A program for the computation of helical parameters from internal coordinates

The bacterial cell is propelled through the liquid environment by means of one or more rotating flagella. The bacterial flagellum is composed of a basal body (rotary motor), hook (universal coupler), and filament (propellor). The filament is a rigid helical assembly of only one protein species — flagellin. The filament can adopt different morphologies and change, reversibly, its helical parameters (pitch and hand) as a function of mechanical stress and chemical changes (pH, ionic strength) in the environment.

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Force field for in-plane vibrations of terephthalonitrile

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19890018 ◽

1989 ◽

Vol 54 (1) ◽

pp. 18-27 ◽

Cited By ~ 3

Author(s):

Juan F. Arenas ◽

Juan I. Marcos ◽

Francisco J. Ramírez

Keyword(s):

Experimental Data ◽

Force Field ◽

Normal Coordinates ◽

Internal Coordinates ◽

Isotopic Shifts ◽

Quadratic Force Field ◽

Semi Empirical

The general quadratic force field for the in-plane vibrations of terephthalonitrile was calculated by the semi-empirical MINDO/3 method. This force field was refined to the frequencies observed experimentally for terephthalonitrile and isotopic shifts of terephthalonitrile-[15N2]. The refined frequencies reproduce the experimental data with errors less than 0.5%. The normal coordinates and the force field in internal coordinates were also calculated from the refined field.

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New solutions to the problems of chain orientation and chain continuity in structure analysis of fibrous polymers. A reconsideration of the structure of polyisobutene

Journal of Applied Crystallography ◽

10.1107/s0021889806044955 ◽

2007 ◽

Vol 40 (1) ◽

pp. 10-15 ◽

Cited By ~ 3

Author(s):

Attilio Immirzi ◽

Davide Alfano ◽

Consiglia Tedesco

Keyword(s):

New York ◽

Degrees Of Freedom ◽

Structure Refinement ◽

General Interest ◽

Structural Refinement ◽

X Ray Diffraction ◽

Chain Orientation ◽

Crystalline Polymers ◽

Internal Coordinates ◽

Fibrous Polymers

Two points of general interest in structural refinement of polymers based on internal coordinates are discussed: the chain orientation and the chain continuity. Using a proprietary computer program, based on revised approaches to these questions, the structure of polyisobutene has been reconsidered, using new X-ray diffraction measurements (Fuji image plate) and performing a structure refinement based on internal coordinates. Three refinement schemes, with a decreasing number of degrees of freedom, have been considered, with the conclusion that the distortion from the 83regular helix, claimed by Tadokoro [(1979).Structure of Crystalline Polymers, p. 136. New York: Wiley-Interscience], is confirmed, though lower than supposed. The new procedures implemented for chain orientation and chain continuity work excellently.

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