Gated Mesoporous SiO2 Nanoparticles Using K+‐Stabilized G‐Quadruplexes

The K⁺‐induced formation of G‐quadruplexes provides a versatile motif to lock or unlock substrates trapped in the pores of mesoporous SiO₂ nanoparticles, MP‐SiO₂ NPs. In one system, the substrate is locked in the MP‐SiO₂ NPs by K⁺‐ion‐stabilized G‐quadruplex units, and the pores are unlocked by the elimination of K⁺ ions using Kryptofix [2.2.2] (KP) or 18‐crown‐6‐ether (CE) from the G‐quadruplexes. In the second system, the substrate is locked in the pores by means of K⁺‐stabilized aptameric G‐quadruplex/thrombin units. Unlocking of the pores is triggered by the dissociation of the aptamer/thrombin complexes through the KP‐ or CE‐mediated elimination of the stabilizing K⁺ ions. In the third system, duplex DNA units lock the pores of MP‐SiO₂ NPs, and the release of the entrapped substrate is stimulated by the K⁺‐ion‐induced dissociation of the duplex caps through the formation of the K⁺‐stabilized G‐quadruplexes. The latter system is further implemented to release the anti‐cancer drug, doxorubicin, in the presence of K⁺ ions, from the MP‐SiO₂ NPs. Preliminary intracellular experiments reveal that doxorubicin‐loaded MP‐SiO₂ NPs lead to effective death of breast cancer cells.     

A dual Lagrange method for contact problems with regularized contact conditions

This paper presents an algorithm for solving quasi‐static, non‐linear elasticity contact problems without friction in the context of rough surfaces. Here, we want to model the transition from soft to hard contact in case of rough surfaces on the micro‐scale. The popular dual mortar method is used to enforce the contact constraints in a variationally consistent way without increasing the algebraic system size. The algorithm is deduced from a perturbed Lagrange formulation and combined with mass‐lumping techniques to exploit the full advantages of the duality pairing. This leads to a regularized saddle point problem, for which a non‐linear complementary function and thus a semi‐smooth Newton method can be derived. Numerical examples demonstrate the applicability to industrial problems and show a good agreement to experimentally obtained results. Copyright © 2014 John Wiley & Sons, Ltd.     

DNA Sensors and Aptasensors Based on the Hemin/G‐quadruplex‐Controlled Aggregation of Au NPs in the Presence of L‐Cysteine

L‐cysteine induces the aggregation of Au nanoparticles (NPs), resulting in a color transition from red to blue due to interparticle plasmonic coupling in the aggregated structure. The hemin/G‐quadruplex horseradish peroxidase‐mimicking DNAzyme catalyzes the aerobic oxidation of L‐cysteine to cystine, a process that inhibits the aggregation of the NPs. The degree of inhibition of the aggregation process is controlled by the concentration of the DNAzyme in the system. These functions are implemented to develop sensing platforms for the detection of a target DNA, for the analysis of aptamer‐substrate complexes, and for the analysis of L‐cysteine in human urine samples. A hairpin DNA structure that includes a recognition site for the DNA analyte and a caged G‐quadruplex sequence, is opened in the presence of the target DNA. The resulting self‐assembled hemin/G‐quadruplex acts as catalyst that controls the aggregation of the Au NPs. Also, the thrombin‐binding aptamer folds into a G‐quadruplex nanostructure upon binding to thrombin. The association of hemin to the resulting G‐quadruplex aptamer‐thrombin complex leads to a catalytic label that controls the L‐cysteine‐mediated aggregation of the Au NPs. The hemin/G‐qaudruplex‐controlled aggregation of Au NPs process is further implemented for visual and spectroscopic detection of L‐cysteine concentration in urine samples.     

Bis-Aniline-Crosslinked Enzyme–Metal Nanoparticle Composites on Electrodes for Bioelectronic Applications

The electrical contacting of redox enzymes with electrodes is the most fundamental requirement for the development of amperometric biosensors and biofuel cell elements. We describe a novel method to prepare electrically contacted metallic nanoparticles (NPs) or carbon nanotubes (CNTs)/enzyme hybrid composites on electrodes that act as amperometric biosensors or as the constituents of biofuel cells. Au NPs or Pt NPs were modified with thioaniline electropolymerizable groups, and so were the enzymes glucose oxidase (GOx) or bilirubin oxidase (BOD). Electrochemical polymerization of the thioaniline-functionalized Pt NPs and GOx on a thioaniline monolayer-modified Au surface led to the formation of a bis-aniline-bridged Pt NPs/GOx composite electrode that enabled the analysis of glucose through the electrocatalyzed reduction of H₂O₂. Similarly, a Pt NPs/BOD composite-functionalized electrode showed electrocatalytic activity toward the reduction of O₂ to H₂O. Also, a Au NPs/GOx composite-functionalized electrode revealed direct electrical contacting between the enzyme and the electrode through the electrocatalytic reduction of the bis-aniline bridges, and this enabled the bioelectrocatalytic oxidation and the amperometric sensing of glucose. Finally, a biofuel cell consisting of an anode modified with Nile blue/NAD⁺/alcohol dehydrogenase on carbon nanotubes, and a cathode composed of the bis-aniline-crosslinked Pt NPs/BOD composite was constructed. The biofuel cell operates with a power output corresponding to 200 μW cm^-2.     

Free volume in PEP-silica nanocomposites with varying molecular weight

The influence of confinement in polymer-nanocomposites on free volume and glass transition of the polymer chains was studied. The molecular weight (Mw) of poly(ethylene-alt-propylene) (PEP) was varied from 3k to 200k and so the end-to end distance of the chains at fixed diameter (∼15 nm) and concentration (15%) of the silica nanoparticles increased. Thus the topological confinement increases with increasing Mw. Using hydrophobic PEP and particles functionalized with short organic molecules, we can rule out contributions of permanent adsorption of the chains. DSC showed no change in glass transition temperature. The decrease in the specific heat capacity could be explained by a simple mixing rule. By positron annihilation lifetime spectroscopy, taking properly into account contributions of the silica particles, we rule out an influence of the geometrical confinement on the free volume in the PEP nanocomposites studied here.     

Zeitverhalten der isothermen Reaktivdestillation beim thermischen Cracken und Desoxygenieren von Rapsöl

Thermal cracking of rapeseed oil under isothermal reactive distillation conditions allows the production of alternative liquid fuels. Temporal changes of the sump phase and the oil condensate show an increased higher heating value due to deoxygenation. The sump phase also shows an increasing thermal stability, accompanied by polymerization and aromatization. This is derived from a changing iodine value, H/C ratio as well as viscosity. The deoxygenation of the oil condensate is confirmed by a decreasing acid value and the reduction of detected carboxylic acids.     

Photostimulated Interactions of Bipyridinium-Azobenzene with a β-Aminocyclodextrin Monolayer-Functionalized Electrode: An Optoelectronic Assembly for the Amperometric Transduction of Recorded Optical Signals

An amino-functionalized β-cyclodextrin is covalently linked to a thiopropionic acid-active ester monolayer associated with a Au electrode to yield a cyclodextrin monolayer electrode. The photoisomerizable electron acceptor trans or cis N-methylpyridinium-4-(4′-N′-methylenepyridinium)-azobenzene, 1t or 1c , respectively, exhibit different binding affinities for the β-cyclodextrin-receptor-monolayer. The photoisomer 1t has a high affinity for the cyclodextrin monolayer while 1c exhibits low binding interactions to the monolayer interface. The photostimulated binding and dissociation of 1t or 1c to and from the monolayer are transduced electrochemically. The association and dissociation of the photoisomerizable substrate to and from the monolayer are confirmed by microgravimetric, quartz-crystal-microbalance experiments.