Gas chromatography/mass spectrometric identification of dopaminergic metabolites in striata of rats treated with L-DOPA

The ex vivo identification of dopaminergic metabolites present in rat striata after (L-DOPA + benserazide) treatment is reported. The different metabolites have been identified as the trimethylsilyl derivatives in the striatal extracts by gas chromatography/mass spectrometry.     

Coherent interactions of dissipative spatial solitons

We report observation of the interaction between two coherent dissipative spatial solitons in a periodically patterned semiconductor optical amplifier with power levels of tens of milliwatts. The interactions are nonlocal and phase dependent and exhibit surprising features, such as soliton birth. The experimental results are in good agreement with the numerical simulations.     

Frequency-mixing scheme for the production of tunable narrowband XUV radiation (91–95 nm): application to precision spectroscopy and predissociation in diatomic molecules

Tunable narrowband extreme ultraviolet radiation in the range 91–95 nm is produced by sum-frequency mixing of the outputs of a visible pulsed dye amplifier (seeded by a ring dye laser) and of a seeded second-harmonic Nd:YAG laser and subsequent frequency tripling in a gas jet of xenon. The capability of this scheme to provide tunable narrowband extreme ultraviolet radiation is demonstrated in several spectroscopic studies. The bandwidth of this system (0.01 cm^-1) is deduced from a recording of absorption spectra of the 4p⁵(²P_1/2)6d, J=1 line in krypton. The applicability of the system for gas-phase molecular spectroscopic studies is demonstrated in recordings of the Werner bands (4,0) in H₂ and (5,0) in D₂ at unprecedented absolute accuracy. Line-broadening studies are performed on the b¹_u⁺,v=5 valence state in N₂, yielding a lifetime of 210±25 ps. A singlet–triplet perturbation, giving rise to an accidental predissociation in an excited ¹ Rydberg state in carbon monoxide at an excitation energy of 107680 cm^-1, is analyzed in high resolution. PACS 42.65.Ky; 32.80.Rm; 33.20.Ni; 33.80.Gj; 42.60.By     

Monolithic catalysts for the fixed-bed hydrogenation of polymers

Monolithic catalysts were successfully applied in a true fixed-bed hydrogenation of polymers such as SBS rubbers and polystyrene.     

Interaction of localized structures in an optical pattern-forming system

We report on the observation and interaction of dissipative localized structures in an optical pattern-forming system. Single localized structures are found to have oscillatory decaying tails originating from diffraction. We observe bound states of two or more constituents. These clusters contain several preferred mutual distances. Numerical simulations show that the corresponding interactions are mediated by the oscillatory tails.     

Electron-impact dissociation and transient properties of a stored LiH2 - beam

The fragmentation of LiH₂ ^- anions after electron impact was investigated at the heavy-ion storage ring TSR. The main reaction channel was found to be electron detachment followed by a breakup into LiH + H. In the first ms after production of the molecular ions in a cesium sputtering ion source, additional contributions were observed in the Li + H₂ and Li^- + H₂ channels, hinting at an initial population of a short-lived state of the anion. To gain a better understanding of the mechanisms underlying the observed behavior of the system, ab initio calculations of relevant potential energy surfaces were performed at selected geometries. The experimental findings are discussed in the light of these calculations.     

Direct in vitro and in vivo monitoring of destruxins metabolism in insects using internal surface reversed-phase high-performance liquid chromatography. I. Behaviour of E destruxin in locusts

High-performance liquid chromatography with internal surface reversed-phase packing provides an analytical tool for studying the in vitro and in vivo metabolism of A and E destruxins in the haemolymph and various organs of male adults of Locusta migratoria. A slight amount of injected E destruxin is shown to be hydrated into E-diol destruxin in the haemolymph. The rest of the toxin is recovered unchanged in the fat-body, pericardial tissues and Malpighian tubules, and some further E-diol destruxin formation occurs in these organs. Because E-diol destruxin is only weakly toxic, this appears to be a detoxication process.     

Neurotoxin II bound to acetylcholine receptors in native membranes studied by dynamic nuclear polarization NMR

Methods enabling structural studies of membrane-integrated receptor systems without the necessity of purification provide an attractive perspective in membrane protein structural and molecular biology. This has become feasible in principle since the advent of dynamic nuclear polarization (DNP) magic-angle-spinning NMR spectroscopy, which delivers the required sensitivity. In this pilot study, we observed well-resolved solid-state NMR spectra of extensively (13)C-labeled neurotoxin II bound to the nicotinic acetylcholine receptor (nAChR) in native membranes. We show that TOTAPOL, a biradical required for DNP, is localized at membrane and protein surfaces. The concentration of active, membrane-attached biradical decreases with time, probably because of reactive components of the membrane preparation. An optimal distribution of active biradical has strong effects on the NMR data. The presence of inactive TOTAPOL in membrane-proximal situations but active biradical in the surrounding water/glycerol "glass" leads to well-resolved spectra, yet a considerable enhancement (ε = 12) is observed. The resulting spectra of a protein ligand bound to its receptor are paving the way for further DNP investigations of proteins embedded in native membrane patches.