ESI MS/MS Study of Calix[4]arene Derivatives and their Metal Complexes

The peptidocalixarenes 1-3 bearing tryptophan, phenylglycine and leucil units at the lower rim and their complexes with alkali-metal (Li+, Na+, K+, Rb+, Cs+) and selected lanthanide cations (La3+, Ce3+, EU3+, Yb3+) were analyzed by ESI MS. The influences of the solvent (acetonitrile, methanol, addition of formic acid or sodium acetate) and the calixarene:cation molar ratio on signal intensities were investigated. Comprehensive MS/MS analyses were performed of all singly and doubly charged ions of 1-3 and their complexes, and fragmentation pathways were proposed. An inductive cleavage was observed during dissociation of protonated ions, while the presence of alkali-metal or lanthanide cations caused homolytic cleavage and formation of radical cations. The results of MS analysis were in accordance with those obtained by other techniques (spectrophotometric, potentiometric, and conductometric titrations). The MS/MS experiments could be used as fast and sensitive method for prediction of relative stabilities of calixarene complexes with metal ions

Association of Nitrate Ion with Metal Cations in Aqueous Solution: a UV-Vis Spectrometric and Factor-Analytical Study

Ion association in aqueous solutions of varied concentrations of LiNO3, NaNO3, Ca(NO3)2, Sr(NO3)2, Ba(NO3)2, Mn(NO3)2, Co(NO3)2, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2, and Cd(NO3)2 was studied by means of UV spectrometry. In all cases, except for Zn(NO3)2(aq) the principal-components (PCA) and evolving-factor (EFA) analyses of the spectra indicated formation of associated ion pairs [MNO3]z-1 (Mz denotes the cation) at higher salt concentrations. The (dis)similarities of the [MNO3]z-1 (Mz spectral profiles (computed by EFA) were examined by means of cluster analysis. The influence of transition-metal ions on the nitrate UV spectrum was found to be remarkably different compared to that of non-transition cations. That could be a consequence of different types of cation-anion interactions. The ion pairs containing non-transition metal ions could be regarded as classical electrostatic ones, whereas a weak coordination interaction was presumably present in the ion pairs formed by the nitrate and the cations of transition metals

Calibration of Glass Electrode in Terms of H+ Concentration by Titration of Weak Acid in Cells with and without Liquid Junction

Calibration of glass-electrode cells with and without transference in terms of hydrogen ion concentration was performed by potentiometric titrations of aqueous solutions of two weak acids, 2-amino-2-hydroxymethyl-1,3-propanediol hydrochloride, TrisHCl, and potassium hydrogenphthalate, with a strong base (KOH). Cell calibration parameters were computed from the titration data, along with the values of stoichiometric protonation equilibrium constants, by using an iterative optimisation procedure. No significant difference between the E vs. [H+] responses of the glass-electrode cells with and without liquid junction was observed. For both kinds of cell, the imposed model of linear E vs. p[H] relation proved to be a satisfactory approximation only in the buffer regions of the titration curves. The values of protonation equilibrium constants, expressed as lg(K1 H/dm3 mol–1), determined at 25 °C, Ic = 0.1 mol dm–3 (KNO3 or KNO3 + KCl) in the cell with transference (Tris: 8.058, phthal2–: 4.933) are in very good agreement with those determined in the cell without transference (Tris: 8.091, phthal2–: 4.928), as well as with comparable literature values

Complexation of Oxonium and Ammonium Ions by Lower-rim Calix[4]arene Amino Acid Derivatives

Complexation of oxonium and ammonium cations with two calix4arene amino acid derivatives, namely 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis-(O-methyl-D-α-phenylglycylcarbonylmethoxy)-calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-26,28,25,27-(O-methyl-L-leucylcarbonylmethoxy)calix[4]¬arene (2), in acetonitrile and methanol was studied by means of spectrophotometric and calorimetric titrations at 25 °C. The classical molecular dynamics simulations of the macrocycles and the corresponding complexes with NH4+ and H3O+ were carried out in order to investigate their possible structures in solution. The examined calix[4]arene derivatives were shown to be rather efficient binders for H3O+ cation and moderately efficient for NH4+ in acetonitrile, whereas the complexation of these cations in methanol could not be observed. The structures of the complexes obtained by means of molecular dynamics simulations suggested the involvement of ether and carbonyl oxygen atoms in the complexation of both NH4+ and H3O+. An inclusion of an acetonitrile molecule into the hydrophobic cavity of the free and complexed ligands was observed as well. The difference in binding affinities of 1 and 2 towards NH4+ and H3O+ ions could be explained by taking into account cation solvation, difference in their size and in the strength of hydrogen bonding between cations and the ligand binding sites. (doi: 10.5562/cca2172

Nitrozobenzenska biblioteka: Model za proučavanje selektivnosti dimerizacije nitrozo-azodioksida u čvrstom stan

Cross-linking of nitroso benzenes to heterodimers (azodioxides), in the case when they are not sterically crowded with large groups in ortho-position, was studied by NMR, UV-VIS, and Raman spectroscopy as well as by powder X-ray crystallography. Dimerization of nitroso compounds to azodioxides can, in principle, be used for the construction of novel supramolecular structures. As a preliminary investigation, the selectivity of nitrosobenzenes to form dimers in the solid state was studied. Observations by NMR and vibrational spectroscopy show that selectivity for cross-linking is quite different in the solid state from that in solution. This is explained by a considerable influence of packing factors in the former. Selectivities for cross- -linking in the solid state in a complex chemical library of monomers were formulated and measured using simple spectroscopic and diffraction methods. For every member of such a nitrosobenzene chemical library it is possible to measure and, using the Tanimoto similarity coefficients, calculate two selectivity parameters, chemical selectivity and packing selectivity. While packing selectivity is correlated with total dipole moments of nitroso monomer molecules, chemical selectivity is in correlation with the x-component of the molecular dipole, i.e., the axis that is nearly collinear with the C-N bond in nitroso group. The method developed in this work could, in principle, be proposed for more general use in investigations of similar chemical libraries with binary combined components.Dimerizacija različito supstituiranih nitrozobenzena, do koje dolazi kristalizacijom, rabljena je kao model za kvantificiranje reaktivnosti i selektivnosti u čvrstome stanju. Predloženi parametri selektivnosti dobiveni su na temelju IR spektroskopije i difrakcije X-zraka na prahu za kemijsku biblioteku nitrozobenzena supstituiranih u m- i p- položaju

Potentiometric Titrations as a Tool for Surface Charge Determination

This article summarizes methods for determining proton surface charge at mineral/water interfaces. It covers conventional experimental procedures and discusses problems with the techniques. Also it involves recommendations for obtaining reasonable and comparable results. The term "comparable results" refers to comparison between results for the same solid as obtained in different laboratories. The most important parameters for the surface titrations are discussed. We also propose a reference titration procedure that would allow direct, unbiased comparisons of experimental data. The article finally includes a check-list for researchers and reviewers which should allow limiting the amount of titration data that are not useful for future uses. (doi: 10.5562/cca2062