Compounds in Living Systems

Coordination compounds play many important roles in animals and plants. They are essential in the storage and transport of oxygen, as electron transfer agents, as catalysts, and in photosynthesis. Here we focus on coordination compounds containing iron and magnesium. 

The porphine molecule forms an important part of the hemoglobin structure. Upon coordination to a metal, the H ions that are bonded to two of the four nitrogen atoms in porphine are displaced. Complexes derived from porphine are 

Simplified structures of the porphine molecule and the Fe -porphyrin complex. The dashed lines represent coordinate covalent bonds. 

The heme group in hemoglobin. The Fe ion is coordinated with the nitrogen atoms of the heme group. The ligand below the porphyrin is the histidine group, which is attached to the protein. The sixth ligand is a water molecule. 

Three possible ways for moleeular oxygen to bind to the heme group in hemoglobin. The strueture shown in (a) would have a eoordination number of 7, which is considered unlikely for Fe(ll) complexes. Although the end-on arrangement in (b) seems the most reasonable, evidence points to the structure in (c) as the correct one. 

---

Characteristics of biological systems, coupled with the rich chemistry of vanadium in aqueous solutions, make the study of effects of vanadium compounds in living systems difficult. The cell is divided into different organelles and vesicles by mem-... 

Phosphoenolpyruvate is a biologically important enol. In fact, it is the highest energy phosphorylated compound in living systems. 

Coordination Compounds in Living Systems Coordination compounds play many important roles in animals and plants. They are also used as therapeutic drugs. 

There is a very wide range of aromatic compounds present in living systems, e.g. the amino acids phenylalanine and tyrosine, and catecholamines such as norepinephrine. Although these speciesi are very useful for in vitro investigations of OH radical generation, their applicability as suitable aromatic detector molecules for OH radical in vivo largely depends on their concentration (i.e. their ability to compete with alternative... 

Lipids in living systems are by solvents extractable compounds. Among the lipids are the fatty acids, glycerides, steroids, terpenes, and complex lipids as lipoproteins. 

The Role of Phosphonates in Living Systems, Hilderbrand, R.L., Ed., CRC Press, Boca Raton, FL, 1983 — Contributed chapters survey the role of naturally occurring organophosphorus compounds (containing a C-P bond) in biological systems and the use of a wide variety of organophosphorus compounds for the regulation of metabolism and the treatment of disease. 

Organic chemistry is important because the vital biological molecules in living systems are largely organic compounds. Nearly all commonly used plastics are prepared from organic compounds. 

With each of the C, P and S centers, compounds with several oxidation states are possible, thus multiplying the types of nucleophilic reactions extant. Importantly, the types of compounds cover a variety of classes each with its characteristic behaviors and reactivities, each defining a specific area in chemistry. Since the C, P and S reactive centers are incorporated in the majority of molecules in living systems it follows that the chemistry to be considered in this chapter is closely tied with the chemistry of life, i.e. bioorganic reaction mechanisms. It is known in fact that many organophosphorus and organosulfur compounds are toxic toward mammalian organisms which renders their destruction under mild conditions of critical importance. 

Indole-3-acetic acid is rather readily oxidized by peroxidases and is, in fact, probably not present in the plant in the free form to any appreciable extent. The nature of the complexing groups is not clear. The inherent instability of the compound in living tissue has made experimental observations difficult, and (the more stable) 1-naphthaleneacetic acid has often been used instead, although it is by no means certain that the biological activities are comparable. One view held is that auxin herbicides are effective either because they do not readily form conjugate systems, or because the conjugate retains the phytotoxic properties. 

---