Comparison of UHPLC-ESI-MS and Hadamard transform atmospheric pressure ion mobility-ESI-MS for rapid profiling of isomeric flavonoids.

Hadamard transform atmospheric pressure ion mobility-MS and rapid UHPLC-MS methods were investigated for analysis of closely related isomeric flavonoids and their glycosides using a test set of seven standards. On a time scale of a few minutes, the flavonoid aglycones were all separated by ion mobility, but not by UHPLC. The glycosides were better resolved by IMS but not completely separated by both methods. The results suggest that IMS provides sufficient resolution for separation of isomeric polyphenols such as flavonoids in high-throughput metabolomics studies.

Towards high-throughput identification of endocrine disrupting compounds with mass spectrometry.

High-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with chemical cross-linking has the ability to monitor the ligand-dependent dimerization of the human estrogen receptor alpha ligand binding domain (hERalpha LBD) in solution. Because only ER ligands enhance the homodimer abundance, we evaluated the ability of this label-free approach for identifying endocrine disrupting compounds (EDCs) in a high-throughput manner. This was achieved by combining an automated liquid handler with an automated MS acquisition procedure, which allowed a five-fold gain in operator time compared to a fully manual approach. To detect ligand binding with enough confidence, the receptor has to be incubated with at least a 10 microM concentration of the test compound. Based on the increase of the measured homodimer intensity, eight compounds with a relative binding affinity (RBA, relative to the natural hormone estradiol) >7% were identified as ER ligands among the 28 chemicals tested. Two other compounds, quercetin and 4-tert-amylphenol, were also identified as ER ligands, although their RBAs have been reported to be only 0.01% and 0.000055%, respectively. This suggests that these two ligands have a higher affinity for hERalpha LBD than reported in the literature. The high-mass MALDI approach thus allows identifying high affinity EDCs in an efficient way.

Competing gas-phase substitution and elimination reactions of gemini surfactants with anionic counterions by mass spectrometry. Density functional theory correlations with their bolaform halide salt models.

Understanding ion specific effects on the solution properties of association colloids is a major unsolved problem, and we are studying the chemistry of gemini surfactants in the gas-phase by mass spectrometry and density functional theory (DFT) to probe ion specific effects in the absence of water. Products from gas-phase fragmentation chemistry of dication-monoanion pairs, M2+X(-), of C16H33(CH3)2N+-(CH2)(n-) +N(CH3)2C16H33.2X(-) gemini surfactants were determined by using sequential collision induced dissociation mass spectrometry. The spacer length "n" was systematically varied (n = 2, 3, 4, and 6) for each counterion investigated (X(-) = F(-), Br(-), Cl(-), I(-), NO3(-), CF3CO2(-), and PF6(-)). The M2+X(-) pairs fragment into monocationic products from competing E2 and S N2 pathways that are readily quantified by tandem MS. The dominant reaction pathway depends on dication and anion structure because it switches from E2 to S N2 with decreasing anion basicity and increasing spacer length. For spacer lengths n = 4 and 6, the major S N2 product shifts from attack at methylene to methyl on the quaternary ammonium group. DFT calculations of gemini headgroup model bolaform salts, CH3(CH3)2N+-(CH2)(n-)+N(CH3)2CH3.2X(-) (X(-) = F(-), Cl(-), Br(-), and I(-), n = 2-4), primarily of activation enthalpies, DeltaH, but also of free energies and entropies for the dication-monoanion pairs, M2+X(-), provide qualitative explanations for the MS structure-reactivity patterns. DeltaH values for S N2 reactions are independent of X(-) type and spacer length, while E2 reactions show a significant increase in DeltaH with decreasing anion basicity and a modest increase with spacer length. Comparisons with the DeltaH values of model CH3CH2(CH3)3N+X(-) halides show that the second charge on the dicationic ion pairs does not significantly affect DeltaH and that the change in distance between the nucleophile and leaving group in the ground and transition states structures in S N2 reactions is approximately constant indicating that DeltaH is governed primarily by electrostatic interactions.

Influence of wine pectic polysaccharides on the interactions between condensed tannins and salivary proteins.

Alpha-amylase, a major human salivary protein, and IB8c, a representative of the proline-rich proteins, were obtained by isolation from saliva and by solid-phase synthesis, respectively. The interactions between these proteins and condensed tannins isolated from grape seeds were studied at different protein and tannin concentrations by measuring their aggregation. Pectic polysaccharides were isolated from wine, and their effect on protein tannin aggregation was assessed. The results presented in this study showed that the most acidic fractions of arabinogalactan proteins have the ability to inhibit the formation of aggregates between the grape seed tannins and the two different salivary proteins. Rhamnogalacturonan II has the same ability toward alpha-amylase but not IB8c under the conditions of the present study. Polysaccharides show effects at concentrations at which they are present in wine, which could mean an influence in wine astringency. The interaction between condensed tannins and alpha-amylase is differently affected by ionic strength when compared with IB8c.