Kinetic Control of High-Pressure Solid-State Phase Transitions: A Case Study on l-Serine

Abstract

This study demonstrates that the compression rate adds a new perspective to phase diagrams of solids. A particular pressure increase rate may trigger unexpected solid-state transformations, producing otherwise inaccessible phases. Our test case is l-serine, characterized by a complex high-pressure behavior with three known polymorphs. However, the critical pressure of each transition, the ranges of coexistence of polymorphs, and the existence of an elusive fourth phase remained open questions, here analyzed and solved using synchrotron powder X-ray diffraction at high pressure, under controlled pressure increase rates. Two parallel paths exist, and the composition of the system depends on the pressure increase rate and the steps during the compression. A slow and continuous compression favors phase IV, whereas phase II can be observed only with a rapid and sharp compression. No direct interconversion occurs between these phases. Moreover, phase III originates only from phase II but never from phase IV. By controlling the strategy of pressure increase, we obtained a powder of phase IV that enabled solving its unknown structure, which resulted as a distorted superstructure of phase I with a tripled a-axis.

Unusual seeding effect in the liquid-assisted high-pressure polymorphism of chlorpropamide

“…The role of kinetic factors known to influence crystallization at ambient conditions increases enormously at high pressure, when molecular motions are even more restricted, the sample is located in a confined space of a gasket hole, the pressuretransmitting fluid is not mixed and is often viscous, so that diffusion and convection processes are hindered. As a result of the kinetic control of nucleation and nuclei growth [28] , different phases can form, depending on the choice of the starting polymorph [29][30][31] , the hydrostatic medium [32][33][34][35][36][37] , or the compression/decompression protocol [26,[38][39][40][41][42] . An antidiabetic drug, chlorpropamide (4-chloro-N-(propylamino-carbonyl)benzenesulfonamide, C 10 H 13 ClN 2 O 3 S), is particularly prone to polymorphism [43,44] .…”

The benefits of one-dimensional detectors for high-pressure powder X-ray diffraction

“…The pressure was raised with steps of < 0.6 (1) GPa circa each 30 min as measured from ruby fluorescence (Syassen, 2008). The final pressure was determined from the l-serine lattice parameters (Fisch et al, 2015). Furthermore, a DAC with 0.3 mm culets was loaded with NIST SRM 660a LaB 6 but not compressed (Table 1).…”

“…Moreover and unfortunately, the two samples do not contain the same relative amounts of l-Ser II and IV. The reason is that it is almost impossible to maintain exactly the same pressure increase rate during the compression of the DACs, which is a crucial factor for the formation of the different polymorphs, even when the same final pressure is reached (Fisch et al, 2015). Rietveld quantitative phase analyses yielded 10 wt% l-Ser I, 12 wt% l-Ser II and 78 wt% l-Ser IV for sample SerA-, and 8, 38 and 54 wt%, respectively, for sample SerB-2D.…”

“…This is showcased by investigating l-serine. An unsolved HP polymorph (l-Ser IV) was observed only in powder samples (Fisch et al, 2015;Boldyreva et al, 2006) and always coexisted with l-Ser I (ambient form) and l-Ser II (an already known HP form). The large cell of l-Ser IV results in severe peak overlap with the other phases.…”

“…Moreover, powder samples may be preferred when the phase evolution and transition points with increasing pressure are different for single crystals or powders, or in time-resolved investigations as experiments are faster (Boldyreva, 2007;Lanza et al, 2014;Fisch et al, 2015;Shekar & Rajan, 2001;Perillat, 2008;Evans et al, 2007;Velisavljevic et al, 2014).…”