New Insight into the Mode of Action of Nickel Superoxide Dismutase by Investigating Metallopeptide Substrate Models

For the first time, the existence of a substrate adduct of a nickel superoxide dismutase (NiSOD) model, based on the first nine residues from the N terminus of the active form of Streptomyces coelicolor NiSOD, has been proven and the adduct has been isolated. This adduct is based on the cyanide anion (CN^?), as a substrate analogue of the superoxide anion (O₂^.?), and the nickel metallopeptide H‐HCDLPCGVY‐NH₂‐Ni. Spectroscopic studies, including IR, UV/Vis, and liquid‐ and solid‐state NMR spectroscopy, show a single nickel‐bound cyanide anion, which is embedded in the metallopeptide structure. This complex sheds new light on the question of whether the mode of action of the NiSOD enzyme is an inner‐ or outer‐sphere mechanism. Whereas discussion was previously biased in favor of an outer‐sphere electron‐transfer mechanism due to the fact that binding of cyanide or azide moieties to the nickel active site had never been observed, our results are a clear indication in favor of the inner‐sphere electron‐transfer mechanism for the disproportionation of the O₂^.? ion, whereby the substrate is attached to the Ni atom in the active site of the NiSOD.     

Efficient methods for the synthesis of 2-hydroxyphenazine based on the Pd-catalyzed N-arylation of aryl bromides

[reaction: see text] Substituted diphenylamines can be synthesized by Pd(0)-catalyzed N-arylation using o-nitroanilines and nitro-substituted aryl bromides for a substrate. Cyclization of the diphenylamines by various methods, including the intramolecular Pd(0)-catalyzed N-arylation, produces 2-methoxyphenazine which can easily be deprotected to give 2-hydroxyphenazine. This phenazine is required to synthesize methanophenazine, a novel redoxactive cofactor isolated from methanogenic archaea.     

Summary and comparison of gradient-restoration algorithms for optimal control problems

This paper considers the problem of minimizing a functionalI which depends on the statex(t), the controlu(t), and the parameter . Here,I is a scalar,x ann-vector,u anm-vector, and ap-vector. At the initial point, the state is prescribed. At the final point, the state and the parameter are required to satisfyq scalar relations. Along the interval of integration, the state, the control, and the parameter are required to satisfyn scalar differential equations.Four types of gradient-restoration algorithms are considered, and their relative efficiency (in terms of number of iterations for convergence) is evaluated. The algorithms being considered are as follows: sequential gradient-restoration algorithm, complete restoration (SGRA-CR), sequential gradient-restoration algorithm, incomplete restoration (SGRA-IR), combined gradient-restoration algorithm, no restoration (CGRA-NR), and combined gradient-restoration algorithm, incomplete restoration (CGRA-IR).Evaluation of these algorithms is accomplished through six numerical examples. The results indicate that (i) the inclusion of a restoration phase is necessary for rapid convergence and (ii) while SGRA-CR is the most desirable algorithm if feasibility of the suboptimal solutions is required, rapidity of convergence to the optimal solution can be increased if one employs algorithms with incomplete restoration, in particular, CGRA-IR.This research was supported by the Office of Scientific Research, Office of Aerospace Research, United States Air Force, Grant No. AF-AFOSR-72-2185.     

Differentieller Wirkungsquerschnitt für die Photospaltung des Deuterons zwischen 20 und 35 MeV

The differential cross section of the deuteron photodisintegration was determined in the photon energy range 20 to 35 MeV at the angle of 90 degrees in the laboratory system. The experimental points were fitted in this range by a parabola $$d\sigma _D (90^\circ )/d\Omega = 140.6 - 5.41{\rm E}_\gamma + 0.0621E_\gamma ^2 $$ withE in MeV anddσ _D /dΩ in 10^?30 cm²/sr.