Gas‐phase ozonolysis: Rate coefficients for a series of terpenes and rate coefficients and OH yields for 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene

The kinetics of the gas‐phase reactions of O₃ with a series of selected terpenes has been investigated under flow‐tube conditions at a pressure of 100 mbar synthetic air at 295 ± 0.5 K. In the presence of a large excess of m‐xylene as an OH radical scavenger, rate coefficients k(O₃+terpene) were obtained with a relative rate technique, (unit: cm³ molecule^?1 s^?1, errors represent 2σ): α‐pinene: (1.1 ± 0.2) × 10^?16, ³Δ‐carene: (5.9 ± 1.0) × 10^?17, limonene: (2.5 ± 0.3) × 10^?16, myrcene: (4.8 ± 0.6) × 10^?16, trans‐ocimene: (5.5 ± 0.8) × 10^?16, terpinolene: (1.6 ± 0.4) × 10^?15 and α‐terpinene: (1.5 ± 0.4) × 10^?14. Absolute rate coefficients for the reaction of O₃ with the used reference substances (2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene) were measured in a stopped‐flow system at a pressure of 500 mbar synthetic air at 295 ± 2 K using FT‐IR spectroscopy, (unit: cm³ molecule^?1 s^?1, errors represent 2σ ): 2‐methyl‐2‐butene: (4.1 ± 0.5) × 10^?16 and 2,3‐dimethyl‐2‐butene: (1.0 ± 0.2) × 10^?15. In addition, OH radical yields were found to be 0.47 ± 0.04 for 2‐methyl‐2‐butene and 0.77 ± 0.04 for 2,3‐dimethyl‐2‐butene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 394–403, 2002     

Copper(II) Complexes of ω‐Hydroxy‐Functionalized N‐Salicylidenehydrazides show pH‐Controlled Switching between Dicationic Dimers and Neutral One‐Dimensional Coordination Polymers

New copper(II) complexes of the hydrazone ligands H₂salhyhb, H₂salhyhp, and H₂salhyhh, derived from salicylaldehyde and ω‐hydroxy carbonic acid hydrazides, have been synthesized and physically characterized. Two fundamental structures were found in solid state depending on the pH‐value of the reaction solution. Acidic conditions lead to the formation of the di‐μ‐phenoxo‐bridged dicationic complex dimers [{Cu(Hsalhyhb)}₂]²⁺ ( 1a ), [{Cu(Hsalhyhp)}₂]²⁺ ( 2a ), and [{Cu(Hsalhyhh)}₂]²⁺ ( 3a ), isolated as perchlorate salts. The dimeric complexes show strong antiferromagnetic coupling with J = ?399 ( 1a ), ?410 ( 2a ), and ?311 cm^?1 ( 3a ). Higher pH‐values resulted in the aggregation of neutral copper ligand fragments to the one‐dimensional coordination polymers [{Cu(salhyhb)}_n] ( 1b ), [{Cu(salhyhp)}_n] ( 2b ), and [{Cu(salhyhh)}_n] ( 3b ). 3b has been examined by means of X‐ray crystallography and represents the first example of a structurally characterized neutral copper(II) N‐salicylidenehydrazide complex without additional ligands. The magnetic interactions in the polymers are also antiferromagnetic with J = ?125 ( 1b ), ?136 ( 2b ), and ?148 cm^?1 ( 3b ), but strongly reduced compared to the corresponding dimeric complexes. The two basic structure types can be reversibly interconverted simply by pH‐control.     

The rat liver mitochondrial proteins

Subcellular fractionation increases the probability of detection of low-abundance proteins. We prepared a fraction highly enriched in mitochondrial proteins from rat liver. The proteins were analyzed by two-dimensional (2-D) electrophoresis using broad-and narrow-range immobilized pH gradient strips, and identified by matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS). 192 different gene products were detected, of which approximately 70% were enzymes with a broad spectrum of catalytic activities. Most of the identified proteins were detected in other rat protein samples as well, which were analyzed in our laboratory. Eight gene products were detected for the first time. These were represented by one spot each, whereas most of the frequently detected proteins were represented by multiple spots. In average, approximately 10-15 spots corresponded to one gene product.     

Channel activity of a viral transmembrane peptide in micro-BLMs: Vpu(1-32) from HIV-1

We report for the first time on pore-suspending lipid bilayers, which we call micro-black lipid membranes (micro-BLMs), based on a highly ordered macroporous silicon array. Micro-BLMs were established by first functionalizing the backside porous silicon surface with gold and then chemisorbing 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol followed by spreading 1,2-diphytanoyl-sn-glycero-3-phosphocholine dissolved in n-decane. Impedance spectroscopy revealed the formation of single lipid bilayers confirmed by a mean specific capacitance of 0.6 +/- 0.2 microF/cm2. Membrane resistances were in the G omega-regime and beyond. The potential of the system for single channel recordings was demonstrated by inserting the transmembrane domain of the HIV-1 accessory peptide Vpu(1-32), which forms helix bundles with characteristic opening states. We elucidated different amilorides as potential drugs to inhibit channel activity of Vpu.     

Über die Reaktionen von Guanidin bzw. Harnstoff mit Cyanhydrinen

Action of guanidine or urea on cyclohexanone-, cyclopentanone-, cycloheptanone-and acetonecyanohydrine3 a?3 d generates very different products: 3 a reacts with guanidine inDMF to yield 1,3-diazaspiro[4.5]decane-2,4-diimine (5 a). Heating the components without solvent affords 7,14-diazadispiro[5.1.5.2]pentadecan-15-one(7)^15–17, the guanidine not participating in the reaction; similarly3 b is transformed by guanidine to a pentacyclic dispirocompound (possible formulae19 and20), whereas3 d reacts to give 3,3,5,5-tetramethylpiperazine-2,6-dione(21)¹⁹. In 3-pentanone guanidine-cyanide condensates itself to give 2,4-diamino-triazine (22)^{21, 22}. Action of urea on3 a?3 d yields the 4-imino-1,3-diazaspiroalkan-2-ones6 a?6 c and the 4-imino-5,5-dimethylimidazolidin-2-one6 d ^6–8 resp. If the reaction of urea and3 d is carried out inDMF, however, 5,5-dimethyl-4-ureido-3-imidazolin-2-one (28) (or the tautomeric carbamoyliminoimidazolidinone27) is produced. The structures of the compounds prepared are proved by NMR-, IR- and mass spectra.     

Silberhalogenide als Spurenfänger für Chelatkomplexe

The power of detection of flame AAS for trace elements decreases considerably in presence of manganese. For the purity control of manganese and manganese compounds, therefore, it is necessary to separate the traces from the main component of the samples. For that purpose the traces were complexed by 1,10-phenanthroline and coprecipitated by silver iodide as trace collector. To receive a trace solution of 10 ml being free of manganese the filtered AgI was boiled with HNO₃. The enriched elements (Fe, Co, Ni, Cu, Zn, Cd, Pb, Bi and Tl) were determined by flame AAS. Using samples of 5 to 10 g of manganese or manganese compounds of different stages of oxidation the limits of detection of the various elements were found to be in a range between 0.01 and 1 ppm. By evaporation of the trace solution down to 1 ml and determination of the traces by the “injection method” of flame AAS limits of detection are obtained between 0.007 and 0.1 ppm.     

Simultaneous determination of capecitabine and its metabolite 5-fluorouracil by column switching and liquid chromatographic/tandem mass spectrometry

A liquid chromatographic/tandem mass spectrometric method was developed and validated for the quantitation of capecitabine and its metabolite 5-fluorouracil in human plasma. The simultaneous determination of both analytes was achieved by a column switching method using a trapping column and two analytical columns with different stationary phases. Isocratic elution was used for the separation of capecitabine on a C18 column whereas 5-fluorouracil was separated using gradient elution on an non-polar carbon phase. The calibration curves were linear for both compounds with a correlation factor (R2) > 0.9993 for 5-fluorouracil and >0.9942 for capecitabine. The assay was validated in the concentration range 5.00-1000 ng ml(-1) for both compounds. The intra-day precision was better than 10% for 5-fluorouracil and better than 11% for capecitabine whereas the inter-day precision was better than 8% for 5-fluorouracil and better than 14% for capecitabine.     

13C-ESR-Kopplungskonstanten des radikalanions des 3,5-di-tert-butyl-nitrobenzols

¹³C-ESR coupling constants of all ring carbon atoms of the radical anion of 3,5-di-tert-butyl-nitrobenzene are determined on samples with ¹³C in natural abundance and assigned on the basis of their solvent dependence. The assignment of a ¹³C coupling constant described for the radical anion of nitrobenzene is revised.     

Preconcentration of trace elements from pure manganese and manganese compounds with activated carbon as collector

A method is described for separation of traces of Bi, Cd, Co, Cu, Fe, In, Ni. Pb, Tl, and Zn from pure manganese and manganese compounds and their determination by flame a.a.s. After the metal or manganese dioxide samples have been dissolved in acid (and manganese salts in water) the trace elements are compleed with potassium xanthogenate. The solution is then filtered through a small filter paper covered with activated carbon, whereby complex compounds are separated from the matrix. When the charcoal is treated with acid, a trace concentrate is obtained which is nearly free of manganese. The detection limits for the analysis of 10-g samples of manganese metal are <0.5 p.p.m., and for 30-g samples of MnCl₂-4H₂O are ? 0.1 p.p.m. The relative standard deviation, in general,is lower than 5%.