Application of a novel lipophilized fluorescent dye in an optical nitrate sensor

A new lipophilic pH probe (1-hydroxypyrene-3,6,8-tris-octadecylsulfonamide) has been synthesized, and its spectral properties and applications in a solid state nitrate sensor are shown. The sensor is investigated with respect to sensitivity, limits of detection, and selectivity over other anions found in drinking water.Abbreviations used HPTS trisodium-1-hydroxy-pyrene-3,6,8-trisul-fonate - HPTS-TO 1-hydroxypyrene-tris-3,6,8-octadecylsulfonamide - TDMACl tridodecylmethylammonium chloride - PVC poly(vinyl chloride) - DOS bis-(2-ethylhexyl)-sebacate - THF tetrahydrofurane - DMF dimethylformamide     

On Steiner trees and minimum spanning trees in hypergraphs

The bottleneck of the state-of-the-art algorithms for geometric Steiner problems is usually the concatenation phase, where the prevailing approach treats the generated full Steiner trees as edges of a hypergraph and uses an LP-relaxation of the minimum spanning tree in hypergraph (MSTH) problem. We study this original and some new equivalent relaxations of this problem and clarify their relations to all classical relaxations of the Steiner problem. In an experimental study, an algorithm of ours which is designed for general graphs turns out to be an efficient alternative to the MSTH approach.     

A new class of flexure-free torsional vibrations of annular rods

It is shown that the system of partial differential equations governing small amplitude vibrations of an elastic ring has solutions describing motions in which the axial curve C of the ring remains rigid, but executes a rocking motion while the cross-sections undergo torsional rotations about C that vary periodically both in time and in distance along C. This type of flexure-free torsional vibration can occur both in rings that are stress-free in a circular equilibrium configuration and in rings formed by bringing together and sealing, with or without the addition of twist, the ends of rods that are stress-free when straight.

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Sommario Si mostra che le equazioni che governano le oscillazioni di piccola ampiezza di travi elastiche anulari hanno soluzioni che corrispondono a moti nei quali l'asse C della trave è sottoposto a un'oscillazione rigida e le sezioni trasversali subiscono una rotazione torsionale che varia periodicamente nel tempo e con l'ascissa lungo C. Questo tipo di vibrazione torsionale, non accompagnata da flessione dell'asse, si presenta sia quando la configurazione anulare è priva di sforzi sia quando tale configurazione può pensarsi ottenuta inflettendo una trave che in uno stato privo di sforzi è ad asse rettilineo, imprimendo ad essa una eventuale deformazione torsionale, e collegando fra loro le sue estremità.

     

Characterisation and properties of new ionic liquids with the difluoromono[1,2-oxalato(2-)-O,O′]borate anion

Three ionic liquids with borate anions of low symmetry, tetraethylammonium difluoromono[1,2-oxalato(2-)-O,O′]borate, 1-ethyl-3-methylimidazolium difluoromono[1,2-oxalato(2-)-O,O′]borate, and 1-butyl-3-methylimidazolium difluoromono[1,2-oxalato(2-)-O,O′]borate were synthesised and characterised by physicochemical and electrochemical measurements including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), cyclic voltammetry (CV), viscosity and conductivity measurements.     

Pyran annulation: asymmetric synthesis of 2,6-disubstituted-4-methylene tetrahydropyrans

[reaction: see text] A reaction process for the asymmetric construction of a variety of cis or trans disubstituted pyrans is described. This sequences allows for the asymmetric convergent union of two aldehydes with silyl-stannane reagent 1 in a two-step process: catalytic asymmetric allylation of the first aldehyde using 1 with a BITIP catalyst, followed by reaction of the alcohol so obtained with a second aldehyde and TMSOTf.     

A borderline case between meso and stable C1: an axially chiral, yet configurationally semi-stable biphenyl with two oppositely configured [10]paracyclophane portions

The synthesis of the bi[10]paracyclophanes 2 and 4 from the meso-configured bioxepine 3 is described. These compounds are stereochemically remarkable: the biaryl axis that connects the constitutionally identical, but oppositely configured planar-chiral paracyclophane portions, is configurationally semi-stable. Thus, 2 is an unprecedented borderline case of a (planar-chiral)-(axially chiral)-(planar-chiral) molecule that is right in between a meso-compound (as a macroscopical result of the—albeit slow—rotation about the central C,C-bond) and C₁-symmetry (with respect to the existence of separable—even though configurationally unstable—discrete atropo-enantiomers). Despite their restricted configurational stability, these atropo-enantiomers were resolved on a chiral phase at 5 °C and were stereochemically assigned by LC-CD coupling, in combination with quantum chemical CD calculations.     

Instantaneous SmI2/H2O/amine mediated reduction of nitroalkanes and α,β-unsaturated nitroalkenes

A rapid method for efficient reduction of nitroalkanes and α,β-unsaturated nitroalkenes using SmI₂/H₂O/amine has been developed.     

Direct observation of o-benzyne formation in photochemical hexadehydro-Diels–Alder (hν-HDDA) reactions

Reactive ortho-benzyne derivatives are believed to be the initial products of liquid-phase [4 + 2]-cycloadditions between a 1,3-diyne and an alkyne via what is known as a hexadehydro-Diels–Alder (HDDA) reaction. The UV/VIS spectroscopic observation of o-benzyne derivatives and their photochemical dynamics in solution, however, have not been reported previously. Herein, we report direct UV/VIS spectroscopic evidence for the existence of an o-benzyne in solution, and establish the dynamics of its formation in a photoinduced reaction. For this purpose, we investigated a bis-diyne compound using femtosecond transient absorption spectroscopy in the ultraviolet/visible region. In the first step, we observe excited-state isomerization on a sub-10 ps time scale. For identification of the o-benzyne species formed within 50–70 ps, and the corresponding photochemical hexadehydro-Diels–Alder (hν-HDDA) reactions, we employed two intermolecular trapping strategies. In the first case, the o-benzyne was trapped by a second bis-diyne, i.e., self-trapping. The self-trapping products were then identified in the transient absorption experiments by comparing their spectral features to those of the isolated products. In the second case, we used perylene for trapping and reconstructed the spectrum of the trapping product by removing the contribution of irrelevant species from the experimentally observed spectra. Taken together, the UV/VIS spectroscopic data provide a consistent picture for o-benzyne derivatives in solution as the products of photo-initiated HDDA reactions, and we deduce the time scales for their formation.

We report the transient ultraviolet/visible absorption spectrum of an o-benzyne species in solution for the first time.     

Unprecedented formation of stable ketene-N,O-acetals and their rearrangement under basic conditions

Treatment of 2,4-disubstituted glutaryl dichlorides with benzimidic acid ethyl ester hydrochloride in the presence of triethylamine did not give the expected bis(acylbenzimidates), but delivered O-acyl-N-ethoxybenzylidene-ketene-N,O-acetals in good to excellent yields. These compounds, which are stable to moisture and chromatography on silica gel, underwent an unprecedented rearrangement to cyclic enamides under stronger basic conditions. A mechanism for this rearrangement is proposed.