Crossing angle

Another new twist in CMB reactive scattering which has very recently been implemented in our laboratory, will also be briefly discussed in this chapter. It consists in carrying out CMB experiments with a crossing angle of the reactant beams of 135°, rather than the... 

CMB Experiments with Variable Beam Crossing Angle 346... 

Fig. 6. Variation of the center-of-mass velocity with beam crossing angle, 7, for the reaction 0(3P) + C2H2 with the 0(3P) and C2H2 beam velocities of 2798ms-1 and 827ms 1, respectively. The Newton diagrams for 7 = 45°, 90°, and 135° are shown (see text).

Product Angular and TOF Distributions with Beam Crossing Angle 7 = 135°... 

Fig. 12. Comparison of HCCO product lab angular distributions and TOF spectra at = 22° from the 0(3P) + C2H2 reaction for a beam crossing angle of 7 = 90° (Ec = 9.5 kcal mol 1, setup of Fig. 1) and of 7 = 135° (Ec = 12.6 kcal mol l, setup of Fig. 7). The corresponding Newton diagrams are also shown. Note the higher angular and TOF resolution obtained when 7 = 135°, as witnessed by the wider HCCO lab angular distribution and slower (and wider) TOF spectrum.

The ways in which a-helices pack against one another were initially described by Crick (1953) as knobs into holes side chain packing which could work at either a shallow left-handed crossing angle or a... 

Fig. 3. Schematic representation of a tetrameric coiled coil, showing the main parameters. 0n marks the center of one a-helix, An the Ca position of a constituent residue, and Cn the superhelix axis n is the u-helix radius, r0 the superhelix radius, a the pitch angle, Q the pairwise helix-crossing angle, ip the positional orientation angle of a residue or phase of the helix, and to is the phase of the supercoil.

In the structure of coiled coils, the values for pitch and crossing angle follow directly from the degree of distortion necessary to reach a periodically recurring position for the core residues Phillips (1992), Seo and... 

Fig. 12. Coiled coils arising between helices that are part of different folds, (a) Soluble proteins, (b) Example of a membrane protein. Inner membrane proteins are Q-helical proteins with an up-and-down topology their helices therefore favor low crossing angles and frequently show mixtures of knobs-into-holes and ridges-into-...

What happens if the helices are not parallel, but instead are oriented at an angle relative to each other Various studies have indicated that counterions near junction sites are generally confined, due to inhomogeneity in the electrostatic field [43, 71, 74, 117]. Furthermore, there is an orientation dependence to the distribution of the delocalized counterions [43, 74, 117, 118], These ideas were exploited by Murthy and Rose to rationalize the observed crossing angles of various helices in crystal structures of nucleic acids [117],... 

Model construction of the analyzed peptides involved the Deep View spdbv 3.7 software (Glaxo Smith Kline, Bredford, UK) followed by distance geometry minimization. Figures were created using the PyMol software (DeLano Scientihc LLS, San Carlos, CA, USA). Symmetric tetramers were modeled using CHI suite of macros for CNS 1.1 (Adams et ah, 1995). Calculation was carried out in vacuo in initial coordinates of a canonical alpha helix (3.6 res. per turn) and initial cross angle (25°). 

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