The structure of crystalline tris: a plastic crystal precursor, buffer, and acetylcholine attenuator.

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.

Flash X-ray Microscopy.

Soft x-ray contact microscopy, utilizing single-shot exposures of approximately 60 nanoseconds duration in polymethyl methacrylate, has been realized with a resolution of 300 angstroms. The radiation spectrum is intense in the "window" between 23 and 44 angstroms where water is transparent compared to biological materials, and therefore permits viewing of wet samples.