Retention of ionizable compounds on HPLC. Modelling retention for neutral and ionizable compounds by linear solvation energy relationships

Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes, both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity and basicity, dipolarity/polarizability…). This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various journals.     

Hydrogen dissociation on high-temperature tungsten

H₂ dissociation on polycrystalline tungsten is measured from 1700 to 3000 K using the filament temperature (T) change and a normalized H-atom density at the chamber surface. The dissociation probability per H₂ filament collision (P_diss) saturates at 0.40 at high T and has a 2.25 ± 0.05 eV apparent activation energy when P_diss ? 1. This activation energy is consistent with prior data and models, but the H₂ pressure dependence is not. P_diss is independent of the H₂ pressure for this entire T range and the 1-85 mTorr pressure range studied, contradicting the primary model that has been used to explain H₂ dissociation on tungsten and other metals. We show that some apparently contradictory prior measurements are actually consistent with our observations and with each other, once this pressure dependence of P_diss is recognized.     

Compressibility and isotope effect of fluid hydrogen

The calculations of the P-V isotherms, Hugoniots, dissociation and ionization degrees of fluid (liquid) hydrogen isotopes have been performed by using the self-consistent fluid variational theory under isothermal and shock compression. The isotope effect of fluid hydrogen was discussed. The present results are compared with the available experiments and calculations.     

NO dissociation pathways on Rh(1 0 0), (1 1 0), and (1 1 1) surfaces: A comparative density functional theory study

The chemisorption and dissociation pathways of NO on the Rh(1 0 0), (1 1 0), and (1 1 1) surfaces are studied by the plane-wave density functional theory (DFT) with CASTEP program. In addition, the electronic and geometrical effects that affect the NO dissociation reactions have been investigated in detail. The calculation results are presented as following: The effective activation energies of the best NO dissociation pathways on the Rh(1 0 0), the Rh(1 1 0), and the Rh(1 1 1) are 0.63, 0.66 and 1.77 eV, respectively. The activity of the Rh planes for NO dissociation is in the order of Rh(1 0 0) ≈ Rh(1 1 0) > Rh(1 1 1). The low dissociation barrier for Rh(1 0 0) and Rh(1 1 0) is associated with the existence of a lying-down NO structure which acts as a precursor for dissociation. By Mulliken population analysis and structure analysis, both electronic and geometrical effects are found to affect the NO dissociation reactions, but the geometrical effect exceed the electronic. The energy decomposition scheme has been used to provide further insight into the NO dissociation reactions. Based on the calculations, the interaction energy between N and O in the transition state on the Rh(1 1 1) is found much larger than that on the Rh(1 0 0) and the Rh(1 1 0). The major differences of should originate from the variation of the bonding competition effect.     

The influence of exciton behavior on luminescent characteristics of organic light-emitting diodes

We used N,N′-bis-(1-naphthyl)-N,N′-1-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), 4,4′-N,N′-dicarbazole-biphenyl (CBP) and tris(8-hydroxyquinoline) aluminum (Alq₃) to fabricate tri-layer electroluminescent (EL) device (device structure: ITO/NPB/CBP/Alq₃/Al). In photoluminescence (PL) spectra of this device, the emission from NPB shifted to shorter wavelength accompanying with the decrease of its emission intensity and moreover the emission intensity of Alq₃ increased relatively with the increase of reverse bias voltage. The blue-shifted emission and the decrease in emission intensity of NPB were attributed to the polarization and dissociation of NPB excitons under reverse bias voltage. The increase of emission intensity of Alq₃ benefited from the recombination of electrons (produced by the dissociation of NPB exciton) and holes (injected from the Al cathode).     

均三溴氯磺酚离解与质子化作用的研究

本文报道测钪新试剂均三溴氯磺酚在水溶液中的离解与质子化作用，用电位法和光度法测得了它的逐级离解常数与质子化常数，以及热力学参数，并由分布函数获得试剂主要存在形式和ｐＨ值的关系。     

Structure elucidation of cyclohexene (9Z)-octadec-9-enyl ethers isolated from the leaves of Uvaria cherrevensis (Annonaceae)

The phytochemical investigation of the leaf extract of Uvaria cherrevensis (Annonaceae) yielded three new cyclohexene (9Z)-octadec-9-enyl ethers, cherrevenols M-O (1–3), and a known fatty ester derivative (4). The structures of the isolated compounds were elucidated by spectroscopic and computer-aided molecular modelling methods. Ozone Induced Dissociation (OzID) mass spectrometry was employed to determine the C-9 position of the side chain olefinic double bonds, while ¹³C NMR spectroscopy indicated their (Z)-configurations. All isolated compounds were evaluated for their antimalarial and cytotoxic activities; all were inactive.     

Thermodynamic determination of solvation potentials of various metal chlorides by (1,4-dioxane + water) mixtures through EMF measurements

The EMF data of different metal chlorides (2:1 electrolytes) were obtained by using a cell [M_X Hg|MCl₂ (m)|AgCl–Ag] at two temperatures. Stock solutions of metal chlorides (CoCl₂, CuCl₂ and ZnCl₂) were prepared by weight in 1,4-dioxane–aqueous mixtures. There was a significant change in the EMF values with change of metal chloride, its concentration and solvents composition. The standard electrode potential (E°) values of the above cell were calculated from the measured EMF of these mixtures. The standard thermodynamic functions (ΔG°, ΔH° and ΔS°) and respective transfer parameters of MCl₂ from water to 20, 45 and 70% dioxane–water mixtures were also evaluated. Equilibrium dissociation constants (K₁ and K₂) as well as the degrees of dissociation (α₁ and α₂) were obtained by iterative procedures. The data were analyzed in terms of solute–solvent interactions depending on standard and transfer thermodynamic parameters and mean activity coefficients (γ_±) of electrolytes.     

Synthesis and properties of fringelite D (1,3,4,6,8,10,11,13-octahydroxy-phenanthro[1,10,9,8,o,p,q,r,a]perylene-7,14-dione)

Summary Fringelite D was synthesized from 1,3,6,8-tetramethoxyanthracen-9-olvia two different efficient routes. The first one involved demethylation and subsequent dimerization. The other one started with dimerization to yield octamethylfringelite D and subsequent demethylation. The starting material was prepared in four steps from commercially available educts, the key step being a benzamideortho-lithiation. The spectroscopic properties of fringelite D were measured and are discussed. The dissociation, deprotonation, and protonation equilibria of fringelite D were characterized by their respectivepK values in ground and excited states and compared with those of hypericin. Homo- and heteroassociation properties of fringelite D were found to be similar to those of hypericin.

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Synthese und Eigenschaften von Fringelit D (1,3,4,6,8,10,11,13-Octahydroxy-phenanthro[1,10,9,8,o,p,q,r,a]perylen-7,14-dion)

Zusammenfassung Fringelit D wurde auf zwei effizienten Routen aus 1,3,6,8-Tetramethoxyanthracen-9-ol synthetisiert. Die erste umfaßt Demethylierung und anschließende Dimerisierung. Die andere beginnt mit der Dimerisierung zu Octamethylfringelit D und endet mit einer Demethylierung. Das Ausgangsmaterial wurde in vier Stufen aus kommerziell zugänglichen Edukten dargestellt; der Schlüsselschritt ist eineortho-Lithiierung eines Benzamids. Die spektroskopischen Eigenschaften von Fringelit D wurden gemessen und werden diskutiert. Die Dissoziations-, Deprotonierungs- und Protonierungsgleichgewichte wurden durch ihrepK-Werte in Grundzustand und angeregtem Zustand charakterisiert und mit jenen des Hypericins verglichen. Die Homo- und Hetero-assoziationseigenschaften von Fringelit D sind jenen des Hypericins ähnlich.

     

Studies on 1,2-Bis(O-Aminophenoxy)Ethane-N,N,N′,N′;-Tetraacetic Acid Chelates of the Tripositive Lanthanide Ions

The acid dissociation constants of 1,2-bis(cis-aminophenoxy)ethane-N,N,N′,N′;-tetraacetic acid (H₄BAPAT or H₄Z), and the stability constants of its chelates with tripositive rare-earth metal ions have been determined by the potentiometric titration and mercury indicator electrode methods at 15°, 25′ and 35°C and an ionic strength of 0.1 (KNO₃). The existence of a monohydrogen chelate species, LnHZ, and the normal chelate, LnZ^?, is illustrated. Enthalpy and entropy changes characterizing the formation of the normal chelates and the dissociation of the last two protons of chelating acid have been calculated at 25°C. These functions have been compared with corresponding values for related chelating agents.