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Ferredoxin I (Fd I) from Equisetum arvense is an iron-sulfur protein composed of 95 amino-acid residues and one [2Fe-2S] cluster. It crystallized in the space group P2(1), a = 30.4, b = 57.4, c = 47.5 A and beta = 78.7 degrees with two molecules per asymmetric unit. X-ray diffraction data up to 1.8 A resolution were collected by using a Rigaku four-circle diffractometer. The initial model of Fd I, which was derived by the molecular replacement method using a structure of the Fd I from the blue-green alga Aphanothece sacrum, was refined by molecular dynamics simulation and a least-squares minimization with stereochemical restraints. Positional parameters and isotropic temperature factors for 1420 non-H protein atoms and 183 water molecules were refined on 13 838 observed structure factors (F(o) > sigma(Fo)) between 10.0 and 1.8 A resolution. The final Rfactor was 17.0%, and the standard deviation of atomic position estimated by Luzzati plot [Luzzati (1952). Acta Cryst. 5, 802-810] was 0.2 A. The electron-density map was well defined for the two independent molecules except for the N-terminal residue and the three C-terminal residues. Equivalent Calpha atoms of two independent molecules in the asymmetric unit were superposed by the least-squares method with root-mean-square deviations of 0.26 A. Reasonable structural differences were observed at a polypeptide segment having few intramolecular interactions. Highly flexible regions of the molecule were assigned from the structural differences between the two independent molecules in the crystal and the distribution of temperature factors along the polypeptide chain.

Both the (1S,2R) and (1R,2S) isomers of 2,6,6‐trimethylbicyclo[5.4.0]undec‐7‐en‐9‐one (1) were synthesized by starting from (S)‐ and (R)‐citronellal (5), respectively. The stereochemistry of (1R,2S)‐(−)‐1 was established by an X‐ray analysis; it exhibits a CD spectrum similar to that of cholest‐4‐en‐3‐one, in agreement with its absolute configuration. The ketones (1S,2R)‐ and (1R,2S)‐1 were converted into the enantiomers of three other himachalene hydrocarbons, 2,2,6‐trimethyl‐10‐methylenebicyclo[5.4.0]undec‐1(11)‐ene (2), 1,1,5,8‐tetramethyl‐1,2,3,4,5,6,5a‐heptahydrobenzo[1,2‐a][7]annulene (3), and 1,1,5,8‐tetramethyl‐1,2,3,4,5‐pentahydrobenzo[a][7]annulene (ar‐himachalene, 4). The stereochemistry of these himachalene‐type sesquiterpenes isolated from flea beetles such as Aphthona flava and Phyllotreta cruciferae as their male‐pheromone components was revised to (1S,2R)‐1, (6R,7S)‐2, (5R,5aS)‐3, and (R)‐4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

This study introduces a new robust nonlinear control scheme based on the theory of nonsingular terminal sliding mode control (NTSMC). Since conventional NTSMC utilizes a discontinuous switching function, a significant flaw called chattering can occur. The main purpose of this study is to design a new switching function based upon Lyapunov stability in order to alleviate this drawback over time. There are many approaches to mitigate the chattering drawback in SMC such as utilizing a smooth approximation of the switching element, or employing higher order sliding mode control (HOSMC) strategy. However, the use of a continuous approximation affects the system's performance and a finite reaching time to the sliding manifold, and in HOSMC the estimation of high‐order derivatives of states is usually difficult and it still exhibits chattering in the presence of parasitic dynamics. In this study by employing a new sliding manifold including a time function, the chattering is attenuated as well as keeping the robustness. Finally, a second‐order nonlinear dynamical system subject to disturbance is simulated to highlight the validity and applicability of the proposed method.