Colloidal interactions: contact limiting laws,double-layer dissociation,and "non-DLVO" (Derjaguin–Landau–Verwey–Overbeek) forces

The conceptual basis and main results of a new model of the dissociative electrical double layer augmented with Lubetkin-Middleton-Ottewill (LMO) dissociative law are summarized. The main results are: the derivation of fundamental limiting laws of planar repulsions in the limit of surface contact, and their transition to the Debye-Hückel limiting laws at infinite separation; the prediction of stronger and longer-range electrostatic forces, quantitatively and consistently accounting for repulsions in colloidal montmorillonites; the discovery of the classical Debye-Hückel interionic effect being operative in increasing double-layer dissociation by lowering the activities of diffuse ions via the LMO law; the prediction of maxima of Stern potentials in spherical symmetry without any further assumptions, and the prediction of no maxima for platelike montmorillonites. In the light of these new insights, the concepts of "hydration forces" and other close-range "non-DLVO" forces may need to be revised, as well as the origin of the maxima of electrophoretic mobilities (Stern potentials) for spherical colloids.     

Studium der Reduktion von Resazurin

Zusammenfassung In dieser Arbeit wurden Schlußfolgerungen über den simultanen Verlauf der beiden Reduktionsphasen von Resazurin überprüft.Weiters wurden Bedingungen für die quantitative titanometrische Bestimmung von Resazurin und seiner Derivate ermittelt.

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The conclusions about the simultaneous course of reduction of Resazurin to Resorufin and Resorufin to Dihidroresorufin were verified in this work.The conditions for the quantitative titanometric determination of Resazurin and its derivatives were found.

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Mit 4 Abbildungen     

E-olefin dipeptide isostere incorporation into a polypeptide backbone enables hydrogen bond perturbation: probing the requirements for Alzheimer's amyloidogenesis

Herein, we report a stereospecific E-olefin dipeptide isostere synthesis that can be used to make gram quantities of the Phe-Phe isostere desired for eliminating a specific backbone H-bond donor and acceptor in the Alzheimer's disease related Abeta peptide. The Phe19-Phe20 E-olefin analogue of Abeta(1-40) was prepared by solid-phase peptide synthesis and was subjected to amyloidogenesis conditions. This analogue can aggregate into spherical morphologies but does not progress on to form protofibrils or fibrils as is the case for the all-amide sequence, providing insight into the structural requirements for amyloidogenesis.     

State vectors and propagators in many-electron theory. A unified approach

A unitary group formulation of the many-electron problem is employed to give explicit representations of state vectors which are convenient for the discussion of progerties derived from propagatorcalculations. New results are obtained concerning the nature of various random-phase-like approximations and ground state representatives are generated from consistency requirements for the spectral resolution of the polarization propagator. The explicit solution admits the calculation of ground state average values for arbitrary operators and a variational upper bound to the ground state energy.     

Splicing I: Using mixed basis sets in ab initio calculations

The effect of mixing (or “splicing”) extended and minimal basis sets on molecular properties such as geometries, Mulliken charges, dipoles, and internal rotation barriers was studied for several test molecules. The effect is gauged by comparison with full extended basis set calculations. It is found that splicing improves most properties relative to full minimal basis set calculations, and little accuracy is lost if the splicing is done in a judicious manner.     

The effect of morphological changes on the coprecipitation of strontium by calcium phosphate

The coprecipitation of strontium by a calcium phosphate phase formed at an elevated pH 10.8 was investigated. The first phase obtained under these conditions in the amorphous calcium phosphate (ACP) which is transformed into crystalline hydroxyapatite (HA) after the induction period. Is has been shown that this transformation together with morphological changes of the precipitated solid phase, influences the amount of the sorbed strontium significantly. The possible consequences of this finding on practical application of coprecipitation of strontium by calcium phosphate have been discussed.     

AB initio SCF LCAO MO Calculations on styrene

Minimal basis set ab initio SCF LCAO MO calculations with gaussian-type have been performed for different conformations of the styrene molecule. The computations show the molecule to be planar and the rotational barrier of the vinyl group is estimated to 3.9 kcal/mole.     

Excess and partial excess molar volumes of mixing of N,N-dibutyl-2-ethylhexamide with dodecanol

Excess and excess partial molar volumes of mixing of the system N,N-dibutyl-2-ethylhexylamide (DBEHA) + dodecanol (DDA) were determined at 25, 35, 45, 55 and 65°C. The excess molar volumes exhibit a maxima at each temperature at approximatelyx _DBEHA = 0.3 and a minima close tox _DBEHA = 0.9. The values of the excess volumes in general increase with the temperature. The partial excess molar volumes are calculated from the smoothed data and the results are discussed in the light of postulated amide-alcohol interactions.     

Analytische Aspekte der Oxydation organischer Stickstoffverbindungen mit Chromsäure. XXIII

Zusammenfassung Die früher beschriebene Halbmikromethode zur Bestimmung von Isonitrosogruppen in organischen Verbindungen wurde in den Mikromaßstab übergeführt. Sie beruht auf der Reaktion der Substanz mit Eisen(III)-sulfat in verd. Schwefelsäure. Dabei wird der Oximstickstoff als Distickstoffoxid frei, das mit Kupfer zu elementarem Stickstoff reduziert und im Mikroazotometer gemessen wird. Für die Berechnung des Oximstickstoffgehaltes aus den abgelesenen Gasvolumina wurden Werte für die konstante und proportionale Volumenkorrektur mit Hilfe der Methode der Regressionsgeraden experimentell festgestellt. Beide Werte sind den bei der N-N-Gruppenbestimmung benützten Volumenkorrekturen fast gleich. Die Bestimmung von Oximgruppen ist durch die Anwesenheit von Nitro- oder Aminogruppen nicht gestört. Diese Gruppen können aus derselben Einwaage durch nachfolgende Oxydation mit Chromsäure bestimmt werden.

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Analytical aspects of the oxidation of organic nitrogen compounds with chromic acid. XXIII

Summary The semimicro method previously described for the determination of isonitroso groups in organic compounds has been converted to the microscale. It is based on the reaction of the material with iron(III)-sulfate in dilute sulfuric acid. The oxime nitrogen is thus liberated as dinitrogen oxide, which is reduced to elementary nitrogen by copper and measured in the mieroazotometer. To calculate the oxime nitrogen content from the read-off gas volume, values for the constant and proportional volume correction with the aid of the regression lines were established experimentally. Both values are almost equal in the case of the determination of the volume corrections employed in the determination of the N-N-groups. The presence of nitro-or amino groups does not interfere with the determination of oxime groups. These groups may be determined from the same sample by subsequent oxidation with chromic acid.

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XXII. Mitteilung s.¹.