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A new concept in bactericidal agents is described: the entrapment of an organic biocidal agent within a bactericidal metal, which leads to synergism between the two components. Specifically this concept is demonstrated for the entrapment of chlorhexidine digluconate (CHD) within an aggregated silver matrix, a metal known for its own biocidal qualities, forming the CHD@silver composite. The bactericidal efficacy against E. coli is evaluated and compared with the separate components. While the bactericidal efficacy of the individual ingredients (CHD and metallic silver) is very low, CHD@silver exhibits a markedly enhanced efficacy. This enhanced bactericidal effect is partially attributed to the simultaneous release and presence of the active biocidal ingredients CHD and Ag+ in the solution. Detailed composite characterization is provided.

The entrapment of chlorhexidine (CH) within metallic silver (CH@Ag) results in a composite material bearing powerful synergetic bactericidal action towards two opportunistic wound pathogenic bacteria, the Gram-negative Pseudomonas aeruginosa and the Gram-positive Staphylococcus epidermidis. TEM and STEM imaging revealed morphological abnormalities in bacteria exposed to the composite. Release profiles of the active ingredients, CH and ionic silver, from the composite were evaluated by UV spectroscopy and by ICP-MS elemental analysis, and indicated that the strong bactericidal effects were associated with their co-release and presence in the solution. The use of both powder form and pressed form of CH@Ag provides means to control the release kinetics of entrapped CH from the composite and demonstrates the potential application of such composites in wound treatments.

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Chemically reactive sol-gel matrices hold the ability of protecting entrapped enzymes from destruction by external harsh chemicals. We show this concept by exposing alkaline phosphatase (AlP) to a strong oxidizing agent-bromine. In solution, AlP is immediately destroyed by this oxidant. When AlP was entrapped in hybrid silica sol-gel materials carrying double bonds, the reactivity of AlP was preserved after exposure to bromine under conditions which totally destroy it in solution. The matrices studied were vinylated and allylated silicas, and their protectability was compared to n-alkylated silicas and to silica itself. For instance, the reactivity of AlP entrapped in allylated silica after exposure to 25.6 mM bromine solution is 40 times higher than its reactivity when entrapped in pure silica; and in solution the enzyme is totally destroyed at this concentration. Molecular level mechanisms for these observations are proposed.Keywords Sol-gel Á Sol-gel preserved enzymes Á Oxidizing agent Á Ormosil BackgroundAlkaline phosphatase (AlP), like most other enzymes, is totally destructed when exposed to a strong oxidant such as bromine. Here we show how to protect an enzyme when exposed to such conditions. We do so by using the sol-gel materials methodology for enzyme entrapment [1]. Sol-gel entrapped enzymes [2-4] have already been shown to provide significant thermal stability [5][6][7][8], stability to extreme pH values [9][10][11], and stability to non-native environments [12][13][14]. In these earlier studies the protectability was attributed to the encaging itself [15]; here we extend these observations by showing protection against an oxidant due to active chemical scavenging of the destructive chemical by the matrix. Thus when the enzyme is entrapped within sol-gel derived olefinated silicas, and then exposed to bromine solution, the double bonds react with the bromine, and protect the enzyme. By comparing this mode of protection to entrapments in non-reactive matrices-sol-gel derived silicas and sol-gel-derived alkylated silicas-we were able to evaluate the weights of the bromine scavenging and of the physical entrapment to the protection of the enzyme; we find that this relative weight depends on the alkyl and alkenyl chain. Thus, the hybrid sol-gel material we used was based on vinyl (CH 2 =CH-Si; VTS; here and below we use the name of the monomer as the name of the material), or allyl (CH 2 =CH-CH 2 -Si; ATS). In earlier studies we showed these olefinated sol-gel materials are highly reactive towards bromine, undergoing in water an hydrobromination reaction [16,17] which proceeds according to Markovnikov's rule [18], as shown in Scheme 1, resulting in a bromohydrin and HBr. The formation of an acid is an environmental change that the entrapped enzyme can withstand. We recall that we showed that sol-gel entrapped alkaline phosphataseThe online version of the original article can be found under