Silver Coated Platinum Core–Shell Nanostructures on Etched Si Nanowires: Atomic Layer Deposition (ALD) Processing and Application in SERS

A new method to prepare plasmonically active noble metal nanostructures on large surface area silicon nanowires (SiNWs) mediated by atomic layer deposition (ALD) technology has successfully been demonstrated for applications of surface‐enhanced Raman spectroscopy (SERS)‐based sensing. As host material for the plasmonically active nanostructures we use dense single‐crystalline SiNWs with diameters of less than 100 nm as obtained by a wet chemical etching method based on silver nitrate and hydrofluoric acid solutions. The SERS active metal nanoparticles/islands are made from silver (Ag) shells as deposited by autometallography on the core nanoislands made from platinum (Pt) that can easily be deposited by ALD in the form of nanoislands covering the SiNW surfaces in a controlled way. The density of the plasmonically inactive Pt islands as well as the thickness of noble metal Ag shell are two key factors determining the magnitude of the SERS signal enhancement and sensitivity of detection. The optimized Ag coated Pt islands on SiNWs exhibit great potential for ultrasensitive molecular sensing in terms of high SERS signal enhancement ability, good stability and reproducibility. The plasmonic activity of the core‐shell Pt//Ag system that will be experimentally realized in this paper as an example was demonstrated in numerical finite element simulations as well as experimentally in Raman measurements of SERS activity of a highly diluted model dye molecule. The morphology and structure of the core‐shell Pt//Ag nanoparticles on SiNW surfaces were investigated by scanning‐ and transmission electron microscopy. Optimized core–shell nanoparticle geometries for maximum Raman signal enhancement is discussed essentially based on the finite element modeling.     

Phase behaviour of binary systems of lactones in carbon dioxide

Experimental phase equilibrium data for binary systems involving ε-caprolactone, δ-hexalactone, and γ-caprolactone with carbon dioxide have been measured applying the synthetic method using a high-pressure, variable-volume view cell over the temperature range of (303 to 343) K and pressures up to 21 MPa. For the systems investigated, (vapour + liquid) (VLE), (liquid + liquid) (LLE), and (vapour + liquid + liquid) (VLLE) equilibrium were visually recorded. It was observed that an increase in temperature or in carbon dioxide concentration led to a pronounced raise in transition pressure values. The experimental results were modelled using the Peng–Robinson equation of state with the conventional quadratic mixing rule, affording a satisfactory representation of the experimental values.     

Phase behaviour of the ternary system {poly(ε-caprolactone) + carbon dioxide + dichloromethane}

Recently, production of biocompatible and biodegradable polymer microparticles has been a matter of growing interest in pharmaceutical and food areas such as drug or active compounds delivery. To conduct production of microparticles, polymeric particle coating, impregnation of active compounds in polymeric films, the knowledge of phase behaviour involving the biodegradable polymer in supercritical carbon dioxide in the presence of a modifier may be needed to allow developing new industrial applications. In this sense, the aim of this work was to investigate the phase behaviour of the ternary system formed by the biodegradable polymer poly(ε-caprolactone) in (carbon dioxide + dichloromethane). Experimental phase transition (bubble and cloud point) values were obtained by applying the static-synthetic method using a variable-volume view cell over the temperature range of (303 to 343) K and pressures up to 21 MPa, in the CO₂ overall composition range of (25–46) wt%, while polymer concentrations studied were (1, 3, 5, and 7) wt%. For the system investigated, depending on the polymer concentration, vapour–liquid, liquid–liquid, and vapour–liquid–liquid phase transitions were verified.     

Preparation of pure hydrogen peroxide and anhydrous peroxide solutions from crystalline serine perhydrate

Hydrogen peroxide is one of the most versatile oxidation reagents, still it has not fully been exploited by synthetic chemists since anhydrous (let alone pure) hydrogen peroxide requires hazardous preparation protocols. We have recently reported on the crystallization of serine and other amino acid perhydrates, thus paving the way for a new method for laboratory-scale production of anhydrous hydrogen peroxide solutions. Serine is insoluble in most organic solvents (e.g., methanol, ethyl acetate, and methyl acetate) that readily dissolve hydrogen peroxide. Moreover, since the adduct of hydrogen peroxide and serine is unstable in these organic solvents, crystalline serine perhydrate readily decomposes to give anhydrous solutions of hydrogen peroxide and crystalline precipitate of the amino acid. This procedure can then yield an anhydrous hydrogen peroxide solution in a single step. Moreover, filtration of the amino acid, and room temperature evaporation of the volatile solvent (e.g., methyl acetate), yields over 99% hydrogen peroxide.     

A modular approach to a new class of phosphinohydrazones and their use in asymmetric allylic alkylation reactions

A group of five phosphino hydrazones with a pendant binaphthyl unit as a chiral modifier has been synthesized from non-racemic 2,2′-bis(bromomethyl)-1,1′-binaphthyl and 3,3′-diiodo-2,2′-bis(bromomethyl)-1,1′-binaphthyl as the key intermediates. Their efficiency as chiral ligands in palladium-catalyzed allylic alkylation reactions has been investigated showing up to 95% ee under optimized conditions. X-ray diffraction structures of mono- and dimeric Pd complexes are also reported.     

A Safe Way of Performing Some Dangerous Experiments. II. Construction of a Safety Dropper

Due to the high safety risks, chemistry instructors avoid demonstrating many remarkable experiments based on the addition of a liquid to a solid. Well-known examples of such demonstrations are various pyrotechnic mixtures of potassium chlorate and sugar (sucrose), which are usually activated with a drop of concentrated sulfuric acid. Other attractive demonstrations are the addition of water to freshly prepared magnesium phosphide and addition of water to burning magnesium. In all of these demonstrations the reaction that takes place immediately is very vigorous and can be hazardous for the instructor. Because chemistry teachers and instructors usually try to avoid performing experiments that include a hazard, a number of highly attractive experiments may remain unknown to the public. Using a simple homemade device called a safety dropper, one can perform all of these experiments with complete safety, both for the audience and the demonstrator. Details for performing some of these experiments as well as for the construction of the safety dropper are given in this paper. Video clips of demonstrations are included as an aid for inexperienced instructors.     

A Watersoluble Sulfonatomethylated Calix[4]resorcinarene as Artificial Receptor of Metal Complexes

The binding of different sized and shaped metal complexes [Co(His)₂]ClO₄(1), [Co(en)₂C₂O₄]Cl (2) and [K18-crown-6]SCN (3)(en-ethylendiamine, His-L-histidynate-anion) with a new tetrasulfonatomethylcalix[4]resorcinarene([H₈X]Na4) was investigated in neutral and alkaline aqueous media by NMR and pH-metrictitration methods and compared with those of recently studied NMe₄Br (4). The resultsobtained indicate that the outer-sphere coordination of complexes 1–3 by[H₈X]^4- proceeds via the interaction of hydrophobic fragments of the guestswith both the negatively charged rim and the hydrophobic cavity as a -base. Thenature of binding does not change for cations 1, 2 and 4 on going from[H₈X]^4- in neutral to [H₄X]^8- in alkaline media, while the inclusionof 3 decreases on going from [H₈X]^4- to [H₄X]^8-.     

Changing DNA grooves--a 1,4,5,8-naphthalene tetracarboxylic diimide bis-intercalator with the linker (beta-Ala)(3)-Lys in the minor groove

We have been investigating a modular, threading DNA polyintercalator design based upon the 1,4,5,8-naphthalene tetracarboxylic diimide (NDI) intercalating unit. Previously, we have reported the NMR analysis of a bis-intercalator-DNA complex in which the peptide linker between NDI units was found to occupy the DNA major groove (Guelev, Lee, Sorey, Hoffman, Iverson, Chem. Biol. 2001, 8, 415-425). Here we describe the NMR analysis of a complex between a related bis-intercalator known to display altered DNA sequence specificity. In this case, the linker resides in the DNA minor groove. We have thus shown that within this set of sequence specific bis-intercalators, both DNA grooves can be accessed, setting the stage for longer threading polyintercalators designed to have linkers occupying both grooves in an alternating fashion.