A new coated-wire cobalt(II)-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair

A cobalt-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair is described. The response is Nemstian (slope 29.3 $\text{mV}\text{pCo}$) in the cobalt concentration range 10^-1–10^-4 M in solutions with a constant ionic strength of 3.0 M made up with KSCN at 25°C. The electrode is suitable for end-point detection in titrations of cobalt(II) with EDTA as well as for direct potentiometric determinations of cobalt(II), even in the presence of large amounts of several metal ions (Ni²⁺, Fe²⁺, Mn²⁺, Mg²⁺, Ca²⁺, Ba²⁺) and anions (HCO₃^-, Br^-, I^-, NO₃^-, SO₄^2-).     

Bioactivity screening by chromatography-bioluminescence coupling

Summary Because luminescent microorganisms change their light emission in the presence of bioactive substances, they provide an effective way of monitoring toxicity. Here we report the direct coupling of bioluminescence to chromatography which is capable of detecting single toxic components in complex mixtures. Two approaches were investigated, utilizing thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). The TLC-bioluminescence imaging technique was developed into a versatile and rugged method and proved to be superior to the HPLC-based design. Employing genetically engineered luminescent bacteria gives customized selectivity of bioactivity detection. The combination of analytical separation technology with the biospecific sensing ability of living cells provides a novel screening tool for targeting bioactive components in complex samples.     

Synthesis of 8-(omega-Hydroxyalkyl)-, 8-(omega-hydroxyalk-1-enyl)-, and 8-(omega-hydroxyalk-1-ynyl)adenines using the tert-butyldimethylsilyloxymethyl group, a new and versatile protecting group of adenine

The synthesis of 12 analogues of adenine substituted at C-8 by an omega-hydroxyalkyl, omega-hydroxyalk-1-enyl, or omega-hydroxyalk-1-ynyl chain of various length has been carried out in five or six steps starting from adenine. The analogues were obtained using a new protecting group of adenine, the tert-butyldimethylsilyloxymethyl group. 9-tert-Butyldimethylsilyloxymethyl-adenine is more soluble than adenine in organic solvents. It was prepared regiospecificaly in two steps from adenine and was amenable to C-8 iodination under basic conditions and to subsequent introduction of the various carbon chains at C-8 by palladium-catalyzed cross-coupling reactions (Stille or Sonogashira). The protecting group was removed under acidic conditions, thus demonstrating its versatility.     

Phase diagrams of urea inclusion compounds

The stearic acid-urea binary system exhibits an unusual phase diagram, which, on the one hand, indicates an incongruently melting inclusion compound and on the other hand a miscibility gap in the liquid phases. The peritectic point lies near the melting point of urea and the unstable congruent melting point of the inclusion compound coincides with the melting point of urea. In addition to the processing of the phase diagram, the pure inclusion compound was prepared and its DSC curve, FTIR spectrum and X-ray diffractogram were recorded.     

Pyrazolat und Tetrazolat als Brückenliganden in [Pt(pz)2]3, [Pt(pz)2]∞ und [Pt(tz)2]∞ Die Kristallstruktur von [Pt(pz)2]3

Pyrazolat and Tetrazolat as Bridging Ligands in [Pt(pz)₂]₃, [Pt(pz)₂]_∞, and [Pt(tz)₂]_∞ Crystal Structure of [Pt(pz)₂]₃ . [Pt(pz)₂(Hpz)₂]₂ (Hpz = pyrazole) suspended in mesitylene decomposes at 185°C in a sealed tube to [Pt(pz)₂]₃ and [Pt(pz)₂]_∞. The reaction of K₂PtCl₄ with K(pz) under hydrothermal conditions at 150°C yields [Pt(pz)₂H₂O]_∞. [Pt(tz)₂ H₂O]_∞ (Htz = tetrazole) is obtained at 25°C from K₂PtCl₄ and Li(tz) in water. [Pt(pz)₂]₃ crystallizes in the tetragonal space group I4₁/a with a = 1694.9 pm, c = 3127.5 pm and Z = 16. It forms a ring structure with the symmetry D_3h. In the structure the Pt atoms are each bridged by two pyrazolato ligands. Short but nonbonding Pt? Pt distances range from 303.4 pm to 306.7 pm. The average Pt? N distance is 201 pm.     

The Influence of the Axial Chirality of Dibenzo[a,c]cyclooctene on the Configuration of Its Photo-Diels-Alder Adducts

Triazole-diones and naphthoquinone are shown to add in a photochemical [4+2] reaction to the strongly twisted title diene 1 . With 1, 4-naphthoquione, the process is also accompanied by a [2+2] cycloaddition. When the pure atropisomer (?)- 1 is irradiated in presence of 2, 3-dichloro- 1, 4-naphthoquinone ( 9 ), the axial chirality of the diene is preserved. Moreover, it is found to exert complete control over the chirality induced in the resulting spiro-dihydropyrane 10 . Absolute configuration are determined by X-ray crystallography. In absence of a photo-dienophile, the axially chiral, dextrorotatory 6-phenyldibenzo[a,ccyclootene] ((++)- 11 ) undergoes a stereospecific electrocyclization to give levorotatory 4b,6a-dihydro-5-phenylcyclobuta[l]phenanthrene ((?)- 13 ). Thus, only one out of two possible, disrotatory modes of ring closure is preferred.     

The Acetolysis of exo- and endo-5,6-Dimethylidene-2-Norbornyl p-Bromobenzenesulfonates and of their Optically Active and Deuterium-Labelled Derivatives

The buffered (AcOK) acetolyses of exo, (11) and endo-5, 6-dimethylidene-2-norbornyl brosylate (12) yielded exo5, 6-dimethylidene-2-norbornyl (16) and (3-methylidene-2-nortricyclyl)methyl acetates (18) . Endo-5, 6-dimethylidene-2-norbornyl (17) and 2-methylidene-3-tricyclo [3.2.1.0^3,6]octyl acetates (20) could not be detected. The titrimetric rate constants of the acetolysis of 11 (k_t(exo)=4.49 ± 0.02) · 10^?5 s^?1 at 25°, ΔH^≠=23.6 ±0.7 kcal mol^?1, ΔS^≠=0.7 ±2 calmol^?1 K^?1 and 12 (k_t(endo)=1.9 ±0.08) · 10^?9 s^?1 at 25°, ΔH^≠=27 ±1 kcal mol^?1, ΔS^≠=-8 ±2.5 calmol^?1 K^?1) were measured and compared with the polarimetric rate constants (k_α/k_(exo)=6.8 at 25°,(k_α/k_(exo)=1.0 at 121°) of the buffered acetolyses of the optically active brosylates (+)- 11 and (+)- 12 . Neither a common-ion (KOBs) nor a special ion effect (LiClO₄) on k_t(endo) could be detected, although external return might well intervene as some exo-5,6-dimethylidene-2-norbornyl tosylate (21) was formed upon solvolysis in the presence of KOTs. Acetolysis of (+)- 11 yielded completely racemized products, whereas (+)- 12 led to incomplete racemization. The buffered acetolysis of exo-(3exo-D)-5,6-dimethylidene-2-norbornyl brosylate (24) furnished (3exo-D)-( 26 :37.5%), exo-(7syn-D)-5,6-dimethylidene-2-norbornyl brosylate (27 : 37.5%) and [(5anti-D)-3-methylidene-2-nortricyclyl]methyl acetates (28 : 25 %). The acetolysis of endo-(2exo-D)-5,6-dimethylidene-2-norbornyl brosylate (25) yielded (2endo-D)-( 29 : 54%), exo-(1-D)-5,6-dimethylidene-2-norbornyl ( 30 : 36%) and [(6-D)-3-methylidene-2-nortricyclyl]methyl acetates ( 31 : 10%). Product analysis and deuterium label distribution was established by a combination of GC., ¹H-NMR., ²H-{¹H}-NMR. and MS. techniques. The results are rationalized by invoking anchimerically assisted ionization of the exo-brosylate 11 to symmetrical ion-pairs (cyclopropylcarbinyl cation intermediates) which undergo internal (and probably also external) return. Acetolysis of the endo-brosylate 12 is not anchimerically assisted and leads initially to non-symmetrical ion pairs. These evolve to symmetrical ion pair intermediates or, to a minor extent, are intercepted by solvent.     

Gas chromatography of amino acids: Use of a fused-silica capillary column in the determination of plasma amino acids

A capillary chromatographic procedure using a fused silica column is described which can be used to quantitatively determine amino acids in plasma following the pre-chromatographic “clean-up” described in a recent paper [1]. In substituting this procedure for that involving a packed column, advantage has been taken of the greater resolving power to separate amino acids from background component peaks. In order to extend this advantage and provide a sound basis for quantitative analysis, the technique of cold on-column injection was employed. As a result, good precision of standard analysis was obtained with relative standard deviation (RSD) values for all amino acids of less than 4%. Application of the entire procedure to plasma samples yields RSD values of better than 10% for all amino acids with recoveries ranging from 72% to 104%. Simultaneous determination of plasma amino acid levels by gas chromatography (GC) using capillary columns and by classical ion exchange (CIE) showed reasonable agreement. Statistical evaluation showed no significant difference between twelve amino acids. Values for the remaining two, namely, phenylalanine and histidine are significantly different (p < 0.005). Comparison of the values obtained from GC capillary and packed columns reveals no significant difference between fourteen amino acids. Significant differences exist between results for phenylalanine and tyrosine (p < 0.001). It is concluded that there is good agreement between data obtained by GC capillary and CIE techniques and that differences between results for phenylalanine and histidine are method related.     

UV-mediated DNA strand breaks in corneal epithelial cells assessed using the comet assay procedure

Ultraviolet (UV)-mediated DNA damage in various tissues has been well documented. However, research on the damaging effect of UV irradiation on the DNA of corneal epithelium is scarce, even though this is of interest because the cornea is directly exposed to damaging solar (UV) radiation. In this study, we developed a corneal epithelium Comet assay model to assess the background DNA damage (as strand breaks) in cells retrieved from different layers of the porcine corneal epithelium, and to investigate the effect of UV irradiation on DNA damage in corneal epithelial cells. Results show that the background DNA strand breaks decreased significantly (P < 0.001) toward deeper layers of the epithelium. Exposure to the same intensity (0.216 J/cm2) of UVA, UVB and UVC caused a significant (P < 0.001) increase in DNA strand breaks of deeper-layer cells: mean +/- SD %DNA scores (10 gels per treatment, with 100 irradiated cells scored per gel) were 10.2% +/- 1.4% for UVA, 27.4% +/- 4.6% for UVB, and 14.7% +/- 1.8% for UVC compared with 4.2% +/- 0.5% for controls (ambient room light). This study has shown for the first time that the Comet assay for DNA strand breaks can be used successfully with corneal epithelial cells. This report will support future studies investigating environmental influences on corneal health and the assessment of possible protective strategies, and in applying DNA lesion-specific versions of the Comet assay in this corneal epithelial cell model.     

Stereoselective synthesis of (3S,4S)-tert-butyl-N-Boc-3-ethyl-4-hydroxy-l-prolinate and (3S,4R)-tert-butyl-N-Boc-3-ethyl-4-hydroxy-l-prolinate

Diastereomers of tert-butyl-N-Boc-3-ethyl-4-hydroxy-l-prolinate 1 and 2 have been synthesized in six steps starting from readily available Boc-protected trans-4-hydroxy-l-proline. The key reactions in the synthesis are asymmetric reductions, firstly on the 4-ketoproline intermediate 6 and secondly on the 3-exocyclic olefin bond of the resulting allylic alcohol 7 or 8. Reaction conditions were optimized in order to control the stereochemistry of the three chiral centers.