Electronic Journal of Biotechnology E-ISSN: 0717-3458 [email protected] Pontificia Universidad Católica de Valparaíso Chile Kim, Yun-mi; Farrah, Samuel; Baney, Ronald H. Silanol - A novel class of antimicrobial agent Electronic Journal of Biotechnology, vol. 9, núm. 2, abril, 2006, pp. 176-180 Pontificia Universidad Católica de Valparaíso Valparaíso, Chile Available in: http://www.redalyc.org/articulo.oa?id=173313794012 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Electronic Journal of Biotechnology ISSN: 0717-3458 Vol.9 No.2, Issue of April 15, 2006 © 2006 by Pontificia Universidad Católica de Valparaíso -- Chile Received July 18, 2005 / Accepted September 12, 2005 DOI: 10.2225/vol9-issue2-fulltext-4 TECHNICAL NOTE Silanol - A novel class of antimicrobial agent Yun-mi Kim Department of Materials Science and Engineering University of Florida Gainesville, FL 32611, USA Tel: 1 352 846 3793 Fax: 1 352 846 3355 E-mail: [email protected] Samuel Farrah Department of Microbiology and Cell Science University of Florida Gainesville, FL 32611, USA Tel: 1 352 392 5925 Fax: 1-352 392 5922 E-mail: [email protected] Ronald H. Baney* Department of Materials Science and Engineering University of Florida Gainesville, FL 32611, USA Tel: 1 352 846 3785 Fax: 1 352 846 3355 E-mail: [email protected] Financial support: Air force Research Lab. Keywords: antimicrobial agents, bacteria, biocide, silanols. Abbreviations: cfu: Colony Forming Units. MLC: Minimum Lethal Concentration. Recently, a significant amount of attention has been Various types of biocides are used in antiseptics and directed toward development of novel classes of biocides disinfectants to inhibit or destroy selective bacteria or other because of the potential for microbial contamination microorganisms (McDonnell and Russell, 1999). On the and infection risks to military personnel and in the basis of their activity against microbes, antimicrobial agents general population. We have recently discovered a new can be classified into two groups, bacterialcidal and and unexpected class of powerful biocides based upon sporocidal. Quaternary ammonium compounds and compounds derived through simple chemistry from alcohols are frequently used as bacterialcidal. Peracetic silicone intermediates, “silicon alcohols” called, silanols. acid, glutaraldehyde, and chlorine-releasing agents show One example is trialkylsilanols, R3SiOH. Antimicrobial both bacterialcidal and sporocidal activity, although a much tests were carried out against Gram-negative higher concentration is needed to achieve the sporocidal bacterium, Escherichia coli, and Gram-positive, effect due to the high resistance of spores. Chlorine dioxide Staphylococcus aureus, with silanols, t-butanol, and was recently used for decontamination of Bacillus siloxanes. Trialkylsilanols were very effective biocides anthracis by Bio·ONETM, Sabre/Giuliani Company, against Escherichia coli and Staphylococcus aureus. The however, concerns were raised due to its highly toxic and number of viable bacteria reduced was more than eight corrosive properties. orders of magnitude with silanol treatments. Triethylsilanol, in particular, exhibited a strong We have recently discovered a new class of strong biocides antimicrobial effect at a very low concentration within called silanols, demonstrated an enhanced antimicrobial 10 min. These novel biocide silanols can be prepared activity compared to the analogous organic alcohols. from low cost intermediates derived from the Organosilicon compounds showed a greater hydrophobicity commercial processesassociated with the silicone than organic compounds due to low group rotational energy industry. Silanols are considered environmentally (Owen, 1990) and silanols demonstrated a greater acidity benign because of their transitory nature and ultimate compared to the corresponding organic alcohols because of conversion to CO2, SiO2, and H2O. electron back donation from oxygen through (p→d * Corresponding author This paper is available on line at http://www.ejbiotechnology.info/content/vol9/issue2/full/4/ Kim, Y. et al. orbital)π bond (West and Baney, 1959). We hypothesized against Escherichia coli (E. coli) and Staphylococcus that these unique properties of organosilicon compounds aureus (Staph. aureus) to estimate their relative such as silanols may enhance the antimicrobial activity of antimicrobial activities. Octamethylcyclotetrasiloxane and silanols. Although a mechanism of the antimicrobial effect siloxanes formed by the condensation of the silanols were of silanols has not yet been clearly determined. also evaluated. Antimicrobial tests involving a wide range of microorganisms and fundamental studies to understand the mechanism of the bioactivity are currently underway. Silanols can be applied by a various delivery systems such as a neat liquid phase, vapor phase due to their high volatility, and as bound antimicrobial agents. Figure 1. Chemical structures of : Figure 2. Antimicrobial test with E. coli at 10% g/g of materials. a) t-butanol b) Trimethylsilanol. MATERIALS AND METHODS There is a significant amount of evidence that suggests possible interactions between silicon compound and The trialkylsilanols were prepared by the hydrolysis of their biological systems. It has been known for several years that organosilicon halide precursors by a method similar to silicone elastomers exhibits excellent marine fouling Kantor (Sauer, 1944; Kantor, 1953). Organosilicon halides release properties (Stein et al. 2003a; Stein et al. 2003b). and water were mixed for 15 min in diethyl ether solution The antifouling effect of silicone elastomers suggests that with ammonium hydroxide as a catalyst. The silanol 29 1 there could be a specific interaction between silicone and content of trimethylsilanol measured by Si and H NMR microorganisms preventing silicone surface from (Nuclear Magnetic Resonance spectroscopy) method was accumulating microorganisms. Toxicity research of 95 ± 3%. The impurity of trimethylsilanol was identified as silicones was reported several years ago (Bennett and hexamethyldisiloxane. Triethylsilanol obtained from Gelest Staratt, 1973) in a short abstract. Trimethylsilanol, a Inc. was used as received and the measured silanol content potential end group hydrolysis product of linear was 95 ± 3%. The impurity of triethylsilanol was polydimethylsiloxane, had been evaluated toxicologically hexaethyldisiloxane. t-butanol was obtained from Acros by testing on mouse, rat, rabbit, and monkey models organics and octamethylcyclotetrasiloxane, (Bennett and Staratt, 1973). These authors claimed that hexamethyldisiloxane, and hexaethyldisiloxane were trimethylsilanol was about three times as potent as t-butanol acquired from Gelest Inc. on an equimolar basis. Chemical structure of t-butanol is analogous to trimethylsilanol but central atom is silicon as The bacterial strains employed were E. coli C3000 (ATCC shown Figure 1. 15597) and Staph. aureus laboratory strain. E. coli and Staph. aureus suspension were prepared according to the The environmental fate of silicones has been recently procedure of Rincón (Rincón and Pulgarin, 2003). The reviewed (Graiver et al. 2003). The hydrolysis of bacteria were inoculated in Columbia broth overnight at polydimethylsiloxane elastomer occurs in aqueous 37ºC with constant agitation under aerobic conditions. The environments to generate cyclic volatile methyl siloxane bacterial cells were collected by centrifugation at 500 rcf such as octamethylcyclotetrasiloxane, and further degrades (relative centrifugal force) for 10 min at 4ºC and washed into dimethylsilanediol and trimethylsilanol, ultimately three times with sterilized distilled water. A bacterial pellet oxidize to environmentally benign silica, carbon dioxide was resuspended in the sterilized water after final washing. The concentration of E. coil and Staph. aureus was 2-6 x and water in the environment. Graiver et al. 2003 suggested 8 that the silicone compounds are environmentally friendly 10 cfu/ml (colony forming units). materials since the degradation process occurs in a short period and generates benign materials. The antimicrobial test of the materials were carried out by adding a given amount of antimicrobial agent into 10 g of Trimethylsilanol, triethylsilanol and t-butanol were tested aqueous solution that contains the bacteria at a 177 Silanol - A novel class of antimicrobial agent concentration of 2-6 x 108 cfu/ml. The solution was mixed the alcohols was estimated by using the partition coefficient for an hour by stirring. Samples were diluted by a calculated by the Atom/Fragment Contribution method phosphate buffered saline and then plated on plate-count (Meylan and Howard, 1995).The partition coefficient of agar (Difco) (Collins et al. 1995). After 24 hrs incubation at trimethylsilanol calculated was 1.14, whereas that of t- 37ºC the colonies that grew on the medium were counted in butanol was 0.73.Hexamethyldisiloxane and order to estimate the number of viable bacterial. Error bars hexaethyldisiloxane were tested because they can be in the figures were determined by taking the mean of 3-5 formed by the condensation of the silanols in water and tests. were identified as an impurity of trimethylsilanol and triethylsilanol respectively. The siloxanes showed a very low antimicrobial