Luminescent Supramolecular Metallogels: Drug Loading and Eu(III) as Structural Probe.

Supramolecular metallogels combine the rheological properties of gels with the color, magnetism, and other properties of metal ions. Lanthanide ions such as Eu(III) can be valuable components of metallogels due to their fascinating luminescence. In this work, we combine Eu(III) and iminodiacetic acid (IDA) into luminescent hydrogels. We investigate the tailoring of the rheological properties of these gels by changes in their metal:ligand ratio. Further, we use the highly sensitive Eu(III) luminescence to obtain information about the chemical structure of the materials. In special, we take advantage of computational calculations to employ an indirect method for structural elucidation, in which the simulated luminescent properties of candidate structures are matched to the experimental data. With this strategy, we can propose molecular structures for different EuIDA gels. We also explore the usage of these gels for the loading of bioactive molecules such as OXA, observing that its aldose reductase activity remains present in the gel. We envision that the findings from this work could inspire the development of luminescent hydrogels with tunable rheology for applications such as 3D printing and imaging-guided drug delivery platforms. Finally, Eu(III) emission-based structural elucidation could be a powerful tool in the characterization of advanced materials.

Consequences of thimerosal on human erythrocyte hemoglobin: Assessing functional and structural protein changes induced by an organic mercury compound.

BACKGROUND: Thimerosal (TM) is an organic mercury compound used as a preservative in many pharmacological inputs. Mercury toxicity is related to structural and functional changes in macromolecules such as hemoglobin (Hb) in erythrocytes (Ery). METHOD: Human Hb and Ery were used to evaluate O2 uptake based on the TM concentration, incubation time, and temperature. The influence of TM on the sulfhydryl content, production of reactive oxygen species (ROS), and membrane fragility was also evaluated. Raman spectra and atomic force microscopy (AFM) profiles for Ery in the presence and absence of TM were calculated, and docking studies were performed. RESULTS: At 37 °C, with 2.50 µM TM (higher concentration) and after 5 min of incubation in Hb and Ery, we observed a reduction in O2 uptake of up to 50 %, while HgCl2, which was used as a positive control, showed a reduction of at least 62 %. Total thiol assays in the presence of NEM (thiol blocker) quantified the preservation of almost 60 % of free SH in Ery. Based on the Raman spectrum profile from Ery-TM, structural differences in the porphyrinic ring and the membrane lipid content were confirmed. Finally, studies using AFM showed changes in the morphology and biomechanical properties of Ery. Theoretical studies confirmed these experimental results and showed that the cysteine (Cys) residues present in Hb are involved in the binding of TM. CONCLUSION: Our results show that TM binds to human Hb via free Cys residues, causing conformation changes and leading to harmful effects associated with O2 transport.

Tuning the luminescence efficiency by perfluorination of side chains in Eu3+ complexes with ß-diketones of the thiophene series.

A series of europium and gadolinium complexes comprising a ß-diketone moiety modified with a fluorinated side-group and thiophene ring have been designed and synthesized and a comparative study of their luminescence properties has been carried out. In this study, when the methyl side group was modified by sequential addition of fluorine substituents and then the perfluorinated carbon chain was extended up to n-C8F17 by adding CF2 fragments, it transpired that the non-radiative energy processes are significantly suppressed in structurally more rigid polyfluorinated ß-diketonate compounds of the series as C-H oscillators are replaced with low-energy C-F oscillators. The impact of other electron-withdrawing and electron-donating substituents on the spectroscopic and photophysical properties of the complexes in the present study has also been observed. Despite the presence of low-lying ligand-to-metal charge transfer states, the fluorinated Eu3+ complexes proved to be bright luminophores capable of delivering ca. 50% quantum yield under UV radiation. The role of fluorination and carbon chain length was examined by using experimental spectroscopic methods and the results obtained were largely in good agreement with theoretical calculations (Judd-Ofelt theory analysis, and semiempirical quantum chemistry calculations) supporting our key experimental findings.

Experimental and Theoretical Studies of Glyphosate Detection in Water by an Europium Luminescent Complex and Effective Adsorption by HKUST-1 and IRMOF-3.

Designing an effective and simple detection method to quantify glyphosate (GLY) herbicide is desirable. Current chromatography-mass spectrometry and electrochemical methods can be used for this purpose, but these methods are difficult to be made portable and need high-cost equipment. Here, we evaluate a luminescent ß-diketonate-Eu-ethylenediaminetetraacetic acid complex for GLY quantification in aqueous media on the basis of the luminescent quenching process. This complex successfully measured GLY at concentrations ranging from 5 × 10-7 to 10-5 mol L-1. Theoretical methods (LUMPAC) are also performed to identify the complex most probable structure in solution. We also demonstrate that the metal-organic frameworks HKUST-1 and IRMOF-3, easily synthesized, effectively adsorb GLY in water in about 30 min of contact.

Mononuclear lanthanide(III)-oxamate complexes as new photoluminescent field-induced single-molecule magnets: solid-state photophysical and magnetic properties.

Implementing additional optical (luminescent) properties into the well-known class of single-molecule magnets (SMMs) is considered as a promising route toward obtaining the next generation of optomagnetic materials for quantum information storage and computing. Herein, we report a joint optical and magneto-structural study for the two novel series of lanthanide(iii) complexes of general formula Bu4N[LnIII(HL)4(dmso)]·nH2O where H2L = N-(4-Xphenyl)oxamic acid with X = Cl and n = 2 [Ln = Eu (1_Cl), Gd (2_Cl), Dy (3_Cl), and Tb (4_Cl)] and X = F and n = 3 [Ln = Eu (1_F), Gd (2_F), Dy (3_F), and Tb (4_F)]. All these compounds are mononuclear species with each lanthanide(iii) cation in a low-symmetry nine-coordinate environment (LnO9) which is constituted by four didentate monoprotonated oxamate groups and one dmso molecule. Magnetic measurements show the occurrence of field-induced SMM behavior for the Gd3+ (2_Cl and 2_F), Dy3+ (3_Cl and 3_F), and Tb3+ complexes (4_Cl and 4_F). Solid-state photophysical measurements for the Eu3+ (1_Cl and 1_F) and Tb3+ complexes (4_Cl and 4_F) reveal that both monoprotonated chloro- and fluoro-substituted phenyl(oxamate) ligands are able to sensitize the lanthanide(iii)-based luminescence in the visible region, through an energy transfer process ("antenna effect"), as supported by theoretical calculations for Eu3+ compounds. In particular, 1_Cl and 1_F present a quantum efficiency of approximately 50%, being potentially suitable as efficient light conversion molecular devices (LCMDs).

Lanthanide Contraction in Lanthanide Organic Frameworks: A Theoretical and Experimental Study.

In this work, the lanthanide (Ln) contraction phenomenon has been analyzed for three-dimensional structures in the solid state. We chose to study an isostructural series of lanthanide organic frameworks (LOFs) of formula [Ln2(C4H4O4)3(H2O)2]n·H2O and 14 crystallographic structures (except promethium complex). The analysis of Ln contraction was made by analyzing the sum of all Ln-O bond lengths and the sum of all O-O distances, for the oxygen atoms of the coordination polyhedra, calculated with different semiempirical quantum mechanical models. The ∑Ln-O and ∑O-O for this LOF can be fit to a second-order polynomial. Based on the crystallographic structures, it is concluded that the phenomenon of Ln contraction is observed. Our results also suggest that the semiempirical Sparkle/PM3 and Sparkle/RM1 models reproduce the Ln contraction phenomenon well, and similar fits were obtained for ∑Ln-O and ∑O-O bond lengths.

Are the Absorption Spectra of Doxorubicin Properly Described by Considering Different Tautomers?

The elucidation of the action of doxorubicin (DOX) has been considered a challenge for cancer therapy. Using theoretical approaches, we investigated the structure and electronic properties of DOX as a function of pH, which we thought likely to be related to the influence of its tautomers. Regarding the relative stabilities among the tautomers, the results obtained from PM6 were the most similar to those obtained from DFT. The theoretical absorption spectrum for each tautomeric species simply showed a single absorption peak located around 400 nm, in contrast to the experimental absorption spectra in the literature that showed four absorption bands. The experimental evidence was properly explained by considering four tautomeric conformers of DOX. The spectroscopic study of the deprotonated tautomers also suggested the presence of four deprotonated tautomers at more basic pH values. The spectrum at pH 10.08 can be explained by the presence of protonated and deprotonated doxorubicin species.

Estimating the Individual Spectroscopic Properties of Three Unique EuIII Sites in a Coordination Polymer.

We isolated a coordination polymer with the formula [Eu3(3,5-dcba)9(H2O)(dmf)3]·2dmf, with three unique EuIII coordination sites in the asymmetric unit, with the EuIII ions bridged by 3,5-dichlorobenzoato (3,5-dcba) ligands. The coordination polymer crystallized in the triclinic space group P1̅ with unit cell dimensions a = 12.4899(15), b = 16.326(2), and c = 25.059(3) Å, α = 84.271(3)°, ß = 84.832(3)°, and γ = 68.585(3)° and V = 4725.2(10) Å3. The characteristic 5D0 → 7F J ( J = 0-4) EuIII transitions were observed upon ligand-centered excitation. Emission lifetimes of 0.825 ± 0.085 and 1.586 ± 0.057 ms were observed and were attributed to the sites with coordination of water or dimethylformamide (dmf) molecules to each ion, respectively. Through a combination of spectroscopy and calculations, we determined the photophysical properties of each unique EuIII site. Energy-transfer rates ligand → EuIII were determined for each unique site using the overlapped polyhedra method. The rates depend on the coordinated water molecules and the different donor-acceptor distances. The two sites without coordinated water molecules and shortest donor-acceptor distance display the fastest energy-transfer rate ligand → EuIII, whereas the site with coordinated water molecules and longest donor-acceptor distance displays the slowest energy-transfer rate. Donor-acceptor distances were estimated computationally and were confirmed by calculating the frontier orbitals in the asymmetric units of the polymer using density functional theory.

Parameters for the RM1 Quantum Chemical Calculation of Complexes of the Trications of Thulium, Ytterbium and Lutetium.

The RM1 quantum chemical model for the calculation of complexes of Tm(III), Yb(III) and Lu(III) is advanced. Subsequently, we tested the models by fully optimizing the geometries of 126 complexes. We then compared the optimized structures with known crystallographic ones from the Cambridge Structural Database. Results indicate that, for thulium complexes, the accuracy in terms of the distances between the lanthanide ion and its directly coordinated atoms is about 2%. Corresponding results for ytterbium and lutetium are both 3%, levels of accuracy useful for the design of lanthanide complexes, targeting their countless applications.

Chemical Partition of the Radiative Decay Rate of Luminescence of Europium Complexes.

The spontaneous emission coefficient, Arad, a global molecular property, is one of the most important quantities related to the luminescence of complexes of lanthanide ions. In this work, by suitable algebraic transformations of the matrices involved, we introduce a partition that allows us to compute, for the first time, the individual effects of each ligand on Arad, a property of the molecule as a whole. Such a chemical partition thus opens possibilities for the comprehension of the role of each of the ligands and their interactions on the luminescence of europium coordination compounds. As an example, we applied the chemical partition to the case of repeating non-ionic ligand ternary complexes of europium(III) with DBM, TTA, and BTFA, showing that it allowed us to correctly order, in an a priori manner, the non-obvious pair combinations of non-ionic ligands that led to mixed-ligand compounds with larger values of Arad.

Europium Luminescence: Electronic Densities and Superdelocalizabilities for a Unique Adjustment of Theoretical Intensity Parameters.

We advance the concept that the charge factors of the simple overlap model and the polarizabilities of Judd-Ofelt theory for the luminescence of europium complexes can be effectively and uniquely modeled by perturbation theory on the semiempirical electronic wave function of the complex. With only three adjustable constants, we introduce expressions that relate: (i) the charge factors to electronic densities, and (ii) the polarizabilities to superdelocalizabilities that we derived specifically for this purpose. The three constants are then adjusted iteratively until the calculated intensity parameters, corresponding to the (5)D0→(7)F2 and (5)D0→(7)F4 transitions, converge to the experimentally determined ones. This adjustment yields a single unique set of only three constants per complex and semiempirical model used. From these constants, we then define a binary outcome acceptance attribute for the adjustment, and show that when the adjustment is acceptable, the predicted geometry is, in average, closer to the experimental one. An important consequence is that the terms of the intensity parameters related to dynamic coupling and electric dipole mechanisms will be unique. Hence, the important energy transfer rates will also be unique, leading to a single predicted intensity parameter for the (5)D0→(7)F6 transition.

RM1 Semiempirical Quantum Chemistry: Parameters for Trivalent Lanthanum, Cerium and Praseodymium.

The RM1 model for the lanthanides is parameterized for complexes of the trications of lanthanum, cerium, and praseodymium. The semiempirical quantum chemical model core stands for the [Xe]4fn electronic configuration, with n =0,1,2 for La(III), Ce(III), and Pr(III), respectively. In addition, the valence shell is described by three electrons in a set of 5d, 6s, and 6p orbitals. Results indicate that the present model is more accurate than the previous sparkle models, although these are still very good methods provided the ligands only possess oxygen or nitrogen atoms directly coordinated to the lanthanide ion. For all other different types of coordination, the present RM1 model for the lanthanides is much superior and must definitely be used. Overall, the accuracy of the model is of the order of 0.07Å for La(III) and Pr(III), and 0.08Å for Ce(III) for lanthanide-ligand atom distances which lie mostly around the 2.3Å to 2.6Å interval, implying an error around 3% only.

A Eu(III) tetrakis(ß-diketonate) dimeric complex: photophysical properties, structural elucidation by Sparkle/AM1 calculations, and doping into PMMA films and nanowires.

Reaction of Ln(III) with a tetrakis(diketone) ligand H4L [1,1'-(4,4'-(2,2-bis((4-(4,4,4-trifluoro-3-oxobutanoyl) phenoxy)methyl)propane-1,3-diyl)bis(oxy)bis(4,1-phenylene))bis(4,4,4-trifluorobutane-1,3-dione)] gives new podates which, according to mass spectral data and Sparkle/AM1 calculations, can be described as dimers, (NBu4[LnL])2 (Ln = Eu, Tb, Gd:Eu), in both solid-state and dimethylformamide (DMF) solution. The photophysical properties of the Eu(III) podate are compared with those of the mononuclear diketonate (NBu4[Eu(BTFA)4], BTFA = benzoyltrifluoroacetonate), the crystal structure of which is also reported. The new Eu(III) dimeric complex displays bright red luminescence upon irradiation at the ligand-centered band in the range of 250-400 nm, irrespective of the medium. The emission quantum yields and the luminescence lifetimes of (NBu4[EuL])2 (solid state: 51% ± 8% and 710 ± 2 µs; DMF: 31% ± 5% and 717 ± 1 µs) at room temperature are comparable to those obtained for NBu4[Eu(BTFA)4] (solid state: 60 ± 9% and 730 ± 5 µs; DMF: 30 ± 5% and 636 ± 1 µs). Sparkle/AM1 calculations were utilized for predicting the ground-state geometries of the Eu(III) dimer. Theoretical Judd-Ofelt and photoluminescence parameters, including quantum yields, predicted from this model are in good agreement with the experimental values, proving the efficiency of this theoretical approach implemented in the LUMPAC software (http://lumpac.pro.br). The kinetic scheme for modeling energy transfer processes show that the main donor state is the ligand triplet state and that energy transfer occurs on both the (5)D1 (44.2%) and (5)D0 (55.8%) levels. Furthermore, the newly obtained Eu(III) complex was doped into a PMMA matrix to form highly luminescent films and one-dimensional nanowires having emission quantum yield as high as 67%-69% (doping concentration = 4% by weight); these materials display bright red luminescence even under sunlight, so that interesting photonic applications can be foreseen.

Unusual photoluminescence properties of the 3D mixed-lanthanide-organic frameworks induced by dimeric structures: a theoretical and experimental approach.

The present work describes a complementary experimental and theoretical investigation of the spectroscopic properties of the four isostructural 3D Ln-MOFs (wherein PDC = pyrazole-3,5-dicarboxylate, [La2(PDC)3(H2O)4]·2H2O (1), [(La0.9Eu0.1)2(PDC)3(H2O)4]·2H2O (2), [(La0.9Tb0.1)2(PDC)3(H2O)4]·2H2O (3) and [(La0.9Eu0.5Tb0.5)2(PDC)3(H2O)4]·2H2O (4)). The experimental data and theoretical calculations show that the singular photophysical properties presented by these Ln-MOFs are induced by strong interaction between the Ln(3+) ions.

LUMPAC lanthanide luminescence software: Efficient and user friendly.

In this study, we will be presenting LUMPAC (LUMinescence PACkage), which was developed with the objective of making possible the theoretical study of lanthanide-based luminescent systems. This is the first software that allows the study of luminescent properties of lanthanide-based systems. Besides being a computationally efficient software, LUMPAC is user friendly and can be used by researchers who have no previous experience in theoretical chemistry. With this new tool, we hope to enable research groups to use theoretical tools on projects involving systems that contain lanthanide ions.

Semiempirical quantum chemistry model for the lanthanides: RM1 (Recife Model 1) parameters for dysprosium, holmium and erbium.

Complexes of dysprosium, holmium, and erbium find many applications as single-molecule magnets, as contrast agents for magnetic resonance imaging, as anti-cancer agents, in optical telecommunications, etc. Therefore, the development of tools that can be proven helpful to complex design is presently an active area of research. In this article, we advance a major improvement to the semiempirical description of lanthanide complexes: the Recife Model 1, RM1, model for the lanthanides, parameterized for the trications of Dy, Ho, and Er. By representing such lanthanide in the RM1 calculation as a three-electron atom with a set of 5 d, 6 s, and 6 p semiempirical orbitals, the accuracy of the previous sparkle models, mainly concentrated on lanthanide-oxygen and lanthanide-nitrogen distances, is extended to other types of bonds in the trication complexes' coordination polyhedra, such as lanthanide-carbon, lanthanide-chlorine, etc. This is even more important as, for example, lanthanide-carbon atom distances in the coordination polyhedra of the complexes comprise about 30% of all distances for all complexes of Dy, Ho, and Er considered. Our results indicate that the average unsigned mean error for the lanthanide-carbon distances dropped from an average of 0.30 Å, for the sparkle models, to 0.04 Å for the RM1 model for the lanthanides; for a total of 509 such distances for the set of all Dy, Ho, and Er complexes considered. A similar behavior took place for the other distances as well, such as lanthanide-chlorine, lanthanide-bromine, lanthanide, phosphorus and lanthanide-sulfur. Thus, the RM1 model for the lanthanides, being advanced in this article, broadens the range of application of semiempirical models to lanthanide complexes by including comprehensively many other types of bonds not adequately described by the previous models.

RM1 Model for the Prediction of Geometries of Complexes of the Trications of Eu, Gd, and Tb.

All versions of our previous Sparkle Model were very accurate in predicting lanthanide-lanthanide distances in complexes where the two lanthanide ions directly face each other, and mainly lanthanide-oxygen, and lanthanide-nitrogen distances, which are by far the most common ones in lanthanide complexes. In this article, we are advancing for the first time the RM1 model for lanthanides. Designed to be a much more general NDDO model, the RM1 model for lanthanides is capable of predicting geometries of lanthanide complexes for the cases when the central lanthanide trication is directly coordinated to any other atoms, not only oxygen or nitrogen. The RM1 model for lanthanides is defined by three important attributes: (a) the orbitals, the lanthanide ion has now three electrons and a NDDO basis set made of 5d, 6s, and 6p functions; (b) the parametrization, via cluster analysis and an adequate sampling; and (c), the statistical validation of the parameters to make sure the errors behave as random around a mean. All three aspects are described in detail in the article. Results indicate that the RM1 model does extend the accuracy of the previous Sparkle Models to types of coordinating bonds other than Ln-O and Ln-N; the most common ones for Eu, Gd, and Tb, being Ln-C, Ln-S, Ln-Cl, and Ln-Br. Overall, these other coordinating bonds are now predicted within 0.06 Å of their correct values. Therefore, the RM1 model here presented is capable of predicting geometries of lanthanide complexes, materials, metal-organic frameworks, etc., with useful accuracy.

Lanthanide complexes with aromatic o-phosphorylated ligands: synthesis, structure elucidation and photophysical properties.

Lanthanide complexes LnL3 (Ln = Sm, Eu, Tb, Dy, Tm, Yb, Lu) with aromatic o-phosphorylated ligands (HL(1) and HL(2)) have been synthesized and identified. Their molecular structure was proposed on the basis of a new complex approach, including DFT calculations, Sparkle/PM3 modelling, EXAFS spectroscopy and luminescent probing. The photophysical properties of all of the complexes were investigated in detail to obtain a deeper insight into the energy transfer processes.

Theoretical methodologies for calculation of Judd-Ofelt intensity parameters of polyeuropium systems.

When Judd-Ofelt intensity parameters of polynuclear compounds with asymmetric centers are calculated using the current procedure, the results are inconsistent. The problem arises from the fact that the experimental intensity parameters cannot be determined for each asymmetric polyhedron, and this precludes the individual theoretical adjustment. In this study, we then propose three different methods for calculation of these parameters of polyeuropium systems. The first, named the centroid method, proposes the calculation considering the center of the dimeric system as the half distances between the two europium centers. The second method, called the overlapped polyhedra method, proposes the calculation considering the overlapping of both europium polyhedra, and the last one, the individual polyhedron method, proposes the use of theoretical mean values of charge factors and polarizabilities associated with each europium-ligand atom bond to calculate the intensity parameters. One symmetric polyeuropium system and one asymmetric system were assessed by using the three methods. Among the methods assessed, the one based on the overlapped polyhedra produced more consistent results for the study of both kinds of systems.

Sparkle/PM7 Lanthanide Parameters for the Modeling of Complexes and Materials.

The recently published Parametric Method number 7, PM7, is the first semiempirical method to be successfully tested by modeling crystal structures and heats of formation of solids. PM7 is thus also capable of producing results of useful accuracy for materials science, and constitutes a great improvement over its predecessor, PM6. In this article, we present Sparkle Model parameters to be used with PM7 that allow the prediction of geometries of metal complexes and materials which contain lanthanide trications. Accordingly, we considered the geometries of 224 high-quality crystallographic structures of complexes for the parameterization set and 395 more for the validation of the parameterization for the whole lanthanide series, from La(III) to Lu(III). The average unsigned error for Sparkle/PM7 for the distances between the metal ion and its coordinating atoms is 0.063Å for all lanthanides, ranging from a minimum of 0.052Å for Tb(III) to 0.088Å for Ce(III), comparable to the equivalent errors in the distances predicted by PM7 for other metals. These distance deviations follow a gamma distribution within a 95% level of confidence, signifying that they appear to be random around a mean, confirming that Sparkle/PM7 is a well-tempered method. We conclude by carrying out a Sparkle/PM7 full geometry optimization of two spatial groups of the same thulium-containing metal organic framework, with unit cells accommodating 376 atoms, of which 16 are Tm(III) cations; the optimized geometries were in good agreement with the crystallographic ones. These results emphasize the capability of the use of the Sparkle Model for the prediction of geometries of compounds containing lanthanide trications within the PM7 semiempirical model, as well as the usefulness of such semiempirical calculations for materials modeling. Sparkle/PM7 is available in the software package MOPAC2012, at no cost for academics and can be obtained from http://openmopac.net.