The nadir (UK: /ËnÃ¦dÉªÉr/), (US: /ËneÉªdÉªÉr/) (from Arabic: ÙØ¸ÙØ±ââ / ALA-LC: naáºÄ«r, meaning counterpart) is the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there.
Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen preferentially to one of two faces of an unsaturated substrate molecule, such as an alkene or ketone.ne of these is in the asymmetric hydrogenation of N-unfunctionalized imines to give primary amines. Such species can be difficult to selectively reduce because they tend to exist in complex equilibria of imine and enamine tautomers, as well as (E) and (Z) isomers.
Fixation (histology) In the fields of histology, pathology, and cell biology, fixation is a critical step in the preparation of histological sections by which biological tissues are preserved from decay, thereby preventing autolysis or putrefaction. The structure of a tissue is determined by the shapes and sizes of macromolecules in and around cells. The principal macromolecules inside a cell are proteins and nucleic acids. Fixation terminates any ongoing biochemical reactions, and may also increase the mechanical s