22 research outputs found
The study of energy transfer mechanism in lanthanide coordinated organic complexes and their applications
No full textDepuis la découverte de la sensibilisation indirecte des ions lanthanides uniques par des ligands organiques, à savoir l'effet d'antenne en 1942, les complexes organiques de lanthanides ont été largement appliqués dans divers domaines, y compris les matériaux pour les dispositifs d'éclairage, les diagnostics biomédicaux et l'imagerie, ainsi que les agents de détection. Le mécanisme de transfert d'énergie joue un rôle important dans l'amélioration de l'efficacité de la collecte de lumière, qui est généralement associée à la voie S1 → T1 → Ln3+, bien que la voie directe du singulet soit également observée et rapportée.Dans ce travail, l'évolution des propriétés photophysiques en fonction de la température d'une série de complexes de lanthanide, Lnphen(TTA)3, a été étudiée. L'utilisation des équations de transfert d'énergie à barrière unique permet de mieux comprendre le mécanisme de transfert d'énergie. La dernière partie du travail se concentre sur l'étude de EuL1(TTA)3, qui est le premier complexe d'europium observable à transfert d'énergie singulet. L'étude de ce complexe à l'aide de diverses techniques de spectroscopie et de calculs ab initio permet de mieux comprendre le mécanisme de transfert d'énergie. Une phosphorescence ultralongue, observable jusqu'à 30 secondes à l'œil nu, est également observée dans le composé analogue, LaL1(TTA)3, dans un environnement cryogénique. Le mécanisme à l'origine de ce phénomène est révélé et l'application potentielle est également démontrée dans ce travail.Ever since the discovery of indirect sensitization of the unique lanthanide ions through organic ligands, namely antenna effect in 1942, lanthanide organic complexes were widely applied in various fields, including materials for lighting devices, biomedical diagnostics and imaging, and sensing agent. The energy transfer mechanism play an important role in improving the efficiency of light harvesting, which are usually associated with the S1 → T1 → Ln3+ pathway, although the direct singlet pathway is also observed and reported.In this work, the evolutions of the photophysical properties with temperature of a series of lanthanide complex, Lnphen(TTA)3 were investigated. Employing the single barrier back energy transfer equations, a deeper understanding on the energy transfer mechanism is elucidated. The latter part of the work focuses upon the investigation of EuL1(TTA)3, which is the first observable singlet energy transfer europium complex. Further in-depth insights on the energy transfer mechanism are provided upon investigating this complex using various spectroscopy techniques and ab initio calculations. An ultralong phosphorescence, observable up to 30 seconds by naked eye is also observed from the analogous compound, LaL1(TTA)3 under cryogenic environment. The mechanism behind this phenomenon is revealed and the potential application is also demonstrated in this work
Erratum: Reactivation of Epstein–Barr virus by a dual-responsive fluorescent EBNA1-targeting agent with Zn2+-chelating function (Proceedings of the National Academy of Sciences of the United States of America (2019) 116 (26614-26624) DOI: 10.1073/pnas.1915372116)
No full textCorrection for “Reactivation of Epstein–Barr virus by a dualresponsive fluorescent EBNA1-targeting agent with Zn2+- chelating function,” by Lijun Jiang, Hong Lok Lung, Tao Huang, Rongfeng Lan, Shuai Zha, Lai Sheung Chan, Waygen Thor, Tik-Hung Tsoi, Ho-Fai Chau, Cecilia Boreström, Steven L. Cobb, Sai Wah Tsao, Zhao-Xiang Bian, Ga-Lai Law, Wing-Tak Wong, William Chi-Shing Tai, Wai Yin Chau, Yujun Du, Lucas Hao Xi Tang, Alan Kwok Shing Chiang, Jaap M. Middeldorp, Kwok-Wai Lo, Nai Ki Mak, Nicholas J. Long, and Ka-Leung Wong, which was first published December 10, 2019; 10.1073/pnas.1915372116 (Proc. Natl. Acad. Sci. U.S.A. 116, 26614–26624). The authors note that Fig. 6 appeared incorrectly. Part of panel D of the published figure was inadvertently omitted. The corrected figure and its legend appear below. (Figure Presented)
Bimetallic porphyrin PET radiotracers for Low-Dose MRI contrast enhancement
No full textIn medical imaging, concerns over the risks associated with imaging agents have been consistently raised by doctors and patients, and ongoing efforts are being made to cautiously explore safer and more efficient compounds. There is continued interest in combining the well-known imaging modalities of positron emission tomography (PET) and magnetic resonance imaging (MRI). However, there has not been reported a singlemolecule probe offering dual-modal imaging without performance degradation. We herein present a potential solution wherein the compound, PGaLGd, incorporates radioactive Ga(III) for PET imaging whilst simultaneously being able to exhibit MRI contrast through a coordinated Gd(III) ion but at low concentrations/doses. Besides
elucidating MRI enhancing mechanisms through computational chemistry techniques, our compound has proven to be a successful dual-imaging agent for both PET and MRI in mice. Additionally, we conducted comprehensive in vitro and in vivo studies, assessing biosafety and photodynamic therapeutic potential across various cell lines and organoids. We have placed importance on interlinking structures, coordinated metals, adjacent ligands, and frontier molecular orbitals in our probe design to enhance water relaxation ability and move towards the design of next-generation low-dose imaging agents
Substrate Sequence Determines Catalytic Activities, Domain-Binding Preferences, and Allosteric Mechanisms in Pin1
No full textHeteropolynuclear Lanthanide(III) Complexes for Cooperative Sensitization Upconversion in Water
No full textInternational audienceWe report the synthesis of a tritopic ligand, L2, composed of two strongly binding lanthanide (Ln) sites using tris-functionalized triazacyclononane (tacn) scaffolds bridged by a weaker Ln binding triethylene glycol chain. Coordination chemistry of Ln3+ (Ln = Eu, Tb, Yb, Lu) was investigated by using NMR and photoluminescent spectroscopies. The first two Ln3+ ions are coordinated by the tacn scaffolds to form [LnL2] and [Ln2L2] species, followed by tri- and tetranuclear complexes, [Ln(Ln2L2)] and [Ln2(Ln2L2)]. The third and fourth exomacrocyclic binding events occur at the polyethylene glycol binding site, buttressed by a synergistic interaction of the phosphonate arms, confirmed by DFT modeling. [Ln2L2] (Ln = Tb, Eu, Yb, and Lu) homobimetallic complexes were prepared, and characterized and their spectroscopic properties determined in H2O and D2O. Titration of the [Yb2L2] dinuclear complex by Tb salts in D2O confirmed the formation of the tri- and tetranuclear species. Upon excitation into the 2F5/2 ← 2F7/2 absorption band of Yb at 980 nm, a cooperative sensitization upconversion process is evidenced, displaying visible Tb emission bands. Heating resulted in Ln scrambling in the tacn coordination sites, increasing the UC efficiency by ca. 103. The most efficient emitter for UC is the tetranuclear [TbYb(TbYbL2)], with one of each Ln3+ species in the tacn scaffolds and one of each Ln3+ species coordinated by the polyethylene glycol chain. Optimization on the pD led to an overall 9.0 × 10–7 UC quantum yield (λexc = 980 nm, P = 10.8 W·cm–2). The same experiment was repeated in water, affording UC at the molecular level
Complexes
No full textInternational audienceMn 2+ complexes of 2,4‐pyridyl‐disubstituted bispidine ligands have emerged as more biocompatible alternatives to Gd 3+ ‐based MRI probes. They display relaxivities comparable to that of commercial contrast agents and high kinetic inertness, unprecedented for Mn 2+ complexes. The chemical structure, in particular the substituents on the two macrocyclic nitrogens N3 and N7, are decisive for the conformation of the Mn 2+ complexes, and this will in turn determine their thermodynamic, kinetic and relaxation properties. We describe the synthesis of four ligands with acetate substituents in positions N3, N7 or both. We evidence that the bispidine conformation is dependent on N3 substitution, with direct impact on the thermodynamic stability, kinetic inertness, hydration state and relaxivity of the Mn 2+ complexes. These results unambiguously show that (i) solely a chair‐chair conformation allows for favorable inertness and relaxivity, and (ii) in this family such chair‐chair conformation is accessible only for ligands without N3‐appended carboxylates
Substrate Sequence Determines Catalytic Activities, Domain-Binding Preferences, and Allosteric Mechanisms in Pin1
No full textPin1
is a unique phosphorylation-dependent peptidyl–prolyl
isomerase that regulates diverse subcellular processes and an important
potential therapeutic target. Functional mechanisms of Pin1 are complicated
because of the two-domain structural organization: the catalytic domain
both binds the specific pSer/Thr-Pro motif and catalyzes the cis/trans
isomerization, whereas the WW domain can only bind the trans configuration
and is speculated to be responsible for substrate-binding specificity.
Numerous studies of Pin1 have led to two divergent conclusions on
the functional role of the WW domain. One opinion states that the
WW domain is an allosteric effector, and substrate binding to this
domain modulates the binding and catalysis in the distal catalytic
domain. The other opinion, however, argues that the WW domain does
not have any allosteric role. Here, using molecular dynamics and binding
free-energy calculations, we examine catalysis and allosteric mechanisms
in Pin1 under various substrate- and WW-binding conditions. Our results
reveal a strong substrate sequence dependency of catalysis, domain-binding
preferences, and allosteric outputs in Pin1. Importantly, we show
that the different opinions about the WW domain can be unified in
one framework, in which substrate sequences determine whether a positive,
negative, or neural allosteric effect will be elicited. Our work further
elucidates detailed mechanisms underlying the sequence-dependent allostery
of Pin1 and finds that interdomain contacts are key mediators of intraprotein
allosteric communications. Our findings collectively provide new insights
into the function of Pin1, which may facilitate the development of
novel therapeutic drugs targeting Pin1 in the future
Energy Transfer Mechanism and Quantitative Modeling of Rate from an Antenna to a Lanthanide Ion
No full textThe excitation energy transfer (ET) pathway and
mechanism from an organic antenna to a lanthanide ion has been the
subject of discussion for many decades. In the case of europium (Eu3+), it has been suggested that the transfer originates from
the ligand singlet state or a triplet state. Taking the lanthanide
complex Eu(TTA)3(H2O)2 as an example, we have investigated the spectra and luminescence
kinetics, mainly at room temperature and 77 K, to acquire the necessary
experimental data. We put forward an experimental and theoretical
approach to measure the energy transfer rates from the antenna to
different Eu3+ levels using the Dexter formulation. We
find that transfer from the ligand singlet state to Eu3+ may account for the ET pathway, by combined electric dipole–electric
dipole (ED–ED) and ED-electric quadrupole (EQ) mechanisms.
The contributions from the triplet state by these mechanisms are very
small. An independent systems rate equation approach can effectively
model the experimental kinetics results. The model utilizes the cooperative
processes that take place on the metal ion and ligand and considers
S0, S1, and T1 ligand states in addition
to 7F0,1, 5D0, 5D1, and 5DJ (=5L6, 5D3, 5D2 combined) Eu3+ states. The triplet exchange ET rate is estimated to be
of the order 107 s–1. The observation
of a nanosecond risetime for the Eu3+ 5D1 level does not enable the assignment of the ET route or the mechanism.
Furthermore, the 5D1 risetime may be contributed
by several processes. Observation of its temperature dependence and
also that of the ground-state population can supply useful information
concerning the mechanism because the change in metal-ion internal
conversion rate has a greater effect than changes in singlet or triplet
nonradiative rates. A critical comparison is included for the model
of Malta employed in the online software LUMPAC and JOYSpectra. The
theoretical treatment of the exchange mechanism and its contribution
are now being considered
Semiconducting divalent organic spacer-assisted charge transport in lead-free layered perovskites
No full textBulky naphthalene diimide-based cations enable layered Sn–I perovskites with type-II nanoheterojunctions, enhancing charge lifetime, out-of-plane electron mobility, and air stability, advancing prospects for stable tin-based optoelectronics.LIMN
Solution-State Cooperative Luminescence Upconversion in Molecular Ytterbium Dimers
No full textInternational audienceTwo homometallic ytterbium dimers are prepared and their solution-state photoluminescence and upconversion properties are investigated. Both complexes exhibit two-photon cooperative luminescence upconversion in the visible region (lambda(em) approximate to 510 nm) upon excitation into the near-infrared Yb F-2(5/2) <- F-2(7/2) absorption band at 980 nm. This miniaturization of the cooperative luminescence phenomenon down to just two Yb ions unequivocally proves the mechanistic origins of this process. Time-resolved measurements and excited-state modeling indicate the presence of a slow recombination of two singly excited ions Yb*Yb* into a virtual excited state, which ultimately gives rise to the observed emission at approximate to 510 nm
