Barriers to Internal Rotation About Single Bonds

Crystallization from solutions containing multiple conformers: A new modeling approach for solubility and supersaturation

“…3 and found to be 63.6 kcal/mol. This value is much larger than the typical values of the activation energy reported in the literature (9-14 kcal/mol for surface integration (Mullin, 2001;Garside et al, 2002) and 1-10 kcal/mol for equilibration between conformers (Lowe, 1968;March, 1992).…”

“…Eckhardt and Bernstein (1972) reported that for systems having low energy barriers between conformers, crystal forces can modify the conformation of the molecule into the one that is suitable for surface integration. Typical energy barriers of transition between conformers reported in the literature are usually low and lie in the range of 1-10 kcal/ mol (compiled from 194 energy barriers to rotation reported by Lowe (1968) and data reported by March (1992)). Based on these considerations, it is expected that in most cases (i.e.…”

Pursuing structure in microcrystalline solids with independent molecules in the unit cell using 1H–13C correlation data

“…An H-O-C3-C2 dihedral angle of +60°or À60°is proposed (Fig. 12) because such staggered conformations are usually energetically preferred about C-O bonds involving an sp 3 carbon [46]. An unambiguous prediction of the H-O-C3-C2 dihedral angle is not possible from the experimental data, however, because any dihedral angle of +h will have an identical 3-O 1 H-13 C2 distance at Àh.…”

Block catiomer with flexible cationic segment enhances complexation with siRNA and the delivery performance in vitro

“…Herein, we aimed to gain insight on the effect of the flexibility of the cationic segment of the block catiomers on the complexation with siRNA. Thus, to discriminate the contribution of the flexibility of the polycation, we used two corresponding block copolymers bearing polycation segments with different flexibility and PEG, as follows: PEG-PLL with the relatively rigid amide backbone, and PEG-poly(glycidyl butylamine) (PEG-PGBA) having a polyether backbone, which presents ether bonds with low rotational barrier [19,20]. The block catiomer systems have similar PEG length and weight fraction, and equivalent polycation length, i.e., 40 units.…”