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.     

Study of beta-cyclodextrin/fluorinated trimethyl ammonium bromide surfactant inclusion complex by fluorinated surfactant ion selective electrode

The construction and performance of a liquid membrane electrode responsive to N-(1,1,2,2-tetrahydroperfluorooctyl)-N,N,N-trimethylammonium bromide (FTABr) and its use for the study of β-cyclodextrin/fluorinated surfactant inclusion complex is described. The electrode is based on the use of tetrahydroperfluorooctyltrimethylammonium-tetraphenylborate ion pair as electro active material in polyvinyl chloride (PVC) matrix plasticized using 2-Nitrophenyl octyl ether (NPOE). The electrode exhibits a fast, stable, reproducible and “Nernstian” response (59 ± 2 mV) for FTABr over the concentration range of 10⁻⁵ to 2 × 10⁻³ mol L⁻¹ at 298 K. The lowest detection limit is 2 × 10⁻⁶ mol L⁻¹ and the response time is around 20-30 s. The validity of the electrode, for detection of fluorinated surfactant ions and hence to carry out electrochemical measurements to study micellization of fluorinated surfactant, is verified by comparing the critical micelle concentration (cmc) value of FTABr obtained by using the electrode, with that obtained by surface tension measurements. Association constant K for β-cyclodextrin/FTABr complex is evaluated from the potentiometric measurements carried out using this electrode and is observed to be ∼1.26 × 10⁵. The results suggest that β-cyclodextrin forms an equimolar association complex with the FTA⁺ surfactant ion.     

Lanthanide complexation with CMPO and CMPO-calix[4]arenes in solution: spectrophotometric and electrospray mass spectrometric approaches

The binding of lanthanide(III) cations with organophosphorous ligands like CMPO and related calix[4]arene-based derivatives have been investigated using two experimental methods. The stability constants of the lanthanum, europium and ytterbium complexes were first determined in methanol by UV absorption spectrophotometry in the presence of nitrate or chloride anions. The results showed that the stoichiometry and the stability of the complexes formed depend on the position of the CMPO moieties either on the wide or the narrow rim of the calixarene scaffold, the nature of the medium, the conformational mobility of the ligands. Complexation of lanthanum was also followed by ESI-mass spectrometry in the same solvent. This method confirmed the stoichiometry of the complexes, giving also structural information, like coordination of anion or solvent molecules to the complexes, and allowed the calculation of distribution curves in good agreement with those derived from the spectrophotometric results. This is an important result showing that ESI-MS can be used to provide with quantitative information when absorption spectrophotometry is not applicable, i.e. for systems where complexation leads to weak spectral changes.     

Potentiometry of effective concentration of polyacrylate as scale inhibitor

The concentration of polyacrylate (PA) used as a scale inhibitor was potentiometrically determined with a solid state copper ion-selective electrode after addition of Cu²⁺ as a probe. While the conventional methods monitor only the total concentration of PA, the proposed method measures the free, “effective” concentration of PA in equilibrium with species like Ca²⁺ and CaCO₃. The slope of a potential response to PA was −40 mV decade⁻¹ and the limit of detection was 10^−6.3 M (= mol dm⁻³) at a probe concentration of 10⁻⁶ M. The system could be used to control the PA concentration just enough to prevent the scale formation in various circulating water systems.     

Methods for determination of all binding parameters in systems with simultaneous borate and cyclodextrin complexation

Two novel methods for determination of binding constants in the systems with borate and cyclodextrin complexation were developed. The methods enable to determine all binding parameters in these systems and even the binding constants of interaction of a neutral analyte with a neutral cyclodextrin. The first method is based on nonlinear fitting of experimental data and further evaluation of fitting parameters. The second method requires a multiple regression. The methods provide identical results with low experimental error. Only one set of measurements is required for both methods. Thus the binding parameters can be mutually compared. The binding parameters for neutral analytes ((R,R)-(+)-hydrobenzoin and (S,S)-(-)-hydrobenzoin) and neutral cyclodextrin (heptakis(2,6-di-O-methyl)-β-cyclodextrin) were evaluated and the effect of individual types of interaction was revealed. The interaction of the analytes with cyclodextrin governs the chiral recognition, while the complexation of analyte with borate is responsible for electromigration. Very low values of the binding constants of mixed analyte-cyclodextrin-borate complexes indicate that this type of complexation has negligible effect on enantioseparation.     

Solvent isotope effects on the complexation and exchange kinetics of Tl(I), K and Na with 18-crown-6 by competitive NMR spectroscopy: Competition between homo- and heterobimolecular cations exchange

The thermodynamic properties of complexation and exchange kinetics of thallium by 18-crown-6 have been studied by thallium NMR spectroscopy. Effects of solvent isotope, counterion (ClO₄⁻ and NO₃⁻) and presence of competitive cations, such as Na⁺ and K⁺, on the exchange characteristics of the system have been considered. The obvious relationships between the effects of D₂O-H₂O solvent isotope on the thermodynamic properties and activation parameters of complexation have been investigated. In the absence of competitor cations, the mechanism of thallium exchange is unimolecular decomplexation and in the presence of competitor cations, homobimolecular cation exchange is the predominant mechanism at low concentrations of the ligand. At higher concentrations of the ligand, the measured rate constants show that the complexation/decomplexation process obeys a heterobimolecular cation interchange mechanism. The rate constants ratios (k_D2O/k_H2O < 1) for unimolecular mechanisms also show an inverse solvent isotope effect.     

In situ IR monitoring of complexation reaction between 2,6-bis(3,5-dimethylpyrazoyl)pyridine and some metal ions

In situ complexation reactions between 2,6-bis(3,5-dimethylpyrazoyl)pyridine (bdmpp) and some transition metals (Cu²⁺, Co²⁺ and Ni²⁺) were studied with a new method in liquid cell using FT-IR. In this method, the FT-IR spectrum of the solution of ligand was defined as a background, and then the changes in the FT-IR spectra by the addition of the metal salts were investigated. This method allows one to obtain the spectra of the ligand-metal complex before yielding the solid-state product. Complexation ratios (M/L) of these metals with bdmpp were found 1/1, 1/2 and 1/2, for Cu, Co and Ni, respectively. Studying with Mg²⁺ and Ca²⁺ ions showed that there were no interaction between bdmpp and these metal ions in methanol.     

尼群地平磷脂超分子复合物的复合率测定

建立尼群地平磷脂超分子复合物的复合率测定方法。采用紫外分光光度法测定尼群地平磷脂超分子复合物中复合了的药物含量,从而计算复合率。结果表明,尼群地平在237nm处有最大吸收,浓度在2.18—10.89μg·mL^-1范围内与吸光度呈良好的线性关系,回归方程为:A=0.0760C+0.0013,r=0.9999;平均加标回收率为99.3%,RSD为1.2%（n=9）。该法简便、快速,重现性好,结果准确可靠。     

Stability constants of some metal cation complexes of tetraphenyl <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butylcalix[4]arene tetraketone in nitrobenzene saturated with water

Abstract  From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium taking place in the two-phase water–nitrobenzene system (M²⁺ = Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, UO₂ ²⁺, Mn²⁺, Co²⁺, Ni²⁺; 1 = tetraphenyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the 1 · M²⁺ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the cation order Ba²⁺, Mn²⁺ < Co²⁺ < Cu²⁺, Ni²⁺ < Zn²⁺, Cd²⁺, UO₂ ²⁺ < Ca²⁺ < Pb²⁺. Graphical abstract