I found the following explanation in Andreas Kalcker’s book “Forbidden Health" on page 384.
“Chlorine dioxide is a selective oxidant, and unlike other substances, it doesn’t react to most living tissue components.
Chlorine dioxide does react quickly to the phenols and thiols, which are essential to bacterial life. With the phenols, the mechanism consists in attacking the ring of benzene, removing smell, taste and other intermediate compounds.[71]
Chlorine dioxide efficiently eliminates viruses and is ten times more efficient than sodium hypochlorite (bleach)[72], something proved in a comparative study.[73] It also proved high efficiency against small parasites like protozoa.[74]
Something of concern to medical professionals is how chlorine dioxide reacts with essential amino acids. In trials on chlorine dioxide’s reactivity to 21 essential amino acids, only cysteine[75], tryptophan[76], tyrosine[77], proline, and hydroxyproline[78] were reactive in a pH of around 6. These amino acids are relatively easy to replace.
Cysteine and methionine[79] are two aromatic amino acids that contain sulfur, tryptophan, and tyrosine and the two inorganic ions Fe2+ and Mn2+. Cysteine, as it belongs to the thiols groups, is an amino acid up to 50 times more reactive to all microbial systems that the other four essential amino acids, and therefore it is impossible for it to create resistance to chlorine dioxide.
Although it hasn’t been proved to date, pharmacodynamics usually presume that the cause of its antimicrobial effect is based on its reaction to the four amino acids mentioned earlier, or to the residues of proteins and peptides."
The references are linked here:
[71] Stevens, A.; Seeger, D.; Slocum, C., Products of Chlorine Dioxide Treatment
of Organic Materials in Water, Water Supply Research Div., U. S.
Environmental Protection Agency,Cincinnati, Ohio, 1977, 9
[72] Sanekata T, Fukuda T, Miura T, Morino H, Lee C et al. (2010) Evaluation
of the antiviral activity of chlorine dioxide and sodium hypochlorite against feline calicivirus, human influenza virus, measlesvirus, canine distemper virus, human herpesvirus, human adenovirus,canine adenovirus and canine 389 parvovirus. Biocontrol Sci 15/2: 45-49.doi:10.4265/bio.15.45. PubMed:
20616431.
[73] Tanner R (1989) Comparative testing and evaluation of hard-surface disin-
fectants. J Ind Microbiol 4: 145-154. doi:10.1007/BF01569799
[74] EPA Guidance Manual, Alternative Disinfectants and Oxidants, 4.4.3.2
Protozoa Inactivation. Available:
www.epa.gov/ogwdw/mdbp/pdf/
alter/chapt_4.pdf
[75] Ison A, Odeh IN, Margerum DW (2006) Kinetics and mechanisms of
chlorine dioxide and chlorite oxidations of cysteine and glutathione.Inorg
Chem 45: 8768-8775. doi:10.1021/ic0609554. PubMed:17029389
[76] Stewart DJ, Napolitano MJ, Bakhmutova-Albert EV, Margerum DW (2008) Kinetics and mechanisms of chlorine dioxide oxidation of tryptophan. Inorg
Chem 47: 1639-1647. doi:10.1021/ic701761p. PubMed: 18254588
[77] Napolitano MJ, Green BJ, Nicoson JS, Margerum DW (2005) Chlorine
dioxide oxidations of tyrosine, N-acetyltyrosine, and Dopa. Chem Res
Toxicol 18: 501-508. doi:10.1021/tx049697i. PubMed: 15777090
[78] Tan, H.K., Wheeler, W.B., Wei, C.I., Reaction of chlorine dioxide with
amino acids and peptides, Mutation Research, 188: 259-266, 1987
[79] Loginova IV, Rubtsova SA, Kuchin AV (2008) Oxidation by chlorine dioxide
of methionine and cysteine derivatives to sulfoxide. Chem Nat Compd 44:
752-754. doi:10.1007/s10600-009-9182-8