Tuning the Reactivity of Isocyano Group: Synthesis of Imidazoles and Imidazoliums from Propargylamines and Isonitriles in the Presence of Multiple Catalysts

The reaction of propargyl amines with tert‐butylisonitrile in the presence of a catalytic amount of both Yb(OTf)₃ and AgOTf afforded imidazoles, whereas the same reaction with primary and secondary alkylisonitriles, as well as arylisonitriles, in the presence of three metal salts [Yb(OTf)₃/AgOTf/KOTf] resulted in the 1,3,4,5‐tetrasubstituted imidazoliums in excellent yields. Both chiral amines and chiral isonitriles can be used to provide corresponding chiral heterocycles without racemization. In this multiple catalytic system, Yb(OTf)₃ catalyzed the insertion of isonitriles to the N? H bond of amines, AgOTf catalyzed the 5‐exo‐dig cyclization of the resulting amidine nitrogen to the tethered triple bond, and KOTf promoted the salt metathesis, thus providing at the same time the counterion to the imidazolium. Against common knowledge, the isocyano group acted in these reactions as a polarized triple bond instead of conventional carbene‐like function.     

A Highly Stabilizing Silver(I)‐Mediated Base Pair in Parallel‐Stranded DNA

The first parallel‐stranded DNA duplex with Hoogsteen base pairing that readily incorporates an Ag⁺ ion into an internal mispair to form a metal‐mediated base pair has been created. Towards this end, the highly stabilizing 6 FP ‐Ag⁺‐ 6 FP base pair comprising the artificial nucleobase 6‐furylpurine ( 6 FP ) was devised. A combination of temperature‐dependent UV spectroscopy, CD spectroscopy, and DFT calculations was used to confirm the formation of this base pair. The nucleobase 6 FP is capable of forming metal‐mediated base pairs both by the Watson–Crick edge (i.e. in regular antiparallel‐stranded DNA) and by the Hoogsteen edge (i.e. in parallel‐stranded DNA), depending on the oligonucleotide sequence and the experimental conditions. The 6 FP ‐Ag⁺‐ 6 FP base pair within parallel‐stranded DNA is the most strongly stabilizing Ag⁺‐mediated base pair reported to date for any type of nucleic acid, with an increase in melting temperature of almost 15 °C upon the binding of one Ag⁺ ion.     

A Functionalized Ag2S Molecular Architecture: Facile Assembly of the Atomically Precise Ferrocene‐Decorated Nanocluster [Ag74S19(dppp)6(fc(C{O}OCH2CH2S)2)18]

A ferrocene‐based dithiol 1,1′‐[fc(C{O}OCH₂CH₂SH)₂] has been prepared and treated with a Ag^I salt to form the stable dithiolate compound [fc(C{O}OCH₂CH₂SAg)₂]_n (fc=[Fe(η⁵‐C₅H₄)₂]). This is used as a reagent for the preparation of the nanocluster [Ag₇₄S₁₉(dppp)₆(fc(C{O}OCH₂CH₂S)₂)₁₈] which was obtained in good yield (dppp=1,3‐bis(diphenylphosphino)propane).     

High Ethene/Ethane Selectivity in 2,2′‐Bipyridine‐Based Silver(I) Complexes by Removal of Coordinated Solvent

Following removal of coordinated CH₃CN, the resulting complexes [Ag^I(2,2′‐bipyridine)][BF₄] ( 1 ) and [Ag^I(6,6′‐dimethyl‐2,2′‐bipyridine)][OTf] ( 2 ) show ethene/ethane sorption selectivities of 390 and 340, respectively, and corresponding ethene sorption capacities of 2.38 and 2.18 mmol g^?1 when tested at an applied gas pressure of 90 kPa and a temperature of (20±1) °C. These ethene/ethane selectivities are 13 times higher than those reported for known solid sorbents for ethene/ethane separation. For 2 , ethene sorption reached 90 % of equilibrium capacity within 15 minutes, and this equilibrium capacity was maintained over the three sorption/desorption cycles tested. The rates of ethene sorption were also measured. To our knowledge, these are the first complexes, designed for olefin/paraffin separations, which have open silver(I) sites. The high selectivities arise from these open silver(I) sites and the relatively low molecular surface areas of the complexes.     

A facile method for the synthesis of large‐size Ag nanoparticles as efficient SERS substrates

Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface‐enhanced Raman spectroscopy (SERS). However, large‐scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed‐mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as‐prepared Ag NPs substrates indicate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785‐nm excitation, respectively. Significantly, 150‐nm Ag NPs exhibit an enhancement factor exceeding 10⁸ for pyridine (Py) molecules in electrochemical SERS (EC‐SERS) measurements. Furthermore, finite‐difference time‐domain (FDTD) calculation is employed to explain the size‐dependent SERS activity. Finally, the potential of the as‐prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd.     

Raman spectroscopic probing of plant material using SERS

We report surface‐enhanced Raman studies on intact plant material using onion layers as a biological target, and silver nanoaggregates and silver island films as enhancing plasmonic structures. Surface‐enhanced Raman scattering (SERS) enhancement allows the detection of strong Raman signatures of chemical constituents of the surface of the onion layer such as cellulose, proteins, and flavonols. Because of long‐time incubation, SERS sensors can access the extracellular space in the inner of the layer. The location of silver nanoparticles inside the onion layer has been monitored by the SERS images collected from chemicals present in the onion and/or reporter molecules attached to the nanoparticles. Our studies show a competitive adsorption of intrinsic bio molecules of the onion layer and reporter molecules. Different spectra from different places of the layer indicate the complex heterogeneous chemical structure of the plant material. The pH‐sensitive reporter molecule para mercapto benzoic acid attached to the nanoparticles allows us to infer pH values inside the extracellular matrix of the onion layer. Copyright © 2015 John Wiley & Sons, Ltd.     

Probing the nature of the contact between fine particles by using ultrasound propagation

The propagation velocity (vs) of an ultrasonic signal through a granular material depends on the type of interparticle contact. For noncohesive glass beads, a power law behavior for consolidation stresses applied (σc) above 1 MPa has been measured in previous work. This equation is compatible with Hertz's interaction law between elastic solids. In the present work, we have tested the propagation velocity of ultrasound signals through a sample of fine powder. The tensile strength and compactivity of the powder were previously measured by means of the Seville powder tester (SPT), indicating plastic deformation of the surface asperities in contact for small to moderate consolidation stresses. However, the measurements of ultrasound propagation at high consolidations presented here are compatible with Hertz's law. This finding suggests that for high consolidation stresses, surface asperities are flattened, and it is therefore the elastic deformation of the bulk of the particles that determines the transmission of ultrasonic pulses.     

Phase Behavior of Methane-Pentane Mixture in Bulk and in Porous Media

The adiabatic calorimetry method is used to measure the isochoric heat capacity and the dew-bubble curves for the methane-normal pentane mixtures in bulk for three different mixture compositions of n-pentane. The near-critical behavior of the mixture heat capacity indicates that at low n-pentane concentrations, this system is close to the special point of the critical locus. The effect of porous medium has been investigated for one of the mixtures studied in bulk. It has been shown that in porous medium the essential shift of the dew-bubble curve takes place. In our opinion this shift is caused by the formation of wetting film on the surface of porous medium. The estimation of film thickness resulting from the data obtained yields the value 7–8 nm.     

Plasmonic refraction‐induced ultrahigh transparency of highly conducting metallic networks

We demonstrate a high optoelectronic performance and application potential of our random network, with subwavelength diameter, ultralong, and high‐quality silver nanowires, stabilized on a substrate with a UV binder. Our networks show very good optoelectronic properties, with the single best figure of merit of ∼1686, and excellent stability under harsh mechanical strain, as well as thermal, and chemical challenge. Our network transparency strongly exceeds the simple shading limit. We show that this transmission enhancement is due to plasmonic refraction, which in an effective medium picture involves localized plasmons, and identify the inhomogeneous broadening as the key factor in promoting this mechanism. Such networks could become a basis for a next generation of ultrahigh‐performance transparent conductors.