Evaluation of the Rotating-Frame Relaxation (T1ρ) Filter and Its Application in Metabolomics as an Alternative to the Transverse Relaxation (T2) Filter.

Nuclear magnetic resonance (NMR)-based metabolomic studies commonly involve the use of T2 filter pulse sequences to eliminate or attenuate the broad signals from large molecules and improve spectral resolution. In this paper, we demonstrate that the T1ρ filter-based pulse sequence represents an interesting alternative because it allows the stability and the reproducibility needed for statistical analysis. The integrity of the samples and the stability of the instruments were assessed for different filter durations and amplitudes. We showed that the T1ρ filter pulse sequence did not induce sample overheating for a filter duration of up to 500 ms. The reproducibility was evaluated and compared with the T2 filter in serum and liver samples. The implementation is relatively simple and provides the same statistical and analytical results as those obtained with the standard filters. Regarding tissues analysis, because the duration of the filter is the same as that of the spin-lock, the synchronization of the echo delays with the magic angle spinning (MAS) rate is no longer necessary as for T2 filter-based sequences. The results presented in this article aim at establishing a new protocol to improve metabolomic studies and pave the way for future developments on T1ρ alternative filters, in liquid and HR-MAS NMR experiments.

Rapid characterization of cocaine in illicit drug samples by 1D and 2D NMR spectroscopy.

Seized samples of illegally produced cocaine have a very large variability in composition; a fact that may result in a challenge to their analysis. We demonstrate here a simple and fast method to detect the presence of cocaine in both hydrochloride and free-base forms in illicit drug samples by nuclear magnetic resonance (NMR) spectroscopy. This is achieved by combining the commonly used 1D spectra and diffusion-ordered spectroscopy and introducing the 2D maximum-quantum NMR approach to forensic analysis. The protocol allows the facile determination of the cocaine forms even in the presence of multiple adulterants. By relying on non-uniform sampling acceleration of 2D spectroscopy, the identification can be obtained in less than 3 min for 10 mg of product. Moreover, we show that intermolecular interactions of the sample constituents, while affecting the analysis result, do not interfere with the quality of the detection of the proposed protocol.

An EPR study of the radical addition to 3-nitropentan-2-one as an archetype of α-carbonylnitroalkanes.

Carbon, silicon, germanium, tin and lead-centered radicals were reacted with 3-nitropentan-2-one and 3-nitropentan-2-ol inside the cavity of an electron paramagnetic resonance spectrometer. In all cases, selective addition to the nitrogroup was observed with detection of the corresponding oxynitroxide radicals. In the case of the carbonyl substrate, alkyl acyl nitroxides were also detected because of α-photocleavage. The oxynitroxides decayed with a first order kinetics via fragmentation of the carbon-nitrogen bond (denitration). Unexpectedly, the activation parameters were fairly similar to those previously reported for the corresponding tert-butyl oxynitroxides and almost independent from the presence of a carbonyl or a hydroxyl group on the carbon adjacent to the one bearing the nitrogroup.

Elucidation of electron ionization mass spectrometric fragmentation pathways of trimethylsilyl ether derivatives of vicinal diols deriving from haplamine by collision-induced dissociation gas chromatography/tandem mass spectrometry and ¹8O labelling.

RATIONALE: Formation of vicinal diols was observed after in vitro and in vivo studies of the natural product haplamine (9-methoxy-2,2-dimethyl-2,6-dihydropyrano[3,2-c]quinolin-5-one). These compounds, identified as trans- and cis-3,4-dihydroxy-9-methoxy-2,2-dimethyl-2,3,4,6-tetrahydropyrano[3,2-c]quinolin-5-ones and trans- and cis-3,4,9-trihydroxy-2,2-dimethyl-2,3,4,6-tetrahydropyrano[3,2-c]quinolin-5-ones, have a potential interest in oncology. It is therefore essential to elucidate their electron ionization mass spectrometric (EIMS) fragmentation pathways. METHODS: EIMS fragmentation pathways of trimethylsilyl (TMS) derivatives of 3,4-dihydroxy- and 3,4,9-trihydroxyhaplamines were investigated. These pathways have been substantiated by: (i) comparison with EI mass spectra of structural homologues (silylated diols obtained from various chromenes and 1,2-dihydronaphthalene), (ii) low-energy collision-induced dissociation (CID) gas chromatography/tandem mass spectrometry (GC/MS/MS) and (iii) (18)O labelling. RESULTS: CID-MS/MS analyses and (18)O labelling demonstrated that EI mass spectral fragmentation of these TMS derivatives involves a transannular cleavage of the pyran ring with formation of a characteristic intense cyclic ion. The study of the mass spectra of TMS derivatives of different chromenes and 1,2-dihydroxynaphthalene allowed to confirm the proposed fragmentation pathways and to show that they act only when the pyran ring is present. CONCLUSIONS: Elimination of the neutral element [(CH3)2=C(H)OSi(CH3)3] and formation of cyclic ions play a key role during EI mass spectral fragmentation of the TMS derivatives of 3,4-dihydroxy- and 3,4,9-trihydroxyhaplamines. These fragmentation pathways could be generalized to TMS derivatives of cyclic compounds possessing vicinal diols close to a pyran ring.

HRMAS NMR spectroscopy combined with chemometrics as an alternative analytical tool to control cigarette authenticity.

In this paper, we present for the first time the use of high-resolution magic angle spinning nuclear magnetic resonance (HRMAS NMR) spectroscopy combined with chemometrics as an alternative tool for the characterization of tobacco products from different commercial international brands as well as for the identification of counterfeits. Although cigarette filling is a very complex chemical mixture, we were able to discriminate between dark, bright, and additive-free cigarette blends belonging to six different filter-cigarette brands, commercially available, using an approach for which no extraction procedure is required. Second, we focused our study on a specific worldwide-distributed brand for which established counterfeits were available. We discriminated those from their genuine counterparts with 100% accuracy using unsupervised multivariate statistical analysis. The counterfeits that we analyzed showed a higher amount of nicotine and solanesol and a lower content of sugars, all endogenous tobacco leaf metabolites. This preliminary study demonstrates the great potential of HRMAS NMR spectroscopy to help in controlling cigarette authenticity.

The reaction of spiro[indoline-naphthopyrans] with nitrogen oxides. Not a case of biradical double trapping.

The reactions of six differently substituted photochromic spiro[indoline-naphtopyrans] with .NO or .NO(2) under normal daylight conditions have been investigated by means of EPR spectroscopy along with those of three structurally related spiro[indoline-benzopyrans]. The spectra due to cyclic oxynitroxides originating from double trapping of biradicals by .NO were observed with the three latter derivatives, this finding being in agreement with previous results. Similar signals were also observed with the six former compounds, but in this case they were responsible for just a minor component of the spectra, the main spectral signals being due to hitherto unreported paramagnetic species that on the basis of their spectral parameters are identified as iminoxy radicals. DFT calculations at the B3LYP/6-31G* level carried out on a variety of radicals support this assignment.