Calculated properties of the active site of oxidized rubredoxins

For a molecular model of the Fe-S active site complex in oxidized rubredoxin, we have calculated the spin-orbit coupling between the ground sextet state and excited quartet and doublet states which gives rise to the observed zero field splitting of the sextet ground state into three spin-mixed Kramers doublets. Additionally, we have used the six spin-mixed sextet state components to calculate effective magnetic moments, magnetic field energies and nine g values corresponding to transitions between the three pairs of Kramers doublets in applied magnetic fields along three perpendicular axes. We have calculated these properties for eight conformational variations of the ligands around the Fe at the active site. The results of these calculations clearly show the origin of the observed g=4.3 signal previously described only in terms of the phenomenological spin-Hamiltonian formalism. For the eight conformations considered, five have this characteristic signal. Zero field splitting comparable to the observed values could be obtained for all symmetries studied. In addition, the calculated values of magnetic moment in all symmetries correspond to that of high spin ferric ion and do not vary appreciably with temperature above 77° K, in agreement with experimental results. From comparison of all our calculated results with experiment, it appears that the active site in oxidized rubredoxins could have small conformational variations in different rubredoxins and under the various experimental conditions used.     

Characterization of low-energy conformational domains for Met-enkephalin

Summary An extensive exploration of the conformational hypersurface of Met-enkephalin has been carried out, in order to characterize different low-energy conformational domains accessible to this pentapeptide. The search strategy used consisted of two steps. First, systematic nested rotations were performed using the ECEPP potential. Ninety-two low-energy structures were found and minimized using the CHARMm potential. High and low-temperature molecular dynamics trajectories were then computed for the lowest energy structures in an iterative fashion until no lower energy conformers could be found. The same search strategy was used in these studies simulating three different environments, a distance-dependent dielectric =r, and two constant dielectrics =10 and =80. The lowest energy structure found in a distance-dependent dielectric is a Gly-Gly -II-type turn. All other structures found for =r within 10 kcal/mol of this lowest energy structure are also bends. In the more polar environments, the density of conformational states is significantly larger compared to the apolar media. Moreover, fewer hydrogen bonds are formed in the more polar environments, which increases the flexibility of the peptide and results in less structured conformers. Comparisons are made with previous calculations and experimental results.     

On the reaction of aminobis(diorganylamino)phosphanes with halogenophosphanes—P-hydrogeno(iminophosphoranyl)-halogenophosphanes and P-hydrogeno(iminophosphoranyl)-σ2, λ3-iminophosphanes

Reactions of triaminophosphane (R₂N)₂P–NH₂, (R = ¹Pr) 1a, with aminodihalogenophosphanes ¹Pr₂N–PX₂, 2a–c [X = CL (a), Br (b), I(c)], in the presence of a base yielded the P-hydrogeno-iminophosphoranyl-halogenophosphanes (R₂N)₂PH = N–PX–N(¹Pr)₂ 4a–c [X = Cl (a), Br (b), I(c)]. Analogous reactions between 1a and 1b (b: R = c-hexyl) and chloroiminophosphane (Cl–P = N–Mes^*, (Mes^* = 2,4,6-^tBu₃C₆H₂) 6 , gave the P-hydrogeno(iminophosphoranyl)-σ²,λ³-iminophosphanes, (R₂N)₂PH = N–P = N–Mes^* 8a and 8b. In solution 8a, 8b eliminated amine, yielding σ², λ³-iminophosphanyl-substituted 1,3,2,4-diazadiphosphetidines [(R₂N)PN(P = N–Mes^*)]₂, 10a, 10b , and 11 ( 10a and 10b : cis; 11: trans). The X-ray structure analyses of compounds 4a, 4b, 8a, and 11 are discussed. © 1996 John Wiley & Sons, Inc.     

Relaxation spectra of polymers and phenomena of electrical and hydrophobic recovery: Interplay between bulk and surface properties of polymers

Low‐density polyethylene, polypropylene, and polycarbonate were exposed to cold air plasma treatment. The decay of electret response, hydrophobic recovery, and mechanical relaxation of polymers were studied experimentally. The three‐exponential decay kinetic model was used for the treatment of mechanical and electret responses. The characteristic time scales of mechanical and electret responses turned out to be very close. The “longest” relaxation time, extracted from the experimental study of the hydrophobic recovery, was also close to the corresponding characteristic time spans of electret and mechanical responses. The kinetics of surface processes taking place in polymers is controlled by the mobility of their functional groups, represented by the bulk relaxation spectra. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 198–205     

Als eine der empfindlichsten Reactionen auf freien oder in Wasser gel?sten Sauerstoff

Ohne Zusammenfassung     

Aminobis(Diorganylamino)Phosphanes: Versatile Reagents in Hydridophosphazene Chemistry

Abstract

The synthesis, crystal structure, polymerisation and metal complexation of aminobis(diorganylamino)phosphanes are discussed.     

Anorganische Mikrochemie. Qualitative Analyse

Ohne Zusammenfassung     

Molecular orbital calculations of the active site complex of two iron ferredoxins

In this report we present further results of molecular orbital calculations for a model of the active site complex of two iron ferredoxins, using the Iterative Extended Hückel Method for our calculations. In the first paper of this series we dealt mainly with energy-conformation calculations which helped establish the salient chemical and conformational features of the lowest energy forms for such a complex. Presented here are the nature and energy ordering of the 70 molecular orbitals in the active site model, a calculation of room temperature magnetic moment, of the electric field gradient at the Fe nucleus and an assignment of the optical absorption spectra in the one electron approximation for the lowest energy conformer of the oxidized state of these proteins. For each property, we compare our calculated results with experiment whenever possible, and with the results of previous correlations. In addition, we indicate the sensitivity of these properties to variations in conformation about the Fe atoms.

---

Zusammenfassung In der vorliegenden Arbeit werden weitere Resultate der Untersuchung eines Modells des an der aktiven Stelle gebildeten Komplexes von zwei Eisen-ferredoxinen mitgeteilt, die mit Hilfe der iterativen erweiterten Hückel-Methode gewonnen wurden. In der ersten Veröffentlichung dieser Reihe wurden hauptsächlich die Ergebnisse der Berechnungen von Konformationsenergien angegeben, die dazu beitrugen, die wichtigsten chemischen Eigenschaften sowie die Konformationen solcher Komplexe mit der niedrigsten Energie zu ermitteln. Hier werden nun die Eigenschaften der 70 niedrigsten Molekülorbitale des Modells, eine Berechnung des magnetischen Moments bei Raumtemperatur und des elektrischen Feldgradienten am Fe-Kern sowie die Zuordnung des optischen Absorptionsspektrums in der Einelektronennäherung für die Konformation niedrigster Energie des oxydierten Zustandes dieser Proteine veröffentlicht. Die Ergebnisse werden soweit möglich mit dem Experiment und früheren Interpretationen verglichen. Zusätzlich wird auf die Empfindlichkeit dieser Eigenschaften bezüglich einer Variation der Konformation in der Nähe des Fe-Atoms hingewiesen.