Distinguishing isobaric phosphated and sulfated carbohydrates by coupling of mass spectrometry with gas phase vibrational spectroscopy.

An original application of the coupling of mass spectrometry with vibrational spectroscopy, used for the first time to discriminate isobaric bioactive saccharides with sulfate and phosphate functional modifications, is presented. Whereas their nominal masses and fragmentation patterns are undifferentiated by sole mass spectrometry, their distinctive OH stretching modes at 3595 cm(-1) and 3666 cm(-1), respectively, provide a reliable spectroscopic diagnostic for distinguishing their sulfate or phosphate functionalization. A detailed analysis of the 6-sulfated and 6-phosphated d-glucosamine conformations is presented, together with theoretical scaled harmonic spectra and anharmonic spectra (VPT2 and DFT-based molecular dynamics simulations). Strong anharmonic effects are observed in the case of the phosphated species, resulting in a dramatic enhancement of its phosphate diagnostic mode.

Rapid-scan EPR with triangular scans and fourier deconvolution to recover the slow-scan spectrum.

Direct-detected rapid-scan EPR signals were recorded using triangular field scan rates between 1.7 and 150 kG/s for deoxygenated samples of lithium phthalocyanine (LiPc) and Nycomed trityl-CD3. These scan rates are rapid relative to the reciprocals of the electron spin relaxation times and cause characteristic oscillations in the signals. Fourier deconvolution with an analytical function permitted recovery of lineshapes that are in good agreement with experimental slow-scan spectra. Unlike slow-scan EPR, direct detection rapid-scan EPR does not use phase sensitive detection and records the absorption signal directly instead of the first derivative of the absorption signal. The amplitude of the signal decreases approximately linearly with applied magnetic field gradient. Images of phantoms constructed from samples of LiPc and trityl-CD3 were reconstructed by filtered back-projection from data sets with a missing angle. The lineshapes in spectral slices from the image are in good agreement with slow-scan spectra and the spacing between sample tubes matches well with the known sample geometry.

On the analysis of broad Dysonian electron paramagnetic resonance spectra.

We analyze the equation used for simulating the lineshapes of broad electron paramagnetic resonance spectra in conducting samples (i.e., broad Dysonian lineshapes) where it becomes necessary to include the effects of both clockwise and counterclockwise rotating components of the microwave magnetic field. Using symmetry arguments, we propose a modification to the equation. We show that the modified equation fits the experimental results better than the equation used in literature.