The Toxicity of Silver Nanoparticles Depends on Their Uptake by Cells and Thus on Their Surface Chemistry

A set of three types of silver nanoparticles (Ag NPs) are prepared, which have the same Ag cores, but different surface chemistry. Ag cores are stabilized with mercaptoundecanoic acid (MUA) or with a polymer shell [poly(isobutylene‐alt‐maleic anhydride) (PMA)]. In order to reduce cellular uptake, the polymer‐coated Ag NPs are additionally modified with polyethylene glycol (PEG). Corrosion (oxidation) of the NPs is quantified and their colloidal stability is investigated. MUA‐coated NPs have a much lower colloidal stability than PMA‐coated NPs and are largely agglomerated. All Ag NPs corrode faster in an acidic environment and thus more Ag(I) ions are released inside endosomal/lysosomal compartments. PMA coating does not reduce leaching of Ag(I) ions compared with MUA coating. PEGylation reduces NP cellular uptake and also the toxicity. PMA‐coated NPs have reduced toxicity compared with MUA‐coated NPs. All studied Ag NPs were less toxic than free Ag(I) ions. All in all, the cytotoxicity of Ag NPs is correlated on their uptake by cells and agglomeration behavior.     

An unexpected methyl group migration during on-column Stille derivatization of RNA

Postsynthetic Stille cross-coupling for functionalization of oligonucleotides on solid support was applied on iodo modified RNA utilizing different protecting group strategies. As result, the otherwise very successful ACE [bis(acetoxyethyloxy)-methyl orthoester] chemistry was found to be limited since methylated side-products formed as was investigated via enzymatic degradation of RNA and various monomer model reactions. Enzymatic digestion of poly uridine sequences revealed presence of considerable amounts of N³-methylated uridine derivatives due to migration of methyl as phosphate protecting group used in ACE strategy. Monomer test reactions mimicking conditions on RNA clearly indicated an enhanced methylation effect correlated to the Stille coupling procedure.     

A versatile synthetic strategy for nanoporous gold–organic hybrid materials for electrochemistry and photocatalysis

Nanoporous gold (npAu) was employed as high surface area substrate for immobilization of redox- and photooxidative-active organic molecules. A two-step synthetic routine is demonstrated as a versatile and robust method for immobilization of various molecules. First, self-assembled monolayers (SAMs) of thiols containing an azide moiety were prepared on npAu substrates. Then, alkyne-modified ferrocene, tetrathiafulvalene, and zinc(II)phthalocyanine derivatives were covalently bound via the click reaction to this linker. Following the provided synthetic procedures high performance composite materials are generated for electrochemistry and photochemistry. The robust bonding between the organic functional group and the gold support provides stability even under strongly oxidizing conditions (applied potential or singlet oxygen).     

Structure control in PMMA/silica hybrid nanoparticles by surface functionalization

Hydrophilic silica particles need to be hydrophobized to be encapsulated in a polymeric environment, which can be achieved by different methods. We report on the relationship between different hydrophobization techniques of silica and the final structure of poly(methyl methacrylate)/silica hybrid nanoparticles obtained by miniemulsion polymerization. Hydrophobization by cetyltrimethylammonium chloride (CTMA-Cl) uses the ionic interaction between the positively charged ammonium salt and the negatively charged silica surface, as shown by isothermal titration calorimetry. In this case, the interaction between polymer and silica surface needs to be enhanced, so 4-vinylpyridine (4-VP) was used as a co-monomer. Alternatively, the condensation reactions of 3-methacryloxypropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODTMS) were used to provide a covalent bond to the silica surface. The condensation reaction of the trimethoxysilane groups onto the silica surface was proven by Fourier transform infrared spectroscopy and thermogravimetric analysis. Hybrid nanoparticles were successfully formed with silica particles functionalized with the different functionalization agents. However, the structure of the resulting hybrid particles (i.e., the distribution of the silica particles within the polymer matrix) depends on the agent. The MPS-functionalized silica particles copolymerize with poly(methyl methacrylate), leading to a fixation of the silica particles inside the polymer and to a homogeneous distribution. The CTMA-Cl- and ODTMS-functionalized silica particles cannot copolymerize, but aggregate at the interface, leading to a Janus-like structure.     

From Chaos to Global Convergence

The main purpose of this paper is to investigate dynamical systems F : \mathbbR² ? \mathbbR²{F : \mathbb{R}^2 \rightarrow \mathbb{R}^2} of the form F(x, y) = (f(x, y), x). We assume that f : \mathbbR² ? \mathbbR{f : \mathbb{R}^2 \rightarrow \mathbb{R}} is continuous and satisfies a condition that holds when f is non decreasing with respect to the second variable. We show that for every initial condition x₀ = (x ₀, y ₀), such that the orbit

Automated determination of cadmium and lead in whole blood by computerized flow potentiometric stripping with carbon fibre electrodes

A sample pretreatment involving only the dilution (1 + 19) of two 0.2–0.4 ml sample aliquots with 0.5 M hydrochloric acid, with a standard addition to one of the aliquots, precedes the injection of each sample. The computer-controlled flow system used automatically executes a pre-programmed number of cycles on each sample pair before presenting the final result. Each cycle, which has a duration of 80 or 135 s for lead(II) and cadmium(II), respectively, involves the display of the derivative stripping signal on a printer/plotter and integration of the stripping peaks generated. For lead(II), striping is done in 0.5 M hydrochloric acid, which eliminates interferences from copper, though at the cost of a relatively high stripping rate, compared to the 5 M calcium chloride used for cadmium(II). The flow cell consists of a silver chloride-lined silver tube which acts as both reference and counter electrode, and a disposable carbon-fibre working electrode mounted in a PVC tube, which normally will operate for 50–200 cycles. The method was verified for whole blood reference standards and by comparison with results obtained by atomic absorption spectrometry.