High resolution electrospray and electrospray tandem mass spectra of rotenone and its isoxazoline cycloadducts

An evaluation of the gas-phase ion chemistry of rotenone (1) by electrospray ionisation (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS2) is presented, aiming at providing tools for its determination in natural and biological matrices. The behaviour of its cycloadducts with benzonitrile-N-oxide (2) and 2,4,6-trimethylbenzonitrile-N-oxide (3) was also evaluated and the MS data thus obtained have provided evidence into the mechanism of formation of the key product ion at m/z 192 which can be considered a marker in the MS and MS2 spectra of rotenone and its derivatives.     

Evaluation of glycoalkaloids in tubers of genetically modified virus Y-resistant potato plants (var. Désirée) by non-aqueous capillary electrophoresis coupled with electrospray ionization mass spectrometry (NACE–ESI–MS)

The glycoalkaloid content of transgenic potatoes was evaluated by an optimised method based on non-aqueous capillary electrophoresis coupled on-line with electrospray ionization-mass spectrometry (NACE-ESI-MS). The potato material consisted of tubers from a conventional cv. Désirée and from three lines of modified plants resistant, intermediate and susceptible to infection by potato virus Y (PVY). The main glycoalkaloids were confirmed to be alpha-solanine and alpha-chaconine with parent ion masses m/z 852 and 868, respectively. In addition, an unknown minor peak at m/z 850.6 was found both in conventional (control) and susceptible line potato tubers. Such a compound exhibited an MS(2) spectrum with fragments ions at 704 and 396 m/z derived by loss of two ions, i.e. m/z 146 and 307, most likely corresponding to a rhamnose unit and a [glucose-(rhamnose)(2)] moiety, respectively. Up to 30-80-fold higher concentrations of total glycoalkaloids were found in the peel compared to flesh samples of all tubers examined. TGA content was nearly doubled in peel samples of resistant compared to control lines, and these levels were lower than the limit recommended for food safety, i.e. 20-60 mg of TGA per 100 g fresh weight. Moreover, it was established that tubers produced by virus-resistant clones are substantially equivalent in glycoalkaloid contents to those produced by conventional potato varieties.     

Time-resolved spectroscopy of solid poly(1-vinyl naphthalene)following electron beam pulse radiolysis: pulse radiolytic studies on polymers

Transient emission studies following pulse radiolysis of solid poly(1-vinyl naphthalene) show existence of excited monomers and two excimers. Quenching experiments indicate that excimers are not formed directly by recombination of ions but probably by trapping of migrating monomeric excitation in performed traps whose density is approximately one in 10³.     

Structural and dynamical properties of surfaces from ab-initio molecular dynamics

The recent application to the semiconductor surfaces of the powerful ab-initio molecular dynamics (Car-Parrinello) method [R. Car, M. Parrinello, Phys. Rev. Lett. 55, 2471 (1985)] will be reviewed. The essential features of the method will be addressed first, then we will review a number of recent studies on the properties of the clean and adsorbate covered surfaces of Si, Ge and GaAs, obtained through Car-Parrinello simulations. Finally an original application of the ab-initio molecular dynamics for the clean and hydrogenated GaAs(110) surfaces is presented.     

X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin

We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character.     

Photocatalysis of sprayed nitrogen-containing Fe2O3–ZnO and WO3–ZnO composite powders in gas-phase acetaldehyde decomposition

Two series of nano-sized N-containing MO_x–ZnO (M: Fe, W) composite powders were synthesized by spray pyrolysis. The nitrogen content was controlled from 500 to 2100 ppm by changing the powder ingredients and spray pyrolysis temperature. Ultraviolet-visible (UV-Vis) spectra indicated that the N-containing MO_x–ZnO powders absorbed not only ultraviolet light (λ<387 nm) like pure ZnO powder, but also part of visible light (λ<650 nm). Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalysis of these composite powders. The photocatalytic activity of the N-containing ZnO powder was pronouncedly enhanced by the WO₃ addition under both UV and visible-light irradiation. However, that of the N-containing ZnO powder was suppressed by the Fe₂O₃ addition. A model of the semiconductor energy-band structure is proposed to explain the enhancement and suppression of photocatalytic activity.     

Matrix-assisted laser desorption/ionization mass spectrometric peptide mapping of high molecular weight glutenin subunits 1Bx7 and 1Dy10 in Cheyenne cultivar

This study describes the verification of the cDNA-deduced amino acid sequences of high molecular weight glutenin subunits 1Dy10 and 1Bx7 in Cheyenne cultivar by direct matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of their tryptic fragments omitting chromatographic pre-separation. These polypeptides have a conserved structure consisting of a long central repetitive domain that prevents the application of conventional sequencing procedures such as Edman degradation. The published sequence of subunit 1Dy10 contains 7 Lys and 13 Arg residues; thus the production of 21 tryptic peptides is expected. The cDNA-deduced sequence for 1Bx7 subunit includes 5 Lys and 15 Arg residues, but the presence of three Arg-Pro bonds, which are normally not cleaved by trypsin, predicts only 19 tryptic peptides. Three different matrices (DHB, SA and HCCA) in combination with the most compatible sample preparation procedures were used in order to obtain the maximum 1Dy10 and 1Bx7 sequence coverage. MALDI analysis of the 1Dy10 tryptic digest resulted in the identification of all 21 expected peptides. In the case of 1Bx7 MALDI analysis resulted in the identification of 17 of the 19 expected peptides, giving a sequence coverage of 99.3%. These results were sufficient to rule out glycosylation of the 1Dy10 and 1Bx7 proteins and to assess the absence of any other post-translational modification, to within the detection limits of the method.     

二苯并-18-冠-6-甲醛聚合物柱色谱分离富集化学发光法测定痕量金

研究了用一种新的高分子冠醚聚合物(二苯并-18-冠-6-甲醛聚合物)作为色谱柱的固定相，分离富集痕量金，再用化学发光法进行测定；在盐酸介质中，高分子冠醚对金的吸附率可达100％，吸附的金可被硫脲完全解吸，吸附容量为19.40mg/g；化学发光法测定操作简便，效果令人满意；研究结果表明：把高分子冠醚聚合物作为分离富集手段与具有高灵敏度的化学发光法结合进行痕量分析是一种很有前途的方法。     

立方介孔相含钕氧化硅的合成与表征

以十六烷基三甲基溴化铵为结构导向剂，通过水热法合成了具有立方结构的含钕Nd-MCM-48介孔分子筛材料。XRD和TEM测试表明当n_Nd/n_Si<0.05时可以获得典型的长程有序介孔立方结构相，随n_Nd/n_Si比的增加，晶胞参数的增大和红外吸收光谱(FT-IR)的变化为Nd进入介孔分子筛骨架中提供了有力证据。N₂吸附-脱附实验给出了其BET表面积为1 195 m²·g^-1，BJH平均孔径为3.6 nm。紫外-可见漫反射光谱(UV-Vis)证明钕氧形成一种八面体结构。X射线光电子能谱(XPS)进一步证明钕主要以三价形式存在于立方介孔分子筛骨架中。     

Supramolecular adducts between macrocyclic Gd(iii) complexes and polyaromatic systems: a route to enhance the relaxivity through the formation of hydrophobic interactions

The set-up of reversible binding interactions between the hydrophobic region of macrocyclic GBCAs (Gadolinium Based Contrast Agents) and SO₃⁻/OH containing pyrene derivatives provides new insights for pursuing relaxivity enhancements of this class of MRI contrast agents. The strong binding affinity allows attaining relaxation enhancements up to 50% at pyrene/GBCA ratios of 3 : 1. High resolution NMR spectra of the Yb-HPDO3A/pyrene system fully support the formation of a supramolecular adduct based on the set-up of hydrophobic interactions. The relaxation enhancement may be accounted for in terms of the increase of the molecular reorientation time (τ_R) and the number of second sphere water molecules. This effect is maintained in blood serum and in vivo, as shown by the enhancement of contrast in T_1w-MR images obtained by simultaneous injection of GBCA and pyrene derivatives in mice.

The set-up of reversible binding interactions between the hydrophobic region of macrocyclic gadolinium based contrast agents and SO₃⁻/OH containing pyrene derivatives provides new insights for pursuing relaxivity enhancement of MRI contrast agents.