17O MQMAS NMR studies of Na-A and Ca-A

We report, for the first time, 17O MQMAS and 17O/23Na double resonance NMR studies on calcium-exchanged zeolite sodium-A; the results show that the isotropic shifts of the framework sites are strongly affected by factors including the hydration level and nature of the charge-balancing cations.     

Die Bestimmung des Phosphors in Bronzen und anderen Legierungen

Ohne Zusammenfassung     

Emitting-state displacements in ligand-centered vibrational modes in the trans-[OsO2(NCS)4]2- complex determined from near-infrared luminescence spectroscopy

Low-temperature luminescence spectra from three salts of the trans-[OsO(2)(NCS)(4)](2-) complex exhibit highly resolved vibronic structure in both metal-ligand high-frequency O=Os=O (885 cm(-1)) and lower-frequency Os-N(CS) (255 cm(-1)) symmetric stretching modes as well as in a ligand-centered CS stretching mode (858 cm(-1)). Band maxima range from 10000 to 12000 cm(-1), and spectra contain irregular frequency intervals that correspond to transitions from more than one origin and phonon sidebands. Experimental band shapes are distinctly different for all three compounds and are calculated assuming harmonic potential energy surfaces for both the ground and emitting states. Normal-coordinate offsets along all displaced vibrational modes are determined and compared for the three compounds. The analyses reveal emitting-state displacement of high-frequency ligand-centered (CS) and metal-ligand (O=Os=O) symmetric stretching modes, leading to observed high-frequency intervals (855-880 cm(-1)) that do not match any frequencies determined from ground-state Raman spectra. The values for the high-frequency normal-coordinate offsets, DeltaQ(O=Os=O) and DeltaQ(CS), were found to be on the order of 0.06 A. Offsets along the 255 cm(-1) Os-N mode varied noticeably between the three compounds and were largest for the compound with the largest value of DeltaQ(CS).     

Effect of surface composition on the adsorption of photosystem I onto alkanethiolate self-assembled monolayers on gold

We have used self-assembled monolayers (SAMs) prepared from omega-terminated alkanethiols on gold to generate model surfaces and examine the effect of surface composition on the adsorption of Photosystem I (PSI), stabilized in aqueous solution by Triton X-100. Triton-stabilized PSI adsorbs to high-energy surfaces prepared from HO- and HO2C-terminated alkanethiols but does not adsorb to low-energy surfaces. The inhibition of PSI adsorption at low-energy surfaces is consistent with the presence of a layer of Triton X-100 that adsorbs atop the hydrophobic SAM and presents a protein-resistant poly(ethylene glycol) (PEG) surface. While the presence of the PEG surface prevents the adsorption of PSI, the displacement of the inhibiting layer of Triton X-100 by dodecanol, a more active surfactant, greatly enhances the adsorption of PSI. This inhibiting effect by Triton X-100 can be extended to other protein systems such as bovine serum albumin.     

Dynamic effects in MAS and MQMAS NMR spectra of half-integer quadrupolar nuclei: calculations and an application to the double perovskite cryolite

Dynamic processes such as chemical exchange or rotations between inequivalent orientations can affect the magic-angle spinning (MAS) and the multiple-quantum (MQ) MAS NMR spectra of half-integer quadrupolar nuclei. The present paper discusses such dynamic multisite MAS and MQMAS effects and applies them to study the dynamic processes that occur in the double perovskite cryolite, Na3AlF6. Dynamic line shape simulations invoking a second-order broadening of the central transition and relying on the semiclassical Bloch-McConnell formalism for chemical exchange were performed for a variety of exchange models possessing different symmetries. Fitting experimental variable-temperature cryolite 23Na NMR data with this formalism revealed that the two inequivalent sodium sites in this mineral undergo an exchange characterized by a broad distribution of rates. To further assess this dynamic process a variety of 27Al and 19F MAS NMR studies were also undertaken; quantitative 27Al-19F dipolar coupling measurements then revealed a dynamic motion of the AlF6 octahedra that were qualitatively consistent with predictions stemming from molecular dynamic simulations on this double perovskite.     

Liquid chromatography-electrospray ionization isotope dilution mass spectrometry analysis of paraquat and diquat using conventional and multilayer solid-phase extraction cartridges

The performance of alkyl-silica sorbent packed solid-phase extraction (SPE) cartridges and a mixed-mode, polymeric sorbent packed SPE cartridge (resin SPE cartridge) were evaluated for the sample preparation of paraquat and diquat in environmental water and vegetation matrices. Also the recoveries of the native and 2H-labeled paraquat and diquat were correlated to validate that the 2H-labeled species can be used for the isotopic dilution mass spectrometry (IDMS) analysis of paraquat and diquat. The results show that the extraction efficiency of alkyl-silica SPE is dependent on the carbon loading of the sorbent and deteriorates with an increasing sample pH. The resin SPE cartridge required no pH adjustment and showed excellent correlation between the native and 2H-labeled species, therefore, allowing us to develop the first liquid chromatography-electrospray ionization IDMS analytical method for the analysis of paraquat and diquat in environmental water and vegetation matrices. Method detection limits derived using standard EPA protocol were 0.2 and 0.1 microg/l for paraquat and diquat in water matrices, and 0.02 and 0.01 microg/g in vegetation matrices, respectively.