Radical Anions of Oxidized vs. Reduced Oxytocin: Influence of Disulfide Bridges on CID and Vacuum UV Photo-Fragmentation

The nonapeptide oxytocin (OT) is used as a model sulfur-containing peptide to study the damage induced by vacuum UV (VUV) radiations. In particular, the effect of the presence (or absence in reduced OT) of oxytocin’s internal disulfide bridge is evaluated in terms of photo-fragmentation yield and nature of the photo-fragments. Intact, as well as reduced, OT is studied as dianions and radical anions. Radical anions are prepared and photo-fragmented in two-color experiments (UV?+?VUV) in a linear ion trap. VUV photo-fragmentation patterns are analyzed and compared, and radical-induced mechanisms are proposed. The effect of VUV is principally to ionize but secondary fragmentation is also observed. This secondary fragmentation seems to be considerably enabled by the initial position of the radical on the molecule. In particular, the possibility to form a radical on free cysteines seems to increase the susceptibility to VUV fragmentation. Interestingly, disulfide bridges, which are fundamental for protein structure, could also be responsible for an increased resistance to ionizing radiations.

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Quantitative SIMS-analysis of erbium profiles in LiNbO3

Modern fiberoptic communication technology uses light of 1.5 m wavelength and Er³⁺ is the laser active ion for this wavelength. Doping of crystalline LiNbO₃ (an electrooptical material) with erbium ions permits the fabrication of signal-amplifying electrooptic devices. Novel results of three different approaches have been presented to dope the near surface area of LiNbO₃ for its application in planar optoelectronics: erbium indiffusion from the surface, implantation of erbium into LiNbO₃ and subsequent annealing schemes, and the homoepitaxial growth of Er-doped LiNbO₃ on LiNbO₃ single crystalline material by a laser deposition method. These experiments are not only useful for creating integrated optical devices with active amplifying functions, but they are also important examples for fabricating and studying novel thin ferroelectric films. Secondary ion mass spectrometry (SIMS) has been employed as the main analytical tool for quantitative determination of the erbium concentration profiles.     

Zum massenspektrometrischen Verhalten von Diarylaminen

The fragmentation behaviour of diarylamines in a mass spectrometer can be interpreted most plausib by assuming carbazole cyclization reactions. As a first step the loss of a hydrogen atom is presumed, followed by another hydrogen loss resulting in the formation of the carbazale structure. Investigations of 10 diarylamines show that the probability of cyclization depends on the size of the π-electron system.     

Entropic stabilization of isolated beta-sheets

Temperature-dependent electric deflection measurements have been performed for a series of unsolvated alanine-based peptides (Ac-WA(n)-NH(2), where Ac = acetyl, W = tryptophan, A = alanine, and n = 3, 5, 10, 13, and 15). The measurements are interpreted using Monte Carlo simulations performed with a parallel tempering algorithm. Despite alanine's high helix propensity in solution, the results suggest that unsolvated Ac-WA(n)-NH(2) peptides with n > 10 adopt beta-sheet conformations at room temperature. Previous studies have shown that protonated alanine-based peptides adopt helical or globular conformations in the gas phase, depending on the location of the charge. Thus, the charge more than anything else controls the structure.     

C-C and C-H bond activation reactions in N-heterocyclic carbene complexes of ruthenium

Thermolysis of Ru(PPh3)3(CO)H2 with the N-heterocyclic carbene bis(1,3-(2,4,6-trimethylphenyl)imidazol-2-ylidene) (IMes) results in C-C activation of an Ar-CH3 bond in one of the mesityl rings of the carbene ligand. Upon addition of IMes to Ru(PPh3)3(CO)H2 at room temperature in the presence of an alkene, C-H bond activation is observed instead. The thermodynamics of these C-C and C-H cleavage reactions have been probed using density functional theory.     

Off-axis pulsed laser deposition system for epitaxial oxide growth on substrates up to 2 inches in diameter

A novel off-axis pulsed-laser deposition (PLD) system for ferroelectric oxide thin films has been developed. The substrates are mounted "upside-down" and are rotating. The maximum substrate size is 2 inches in diameter. The optical and structural properties of the grown BaTiO₃ films are compared to the films produced by an on-axis PLD system. The stoichiometry and thickness were checked with Rutherford backscattering spectrometry (RBS). The crystalline quality and orientation were investigated with X-ray diffraction (XRD) and Rutherford backscattering spectrometry in channeling configuration (RBS/C). Using atomic force microscopy, the rms surface roughness was measured. The BaTiO₃ films grown on MgO form a planar optical waveguide. The optical losses and the refractive indices of these waveguides were determined with a prism coupling setup. Films grown on 10᎒ mm² MgO (100) substrates in on-axis geometry show optical waveguide losses less than 3 dB/cm.     

Formation and spectroscopy of a tryptophan radical containing peptide in the gas phase

A doubly deprotonated tryptophan containing peptide was electrosprayed and isolated in an ion trap. UV excitation on this peptide leads to electron detachment and to the formation of an indolyl radical. The photogenerated radical was fragmented by a second laser. The visible spectrum of the gas-phase neutral tryptophan radical containing peptide has been recorded and constitutes a benchmark for calculations and optical measurements.