Standard enthalpy of formation of 3,4,5-trimethoxybenzoic acid

The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.9±1.3 kJ mol^-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline and gaseous states at T=298.15 K, Δ_fH_m ^Θ (cr) and Δ_fH_m ^Θ (g), were -852.9±1.9 and -721.7±2.0 kJ mol^-1, respectively. The reliability of the results obtained was commented upon and compared with literature values. This revised version was published online in August 2006 with corrections to the Cover Date.     

An efficient synthesis of the orally-active GpIIb/IIIa antagonist FR184764

An efficient synthesis of the orally-active GpIIb/IIIa antagonist FR184764 was achieved. The key intermediate, an optically active ethynyl β-amino ester, was synthesized efficiently by utilizing a lipase catalyzed kinetic resolution step.     

Certification of reference materials and accreditation of reference material producers: Questionable terminology leads to confusion

In the view of the Deutscher Kalibrierdienst (DKD) , a certifying body for reference materials can be considered to be a calibration laboratory. Therefore, accreditation of calibration laboratories in accordance with ISO/IEC 17025 is the most appropriate way to establish confidence in certificates for reference materials. If necessary, the criteria of ISO/IEC 17025 can be tailored to specific cases. There is no need to provide any new kind of reference-material specific accreditation. However, in view of the variety of reference materials and the practice existing in other countries, accreditation of testing laboratories and product certification bodies may optionally be acceptable as long as the same stringent principles with respect to traceability and measurement uncertainty are applied. Such accreditations but not accreditations of reference material producers (ISO Guide 34) are also covered by existing international mutual recognition arrangements (MRA).     

C→N Migrations of the ethoxycarbonyl group in reactions of ortho-substituted aryl isocyanates with the 1,3-zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate

The reactions of meta—para-substituted aryl isocyanates with phosphorus-containing 1,3-zwitterions, which proceed with the CN migration of the CO₂Et group to form the corresponding carbamates, were extended to ortho-substituted aryl isocyanates. The influence of the steric and electronic effects of the ortho substituents in the aromatic rings of aryl isocyanates on the ease of this rearrangement is qualitatively considered.     

TheSemmler-Wolff aromatization andSchmidt reaction applied to some pyrido[2′,3′:3,4]pyrazolo[5,1-c][1,2,4]benzotriazines

Pyrido[2,3:3,4]pyrazolo[5,1-c][1,2,4]benzotriazin-4(1H)ones were transformed via their oximes in aSemmler-Wolff aromatization process in the tetracyclic heteroaromatic amines4 or bySchmidt reaction into a mixture of the same amine4 and a ring enlarged lactam3. Syntheses of some halo pyrazolo[3,4-b]pyridines and a photochemical transformation of 3-azidopyrazolo[3,4-b]pyridine are also described.

---

Über dieSemmler-Wolff- undSchmidt-Reaktion einiger Pyrido[2,3:3,4]pyrazolo[5,1-c][1,2,4]benzotriazine

Zusammenfassung Pyrido[23:3,4]pyrazolo[5,1-c][1,2,4]benzotriazin-4(1H)one werden über Oxime in einerSemmler-Wolff-Reaktion in die tetracyklischen aromatischen Amine4 umgewandelt. In einerSchmidt-Reaktion wurden dieselben Ketone in ein Gemisch aus Amin4 und Lactam3 übergeführt. Synthesen von halogensubstituierten Pyrazolo[3,4-b]pyridinen und photochemische Umwandlung von 3-Azidopyrazolo[3,4-b]pyridin werden beschrieben.

     

Simultaneous determination of theophylline,tolbutamide, mephenytoin,debrisoquin, and dapsone in human plasma using high‐speed gradient liquid chromatography/tandem mass spectrometry on a silica‐based monolithic column

Theophylline, tolbutamide, mephenytoin, debrisoquin, and dapsone are marker substrates for CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, respectively. A silica‐based monolithic column (Chromolith SpeedROD RP‐18e, 50×4.6 mm) was used to separate these five marker substrates of cytochrome P450 within only 84 s. Linear gradient elution was from acetonitrile‐water‐formic acid (10 : 90 : 1, v/v/v) to acetonitrile‐water‐formic acid (90 : 10 : 1, v/v/v) in 1.4 min. The flow rate was 2.5 mL/min. The retention time was 0.52 min for theophylline, 0.67 min for debrisoquin, 0.78 min for dapsone, 0.96 min for mephenytoin, and 1.13 min for tolbutamide. Detection was by tandem mass spectrometry using a PE Sciex API 3000 mass spectrometer with a Turbo‐Ionspray source in positive mode. A simple protein precipitation method was used. This method was validated over the concentration range of 5–2000 ng/mL based on the sample volume of 0.1 mL.     

α-Oxolactam enamines as new synthons in the Nenitzescu reaction

-Oxolactam enamines, namely, 3-piperidino-5,6-dihydropyridin-2(1H)-one (1a) and 3-piperidino-1,5,6,7-tetrahydroazepin-2-one (1b), were introduced for the first time into the Nenitzescu reaction. The processes yield cyclic adducts 3a—e, 6. On heating in acetic acid, they are transformed into benzofuropyridone 7 and benzofuroazepinones 10a,d, and 12 and, unexpectedly, into chromenopyrrole 8 and chromenopyridines 9a—d and 11.     

Direct Electrochemistry of Multi‐Copper Oxidases at Carbon Nanotubes Noncovalently Functionalized with Cellulose Derivatives

This study describes the direct electron transfer of multi‐copper oxidases, i.e., laccase (from Trametes versicolor) and bilirubin oxidase (BOD, from Myrothecium verrucaria) at multiwalled carbon nanotubes (MWNTs) noncovalently functionalized with biopolymers of cellulose derivatives, i.e., hydroxyethyl cellulose (HEC), methyl cellulose (MC), and carboxymethyl cellulose (CMC). The functionalization of the MWNTs with the cellulose derivatives is found to substantially solubilize the MWNTs into aqueous media and to avoid their aggregation on electrode surface. Under anaerobic conditions, the redox properties of laccase and BOD are difficult to be defined with cyclic voltammetry at either laccase/MWNT‐modified or BOD/MWNT‐modified electrodes. The direct electron transfer properties of laccase and BOD are thus studied in terms of the bioelectrocatalytic activities of the laccase/MWNT‐modified and BOD/MWNT‐modified electrodes toward the reduction of oxygen and found to be facilitated at the functionalized MWNTs. The possible application of the laccase‐catalyzed O₂ reduction at the laccase/MWNT‐modified electrode is illustrated by constructing a CNT‐based ascorbate/O₂ biofuel cell with the MWNT‐modified electrode as the anode for the oxidation of ascorbate biofuel.     

Nanometer-sized zirconium dioxide microcolumn separation/preconcentration of trace metals and their determination by ICP-OES in environmental and biological samples

A new method is proposed using a microcolumn (20 mm × 2.0 mm) packed with nanometer-sized zirconia as solid-phase extractor for the separation/preconcentration of Mn, Cu, Cr, Zn, Ni and Co prior to their determination by inductively coupled plasma optical emission spectrometer (ICP-OES) in environmental samples. The factors affecting the separation and preconcentration of analytes such as pH, sample flow rate and volume, eluent concentration and volume were determined, interfering ions were studied, and the optimal experimental conditions were established. The adsorption capacity of nanometer-sized ZrO₂ for Mn, Cu, Cr, Zn, Ni and Co was found to be 1.3, 1.3, 1.7, 2.0, 3.9 and 1.5 mg g⁻¹, respectively. The detection limits of the method were 12, 58, 24, 2, 7 and 36 ng L⁻¹, respectively, with a preconcentration factor of 25. The precision of this method was 1.7% (Mn), 2.9% (Cu), 5.9% (Mn), 3.8% (Mn), 6.2% (Mn) and 4.3% (Mn) with 9 determinations of 10 ng mL⁻¹ of target analytes, respectively. The method was successfully applied to the determination of trace metals in lake water, dried fish samples, certified reference materials of human hair and milk, and provided satisfactory results.