Lanthanide Podates with Programmed Intermolecular Interactions: Luminescence Enhancement through Association with Cyclodextrins and Unusually Large Relaxivity of the Gadolinium Self-Aggregates

Structure Kinetics Relationships and Molecular Dynamics Show Crucial Role for Heterocycle Leaving Group in Irreversible Diacylglycerol Lipase Inhibitors

Drug discovery programs of covalent irreversible, mechanism-based enzyme inhibitors often focus on optimization of potency as determined by IC₅₀-values in biochemical assays. These assays do not allow the characterization of the binding activity (K_i) and reactivity (k_inact) as individual kinetic parameters of the covalent inhibitors. Here, we report the development of a kinetic substrate assay to study the influence of the acidity (pK_a) of heterocyclic leaving group of triazole urea derivatives as diacylglycerol lipase (DAGL)-α inhibitors. Surprisingly, we found that the reactivity of the inhibitors did not correlate with the pK_a of the leaving group, whereas the position of the nitrogen atoms in the heterocyclic core determined to a large extent the binding activity of the inhibitor. This finding was confirmed and clarified by molecular dynamics simulations on the covalently bound Michaelis–Menten complex. A deeper understanding of the binding properties of covalent serine hydrolase inhibitors is expected to aid in the discovery and development of more selective covalent inhibitors.

Tunable Luminescence Contrast of Na0.5Bi4.5Ti4O15:Re (Re = Sm, Pr, Er) Photochromics by Controlling the Excitation Energy of Luminescent Centers

High luminescent switching contrast of photochromic materials is extremely important in improving the sensitivity and resolution of optical switches and high-density optical data storage devices. To date, conventional methods, such as tuning absorption and emission bands based on electron or resonance energy transfer mechanisms in well-known organic photochromic molecules or compounds, have routinely been adopted to tune luminescent switching behavior. However, these strategies and mechanisms are not effectively applied to luminescence switching in inorganic materials because their crystal structures differ strongly from those of organic materials. In this paper, we report a new method to significantly tune the luminescent switching contrast by modifying the excitation energy of luminescent centers in a newly synthesized photochromism material: Na_0.5Bi_4.5Ti₄O₁₅:Re (Re = Sm, Pr, Er). A significant enhancement of luminescence switching contrast was achieved when the luminescent centers were excited by low energy photons at a given irradiation wavelength, intensity, and time, compared with high excitation energy photons. The trend "the lower the excitation energy, the higher the luminescence switching contrast" is universal in different rare earth ion-doped Na_0.5Bi_4.5Ti₄O₁₅ ferroelectrics. The changes in the luminescent switching contrast based on excitation energy are ascribed to nonradiative energy transfer from the luminescent center to the color center by dipole-dipole interactions according to Dexter theory. This possible utilization of excitation energy at lower energy levels is usually less destructive to both information recording and the recording material itself during luminescent readout processes while achieving higher luminescence switching contrast.

3-Substituted pyrazoles and 4-substituted triazoles as inhibitors of human 15-lipoxygenase-1

Investigation of 1N-substituted pyrazole-3-carboxanilides as 15-lipoxygenase-1 (15-LOX-1) inhibitors demonstrated that the 1N-substituent was not essential for activity or selectivity. Additional halogen substituents on the pyrazole ring, however, increased activity. Further development led to triazole-4-carboxanilides and 2-(3-pyrazolyl) benzoxazoles, which are potent and selective 15-LOX-1 inhibitors.

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.

Combined approaches for drug design points the way to novel proline racemase inhibitor candidates to fight Chagas' disease

Chagas' disease is caused by Trypanosoma cruzi, a protozoan transmitted to humans by blood-feeding insects, blood transfusion or congenitally. Previous research led us to discover a parasite proline racemase (TcPRAC) and to establish its validity as a target for the design of new chemotherapies against the disease, including its chronic form. A known inhibitor of proline racemases, 2-pyrrolecarboxylic acid (PYC), is water-insoluble. We synthesized soluble pyrazole derivatives, but they proved weak or inactive TcPRAC inhibitors. TcPRAC catalytic site is too small and constrained when bound to PYC to allow efficient search for new inhibitors by virtual screening. Forty-nine intermediate conformations between the opened enzyme structure and the closed liganded one were built by calculating a transition path with a method we developed. A wider range of chemical compounds could dock in the partially opened intermediate active site models in silico. Four models were selected for known substrates and weak inhibitors could dock in them and were used to screen chemical libraries. Two identified soluble compounds, (E)-4-oxopent-2-enoic acid (OxoPA) and its derivative (E)-5-bromo-4-oxopent-2-enoic acid (Br-OxoPA), are irreversible competitive inhibitors that presented stronger activity than PYC on TcPRAC. We show here that increasing doses of OxoPA and Br-OxoPA hamper T. cruzi intracellular differentiation and fate in mammalian host cells. Our data confirm that through to their binding mode, these molecules are interesting and promising as lead compounds for the development of chemotherapies against diseases where active proline racemases play essential roles.

Synthesis and optical properties of macrocyclic lanthanide(III) chelates as new reagents for luminescent biolabeling

The convenient and efficient synthesis of two macrocyclic ligands (15- and 18-membered) based on a dipyrido-6,7,8,9-tetrahydrophenazine (dpqc) or 2,2':6',2''-terpyridine (tpy) heterocycle and a DTTA (diethylenetriaminetriacetic acid) skeleton is described. In these ligands the DTTA skeleton contains an additional extracyclic functionality (NH(2) group) suitable for covalent attachment to bioactive molecules. These octa- and nonadentate ligands form very stable and luminescent neutral lanthanide complexes in aqueous solutions at physiological pH. The corresponding Eu(III) and Tb(III) complexes are characterized by a maximum absorption wavelength compatible with nitrogen laser excitation (337 nm) and attractive lifetimes and quantum yields. Further introduction of a maleimide bioconjugatable handle in the Eu(III) complexes was investigated and a valuable luminescence brightness above 1500 dm(3) mol(-1) cm(-1) at 337 nm was obtained with the corresponding Eu(III) tpy-derivative. Finally, these two luminescent chelates were grafted onto thiol residues of a model antibody (Mab GSS11) without loss of their luminescent properties.

Cyclometalated Ir(III) Complexes Containing Pyrazole/Pyrazine Carboxylate Ligands

Two cyclometalated Ir(iii) complexes using 2-phenylpyridine (ppy-H) as the cyclometalating ligand, and pyrazole-3-carboxylic acid (prca-H) and pyrazine 3,5-dicarboxylic acid (pzdca-H2) as ancillary ligands; were synthesized from the chloro-bridged dimer precursor [{(ppy)2Ir}2(μ-Cl)2]. The title compounds [Ir(ppy)2(prca)] (1) and [{Ir(ppy)2}2(pzdca)] (2) are monomeric and dimeric neutral Ir(iii) complexes, respectively. Their electrochemical and photophysical properties were examined. They exhibit metal-based oxidations and ligand-based reductions. These complexes exhibit emission in the blue-green region with lifetimes in the micro-second range at room temperature. The nature of the emission spectra indicates differences in the origin of emission in these two compounds.

Effect of a mesitylene-based ligand cap on the relaxometric properties of Gd(III) hydroxypyridonate MRI contrast agents

A series of new Gd(III) hydroxypyridonate complexes featuring a mesitylene (ME)-derived ligand cap has been prepared. Relaxometric characterization reveals that the complexes tend to form large aggregates in solution with slow tumbling rates, as estimated from NMRD analysis, and unique pH-dependent relaxivities. The solution behavior and relaxometric properties are compared with those observed for analogous TREN-capped compounds, and the potential for use of these new ME-capped complexes as pH-responsive MRI contrast agents is explored.

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

Solid complexes of lanthanide nitrates, picrates and perchlorates with a novel multipodal ligand, 1,2,4,5-tetramethyl-3,6-bis{N,N-bis[((2'-benzylaminoformyl)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 Eu and Tb 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 T(1) of this ligand matches better to the lowest resonance energy level of Tb(III) than to Eu(III) ion. The influence of the counter anion on the luminescent intensity was also discussed.

Assessing the Slow Magnetic Relaxation Behavior of LnIII4MnIII6 Metallacrowns

A Dy(III)4Mn(III)6 complex with a metallacrown (MC)-like topology possesses frequency-dependent magnetic behavior, indicating possible single-molecule magnet behavior.

New Luminescent Europium(III) Chelates for DNA Labeling

The new europium(III) chelate [2,2',2'',2'''-[[4'-(aminobiphenyl-4-yl)-2,2':6',2''-terpyridine- 6,6''-diyl]bis(methylenenitrilo)]tetrakis(acetato)] europium(III) (ATBTA-Eu3+) and its 4,6-dichloro-1,3,5-triazinyl and succinimidyl derivatives (DTBTA and NHS-ATBTA, respectively) were synthesized and characterized. Both labeling complexes DTBTA-Eu3+ and NHS-ATBTA-Eu3+ are luminescent. Especially DTBTA-Eu3+ is strongly luminescent, with a luminescence quantum yield of 9.1%, molar extinction coefficient of 3.1 x 10(4) cm(-1) M(-1) (335 nm), and luminescence lifetime of 1.02 ms. The excitation and emission maximum wavelengths of DTBTA-Eu3+ are 335 and 616 nm, respectively. The complex is very stable in aqueous buffers, with a conditional formation constant log K(DTBTA-Eu) of 25.0 at pH 8, and can be conjugated to DNA and proteins. The chelates are also highly resistant to thermal decomposition, photodegradation, and ozone oxidation. These properties prove that DTBTA-Eu3+ is suitable as a luminescence label in DNA assays.

Lanthanides in magnetic resonance imaging

Magnetic Resonance Imaging is perhaps the most important and prominent technique in diagnostic clinical medicine and biomedical research. Its success and development as an imaging technique has been aided by the characteristics of contrast agents that enhance signal intensities and improve specificity. Gadolinium(iii) remains the dominant starting material for contrast agent design but other lanthanide ions (and other oxidation states i.e. +2) are also being increasingly investigated as alternatives to gadolinium(III) within laboratory conditions. This critical review provides a concise summary of the MRI-active gadolinium(III) complexes to date--their pros and cons, an outline of contrast agents based on other lanthanide ions (e.g. europium, dysprosium), and directs the reader to newer, more speculative areas of lanthanide-containing contrast agent design.

Synthesis and infrared and luminescence spectra of rare earth complexes with a new hexapodal ligand

Solid complexes of rare earth nitrates and picrates with a new hexapodal ligand, 1,2,3,4,5,6-hexa{[(2'-benzylamino-formyl)phenoxyl]methyl}-benzene (L) have been prepared. These complexes were characterized by elemental analysis, IR and molar conductivity. At the same time, the luminescence properties of the Eu(III) and Tb(III) nitrates and picrates complexes in solid state were also investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of europium and terbium ions. The influence of the counter anion on the luminescent intensity was also discussed.

Benefiting from the unique properties of lanthanide ions

The recent upsurge of interest in contrast agents for magnetic resonance imaging, of luminescent chemosensors for medical diagnostic, and lately, for optical imaging of cells has generated an impressive momentum for the coordination and supramolecular chemistry of trivalent lanthanide ions. We shortly review the synthetic methods allowing the introduction of these spherical ions with fascinating optical and magnetic properties into elaborate mono- and polymetallic edifices. We then illustrate these methods by selected examples describing the use of (i) a coronand to produce luminescent liquid crystals, (ii) derivatized calixarenes for 4f-5f element separation, (iii) podates for the production of nanoparticles with high relaxivity and for sensitizing the near-infrared (NIR) emission, and (iv) self-assembly processes for producing functional bimetallic edifices.

Isophthalato-Based 2D Coordination Polymers of Eu(III), Gd(III), and Tb(III): Enhancement of the Terbium-Centered Luminescence through Thiophene Derivatization

We present here the first examples of lanthanide ion complexes with only isophthalic acid or thiophenylisophthalic acid ligands. The complexes of isophthalic acid with Eu(3+) (1) and Tb(3+) (2) and the moderately soluble complexes of 5-thiophen-3-ylisophthalate with Eu(3+) (3), Gd(3+) (4), and Tb(3+) (5) were isolated as single crystals through gel crystallization. X-ray diffraction studies confirm the cross-linking structure of these complexes, which, in case of the thiophenyl derivatives, results in low solubility in common solvents. The two-dimensional isophthalato complex of Eu(3+) (1) crystallizes in the C2/c space group, with a = 22.154(4), b = 12.649(3), and c = 15.921(3) A, beta = 112.34(3) degrees, and V = 4126.7(14) A(3), while the one-dimensional Tb(3+) complex of the same ligand, 2, crystallizes in the space group P2(1)/c with a = 11.921(2), b = 10.838(2), and c = 17.499(4) A, beta = 92.44(3) degrees, and V = 2258.9(8) A(3). The thiophenylisophthalato complexes of Eu(3+) (3) and Gd(3+) (4) are two-dimensional and crystallize in the P2/n space group with parameters for 3 of a = 14.139(3), b = 10.684(2), and c = 15.138(3) A, beta = 102.51(3) degrees, and V = 2232.3(8) A(3) and parameters for 4 of a = 14.1195(13), b = 10.6594(10), and c = 15.1149(14) A, beta = 102.529(2) degrees, and V = 2220.7(4) A(3), while the Tb(3+) complex, 5, also two-dimensional, crystallizes in the P space group with a = 11.051(2), b = 14.528(3), and c = 15.041(3) A, alpha = 77.63(3), beta = 87.86(3), and gamma = 83.51(3) degrees, and V = 2343.48 A(3). All complexes of Eu(3+) and Tb(3+) luminesce in aqueous solution, and the luminescence lifetimes and quantum yields are 123.8 +/- 7.4, 0.14% (1), 475.1 +/- 14.5, 3.58% (3), 129.3 +/- 3.5, 0.19% (4), and 213.9 +/- 2.2 micros, 7.46% (5).

First Octameric Ellipsoid Lanthanide(III) Complexes: Crystal Structure and Nonlinear Optical Absorptive and Refractive Properties

The ligand N,N'-bis(1,3,4-thiobiazolyl)-2,6-pyridyldicarboxamide (btapca) has been synthesized and its coordination properties toward La(III) and Ce(III) in the presence of air have been investigated. The complexes [Ln8(tbzcapc)12(H2O)24].6DMF (Ln = La, 1, Ce, 2; tbzcapc = 6-[2-N-(1,3,4-thiabiazolyl)carboxamido]-2-pyridylcarboxylate) show octameric ellipsoid structures. We found the starting ligand btapca had been altered into tbzcapc during the formation process of [Ln8(tbzcapc)12(H2O)24].6DMF. The NLO properties of complexes 1 and 2 were investigated via Z-scan techniques. It is interesting that the two isostructural complexes show completely different NLO properties. Complex 1 shows NLO refractive effects without absorption, while complex 2 possesses NLO absorptive behavior without refraction.

First soluble M@C60 derivatives provide enhanced access to metallofullerenes and permit in vivo evaluation of Gd@C60[C(COOH)2]10 as a MRI contrast agent

M@C(60) and related endohedral metallofullerenes comprise a significant portion of the metallofullerene yield in the traditional arc synthesis, but their chemistry and potential applications have been largely overlooked because of their sparse solubility. In this work, procedures are described to solublize Gd@C(60) species for the first time by forming the derivative, Gd@C(60)[C(COOCH(2)CH(3))(2)](10), and its hydrolyzed water-soluble form, Gd@C(60)[C(COOH)(2)](10). Imparting water solubility to Gd@C(60) permits its evaluation as a magnetic resonance imaging (MRI) contrast agent. Relaxometry measurements for Gd@C(60)[C(COOH)(2)](10) reveal it to possess a relaxivity (4.6 mM(-1) s(-1) at 20 MHz and 40 degrees C) comparable to that of commercially available Gd(III) chelate-based MRI agents. An in vivo MRI biodistribution study in a rodent model reveals Gd@C(60)[C(COOH)(2)](10) to possess the first non-reticuloendothelial system (RES) localizing behavior for a water-soluble endohedral metallofullerene species, consistent with its lack of intermolecular aggregation in solution as determined by light-scattering measurements. This first derivatization and use of a M@C(60) species suggests new potential for metallofullerene technologies by reducing reliance on the chromatographic purification procedures normally employed for the far less abundant M@C(82) and related endohedrals. The recognition that water-soluble fullerene derivatives can be designed to avoid high levels of RES uptake is an important step toward fullerene-based pharmaceutical development.

Cation-controlled self-assembly of a hexameric europium wheel

The simple asymmetric tetradentate ligand 2,2':6',2' '-terpyridine-6-carboxylic acid leads to the self-assembly of the first europium nanowheel containing europium ions in two different coordination environments. Moreover the self-assembly of bis(terpyridinecarboxylate) europium species to form a hexameric wheel capable of strongly binding LnIII cations is controlled by the ligand/cation ratio.

Noncovalent binding of sensitizers for lanthanide(III) luminescence in an EDTA-bis(beta-cyclodextrin) ligand

EDTA-linked beta-cyclodextrin dimer 3 was synthesized from EDTA bis(anhydride) 1 and mono(propylamino)-appended beta-cyclodextrin 2. p-tert-butylbenzoate 5, bound by the beta-cyclodextrin cavities of 3 with an association constant of 10(4) M(-1) in water, acts as a sensitizer for the Eu(III) and Tb(III) complexes of 3. Luminescence spectroscopy, microcalorimetry, and Gd(III)-induced NMR relaxation rate measurements prove that 3 forms a 1:2 complex with 5 and that one of the beta-cyclodextrin-bound sensitizers coordinates to the EDTA-encapsulated Ln(III) ion. The Eu(III) complex of 3 forms strong 1:1 complexes (K approximately 10(7) M(-1)) with bis(propylamido adamantyl)-functionalized biphenyl sensitizers 7 and 8 in water. Both beta-cyclodextrins of 3 are involved in the binding of these guests. The amide functionality adjacent to the biphenyl unit in 7 and 8 coordinates to the EDTA-encapsulated Ln(III) ion. For these biphenyl-based antennae both binding to beta-cyclodextrin and coordination to the Ln(III) center are crucial for efficient sensitization.