Luminescent Peptide/Lanthanide(III) Complex Conjugates with Push–Pull Antennas: Application to One- and Two-Photon Microscopy Imaging

Abstract

Lanthanide(III) (Ln 3+ ) complexes feature desirable luminescence properties for cell microscopy imaging, but cytosolic delivery of Ln 3+ complexes and their use for 2P imaging of live cells are challenging. In this article, we describe the synthesis and spectroscopic characterizations of a series of Ln 3+ complexes based on two ligands, L1 and L2, featuring extended picolinate push−pull antennas for longer wavelength absorption and 2P absorption properties as well as a free carboxylate function for conjugation to peptides. Several cell penetrating peptide/ Ln 3+ complex conjugates were then prepared with the most interesting luminescent complexes, Tb(L1) and Eu(L2), and with two cell penetrating peptides (CPPs), ZF5.3 and TP2. A spectroscopic analysis demonstrates that the luminescence properties of the complexes are not affected by conjugation to the peptide. The conjugates were evaluated for one-photon (1P) time-gated microscopy imaging, which suppresses biological background fluorescence, and 2P confocal microscopy. Whereas TP2-based conjugates were unable to enter cells, successful 1P and 2P imaging was performed with ZF5.3[Tb(L1)] . 2P confocal imaging suggests proper internalization and cytosolic delivery as expected for this CPP. Noteworthy, 2P confocal microscopy also allowed characterization of the luminescence properties of the complex (spectrum, lifetime) within the cell, opening the way to functional luminescent probes for 2P confocal imaging of live cells.

Current Development of Lanthanide Complexes for Biomedical Applications

“…A zinc finger water–soluble peptide featuring a peculiar penta‐arginine motif, referred to as ZF5.3, was applied to conjugate with Tb(III) cyclam complex (ZF5.3‐[ Tb ( L11 )], Figure 7). [66] The conjugation of the peptide ZF5.3 enhanced both water‐solubility and biocompatibility without altering the photophysical property of Tb(III) cyclam complex. The functionalized ZF5.3‐[ Tb ( L11 )] displayed luminescence with a quantum yield of 61% and an emission lifetime of 2.32 ms.…”

Comprehensive Photophysical and Nonlinear Spectroscopic Study of Thioanisolyl‐Picolinate Triazacyclononane Lanthanide Complexes

“…Such chromophores as the antenna in EuL 1 were combined with various azamacrocyclic platforms, such as tacn, [1e,9a,10,12] pyclen, [13] cyclen, [1e,14] DO3A, [1e,15] cyclam [16] and others [17] . Among these complexes, the cationic Eu(III) species were found to be spontaneously internalised in cellulo , [14a,17a] or used as sensors for anion analytes, [18] while neutral or anionic complexes found interesting applications as bioconjugates [10,15b,c,19] …”

“…Why using these complexes for the above‐mentioned biological applications, some unexpected drawbacks have been identified by the groups of Tripier and Sénèque: (i) the triple bond in the antenna structure is not perfectly stable and (ii) is sensitive towards cysteine‐containing peptides and proteins in cellular media [15b] or it is partially destroyed in strongly acidic TFA media generally used during peptide synthesis [13c] . As an example, the alkoxyphenyl‐ethynyl‐picolinate complex of DO3A ( EuLc 1 , Figure 1c) underwent thiol‐yne addition of the cysteine‐ and methionine‐containing peptides [15b] …”

Nonlinear and Emissive {[MIII(CN)6]3–···Polyresorcinol} (M = Fe, Co, Cr) Cocrystals Exhibiting an Ultralow Frequency Raman Response

“…Optical properties of matter based on nonlinear response and/or photoluminescence have attracted strong interest in fields such as bioimaging, − anticancer therapy, or multifunctional molecular materials for photonic application, e.g . toward optical modulation of light and for luminescent thermometry. , The phenomenon known as second-harmonic generation (SHG) has been extensively researched and utilized due to its ability to convert two incident photons into a single emitted photon with a doubled frequency.…”