Solid state and solution studies of lanthanide(III) complexes of cyclohexanetriols, models of the coordination sites found in sugars

Understanding the Localization of Berylliosis: Interaction of Be2+ with Carbohydrates and Related Biomimetic Ligands

The interplay of metal ions with polysaccharides is important for the immune recognition in the lung. Due to the localization of beryllium associated diseases to the lung, it is likely that beryllium carbohydrate complexes play a vital role for the development of berylliosis. Herein, we present a detailed study on the interaction of Be²⁺ ions with fructose and glucose as well as simpler biomimetic ligands, which emulate binding motives of saccharides. Through NMR and IR spectroscopy as well as single‐crystal X‐ray diffraction, complemented by competition reactions we were able to determine a distinctive trend in the binding affinity of these ligands. This suggests that under physiological conditions beryllium ions are only bound irreversibly in glycoproteins or polysaccharides if a quasi ideal tetrahedral environment and κ⁴‐coordination is provided by the respective biomolecule. Furthermore, Lewis acid induced conversions of the ligands and an extreme increase in the Brønstedt acidity of the present OH‐groups imply that upon enclosure of Be²⁺, alterations may be induced by the metal ion in glycoproteins or polysaccharides. In addition the frequent formation of Be‐O‐heterocycles indicates that multinuclear beryllium compounds might be the actual trigger of berylliosis. This investigation on beryllium coordination chemistry was supplemented by binding studies of selected biomimetic ligands with Al³⁺, Zn²⁺, Mg²⁺, and Li⁺, which revealed that none of these beryllium related ions was tetrahedrally coordinated under the give conditions. Therefore, studies on the metabolization of beryllium compounds cannot be performed with other hard cations as a substitute for the hazardous Be²⁺.

Crystal structures of two mononuclear complexes of terbium(III) nitrate with the tripodal alcohol 1,1,1-tris-(hy-droxy-meth-yl)propane

Two new mononuclear cationic complexes in which the TbIII ion is bis-chelated by the tripodal alcohol 1,1,1-tris-(hy-droxy-meth-yl)propane (H3LEt, C6H14O3) were prepared from Tb(NO3)3·5H2O and had their crystal and mol-ecular structures solved by single-crystal X-ray diffraction analysis after data collection at 100 K. Both products were isolated in reasonable yields from the same reaction mixture by using different crystallization conditions. The higher-symmetry complex dinitratobis[1,1,1-tris-(hy-droxy-meth-yl)propane]-terbium(III) nitrate di-meth-oxy-ethane hemisolvate, [Tb(NO3)2(H3LEt)2]NO3·0.5C4H10O2, 1, in which the lanthanide ion is 10-coordinate and adopts an s-bicapped square-anti-prismatic coordination geometry, contains two bidentate nitrate ions bound to the metal atom; another nitrate ion functions as a counter-ion and a half-mol-ecule of di-meth-oxy-ethane (completed by a crystallographic twofold rotation axis) is also present. In product aqua-nitratobis[1,1,1-tris-(hy-droxy-meth-yl)propane]-terbium(III) dinitrate, [Tb(NO3)(H3LEt)2(H2O)](NO3)2, 2, one bidentate nitrate ion and one water mol-ecule are bound to the nine-coordinate terbium(III) centre, while two free nitrate ions contribute to charge balance outside the tricapped trigonal-prismatic coordination polyhedron. No free water mol-ecule was found in either of the crystal structures and, only in the case of 1, di-meth-oxy-ethane acts as a crystallizing solvent. In both mol-ecular structures, the two tripodal ligands are bent to one side of the coordination sphere, leaving room for the anionic and water ligands. In complex 2, the methyl group of one of the H3LEt ligands is disordered over two alternative orientations. Strong hydrogen bonds, both intra- and inter-molecular, are found in the crystal structures due to the number of different donor and acceptor groups present.

Electrospray ionization mass spectrometric studies on uranyl complex with α-hydroxyisobutyric acid in water-methanol medium

RATIONALE

Hydroxycarboxylic acids are extensively used as chelating agents in the liquid chromatographic separation of actinides and lanthanides. They are also used as model compounds to understand the binding characteristics of humic substances. A systematic study of the speciation of uranyl-α-hyydroxyisobutyric acid (HIBA) in water-methanol is essential, as it is important to understand the various mechanisms responsible for the separation of these species in liquid chromatography.

METHODS

ESI-MS studies were carried out using a tandem quadrupole-time-of-flight mass spectrometer in positive and negative ion mode. The effects of solution composition, solute concentration and supporting electrolyte concentration on the ESI-MS behavior of the uranyl species were studied. Transmission parameters such as the quadrupole ion energy and collision cell energy were optimized for acquiring the spectra of uranyl-HIBA species, ensuring that the spectra reflect the solution equilibrium conditions.

RESULTS

The solution composition and concentration of the uranyl salt were found to influence the major uncomplexed uranyl species. Although the ESI parameters did not influence the species distribution of uranyl-HIBA, the transmission parameters did have a significant effect. The overall trend in the complexation reaction between uranyl and HIBA was studied as a function of ligand-to-metal ratio. The species distribution obtained in positive ion mode was similar to that obtained in negative ion mode.

CONCLUSIONS

The study presents the optimization of the mobile phase conditions and the ESI-MS parameters for the speciation of the uranyl-HIBA system. The methodology was applied to obtaining the distribution of complexed and uncomplexed uranyl species for monitoring the trend in the complexation reaction.

Sugar-metal ion interactions: the coordination behaviors of lanthanum with erythritol

Three novel lanthanum chloride-erythritol complexes (LaCl(3)·C(4)H(10)O(4)·5H(2)O (LaE(I)), LaCl(3)·C(4)H(10)O(4)·3H(2)O (LaE(II)), and LaCl(3)·1.5C(4)H(10)O(4) (LaE(III)) were synthesized and characterized by single crystal X-ray diffraction, FTIR, far-IR, THz, and Raman spectroscopy. The coordination number of La(3+) is nine. LaE(I) and LaE(II) have similar coordination spheres, but their hydrogen bond networks are different. Erythritol exhibits two coordination modes: two bidentate ligands and tridentate ligands in LaE(III). Chloride ions and water coordinate with La(3+) or participate in the hydrogen-bond networks in the three complexes. Crystal structures, FTIR, FIR, THz, and Raman spectra provide detailed information on the structures and coordination of hydroxyl groups to metal ions in the metal-carbohydrate complexes.

Interactions between metal ions and carbohydrates. Spectroscopic characterization and the topology coordination behavior of erythritol with trivalent lanthanide ions

The coordination of carbohydrate to metal ions is important because it may be involved in many biochemical processes. The synthesis and characterization of several novel lanthanide-erythritol complexes (TbCl(3)·1.5C(4)H(10)O(4)·H(2)O (TbE(I)), Pr(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (PrEN), Ce(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (CeEN), Y(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (YEN), Gd(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (GdEN)) and Tb(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (TbEN) are reported. The structures of these complexes in the solid state have been determined by X-ray diffraction. Erythritol is used as two bidentate ligands or as three hydroxyl group donor in these complexes. FTIR spectra indicate that two kinds of structures, with water and without water involved in the coordination sphere, were observed for lanthanide nitrate-erythritol complexes. FIR and THz spectra show the formation of metal ion-erythritol complexes. Luminescence spectra of Tb-erythritol complexes have the characteristics of the Tb ion.

Interaction between Metal Nitrates and Carbohydrates: The Topology Coordination Behavior of Galactitol with Trivalent Lanthanide and Divalent Alkaline Earth Ions

It has long been known that metal ions and saccharides are involved in many biochemical processes. In this paper, metal nitrates were used as reactants to detect the coordination structures of the hydroxyl groups of galactitol in different environments. Three novel crystal structures and FT-IR spectra of metal nitrate-galactitol complexes of La(NO3)3.C6H14O6.(4)H2O, 2Ca(NO3)2.C6H14O6.H2O, and Sr(NO3)2.C6H14O6 were examined in an effort to clarify the structural factors that control metal ion interactions with saccharides in aqueous and biological systems. The coordination structures of galactitol with alkaline earth and lanthanide nitrates in the solid state were compared using FT-IR, Raman, and X-ray diffraction techniques to extensively discuss the coordination rules of different kinds of metal ions. Results provided a model of the coordination sites found in sugars and showed that the introduction of NO3- made the coordination modes of galactitol more diverse and complex than those of the corresponding chloride complexes. Specifically, new coordination modes of galactitol and complicated topology networks were found in 2Ca(NO3)2.C6H14O6.H2O and Sr(NO3)2.C6H14O6. FT-IR results are consistent with the crystal structures and thus provide the possibility of using the similarity of IR spectra to speculate about unknown structures when the compounds are difficult to prepare as single crystals.

Electrospray mass spectrometry (ESI-MS) in the study of metal-ligand solution equilibria

In the 20 years, since the introduction of electrospray mass spectrometry (ESI-MS), the use of this technique in various fields of inorganic, organometallic, and analytical chemistry has been steadily increasing. In this study, the application of ESI-MS to the study of metal-ligand solution equilibria is reviewed (till 2004 included). In a first section, advantages and drawbacks of ESI-MS in this type of application are described. Subsequently, a list of ca. 300 studies is reported, in which ESI-MS was used to give number and stoichiometry of the species at equilibrium, or also to estimate their stability constants. All studies are classified according to the metal ions under examination. Other related applications, such as host-guest interactions and metal ion-protein binding studies, are briefly reviewed as well.

Interactions between metal ions and carbohydrates. The coordination behavior of neutral erythritol to lanthanum and erbium ions

Lanthanide ions and erythritol form metal-alditol complexes with various structures. Lanthanum nitrate and erbium chloride coordinate to erythritol to give new coordination structures. The lanthanum nitrate-erythritol complex (LaEN), 2La(NO3)3.C4H10O(4).8H2O, La3+ exhibits the coordination number of 11 (namely 11 polar atoms bound to one lanthanum) and is 11-coordinated to two hydroxyl groups from one erythritol molecule, six oxygen atoms from three nitrate ions and three water molecules. One erythritol molecule is coordinated to two La3+ ions and links the two metal ions together. The ratio of M:L is 2:1. The erbium chloride-erythritol complex (ErE), ErCl2.C4H9O(4).2C2H5OH was obtained from ErCl3 and erythritol in aqueous ethanol solution and the structure shows that deprotonation reaction occurs in the reaction process. The Er3+ cation is 8-coordinated with three hydroxyl groups of one erythritol molecule, two hydroxyl groups from another erythritol molecule, two ethanol molecules, and one chloride ion. Erythritol provides its three hydroxyl groups to one erbium cation and two hydroxyl groups to another erbium cation, that is, one hydroxyl group is coordinated to two metal ions and therefore loses its hydrogen atom and becomes a oxygen bridge. Another chloride ion is hydrogen bonded in the structure. The results indicate the complexity of metal-sugar coordination.

Sulfate Complexation of Trivalent Lanthanides Probed by Nanoelectrospray Mass Spectrometry and Time-Resolved Laser-Induced Luminescence

Sulfate complexation of lanthanides is of great interest for predicting speciation of radionuclides in natural environments. The formation of LaSO4+(aq) in HNO3/H2SO4 aqueous solutions of low ionic strength (I) was studied by nanoelectrospray ionization mass spectrometry (nanoESI-MS). Several gaseous species containing LaSO4+ were detected. The formation constant of LaSO4+(aq) was determined and extrapolated to I = 0 (log = 3.5 +/- 0.3) by using a simple specific ion interaction theory (SIT) formula. This value supports the potential of nanoESI-MS for the study of kinetically labile species. The species La(SO4)(2-) was also detected. In addition, time-resolved laser-induced luminescence (TRLIL) was used to study Eu(III) speciation under ionic conditions of 0.02-0.05 M H+ (H2SO4/HClO4) and 0.4-2.0 M Na+ (Na2SO4/NaClO4). The data were interpreted with the species EuSO4+ (log = 3.7(8) +/- 0.1) and Eu(SO4)(2-) (log = 1.5 +/- 0.2). For extrapolating to I = 0, all of the major ions were taken into account through several SIT ion-pair parameters, epsilon. Most of the epsilon values were estimated by analogy to known parameters for similar ion-pair interactions using linear correlations, while epsilon(Eu)3+,SO4(2-) = 0.8(6) +/- 0.5 was fitted to the experimental data because, to date, SIT coefficients between multicharged species are not reported. The formation constants obtained here confirm some of those previously measured for Ln(III) and An(III) by various experimental techniques, and conversely do not give credit to the idea that in equilibrium conditions TRLIL and other spectroscopic techniques would provide stability constants of only inner-sphere complexes. The fluorescence lifetimes measured for EuSO4+ and Eu(SO4)(2-) were consistent with the replacement of one H2O molecule in the first coordination sphere of Eu3+ for each added SO4(2-) ligand, suggesting a monodentate SO4(2-) coordination.

On the use of spectroscopic techniques for interaction studies, part I: complexation between europium and small organic ligands

In the framework of environmental studies, it is important to understand the interaction of humic substances with cations (heavy metals, radionuclides) and to determine their complexation constants in order to evaluate their potential impact on their fate. For this purpose, two techniques have been used: electrospray ionization mass spectrometry, a newly used technique in speciation studies, and time-resolved laser-induced fluorescence spectrometry, a well-known technique for such studies. As a first step, for simplification purposes and to compare both techniques, simple molecules having functional groups present in humic substances have been selected, such as acetic, glycolic, and 4-hydroxyphenylacetic acids. Both techniques have been used to obtain stoichiometries and complexation constants between these simple molecules and europium (III).

Complexation of trivalent lanthanide cations by erythritol in the solid state. The crystal structure and FT-IR study of 2EuCl3·2C4H10O4·7H2O

Erythritol was chosen to study the interactions between metal ions and carbohydrates. FTIR spectroscopy results indicate that a EuCl3-erythritol complex different from a previously reported one was obtained. The crystal structure of EuCl3-erythritol complex, 2EuCl3.2C4H10O4.7H2O, Mr=443.49, a=13.846(3) A , b=7.4983(15) A, c=14.140(3) A, beta=116.39(3) degrees, V=1315.1(5) A(3), Z=4, mu=5.394 mm(-1) and R=0.0395 for 2965 observed reflections and 143 parameters, was determined. Characteristic of this complex is the presence of binuclear europium ions with different coordination structures. One Eu3+ ion is nine-coordinated, with five Eu-O bonds from water molecules, and four from hydroxyl groups of two erythritol molecules and another Eu3+ is eight-coordinated with two water molecules, two chloride ions, and four hydroxyl groups from two erythritol molecules. Erythritol provides two hydroxyl groups to one lanthanide ion and the other two to another rare earth ion. The OH, CO stretching and other vibrations are shifted in the IR spectra of the complexes and the results are consistent with the crystal structure.

Sugar complexes with neodymium nitrate

Two different Nd(NO3)3-galactitol complexes, 2Nd(NO3)3.C6H14O6.8 H2O and Nd(NO3)3.C6H14O6 have been obtained and were characterized by FT-IR and X-ray diffraction techniques. The spectral differences of the two complexes were consistent with the crystal-structure data.

Use of electrospray mass spectrometry (ESI-MS) for the study of europium(III) complexation with bis(dialkyltriazinyl)pyridines and its implications in the design of new extracting agents

ESI mass spectrometry was used to investigate the europium complexation by tridentate ligands L identical with 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridines (DATP) that have shown unique separation properties of actinides(III) from lanthanides(III) in nitric acid solutions. Complexes of three ligands, namely methyl (DMTP), n-propyl (DnPTP), and iso-propyl (DiPTP), have been investigated in acidic solutions to check the aqueous-phase stability of Eu(L)(3)(3+) ions identified previously in the solid state. The data obtained show, first, the presence of stable Eu(L)(3)(3+) ions with DnPTP (log beta(3)(app) = 12.0 +/- 0.5) and DiPTP (log beta(3)(app) = 14.0 +/- 0.6) in methanol/water (1:1 v/v) solutions under pH range 2.8-4.6 and, second, a mechanism whereby alkyl moieties contribute to a self-assembling process leading to the formation of Eu(L)(3)(3+) ions. Other complexes such as Eu(L)(2)(3+) ions are only observed for DnPTP (log beta(2)(app) = 6.7 +/- 0.5) and DMTP (log beta(2)(app) = 6.3 +/- 0.1) and Eu(L)(3+) only for DMTP (log beta(1)(app) = 2.9 +/- 0.2). The log beta(n)(app) values for the Eu(L)(n)(3+) (n = 1-3) complexes were determined at pH 2.8. Better insight was given in this study concerning the role of the hydrophobic exterior of the ligands for the design of a new range of extracting agents.