Automatic coulometric micro-determination of unsaturation with kinetic proof of real equivalence-point

Summary A fully automatic coulometric method has been applied successfully to the determination of unsaturated compounds on the micro-scale. Results are quoted which show a reproducibility of ± 0.3% for monoolefinic hydrocarbons. It is possible to control by means of a simple operation whether the addition reaction is complete and unaccompanied by side reactions. It has been shown that the concentrations of olefines in a mixture can be determined when their bromination speeds differ sufficiently from each other.

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Zusammenfassung Eine für kinetische Zwecke entwickelte vollautomatische, coulometrische Methode wurde mit Erfolg auf die Bromtitration ungesättigter Verbindungen im Mikromaßstab angewandt. Die angeführten Testuntersuchungen zeigen, daß bei monoolefinischen Kohlenwasserstoffen und ähnlichen Verbindungen die erreichbare Reproduzierbarkeit besser ist als ± 0,3%. Die Anordnung ermöglicht auf einfache Weise die Feststellung, ob die Addition vollständig abgelaufen ist und ob der Titrationswert nicht durch eine Nebenreaktion verfälscht wird. An Beispielen wird gezeigt, wie bei Gemischen olefinischer Verbindungen, die Bestandteile ausreichend verschiedener Reaktivität enthalten, die einzelnen Anteile nebeneinander bestimmt werden können.

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Résumé Les auteurs ont appliqué avec succès une méthode coulométrique entièrement automatique pour le dosage des composés non saturés à l'échelle microanalytique. Les résultats obtenus sont reproductibles à ± 0,3% près pour les hydrocarbures mono-oléfiniques. Une opération simple permet de contrôler que la réaction d'addition est complète et qu'elle n'est pas accompagnée par des réactions secondaires. Les auteurs ont montré également qu'il était possible de déterminer les concentrations de diverses oléfines dans un mélange lorsque leurs vitesses de fixation du brome diffèrent suffisamment les unes des autres.

     

Chemical autocatalysis in the NO + CO reaction on Pt(100)

It is shown that the reaction between NO and CO on Pt(100) is autocatalytic and probably involves a surface species which accelerates the reaction. Temperature-programmed desorption (TPD) of co-adsorbed NO and CO yields complete reaction, with N₂ and CO₂ desorbing simultaneously in sharp peaks at ≈410 K. Isothermal desorption also yields rates characteristic of chemical autocatalysis.     

Atomabsorptionsspektroskopische Bestimmung von Edelmetallen

Zusammenfassung Die atomabsorptionsspektroskopische Palladiumbestimmung wird vom Platin nicht und vom Rhodium nur wenig beeinflußt. Berücksichtigt man, daß ein Zusatz von Uran die Palladiumbestimmung neben Rhodium desaktiviert, so liegen allgemein die günstigsten Bedingungen für die Palladiumbestimmung vor, wenn Lanthan als spektroskopischer Puffer zugesetzt wird. Korrekturgleichungen werden gegeben.

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Determination of noble metals by atomic absorption spectroscopy3. Effect of platinum and rhodium on the determination of palladium

The atomic-absorption determination of Pd is not affected by Pt, but there is a small influence by Rh. The aim of this investigation is to determine these effects quantitatively, furthermore under the releasing effects of uranium and lanthanum. Equations to correct the results are given.

     

Approximating Ito integrals of differential forms and geodesic deviation

Summary Suppose X is a semimartingale on a differential manifold M with a linear connection . The main purpose of this paper is to show that the Ito integral (with respect to ) of a differential form along the path of X is the limit in probability of certain Riemann sums, constructed in a natural way using the exponential map in differential geometry. For this, we study the deviation between the stochastic development of X in the tangent space at some point, and the image of X under the inverse of the exponential map at the point.     

Generalized kinetic equations

We study the abstract differential equation on a Hilbert space H, which represents a variety of different kinetic equations. T is assumed bounded and self-adjoint on H, and A (unbounded) positive self-adjoint and Fredholm. For partial range boundary conditions and 0x<, we prove existence and (non-) uniqueness theorems and give representations of the solution. Various examples from neutron transport, radiative transfer of polarized and unpolarized light, and electron transport are given.This paper is dedicated to K.M. Case on the occasion of his sixtieth birthday     

Interaural intensity discrimination: insensitivity at 1000 Hz

Recent data from three laboratories have replicated Mills' [J. Acoust. Soc. Am. 32, 132-134 (1960)] finding that interaural intensity discrimination is relatively poorer for tones of 1000 Hz than for tones of either higher or lower frequencies. To get a finer look at this frequency effect, interaural intensity difference thresholds were obtained from four subjects for tones of several frequencies around 1000 Hz. An adaptive two-interval forced-choice procedure was employed, in which the overall intensity of the signals was varied randomly in order to prevent subjects from listening to monaural loudness changes. Despite large intersubject differences in overall sensitivity to interaural intensity differences, all four subjects showed a local peak in their threshold functions at or near 1000 Hz. This curious "1000-Hz effect" might be explained by imagining that an interaural intensity comparator operates more efficiently as frequency increases, but that a peripheral interaural intensity difference to interaural-time difference conversion contributes to laterality judgments for low-frequency tones, thus acting to lower thresholds again for frequencies below 1000 Hz.     

Differentiation and quantitation of isomeric dipeptides by low-energy dissociation of copper(II)-bound complexes

Application of the kinetic method based on the dissociation of transition metal centered cluster ions is extended from chiral analysis (Tao, W. A.; Zhang, D.; Nikolaev, E. N.; Cooks, R. G. J. Am. Chem. Soc. 2000, 122, 10598) to quantitative analysis of isomeric mixtures, including those with Leu/Ile substitutions. Copper(II)-bound complexes of pairs of peptide isomers are generated by electrospray ionization mass spectrometry and the trimeric complex [CuII(ref)2(A) - H]+ (analyte A, a mixture of isomeric peptides; reference compound ref, usually a peptide) is caused to undergo collisional dissociation. Competitive loss of the neutral reference compound or the neutral analyte yields two ionic products and the ratio of rates of the two competitive dissociations, viz. the product ion branching ratio R is shown to depend strongly on the regiochemistry of the analyte in the precursor [CuII(A)(ref)2 - H]+ complex ion. Calibration curves are constructed by relating the branching ratio measured by the kinetic method, to the isomeric composition of the mixture to allow rapid quantitative isomer analysis.     

A case study in conformation design: learning by doing

Efforts are described to design simple, fully flexible but conformationally preorganised omega-hydroxy-nonanoic acids that could serve as the conformation controlling unit in analogues of the potent protein-kinase C activator aplysiatoxin. Such analogues are macrodilactones incorporating the designed omega-hydroxy-nonanoic acid and 3,4-dihydroxy-pentanoic acid, which contains the pharmacophoric groups. The design process (replacement of CH(2) groups by an oxygen atom, annelation of a six-membered ring and placement of alkyl substituents) of the omega-hydroxy-nonanoic acids was monitored by force-field calculations. In the end of this process simple analogues of aplysiatoxin are proposed in which the proper disposition of the pharmacophoric groups is secured by a conformationally flexible but preorganised template structure as part of the macrodilactone ring.     

Der Transport von VO2 mit Cl2 und HCl + Cl2 und der Einfluß des O2-Bodenkörpergleichgewichtsdruckes auf den Transport

The Chemical Transport of VO₂ with Cl₂ and HCl + Cl₂ and the Influence of the O₂-Coexistence Equilibrium Pressure on the Transport Behaviour The transport behaviour of VO₂ with Cl₂, HCl, and Cl₂ was calculated and compared with the experimental results. VO₂ with the upper phase boundary transports with HCl and HCl + Cl₂ from the colder to the hotter zone, VO₂ of the lower phase boundary does not transport with HCl. The composition of the deposited VO₂ is near the upper boundary oxygen richer than in the start space. VO₂ does not transport with Cl₂.