Microbiological control |
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Formaldehyde The structure of formaldehyde is shown below.
The electrons of the carbon-oxygen double bond hold together atoms that have variable electronegativity. Thus, the C=O bond is said to have "partial ionic character." This ionic character results in a charge distribution in the bond such that oxygen becomes the negative end, carbon the positive end. This uneven sharing of electrons imparts a strong polarity to the formaldehyde molecule. The positive character of the carbon atom causes it to behave as an electrophilic center, making it susceptible to nucleophilic attack. This attack is borne out of the following:
where "R" is the substituting reactant. This is exactly the type of reaction that occurs between formaldehyde and the amino groups of proteins and polyhydroxy compounds. The amines add to the carboxyl group to form products that contain a carbon-nitrogen double bond as follows:
This is the reaction that occurs with bacterial cells. Chemically the cell walls of bacteria contain a unique protein which, specifically, is a combination often different amino acids. The amino groups are typical organic bases and effective nucleophilic compounds. Formaldehyde reacts with the free (unprotonated) amino groups on the outside of the cell wall via the aforementioned nucleophilic substitution reaction. In so doing, it cross-links and binds the amino groups on the cell wall, preventing the cell from functioning by inhibiting nutrients from entering the cell and waste products from leaving the cell.
Like glutaraldehyde, formaldehyde functions well in the control of sulfate-reducing bacteria, is effective in oil contaminated systems and works more rapidly to control microorganisms in the alkaline pH ranges. |
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