Validation of analytical methods used for determination of nitrate in soil

The standard method (ISO/DIS 14255) and the quick test were used for determination of nitrate in soil. We validated both methods using parameters such as accuracy, reproducibility within 1 day and between days, limit of detection and limit of quantification. The accuracy of the results was determined using the analysis of samples from the international interlaboratory scheme WEPAL. The accuracy of the standard method was good, while for the quick test the results were not accurate. The standard method showed a solid reproducibility of measurement results (in 1 day, relative standard deviation, RSD=0.2%; between days, RSD=0.8%). The quick test gave poorer results (in 1 day, RSD=6%; between days, RSD=7%). We tried to established the compatibility of both methods on real soil samples and we were satisfied to obtain the correlation coefficient 0.98 using the regression straight line. The analyses with the quick field instrument are much simpler and cheaper than the standard laboratory analyses and can be used for advising on nitrogen fertilisation.     

Highly compact 2D graphical representation of DNA sequences

Most 2D graphical representations of primary DNA sequences, while offering visual geometrical patterns for depicting sequences, do require considerable space if enough details of such representations are to be visible. In this contribution, we consider a highly compact graphical representation of DNA, which allows visual inspection and numerical characterization of DNA sequences having a large number of nucleic acid bases. The approach is illustrated on the DNA sequences of the first exon of human beta-globin. The same graphical approach not only allows one to depict differences in composition within a single DNA, but makes possible graphical representation of protein sequences, which have hitherto evaded similar 2D visual representations.     

Visible light induced ‘on water’ benzylic bromination with N-bromosuccinimide

Benzylic bromination of various 4-substituted toluenes (Me, tert-Bu, COOEt and COMe) was effectively conducted with NBS in pure water and with a 40 W incandescent light-bulb as an initiator of the radical chain process, while electron donating groups (OMe and NHAc) directed the reaction to electrophilic aromatic substitution.     

Density functional LCAO calculations for solids: Comparison among Hartree–Fock,DFT local density approximation,and DFT generalized gradient approximation structural properties

In this article, the results of a recently implemented DFT a posteriori and Kohn-Sham (KS ) linear combination of atomic orbital computational scheme for solids are presented. The equilibrium lattice parameters, bulk moduli, and lattice energies are calculated for eight crystallized systems. Local density approximation (LDA ) and generalized gradient approximation (GCA ) functionals and potentials are used. The maps of the Hartree-Fock (HF ) and Ks electronic densities and band structures are depicted. The KS results confirm the trend of the a posteriori scheme. Very good agreement between calculated and experimental lattice energies has been found for GGA potentials. © 1995 John Wiley & Sons, Inc.     

Free radical bromination by the H2O2-HBr system on water

An aqueous solution of hydrogen peroxide and hydrogen bromide illuminated by a 40 W incandescent light bulb serves as a source of bromine radicals. Various substituted toluenes (H, Me, tBu, Br, COOEt, COPh, NO₂) were brominated at the benzyl position. This haloperoxidase-like system for benzylic bromination does not require the presence of metal ions or an organic solvent for efficient conversion of methyl-arenes to benzyl bromides.     

Beitrag zur Synthese von Äthylmercuriphosphat

Zusammenfassung Es ist gelungen, Di- und Mono-äthylmercuriphosphat aus Äthylmercurichlorid über Äthylmercuriacetylid zu synthetisieren. Das als Zwischenprodukt gebildete Äthylmercuriacetylid ermöglicht den Zugang zum Endprodukt unter gleichzeitiger Beseitigung des an Alkyl gebundenen Säurerestes. Für die Bildung des äthylmercuriphosphats ist das molare Verhältnis H₃PO₄/Hg in starkem Maße ausschlaggebend. Im Bereich der Werte dieses Molverhältnisses bis etwa 1,0 entsteht hauptsächlich Diäthyl-MP, bei höheren Werten wird ein Gemisch von Mono- und Diäthyl-MP, gebildet, bei Werten um etwa 2,0 wird dagegen mehr oder weniger reines Monoäthyl-MP erhalten. Triäthylmercuriphosphat ist nach dieser Methode nicht zugänglich, obwohl dies bei einem Molverhältnis H₃PO₄/Hg=0,3 zu erwarten wäre. Unter diesen Bedingungen wird aber stets nur Diäthylmercuriphosphat unter gleichzeitigem Ausscheiden des überschüssigen Quecksilbers erhalten.Bei der Durchführung dieser Synthese, die in zwei Stufen verläuft, wurden die optimalen Bedingungen für die Bereitung der alkalischen äthylmercurichloridlösung und die darauffolgende Fällung des äthylmercuriacetylids experimentell festgestellt.Mit 1 Abbildung     

Polymers as reagents and catalysts. part x. Halogenations of acetophenone and 1,3-diketones with polymer-supported reagents

A crosslinked copolymer of styrene and 4-vinylpyridine (40-43% of monomer units) was reacted with hydrogen iodide to give a polymer containing pyridinium iodide residues. Reaction of this with chlorine in chloroform at 0° gave a polymer containing pyridinium tetrachloroiodate residues. In a similar manner but using methyl iodide in place of hydrogen iodide, crosslinked polymers containing N-methylpyridinium iodide and N-methylpyridinium tetrachloroiodate residues were prepared. The latter contained up to three chlorine molecules per iodine atom. Both reagents reacted with acetophenone, thus forming iodomethyl-phenyl ketone ($\text{4}$) and chloromethyl-phenyl ketone ($\text{5}$), the ratios depending on the reagent used and the reaction time. Chlorinations of 5,5-dimethyl cyclohexane-l,3-dione and indane-1,3-dione with polymer-supported reagent ($\text{2}$) resulted in the formation of geminal dichlorides in high yields.     

Halofluorination. Part II. bromofluorination of arylcyclohexenes

Bromofluorination of 1-phenylcyclohexene with N-bromosuccinimide-hydrogen fluoride-pyridine in ether proceeds with Markovnikov-type regioselectivity. The reaction is stereospecific anti. Bromofluorination of 2-phenyl-3-bromocyclohexene results in the formation of $\text{r}$-1-bromo, $\text{t}$-2-fluoro-2-phenyl, $\text{t}$-3-bromocyclohexane.     

Pyridazines. XXXVIII. Pyrrolo[1,2-b] pyridazines and 4H-4a,7b-diazacyclopent[cd] indenes

Pyrrolo[1,2-b] pyridazines have been prepared and investigated for electrophilic substitutions. Depending on the electrophile and reaction conditions, mono, di, tri or tetrasubstituted derivatives were formed. Some investigations are reported also for the related 4H-4a,7b-diazacyclopent[cd]-indenes.