Green method for ultrasensitive determination of Hg in natural waters by electrothermal-atomic absorption spectrometry following sono-induced cold vapor generation and ‘in-atomizer trapping’

Sono-induced cold vapor generation (SI-CVG) has been used for the first time in combination with a graphite furnace atomizer for determination of Hg in natural waters by electrothermal-atomic absorption spectrometry after in situ trapping onto a noble metal-pretreated platform (Pd, Pt or Rh) inserted into a graphite tube. The system allows ‘in-atomizer trapping’ of Hg without the use of conventional reduction reactions based on sodium borohydride or tin chloride in acid medium for cold vapor generation. The sono-induced reaction is accomplished by applying ultrasound irradiation to the sample solution containing Hg(II) in the presence of an organic compound such as formic acid. As this organic acid is partly degraded upon ultrasound irradiation to yield CO, CO₂, H₂ and H₂O, the amount of lab wastes is minimized and a green methodology is achieved.     

Thin‐Film Infrared Spectroscopy of Acetonitrile

Acetonitrile and [D₃]acetonitrile in the vicinal region of a planar AgX fiber contain linear dipole–dipole linked oligomers as shown by 1) comparison of infrared band intensity ratios in the gaseous and condensed phases and 2) remarkable plots of absorbance (C? N stretch) versus time during evaporation from an AgX planar fiber element. The plots (CH₃CN 2252 cm^?1, CD₃CN 2262 cm^?1) reveal the presence of octamers, hexamers, tetramers, and dimers along with some heptamer, trimer, and monomer structures. A novel isotope effect arises from the somewhat smaller size of the CD₃CN resulting in an increase in the CN band intensity. The organized oligomers may be termed pseudocrystals and are the main components responsible for absorption intensity in the infrared spectrum of acetonitrile, on the AgX planar fiber or in an IR cell.     

Slow water diffusion in micellar solutions

Slowly diffusing water molecules were found by quasi-elastic neutron scattering (QENS) in a sodium dodecyl sulfate (SDS) micellar solution, and both their diffusion coefficient (4.33 x 10(-6) cm2 x s(-1)) and mole fraction (0.057) were determined. After successfully checking the mean slowing down of solvent molecules by the gradient compensated stimulated spin-echo (GCSTE) pulse sequence NMR method, a similar effect was observed with this technique in the solvent phase of dodecyl trimethylammonium bromide (DTAB) and differing chain length (X = 12, 20, 30, and 40) ethoxylated nonyl phenol (9NX) micellar systems. Following the literature, the experimental results are qualitatively explained by assuming that, apart from ionic hydration, H-bonds may form between the solvent molecules and the O or N atoms present in the hydrophilic (head)groups of the micelle-forming monomers.     

Novel method for the preparation of anionic surfactant-selective electrodes

A simple one-step synthesis is described for the functionalization of poly(vinyl chloride) used for the preparation of anionic surfactant-selective membrane electrodes. The method is based on the nucleophilic substitution of a fraction of the chlorine atoms bound to the poly(vinyl chloride) backbone by trimethylamine. The prepared slightly charged polymer gave rise to high-quality surfactant-selective electrode membranes, which had a Nernstian response, short response time, and appropriate stability.     

Equations of state of mixtures of hard dumbbells

Two ways to predict pVT behavior of hard-dumbbell mixtures in the fluid region are proposed. These are adaptations of the hard convex body equation devised by Boublik and an extension of the first Barker-Henderson perturbation theory. Calculated compressibility factors show good agreement with the ideal mixing assumption and yield a useful equation of state.     

Deazapurine solid-phase synthesis: construction of 3-substituted pyrrolo[3,2-d]pyrimidine-6-carboxylates on cross-linked polystyrene bearing a cysteamine linker

The first solid-phase methodology for the preparation of pyrrolo[3,2-d]pyrimidines is presented. Merrifield resin bearing a cysteamine "traceless" linker was treated with 4-oxo-N-(PhF)proline benzyl ester (10; PhF = 9-(9-phenylfluorenyl)) to provide resin-bound aminopyrrole 20, which was treated with ethyl, phenyl, 4-phenoxyphenyl, and 2,4-dimethoxyphenyl isocyanates to furnish resin-bound ureidopyrroles 21a-d. Resin-bound pyrrolo[3,2-d]pyrimidines 22a-d were then obtained by acylation of 21 using trichloroacetyl chloride in dioxane followed by treatment with Cs2CO3 in DMF. Cleavage of pyrrolo[3,2-d]pyrimidines 22a-d from the resin was achieved in two steps, by oxidation of the sulfur to the sulfone followed by beta-elimination in the presence of t-BuONa. Four pyrrolo[3,2-d]pyrimidines, 24a-d, with different alkyl and aryl substituents at the N3 pyrimidine nitrogen, were thus obtained in overall yields of 42-50% and purities of 90-100%.     

Synthesis of Functionalized Spiro[cycloalkanono-2,3'-thiophenes] via Tandem Conjugate Addition-Cyclization of 3-Oxoacid Thioanilides to Nitroalkenes

A convenient method is described for the synthesis of functionalized spiro[cycloalkanono-2,3-thiophenes] by treatment of cyclic 3-oxoacid thioanilides with -nitrostyrenes. Reaction of the obtained products with acetic anhydride yielded the corresponding oxime acetates.     

Reference-free NOE NMR analysis

Nuclear Overhauser Effect (NOE) methods in NMR are an important tool for 3D structural analysis of small molecules. Quantitative NOE methods conventionally rely on reference distances, known distances that have to be spectrally separated and are not always available. Here we present a new method for evaluation and 3D structure selection that does not require a reference distance, instead utilizing structures optimized by molecular mechanics, enabling NOE evaluation even on molecules without suitable reference groups.

A quantitative Nuclear Overhauser Effect (NOE) analysis approach that avoids the use of and internal reference distance to perform molecular configuration selection.     

Quantum chemical study of several monocyclic complex β‐lactam C‐3, C‐4, and N‐derivatives,and β‐ring model molecules

A quantum chemical study of several complex monocyclic 4‐benzoyl‐4‐phenyl‐β‐lactam derivatives was carried out using cyclobutane, azetidine, 2‐azetidinone, 1‐methyl‐2‐azetidinone, and 3‐methyl‐2‐azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the β‐lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform–infrared (FT‐IR) spectra of the β‐lactam monocyclic derivatives were recorded in CCl₄, C₆H₆, and CHCl₃ solutions. The normal vibrations of the β‐lactam ring in the model compounds were characterized and used in the analysis of the β‐ring of more complex derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002