Synthesis and diels-alder reactions of 5,5-dicyanocyclopentadiene: regioselective synthesis of 1,5-disubstituted-1,3-cyclohexadienes

5,5-Dicyanocyclopentadiene, readily prepared in three steps from commercially available cis-1,4-dichloro-2-butene, undergoes Diels-Alder reactions with a number of dienophiles to give 5-substituted 7,7-dicyanobicyclo[2.2.1]hept-2-enes with high endo-selectivity. The adduct produced with methyl acrylate undergoes base-induced retro-Michael reactions to give 1-carbomethoxy-5-dicyanomethyl-1,3-cyclohexadiene.     

An improved thin-layer chromatography/mass spectrometry coupling using a surface sampling probe electrospray ion trap system

A combined surface sampling probe/electrospray emitter coupled with an ion trap mass spectrometer was used for the direct read out of unmodified reversed-phase C18 thin-layer chromatography (TLC) plates. The operation of the surface sampling electrospray ionization interface in positive and negative ionization modes was demonstrated through the direct analysis of TLC plates on which a commercial test mix comprised of four dye compounds viz., rhodamine B, fluorescein, naphthol blue black, and fast green FCF, and an extract of the caffeine-containing plant Ilex vomitoria, were spotted and developed. Acquisition of full-scan mass spectra and automated collection of MS/MS product ion spectra while scanning a development lane along the surface of a TLC plate demonstrated the advantages of using an ion trap in this combination. Details of the sampling system, benefits of analyzing a developed lane in both positive ion and negative ion modes, levels of detection while surface scanning, surface scan speed effects, and the utility of three-dimensional data display, are also discussed.     

Multipesticide residue method for fruits and vegetables: California Department of Food and Agriculture

Summary This procedure describes the CDFA method for multipesticide residue analysis of fresh fruits and vegetables. An aliquot of chopped sample is blended with acetonitrile. The resulting aqueous acetonitrile extract is filtered and cleaned up via reverse phase solid phase extraction apparatus. The pH of the filtrate is adjusted to neutral using phosphate buffer and the acetonitrile layer is separated from the aqueous layer by a salting out process. An aliquot of the acetonitrile layer is concentrated with a K-D evaporator by forming an azeotrope with n-hexane. The prepared sample is assayed for pesticide residues using GLC and HPLC. The performance of this method was evaluated by fortifying 6 representative fruits and vegetables with 7 chlorinated hydrocarbons, 7 organophosphate and 7 N-methylcarbamate pesticides at 0.1–0.2 ppm. No matrix interference was observed and the recovery of residues varied among different samples as well as different pesticides. Chlorothalonil results varied widely with irreproducible recoveries. In general, the method appears to be fast, rugged, and able to detect routinely at the 0.01 ppm level.     

A novel method for measuring initial-burst chemiluminescence in a liquid scintillation counter using the myeloperoxidase-H20Cl− reaction

These studies show that there is an initial quantifiable burst of luminol-enhanced CL associated with the interaction of MPO with H₂O₂ and Cl^?. They also confirm that the reaction is H₂O₂-concentration dependent (2). The novel method for quantifying initial-burst CL in a liquid scintillation counter introduced in this study provides many advantages over previous CL studies using the same counter, as noted above. This method provides for more efficient representation of CL associated with the MPO reaction, and allows for valid conclusions concerning the drug effects on this reaction. The ability to “see” the initial part of the reaction may also allow kinetic analysis of this (and other) enzyme CL reactions.     

Organic-free water for total organic carbon determination

Commercially available “organic-free” water is compared with water cleaned by ultraviolet (u.v.) radiation for applicability to total organic carbon determinations. The u.v.-treated water contains an organic carbon concentration less than the detection limit of the method used (0.056 mg C l^-1). The commercially processed water lacks the consistently low blank level required for use in TOC determinations.     

α-Fluorination of β-keto sulfoxides

We have developed an efficient new procedure for α-fluorination of β-keto sulfoxide enolate anions which are generated $\text{in situ}$ via nucleophilic addition reactions to cyclopentenone sulfoxide 7. Perchloryl fluoride is used as the fluorinating agent. Characterization of the product α-fluoro β-keto sulfoxides includes ¹⁹F NMR spectroscopy.     

Rapid high-resolution electrophoresis of multimeric von Willebrand Factor using a thermopiloted gel apparatus

Rapid and highly reproducible nonreducing agarose gel electrophoresis (NRAGE) of von Willebrand Factor (vWF) multimers was performed using a thermostated minigel apparatus that monitors and precisely controls internal gel temperature. The substitution of lithium dodecyl sulfate (LiDS) for sodium dodecyl sulfate (SDS) allowed electrophoresis to be performed below the 16 degrees C Krafft point of SDS and facilitated NRAGE of vWF over the entire range of 0-35 degrees C. Internal gel temperature was regulated by a thermocouple probe inserted directly into the gel during electrophoresis which interfaced with a thermopilot that continually measures and adjusts temperature to within +/- 0.5 degrees C. At 10 degrees C operative temperature, NRAGE at 1.5% agarose concentration was completed in 20 min at 250 V. Electrophoresis could be performed in only 10 min at 500 V, but at such high voltages, localized temperature fluctuations as much as 6 degrees C resulted in perturbation of banding patterns in those vicinities. In the optimized method, both high molecular weight multimers and proteolytic fragments of vWF were separable suggesting clinical applicability of this system for the diagnosis of von Willebrand Disease and thrombotic thrombocytopenic purpura.     

A recoverable enzymatic microgel based on biomolecular recognition

The enzyme beta-galactosidase has been immobilized through incorporation into a selectively soluble microgel, prepared from DNA, biotinylated peptide nucleic acid (PNA), and the protein avidin. The enzyme was conjugated to avidin, allowing it to be integrated directly into the microgel network. Efficient hydrolysis of a small-molecule substrate occurred at 37 degrees , but cooling and centrifuging led to precipitation of the microgels and product separation. The microgels were then reconstituted by adding fresh buffer and shaking. The enzymatic activity was completely recovered through repeated cycles. This method should be generalizable to a wide variety of other enzymes and substrates.     

Dynamic solid phase microextraction for sampling of airborne sarin with gas chromatography-mass spectrometry for rapid field detection and quantification

A portable dynamic air sampler and solid phase microextraction were used to simultaneously detect, identify, and quantify airborne sarin with immediate analysis of samples using a field portable gas chromatography-mass spectrometry system. A mathematical model was used with knowledge of the mass of sarin trapped, linear air velocity past the exposed sampling fiber, and sample duration allowing calculation of concentration estimates. For organizations with suitable field portable instrumentation, these methods are potentially useful for rapid onsite detection and quantification of high concern analytes, either through direct environmental sampling or through sampling of air collected in bags.     

2,7-DIIODO-9-DIAZOFLUORENE: A POTENTIAL REAGENT FOR PHOTOLABELING

Abstract— The photochemistry of 2,7-diiodo-9-diazofiuorene was studied to examine its suitability as a photolabeling agent of hydrophobic sites in biological assemblies. Irradiation of the diazo compound generates 2,7-diiodofluorenylidene. The carbene was detected by laser transient absorption spectroscopy and characterized by its chemical and physical properties. Like fluorenylidene, the triplet is the ground state of 2,7-diiodofluorenylidene. However, the substituted triplet carbene does not reform its higher energy, electrophilic singlet state fast enough for reactions of the upper state to compete with the irreversible consumption of the triplet. Thus, the products from the reactions of diiodofluorenylidene contain a higher proportion of those characteristic of the triplet carbene than occurs in the reactions of fluorenylidene. This will limit the utility of this diazocompound as a photolabeling agent.