Toward the peri‐Pentacene Framework

Based on modern pyrene chemistry, a new route toward the synthesis of the peri‐pentacene framework was developed. Firstly, the tetraketo form as stable precursor was targeted, because the fully aromatic peri‐pentacene is predicted to suffer from high instability and reactivity. Therefore, a recently developed 4,5,9,10‐tetrafunctionalization of pyrene was utilized to build up a planar and a dragonfly‐shaped derivative in five steps, which only differ in the two outer bonds between the peripheral benzene rings. The planar tetraketone could only be dissolved in strong acids upon protonation, which limited the use of analytical methods. In contrast, the dragonfly‐shaped form showed excellent organosolubility. In‐depth investigation by NMR spectroscopy revealed co‐existence of atropo‐isomers in solution. The optical and electronic properties were analyzed by UV/Vis spectroscopy and cyclic voltammetry. To approach aromatic conjugation, stepwise reduction in solution by using tetrabutylammonium borohydride was carried out. Reduced species were studied by ESR and UV/Vis spectroscopy, as well as by MALDI‐TOF MS, confirming the formation of the radical anion.     

Separation of 9 Sulfonamide Drugs in ≈4 Min by Ultra-High Performance Supercritical Fluid Chromatography (UHPSFC): with a Feasibility Study for Detection in Milk

Nine widely used veterinary sulfonamide drugs were baseline separated (R _s ≥1.5) in just over 4 min using a 3 × 100 mm, 1.8 μm RX-Sil column, with 9.2 % methanol in carbon dioxide, at 110 bar and 30 °C, with direct UV detection at 260 nm using a 3 mm, 2 μL tapered flow cell. Pressure drop was only 172 bar. Optimization was difficult due to the similarity in structures. Small changes in modifier concentration, temperature and pressure, each tended to improve the resolution of some peak pairs but degraded the resolution of others. There were four critical pairs, each responding differently to changes in conditions. Optimization was performed by plotting resolution between pairs as a function of modifier concentration first, temperature second, and outlet pressure third. Retention time was then minimized by changing flow rate. The estimated limit of quantitation (LOQ, S/N >10), for direct injections, was ≈200–400 ng/g of each, inadequate for regulatory requirements. Solid phase extraction (SPE) attempted to pre-concentrate samples spiked with sulfamethazine by ≈20:1. From water, the limit of detection (LOD) was ≈2.7 ng/mL with LOQ ≈9 ng/mL using UV at 260 nm. The LOD for milk was 6.2 ng/mL, and LOQ was 20.1 ng/mL. A better pre-concentration step or a more sensitive detector such as MS–MS is required. Even with these inadequacies, SFC was shown to be a feasible, faster, “greener” alternative to HPLC for the separation of these drugs.

     

Ion Mobility Sensor In Environmental Analytical Chemistry—Concept And First Results

Abstract

Ion mobility spectrometry is a technique for generating ions at atmospheric pressure via ion-molecule reactions, and for analysing them in an ion drift tube.

The time required for the ions to traverse the length of the drift tube is mainly a function of the mass and the charge of the ions. Besides, ion shape and polarizability also affect the drift time.

Ion mobility spectrometry does not allow structural identification and quantification of unknown substances in mixtures. However, under certain boundary conditions it provides selective fingerprints of the substances to be observed, and operates at the ppbv concentration level and the millisecond time scale.

Through further miniaturization of a recently developed instrument of this type an ion mobility sensor is to be constructed. This sensor includes drift channel, operating shutter, collecting electrode, electronic data acquisition and translation board. The sensor makes possible to obtain real-time ion mobility spectra.

We present and discuss the concept of a small ion mobility spectrometer, its operation principle and first results on the way towards its further miniaturization.     

Synthesis of Some New 6,7-Unsaturated Octuronates From 5-O-tert-Butyldimethylsilyl-1,2-O-Isopropylidene-α-D-gluco-and β-L-ido-Hexodialdose and their Transformation into Octoses and Octitols via Osmylation

Abstract

Carbon chain extensions of 5-O-tert-butyldimethylsilyl-1,2-O-isopropylidene-α-D-gluco-and β-L-ido-hexodialdose with ethoxycarbonylmethylenetriphenylphosphorane or triethyl phosphonoacetate gave the corresponding α,β-unsaturated octuronic esters, the (E)/(Z)-ratios of which strongly depending on the reagent used as well as the starting material. After conventional reduction of the ester moieties the corresponding O-acetyl protected allylic alcohols were subjected to osmylation leading to the respective 1,2-O-isopropylidene protected octoses, which were subsequently converted to some previously unreported octitols. Unambiguous structure proofs, demonstrating the validity of Kishi's empirical rule for the stereochemical outcome of the osmylation reactions reported, were obtained from the NMR spectroscopic features of these products as well as regiospecific chemical degradations to corresponding known heptitols.     

Synthesis of New Potential NMDA Antagonist Based on Acylphosphonate Derivatives

Abstract

In recent years intensive pharmacological research is focused on the N-methyl-D-aspartate (NMDA) receptor, which has been implicated in normal neuronal hnctioning, including excitatory synaptic transmission, as well as in the pathologies of the central nervous system such epilepsy, Alzheimer and Parkinson's disease, and neurodegeneration following a stroke.     

Spectroscopic Detection of Oxygen in Nitrogeneous Gas Mixtures

A pulsed high-frequency discharge was used to excite a non-LTE (local thermal equilibrium) plasma with a high specific power density sufficiently high to dissociate oxygen and gaseous oxides. If traces of hydrocarbons were present in the gas mixture, in the spectrum the Violet system of CN appeared with a long radiation decay time. The CN bands are excited preferentially by inelastic collisions with metastable nitrogen molecules (A³σ). These levels can be efficiently depopulated by competing impact with atomic oxygen. By measuring the radiation signal during the radiation decay a dynamic range of 6 was achieved for a variation of the oxygen content between 1 and 100 ppm. The measured radiation decay of the violet CN 0–0-bands at 388 nm was simulated by a simple model of rate equations valid in the time region where diffusion processes may be neglected.