A Quantum Chemical Study of the Abnormal Reactivity of 2‐Methoxyfuran

The gas‐phase pyrolytic and oxidative chemistry of furans has received much attention recently because of their potential as platform chemicals and biofuels. Typically these compounds exhibit very strong ring carbon to H or CH₃ bonds. 2‐Methoxyfuran had been reported to be exceptionally unstable in comparison to related substituted heterocycles in pyrolytic experiments. The origins of its reactivity are shown to be due to the very weak O–CH₃, which at 189.5 ± 1.9 kJ mol^?1 is some 200 kJ mol^?1 weaker than C–H bonds in the molecule. We show that the reported reactivity is somewhat overestimated but that does not alter the fact that 2‐methoxyfuran is exceptionally unstable. It may prove to be a useful alternative to azomethane as a thermal source of methyl radicals.     

Genotoxic properties of 2-dodecylcyclobutanone, a compound formed on irradiation of food containing fat

When food containing fat is treated by ionizing radiation, a group of 2-alkylcyclobutanones is formed. These components contain the same number of carbon atoms as their precursor fatty acids and the alkyl group is located in ring position 2. Thus, from palmitic acid 2-dodecylcyclobutanone is derived. To date, there is no evidence that the cyclobutanones occur in unirradiated food. Therefore, these components cannot be considered inherent to food, and for questions pertaining to risk assessment of irradiated food it would be advisable to determine the genotoxic and toxic potentials of cyclobutanones. Measurements of DNA damage in cells exposed to 2-dodecylcyclobutanone, employing the single cell microgel electrophoresis technique, have been carried out. In vitro experiments using rat and human colon cells indicate that 2-docylcyclobutanone in the concentration range of about 0.30 – 1.25 mg/ml induces DNA strand breaks in the cells. Simultaneously, a concentration related cytotoxic effect is observed as was determined by trypan blue exclusion. To which extent these in vitro findings are of relevancy for the in vivo human exposure situation needs to be investigated in further studies. In vivo tests in rats are in progress.     

Single-run analysis of retinal isomers, retinol and photooxidation products by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) procedure was developed to allow the rapid separation, in a single run, of a mixture of the main retinal isomers (all-trans, 13-cis, 9-cis), all-trans-retinol, and of the two major photooxygenated photoproducts (5,8-peroxyretinal and 5,6-epoxyretinal). The mixture was separated by HPLC on an octadecyl (ODS) column with 16% (v/v) diethyl ether in hexane as mobile phase and anthracene as the internal standard. A commercial type cosmetic formulation containing 0.05% all-trans-retinal was analyzed successfully for this analyte.     

Synthesis of β-tosylethylhydrazine and its use in preparation of N-protected pyrazoles and 5-aminopyrazoles

β-Tosylethylhydrazine (6) can be prepared efficiently in one step from commercially available p-tolyl vinyl sulfone (7) and hydrazine hydrate. This hydrazine reacts with both 1,3-diketones and conjugated ynones in glacial acetic acid to provide a variety of N-tosylethyl-protected (TSE) pyrazoles in good yields. The TSE group can be removed from the pyrazoles using potassium t-butoxide in THF at −30 °C-rt. In addition, hydrazine 6 condenses with β-ketonitriles and β-aminoacrylonitriles to afford 5-aminopyrazoles, which can be deprotected by brief treatment with NaOEt in EtOH/DMSO at 45 °C.     

Acid digestion of geological and environmental samples using open-vessel focused microwave digestion

The application of open vessel focused microwave acid digestion is described for the preparation of geological and environmental samples for analysis using inductively coupled plasma-mass spectrometry (ICP-MS). The method is compared to conventional closed-vessel high pressure methods which are limited in the use of HF to break down silicates. Open-vessel acid digestion more conveniently enables the use of HF to remove Si from geological and plant samples as volatile SiF4, as well as evaporation-to-dryness and sequential acid addition during the procedure. Rock reference materials (G-2 granite, MRG-1 gabbros, SY-2 syenite, JA-1 andesite, and JB-2 and SRM-688 basalts) and plant reference materials (BCR and IAEA lichens, peach leaves, apple leaves, Durham wheat flour, and pine needles) were digested with results comparable to conventional hotplate digestion. The microwave digestion method gave poor results for granitic samples containing refractory minerals, however fusion was the preferred method of preparation for these samples. Sample preparation time was reduced from several days, using conventional hotplate digestion method, to one hour per sample using our microwave method.     

Quantitative Modelization of Hydrogen-Bonding in Polyoxometalate Chemistry

The PACHA (Partial Atomic Charges and Hardnesses Analysis) formalism is applied to polyoxometalate chemistry. Using the Ca₂(H₃O)₂[V₁₀O₂₈]16H₂O crystal structure, it was shown that the relative affinity for protons of the various oxygen sites may be quantitatively determined. The charge distribution was also found to be in good agreement with ¹⁷O and ⁵¹V NMR measurements. The H-bond energy in this kind of compound was found to be about –17 kJmol^–1, i.e., about 20% lower than in hexagonal ice. Finally, the 57 H-atom coordinates characterizing this structure were successfully recovered from a crystal structure optimization in the solid-state through electrostatic balance minimization. The importance of considering neutral clusters for a good modelization was demonstrated not only in the case of the decavanadate structure, but also in polysilicate chemistry. For the first time a clear picture emerges explaining the widespread occurrence of four- and five-membered rings in zeolite and silicate chemistry. The possibility of forming much larger polyanions with transition metal cations, is well explained using the crystal structure of the superfullerene keplerate [Mo₁₃₂O₃₇₂(HCO₂)₃₀(H₂O)₇₂]^42– as a benchmark compound. The possibility of performing an ab-initio retrosynthetic analysis of this cage is demonstrated.     

环境水中甲基对硫磷、对硫磷和辛硫磷农药残留的SPE-HPLC分析

采用离线固相萃取 (SPE)富集 -高效液相色谱(HPLC)分离和紫外分光光度法检测 ,对环境水中甲基对硫磷、对硫磷和辛硫磷3种有机磷农药进行分析;固相萃取用C18 萃取柱 ,用甲醇洗脱 ,高效液相色谱分离以Shim_PackCLCODS柱(150mm×4.6mmid,5μm)为分离柱 ,流动相为甲醇 -水(体积比70∶30) ,紫外检测波长为280nm;该法稳定可靠 ,回收率高     

硅表面嫁接有机单分子膜的研究近况

由于在微电子、化学 /生物化学传感器、纳米技术及太阳能等领域具有潜在的应用价值 ,通过 Si— C键在硅表面上直接嫁接有机单分子膜 ,已成为近几年新开展的研究热点 .对这一研究领域进行了概要综述     

Electrophoretic separations in poly(dimethylsiloxane) microchips using mixtures of ionic,nonionic and zwitterionic surfactants

The use of surfactant mixtures to affect both EOF and separation selectivity in electrophoresis with PDMS substrates is reported, and capacitively coupled contactless conductivity detection is introduced for EOF measurement on PDMS microchips. First, the EOF was measured for two nonionic surfactants (Tween 20 and Triton X‐100), mixed ionic/nonionic surfactant systems (SDS/Tween 20 and SDS/Triton X‐100), and finally for the first time, mixed zwitterionic/nonionic surfactant systems (TDAPS/Tween 20 and TDAPS/Triton X‐100). EOF for the nonionic surfactants decreased with increasing surfactant concentration. The addition of SDS or TDAPS to a nonionic surfactant increased EOF. After establishing the EOF behavior, the separation of model catecholamines was explored to show the impact on separations. Similar analyte resolution with greater peak heights was achieved with mixed surfactant systems containing Tween 20 and TDAPS relative to the single surfactant system. Finally, the detection of catecholamine release from PC12 cells by stimulation with 80 mM K⁺ was performed to demonstrate the usefulness of mixed surfactant systems to provide resolution of biological compounds in complex samples.