Microcoulometric determination of total organochlorine pesticide and polychlorinated biphenyl residues in grey seal (Halichoerus grypus) blubber.

The determination of iron(III) with thiocyanate by means of sample injection into a chamber in a closed loop system of circulating reagent is described. Restitution of the absorbance to baseline by ligand exchange and by a redox process in the presence of iodide is discussed, together with some kinetic aspects of the decolorization reaction responsible for the return to the baseline. The iron content of the samples is deduced from the height of the generated transient signal, which is directly proportional to the iron(III) content. As many as 350 determinations/h can be processed when ligand exchange is used and 120/h when iodide is used for baseline restitution. Sample injection techniques of this type are particularly useful in industrial processes and quality control, and environmental monitoring, since they result in a decrease in operating cost and time.     

NMR evidence of pentaoxo organosilicon complexes in dilute neutral aqueous silicate solutions

Silicon-29 NMR spectra of a neutral, dilute aqueous silicic acid solution, with a pH and Si concentration typical of soil solutions, reveal that a significant fraction of the silicon is incorporated in two five-coordinated organosilicon complexes when sodium gluconate is present.     

A kinetic study of the displacement reaction between nickel(II) and zinc-ethylenediaminetetraacetate by a radiometric method

A radiometric study of the kinetics of the displacement reaction between nickel(II) and⁶⁵Zn-labeled zinc salt of ethylenediaminetetraacetic acid, which was previously used by the authors for the analysis of trace quantities of nickel, has been carried out under varying conditions of temperature, pH etc. The above reaction was confirmed to be first order with respect to both Ni²⁺ and to^*ZnEDTA. The overall reaction rate constant, k_f, has been shown to be inversely proportional to the concentration of Zn²⁺ and directly proportional to the concentration of H⁺. From the dependence of the rate constant on the concentration of Zn²⁺ and H⁺ a three-step mechanism is proposed for the above reaction. The values for E_a, ΔH^‡, ΔG^‡ and ΔS^‡ for the overall reaction have been computed from the experimental data.     

Nitronate anion recognition and modulation of ambident reactivity by hydrogen-bonding receptors

Nitronate anions were shown to form complexes in DMSO with hydrogen-bonding receptors such as 1,3-dimethylthiourea 1 (K(a)= 120M(-1)) and bicyclic guanidinium 2 (K(a) = 3200M(-1)). A ditopic bis-thiourea exhibited increased association with substrates, that contained either two nitronates (K(a)= 7000M(-1)) or a combination of nitronate and carboxylate (K(a)=7200M(-1)). Complexation of nitronate resulted in a change in the ambident reactivity during alkylation with p-nitrobenzyl bromide. The predominant reaction pathway was shifted from oxygen alkylation to carbon alkylation as receptor binding strength increased. Kinetic analysis indicated an overall inhibition of nitronate reactivity, and this suggests that greater suppression of the oxygen pathway allows carbon alkylation to predominate.     

Direct observation of the spinorbit splitting in the Ar+ ion with a diode laser

The ²P_{$\text{1}\text{2}$}-²P_{$\text{3}\text{2}$} fine structure transition in the ground (3p⁵) state of the argon atomic ion. Ar⁺, has been detected in absorption using a tunable diode laser. The transition was calibrated against water vapour lines and measured to be 1431.644 ± 0.001 cm^?1 in ⁴⁰Ar⁺ and 3.0 × 10^?3 cm^?1 (91 MHz) smaller in ³⁶Ar⁺.     

Physical Sorting of Coded Documents

A large number of coded items such as bank checks are initially mixed randomly. It is desired to sort them into k categories using a sorting device with m pockets (m < k). Several possible objectives are noted, and a new criterion oriented to the average time until categories are sorted out is analyzed. A simple strategy is shown to minimize the average number of sorting passes that elapse until an item is sorted out.     

Peracetylated sugar derivatives show high solubility in liquid and supercritical carbon dioxide

[structure: see text] Acetylated sugars derivatives exhibit high solubility in liquid and supercritical carbon dioxide (scCO(2)). Peracetylated sorbitol and beta-D-galactose are soluble under mild conditions in scCO(2), high pressures are required to dissolve peracetylated beta-cyclodextrin, and peracetoxyalkyl chains impart CO(2)-solubility to amides.     

Stereochemical diversity in chiral ligand design: discovery and optimization of catalysts for the enantioselective addition of allylic halides to aldehydes

[reaction: see text] We have identified a new set of stereochemically diverse oxazoline ligands derived from simple amino acids that promote the Cr-catalyzed enantioselective addition of allylic halides to aldehydes in up to 95% ee. The Cr-catalyzed allylation using ligand 1d is rather insensitive to the nature of the allylic bromide (crotyl, allyl, and methallyl) in that >90% ee is observed for all three bromides evaluated in the addition to benzaldehyde.     

A ruthenium-dihydrogen putative intermediate in ketone hydrogenation

The compound fac-[Ru((R)-BINAP)(H)(2-PrOH)3]+ (6) (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) reacts with (R,R)-dpen (dpen = 1,2-diphenylethylenediamine) under H2 at -60 degrees C in 2-PrOH-d8/CD2Cl2 to generate the cationic dihydrogen putative intermediate trans-[Ru((R)-BINAP)(H)(eta2-H2)((R,R)-dpen)]+ (2') without H-D exchange between the hydrogen ligands and the solvent. A 1H NMR study concludes that the dihydrogen ligand in 2' does not protonate 2-PrOH to a catalytically significant extent, and that 2' requires an added base or hydride source to be an active catalyst.