The structure of hyperalkaline aqueous solutions containing high concentrations of gallium--a solution X-ray diffraction and computational study.

Highly concentrated alkaline NaOH-Ga(OH)3 solutions with 1.18 M ≤ [Ga(III)]T ≤ 2.32 M and 2.4 M ≤ [NaOH]T ≤ 4.9 M (where the subscript T denotes total or analytical concentrations) have been prepared and investigated by solution X-ray diffraction and also by ab initio quantum chemical calculations. The data obtained are consistent with the presence of only one predominant Ga(III)-bearing species in these solutions, which is the tetrahedral hydroxo complex Ga(OH)4(-). This finding is in stark contrast to that found for Al(III)-containing solutions of similar concentrations, in which, besides the monomeric complex, an oxo-bridged dimer was also found to form. From the solution X-ray diffraction measurements, the formation of the dimeric (OH)3Ga-O-Ga(OH)3(2-) could not unambiguously be shown, however, from the comparison of experimental IR, Raman and (71)Ga NMR spectra with calculated ones, its formation can be safely excluded. Moreover, higher mononuclear stepwise hydroxo complexes, like Ga(OH)6(3-), which have been claimed to exist by others in the literature, were not possible to experimentally detect in these solutions with any of the spectroscopic techniques used.

Hydrolysis of dinucleoside phosphates - mRNA 5' cap analogues - promoted by a binuclear copper(II)-zinc(II) complex.

The hydrolysis of a 5' cap analogue, diadenosinyl-5',5'-triphosphate (ApppA), and two dinucleoside monophosphates: adenylyl(3',5')adenosine (ApA) and uridylyl(3',5')uridine (UpU) promoted by an imidazolate-bridged heterobinuclear copper(II)-zinc(II) complex, Cu(II)-diethylenetriamino-micro-imidazolato-Zn(II)- tris(aminoethyl)amine trisperchlorate (denoted as Cu,Zn-complex in the followings) has been investigated. Kinetic measurements were performed in order to explore the effects of pH, the total concentration of the Cu,Zn-complex and temperature on the cleavage rate. The catalytic activity of the Cu,Zn-complex was quantified by pseudo-first-order rate constants obtained in the excess of the cleaving agent. The results show that the Cu,Zn-complex and its deprotonated forms have phosphoesterase activity and with ApppA the metal complex promoted cleavage takes place selectively within the triphosphate bridge.

Comparison of the Ca2+ complexing properties of isosaccharinate and gluconate - is gluconate a reliable structural and functional model of isosaccharinate?

The calcium complexation and acid-base properties of α-d-isosaccharinate (Isa-) in neutral and in (hyper)alkaline solutions have been investigated via potentiometric titrations, multinuclear NMR, ESI-MS and quantum chemical calculations. Isa- is the primary alkaline degradation product of cellulose, and may be present in radioactive waste repositories and therefore, it could contribute to the mobilization of radioactive nuclei. Because of its limited availability, d-gluconate (Gluc-) is commonly used as a structural and functional model of Isa-. Therefore, the thermodynamic and structural data obtained for Isa- were compared with those of Gluc-. The formation constants of the CaIsa+ and CaGluc+ complexes present in neutral solutions are practically identical, but the binding sites are in different positions and the CaIsa20 solution species cannot be detected. The stepwise formation constant of the CaIsaH-10 complex (forming in alkaline medium) is somewhat larger than that of CaGlucH-10, which is in line with the observation that IsaH-12- is a stronger base than GlucH-12-. The most striking difference is that, unlike Gluc-, Isa- does not form polynuclear complexes with Ca2+. The structural reason for this is that the alcoholate groups on C2 and C3 adjacent to the carboxylate moiety on Gluc- are able to simultaneously bind Ca2+, making the formation of polynuclear Ca-complexes possible. On Isa-, only the alcoholate on C2 is involved, while the other one on C6 is not (supposedly for steric reasons). In conclusion, during the interactions of Gluc- and Isa- with Ca2+, differences rather than similarities prevail.

Speciation study of an imidazolate-bridged copper(II)-zinc(II) complex in aqueous solution.

The solution equilibrium and the binding mode of the species in the five-component system containing two metal ions (copper(II) and zinc(II)) and three ligands (A=diethylenetriamine, B=imidazole, C=tris(2-aminoethyl)amine) were investigated by pH-potentiometric titration, UV-visible spectrophotometry and EPR (electron paramagnetic resonance) spectroscopic titration in aqueous solution in the 2-11 pH range. An imidazolate-bridged heterobinuclear complex (ACuBH(-1)ZnC) was found to evolve above pH=7 and was stable between pH 7 and 11. The existence of the ACuBH(-1)ZnC complex (by determination of its molecular weight) was proved by mass spectrometry (ESI-MS (electrospray ionization mass spectrometry) and MALDI (matrix-assisted laser desorption/ionization) techniques). The electrochemical behaviour and the superoxide dismutase activity of this complex were also tested by cyclic voltammetry and the Riboflavin/NBT (nitro blue tetrazolium) assay, respectively.

Preparation and Characterization of Hybrid Organic-Inorganic Composite Materials Using the Amphoteric Property of Amino Acids: Amino Acid Intercalated Layered Double Hydroxide and Montmorillonite.

Deprotonated and protonated forms of L-tyrosine or L-phenylalanine were intercalated by Zn-Al hydrotalcite (HT) and Na-montmorillonite (Na-mont), respectively. The intercalated materials were characterized by powder X-ray diffraction, BET measurements, and FT-IR spectroscopy. Intercalation was successful as the increased basal spacings attested. For hydrotalcite this increase was always significantly larger than for montmorillonite. This fact indicated that the spatial arrangement of the amino acid moieties was very different. A model for this arrangement has been suggested. A variety of methods showed that L-Tyr(Phe)-HT was thermally less stable than HT, while the heat resistance of L-Tyr(Phe)-mont did not change.

Hydrogen-bonding interactions in the crystalline-phase structures of cinnamic acid derivatives.

Secondary interactions responsible for the crystalline-phase structures of various cinnamic acids and cinnamic acid esters drawn from the Cambridge Structural Database were studied with the help of the Cerius package implemented on an SGI workstation. Primarily hydrogen-bonding interactions were sought, but deviation from planarity was also measured. For the acids, the main structural feature is the strong hydrogen bonding between the carboxyl groups. The dimers are interconnected by C-H.O intermolecular hydrogen bonds. In most cases the C atom of the C-H unit was a member of the aromatic ring. Intramolecular (olefinic) C-H.O bonds were found to be frequent, fixing synperiplanar and antiperiplanar C=C-C=O conformations with about the same abundance in the acids and exclusively synperiplanar conformations in the esters. The carbonyl group of the ester is always involved in C-H.O hydrogen bonding. Here, the C atom of the C-H unit was either a member of the aromatic ring or the olefinic group, or was attached to the alcoholic O atom of the ester group. The beta-phenyl and the carboxyl or the ester groups are almost coplanar. The crystals have a layered structure and in the most frequent parallel arrangement the phenyl groups are offset by varing amounts (but always to a small extent) in neighbouring layers. The common hydrogen bonds are mostly within a layer.