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Small molecules (up to ca. 1000 atoms) usually form better-ordered crystals than large molecules, and thus it is possible to attain lower R-factors. In the Cambridge Structural Database of small-molecule structures, more than 95% of the 500,000+ crystals have an R-factor lower than 0.15, and 9.5% have an R-factor lower than 0.03.
COOH, R, NH 2 and H (where R is the side-chain) are arranged around the chiral center carbon atom. With the hydrogen atom away from the viewer, if the arrangement of the CO→R→N groups around the carbon atom as center is counter-clockwise, then it is the L form. [14] If the arrangement is clockwise, it is the D form. As usual, if the ...
After much work, Cech proposed that the intron sequence portion of the RNA could break and reform phosphodiester bonds. At about the same time, Sidney Altman, a professor at Yale University , was studying the way tRNA molecules are processed in the cell when he and his colleagues isolated an enzyme called RNase-P , which is responsible for ...
Moses Gomberg (1866–1947), the founder of radical chemistry. Until late in the 20th century the word "radical" was used in chemistry to indicate any connected group of atoms, such as a methyl group or a carboxyl, whether it was part of a larger molecule or a molecule on its own. A radical is often known as an R group. The qualifier "free" was ...
In organic chemistry and biochemistry, a side chain is a chemical group that is attached to a core part of the molecule called the "main chain" or backbone.The side chain is a hydrocarbon branching element of a molecule that is attached to a larger hydrocarbon backbone.
Electrical resistance (R) Roentgen (unit) (R), a unit of measurement for ionizing radiation such as X-ray and gamma rays; Rydberg constant (R ∞, R H), a physical constant relating to energy levels of electrons within atoms Rydberg unit of energy (R y), the energy of the photon whose wavenumber is the Rydberg constant
T is the temperature, T TPW = 273.16 K by the definition of the kelvin at that time; A r (Ar) is the relative atomic mass of argon and M u = 10 −3 kg⋅mol −1 as defined at the time. However, following the 2019 revision of the SI , R now has an exact value defined in terms of other exactly defined physical constants.
Change in the receptor conformation such that binding of the agonist does not activate the receptor. This is seen with ion channel receptors. Uncoupling of the receptor effector molecules is seen with G protein-coupled receptors. Receptor sequestration (internalization), [18] e.g. in the case of hormone receptors.