Hypochlorites antimicrobial activity

At low pH the existence of HOCl is favoured over OCl" (hypochlorite ion). The relative microbiocidal effectiveness of these forms is of the order of 100 1. By lowering the pH of hypochlorite solutions the antimicrobial activity increases to an optimum at about pH 5 however, this is concurrent with a decrease in stability of the solutions. This problem may be alleviated by addition of NaOH (see above equation) in order to maintain a high pH during storage for stability. The absence ofbuffer allows the pH to be lowered sufficiently for activity on dilution to use-strength. It is preferable to prepare use-dilutions of hypochlorite on a daily basis. 

Firestone and Christensen (1973) employed phenyllithium rather than lithium methoxide to achieve direct introduction. Penicillin G benzyl ester (81), when reacted with phenyllithium in THF at -78 C, followed by /ert-butyl hypochlorite and finally quenched with methanol, gave 6a-methoxypenicillin G benzyl ester (82). Analogously, quenching of the acylimine intermediate with water or triethylammonium formate gave 83 and 84, respectively. Hydrogenolysis of these materials was achieved with 10% Pd-C, NaHCOj, and methanol-water, at 40 psi. The resulting sodium salts exhibited markedly lower antimicrobial activity than 37. A major by-product always formed in these conversions was assigned structure 85. 

Hypochlorite has high antimicrobial activity even at low concentrations (e.g., a few ppm). As with bleaching, the activity is principally due to free HGIO and is thus pH dependent. Although several effects may contribute, bactericidal activity is thought to largely derive from oxidation of relatively labile sulfhydryl (-SH) groups in vital enzymes [8]. 

The spectmm of antimicrobial activity of sodium hypochlorite has been advantageously compared to other disinfectants which display a narrower activity range. This is well documented by the scientific literature, where the content of Table 2 has been presented and discussed [34]. 

The dissociation of hypochlorous acid depends on the pH. The unionized acid is present in greater quantities in acid solution, although in strongly acid solution the reaction with water is reversed and chlorine is Hberated. In alkaline solutions the hypochlorite ion OCL is increasingly Hberated as the pH is increased. The pH is important because unionized hypochlorous acid is largely responsible for the antimicrobial action of chlorine in water. Chlorine compounds are therefore more active in the acid or neutral range. The hypochlorites most commonly employed are sodium hypochlorite [7681-52-9] or calcium hypochlorite [7778-54-3]. 

Chlorine Vehicle and Stabilizer. Sulfamic acid reacts with hypochlorous acid to produce IV-chlorosulfamic acids, compounds in which the chlorine is still active but more stable than in hypochlorite form. The commercial interest in this area is for chlorinated water systems in paper mills, ie, for slimicides, cooling towers, and similar applications (54) (see INDUSTRIAL ANTIMICROBIAL AGENTS). 

A new and novel approach to bound antimicrobials was recently introduced. Cotton reacted with methylol-5,5-dimethyldyantoin is then treated with hypochlorite to form chloramines in the fibre (Fig. 15.3). These chloramine sites have antibacterial activity and can function as renewable antimicrobial agents by continued treatment with hypochlorite through household bleaching and washing... 

The degree of ionization of acidic and basic antimicrobial agents depends on pH. Some compounds are active only in the unionized state (e.g., phenolics) whereas others are preferentially active as either the anion or cation. It therefore follows that the activity of a particular concentration of an agent will be enhanced at a pH that favors the formation of the active species. Thus, cationic antibacterials such as acridines and quaternary ammonium compounds are more active under alkaline conditions. Conversely, phenols and benzoic acid are more active in an acid medium. Chlorbutol is less active above pH 5 and unstable above pH 6. Phenylmercuric nitrate is only active at above pH 6 whereas thiomersal is more active under acid conditions. The sporicidal activity of glutaraldehyde is considerably enhanced under alkaline conditions whereas hypochlorites are virtually ineffective at above pH 8. 

Chlorine in its active form, hypochlorous acid (HOCl), is a powerful oxidant and antimicrobial agent. Hypochlorous acid is present in highest concentration at near pH 4, decreasing rapidly with increased pH. At pH >5 hypochlorite (OCl ) increases, whereas at pH <4, chlorine gas (CI2) increases. Neither chlorine gas nor hypochlorite have been shown to be active toward microorganisms (Mercer and Somers, 1957) however, both are very corrosive. Formation of Cl2(g) is also a safety issue for employees. In that there is still substantial amounts of HOCl present at pH >6.5, sanitizing operations are typically carried out in the pH range 6.5-7.0. 

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