An improved residue analytical method for phenylurea herbicides

Summary An improved HPLC method with electrochemical detection is applied to the determination of phenyl urea herbicide residues in crops. The analysis includes extraction and hydrolysis with NaOH, clean-up by steam distillation and partition into methanol/HCl and quantitation of the aniline by HPLC with 2-column switching technique and amperometric detection.     

Diphenylamin im DC-Flie?mittel als universelles Detektionsmittel

Ohne Zusammenfassung

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Diphenylamine in the mobile phase as a universal detection reagent in TLC

     

Calculation of one bond C,C coupling constants as a product of two empirical structure-relied factors

Empirical factors I(C) have been evaluated from experimental ¹J(C,C) data for a variety of structural fragments. It is also shown how I(C) factors can be obtained from ¹J(C,H) or from Malinowski's ξ increments. The product of such I(C) values reproduces ¹J(C,C) for very different combinations of carbon fragments.     

Sur la composition de l'arôme de tomate

A gas-chromatographic investigation of tomato aroma has revealed 46 components of which 32 are new. The isolation and identification of 2-isobutyl-thiazole, substance for the first time found in a natural aroma, are given in detail.     

γ‐Azaproline Confers pH Responsiveness and Functionalizability on Collagen Triple Helices

Proline derivatives bearing substituents at Cγ are valuable tools for biological and materials investigations. However, the stereochemistry at Cγ can produce undesired steric or stereoelectronic interactions. Here, we introduce γ‐azaproline (γ‐azPro), which lacks a stereogenic center at Cγ, as a pH‐responsive and functionalizable proline analogue that can adapt to its environment. Conformational analyses by NMR spectroscopy and DFT calculations revealed that the imidazolidine ring of γ‐azPro is flexible. Incorporation of γ‐azPro into collagen model peptides (CMPs) produced pH‐responsive triples helices and triple helices that can be easily functionalized.     

Lipophilic Tartaric Acid Esters as Enantioselective Ionophores

Tartaric acid esters with lipophilic alcohol moieties can discriminate between enantiomeric ammonium ions such as norephedrinium ions. Quantitative results were obtained by partitioning the components between water and 1, 2-dichloroethane. The stereoselectivity was characterized by the free energy difference of the partition process (ΔΔG). Diamond-lattice sectors were used to construct models of the (unstable) lipophilic ester/ammonium salt complexes from X-ray structures of the individual components (esters and ammonium salts). These models can be used to interpret the effect of structure and configuration of the alcohol moiety on the stereoselectivity and enantioselectivity towards 1-phenyl-2-amino-1-propanol (norephedrine) salts.     

Selenium-assisted nucleic acid crystallography: use of phosphoroselenoates for MAD phasing of a DNA structure

The combination of synchrotron radiation and a variety of atoms or ions (either covalently attached to the biomolecule prior to crystallization or soaked into crystals) that serve as anomalous scatterers constitutes a powerful tool in the X-ray crystallographer's repertoire of structure determination techniques. Phosphoroselenoates in which one of the nonbridging phosphate oxygens in the backbone is replaced by selenium offer a simplified means for introducing an anomalous scatterer into oligonucleotides by conventional solid-phase synthesis. Unlike other methods that are used to derivatize DNA or RNA by covalent attachment of a heavy atom (i.e., bromine at the C5 position of pyrimidines), tedious synthesis of specialized nucleosides is not required. Introduction of selenium is readily accomplished in solid-phase oligonucleotide synthesis by replacing the standard oxidation agent with a solution of potassium selenocyanide. This results in a diastereomeric mixture of phosphoroselenoates that can be separated by strong anion-exchange HPLC. As a test case, all 10 DNA hexamers of the sequence CGCGCG containing a single phosphoroselenoate linkage (PSe) were prepared. Crystals were grown for a subset of them, and the structure of [d(C(PSe)GCGCG)](2) was determined by the multiwavelength anomalous dispersion technique and refined to 1.1 A resolution.