Silver covalently bound to cyanographene overcomes bacterial resistance to silver nanoparticles and antibiotics

The ability of bacteria to develop resistance to antibiotics is threatening one of the pillars of modern medicine. It was recently understood that bacteria can develop resistance even to silver nanoparticles by starting to produce flagellin, a protein which induces their aggregation and deactivation. This study shows that silver covalently bound to cyanographene (GCN/Ag) kills silver-nanoparticle-resistant bacteria at concentrations 30 times lower than silver nanoparticles, a challenge which has been so far unmet. Tested also against multidrug resistant strains, the antibacterial activity of GCN/Ag is systematically found as potent as that of free ionic silver or 10 nm colloidal silver nanoparticles. Owing to the strong and multiple dative bonds between the nitrile groups of cyanographene and silver, as theory and experiments confirm, there is marginal silver ion leaching, even after six months of storage, and thus very high cytocompatibility to human cells. Molecular dynamics simulations suggest strong interaction of GCN/Ag with the bacterial membrane, and as corroborated by experiments, the antibacterial activity does not rely on the release of silver nanoparticles or ions. Endowed with these properties, GCN/Ag shows that rigid supports selectively and densely functionalized with potent silver-binding ligands, such as cyanographene, may open new avenues against microbial resistance.Web of Scienceart. no. 200309

Electrorheological properties of suspensions of silica nanoparticles modified by urea and N,N-dimethylformamide

V této práci bylo studováno elektroreologické (ER) chování nanočástic siliky upravené močovinou a N,N-dimethylformamidem. Zatímco ER efekt původní siliky byl velmi slabý, modifikace zlepšila kompatibilitu tuhé a kapalné fáze suspenze a významně zvýšila ER aktivitu systému. Závislost dynamického prahového napětí na intenzitě elektrického pole se řídí mocninným zákonem, kde exponent závisí na intenzitě ztuhnutí suspenze v elektrickém poli. 25% suspenze vykazuje vysokou absolutní hodnotu prahového napětí, ale jeho relativní vzrůst byl v důsledku vysoké hodnoty při vypnutém elektrickém poli mnohem nižší než u suspenze 20%, která je tak mnohem vhodnější pro praktické aplikace.In this study, electrorheological (ER) behaviour of suspensions of silica nanoparticles treated with urea and N,N-dimethylformamide in DC electric field has been investigated. While the ER effect of the neat silica was very low, its modification improved compatibility of the solid and liquid phase and considerably increased ER activity of the system. The dependence of the dynamic yield stress ?0 on the electric field strength E obeyed the power law ?0 = qE?, where the exponent ? depended on the intensity of solidification of the suspension in the electric field. The 25 wt.% fluid showed a high absolute value of dynamic yield stress, but its relative increase due to high field-off value was much lower than for 20 wt.% suspension, so the latter is more suitable for practical applications

Effect of field strength and temperature on viscoelastic properties of electrorheological suspensions of urea modified silica particles

V publikaci byla studována závislost dynamických vlastností suspenzí nanočástic siliky modifikované močovinou během přechodu z kapalného do kvazi-tuhého stavu vlivem elektrického pole.Temperature dependence of dynamic properties of suspensions of silica nanoparticles modified with urea during transition from liquid to quasi-solid state in the absence or presence of electric field has been investigated. In the absence of electric field the loss modulus continuously decreased, whereas the complex viscosity and storage modulus decreased steeply as a result of increasing thermal motion of suspension particles and higher fluidity of the medium. To eliminate the temperature dependence of the field-off properties in the elastic structure of the particles polarized in the electric field, the relative moduli G /G 0 and G /G 0 have been proposed. Thus, while the relative loss modulus at a single low frequency (1.03 rad s?1) was virtually independent of temperature, the growth of relative storage modulus with temperature reflects higher rigidity of the suspension structure due to increasing particle polarization, in accordance with higher permittivity and lower relaxation time obtained from dielectric measurements

Electrorheological and dielectric properties of urea/SiO2 nanocomposite suspensions modified by N,N-dimethylformamide

In this study, electrorheological (ER) behaviour of silica nanocomposite suspensions treated with urea and N, N - dimethylformamide (DMF) in DC electric field has been investigated. While the ER effect of the neat silica itself was very low, the modification of silica nanoparticles improved compatibility of the solid and liquid phase and increased considerably ER activity of the system. In contrast to maximum possible concentration about 5 wt.% of neat silica due to particle aggregation 20 wt.% suspension of treated particles with low field-off viscosity could be prepared. The dielectric measurements showed that with increasing amount of urea deposited on the silica particles both the difference between the limit values of the relative permittivities and the relaxation frequency increased. This indicates a great influence of both particle polarizability and the rate of rearrangement of the ER structure in the electric field on the ER intensity. After DMF addition the changes in dielectric properties reflected the higher ER activity. At higher particle loading (25 wt.%) mutual particle interaction increased and field-off viscosity steeply rose. The comparison of the behaviour of 20 and 25 wt.% suspensions of modified particles showed that even if high yield stress at higher particle content under electric field application sets in, its relative increase indicating the ER efficiency due to high field-off value may be much lower than at lower suspension loading

Electrorheological and dielectric properties of urea/SiO2 nanocomposite suspensions modified by N,N-dimethylformamide

V této studii se hodnotí elektroreologické (ER) chování suspenzí nanočástic siliky upravené močovinou a N,N-dimethylformamidem (DMF) ve stejnosměrném elektrickém poli. Zatímco je ER efekt původní siliky velmi slabý, modifikace nanočástic siliky zvyšuje kompatibilitu tuhé a kapalné fáze a významně zvyšuje ER aktivitu systému.In this study, electrorheological (ER) behaviour of silica nanocomposite suspensions treated with urea and N, N - dimethylformamide (DMF) in DC electric field has been investigated. While the ER effect of the neat silica itself was very low, the modification of silica nanoparticles improved compatibility of the solid and liquid phase and increased considerably ER activity of the system. In contrast to maximum possible concentration about 5 wt.% of neat silica due to particle aggregation 20 wt.% suspension of treated particles with low field-off viscosity could be prepared. The dielectric measurements showed that with increasing amount of urea deposited on the silica particles both the difference between the limit values of the relative permittivities and the relaxation frequency increased. This indicates a great influence of both particle polarizability and the rate of rearrangement of the ER structure in the electric field on the ER intensity. After DMF addition the changes in dielectric properties reflected the higher ER activity. At higher particle loading (25 wt.%) mutual particle interaction increased and field-off viscosity steeply rose. The comparison of the behavior of 20 and 25 wt.% suspensions of modified particles showed that even if high yield stress at higher particle content under electric field application sets in, its relative increase indicating the ER efficiency due to high field-off value may be much lower than at lower suspension loading

Electrorheological properties of PANI/BaTiO3 nanocomposites

Electrorheological (ER) effect and dielectric properties of PANI/BaTiO3 nanocomposite suspensions with various amount of PANI have been investigated. Polymerization of aniline was performed under ultrasonic irradiation in the presence of BaTiO3 nanoparticlcs. In spite of the large dielectric constant, BaTiO3 only shows weak ER effect in DC electric field. The treatment of BaTiO3 significantly increases the intensity of the observed ER response, which continuously rises with PANI content in the system. Attention has also been paid to the analysis of dielectric spectra, where an interfacial polarization seems to be dominant. The maximum of dielectric loss shifts to higher frequencies with increasing PANI concentration, which corresponds to shorter relaxation times

Electrorheology of silicone oil suspensions of urea-modified poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)] particles

V této studii byly srovnávány dvě metody modifikace mikrokuliček poly[(glycidyl methacrylát)-co-(ethylene dimethacrylátu)] močovinou. Nejprve byly funkční skupiny močoviny chemicky navázány na výchozí kopolymer. U suspenzí v silikonovém oleji byl pozorován v elektrickém poli výrazný vzrůst soufázového modulu v porovnání se ztrátovým modulem. Na druhou stranu byl elektroreologický efekt u suspenzí částic pokrytých fyzikálně vázanou močovinou pouze mírně silnější než u nemodifikovaného materiálu. Tento rozdíl se může vysvětlovat slabým pokrytím hydrofobního povrchu mikročástic hydrofilní močovinou. Na základě dielektrických měření je mezifázová polarizace odpovědná za formování řetízkové struktury modifikovaných mikrokuliček v elektrickém poli způsobující elektroreologický efekt.Two methods of modi?cation of poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)] microspheres with urea were examined in this electrorheological (ER) study. First, the urea functional groups were introduced by chemical modi?cation of the starting copolymer. A signi?cant increase in storage modulus of the silicone oil suspension was observed compared with the loss modulus when an electric ?eld is applied. On the other hand, the ER effect in suspension of particles coated with physically bonded urea was only slightly higher than that of untreated material. This is explained by poor coating of the hydrophobic microparticle surface with hydrophilic urea. According to dielectric measurements, the interfacial polarization was found to be responsible for the formation of chain structure of modi?ed microspheres in the electric ?eld resulting in the ER effect

Electrorheological properties of new mesoporous material with conducting polypyrrole in mesoporous silica

V této práci byl syntetizován nový mezoporézní material obsahující polovodivý polypyrol (PPy) v pórech mezoporézní siliky (MCM-41), který se používal jako dispergovaná fáze elektroreologických (ER) kapalin. Byly studovány reologické a dielektrické vlastnosti suspenzí na bázi PPy-MCM-41 se závěrem, že vykazují lepší ER chování než bez PPy. Navíc dielektrická spectra ukazují, že zabudovaný PPy zvyšuje mezifázovou polarizovatelnost mezoporézního materiálu a indukuje vyšší ER efekt.In this study, a new mesoporous material with semiconducting polypyrrole (PPy) encapsulated in the channels of mesoporous silica (MCM-41) was synthesized and used as dispersed phase for electrorheological (ER) fluids. Rheological and dielectric properties of PPy-MCM-41 based suspensions were investigated with the conclusion that PPy-MCM-41 fluid exhibits better ER behavior than that without PPy. Furthermore, the dielectric spectra indicate that encapsulated PPy increases the interfacial polarizability of mesoporous material and induces a higher ER effect

The effect of polypyrrole loading on the suspensions electrorheological properties of polypyrrole/sba-15 suspensions

Encapsulated polypyrrole (PPy) with different amount in the channels of mesoporous silica (SBA-I 5) was synthesized. The XRD and N 2 adsorptiorddesorption isotherms analysis show that PPy with different loadings in the channels does not affect the ordered hexagonal structure of resultant PPy/SBA-I 5 nanocomposites. Further, the electrorheological (ER) properties of the nanocomposites with different PPy loadings were investigated by steady and oscillatory shear experiments. The results reveal that PPy/SBA-15 fluids exhibit typical ER and viscoelastic behavior under the applied electric field and ER response depends mainly on PPy loadings and there is an optimum PPy loading for strong ER effect

The effect of polypyrrole loading on the electrorheological properties of polypyrrole/SBA-15 suspensions

Byla připravena mezoporézní silika (SBA-15) s různým obsahem zapouzdřeného polypyrolu (PPy) v kanálcích. Analýza pomocí XRD a absorpčních/desorpčních izoterem N2 ukazuje, že různý obsah PPy v kanálcích neovlivňuje uspořádanou hexagonální strukturu výsledného nanokompozitu PPy/SBA-15. Dále byly zkoumány elektroreologické (ER) vlastnosti nanokompozitů s různým obsahem PPy v ustáleném a oscilačním smykovém poli. Výsledky ukazují, že kapaliny s dispergovaným PPy/SBA-15 vykazují v elektrickém poli typické ER a viskoelastické chování. ER efekt závisí především na obsahu PPy, přičemž existuje optimální obsah PPy, při němž je ER efekt nejvyšší.Encapsulated polypyrrole (PPy) with different amount in the channels of mesoporous silica (SBA-15) was synthesized. The XRD and N-2 adsorption/desorption isotherms analysis show that PPy with different loadings in the channels does not affect the ordered hexagonal structure of resultant PPy/SBA-15 nanocomposites. Further, the electrorheological (ER) properties of the nanocomposites with different PPy loadings were investigated by steady and oscillatory shear experiments. The results reveal that PPy/SBA-15 fluids exhibit typical ER and viscoelastic behavior under the applied electric field and ER response depends mainly on PPy loadings and there is an optimum PPy loading for strong ER effect