An efficient synthesis of cyercene A

An efficient approach to the total synthesis of the marine derived polypropionate cyercene A is described. A key feature of the synthesis is the development of methodology for the diastereoselective Wadsworth-Emmons type condensation of a functionalised γ-pyrone unit.     

Characterization of single- and double-stranded DNA on gold surfaces

Single- and double-stranded deoxy ribonucleic acid (DNA) molecules attached to self-assembled monolayers (SAMs) on gold surfaces were characterized by a number of optical and electronic spectroscopic techniques. The DNA-modified gold surfaces were prepared through the self-assembly of 6-mercapto-1-hexanol and 5'-C(6)H(12)SH -modified single-stranded DNA (ssDNA). Upon hybridization of the surface-bound probe ssDNA with its complimentary target, formation of double-stranded DNA (dsDNA) on the gold surface is observed and in a competing process, probe ssDNA is desorbed from the gold surface. The competition between hybridization of ssDNA with its complimentary target and ssDNA probe desorption from the gold surface has been investigated in this paper using X-ray photoelectron spectroscopy, chronocoulometry, fluorescence, and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The formation of dsDNA on the surface was identified by PM-IRRAS by a dsDNA IR signature at approximately 1678 cm(-)(1) that was confirmed by density functional theory calculations of the nucleotides and the nucleotides' base pairs. The presence of dsDNA through the specific DNA hybridization was additionally confirmed by atomic force microscopy through colloidal gold nanoparticle labeling of the target ssDNA. Using these methods, strand loss was observed even for DNA hybridization performed at 25 degrees C for the DNA monolayers studied here consisting of attachment to the gold surfaces by single Au-S bonds. This finding has significant consequence for the application of SAM technology in the detection of oligonucleotide hybridization on gold surfaces.     

Ion-chromatographic analysis of mixtures of ferrous and ferric iron

Determinations of the aqueous iron species Fe(II) and Fe(III) are essential for a fully-informed understanding of redox processes involving iron. Most previous methods for speciation of iron have been based on the calorimetric determination of Fe(II) followed by reduction of Fe(III) and analysis for total iron. The indirect determination of Fe(III) and the consumption of relatively large sample volumes have limited the accuracy and utility of such methods. A method based on ion-chromatography has been developed for simultaneous direct determination of Fe(II) and Fe(III). Sample pretreatment involves only conventional filtration and acidification. No interferences with the iron(II) determination were found; in determination of iron(III) the only interference observed was an artifact peak (of unknown origin) that occurred only when iron(II) was present, and had an area that was a function of the iron(II) concentration and could hence be corrected for. Solutions of iron(II) free from iron(III) can be prepared by treatment with a mixture of hydrogen and nitrogen in the presence of palladium black as catalyst, to reduce the iron(III). Photoreduction of iron(III) in acidified samples increases the Fe(II)/Fe(III) ratio; no means of circumventing this effect is known, other than storing the samples in the dark and analysing them as soon as possible.     

Finite element investigation of the ground states of the helium trimers 4He3 and 4He2–3He

A three‐dimensional finite element method is applied to the ground states of the symmetric and asymmetric atomic helium trimers ⁴He₃ and ⁴He₂–³He. Three different He–He interaction potentials of hard‐core nature were studied. Two extrapolation procedures based on the convergence properties of the finite element method are investigated. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electron Transfer and Energy Transfer Reactions in Photoexcited α-Nonathiophene/C60 Films and Solutions

Abstract

Photoexcitation of a nonathiophene in film or solution across the π-π* energy gap produces a metastable triplet state. In the presence of C₆₀, on the other hand, an ultra fast electron transfer from the photoexcited nonathiophene onto C₆₀ is observed in films, whereas in solution C₆₀ is involved in an efficient energy transfer reaction with the triplet-state nonathiophene.     

Metal-Free Synthesis of Functional 1-Substituted-1,2,3-Triazoles from Ethenesulfonyl Fluoride and Organic Azides

The boom in growth of 1,4-disubstituted triazole products, in particular, since the early 2000’s, can be largely attributed to the birth of click chemistry and the discovery of the Cu^I-catalyzed azide–alkyne cycloaddition (CuAAC). Yet the synthesis of relatively simple, albeit important, 1-substituted-1,2,3-triazoles has been surprisingly more challenging. Reported here is a straightforward and scalable click-inspired protocol for the synthesis of 1-substituted-1,2,3-triazoles from organic azides and the bench stable acetylene surrogate ethenesulfonyl fluoride (ESF). The new transformation tolerates a wide selection of substrates and proceeds smoothly under metal-free conditions to give the products in excellent yield. Under controlled acidic conditions, the 1-substituted-1,2,3-triazole products undergo a Michael addition reaction with a second equivalent of ESF to give the unprecedented 1-substituted triazolium sulfonyl fluoride salts.     

Novel voltage signal at proximity-induced superconducting transition temperature in gold nanowires

We observed a novel voltage peak in the proximity-induced superconducting gold (Au) nanowire while cooling the sample through the superconducting transition temperature. The voltage peak turned dip during warming. The voltage peak or dip was found to originate respectively from the emergence or vanishing of the proximity-induced superconductivity in the Au nanowire. The amplitude of the voltage signal depends on the temperature scanning rate, and it cannot be detected when the temperature is changed slower than 0.03 K/min. This transient feature suggests the non-equilibrium property of the effect. Ginzburg-Landau model clarified the voltage peak by considering the emergence of Cooper pairs of relatively lower free energy in superconducting W contact and the non-equilibrium diffusion of Cooper pairs and quasiparticles.     

Synthesis and Characterization of Metabolites and Potential Impurities of the Antiulcerative Drug Tenatoprazole

Tenatoprazole (Ulsacare^®) is a recently developed antiulcerative drug used for the treatment of both erosive and nonerosive gastroesophageal reflux disease. During the bulk synthesis of tenatoprazole, we have observed four impurities (tenatoprazole N‐oxide, tenatoprazole sulfone N‐oxide, N‐methyl tenatoprazole, and desmethoxy tenatoprazole) and two metabolites (tenatoprazole sulfide and tenatoprazole sulfone). The present work describes the synthesis and characterization of these impurities.     

Virtual isotropic‐nematic transitions in alkyl cyanobiphenyls

Pretransitional fluctuations in the isotropic phase of liquid crystalline and non‐liquid crystalline alkyl cyanobiphenyls have been investigated using light scattering and magnetic birefringence measurements. We find evidence for a virtual isotropic‐nematic phase transition in short‐chain alkyl cyanobiphenyls with no observable nematic phase. The measured temperature dependence of fluctuations is well‐described by mean‐field theory. Virtual phase transition temperatures extrapolated from separate light scattering and magnetic birefringence experiments are in good agreement. Landau–de Gennes model parameters for the compounds investigated are calculated from the experimental results.     

An efficient synthesis of furano analogs of duocarmycin C1 and C2: seco-iso-cyclopropylfurano[e]indoline-trimethoxyindole and seco-cyclopropylfurano[f]quinoline-trimethoxyindole

seco-Iso-cyclopropylfurano[e]indoline-trimethoxyindole 1 and seco-cyclopropylfurano[f]quinoline-trimethoxyindole 2 are potent cytotoxic agents. Previous synthesis of these compounds was inefficient and the approach required separation of a mixture containing the isomeric indoline and quinoline intermediates 11 and 12, formed from radical cyclization of allylic bromide 10. Reported herein is an efficient and selective synthesis of either intermediate 11 or 12, thus product 1 or 2, as needed. The conditions of the Stobbe condensation, bromination, 5-exo-trig radical cyclization, amine-carboxylic acid coupling, and debenzylation were optimized for multi gram scale. As a result, the reaction times were shortened, the products were readily isolated, and the yields and purity improved.