What is the difference among these compounds?

Question

I'll preface this question by making clear that I'm not not well versed in biology.

Anyway, within the context of biocides/antimicrobial products using them as active substances, what is the difference among these three quaternary ammonium compounds:

benzyl-C12-16-alkyldimethyl, chlorides (CAS number - 68424-85-1)

benzyl-C8-18-alkyldimethyl, chlorides (CAS number - 63449-41-2)

dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (CAS number - 27668-52-6)

How does one's antimicrobial properties differ from the other? And which is more hazardous? And which is least hazardous?

Answer 1

As you point out, these are all quaternary ammonium compounds that are likely to work in a similar way (membrane disruption) and are very broad spectrum. Any differences in efficacy against a given pathogen would need to be established by empirical testing on that particular organism, as these kind of things are highly idiosyncratic--it's not like an enzyme inhibitor where you can ask whether the organism has the relevant enzyme or not. The first two are even not pure compounds, they're mixtures whose precise composition is not known a priori.

As for hazards, these kind of quaternary ammonium compounds are frequently used in topical disinfectants for use on human skin, and even in low concentration in things like eye drops that go in the eye. Obviously as with anything, the dose makes the poison, and a concentration you would use to scrub your bathroom sink is not safe to put on a mucous membrane on your body.