Results from solvophobic theory applied to methylene selectivity in reversed-phase HPLC

A significant amount of work has been previously dedicated to the understanding of methylene selectivity parameter. The conventional theory applied for this understanding was mostly based on the assumption that the difference in the Gibbs free energy of transfer from the mobile phase to the stationary phase is a constant for any two compounds in a homologous series that differ by a CH₂ group. In the present study, it is shown based on solvophobic theory that this assumption is indeed correct, but it provides a theoretical justification for it. Exemplification of the results of theory was obtained using the values for methylene selectivity (α(CH₂)) measured experimentally for seven different C18 chromatographic columns including two core–shell columns and using water and either methanol or acetonitrile as an organic component. Four different homologous series of compounds were used for evaluation. The study proved the theoretical prediction that the values for α(CH₂) obtained using different homologous series of compounds are only slightly different from those obtained using the toluene–butylbenzene series. Even using different homologous series, the same type of information regarding the columns comparison, and the changes in log α(CH₂) with the solvent composition was obtained.     

A new stable porous Pr-organic framework constructed by multi-iodine-substituted aromatic polycarboxylates: Synthesis,characterization, and selective adsorption of dyes

abstract

Poly[tris(dimethylformamide)(μ3-2,4,6-triiodol-1,3,5-benzene tricarboxylic acid)-praseodymium (III)] {Pr(TIBTC)(DMF)₃}_n (1) (H₃TIBTC = 2,4,6-triiodo-1,3,5-benzene tricarboxylic acid) was synthesized by the reaction of Pr(NO₃)₃·6H₂O and H₃TIBTC at 85°C in a pyrex vial. 1 was characterized by elemental analysis, IR, UV–vis, TGA, PXRD, and atomic force microscopy analytical means. Each of the central Pr ions and the three carboxyl groups from the same ligand constitute a SBU, which is then joined by a carboxyl group to form a building block. In order to further explore the functional properties of 1, we used this compound for adsorption experiments. It is found that 1 can effectively adsorb anionic dyes in aqueous solutions. In particular, there is a good adsorption efficiency for coomassie brilliant blue R-250. Therefore, 1 shows good prospects for selective adsorption of anionic dyes from wastewater solution.     

Selectivity of seismic electric signal (SES) of the 2000 Izu earthquake swarm: a 3D FEM numerical simulation model

Although seismic electric signal (SES) has been used for short-term prediction of earthquakes, selectivity of SES still remains as one of the mysterious features. As a case study, we made a numerical simulation based on a 3D finite element method (FEM) on the selectivity of SES observed in the case of the 2000 Izu earthquake swarm. Our numerical results indicated that the existence of conductive channel under Niijima island could explain the reported SES selectivity.     

Synthesis and Comparison of Extraction Properties of p‐tert‐Butylcalix[n]arene Nitrile Derivatives for Selected Metals and Dichromate Anions

The article describes the syntheses and extraction properties of two p‐tert‐butylcalix[6]arene nitrile derivatives (3 and 4). The trinitrile derivative 3 has been synthesized from 5,11,17,23,29,35‐hexa‐tert‐butyl‐37,38,39,40,41,42‐hexahydroxycalix[6]arene 1. The compound 1 was directly converted to its hexanitrile derivative 4. In these syntheses, it was thought to explore the role of nitrile sites in the extraction of various metal cations and HCr₂O₇ ^?/Cr₂O₇ ^2? anions. The liquid‐liquid extraction properties of 3 and 4 towards selected alkali/transition metal cations and HCr₂O₇ ^?/Cr₂O₇ ^2? anions are reported. It has been observed that receptor 3 does not extract alkali/transition metal cations effectively, but shows affinity towards HCr₂O₇ ^?/Cr₂O₇ ^2? anions at low pH. The compound 4 is an effective form for transferring Ni²⁺ selectively, while it shows poor transferring ability for HCr₂O₇ ^?/Cr₂O₇ ^2? anions from an aqueous into a dichloromethane layer. It was observed that the cavity size of the calix[n]arenes and the cooperativity of the functionalities play important roles in two phase extraction systems.     

A Cyclodextrin Molecular Reactor for the Regioselective Synthesis of 1,5-disubstituted-1,2,3-triazoles

6^A-Deoxy-6^A-propynamido-β-cyclodextrin reacts with 4-tert-butylphenyl azide in aqueous solution, to form the 5-(aminocarbonyl)-substituted triazole in preference to the 4-(aminocarbonyl)-substituted analogue, in a ratio of 25:1. The cyclodextrin moiety templates the reaction through the formation of a host-guest complex of the dipole with the dipolarophile, controlling the regioselectivity of cycloaddition. In a control reaction under similar conditions, with propiolamide instead of the cyclodextrin derivative, 5- and 4-(aminocarbonyl)-1-(4-tert-butylphenyl)-1,2,3-triazole were formed in a ratio of 1:4. As well as reversing the regioselectivity, the cyclodextrin substituent increases the rate of cycloaddition, by at least two orders of magnitude for the reaction to give the 5-substituted cycloadduct. Even the rate of formation of the 4-substituted cycloadduct is increased by a factor of two. Less marked effects are observed with phenyl azide and 4-tert-butylbenzyl azide as dipoles.     

Syntheses of dibenzo-18-crown-6 lariat isomers and their complexation with lanthanoid nitrates

Two constitutional isomers of dibenzo-18-crown-6 derivatives (6 and 7) were synthesised and their binding behaviours towards trivalent lanthanoid cations (La^3 + , Ce^3 + , Pr^3 + , Nd^3 + , Sm^3 + , Eu^3 + , Gd^3 +  and Tb^3 + ) were investigated. Both isomers expressed better binding affinities towards Sm^3 +  and Tb^3 +  than a group of other lanthanoids, as measured by the ligand-to-metal charge-transfer (LMCT) band intensity at ca. 425 nm using UV–vis spectroscopic method. Additionally, the trans isomer 7 was shown to have a higher binding ability than the cis isomer 6 towards Tb^3 + .

     

A Highly Selective Colorimetric Sensor for Cu2+ Based on Phenolic Group Biscarbonyl Hydrazone

A novel copper selective sensor 2 based on hydrazide and salicylaldehyde has been designed and prepared. Sensor 2 behaves a single selectivity and sensitivity in the recognition for Cu²⁺ over other metal ions such as Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ni²⁺, Co²⁺, Cr³⁺ and Mg²⁺ in DMSO. The distinct color change and the rapid changement of fluorescence emission provide naked‐eyes detection for Cu²⁺. The UV‐vis data indicate that 1:2 stoichiometry complex is formed by sensor 2 and Cu²⁺. The association constant K_s was 3.51×10⁴ mol^?1·L. The detection limitation of Cu²⁺ with the sensor 2 was 2.2×10^?7 mol·L^?1. The sensing of Cu²⁺ by this sensor was found to be reversible, with the Cu²⁺‐induced color being lost upon addition of EDTA.     

Separation selectivity patterns of fully charged achiral compounds in capillary electrophoresis with a neutral cyclodextrin

Based on the separation selectivity equation, related to the dimensionless parameters for fully charged achiral analytes using a neutral CD, the separation selectivity can be classified into seven patterns. With respect to CZE without CD, the presence of CD in the buffer may improve, or reduce, the separation selectivity with this effect being accompanied by the same or reversed electrophoretic mobility order for charged analytes. This can depend on the separation selectivity of the two analytes in free solution, the binding selectivity, the separation selectivity of analyte–CD complexes and the ratio of electrophoretic mobility of the analytes in free, and complexed forms. Using positional isomers of benzoic acids and phenoxy acids as test analytes and α‐CD as a selector, the observed separation selectivity shapes were found to be in excellent agreement with the predicted separation selectivities.     

Trichloromelamine (TCM) – Catalyzed Efficient and Selective Thioacetalization of Aldehydes and Transthioacetalization of Acetals and Oxathioacetals under Mild Reaction Conditions

Trichloromelamine was used effectively as a catalyst for thioacetalization of aldehydes and transthioacetalization of acetals and oxathioacetals under mild and almost neutral reaction conditions. By this method, aldehydes, acetals, and oxathioacetals were selectively protected in the presence of ketones as their 1,3-dithiolanes or 1,3-dithianes.