Conformation in crystal

This is supported by our data obtained for TGF-fi3 dynamics in solution [14], according to which the average conformation of the TGF-fi3 dimer is less extended than its conformation in crystal [51], as evidenced by the... 

Meso configurations can have enantiomeric conformers in crystals. Ribitol and xylitol have meso configurations and are optically inactive in solution. In the crystalline state, they have the bent-chain enantiomorphic conformations. Xylitol crystallizes in space group P212121, so each crystal contains either only the optically active left-handed or the optically active right-handed conformers. There are, of course, an equal number of left- and right-handed crystals in any one batch, which on dissolution give no optical activity.1... 

The C—C backbone of SPS takes a planar zig-zag conformation in the crystal whereas IPS takes a 3/1 helical conformation in crystal. This difference in chain conformation in the crystal affects the crystallization rate of these polystyrenes. Table 18.1 [32] compares the crystallization parameters between SPS and IPS. The work of chain folding, Q, of SPS is smaller than that of IPS, which suggests that the chain folding of SPS can take place more easily than that of IPS. Also, SPS has a smaller surface free energy. These differences are related to the crystallization rate difference between SPS and IPS, which have different stereoregularities. 

The most extensive studies of phenylethylamines have been done by Pullman and coworkers (59,65,67/68). Their PCILO calculations indicated that gauche and trans conformers have nearly identical energies in the majority of phenylethylamines and phenylethanolamines studied. AI studied were carried out using three different basis sets (67) these all indicated a slight but definite preference for gauche conformers. These authors noted the preponderance of extended conformers in crystal structures and in solution they attributed this to environmental forces. To test this hypothesis, computations were repeated with the inclusion of water molecules, and a tendency toward the extended conformation was indeed observed. 

Fig. 30, Conformational energy map of acetylcholine. Isoenergy curves in kcal/mole with respect to the global minimum + taken as energy zero. Experimental conformations in crystals of acetylcholine derivatives...

Conformation in crystal appropriate for interflavin electron transfer... 

Subsequently due to specific chain conformation in crystal unit cell and providing the highest remnant polarization, p phase has attracted more attention than the others in pyro-and piezoelectric applications (J.Jungnickel, 1996). 

Thompson s study of conformations in crystal structures also provides information on typical strain energies, in molecular crystals, by reporting the change in... 

New biphenyl derivative with planar phenyl-phenyl conformation in crystal at room temperature exhibits highly efficient UV light-emitting, J. Phys. Chem. B, 108, 9571-9573 (2004) (c) J. Gierschner, H.-G. Mack, L. Ltier, D. Oelkrug, Fluorescence and absorption spectra of oligophenylenevinylenes vibronic coupling, band shapes and solvatochromism, J. Chem. Phys., 116, 8596-8609 (2002). 

It should be remembered that conformations in crystal lattices are influenced... 

As described in X-ray Crystal Analyses section, DBF oligomers have been shown to have a jc-stacked, single-handed helical conformation in crystal. A jc-stacked structure was indicated also for poly(PDBF) by remarkable hypochromicity in absorption and exclusive dimer emission in fluorescence spectra (Fig. 34). Therefore, it will be reasonably assumed that the CD absorptions observed in this work are based on a helical conformation of poly(PDBF) with excess single handedness. Because the polymers showing clear CD bands in film did not show chiroptical properties in solution, molecular aggregation may amplify and stabilize the single-handed helical conformation induced by the asymmetric polymerization possibly due to intermolecular cooperative effects in the solid state. Atomic force microscopic (AFM) analyses supported this assumption (Fig. 39). The samples were prepared by... 

In order to obtain information on the poly(PDBF) molecular structure, molecular dynamics (MD) simulations were performed for a PDBF 20-mer model created on the basis of the DBF oligomer conformation in crystal (see X-ray Crystal Analyses section) under a constant NVT condition with COMPASS force field at 300 K for 8.6 ns. The simulation afforded the structure shown in Fig. 40 in which the neighboring fluorene moieties stack on top of each other in a chiral, slightly twisted arrangement. The entire chain formed a relatively long-pitched helical structure in the simulation. Hence, the local twist and the helix may contribute to the CD spectra. 

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