Aldehydes

Chemical structure
Aldehydes are organic compounds, which consist of a hydrocarbon chain and a terminal carbonyl group. The term ‘aldehyde’ is derived from the term ‘alcohol dehydrogenatus’ and was established by Justus von Liebig (1803-1870). Aldehydes evolve from the oxidation of alcohols or from the reduction of carboxylic acid. An aldehyde group consists of one oxygen atom double bonded to one carbon atom. The respective carbon atom is joined to at least one hydrogen atom.

Chemical structure of glutaraldehyde:

Characteristics
The carbonyl group and the aldehyde group respectively are so-called osmophore, i.e. odor carrying, groups. Hence, many aldehydes possess an intensive smell. The spectrum of effect of aldehydes used for disinfection depends on the used type, exposure time and concentration. In general, aldehydes possess a broad spectrum of effect against fungi, bacteria, mycobacteria, bacterial spores and viruses. Through the combination with other substances their microbiocidal activity can be enhanced. Alcohols, for instance, shorten the exposure time, soaps and washing active substances increase the efficacy. Except for formaldehyde, all aldehydes and aldehyde derivatives are only optimally effective at specific pH-values. Therefore, industrially produced disinfectants with these active ingredients contain particular stabilizers. Depending on the type, aldehydes show minor or major protein effects, i.e. if a fixation occurs, they loose disinfection power when having contact with protein, blood, serum and sputum. This agent class has the advantage that aldehydes are readily biodegradable and material compatible.

Effect mechanisms
Essentially, the effect mechanism of aldehydes is based on the denaturation of proteins. Denaturation amends the structures of biomolecules. Aldehydes impair the protein structure – the most important cell component – of bacteria, fungi and viruses. Once the structure is changed, proteins cannot carry out their initial function. That way, organisms are inactivated. In addition, a chemical denaturation of enzymes, RNA and DNA takes place.

Fields of application
In the organic chemistry aldehydes constitute important interstage products for the production of plastics, and serve as disinfectant and preservative. Longer-chain aldehydes are used as odorous substances in the perfume industry. In the field of disinfection, aldehydes are predominantly used for instrument and surface disinfection. For instrument disinfection for example, they are the only active ingredient besides peracetic acid to fulfill the Robert Koch-Institute’s (RKI) demand for virucidal activity, when the reprocessing procedure does not include a subsequent sterilization.

In the past, particularly the good water-soluble, gaseous formaldehyde played a major role for disinfection, as it possesses an excellent efficacy, also against non-enveloped viruses. Despite intensive research it has not been possible yet to completely replace formaldehyde by substances with similar efficacy but lesser side effects. Formaldehyde should only be used systematically and in consideration of protection and safety instructions, e.g. adherence to prescribed use concentrations, avoidance of direct skin contact by wearing gloves, covering instrument trays if required and working in well-aired rooms.

Already in 1962, Pepper and Liebermann tried to replace formaldehyde with glutaraldehyde as effective alternative. Glutaraldehyde possesses a broad and fast efficacy against most microorganisms. The excellent activity of glutaraldehyde against spores and non-enveloped viruses has to be highlighted in particular. Today, glutaraldehyde ranks among the most important aldehydes used for instrument and surface disinfection (see above).