Chain angle

Fig. 19—Shear stress and chain angle as a function of sliding distance, from simulations of alkanethiolates on Au(111) at temperature 1 K (a) results from commensurate sliding show a stick-slip motion with a period of 2.5 A, (b) in incommensurate case both shear stress and chain angle exhibit random fluctuations with a much smaller average friction [45],...

In this expression ex is the modulus perpendicular to the chain axis and wj is the work of fracture for the transverse tensile stress. Equation 39 demonstrates that the Griffith length Lq increases rapidly with decreasing orientation of the chain angle 0. 

Since about 15 years, with the advent of more and more powerfull computers and appropriate softwares, it is possible to develop also atomistic models for the diffusion of small penetrants in polymeric matrices. In principle the development of this computational approach starts from very elementary physico-chemical data - called also first-principles - on the penetrant polymer system. The dimensions of the atoms, the interatomic distances and molecular chain angles, the potential fields acting on the atoms and molecules and other local parameters are used to generate a polymer structure, to insert the penetrant molecules in its free-volumes and then to simulate the motion of these penetrant molecules in the polymer matrix. Determining the size and rate of these motions makes it possible to calculate the diffusion coefficient and characterize the diffusional mechanism. 

Figure 16.7 Fluorinated prolines in collagen, (a) The trans/cis isomerization of amide bonds and main-chain angles of proline residues. The n —> interaction, depicted by a dashed line,...

Lohr and Riiterjans have proposed a HN(CO)CG-[ H- N]-TROSY sequence for the simultaneous determination of the and Jccy couplings related to the side chain angle of aromatic residues in -enriched... 

FIGURE 4.3 Definition of the chain angles 8 (bond angle ring-amine N-ring) and 0 (ring torsional twist). 

Figure 20. Density and chain-angle distributions at three different areas from the simulation by Bareman et al. ...

Figure 5.2 Energy surface associated with two variable torsional angles in one of the side chains of an iron sulphur complex (structure taken from Kanatzidis et ah, 1984). The resulting energy map, a function of the two variable side chain angles highlighted, a and b, is shown on the right-hand side of the figure, as both a contour map and a three-dimensional histogram. A variety of maxima and minima are readily apparent in the...

Aligned P packing in which P-strands in different sheets are linked by loops and right-handedly twist, resulting in the main chain angle between the two packed P sheets with an angle of —30°. 

In a first approximation we therefore have one single bond to the equatorial Cl and two half bonds within the chains (chain angle 105.6°). In the real structure each single Cl atom makes weak bonds (Sn—Cl =3.06 A) with two Sn atoms of the neighboring chain, thus linking the chains pairwise. These twin chains are arranged in a layered manner, with distances Sn—Cl = 3.22 A to the next twin chain. The distance between these pseudolayers is Sn—Cl = 3.30 A. The structure thus is intermediate between fibrous and layered. 

Chains kPreserveZigZags kPreserveChain Angle Preserve directions of chain zigzags. (Otherwise the COS may be ignored at chain atoms.) Keep the preexisting chain angle, if any. 

Desired chain angle (see later section on Chains in Preassembly Analysis), defaulting to 120°. 

Figure 30 Varying the chain angle. (Relative scaling applied for fit.

The chain angle is the angle between three consecutive chain atoms. 

A. If the zigzag preservation flag is clear (necessarily the case if one is drawing de novo), assign all core atoms to FxAS, use the default chain angle, and skip to step 5 of this algorithm. 

FxAS. If the separation between one pair is value K, and the other separations are all a different value and A is either the present chain angle or is at least 10% different from B, then assign the atom to FxAS. 

A. If there was no prevailing chain angle (step 3), or if there was one and it was 120°, convert all sites of type Ambiguous to FxAS. 

Correct for fixed angle spacing. If the seed atom is a core chain atom, decrement NumSub, and increase the angular demand by the chain angle. 

If s is part of the same chain, and in particular takes a rightward bend relative to the seed atom and its predecessor, add the chain angle to the CFS/o of the seed atom (Figure 39). Otherwise, add to it the residual angle separation. 

B. If the seed atom has two neighbors, no triple bonds, and no more than two double bonds, make it pseudotrigonal change the substituent spacing to 120° (not the prevailing chain angle). 

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