The melting diagram of the system tetramethylammonium hydroxide-water has been reinvestigated in the region of 66.67 - 100 mol% H2O , using DTA , DSC and temperature-dependent X-ray powder diffraction. This was done as correction and supplementation of a previous study in the same laboratory (D. Mootz, R. Seidel, J. Incl. Phenom. 8 , 139 (1990)). The system is now considered to contain as many as eight stable hydrates, three of them dimorphic with a low-temperature α and a high-temperature β form. The compositions are Me4NOH · χH2O with χ = 2 (α and β), 4, 4.6 (α and β), 5 (α and β), 6.67, 7.5, 8.75 and 10. A second 7.5-hydrate, called 7 .5 α in the previous study, is now regarded as metastable. - Structure determinations have been performed for the new phases with x = 4.6 (α), 6.67 and 8.75. The 4.6 α-hydrate, transforming to 4.6 β at 32 °C, is cubic with space group Pa3̄ and Z = 40 formula units per unit cell. The lattice constant is a = 21.493 Å at -160 °C. The 6.67-hydrate, melting with decomposition at 13 °C, is monoclinic with space group P21/m and Z = 6 . It was studied as the O-deuterated isotype with unit-cell dimensions a = 11.874, b = 20.019, c = 8.272 Å and β = 103.84° at 3 °C. The 8.75-hydrate, melting with decomposition at - 3 °C, is cubic with space group 14̄3 d, Z = 16 and a = 18.38(2) Å at - 20 °C. The three structures, as most others of the higher hydrates of the system studied previously, are those of polyhedral clathrate hydrates. For the hydrates 4 .6 α and 6.67 deviations of the anionic, i.e. proton-deficient, new water structures from being fully four-connected are described in detail. The 8.75-hydrate is isostructural with the hitherto unparalleled 9.75-hydrate of t-butyl amine. - The phase identity and structure of the 4.6 β-hydrate were recognized as those attributed to an erroneously assumed 5 β-phase in the previous study. 5 β now denotes the room-temperature form of the pentahydrate, previously called 5 α. The present 5 α is another of the new phases and the only one of the system with its structure still undetermined.
Crystallization of the Fv fragment of mouse myeloma protein M315