Indirect detection in reversed-phase liquid chromatography: Ion-pair retention models for cations on polystyrene polymers

Summary The distribution equilibria of cationic compounds in reversed-phase chromatographic systems (ion-pair chromatography) have been studied on the basis of their effect on a detectable mobile phase component. The solid phase was a polystyrene-divinylbenzene copolymer and the detectable component, a quaternary ammonium ion, 1-methylpyridine. The solutes were mono- and divalent amines and quaternary ammonium ions. The cations can be retained by ion-pair adsorption and ion exchange. Expressions for the ion-pair retention of the solutes and the mobile phase cation (system peak) have been developed assuming Langmuir distribution of ion pairs to a solid phase with one kind of binding site. The validity of the expressions has been tested by evaluation of ion-pair distribution constants using non-linear curve fitting techniques. Good agreement for the constants of common ion pairs was obtained from different kinds of capacity ratio expressions. Ion exchange retention can appear beside ion-pair retention, and it has been observed in the pH range 1.6–6.1. The effect depends not only on cations in the mobile phase, but also on the nature of the buffering systems.     

The thermorheological complexity of photoelastic behaviour of 2-hydroxyethyl methacrylate — dodecyl methacrylate copolymers

The viscoelastic photoelastic behaviour of networks of 2-hydroxyethyl methacrylate — dodecyl methacrylate (DMA) copolymers in the main transition and rubberlike region was investigated. With increasing DMA content, photoelastic functions are quickly shifted to lower temperatures or shorter times; a detailed course of the functions suggests heterogeneity of the copolymers. Due to the existence of long side chains, optical function of all samples change the sign from positive to negative with increasing temperature. While the temperature dependences of the moduli of copolymers can be described by the two-phase Takayanagi model, the temperature dependences of optical functions cannot be described by using this model. It has been found, however, that the tempeature and time dependences of photoelastic functions can be described semiquantitatively by a three-phase model with a hypothetical statistical copolymer as the third component. The high values of the volume fraction of the hypothetical statistical copolymer found for the individual samples, suggest a considerable miscibility and a strong influence of the interphase boundary on the photoelastic behaviour of the copolymers.     

Hydrogen-induced metal-oxide interaction studied on noble metal model catalysts

Summary The effect of hydrogen reduction on the structure and catalytic properties of “thin film”and “inverse”model systems for supported metal catalysts is discussed. Thin film model catalysts were obtained by epitaxial growth of Pt and Rh nanoparticles on NaCl(001), which were coated with amorphous or crystalline supports of alumina, silica, titania, ceria and vanadia. Structural and morphological changes upon hydrogen reduction between 473 and 973 K were examined by high resolution electron microscopy. Metal-oxide interaction sets in at a specific reduction temperature and is characterized by an initial “wetting”stage, followed by alloy formation at increasing temperature, in the order VO_x< TiO_x< SiO₂< CeO_x< Al₂O₃. “Inverse”model systems were prepared by deposition of oxides on a metal substrate, e.g. VO_x/Rh and VO_x/Pd. Reduction of inverse systems at elevated temperature induces subsurface alloy formation. In contrast to common bimetallic surfaces, the stable subsurface alloys of V/Rh and V/Pd have a purely noble metal-terminated surface, with V positioned in near-surface layers. The uniform composition of the metallic surface layer excludes catalytic ensemble effects in favor of ligand effects. Activity and selectivity, e.g. for CO and CO₂methanation and for partial oxidation of ethene, are mainly controlled by the temperature of annealing or reduction. Reduction above 573 K turned out to be beneficial for the catalytic activity of the subsurface alloys, but not for the corresponding thin film systems which tend to deactivate viaparticle encapsulation.</o:p>     

Use of Local Lagrange Interpolation for calculation of retention indices in linear temperature-programmed gas chromatrography

Summary The influence of the isothermal temperature, program rate, initial temperature and flow rate on retention indices was studied. The methods of Kováts, Van Den Dool and Local Lagrange Interpolation are compared. Ten experimental measurements were carried out on a capillary column coated with OV-101 stationary phase.     

Reactivity of pyrrole pigments. Part 9 MINDO/3 calculations on dipyrrolic partial models of bile pigments

The applicability of the MINDO/3 method is evaluated for calculations on dipyrrolic partial structures of bile pigments. It is shown that this method cannot be used for an accurate conformational analysis. However, when applying the frontier orbital model for reactivity parameters, a good picture of the HOMO and the LUMO distribution can be obtained in this type of molecules.

---

Reaktivität von Pyrrolpigmenten, 9. Mitt. MINDO/3-Rechnungen von dipyrrolischen Partialmodellen von Gallenpigmenten

Zusammenfassung Es werden die Einsatzmöglichkeiten von MINDO/3 für den Fall dipyrrolischer Partialstrukturen der Gallenpigmente aufgezeigt. Die Methode ist für eine genaue Konformationsanalyse nicht geeignet. Unter Verwendung der Reaktionsparameter des Frontier-Orbital-Modells läßt sich jedoch ein gutes Bild der HOMO- und LUMO-Verteilung für diesen Verbindungstyp gewinnen.

     

溶液中(RC2R')Co(CO)(PR″3)2的配体PR″3之间的交换作用——三跳动力学模型

本文成功地运用了三跳动力学模型,通过相关函数和超精细分裂常数的关系, 推出了电子自旋共振波谱的线宽与基本线宽T_(2,0)~(-1)、溶液中各种异构体的超精细分裂常数、配体的交换寿命等之间的关系。求出了在290 K温度下(Ph_2C_2)Co(CO)[P(OEt)_3]_2的THF溶渡中P(OEt)_3配体的交换寿命是5.6×10~(-11)秒。     

High acidity of polycyano azatriquinanes—theoretical prediction by the DFT calculations

It is shown by the B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d) calculations that the hexacyano derivative of aza-acepentalene is an extremely powerful superacid both in the gas phase and in DMSO as evidenced by the ΔH_acid = 255.1  kcal mol⁻¹ and pK_a (DMSO) = −26.5. Its synthesis is strongly recommended, in particular, since the related conjugate base hexachloro aza-acepentalenide anion was prepared recently.     

Symmetries and correlation inequalities for classicaln-vector models

We describe a new class of single spin measures on then-dimensional sphereS _r ⁿ of radiusr (n 4) for which Lebowitz-type [J. Lebowitz,J. Stat. Phys. 16:463 (1977)] inequalities hold. This is achieved by an appropriate parametrization ofS _r ⁿ . The above class includes the uniform measures onxs Rⁿ ¦x¦ r for any 0 p r. The second topic of this paper is an abstract formulation of the first Griffiths inequality [R. B. Griffiths,J. Math. Phys. 8:478 (1967)] and the underlying symmetry property.     

Absence of continuous symmetry breaking in a one-dimensional n−2 model

For a one-dimensional array ofS ^N–1 spins (N 2) with isotropic pair interactions (and more general systems) with J(j–i) obeying sup_n[n^–1 ₁ ⁿ j ²|J(j)|]<, we prove that every equilibrium state is invariant under the natural action ofSO(N). In particular, there is no long-range order of the conventional type. Included is the caseJ(n)=n ^–2.Research partially supported by U.S.N.S.F. Grant No. MCS-78-01885.S. Fairchild Scholar at Caltech. On leave from Departments of Mathematics and Physics, Princeton University, Princeton, New Jersey 08544.     

Ising-like field theory

A field theory model onR ² in which the basic fields are Ising spins instead of Gaussian spins is examined. Using statistical mechanics techniques we discuss the ultraviolet and the infrared problems. In particular we discuss a technique yielding the asymptotic expansion in of the ground state energy, as 0, without using the cluster expansion.Supported in part by Consiglio Nazionale delle Ricerche.