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Mechanism of action::Bleach

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Mechanism of action

Whitening

Colors typically arise from organic dye and pigments, such as beta carotene. Chemical bleaches work in one of two ways:

  • An oxidizing bleach works by breaking the chemical bonds that make up the chromophore. This changes the molecule into a different substance that either does not contain a chromophore, or contains a chromophore that does not absorb visible light. This is the mechanism of bleaches based on chlorine.
  • A reducing bleach works by converting double bonds in the chromophore into single bonds. This eliminates the ability of the chromophore to absorb visible light. This is the mechanism of bleaches based on sulfur dioxide.<ref>{{#invoke:citation/CS1|citation

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Sunlight acts as a bleach through a process leading to similar results: high energy photons of light, often in the violet or ultraviolet range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless. Extended exposure often leads to massive discoloration usually reducing the colors to white and typically very faded blue spectrums.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Antimicrobial efficacy

The broad-spectrum effectiveness of bleach, particularly sodium hypochlorite, is owed to the nature of its chemical reactivity with microbes. Rather than acting in an inhibitory or toxic fashion in the manner of antibiotics, bleach quickly reacts with microbial cells to irreversibly denature and destroy many pathogens. Bleach, particularly sodium hypochlorite, has been shown to react with a microbe's heat shock proteins, stimulating their role as intra-cellular chaperone and causing the bacteria to form into clumps (much like an egg that has been boiled) that will eventually die off.<ref name=Winter>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> In some cases, bleach's base acidity compromises a bacterium's lipid membrane, a reaction similar to popping a balloon. The range of micro-organisms effectively killed by bleach (particularly sodium hypochlorite) is extensive, making it an extremely versatile disinfectant. The same study found that at low (micromolar) sodium hypochlorite levels, E. coli and Vibrio cholerae activate a defense mechanism that helps protect the bacteria, though the implications of this defense mechanism have not been fully investigated.<ref name="Winter"/>

In response to infection, the human immune system will produce a strong oxidizer, hypochlorous acid, which is generated in activated neutrophils by myeloperoxidase-mediated peroxidation of chloride ions, and contributes to the destruction of bacteria.<ref>Harrison, J. E., and J. Schultz. 1976. Studies on the chlorinating activity of myeloperoxidase. Journal of Biological Chemistry volume 251, pages 1371–74.</ref><ref>Thomas, E. L. 1979. Myeloperoxidase, hydrogen peroxide, chloride antimicrobial system: Nitrogen-chlorine derivatives of bacterial components in bactericidal action against Escherichia coli. Infect. Immun. 23:522–531.</ref><ref>Albrich, J. M., C. A. McCarthy, and J. K. Hurst. 1981. Biological reactivity of hypochlorous acid: Implications for microbicidal mechanisms of leukocyte myeloperoxidase. Proc. Natl. Acad. Sci. USA 78:210–214.</ref>


Bleach sections
Intro   History    Mechanism of action  Classes of bleaches   Environmental impact    Disinfection   Color safe bleach   See also    References    Further reading    External links   

Mechanism of action
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