Observations on a dropping-mercury electrochemical detector for flow-injection analysis and HPLC

An electrochemical detector cell having a dropping-mercury working electrode and an Ag/ AgCl reference electrode is examined with reference to applications in flow-injection analysis and high-performance liquid chromatography. The working electrode, fed by a horizontal capillary, is capable of delivering mercury at fast dropping rates which can be varied by a control device in the cell. Examples of application to inorganic and organic electroreducible species are considered and advantages and limitations relative to other electrochemical detector devices are discussed.     

Automatic spectrophotometric method for the determination of europium in mixtures with yttrium and other lanthanides

Summary An automatic spectrophotometric method for the determination of europium in the presence of yttrium and other lanthanides is described. The method is based on a modification of a recently devised manual procedure consisting of the reduction, on a Jones reductor, of europium(III) to europium(II) which is used to reduce molybdophosphate to a molybdenum blue. The method is capable of analysing solutions containing 10–400 g of europium per ml at a rate of 20 samples per hour. There is no interference from yttrium or other lanthanides and the method is suitable for application to europium determination after a group separation. When applied to mineral samples coefficients of variation between 2.5 and 3.8% were obtained.

---

Automatisches spektralphotometrisches Verfahren zur Bestimmung von Europium im Gemisch mit Yttrium und anderen Lanthaniden

Zusammenfassung Das Verfahren stellt eine Modifikation eines kürzlich ausgearbeiteten manuellen Verfahrens dar, das auf Reduktion (Jones Reduktor) zu Eu(II) und Reaktion mit Molybdophosphat zu Molybdänblau beruht. 20 Proben mit 10–400 g Eu/ml können je Stunde analysiert werden. Yttrium und andere Lanthanide stören nicht. Die Molybdänblaureaktion störende Substanzen können zuvor durch eine Gruppentrennung beseitigt werden. Bei der Analyse von mineralischen Proben wurden Variationskoeffizienten zwischen 2,5 und 3,8% erhalten.

     

Some Results Obtained by Application of the LLT Algorithm

We determine the v-decomposition numbers d _μλ(v) for μ a partition with at most three parts. We use this information to compute the composition factors of the Specht modules of the Hecke algebra ?₀ = ?_{?, ω}( _n ) which correspond to partitions with at most three parts.     

Tetrameric molecular bowl assembled from glycoluril building blocks

Glycoluril derivative--whose bulky Ph-C[triple bond]C- substituents prevent formation of H-bonded tapes--undergoes solvent dependent assembly in the crystal; a tetrameric molecular bowl is formed by R(24) H-bonding interactions from CH(2)Cl(2) whereas DMF results in H-bond dimerization followed by oligomerization via C-H...pi interactions.     

Self-sorting molecular clips

We report the synthesis and characterization of 12 C-shaped methylene-bridged glycoluril dimers (1-12) bearing H-bonding groups on their aromatic rings. Compounds 1, 2, (+/-)-4a, (+/-)-5, (+/-)-7, and 8 form tightly associated homodimers in CDCl3, due to the combined driving force of pi-pi and H-bonding interactions. Compounds 2, (+/-)-5, and 8, having disparate spatial distribution of their H-bonding groups, display the ability to efficiently distinguish between self and nonself even within three-component mixtures in CDCl3. When the spatial distributions of the H-bonding groups of the molecular clips are similar (e.g., 1 and 2), a mixture of homodimers and heterodimers is formed. The effect of various structural modifications (e.g., chirality, side chain steric bulk, number and pattern of H-bonds) on the strength of self-assembly and the fidelity of self-sorting are presented. On the basis of these results we prepared self-sorting systems comprising three (e.g., 1, (+/-)-5, and (+/-)-7) and even four ( 2, (+/-)-5, 9, and 10) components. The potential of molecular clips 1-12 as robust, functionalizable, self-sorting modules to control the noncovalent interaction network in systems chemistry studies is described.     

Refolding foldamers: triazene-arylene oligomers that change shape with chemical stimuli

We describe the preparation of five triazene-arylene oligomers (3, 4, 7, 8, and 11) and investigations of their folding properties in aqueous solution. These oligomers contain four 2-fold rotors and populate a conformational ensemble comprising at least 10 states. Extensive 1D and 2D NMR studies as well as X-ray crystallography establish that the presence of three members of the cucurbit[n]uril family (CB[n]), CB[10], CB[7], and CB[8], results in the selective population of the (a,a,a,a)-, (a,s,s,a)-, and (a,a,a,s)-conformers. As a result of the high affinity and highly selective binding properties of the CB[n] family, it is possible to fold a single foldamer strand (3) into the CB[8].(a,a,a,s)-3 conformer by the addition of CB[8], then unfold and refold it into the CB[7].(a,s,s,a)-3.CB[7] conformer by addition of CB[7] and 3,5-dimethylaminoadamantane (17), then unfold and refold it again into the CB[10].(a,a,a,a)-3 conformer by addition of CB[10].CB[5] and aminoadamantane (18). The transformation of CB[8].(a,a,a,s)-3 into CB[7].(a,s,s,a)-3.CB[7] proceeds through the intermediacy of CB [8].(a,a,s,a)-3.CB[7], which enhances the rate of dissociation of strand 3 from CB[8].     

Discovery of beta-LnNiSb3 (Ln = La, Ce): crystal growth, structure, and magnetic and transport behavior

A new polymorph of CeNiSb3 has been grown from a Sn flux and characterized by single-crystal X-ray diffraction. beta-CeNiSb3 crystallizes in the orthorhombic space group Pbcm (No. 57) with Z = 8. The unit cell parameters are a = 12.9170(2) A, b = 6.1210(5) A, c = 12.0930(6) A, and V = 956.13(9) A3. Its layered structure contains structural motifs similar to that of the first form of CeNiSb3 and consists of Ce atoms inserted between anionic layers of nearly square infinity2[Sb] nets and distorted infinity2[NiSb2] octahedra. We report the synthesis, magnetization, electrical resistivity, and specific heat of the new form of CeNiSb3 and compare the structures and physical properties of both polymorphs.