title: The structure of crystalline tris: a plastic crystal precursor, buffer, and acetylcholine attenuator.
abstract: The crystal and molecular structure of the widely used buffer tris(hydroxymethyl)aminomethane (tris) has been determined from single-crystal diffractometer data to a standard agreement factor (R value) of 0.026 and bond length standard deviations of 0.002 angstrom. Tris crystallizes in the orthorhombic system, space group Pn21a, with four molecules per unit cell; a = 8.844(1) angstroms, b = 7.794(1) angstroms, and c = 8.795(1) angstroms. The center-to-center distances of tris molecules in the ordered phase range from 0.4 to 1.0 angstrom less than they do in the orientationally disordered (plastic) phase of similar molecules.
mesh_terms: D000109:Acetylcholine / Q000037:antagonists & inhibitors; D003461:Crystallography; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D014325:Tromethamine / Q000494:pharmacology
chemical_list: D014325:Tromethamine; D000109:Acetylcholine