CHAPTER-17 ANTIMICROBIALS Hydrogen peroxide Hydrogen peroxide (H2O2) is the simplest peroxide (a compound with an oxygen-oxygen single bond). It is also a strong oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. Due to its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent. The oxidizing capacity of hydrogen peroxide is so strong that it is considered a highly reactive oxygen species. Hydrogen peroxide is therefore used as a propellant in rocketry. Organisms also naturally produce hydrogen peroxide as a by-product of oxidative metabolism. Consequently, nearly all living things (specifically, all obligate and facultative aerobes) possess enzymes known as catalase peroxidases, which harmlessly and catalytically decompose low concentrations of hydrogen peroxide. Reactions Manganese dioxide decomposing a very dilute solution of hydrogen peroxide Hydrogen peroxide decomposes (disproportionates) exothermically into water and oxygen gas spontaneously: 2 H2O2 → 2 H2O + O2 Redox reactions In acidic solutions, H2O2 is one of the most powerful oxidizers known—stronger than chlorine, chlorine dioxide, and potassium permanganate. Also, through catalysis, H2O2 can be converted into hydroxyl radicals (•OH), which are highly reactive. Therapeutic use Hydrogen peroxide is generally recognized as safe (GRAS) as an antimicrobial agent, an oxidizing agent and for other purposes by the U.S. FDA. For example, 35% hydrogen peroxide is used to prevent infection transmission in the hospital environment, and hydrogen peroxide vapor is registered with the US EPA as a sporicidal sterilant. It is a common misconception that hydrogen peroxide is a disinfectant or antiseptic for treating wounds. While it is an effective cleaning agent, hydrogen peroxide is not an effective agent for reducing bacterial infection of wounds. Further, hydrogen peroxide applied to wounds can impede healing and lead to scarring because it destroys newly formed skin cells. • Hydrogen peroxide can be used as a toothpaste, or oral debriding agent, when mixed with correct quantities of baking soda and salt. This use is no more effective than toothpaste alone, however. • Hydrogen peroxide and benzoyl peroxide are sometimes used to treat acne. • Hydrogen peroxide is used as an emetic in veterinary practice. Potassium permanganate Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a + − salt consisting of K and MnO4 ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely purple solutions, the evaporation of which leaves prismatic purplish-black glistening crystals. In 2000, worldwide production was estimated at 30,000 tonnes. In this compound, manganese is in the +7 oxidation state. Structure and preparation Potassium permanganate is produced industrially from manganese dioxide, which also occurs as the mineral pyrolusite. The MnO2 is fused with potassium hydroxide and heated in air or with a source of oxygen, like potassium nitrate or chlorate. This process gives potassium manganate, which upon electrolytic oxidation in alkaline media, or by boiling the manganate solution in the presence of carbon dioxide until all the green color is discharged, gives potassium permanganate. 2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O 2– – – 2 MnO4 + Cl2 → 2 MnO4 + 2 Cl or: 3 K2MnO4 + 2 CO2 → 2 KMnO4 + 2 K2CO3 + MnO2 In which the potassium permanganate is separated by filtering the insoluble manganese dioxide, evaporating the solution to 1/3 and recrystallizing it. Permanganate salts can also be generated by treating a solution of Mn2+ ions with strong oxidants such as lead dioxide (PbO2), or sodium bismuthate (NaBiO3). Tests for the presence of manganese exploit the vivid violet color of permanganate produced by these reagents. KMnO4 forms orthorhombic crystals with constants: a = 910.5 pm, b = 572.0 pm, c = 742.5 pm. The overall motif is similar to that for barium sulfate, with which it forms solid solutions. In the - solid (as in solution), each MnO4 centres are tetrahedral. The Mn-O distances are 1.62 Å. Biomedical uses Related to the use of KMnO4 for water treatment, this salt is often employed as a specialized disinfectant for treating human and animal ailments. Permanganate washes were once used to treat gonorrhea and are still used to treat candidiasis. It can also be used to inactivate the poison strychnine. BLEACHING POWDER Calcium hypochlorite is a chemical compound with formula Ca(ClO)2. It is widely used for water treatment and as a bleaching agent (bleaching powder). This chemical is considered to be relatively stable and has greater available chlorine than sodium hypochlorite (liquid bleach). Preparation It is manufactured by the calcium process: . Bleaching powder is actually a mixture of calcium hypochlorite (Ca(OCl)2) and the basic chloride CaCl2, H2O with some slaked lime, Ca(OH)2 Properties Calcium hypochlorite is a yellow white solid which has a strong smell of chlorine. It is not highly soluble in water, and is more preferably used in soft to medium-hard water. It has two forms: a dry form and a hydrated form. The hydrated form is safer to handle. Calcium hypochlorite reacts with carbon dioxide to form calcium carbonate and release dichlorine monoxide: . A calcium hypochlorite solution is basic. This is due to the hydrolysis performed by the hypochlorite ion, as hypochlorous acid is weak, but calcium hydroxide is a strong base. As a result, the hypochlorite ion is a strong conjugate base, and the calcium ion is a weak conjugate acid: − − ClO + H2O → HClO + OH Similarly, calcium hypochlorite reacts with hydrochloric acid to form calcium chloride, water and gaseous chlorine: CaOCl2 + 2 HCl → CaCl2 + H2O + Cl2 Uses Calcium hypochlorite is used for the disinfection of drinking water or swimming pool water. It is used as a sanitizer in outdoor swimming pools in combination with a cyanuric acid stabilizer, which reduces the loss of chlorine due to ultraviolet radiation. The calcium content hardens the water and tends to clog up some filters; hence, some products containing calcium hypochlorite also contain anti-scaling agents. Calcium hypochlorite is also an ingredient in bleaching powder, used for bleaching cotton and linen. It is also used in bathroom cleaners, household disinfectant sprays, moss and algae removers, and weedkillers. In addition, calcium hypochlorite may be used to manufacture chloroform. Bleaching powder is used also in sugar industry for bleaching sugar cane juice before its crystallization. IODINE SOLUTION Lugol's iodine, also known as Lugol's solution, first made in 1829, is a solution of elemental iodine and potassium iodide in water, named after the French physician J.G.A. Lugol. Lugol's iodine solution is often used as an antiseptic and disinfectant, for emergency disinfection of drinking water, and as a reagent for starch detection in routine laboratory and medical tests. These uses are possible since the solution is a source of effectively free elemental iodine, which is readily generated from the equilibration between elemental iodine molecules and triiodide ion in the solution. It has been used more rarely to replenish iodine deficiency. However, pure potassium iodide, containing the relatively benign iodide ion without the more toxic elemental iodine, is strongly preferred for this purpose. Likewise, in the Chernobyl disaster some Lugol's solution was used as an emergency source of iodide to block radioactive iodine uptake, simply because it was widely available as a drinking water decontaminant, and pure potassium iodide without iodine (the preferred agent) was not available. Formula and manufacture Lugol's solution is available in different potencies of 1%, 2%, or 5% Iodine. The 5% solution consists of 5% (wt/v) iodine (I2) and 10% (wt/v) potassium iodide (KI) mixed in distilled water and has a total iodine content of 130 mg/mL.[2] Potassium iodide renders the elementary iodine soluble in water through the formation of the triiodide (I− 3) ion. It is not to be confused with tincture of iodine solutions, which consist of elemental iodine, and iodide salts dissolved in water and alcohol. Lugol's solution contains no alcohol. Other names for Lugol's solution are I2KI (iodine-potassium iodide); Markodine, Strong solution (Systemic); and Aqueous Iodine Solution BCP.[3] Lugol's is obtained over the counter from drug stores or health food stores. This indicator, also called a stain, is used in many different fields. Applications • As a mordant when performing a Gram Stain. It is applied for 1 minute after staining with crystal violet, but before ethanol to ensure that gram positive organisms' peptidoglycan remains stained, easily identifying it as a gram positive in microscopy. • This solution is used as an indicator test for the presence of starches in organic compounds, with which it reacts by turning a dark-blue/black. Elemental iodine solutions like Lugol's will stain starches due to iodine's interaction with the coil structure of the polysaccharide. Starches include the plant starches amylose and amylopectin and glycogen in animal cells. Lugol's solution will not detect simple sugars such as glucose or fructose. In the pathologic condition amyloidosis, amyloid deposits (i.e., deposits that stain like starch, but are not) can be so abundant that affected organs will also stain grossly positive for the Lugol reaction for starch. • It can be used as a cell stain, making the cell nuclei more visible and for preserving phytoplankton samples. • During colposcopy, Lugol's iodine is applied to the vagina and cervix. Normal vaginal tissue stains brown due to its high glycogen content, while tissue suspicious for cancer does not stain, and thus appears pale compared to the surrounding tissue. Biopsy of suspicious tissue can then be performed. This is called a Schiller's Test. • Lugol's iodine may also be used to better visualize the mucogingival junction in the mouth.