Encyclopedia of chemistry is a concise, comprehensive, and accessible reference. Its intelligential scope ranges from the introductory to the highly technical. As with early editions, the Encyclopedia has been designed to be approachable by students and readers of many ages. | M since the magnetic field leads to the lifting of the degeneracy of electronic orbital and spin states and to the mixing of electronic states. MCD is frequently used in combination with absorption and CD studies to effect electronic assignments. The three contributions to the MCD spectrum are the A-term, due to Zeeman splitting of the ground and/or excited degenerate states; the B-term, due to field-induced mixing of states; and the C-term, due to a change in the population of molecules over the Zeeman sublevels of a PARAMAGNETIC ground state. The C-term is observed only for molecules with ground-state paramagnetism and becomes intense at low temperatures; its variation with field and temperature can be analyzed to provide magnetic parameters of the ground state, such as spin, gfactor, and zero-field splitting. Variable-temperature MCD is particularly effective in identifying and assigning electronic transitions originating from paramagnetic CHROMOPHOREs. macromolecule A large molecule of high molecular mass composed of more than 100 repeated monomers (single chemical units of lower relative mass); a polymer. DNA, proteins, and polysaccharides are examples of macromolecules in living systems; a large complex molecule formed from many simpler molecules. macrophage A type of blood cell that is able to ingest a wide variety of particulate materials. They are a type of PHAGOCYTE. macroscopic diffusion control See MIXING CON- TROL. Madelung constant A term that accounts for the particular structure of an ionic crystal when the lattice energy is evaluated from the coulombic interactions. The value is different for each crystalline structure. magnetic equivalence Nuclei having the same resonance frequency in NUCLEAR MAGNETIC RESONANCE also, identical spin-spin interactions with the nuclei of a neighboring group are magnetically equivalent. The spin-spin interaction between magnetically equivalent nuclei does not appear, and thus has no effect on the multiplicity .
