Characterization of erythromycin analogs by collisional activated dissociation and infrared multiphoton dissociation in a quadrupole ion trap

The effectiveness of two activation techniques, collision activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD), is compared for structural characterization of protonated and lithium-cationized macrolides and a series of synthetic precursors in a quadrupole ion trap (QIT). Generally, cleavage of the glycosidic linkages attaching the sugars to the macrolide ring and water losses constitute the major fragmentation pathways for most of the protonated compounds. In the IRMPD spectra, a diagnostic fragment ion assigned as the desosamine ion is a dominant ion that is not observed in the CAD spectra because of the higher m/z limit of the storage range required during collisional activation. Activation of the lithium-cationized species results in new diagnostic fragmentation pathways that are particularly useful for confirming the identities of the protecting groups in the synthetic precursors. Multi-step IRMPD allows mapping of the fragmentation genealogies in greater detail and supports the proposed structures of the fragment ions.     

The sesquiterpenoid nootkatone and the absolute configuration of a di­bromo derivative

Nootkatone, or (4R,4aS,6R)‐4,4a,5,6,7,8‐hexa­hydro‐4,4a‐di­methyl‐6‐(1‐methyl­ethenyl)­naphthalen‐2(3H)‐one, C₁₅H₂₂O, a sesquiterpene with strong repellent properties against Formosan subterranean termites and other insects, has the valencene skeleton. The di­bromo derivative (1S,3R,4S,4aS,6R,8aR)‐1,3‐di­bromo‐6‐iso­propyl‐4,4a‐di­methyl‐1,2,3,4,5,6,7,8‐octa­hydro­naphthalen‐2‐one, C₁₅H₂₄Br₂O, has two independent mol­ecules in the asymmetric unit, which differ in the rotation of the iso­propyl group with respect to the main skeleton. The C—Br distances are in the range 1.950 (4)–1.960 (4) Å. Both independent molecules form zigzag chains, with very short intermolecular carbonyl–carbonyl interactions, having the perpendicular motif and O⋯C distances of 2.886 (6) and 2.898 (6) Å. These chains are flanked by intermolecular Br⋯Br interactions of distances in the range 4.067 (1)–4.218 (1) Å. The absolute configuration of the di­bromo derivative was determined, from which that of nootkatone was inferred.     

Routine analysis by high precision gas chromatography/mass selective detector/isotope ratio mass spectrometry to 0.1 parts per mil

Stable isotope methods are potentially quite useful for validating natural or enhanced mineral degradation of contaminants. For this reason, a continuous flow gas chromatograph (GC), isotope ratio mass spectrometer (IRMS) has been coupled with a quadrupole mass selective detector (MSD) to allow simultaneous mass spectral and stable carbon isotope ratio data to be obtained from a single chromatographic analysis. This allows the target contaminant and any extra-cellular degradation intermediates to be both qualified and quantified. Previously acceptable limits of precision (0.3 parts per mil) are undesirable given the small fractionation observed during aerobic degradation. To further understand the fate of organic contaminants and to gain information about the metabolic degradative pathway employed by a microorganism, routine isotopic analyses on a range of analytes have been performed. Quantities of sample producing mass-44 ion beam signal (I(44)) of 2 x 10(-10) to 1 x 10(-8) A were analysed. When the IRMS was tuned for high sensitivity, ion source nonlinearities were overcome by peak height correction from an algorithm that was produced using known isotopic standards of varying concentrations. This led to sample accuracy of <0.01 per thousand and sample precision of 0.1 per thousand. Copyright 1999 John Wiley & Sons, Ltd.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Interpretation of heart rate variability via detrended fluctuation analysis and alphabeta filter

Detrended fluctuation analysis (DFA), suitable for the analysis of nonstationary time series, has confirmed the existence of persistent long-range correlations in healthy heart rate variability data. In this paper, we present the incorporation of the alphabeta filter to DFA to determine patterns in the power-law behavior that can be found in these correlations. Well-known simulated scenarios and real data involving normal and pathological circumstances were used to evaluate this process. The results presented here suggest the existence of evolving patterns, not always following a uniform power-law behavior, that cannot be described by scaling exponents estimated using a linear procedure over two predefined ranges. Instead, the power law is observed to have a continuous variation with segment length. We also show that the study of these patterns, avoiding initial assumptions about the nature of the data, may confer advantages to DFA by revealing more clearly abnormal physiological conditions detected in congestive heart failure patients related to the existence of dominant characteristic scales.     

The polarization and dipole moment of lattice water in hydrogen bonded crystals

Dipole moments and charge distributions are calculated for the water molecules in four hydrogen bonded crystals, α and β oxalic dihydrates and the hexagonal and cubic ices.     

Relativistic effect on magnetic moments of negative muons bound to high-Z nuclei

The g factors of the negative muons bound to Zn, Cd, and Pb nuclei have been determined. The observed values after the corrections for the internal fields have shown substantial deviations from the free-muon g factor: $\text{(g}{}_{\mathrm{<mtext>free</mtext>}}\text{-g)}\text{g}{}_{\mathrm{<mtext>free</mtext>}}$ is (1.3±0.6)% for Zn, (2.2±1.4) % for Cd, and (5.0±2.2)% for Pb. These shifts are in good agreement with the relativistic binding corrections for finite-size nuclei calculated by Ford et al.     

Structure of 72,74Se at high spin

Lifetimes of high spin states up to { }=22⁺ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in ^{72, 74}Se. The Q _t values derived from these measurements indicate that prolate shape stabilizes for ⁷²Se, while a triaxial shape develops for ⁷⁴Se at higher spins. Comparison of the observed trend in Q _t with spin for ^{72, 74}Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.     

μCF Experiments in D2 and HD Gases – Final Results

During 1994–1996, a series of μCF experiments were performed at PSI by the PSI-PNPI-IMEP-LBNL-TUM collaboration. These experiments aimed at high-precision studies of the d–μ–d fusion in D₂ and HD gases in a wide temperature range. The Gatchina ionization time projection chamber has been used to detect the dd-fusion reaction products. The main parameters of the d–μ–d fusion have been measured with high absolute precision. In this report, we present the results of the final analysis of the experimental data. The obtained results are compared with the calculations based on a recent μCF-theory. This revised version was published online in August 2006 with corrections to the Cover Date.