The identification of metabolites in complex biological matrices is a challenging task in 1D 1 H NMR based metabolomic studies. Statistical TOtal Correlation Spectroscopy (STOCSY) has emerged for aiding the structural elucidation by revealing the peaks that present high correlation to a driver peak of interest (which would likely belong to the same molecule). However, in these studies the signals from metabolites are normally present as a mixture of overlapping resonances, limiting the performance of STOCSY. 2D 1 H homonuclear J-resolved spectra (JRES), in its usual tilted and symmetrized processed form, were projected and STOCSY was applied on these 1D projections (p-JRES-STOCSY) as an alternative to avoid the overlap issue, but this approach suffers in cases where the signals are very close. In addition, STOCSY was applied to JRES spectra (also tilted) to identify correlated multiplets, although the overlap issue in itself was not addressed directly and the subsequent search in databases is complicated in cases of higher order coupling. With these limitations in mind, in the present work we propose a new methodology based on the application of STOCSY on a set of nontilted JRES spectra, detecting peaks that would overlap in 1D spectra of the same sample set. COrrelation COmparison Analysis for Peak Overlap Detection (COCOA-POD) is able to reconstruct projected 1D STOCSY traces that result in more suitable database queries, as all peaks are summed at their f2 resonances instead of the resonance corresponding to the multiplet center in the tilted JRES (the peak dispersion and resolution enhancement gained are not sacrificed by the projection). Besides improving database queries with better peak lists obtained from the projections of the 2D STOCSY analysis, the overlap region is examined and the multiplet itself is analyzed from the correlation trace at 45° to obtain a cleaner multiplet profile, free from contributions from uncorrelated neighboring peaks.
p-Nitrophenylchlorocarbene reacted reversibly with diethyl ether, di-n-propyl ether, or tetrahydrofuran (THF) to form O-ylides, which were visualized by their UV-visible spectroscopic signatures. Equilibrium constants (K(eq)) were determined spectroscopically and ranged from 0.10 M(-1) (di-n-propyl ether) to 7.5 M(-1) (THF) at 295 K. Studies of K(eq) as a function of temperature afforded ΔH(o), ΔS(o), and ΔG(o) for the di-n-propyl ether and THF/O-ylide equilibria. ΔH(o) was favorable for ylide formation, but ΔS(o) was quite negative, so that ΔG(o)s for the equilibria were small. Electronic structure calculations based on density functional theory provided structures, spectroscopic signatures, and energetics for the carbene/ether O-ylides.
Two novel photoinitiator-free approaches to photopolymerize acrylic monomers with a conventional Hg lamp starting from an acrylates monomer miniemulsion are investigated. In one system the acrylate nanodroplet reaction is self-initiated and in the other the use of a photoactive diphenyl ether surfactant yields phenyl and phenoxyl initiating radicals upon UV irradiation. Photopolymerization kinetics are monitored in situ by real-time Fourier transform near infrared spectroscopy (RT-FTNIR) and the colloidal properties are systematically investigated by dynamic light scattering (DLS). The up-scaling of these PI-free miniemulsion photopolymerizations is carried out in an annular photoreactor.
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