Silver nanoparticles embedded in zeolite membranes: release of silver ions and mechanism of antibacterial action

Amber Nagy1, Alistair Harrison2, Supriya Sabbani3, Robert S Munson, Jr2, Prabir K Dutta3, W James Waldman11Department of Pathology, The Ohio State University; 2Center for Microbial Pathogenesis, Research Institute at Nationwide Children's Hospital, 3Department of Chemistry, The Ohio State University, Columbus, OH, USABackground: The focus of this study is on the antibacterial properties of silver nanoparticles embedded within a zeolite membrane (AgNP-ZM).Methods and Results: These membranes were effective in killing Escherichia coli and were bacteriostatic against methicillin-resistant Staphylococcus aureus. E. coli suspended in Luria Bertani (LB) broth and isolated from physical contact with the membrane were also killed. Elemental analysis indicated slow release of Ag+ from the AgNP-ZM into the LB broth. The E. coli killing efficiency of AgNP-ZM was found to decrease with repeated use, and this was correlated with decreased release of silver ions with each use of the support. Gene expression microarrays revealed upregulation of several antioxidant genes as well as genes coding for metal transport, metal reduction, and ATPase pumps in response to silver ions released from AgNP-ZM. Gene expression of iron transporters was reduced, and increased expression of ferrochelatase was observed. In addition, upregulation of multiple antibiotic resistance genes was demonstrated. The expression levels of multicopper oxidase, glutaredoxin, and thioredoxin decreased with each support use, reflecting the lower amounts of Ag+ released from the membrane. The antibacterial mechanism of AgNP-ZM is proposed to be related to the exhaustion of antioxidant capacity.Conclusion: These results indicate that AgNP-ZM provide a novel matrix for gradual release of Ag+.Keywords: silver nanoparticles, zeolite, antibacterial agent, oxidative stres

Silver confined within zeolite EMT nanoparticles: preparation and antibacterial properties

The preparation of pure zeolite nanocrystals (EMT-type framework) and their silver ion-exchanged (Ag+-EMT) and reduced silver (Ag0-EMT) forms is reported. The template-free zeolite nanocrystals are stabilized in water suspensions and used directly for silver ion-exchange and subsequent chemical reduction under microwave irradiation. The high porosity, low Si/Al ratio, high concentration of sodium and ultrasmall crystal size of the EMT-type zeolite permitted the introduction of a high amount of silver using short ion-exchange times in the range of 2–6 h. The killing efficacy of pure EMT, Ag+-EMT and Ag0-EMT against Escherichia coli was studied semi-quantitatively. The antibacterial activity increased with increasing Ag content for both types of samples (Ag+-EMT and Ag0-EMT). The Ag0-EMT samples show slightly enhanced antimicrobial efficacy compared to that of Ag+-EMT, however, the differences are not substantial and the preparation of Ag nanoparticles is not viable considering the complexity of preparation steps

A tetra-nuclear copper(II) complex stabilizes an extended structure of a water nonamer: synthesis and characterization of [Cu<SUB>4</SUB>(C<SUB>54</SUB>H<SUB>46</SUB>N<SUB>4</SUB>O<SUB>14</SUB>)(OH)<SUB>2</SUB>] &#183; 10H<SUB>2</SUB>O

A tetra-nuclear copper(II) complex [Cu4(C54H46N4O14)(OH)2] &#183; 10H2O (1) has been synthesized starting from l-tyrosine, NaOH, 2,6-diformyl-4-methylphenol (dfp) and CuSO4 &#183; 5H2O. Compound 1 crystallizes from an ethanol-water mixture in triclinic P1&#x0305; space group. In the crystal of 1, two binuclear copper units, related by a center of symmetry, are bridged by two hydroxo bridges and results in the formation of a tetra-nuclear {Cu4} structure. Five lattice water molecules, located in the asymmetric unit, interact among themselves and form an unusual form of a water nonamer. In the crystal, the water nonamer is again hydrogen bonded to the next nonamer forming a chainlike polymer. Each {Cu4} complex unit attaches four such water nonamer chains. Variable temperature magnetic data fit to the Bleaney-Bower's equation with a Curie type of impurity of S = 0.5. The best fit of the magnetic data to this equation yielded 2J = -217, g = 2.019 and a TIP value of 60 &#215; 10-6 cm3 mol-1

Piperidine dispiro-1,2,4-trioxane analogues

Dispiro N-Boc-protected 1,2,4-trioxane 2 was synthesised via Mo(acac)(2) catalysed perhydrolysis of N-Boc spirooxirane followed by condensation of the resulting beta-hydroperoxy alcohol 10 with 2-adamantanone. N-Boc 1,2,4-trioxane 2 was converted to the amine 1,2,4-trioxane hydrochloride salt 3 which was subsequently used to prepare derivatives (4-7). Several of these novel 1,2,4-trioxanes had nanomolar antimalarial activity versus the 3D7 strain of Plasmodium falciparum. Amine intermediate 3 represents a versatile derivative for the preparation of achiral arrays of trioxane analogues with antimalarial activity. (C) 2008 Elsevier Ltd. All rights reserved