470—The proton pump at work: Part I. The basic concept of excess proton/defect proton translocation

The Nagle-Morowitz proton pump, which is based on proton transport in water and ice, is shown to be inapplicable to weakly H-bonded proton transport systems. It is demonstrated that in weakly or non H-bonded systems protons can migrate either as excess protons H using a high-lying proton conduction band or as defect protons H′ using intermediate energy levels. As H? the protons act as positive charge carriers endowed with a very high mobility. As H′ they act as negative charge carriers. The H′ transport mechanism involves thermally activated proton tunneling. Owing to the very large mobility differences between H? and H′, > 10⁶, very high potentials can be self-generated in any situation which creates a concentration gradient. Proton conductivity data on inorganic model compounds are presented. Applying these results to proton transport across biomembranes, transmembrane potentials U_m, acidification Δ pH and transient phenomena can be explained as result of H? and H′ translocation.     

Theoretical studies on the decarboxylation reaction in thiamin catalysis

The conformational behavior and the stability of thiazolium and thiamin diphosphate (ThDP) adducts formed by the C2 addition of the substrates pyruvate and glyoxylate to the corresponding thiamin systems are investigated within the force-field version PIMM 90 as well as the semiempirical AM 1 and PM 3 methods. Moreover, the reaction coordinate of the decarboxylation process of the adducts with respect to the C2α(SINGLEBOND)COO⁻ bond are calculated by PM 3 and AM 1. The calculations on the key intermediates of the Breslow mechanism are performed in order to study the steric aspects of both substrate adducts that show a different pathway in the catalytic cycle. The alternative structural findings for the decarboxylation products are compared with first 6–31C * studies on the corresponding thiazolium model systems. Especially, the PM 3 calculations show that the elimination of CO₂ is favored if the arrangement of the carboxylate group is nearly perpendicular to the plane of the thiazolium ring. These results support the least-motion maximum-overlap mechanism in the enzymatic decarboxylation reaction, proposed by Kluger. The most stable conformers of the ThDP adducts and its decarboxylation products are characterized by V-like structures and the formation of a significant intramolecular hydrogen bonding under participation of the 4′-aminopyrimidine ring. © 1996 John Wiley & Sons, Inc.     

Locking constraints for elastic rods and a curvature bound for spatial curves

The paper presents necessary conditions for curves in R³ subject to the nonholonomic constraint of an upper bound for curvature and suitable boundary conditions. The proof essentially uses a reformulation of the problem by means of framed curves. The Euler–Lagrange equations for nonlinearly elastic Cosserat rods subject to a general class of locking constraints is derived by similar methods. Mathematics Subject Classification (2000) 49K15, 51M16, 74B20, 74K10     

Quantenchemische Untersuchung von Protonierungs-und Deprotonierungsgleichgewichten

Zusammenfassung Unter Anwendung der Omega-HMO(Pi + Sigma)-Methode wird die Ladungsverteilung in Carbonsäuren, Alkoholen, Chinuclidinen und Phosphonsäuren berechnet. Die Nettoladung der aciden Wasserstoffatome von Carbonsäuren, Alkoholen und Phosphonsäuren zeigt eine lineare Beziehung zu den pK _a-Werten dieser Verbindungen. Die berechnete Nettoladung am Stickstoff-Atom der Chinuclidine kann zu deren Basizität in Beziehung gesetzt werden.

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Quantum chemical treatment of protonation and deprotonation equilibria

The charge distribution of organic acids, alcohols, chinuclidines and phosphonic acids has been calculated by the Omega-HMO(Pi + Sigma) method. A linear correlation was found between the net charge of the acidic hydrogen atoms of organic acids, alcohols and phosphonic acids and the acidity of these compounds. The calculated net charge of the nitrogen atom of chinuclidines is related to their basicity.

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Mit 4 Abbildungen     

Konforme Abbildung von Kreisbogenpolygonen. III

Ohne ZusammenfassungDer vorliegende Teil III bildet zusammen mit Teil II die Habilitationsschrift des Verfassers, die von der naturwissenschaftlichen Fakultät der Justus-Liebig-Hochschule Gießen angenommen wurde.     

On N1-free modules with trivial dual

In this paper we generalize the notion of Fountain-Gould order to the context of associative pairs. We give theorems about the existence and uniqueness of the left quotient pair and we obtain a Goldie-like haracterization which describes left orders in semiprime pairs coinciding with their socle.