The punctured droplet electrode – A new three-phase electrode with well defined geometry

A new three-phase electrode allows detailed studies on well-defined three-phase junctions. It consists of a nitrobenzene drop of well controlled size. The drop is dispensed from a capillary and is punctured with a microcylinder electrode. The organic liquid contains an electroactive compound (decamethylferrocene) and, importantly, no supporting electrolyte. The aqueous phase may contain various salts. Well-defined and reproducible linear-scan and square-wave voltammograms and chronoamperograms of oxidation of decamethylferrocene were obtained. The dependence of the formal potential determined from the square-wave voltammograms of decamethylferrocene versus the standard potential of transfer of anions present in the aqueous phase was almost perfectly linear. The developed approach allows the formation of two or more three-phase boundaries within one small drop. Since the drop is well exposed, this electrode geometry also gives a potential possibility of optical/spectrophotometric inspection of the reaction products in the organic phase and of examination of the reaction-layer growth.     

Self-assembled peptide tubelets with 7 A pores

Here we report the preparation and structural characteristics of self-assembling peptide tubelets composed of 32-membered rings formed of alternating alpha-amino acids and cis-3-aminocyclohexanecarboxylic acids. The tubelets possess a partial hydrophobic core environment, provided by the projection of the cyclohexane C2 methylene moiety into the lumen, and a Van der Waals pore diameter of about 7 A.     

A highly selective bifunctional luminescence probe for potassium and fluoride ions

A novel bifunctional molecule 1 by a combination of 1,3-alternate calix[4]-crown-5 and triarylborane moieties through alkynyl linkers has been designed and synthesized. Compound 1 shows intense fluorescence with a photoluminescence quantum yield of 0.70 in CH(2)Cl(2) solution and can serve as a bifunctional luminescent probe for potassium and fluoride ions with high sensitivity and selectivity.     

A pure silica chiral polymorph with helical pores

A microporous polymorph of SiO(2), HPM-1, has a chiral structure and contains helical pores. The defect-free pure SiO(2) composition, which has been previously considered unfeasible for this structure type, bestows a high thermal and hydrothermal stability upon this material.     

Elaboration of modelized surfaces with well defined microtopochemistry–localization of adsorbed proteins

Using microphotolithographic techniques, we have been able to devise silica surfaces bearing two types of microdomains with an average width of 40μm. One of the microdomain types was silanized in order to make them hydrophobic. Fourier transform-infrared (FTIR) and Auger electron spectroscopies (AES) were used to check the presence of the expected chemical groups on the modified silica surface. Silica and silanized surface morphology was studied using Scanning Force Microscopy (SFM). Wetting properties were investigated. Protein adsorption studies were performed using diluted human decalcified plasma. Attention was focused on the topographic distribution of the adsorbed molecules in order to establish a correlation between the protein behaviour and the specific chemistry of each type of microdomain.     

Polydiacetylene liposome arrays for selective potassium detection

Potassium is an important cation in biology, and quantitative detection of the extracellular potassium level is important. However, selective detection of extracellular physiological potassium is a challenging task due to the presence of sodium in a much higher concentration. In this contribution, we describe the development of practical polydiacetylene (PDA) liposome-based microarrays to selectively detect potassium even in the presence of sodium. We utilize the fact that the G-rich ssDNA can fold into a G-quadruplex via intramolecular hydrogen bonding by wrapping around a potassium ion exclusively. We rationally design the PDA liposome in such a way that the G-rich ssDNA probes are presented densely at the liposome surface and form bulky quadruplexes upon binding with K+. The resulting bulky quadruplexes are sterically hindered and repulse each other and impose mechanical stress on the PDA backbone, resulting in the conformational change of the ene-yne backbone of the PDA. As a result, polydiacetylene liposomes turn into the emissive red phase from the nonfluorescent blue phase.     

A Covalent Organic Framework with 4 nm open pores

The synthesis and characterization of a new mesoporous Covalent Organic Framework BTP-COF is described, the latter having fully accessible pores with an open diameter of 4.0 nm.     

A ratiometric probe for the selective time-gated luminescence detection of potassium in water

A europium probe for the ratiometric detection of potassium in water is presented. This probe demonstrates high sensitivity, with an affinity for K(+) in the mM range, and high selectivity for K(+) over Na(+), Ca(2+), Mg(2+) and Li(+). The long luminescence lifetime of the probe and its large Stokes shift further enable accurate determination of the concentration of K(+) in complex aqueous media.     

Synthetic pores with sticky pi-clamps

In this report, we describe design, synthesis, evaluation and molecular dynamics simulations of synthetic multifunctional pores with pi-acidic naphthalenediimide clamps. Experimental evidence is provided for the formation of unstable but inert, heterogeneous and acid-insensitive dynamic tetrameric pores that are sensitive to base and ionic strength. Blockage experiments reveal that the introduction of aromatic electron donor-acceptor interactions provides access to the selective recognition of pi-basic intercalators within the pore. This breakthrough is important for the application of synthetic pores as multianalyte sensors.     

A mini-review of polymeric porous membranes with vertically penetrative pores

Membrane separation technology plays a pivotal role in modern industry and scientific research. The key to developing and improving membrane separation processes lies in designing and fabricating customized porous membranes with specific physical parameters, including pore diameter, porosity, pore size distribution, pore length (membrane thickness), pore geometry, and pore connectivity. Polymeric porous membranes with vertically-penetrative-pores (PPMVs) represent a distinct category among the available membranes due to their unique characteristics such as short transport path, small trans-membrane resistance, and simple pore geometry, as compared to other porous membranes with sponge-like channels. In practical applications, PPMVs offer several advantages, including achieving higher flux rates, facilitating easier unidirectional transport, and enabling harmless biological extraction. Moreover, PPMVs can serve as ideal model systems for theoretical investigations on the fundamental mechanisms of separation and transport in academic research. With substantial advancements in fabrication technologies and application fields of PPMVs in recent years, it warrants a comprehensive perspective. In this mini-review, we provide an overview of widely used fabrication methods for PPMVs, discuss their primary applications, and address the existing challenges and opportunities.     

Ring-opening polymerization of strained cyclotetrasilanes as a new route towards well defined polysilylenes

Ring-opening polymerization of cyclic silanes is described as a new synthetic route to well defined high molecular weight polysilylenes (polysilanes). Strained cyclotetrasilanes with phenyl and methyl substituents at each Si atom in the four-membered ring are prepared by partial dephenylation of octaphenylcyclotetrasilane with triflic acid and the subsequent treatment with methylmagnesium bromide. Chemoselectivity, regioselectivity and stereoselectivity of monomer synthesis is discussed in detail. In addition to classic anionic initiators for the ring-opening process, new catalysts and initiators based on transition metals (Cu, Pd, Pt) are described. They provide much better control of the microstructure than systems with Li⁺ counterion.     

A new fluoride selective fluorescent as well as chromogenic chemosensor containing a naphthalene urea derivative

A new naphthalene derivative containing a urea group at the 1,8-position of naphthalene was synthesized and showed a unique absorption and fluorescence peak with a fluoride ion. Calculations suggested that a new peak was attributed to the increased anion character of urea nitrogen due to the strong interaction of the fluoride and N-H protons.     

Sugar sensing with synthetic multifunctional pores

Recently, synthetic multifunctional pores have been identified as "universal" detectors of chemical reactions. In this report, we show that with the assistance of enzymes as variable co-sensors, synthetic multifunctional pores can serve as similar universal sensors of variable components in mixed analytes. Sugar sensing in soft drinks is used to exemplify this new concept. This is achieved using invertase and hexokinase as co-sensors and a new synthetic multifunctional pore capable of discriminating between ATP and ADP in an "on-off" manner as sensor. The on-off discrimination between ATP as good and ADP as poor pore blocker is shown to be reasonably tolerant of changing experimental conditions. These results identify universal sensing with synthetic multifunctional pores as a robust, sensitive, and noninvasive method with appreciable promise for practical applications.     

Computer simulation study on the concentration distribution of spherical colloids within confined spaces of well‐defined pores

Aside from the virial expansion and density functional methods, theoretical results on the concentration partitioning behavior for charged colloids within cylindrical pores have not been presented so far. With the increase of relative solute size as well as solute concentration, however, the approximate analytic methods have proven to be unreliable. A suitable Monte Carlo simulation, which is proved as a rigorous technique for concentrated colloids, has been applied in the present study. The concentration profiles within the pore representing the effects of solute concentration as well as solution ionic strength are obtained via a stochastic process, from which the partition coefficient is estimated. Previously developed analyses on the linearized Poisson‐Boltzmann (P‐B) equation are employed for the estimation of long‐range electrostatic interaction. Both the singularity method and the analytical solution with series representation properly determine respective interaction energies between pairs of solute particles and between the solute particle and the pore wall. The effect of solute‐solute and solute‐wall interactions associated with repulsive energy is presented on the partitioning of colloids. Simulation results show that the partition coefficient is evidently enhanced when no particle‐wall interaction exists. Hindered diffusion can be predicted by the simplifying assumption of the centerline approximation analogy, where a dependence on the solute concentration becomes greater as the solution ionic strength decreases.     

Macroporous oxide materials with three-dimensionally interconnected pores

Ordered mesoscale hollow spheres (1000 nm diameter) of binary oxides such as TiO₂ and ZrO₂ as well as of ternary oxides such as ferroelectric PbTiO₃ and Pb(ZrTi)O₃ have been prepared by templating against colloidal crystals of polystyrene, by adopting different procedures.     

Nanoscale protein pores modified with PAMAM dendrimers

We describe nanoscale protein pores modified with a single hyperbranched dendrimer molecule inside the channel lumen. Sulfhydryl-reactive polyamido amine (PAMAM) dendrimers of generations 2, 3 and 5 were synthesized, chemically characterized, and reacted with engineered cysteine residues in the transmembrane pore alpha-hemolysin. Successful coupling was monitored using an electrophoretic mobility shift assay. The results indicate that G2 and G3 but not G5 dendrimers permeated through the 2.9 nm cis entrance to couple inside the pore. The defined molecular weight cutoff for the passage of hyperbranched PAMAM polymers is in contrast to the less restricted accessibility of flexible linear poly(ethylene glycol) polymers of comparable hydrodynamic volume. Their higher compactness makes sulfhydryl-reactive PAMAM dendrimers promising research reagents to probe the structure of porous membrane proteins with wide internal diameters. The conductance properties of PAMAM-modified proteins pores were characterized with single-channel current recordings. A G3 dendrimer molecule in the channel lumen reduced the ionic current by 45%, indicating that the hyperbranched and positively charged polymer blocked the passage of ions through the pore. In line with expectations, a smaller and less dense G2 dendrimer led to a less pronounced current reduction of 25%. Comparisons to recordings of PEG-modified pores revealed striking dissimilarities, suggesting that differences in the structural dynamics of flexible linear polymers vs compact dendrimers can be observed at the single-molecule level. Current recordings also revealed that dendrimers functioned as ion-selectivity filters and molecular sieves for the controlled passage of molecules. The alteration of pore properties with charged and hyperbranched dendrimers is a new approach and might be extended to inorganic nanopores with applications in sensing and separation technology.