbis(methylene))dipicolinic acid units that differ in the substituent present at the amine nitrogen atom (acetate: H₃DPAAA; phenyl: H₂DPAPhA; dodecyl: H₂DPAC12A; 4-hexylphenyl: H₂DPAC6PhA). The protonation constants of the hexadentate DPAAA^3- and pentadentate DPAPhA^2- ligands and the stability constants of their Mn²⁺ complexes were determined using pH-potentiometry (25 °C, 0.15 M NaCl). The mono-hydrated [Mn(DPAAA)]^- complex (log K_MnL = 13.19(5)) was found to be considerably more stable than the bis-hydrated [Mn(DPAPhA)] analogue (log K_MnL = 9.55(1)). A detailed ¹H and ¹⁷O NMR relaxometric study was carried out to determine the parameters that govern the proton relaxivities of these complexes. The [Mn(DPAC12A)] complex, which contains a dodecyl lipophilic chain, forms micelles in solution characterized by a critical micellar concentration (cmc) of 96(9) μM. The lipophilic [Mn(DPAC6PhA)] and [Mn(DPAC12A)] derivatives form rather strong adducts with Human Serum Albumin (HSA) with association constants of 7.1 ± 0.1 × 10³ and 1.3 ± 0.4 × 10⁵ M^-1, respectively. The X-ray structure of the complex {K(H₂O)₄}{[Mn(DPAAA)(H₂O)]}₂ shows that the Mn²⁺ ion in [Mn(DPAAA)]^- is coordinated to the six donor atoms of the ligand, a coordinated water molecule completing the pentagonal bipyramidal coordination environment.

DOTA analogues with a phosphinate-iminodiacetate pendant arm: modification of the complex formation rate with a strongly chelating pendant

The formation of highly stable out-of-cage complexes slows down the transfer of the metal ion into the cavity of the macrocyclic ligand.