Editing Porphyrin (section)

==Structure==

[[Porphyrin complexes]] consist of a square planar MN<sub>4</sub> core.  The periphery of the porphyrins, consisting of sp<sup>2</sup>-hybridized carbons, generally display small deviations from planarity.  "Ruffled" or saddle-shaped porphyrins is attributed to interactions of the system with its environment.<ref>{{cite journal | vauthors = Senge MO, MacGowan SA, O'Brien JM | title = Conformational control of cofactors in nature - the influence of protein-induced macrocycle distortion on the biological function of tetrapyrroles | journal = Chemical Communications | volume = 51 | issue = 96 | pages = 17031–17063 | date = December 2015 | pmid = 26482230 | doi = 10.1039/C5CC06254C | hdl-access = free | hdl = 2262/75305 }}</ref>  Additionally, the metal is often not centered in the N<sub>4</sub> plane.<ref>{{cite book |doi=10.1002/9781119951438.eibc0104 |chapter=Iron Porphyrin Chemistry |title=Encyclopedia of Inorganic and Bioinorganic Chemistry |year=2011 | vauthors = Walker FA, Simonis U |isbn=9781119951438 }}</ref>  For free porphyrins, the two pyrrole protons are mutually trans and project out of the N<sub>4</sub> plane.<ref> {{cite journal | vauthors = Jentzen W, Ma JG, Shelnutt JA | title = Conservation of the conformation of the porphyrin macrocycle in hemoproteins | journal = Biophysical Journal | volume = 74 | issue = 2 Pt 1 | pages = 753–763 | date = February 1998 | pmid = 9533688 | pmc = 1302556 | doi = 10.1016/S0006-3495(98)74000-7 | bibcode = 1998BpJ....74..753J }}</ref> These nonplanar distortions are associated with altered chemical and physical properties. [[Chlorophyll]]-rings are more distinctly nonplanar, but they are more saturated than porphyrins.<ref>{{Cite journal | vauthors = Senge MO, Ryan AA, Letchford KA, MacGowan SA, Mielke T | year = 2014 | title = Chlorophylls, Symmetry, Chirality, and Photosynthesis | journal = Symmetry | volume = 6 | issue = 3 | pages = 781–843 | doi = 10.3390/sym6030781 | bibcode = 2014Symm....6..781S | doi-access = free | hdl = 2262/73843 | hdl-access = free }}</ref>