Silver has been known to exhibit strong cytotoxicity towards a broad range of micro-organisms. Silver composites with a tailored slow silver-release rate are currently being investigated for various applications. [1] Silver has an oligodynamic effect, that is, silver ions are capable of causing a bacteriostatic (growth inhibition) or even a bactericidal (antibacterial) impact. Nanometer-sized inorganic particles and composites display unique physical and chemical properties and represent a unique class of materials in the development of novel devices, which can be used in numerous physical, biological, biomedical, and pharmaceutical applications. [2] Silver composites have applications in many industries, such as aerospace, surface coatings (e.g., in refrigerators, food processing, kitchen furniture), and for use in hospitals. Research indicates that silver is also effective in purification systems for disinfecting water or air. [3][4][5][6] However, in order to make the use of silver economical, there is a need to find cheaper ways of using silver in potential applications without jeopardizing its functionalities.The bactericidal behavior of silver nanoparticles is attributed to the presence of electronic effects, which are a result of the changes in the local electronic structure of the surfaces of the smaller-sized particles. These effects are considered to be contributing towards an enhancement of the reactivity of silver-nanoparticle surfaces. It has been reported that ionic silver strongly interacts with thiol groups of vital enzymes and inactivates them. It has been suggested

Grafting of C-6, C-16 and C-18 alkyl chains onto the hydrophilic Mn-Anderson clusters (compounds 2-4) has been achieved. Exchange of the tetrabutyl ammonium (TBA) with dimethyldioctadecyl ammonium (DMDOA) results in the formation of new polyoxometalate (POM) assemblies (compounds 5-6), in which the POM cores are covalently functionalized by hydrophilic alkyl-chains and enclosed by surfactant of DMDOABr. As a result, we have been able to design and synthesize POM-containing hydrophobic materials beyond surfactant encapsulation. In solid state, scanning electron and transmission electron microscopy (SEM and TEM) studies of the TBA salts of compounds 3 and 4 show highly ordered, uniform, reproducible assemblies with unique segmented rodlike morphology. SEM and TEM studies of the DMDOA salts of compounds 5 and 6 show that they form spherical and sea urchin 3D objects in different solvent systems. In solution, the physical properties of compound 5 and 6 (combination of surfactant-encapsulated cluster (SEC) and surface-grafted cluster (SGC)) show a liquid-to-gel phase transition in pure chloroform below 0 degrees C, which are much lower than other reported SECs. By utilizing light scattering measurements, the nanoparticle size for compounds 5 and 6 were measured at 5 degrees C and 30 degrees C, respectively. Other physical properties including differential scanning calorimetry have been reported.

Two series of oligorotaxanes R and R' that contain -CH(2)NH(2)(+)CH(2)- recognition sites in their dumbbell components have been synthesized employing template-directed protocols. [24]Crown-8 rings self-assemble by a clipping strategy around each and every recognition site using equimolar amounts of 2,6-pyridinedicarboxaldehyde and tetraethyleneglycol bis(2-aminophenyl) ether to efficiently provide up to a [20]rotaxane. In the R series, the -NH(2)(+)- recognition sites are separated by trismethylene bridges, whereas in the R' series the spacers are p-phenylene linkers. The underpinning idea here is that in the former series, the recognition sites are strategically positioned 3.5 Å apart from one another so as to facilitate efficient [π···π] stacking between the aromatic residues in contiguous rings in the rotaxanes and consequently, a discrete rigid and rod-like conformation is realized; these noncovalent interactions are absent in the latter series rendering them conformationally flexible/nondiscrete. Although in the R' series, the [3]-, [4]-, [8]-, and [12]rotaxanes were isolated after reaction times of <5-30 min in yields of 72-85%, in the R series, the [3]-, [4]-, [5]-, [8]-, [12]-, [16]-, and [20]rotaxanes were isolated in <5 min to 14 h in 88-98% yields. It follows that while in the R' series the higher order oligorotaxanes are formed in lower yields more rapidly, in the R series, the higher order oligorotaxanes are formed in higher yields more slowly. In the R series, the high percentage yields are sustained throughout, despite the fact that up to 39 components are participating in the template-directed self-assembly process. Simple arithmetic reveals that the conversion efficiency for each imine bond formation peaks at 99.9% in the R series and 99.3% in the R' series. This maintenance of reaction efficiency in the R series can be ascribed to positive cooperativity, that is, when one ring is formed it aids and abets the formation of subsequent rings presumably because of stabilizing extended [π···π] stacking interactions between the arene units. Experiments have been performed wherein the dumbbell is starved of the macrocyclic components, and up to five times more of the fully saturated rotaxane is formed than is predicted based on a purely statistical outcome, providing a clear indication that positive cooperativity is operative. Moreover, it would appear that as the R series is traversed from the [3]- to the [4]- to the [5]rotaxane, the cooperativity becomes increasingly positive. This kind of cooperative behavior is not observed for the analogous oligorotaxanes in the R' series. The conventional bevy of analytical techniques (e.g., HR-MS (ESI) and both (1)H and (13)C NMR spectroscopy) help establish the fact that all the oligorotaxanes are pure and monodisperse. Evidence of efficient [π···π] stacking between contiguous arene units in the rings in the R series is revealed by (1)H NMR spectroscopy. Ion-mobility mass spectrometry performed on the R and R' series yielded the collisional cross sections (CCSs...

Extended modular frameworks that incorporate inorganic building blocks represent a new field of research where "active sites" can be engineered to respond to guest inclusion. [1][2] This process can initiate highly specific chemical reactions [3] that switch the overall nature of the framework, and it may even be developed to facilitate directed chemical reactions similar to those found in enzymatic systems. Achievement of this degree of sophistication requires the ability to control the framework assembly as precisely as in metal-organic frameworks, [1,[4][5][6] combined with the stability and functionality of inorganic zeolites and related systems. [7] Although progress has been made in fine-tuning the reactivity of framework materials, [8] reversible redox single-crystal to single-crystal (SC-SC) transformations that retain long-range order have not yet been observed.[9] Thus, it can be suggested that the best way to engineer redox-and electronically active frameworks would be to incorporate building blocks based on polyoxometalate (POM) clusters, [10][11][12] constructed from {MO x } units where M = Mo, W, V, Nb and x = 4-7. These clusters are attractive units for the construction of such frameworks since they are highly redox active and can incorporate a range of main-group-templating {XO n } units, as exemplified by the Keggin ion [M 12 nÀ . This ion can incorporate anions such as phosphate and silicate, and can bind transition metals within structural vacancies.[13]Herein we show that the directed assembly of a pure metal oxide framework, [(C 4 H 10 NO) 40 [14] based upon substituted Keggin-type POM building blocks, yields a material that can undergo a reversible redox process that involves the simultaneous inclusion of the redox reagent with a concerted and spatially ordered redox change of the framework. Compound 1 ox can also be repeatedly disassembled into its building blocks by dissolution in hot water; subsequent recrystallization results in the reassembly of unmodified 1 ox . These unique properties mean that this compound defines a new class of materials that bridges the gap between coordination compounds, metalorganic frameworks, and solid-state oxides. Furthermore, it has been shown that all the manganese(III) centers in 1 ox can be "switched" to manganese(II) using a suitable reducing agent to give the fully reduced framework 1 red . The redox process occurs with retention of long-range order by cooperative structural changes within the W-O-Mn linkages that connect the Keggin units. The nature of the redox process can be precisely deduced because of the SC-SC transformation between the oxidized and reduced states of the framework. This is important as, until now, covalently connected 3D polyoxometalate-based frameworks with large pockets (greater than 10 ) could be assembled only by the addition of "bridging" electrophiles. However, these solids typically have low stabilities and are not amenable to systematic design strategies, for instance the introduction of redox switchability.The approac...

The process of osmotically driven crystal morphogenesis of polyoxometalate (POM)-based crystals is investigated, whereby the transformation results in the growth of micrometer-scale tubes 10-100 μm in diameter and many thousands of micrometers long. This process initiates when the crystals are immersed in aqueous solutions containing large cations and is governed by the solubility of the parent POM crystal. Evidence is presented that indicates the process is general to all types of POMs, with solubility of the parent crystal being the deciding parameter. A modular approach is adopted since different POM precursor crystals can form tubular architectures with a range of large cationic species, producing an ion-exchanged material that combines the large added cations and the large POM-based anions. It is also shown that the process of morphogenesis is electrostatically driven by the aggregation of anionic metal oxides with the dissolved cations. This leads to the formation of a semi-permeable membrane around the crystal. The osmotically driven ingress of water leads to an increase in pressure, and ultimately rupture of the membrane occurs, allowing a saturated solution of the POM to escape and leading to the formation of a "self-growing" microtube in the presence of the cation. It is demonstrated that the growth process is sustained by the osmotic pressure within the membrane surrounding the parent crystal, as tube growth ceases whenever this pressure is relieved. Not only is the potential of the modular approach revealed by the fact that the microtubes retain the properties of their component parts, but it is also possible to control the direction of growth and tube diameter. In addition, the solubility limits of tube growth are explored and translated into a predictive methodology for the fabrication of tubular architectures with predefined physical properties, opening the way for real applications.