Phenylarsine oxide (PAO or PhAsO) is an organometallic compound with the empirical formula C₆H₅AsO. It contains a

phenyl group In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...

and an oxygen atom both bonded to an arsenic atom.

Structure

Despite its simple empirical formula, phenylarsine oxide does not contain an As=O double bond. In common with other compounds with the

general formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

RAsO, PhAsO forms a cyclic

oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

. A range of ring sizes are possible, but PhAsO crystallizes as the tetramer, cyclo-(PhAsO)₄. RAsO compounds form these species because for heavy elements such as arsenic, two single bonds to oxygen are more stable than one double bond; see double bond rule for details.

Use in biochemical research

The arsenic atom in PAO has a high affinity for the sulfur atom of thiols in organic compounds, in particular, forming stable complexes with vicinal

cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

residues in protein structures. This effect makes it useful for studying ligand–

receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...

binding This binding affinity also makes PAO useful for affinity chromatography by immobilizing it on a resin. It has a high selectivity for structures with vicinal cysteines rather than single cysteine residues or cystine (a disulfide-bridged pair of cysteine residues).

Use in wastewater analysis

Phenylarsine oxide is a reducing agent that is stable in water. As such, solutions of it can be used in iodometric methods for the determination of residual chlorine (Cl⁺) in wastewaters. The accuracy of these methods is enough that the residual chlorine can often be detected to low ppm levels.

References

{{reflist Phenyl compounds Arsenic heterocycles Organoarsenic compounds