Electrochemical Study of Schiff Bases by Means of Self‐Assembled Monolayers

In this paper, Schiffbases were investigated using cyclic voltammetry (CV) and impedance electrochemical spectroscopy (EIS) techniques by means of self‐assembled monolayers for the first time, where a 0.1 M KCl solution and the redox couple of Fe(CN)₆^3?/Fe(CN)₆^4?were used as the electrolyte and probing‐pin, respectively. The monolayers formed by the employed Schiff base were proved to be relatively stable, and its electrochemical response in the studied system with different pH values was also de scribed clearly with CV and EIS plots. The results show that the monolayer of Schiff bases could exist in the solution with pH value from 2 to 10. In the EIS measurement in the concentration range from 10^?5 M to 5× 10^?4 M, a nearly linear relation ship between the charge transfer resistance (R_ct) and the logarithm concentration of Cu²+was observed, suggesting that Cu²+ could be titrated with the EIS method quasi‐quantitatively. The phenomenon agreed with the former report very well. Using the self‐assembled monolayers to study Schiff bases with the electrochemical method is the major contribution of our work.     

Effect of chain compositions on interpolymer specific interaction in solutions

An interpolymer specific interaction of polymers with complementary proton donor units and proton acceptor units was studied with viscometry. In this study, poly(styrene-co-octyl acrylate-co-acrylic acid) as proton donating polymer (PDP) and poly(styrene-co-octyl acrylate-co-4-vinylpyridine) as proton accepting polymer (PAP) with different macromolecular chain compositions were prepared by emulsion copolymerization. Complexed solutions formed by PDP and PAP were studied with a novel interaction criterion k_a based on viscosity enhance factor. The effects of macromolecular chain compositions on the ability to interpolymer interaction and complex stoichiometry were discussed. The results showed that long chain alkyl acrylate units play an important role in the interpolymer specific interaction.     

Synthesis and characterizations of N,N-bis(diphenylphosphino)ethylaniline derivatives and X-ray crystal structure of palladium (II), platinum (II) complexes

N,N-Bis(diphenylphosphino)ethylaniline compounds, [Ph₂P]₂N-C₆H₄-C₂H₅, with ethyl groups at the ortho- and para-positions have been synthesized. Oxidation of the aminophosphines with hydrogen peroxide, elemental sulfur and selenium gave the corresponding oxides, sulfides and selenides [Ph₂P(E)]₂N-C₆H₄-C₂H₅ (E = O, S, Se). Complexes [MCl₂{(Ph₂P)₂N-C₆H₄-(C₂H₅)}] (M = Pd, Pt) and [Cu{(Ph₂P)₂N-C₆H₄-C₂H₅}₂]PF₆ were obtained by the reaction of N,N-bis(diphenylphosphino)ethylaniline with [MCl₂(COD)] (M = Pd, Pt) and [Cu(MeCN)₄]PF₆. The new compounds were characterized by NMR, IR spectroscopy and microanalysis. In addition, representative solid-state structures of the palladium and platinum complexes were determined using single crystal X-ray diffraction analyses.     

In vitro and in vivo studies of N,N′-bis[2(2-pyridyl)-methyl]pyridine-2,6-dicarboxamide–copper(II) and rheumatoid arthritis

The thermodynamic equilibria of copper(II), zinc(II) and calcium(II) with N,N′-bis[2(2-pyridyl)-methyl]pyridine-2,6-dicarboxamide (L1) have been studied at 25 °C and an ionic strength of 0.15 mol dm⁻³. Spectroscopic studies suggest metal ion complexation promotes deprotonation and coordination of the amide nitrogens resulting in overall tetragonal coordination of Cu²⁺. Blood–plasma modelling predicts that Cu(II) competes effectively against Zn(II) and Ca(II) for L1 in vivo. Octanol–water partition coefficient studies show that Cu(II)–L1 complexes are reasonably lipophilic. However, the CuL1H₋₂ species which predominates at the physiological pH of 7.4 has poor superoxide dismutase activity. Bio-distribution experiments showed activity accumulation and retention in the body of about 50% of the injected dose for the [⁶⁴Cu]Cu(II)–L1 complex after 24 h.     

Experimental evidences for some unusual divalent cation complexes of valinomycin

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M ²⁺ (aq) + 1 · Sr²⁺ (nb) ⇄ 1 · M ²⁺ (nb) + Sr²⁺ (aq) taking place in the two-phase water-nitrobenzene system (M ²⁺ = Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, UO₂ ²⁺, Fe²⁺, Co²⁺, and Ni²⁺; 1 = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1 · M ²⁺ complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Fe²⁺ < Cd²⁺, Co²⁺ < Ni²⁺ < UO₂ ²⁺, Zn²⁺ < Cu²⁺ < Pb²⁺. Correspondence: Emanuel Makrlík, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic.     

Solvent extraction of univalent cations into nitrobenzene using sodium dicarbollylcobaltate and tetraphenyl p-tert-butylcalix[4]arene tetraketone

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the equilibrium M ⁺(aq) + 1 · Na⁺ (nb) ⇄ 1 · M ⁺ (nb) + Na⁺ (aq) taking place in the two-phase water-nitrobenzene system (M ⁺ = Li⁺, H₃O⁺, NH₄ ⁺, Ag⁺, K⁺, Rb⁺, Tl⁺, Cs⁺; 1 = tetraphenyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1 · M ⁺ complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Cs⁺ < Rb⁺ < Tl⁺ < K⁺ < NH₄ ⁺ < Ag⁺ < H₃O⁺ < Li⁺. Correspondence: Emanuel Makrlík, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic.     

Diazo-coupled calix[4]arenes for qualitative analytical screening of metal ions

New chromogenic diazophenylcalix[4]arenes 1 and 2 were synthesized in cone conformation. Compound 1 with the ortho-carboxyl groups in CH₃CN solution preferentially binds with alkaline earth and transition metal ions, whereas no significant changes in absorption spectra are observed in the presence of alkali metal ions. While 2 with the ortho-ester groups shows selective complexation properties towards transition metal ions over alkali and alkaline earth metal ions. The detection of metal ions gives rise to bathochromic shifts in the absorption spectra (from orange/yellow to red), which is clearly visible even to the naked eye. According to the selective color changes using both receptors upon cation complexation, one can set up a qualitative analytical routine to screen alkali, alkaline earth, and transition metal ions.     

Energetics of binding and protein unfolding upon amphiphilic drug complexation with a globular protein in different aqueous media

The interactions and complexation process of the structurally related amphiphilic phenothiazines promazine and triflupromazine hydrochlorides with horse myoglobin in aqueous buffered solutions of pH 2.5, 5.5 and 9.0 have been examined by zeta-potential, isothermal titration calorimetry (ITC), UV-vis spectroscopy and dynamic light-scattering techniques with the aim of analyzing the effect of hydrophobic and electrostatic forces, the alteration of protein conformation and the effect of substituents in the drug molecular structure on the binding mechanism and structure of the resulting complexes. The energetics and stoichiometry of the binding process was derived from ITC. The enthalpies of binding obtained are small and exothermic, and the Gibbs energies of binding are dominated by large increases in entropy consistent with hydrophobic interactions. Binding isotherms were obtained from microcalorimetric data by using a theoretical model based on the Langmuir isotherm. zeta-Potential data showed a reversal in the sign of the protein charge at pH 9.0 as a consequence of drug binding. Gibbs energies of drug binding per mole of drug were also derived from zeta-potential data. On the other hand, binding of the phenothiazines causes a conformational transition on protein structure which was followed as a function of drug concentration by using UV-vis spectroscopy. These data were analyzed to obtain the Gibbs energy of the transition in water (DeltaG(w)(degrees)) and in a hydrophobic environment (DeltaG(hc)(degrees)). Finally, the population distribution of the different species in solution and their size was analyzed through dynamic light scattering. The existence of an aggregation process of drug/protein complexes, mainly at pH 2.5, was observed. We think this is a consequence of the already expanded structure of the protein at this pH and the subsequent binding of drug molecules to the protein.     

Remote Control of One-Handed Helicity in Polyacetylenes through Flexible Spacers in Water: Impact of the Spacer Length

We report the unprecedented sergeants and soldiers (S&S)-type remote control of one-handed helicity in copolymers of chiral/achiral biphenylylacetylenes bearing amphiphilic oligo(ethylene glycol) (OEG) side chains. A small amount of chiral binaphthyl residues (≤10 mol %) introduced at the terminal of the achiral OEG spacers as many as 80 bonds away from the polymer backbones induced a complete one-handed helix in water through preferential intramolecular encapsulation of the binaphthyl groups within a cavity of the copolymers. A fully one-handed helix can be induced virtually independent of the OEG spacer length and concentrations. At a specific spacer length, however, its helix-sense was inverted. The copolymers also form an excess one-handed helix in organic solvents in an OEG spacer-length dependent manner, yet far from the polymer backbones. We show the superiority of the present covalent-bond driven S&S-type remote helicity control over the corresponding noncovalent helicity induction approach.