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When hemoglobin is not attached to oxygen (and is then called deoxyhemoglobin), the Fe 2+ ion at the center of the heme group (in the hydrophobic protein interior) is in a high-spin configuration. It is thus too large to fit inside the porphyrin ring, which bends instead into a dome with the Fe 2+ ion about 55 picometers above it. In this ...
The structure of the active site in carbonic anhydrases is well known from a number of crystal structures. It consists of a zinc ion coordinated by three imidazole nitrogen atoms from three histidine units. The fourth coordination site is occupied by a water molecule. The coordination sphere of the zinc ion is approximately tetrahedral.
The ionization energy will be the energy of photons hν i (h is the Planck constant) that caused a steep rise in the current: E i = hν i. When high-velocity electrons are used to ionize the atoms, they are produced by an electron gun inside a similar evacuated tube. The energy of the electron beam can be controlled by the acceleration voltages.
Diverse ions are used by animals and microorganisms for the process of mineralizing structures, called biomineralization, used to construct bones, seashells, eggshells, [53] exoskeletons and mollusc shells. [54] [citation needed] Minerals can be bioengineered by bacteria which act on metals to catalyze mineral dissolution and precipitation. [55]
Metals are also toxic so a balance must be acquired to regulate where the metals are in an organism as well as in what quantities. Many organisms have flexible systems in which they can exchange one metal for another if one is scarce. Metals in this discussion are naturally occurring elements that have a tendency to undergo oxidation. Vanadium ...
[65] [82]: 126–127 While it was previously thought that the heavier alkali metals also formed octahedral hexaaqua ions, it has since been found that potassium and rubidium probably form the [K(H 2 O) 8] + and [Rb(H 2 O) 8] + ions, which have the square antiprismatic structure, and that caesium forms the 12-coordinate [Cs(H 2 O) 12] + ion.
Heme is a coordination complex "consisting of an iron ion coordinated to a tetrapyrrole acting as a tetradentate ligand, and to one or two axial ligands". [5] The definition is loose, and many depictions omit the axial ligands. [ 6 ]
Thus ferrocyanide ([Fe(CN) 6] 4− has no unpaired electrons, meaning it is a low-spin complex. With so-called "weak field ligands" such as water, four of the six electrons are unpaired, meaning it is a high-spin complex. Thus aquo complex [Fe(H 2 O) 6] 2+ is paramagnetic. With chloride, iron(II) forms tetrahedral complexes, e.g. [FeCl 4] 2− ...