Unusual coordination behavior of D-fructose towards dimethyltin(IV): metal-promoted deprotonation of alcoholic OH groups in aqueous solutions of low pH

Deprotonation from an OH on myo-Inositol Promoted by μ2-Bridges with Possible Regioselectivity/Chiral Selectivity

Single-crystal structures of myo-inositol complexes with erbium ([Er₂(C₆H₁₁O₆)₂(H₂O)₅Cl₂]Cl₂(H₂O)₄, denoted ErI hereafter) and strontium (Sr(C₆H₁₂O₆)₂(H₂O)₂Cl₂, denoted SrI hereafter) are described. In ErI, deprotonation occurs on an OH of myo-inositol, although the complex is synthesized in an acidic solution, and the pK_a values of all of the OHs in myo-inositol are larger than 12. The deprotonated OH is involved in a μ₂-bridge. The polarization from two Er³⁺ ions activates the chemically relatively inert OH and promotes deprotonation. In the stable conformation of myo-inositol, there are five equatorial OHs and one axial OH. The deprotonation occurs on the only axial OH, suggesting that the deprotonation possesses characteristics of regioselectivity/chiral selectivity. Two Er³⁺ ions in the μ₂-bridge are stabilized by five-membered rings formed by chelating Er³⁺ with an O-C-C-O moiety. As revealed by the X-ray crystallography study, the absolute values of the O-C-C-O torsion angles decrease from ∼60 to ∼45° upon chelating. Since the O-C-C-O moiety is within a six-membered ring, the variation of the torsion angle may exert distortion of the chair conformation. Quantum chemistry calculation results indicate that an axial OH flanked by two equatorial OHs (double ax-eq motif) is favorable for the formation of a μ₂-bridge, accounting for the selectivity. The double ax-eq motif may be used in a rational design of high-performance catalysts where deprotonation with high regioselectivity/chiral selectivity is carried out.

Unexpected Deprotonation from a Chemically Inert OH Group Promoted by Metal Ions in Lanthanide-Erythritol Complexes

Single-crystal structures of five lanthanide-erythritol complexes are reported. The analysis of the chemical compositions and scrutinization of structural features in the single-crystal data of the complexes led us to find that unexpected deprotonation occurs on the OH group of erythritol of three complexes. Considering these complexes were prepared in acidic environments, where spontaneous ionization on an OH group is suppressed, we suggest metal ions play an important role in promoting the proton transfer. To find out why the chemically inert OH is activated, the single-crystal structures of 63 rare-earth complexes containing organic ligands with multiple hydroxyl groups (OLMHs) were surveyed. The formation of μ₂-bridges turns out to be directly relevant to the occurrence of deprotonation. When an OH group from an OLMH molecule participates in the formation of a μ₂-bridge, the polarization ability of the metal ions becomes strong enough to promote the deprotonation on the OH group. The above structural characteristics may be useful in the rational design of catalysts that can activate the chemically inert OH group and promote the relevant chemical conversions.

Removal of Cu(II) in water by polymer enhanced ultrafiltration: Influence of polymer nature and pH

This study presents an efficient removal of Cu(II) in water using the polymer enhanced ultrafiltration (PEUF) method. Polymer of different molecular weight (MW) (polyethyleneimine (PEI), sodium lignosulfonates (SLS) and dextrans) were investigated to evaluate efficiency in removal of Cu(II) in water by the PEUF method. The decomposition of Cu(II)-polymer complex was also evaluated in order to reuse polymers. Cu(II) complexation depends on the MW of chelating polymer and the pH of feed solution. It was found that the Cu(II) rejection increased with the polymer dosage with high removal of Cu(II) when using PEI and SLS at a 10:20 (mg/mg) ratio ([Cu(II)]:[polymer]). It was found that the maximum chelating capacity was 15 mg of Cu(II) per 20 mg of PEI. The Cu(II)-PEI complex could be decomposed by acid addition and the polymer could be efficiently reused with multiple complexation-decomplexation cycles. A conceptual flow chart of the integrated process of efficient removal of Cu(II) by PEUF method is suggested.

Equilibrium Studies of Dibutyltin(IV)-Zwitterionic Buffer Complexation

Equilibrium studies in aqueous solution are reported for dibutyltin(IV) (DBT) complexes of the zwitterionic buffers “Good’s buffers” Mes and Mops. Stoichiometric and formation constants of the complexes formed were determined at different temperatures and ionic strength 0.1 mol·L⁻¹ NaNO₃. The results show that the best fit of the titration curves were obtained when the complexes ML, MLH₋₁, MLH₋₂ and MLH₋₃ were considered beside the hydrolysis product of the dibutyltin(IV) cation. The thermodynamic parameters ΔH^o, ΔS^o and ΔG^o calculated from the temperature dependence of the formation constant of the dibutyltin(IV) complexes with 2-(N-morpholino)ethanesulfonic acid (Mes) and 3-(N-mor-pholino)-propanesulfonic acid (Mops) were investigated. The effect of dioxane as a solvent on the formation constants of DBT–Mes and DBT–Mops complexes decrease linearly with the increase of dioxane proportion in the medium. The concentration distribution of the various complexes species was evaluated as a function of pH.

Hydrolysis of dimethylphenyltin(IV) and triphenyltin(IV) chlorides in different aqueous ethanol solutions

The hydrolysis of [(Me)2(Ph)Sn(IV)]+ and [(Ph)3Sn(IV)]+ has been investigated at 25 °C and different aqueous solutions of ethanol, using a combination of spectrophotometric and potentiometric techniques. The species formed together with their formation constants have been determined using the computer program Squad over a wide pH range of 1 to 11. The hydrolysis constants in different media were analyzed in terms of Kamlet and Taft parameters. Single-parameter correlation of the formation constants, K11 and K12, versus α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity), and π* (dipolarity/polarizability) for both cases are relatively poor in all solutions, but multiparameter correlation represents significant improvement with regard to the single-parameter models. In this work, we have also used the normalized polarity parameter, ETN, alone and in combination with the Kamlet–Taft parameter to find a better correlation of the formation constants in different aqueous ethanol solutions.Key words: dimethylphenyltin(IV) chloride, triphenyltin(IV) chloride, hydrolysis constant, aqueous ethanol solutions, solvent effect.

Solution structure of R2Sn(iv)-β-N-acetyl-neuraminate (R = Me, Bu) complexes in D2O and DMSO-d6: Experimental NMR and DFT computational study

Two diorganotin(IV)-NANA complexes (NANA (1) = beta-N-acetyl-Neuraminic Acid = 5-amino-3,5-dideoxy-D-glycero-beta-D-galactononulosic acid) with formula Me(2)Sn(iv)NANA (2) and Bu(2)Sn(IV)NANA (3) were synthesized and characterized by (1)H, (13)C and (119)Sn NMR spectroscopy, both in D(2)O and DMSO-d(6) solutions. The experimental data in DMSO suggested the monosaccharide bidentate chelation via O1 carboxylate and vicinal O2 alkoxide atoms, which, in D(2)O, can be dynamically extended to a third binding site (O8 atom) of the pendant chain. Coordination at the tin atom is discussed on the basis of experimental NMR data and DFT calculation.

Evidence of two-step deprotonation of d-mannitol in aqueous solution

Deprotonation of D-mannitol was studied in aqueous basic solutions by means of potentiometry and (13)C NMR spectroscopy. Two-step dissociation in the pH range from 12 to 13.8 was shown, and successive dissociation constants K(a1) and K(a2) were determined. In a solution with ionic strength I = 1.0 M (NaOH + NaNO(3)) pK(a1) = 13.1 +/- 0.1 and pK(a2) = 13.8 +/- 0.2. With increasing ionic strength from 0.75 to 3.0 M, both pK(a1) and pK(a2) values decrease. Deprotonation-induced chemical shifts in pH-variable (13)C NMR spectra show that the OH-groups next to internal carbon atoms C-3 and C-4 dissociate to a greater extent compared to OH-groups next to external carbon atoms C-1 and C-6.

New organotin(IV) ascorbates: synthesis, spectral characterization, biological and potentiometric studies

New organotin(IV) ascorbates of the general formulae R(3)Sn(HAsc) (where R = Me , n-Pr, n-Bu and Ph) and R(2)Sn(Asc) (where R = n-Bu and Ph) have been synthesized by the reaction of R(n)SnCl(4-n) (where n = 2 or 3) with monosodium-l-ascorbate. The bonding and coordination behaviour in these complexes are discussed on the basis of UV-Vis, IR, Far-IR, (1)H and (13)C NMR, and (119)Sn Mossbauer spectroscopic studies. L-Ascorbic acid acts as a monoanionic bidentate ligand in R(3)Sn(HAsc) coordinating through O(1) and O(3). The Mossbauer studies together with IR and NMR studies suggest that for these polymeric derivatives, the polyhedron is trigonal bipyramidal around tin with three organic groups in the equatorial positions. In R(2)Sn(Asc), L-ascorbic acid acts as dianionic tetradentate ligand and a polymeric structure with octahedral geometry around tin with trans organic groups has been tentatively proposed. The complexes have been assayed for their anti-inflammatory and cardiovascular activity. Ph(2)Sn(Asc) has been found to show the highest activity among the studied complexes. It is suggested on the basis of potentiometric studies of Me(2)Sn(IV) and Me(3)Sn(IV) systems with L-ascorbic acid that under physiological conditions (pH = 7.0) Me(2)Sn(HAsc)(OH) (approximately 60%), Me(2)Sn(OH)(2) (approximately 40%) and Me(3)Sn(HAsc) (approximately 60%), Me(3)Sn(OH) (approximately 40%), respectively, are existing, which may be responsible for their biological activities.

Coordination properties of adenosine-5'-monophosphate and related ligands towards Me2Sn(IV)2+ in aqueous solution

The coordination of Me2Sn(IV)2+ to adenosine-5'-monophosphate (AMP) and the related compounds D-ribose-5-phosphate (R5P), D-glucose-1-phosphate (G1P) and D-glucose-6-phosphate (G6P) in aqueous solution was investigated by means of potentiometric titration, and 1H-, 31P-NMR and Mössbauer spectroscopic methods in the pH range 2-11 (I=0.1 M NaClO4, 298 K). The complex of AMP and Me2Sn(IV)2+ precipitated at low pH was characterised by elemental analysis, FT-IR and Mössbauer spectroscopic methods. From a comparison of the pK values obtained in the presence and absence of metal ion and the stability constants for the different systems, the coordination of [N] is excluded, while bidentate coordination of the phosphate group is presumed. Mössbauer spectroscopic measurements recorded in the glassy state confirmed bidentate coordination of the phosphate and the formation of mixed hydroxo complexes in the weakly acidic, neutral and strongly basic pH range. With increasing pH, the phosphate groups were replaced by the deprotonated alcoholic [O] atoms of the sugar moiety. The solid complex proved to be tbp structure with bidentate phosphate coordination.

Equilibrium and structural studies on metal complexes of carbohyrates and their derivatives

A summary is presented of the studies of our group on metal complexes of carbohydrates (aldoses, ketoses, mono-, di- and polysaccharides) and their derivatives (aldonic, alduronic acids, polyalcohols, amino sugars, amino acid sugar adducts, AMP, ATP, etc.). The results are reported of equilibrium, electrochemical, solution and solid-state structural studies of complexes of transition metals [Cu(II), Fe(III), Ni(II), Zn(II), Co(II), Ag(I), Mn in different oxidation states and organotin(IV)]. The structural parameters (coordination number, bond distance, and Debye-Waller factor) obtained by extended X-ray absorption fine structure spectroscopic (EXAFS) spectroscopy are discussed in detail. The general rules concerning the formation and structure of such complexes are emphasized.

Interaction of diphenyltin(IV) dichloride with some selected bioligands

The interaction of diphenyltin(IV) with selected bioligands having a variety of model functional groups were investigated using the potentiometric technique. The hydrolysis constants of diphenyltin(IV) cation and the step-wise formation constants of the complexes formed in solution were calculated using the non linear least-squares program MINIQUAD-75. The participation of different ligand functional groups in binding to organotin is discussed. The concentration distribution of the various complex species was evaluated as a function of pH.

Potentiometric and spectroscopic studies on the dimethyltin(IV) complexes of 2-hydroxyhippuric acid

Equilibrium and spectroscopic (1H, 13C NMR and 119Sn Mössbauer) studies in aqueous solution are reported for dimethyltin(IV) complexes of 2-hydroxyhippuric acid (Sal-Gly). Below pH 4, oxygen-coordinated complexes MLH and ML are formed. In the pH range 5-8.5, the species MLH(-1), predominates at any metal-to-ligand ratio. The ligand exchange of this species is slow on the NMR time scale, which allows its structural characterization by NMR spectroscopy: the coordination polyhedron around the tin atom is distorted trigonal bipyramidal, with tridentate [O-,N-,COO-] coordination of Sal-Gly, involving two equatorial methyl groups. The NMR results reveal that the main cause of the distortion of the polyhedron is the large CH3-Sn-CH3 angle of 136+/-4 degrees. The presented results supplement the data available on the dimethyltin(IV)-promoted amide deprotonation of peptides, and provide further arguments for the fundamental role of the carboxylate as an anchoring group in this process.