On the other hand, within the P21/c structure, the a axis becomes much more stiffer than b and c directions, and also less compressible than the a axis of the low-P P21/n structure. In general, it is evident that the high-P P21/c structure is less compressible than the P21/n structure. We observe indeed that both the polyhedral volumes of Li and Al do not undergo significant RGD Peptides and the main deformation for this structure is represented by the folding mechanism of the A chain, which contracts by about 4.5% in less than 1 GPa of compression interval; the B chain remains practically unchanged over the same pressure range. This last feature is extremely interesting, as indeed (if the kinking rates of the A and B chains were constant with pressure) we would observe a decrease of the A chain down to about 133°, i.e. reaching the same kinking of the B chain, at only 6.034 GPa. Since the two chains in P21/c structure are not symmetry equivalent mainly due to their different chain kinking, such equivalence of kinking at 6.034 GPa should result into a second phase transition, most presumably to C2/c symmetry (as observed in several pigeonites  and some Li-bearing clinopyroxenes  and ). However, even if our structure data were not measured at pressures above 5.3 GPa, our unit-cell parameters clearly do not give any evidence for a second phase transition within the hydrostatic pressure regime of this experiment, but nucleotide sequences might be expected at higher pressures.