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  Halogens

Halogens:

Among the halogens chlorine, fluorine, bromine, iodine and astatine, chlorine and iodine are broadly employed as antiseptics and disinfectants. Chlorine in the form of compressed gas (i.e., in liquid form) is employed in purification of municipal water. Safe handling of gas is hard and needs equipments and thus chlorine compounds are preferred for practical use. The customary practice of application of bleaching powder to fine water in cholera prone regions, in toilets and in unhygienic places gives the chlorine which kills microorganisms. Hypochlorites such as calcium hypochlorite Ca(OCl)2  also termed as chlorinated lime and sodium hypochlorite (NaOCl) and chloramines such as chloramine-T and azochloramides are employed as antiseptics, disinfectants, and as sanitizing agents.

Semmelweis, a Hungarian, employed hypochlorites as antiseptics in obstetrical practice to decrease the incidence of childhood fever. Washing hands in hypochlorite solution avoid the spread of infection after observing the patients. Chlorine compounds are employed to disinfect wounds and treat athlete’s foot. Sodium hypochlorite of 1% concentration is employed for personal hygiene and 5-12% is employed as household bleaches, disinfectants and sanitizing food and dairy processing machines. The concentration of hypochlorite employed must provide at least 1ppm of residual chlorine.

The mode of action of chlorine and its compounds is via formation of antimicrobial hypochlorous acid (HClO) whenever chlorine is added to water or formed due to hydrolysis of hypochlorites and chloramines. The nascent oxygen liberated upon decomposition of hypochlorous acid oxidizes cellular components damaging the cells. The direct action of chlorine with proteins of cell membrane and enzymes too has a killing effect.

Iodine, the oldest germicidal agent is employed in the form of tincture iodine 2% iodine in 2% sodium iodide diluted in alcohol is employed, as iodine is eagerly soluble in alcohol and aqueous solution of potassium iodide as it is only slightly soluble in water.  Iodophores, (example, Polyvinylpyrrolidone) mixtures of iodine and surface active agents which act as carriers and solubilizers for the iodine are also employed as germicides. These are non-staining dissimilar iodine and have less irritant properties than tincture iodine.

Iodine is bactericidal effective against all types of bacteria, sporicidal, fungicIdal and to certain disinfectant on skin. It is also employed for disinfection of water, air and sanitization of apparatus. The antimicrobial act is due to its strong oxidizing power, inactivating proteins along with sulfhydryl group and halo-genation of tyrosine units of enzymes and cellular proteins.

Apart from the chemical agents explained above there are numerous antimicrobial agents employed in day to day use in various places. Triphenylmethane dyes such as malachite green and crystal violet are employed in media to inhibit Gram positive bacteria. Acridine dyes such as acriflavine and tryptoflavin restrain staphylococci and gonococci and are employed in the treatment of burns and wounds previous to antibiotic discovery. Detergents such as soap employed for cleaning surfaces act by wetting or depressing surface tension. Quaternary ammonium salts (i.e., Cetrimide, Ceepryn and so on) are employed in detergents and as well as disinfectants, sanitizing agent, employed on skin, as a preservative in ophthalmic solutions and in cosmetic preparation.

Aldehydes (i.e., formaldehyde and glutaraldehyde) are microbicidal and sporicidal.  Formaldehyde (i.e., Formalin) is employed to sterilize closed region and vaporizes at room temperature and acts in gaseous form. Glutaraldehyde is employed in sterilizing urological tools, lensed instruments and respiratory therapy equipments. There are some gaseous agents such as Ethylene oxide and β-propiolactone. Ethylene oxide is an efficient sterilizing agent for heat and moisture sensitive materials. Spices such as pepper, biological preparations, soil, syringes, plastic, tongs, blood transfusion apparatus and catheterization equipments are sterilized by ethylene oxide fumigation.

 

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