Fast atom bombardment mass spectrometry of carbobenzyloxy-protected amino acids and peptides

The positive fast atom bombardment (FAB) mass spectra of 15 N-carbobenzyloxy derivatives of α-amino acids are presented together with those of some synthetic peptides containing other widely employed protecting groups. The data obtained allow a fragmentation pattern to be established for the N-carbobenzyloxy moiety and to obtain detailed structural information on the main fragment ions. A study of the ion current ratio vs. time pattern shows that important fragments derive from the parent protonated molecule through FAB-induced condensed-phase reactions.     

Carbon-13 magnetic resonance study of lanthanide-substituted muscle calcium binding parvalbumins

High resolution natural abundance carbon-13 NMR has been used previously to examine molecular motions and conformational transitions in the muscle calcium binding parvalbumins isolated from mirror carp. [S. J. Opella, D. J. Nelson, and O. Jardetzky, J. Chem. Phys. 64 , 2533 (1976) and D. J. Nelson, S. J. Opella, and O. Jardetzky, Biochemistry 15 , 5552 (1976).] The carbon-13 NMR spectrum of parvalbumin typically reveals the presence of a number of well-resolved resonances from single-carbon sites in the protein. Since accurate assignment of these resonances to specific carbon atoms in the protein is essential before these resonances can be employed as probes of local conformational events, an investigation of the origin of a number of single-carbon resonances has been performed. Carbon-13 NMR on Tb(III)- and Yb(III)-substituted parvalbumin is the principal spectroscopic technique employed; however, results from terbium fluorescence spectroscopy, γ-ray scintillation spectroscopy, and x-ray difference Fourier analysis all contribute to single-carbon site assignment. The principal conclusions drawn from the combined spectroscopic results are that: (1) the downfield carboxyl resonance at 184.6 ppm, previously attributed to Glu-81, whose carboxyl group is involved in an internal ionic bond, originates rather from a carboxyl function coordinating the solvent exposed metal ion, (2) the carbonyl resonance at 168.9 ppm arises from Lys-96, as was previously suggested; and (3) the 11.2 ppm resonance derives from the δ-methyl carbon of Ile-97, a resonance assignment that could not be made previously.     

Origin of arsenic pollution in Southwest Tuscany: comparison of fluvial sediments

The Colline Metallifere in SW Tuscany are characterized by strong anomalies in arsenic concentrations and distribution. The area is sparsely populated and largely wild, though it has been subject to human impact due to mining and metal processing since Etruscan and Roman times. In the Middle Ages it was exploited intensively for silver and copper. Until 1995, pyrite (FeS2) was mined and roasted to produce sulphuric acid and iron. Hypotheses based on geological and mineralogical factors formulated in the last 20 years have failed to explain the peculiar distribution of arsenic in the Colline Metallifere. Here we report preliminary results of widespread sampling and analysis of the fluvial sediments of rivers originating in this mining area. The data was analysed in relation to the archaeological features of the area, since the presence of ancient mining and ore processing sites can shed light on the peculiar distribution of arsenic. Comparison of data from two rivers and their respective contaminated and uncontaminated coastal lagoons also clarified the general mechanisms of arsenic mobility, pinpointing the source of arsenic contamination. The study methods also promise to be useful for discovering unknown archaeological sites.     

Study on the single crystal growth of concentration gradient Ce:YAP rod and the dopant concentration dependence on the scintillation properties

Micro-pulling down (μ-PD) method allows to prepare single crystals quickly and relatively inexpensively. Since it is a melt growth and taking into account segregation phenomena, the μ-PD method allows also to obtain single crystals characterized by dopant concentration gradients. Especially, taking the advantage of the grown crystal high aspect ratio, it allows to prepare crystalline samples with variable and wide range concentrations of dopants. These samples can help in understanding the correlation between dopant concentration and luminescence properties.     

Gas-phase ion chemistry of BF3/HN3 mixtures: the first observation of [BFnNxHn-1]+ (n=1, 2; x=1, 3) ions

The gas-phase ion chemistry of BF3/HN3 mixtures was investigated by the joint application of mass spectrometric techniques and theoretical methods. The addition of BF2+ to HN3 led to the first observation of [BFnNxHn-1]+ (n=1, 2; x=1, 3) ions in the gas phase. Consistent with collisionally activated dissociation (CAD) mass spectrometric results, theoretical calculations performed at the B3LYP and CCSD(T) levels identified the F2B-NH-N2+, F2B-NH+, FB-N3+, and FBN+ ions as the most stable isomers on the [BFnNxHn-1]+ (n=1, 2; x=1, 3) potential energy surfaces. The F2B-NH+ and FBN+ ions, characterized by a triplet ground state, are formed from F2B-NH-N2+ and FB-N3+ through a spin-forbidden decomposition process. It is worth noting that F2BNH-N2+ is the protonated form of difluoroboron azide, BF2N3, a neutral molecule that has never been experimentally detected. The application of theoretical and experimental methods allowed evaluation of the unknown PA of BF2N3, whose best theoretical estimate 171.2+/-3 kcal mol-1 at the CCSD(T) level is comparable with the experimental one, 170.1+/-3 kcal mol-1. The main interest of all these ionic species is represented by their possible application in boron nitride (BN) physical and chemical vapor deposition.     

Monitoring of fluid motion in a micromixer by dynamic NMR microscopy

The velocity distribution of liquid flowing in a commercial micromixer has been determined directly by using pulsed-field gradient NMR. Velocity maps with a spatial resolution of 29 microm x 43 microm were obtained by combining standard imaging gradient units with a homebuilt rectangular surface coil matching the mixer geometry. The technique provides access to mixers and reactors of arbitrary shape regardless of optical transparency. Local heterogeneities in the signal intensity and the velocity pattern were found and serve to investigate the quality and functionality of a micromixer, revealing clogging and inhomogeneous flow distributions.     

Characterization of Al(III) complexes with hematein in artistic alum logwood inks

The complexes between Al(III) and hematein, the main coloring matter in alum logwood inks, were characterized by Raman and ²⁷Al NMR (nuclear magnetic resonance) spectroscopies. Raman spectra of the crystallized complexes and of the compounds applied on a paper substrate are presented and assigned based on published data for the parent compounds. These Raman spectra show that the coordination of the hematein to the Al(III) ions takes place in both cases through the carbonyl and hydroxyl groups in the molecule, and that the aromatic rings are also involved in the interaction. The Raman spectra of the pure hematein–Al(III) complexes were found to be consistent with those recorded for a logwood ink prepared following a late 19th century recipe, using logwood chips instead of pure hematein, and applied on a paper substrate. These spectra can be used as references for the noninvasive identification of the compounds in works of art. ²⁷Al solid‐state NMR showed that the coordination of the Al(III) atoms in the crystallized powder is predominantly octahedral, while when applied on a paper substrate the colorant is present mainly as a tetrahedral complex, with an octahedral coordination also present in a smaller proportion. The fact that the predominant coordinations for the complexes in the crystallized material and for the ones present on the paper substrate are different is relevant for the study of the lightfastness and thermal stability of works of art bearing these media. Copyright © 2009 John Wiley & Sons, Ltd.