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 [Ln(CHO)(HO)]·HO 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.

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 effect of mechanical grinding on the formation, crystalline changes and dissolution behaviour of the inclusion complex of telmisartan and β-cyclodextrins.

Telmisartan (TEL) was entrapped into β-cyclodextrin aiming the improvement of its biopharmaceutical properties of low solubility. A solid state grinding process was used to prepare the molecular inclusion complex (MIC) for up to 30min. The inclusion ratio of drug and β-cyclodextrin was established as 1:2 and 1:3 (mol/mol) by phase solubility study and Job Plot.

Theoretical spectroscopic study of europium tris(bipyridine) cryptates.

A series of europium cryptates are studied, using semiempirical methods to predict electronic and spectroscopic properties. The results are compared with theoretical (DFT) and experimental results published by Guillaumont and co-workers (ChemPhysChem2007, 8, 480). Triplet energies calculated by semiempirical methods have errors similar to those obtained by TD-DFT methodology but hundreds of times faster.

Physicochemical study and characterization of the trimethoprim/2-hydroxypropyl-γ-cyclodextrin inclusion complex.

Here we report the preparation of a trimethoprim/2-hydroxypropyl-γ-cyclodextrin inclusion complex along with a physicochemical study, structural characterization, and molecular modeling of the complex. As main results, we observed from phase-solubility studies at two temperatures (20 °C and 35 °C) that the association constants decrease with increasing temperature. Values for K(1:1) constant were of the same magnitude order of those found for the parent γ-CD.

Structural and theoretical-experimental physicochemical study of trimethoprim/randomly methylated-β-cyclodextrin binary system.

Here we report the structural characterization, physicochemical study and molecular modeling of the inclusion complex of trimethoprim in randomly methylated beta-cyclodextrin. The phase-solubility diagram obtained at pH 7.0 exhibited a linear behavior for the RAMEB concentrations studied suggesting a 1:1 stoichiometry and absence of aggregation in solution.

Would the pseudocoordination centre method be appropriate to describe the geometries of lanthanide complexes?

The correct prediction of the ground-state geometries of lanthanide complexes is an important step in the development of efficient light conversion molecular devices (LCMD). Considering this, we evaluate here the capability of semiempirical approaches and ab initio effective core potential (ECP) methodology in reproducing the coordination polyhedron geometries of lanthanide complexes. Initially, we compare the facility of two semiempirical approaches: Pseudocoordination centre method (PCC) and Sparkle model.

Theoretical and experimental spectroscopic approach of fluorinated Ln(3+)-beta-diketonate complexes.

In this paper we report the synthesis of two new complexes, [Eu(fod)(3)(phen)] and [Tb(fod)(3)(phen)] (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadionate and phen = 1,10-phenanthroline), and their complete characterization, including single-crystal X-ray diffraction, UV-vis spectroscopy, IR spectroscopy, and TGA. The complexes were studied in detail via both theoretical and experimental approaches to the photophysical properties. The [Eu(fod)(3)(phen)] complex crystallizes in the monoclinic space group P2(1)/c.

Characterization, phase solubility and molecular modeling of alpha-cyclodextrin/pyrimethamine inclusion complex.

An inclusion complex between the dihydrofolate reductase inhibitor pyrimethamine (PYR) and alpha-cyclodextrin (alpha-CD) was prepared and characterized. From the phase-solubility diagram, a linear increase of PYR solubility was verified as a function of alpha-CD concentration, suggesting the formation of a soluble complex. A 1:1 host-guest stoichiometry can be proposed according to the Job's plot, obtained from the difference of PYR fluorescence intensity in the presence and absence of alpha-CD.

Sulfadiazine/hydroxypropyl-beta-cyclodextrin host-guest system: Characterization, phase-solubility and molecular modeling.

In this work we prepared and characterized an inclusion complex of the dihydropteroate synthase inhibitor sulfadiazine (SDZ) in 2-hydroxypropyl-beta-cyclodextrin (HPBCD). From the phase-solubility diagram we observed an increase in the water solubility of the drug, calculating a binding constant of 1879M(-1). The inclusion mode involves a NH(2)-in orientation of the drug in the HPBCD cavity, according to the 2D NMR (ROESY) data and confirmed by molecular modeling using the semiempirical PM6 and RM1 methods.

Sparkle/PM3 Parameters for the Modeling of Neodymium(III), Promethium(III), and Samarium(III) Complexes.

The Sparkle/PM3 model is extended to neodymium(III), promethium(III), and samarium(III) complexes. The unsigned mean error, for all Sparkle/PM3 interatomic distances between the trivalent lanthanide ion and the ligand atoms of the first sphere of coordination, is 0.074 Å for Nd(III); 0.

Inclusion complexes of pyrimethamine in 2-hydroxypropyl-beta-cyclodextrin: characterization, phase solubility and molecular modelling.

The inclusion complexation of pyrimethamine in 2-hydroxypropyl-beta-cyclodextrin has been investigated by 2D (1)H NMR, FTIR and UV/visible spectroscopy and also by molecular modelling methods (AM1, PM3, MM3). From the phase-solubility diagram a linear increase was observed in pyrimethamine aqueous solubility in the presence of 2-hydroxypropyl-beta-cyclodextrin, evidencing the formation of a soluble inclusion complex. According to the continuous variation method (Job's plot) applied to fluorescence measurements, a 1:1 stoichiometry has been proposed for the complex.

Structure modeling of trivalent lanthanum and lutetium complexes: Sparkle/PM3.

The recently defined Sparkle model for the quantum chemical prediction of geometries of lanthanum(III) and lutetium(III) complexes within AM1 (J. Phys. Chem.

Principal component analysis of X-ray diffraction patterns to yield morphological classification of brucite particles.

Principal component analysis was applied to XRD data from a series of Mg(OH)2 samples prepared under different hydrothermal conditions from bischofite (MgCl2.6H2O) and carnallite (KCl.MgCl2.

Fluorescent tetraruthenated porphyrins embedded in monolithic SiO2 gels by the sol-gel process.

In this work silica gels have been prepared by a sol-gel method using tetraethylorthosilicate as gel precursor. The tetraruthenated porphyrins H2(3-TRPyP), Co(3-TRPyP), and H2(4-TRPyP) were incorporated into the systems during gel formation without problems commonly found in the process, such as aggregation. Spectroscopic studies of the resulting silica gels revealed the presence of absorption bands in the range 200-400 nm associated with the transitions of the groups ruthenium-bipyridine, along with the Soret band at the same wavelengths observed in solution.

Sparkle/AM1 structure modeling of lanthanum (III) and lutetium (III) complexes.

The sparkle/AM1 model for the quantum chemical prediction of coordination polyhedron crystallographic geometries from isolated lanthanide complex ion calculations, defined recently for Eu(III), Gd(III), and Tb(III) (Inorg. Chem. 2005, 44, 3299) is now extended to La(III) and Lu(III).

Sparkle/AM1 Parameters for the Modeling of Samarium(III) and Promethium(III) Complexes.

The Sparkle/AM1 model is extended to samarium(III) and promethium(III) complexes. A set of 15 structures of high crystallographic quality (R factor < 0.05 Å), with ligands chosen to be representative of all samarium complexes in the Cambridge Crystallographic Database 2004, CSD, with nitrogen or oxygen directly bonded to the samarium ion, was used as a training set.

Sparkle model for AM1 calculation of lanthanide complexes: improved parameters for europium.

In the present work, we sought to improve our sparkle model for the calculation of lanthanide complexes, SMLC,in various ways: (i) inclusion of the europium atomic mass, (ii) reparametrization of the model within AM1 from a new response function including all distances of the coordination polyhedron for tris(acetylacetonate)(1,10-phenanthroline) europium(III), (iii) implementation of the model in the software package MOPAC93r2, and (iv) inclusion of spherical Gaussian functions in the expression which computes the core-core repulsion energy. The parametrization results indicate that SMLC II is superior to the previous version of the model because Gaussian functions proved essential if one requires a better description of the geometries of the complexes. In order to validate our parametrization, we carried out calculations on 96 europium(III) complexes, selected from Cambridge Structural Database 2003, and compared our predicted ground state geometries with the experimental ones.