Routine determination of major anions in atmospheric aerosols by capillary electrophoresis

Capillary electrophoresis (CE) with indirect UV detection utilizing a pyromellitate-based electrolyte was used for the routine analysis of major anions in atmospheric aerosols collected on filters with high-volume (Hi-Vol) samplers. The long-term reliability of the CE system was checked over an 8-month period during which over 2900 samples were analyzed. In addition, approximately 1100 samples were analyzed in parallel by ion chromatography (IC). It has been shown that acceptable analytical performance can be routinely obtained. The agreement between the CE and IC results is good, generally better than 20% at concentrations larger than 1 mg l⁻¹.     

Kinetics and mechanism of the first aquation stage for the [Cr(pic)3]0 and [Cr(pic)2(OH)]2 0 complexes in HClO4 solutions

Aquation of [Cr(pic)₃]⁰ and [Cr(pic)₂(OH)]₂ ⁰ in aqueous HClO₄ solutions leads to formation of the common product – [Cr(pic)₂(H₂O)₂]⁺. The first, reversible stage, the ring opening via Cr—N bond breaking in [Cr(pic)₃]⁰ is followed by the second, rate-determining step – one-end bonded pic ligand liberation. In the case of the [Cr(pic)₂(OH)]₂ ⁰ complex, the first faster stage produces the singly bridged dimer, which undergoes cleavage into the parent monomers in the second, much slower step. The subsequent aquation of [Cr(pic)₂(H₂O)₂]⁺ is extremely slow and leads to [Cr(pic)(H₂O)₄]²⁺ formation, which practically does not undergo further ligand substitution under the conditions applied. Kinetics of the first aquation stage for [Cr(pic)₃]⁰ and of the second step for [Cr(pic)₂(OH)]₂ ⁰ were studied spectrophotometrically in the 0.1–1.0 M HClO₄ range at I = 1.0 M. The observed pseudo-first order rate constant for [Cr(pic)₃]⁰ decreases with [H⁺] increase according to the rate law: k _obs = k ₁ + k _–1 Q ₁/[H⁺], where k ₁ and k _–1 are the rate constants of the forward and the reverse processes in the unprotonated substrate and Q ₁ is the protonation constant of the pyridine nitrogen atom. In the case of the [Cr(pic)₂(OH)]₂ ⁰ complex, the rate for the singly bridged dimer cleavage does not depend on [H⁺]. The activation parameters for the chelate-ring opening in [Cr(pic)₃]⁰ and for the singly bridged dimer cleavage have been determined and discussed. Some kinetic data of the slow, second aquation stage for the [Cr(pic)₃]⁰ complex and of the fast, first aquation stage for the doubly bridged dimer have been studied; for both reactions the rate increases linearly with the increase in [H⁺].     

The complete 51V MAS NMR spectrum of surface vanadia nanoparticles on anatase (TiO2): vanadia surface structure of a DeNOx catalyst

The first observations of the complete manifold of spinning sidebands (ssbs) including both the central and satellite transitions in (51)V MAS NMR spectra of surface vanadia nanoparticles on titania in DeNO(x) catalysts are presented. (51)V quadrupole coupling and chemical shift anisotropy parameters for the dominating vanadia structure are determined from (51)V MAS NMR spectra recorded at 9.4 and 14.1 T. Based on correlations previously established between (51)V NMR parameters and crystal structure data for inorganic vanadates, the NMR data are consistent with vanadium in a distorted octahedral oxygen coordination environment for the so-called strongly bonded vanadia species on the surface. The investigation includes two vanadia-titania model catalysts and six industrial-type DeNO(x) catalysts.     

Thermal stability and degradation of starch derivatives

Thermal behaviour of different starch derivatives, i.e. starch esters and ethers having degree of substitution (DS) in the range of 0.02–0.18 were studied. Potato, maize and wheat starches were used. Measurements were carried out by coupled thermal analysis/ mass spectrometry method (STA-MS) in air atmosphere. The major DTG peak during the investigation for starch derivatives is observed below 300°C. The mass loss up to a temperature of 300°C is about 50%. The most abundant ions found areH₂O⁺ and CO₂ ⁺. For the studied starch derivatives with a low degree of substitution (DS<0.18) no correlation was found between thermal stability and the level of substitution regardless of the nature of substitution.     

Molecular recognition: comparative study of a tunable host-guest system by using a fluorescent model system and collision-induced dissociation mass spectrometry on dendrimers

Host-guest interactions between the periphery of adamantylurea-functionalized dendrimers (host) and ureido acetic acid derivatives (guest) were shown to be specific, strong and spatially well-defined. The binding becomes stronger when using phosphonic or sulfonic acid derivatives. In the present work we have quantified the binding constants for the host-guest interactions between two different host motifs and six different guest molecules. The host molecules, which resemble the periphery of a poly(propylene imine) dendrimer, have been fitted with an anthracene-based fluorescent probe. The two host motifs differ in terms of the length of the spacer between a tertiary amine and two ureido functionalities. The guest molecules all contain an acidic moiety (either a carboxylic acid, a phosphonic acid, or a sulfonic acid) and three of them also contain an ureido moiety capable of forming multiple hydrogen bonds to the hosts. The binding constants for all 12 host-guest complexes have been determined by using fluorescence titrations by monitoring the increase in fluorescence of the host upon protonation by the addition of the guest. The binding constants could be tuned by changing the design of the acidic part of the guest. The formation of hydrogen bonds gives, in all cases, higher association constants, demonstrating that the host is more than a proton sensor. The host with the longer spacer (propyl) shows higher association constants than the host with the shorter spacer (ethyl). The gain in association constants are higher when the urea function is added to the guests for the host with the longer spacer, indicating a better fit. Collision-induced dissociation mass spectrometry (CID-MS) is used to study the stability of the six motifs using the corresponding third generation dendrimer. A similar trend is found when the six different guests are compared.     

Adsorption of lignite-derived humic acids on coal-based mesoporous activated carbons

The adsorption by a coal-based mesoporous activated carbon of humic acids (HAs) isolated from two Polish lignites was studied. For comparison, a commercial Aldrich humic acid was also included into this study. The differences in chemical structure and functional groups of HAs were determined by elemental analysis and infrared spectroscopy DRIFT. Two activated carbons used differed in terms of mesopore volume, mesopore size distribution, and chemical properties of the surface. The kinetics of adsorption of HAs have been discussed using three kinetic models, i.e., the first-order Lagergren model, the pseudo-second-order model, and the intraparticle diffusion model. It was found that the adsorption of HAs from alkaline solution on mesoporous activated carbon proceeds according to the pseudo-second-order model. The correlation coefficients were close to 1. The intraparticle diffusion of HA molecules within the carbon particle was identified to be the rate-limiting step. Comparing the two activated carbons, the carbon with a higher volume of pores with widths of 10-50 nm showed a greater removal efficiency of HA. An increase in the Freundlich adsorption capacity with decreasing carbon content of HA was observed. Among the HAs studied, S-HA shows characteristics indicating the highest contribution of small-size fraction. The S-HA was removed by both activated carbons to the highest extent. The effect of pH solution on the adsorption of HA was examined over the range pH 5.4-12.2. It was found that the extent of adsorption decreased with decreasing pH of the solution.     

Asymmetric conjugate addition of azide to α,β-unsaturated nitro compounds catalyzed by cinchona alkaloids

The cinchona alkaloid catalyzed asymmetric addition of azide to α,β-unsaturated nitro compounds giving optically active β-azido nitro compounds in high yields and with low enantioselectivity is presented. Subsequent modifications allow for the formation of chiral 1,2-diamines.     

Single crystal Raman study of potassium oxalate monohydrate,K2C2O4. H2O,and potassium oxalate monodeuterate,K2C2O4. D2O

Raman spectra of poly crystalline and single crystal K₂C₂O₄. H₂O and K₂C₂O₄. D₂O have been recorded at room temperature. From an earlier neutron diffraction study it is known that the space group is C⁶₂h. The water molecule occupies a C₂ site and the oxalate ion a C₁ site. The assigned water vibrations show small factor group splitting between g modes (Raman active) and u modes (IR active). The internal oxalate vibrations are found to have wavenumbers in good agreement with those reported from Raman studies of other oxalates.     

Synthesis and characterization of water-soluble phenylene-vinylene-based singlet oxygen sensitizers for two-photon excitation

[reaction: see text] The synthesis and characterization of water-soluble singlet oxygen sensitizers with a phenylene-vinylene motif is presented. The principal motivation for this study was to better understand specific features of a water-soluble molecule that influence the photosensitized production of singlet oxygen upon nonlinear, two-photon excitation of that molecule. To achieve water solubility, sensitizers were synthesized with ionic as well as nonionic substituents. In the ionic approach, salts of N-methylated pyridine, benzothiazole, and 1-methyl-piperazine moieties were used, as were aryl-substituted sulfonic acid moieties. In the nonionic approach, aryl-substituted triethylene glycol moieties were used. Selected photophysical properties of the compounds synthesized were determined, including singlet oxygen quantum yields. Of the molecules examined, the most efficient singlet oxygen sensitizers had triethylene glycol units as the functional group that imparted water solubility. Molecules containing the ionic moieties did not make singlet oxygen in appreciable yield nor did they efficiently fluoresce. Rather, for these latter molecules, rapid charge-transfer-mediated non-radiative processes appear to dominate excited state deactivation.     

Improved excitation schemes for multiple-quantum magic-angle spinning for quadrupolar nuclei designed using optimal control theory

We have investigated the use of optimal control theory for the design of improved multiple-quantum excitation schemes for the popular multiple-quantum magic-angle spinning NMR experiment for quadrupolar nuclei with half-integer quadrupolar spin. The advantage of the new low-power experiments, termed OCFASTER, is demonstrated by sensitivity improvements approaching 50% for 87Rb in RbClO4 and RbNO3 as compared to FASTER and standard strong-pulse excitation schemes.