Spin-state selective carbon-detected HNCO with TROSY optimization in all dimensions and double echo-antiecho sensitivity enhancement in both indirect dimensions

A carbon-detected TROSY-optimized experiment correlating 1HN, 15N, and 13C' resonances, referred to as c-TROSY-HNCO is presented, in which the 1HN and 15N TROSY effects are maintained in both indirect dimensions, while the directly detected 13C' is doubly TROSY-optimized with respect to 1HN and 15N. A new strategy for sensitivity enhancement, the so-called double echo-antiecho (dEA), is described and implemented in the c-TROSY-HNCO experiment. dEA offers sensitivity enhancement of square root of 2 in both indirect dimensions and is generally applicable to many multidimensional experiments. A carbon-detected HNCO experiment, c-HNCO, without TROSY optimization and sensitivity enhancement is also designed for comparison purposes. Relaxation simulations show that for a protein with a rotational correlation time of 10 ns or larger, the c-TROSY-HNCO experiment displays comparable or higher signal-to-noise (S/N) ratios than the c-HNCO experiment, although the former selects only 1/4 of the initial magnetization relative to the later. The high resolution afforded in the directly detected carbon dimension allows direct measurement of the doublet splitting to extract 1JCalphaC' scalar and 1DCalphaC' residual dipolar couplings. Simulations indicate that the c-TROSY-HNCO experiment offers higher precision (lower uncertainty) compared to the c-HNCO experiment for larger proteins. The experiments are applied to 15N/13C/2H/[Leu,Val]-methyl-protonated IIBMannose, a protein of molecular mass 18.6 kDa with a correlation time of approximately 10 ns at 30 degrees C. The experimental pairwise root-mean-square deviation for the measured 1JCalphaC' couplings obtained from duplicate experiments is 0.77 Hz. By directly measuring the doublet splitting, the experiments described here are expected to be much more tolerant to nonuniform values of 1JCalphaC' (or 1JCalphaC' + 1DCalphaC' for aligned samples) and pulse imperfections due to the smaller number of applied pulses in the "out-and-stay" coherence transfer in the c-HNCO-TROSY experiment relative to conventional 1H-detected "out-and-back" quantitative J correlation experiments. A carbon-detected TROSY-optimized experiment correlating 1HN, 15N, and 13C' resonances, referred to as c-TROSY-HNCO is presented, in which the 1HN and 15N TROSY effects are maintained in both indirect dimensions, while the directly detected 13C' is doubly TROSY-optimized with respect to 1HN and 15N. A new strategy for sensitivity enhancement, the so-called double echo-antiecho (dEA), is described and implemented in the c-TROSY-HNCO experiment. dEA offers sensitivity enhancement of in both indirect dimensions and is generally applicable to many multidimensional experiments.     

Solvent Trapping during Large Volume Injection with an Early Vapor Exit,Part 2: Chromatographic Results and Conclusions

Solvent trapping reconcentrates volatile components after injection or on-line transfer of large volumes. When an early vapor exit is used, typically after a 5–10 m × 0.53 mm i.d. uncoated precolumn, the solvent trapping process differs from that described previously. The visual experiments and the conclusions drawn therefrom, as described in a previous paper, are supplemented with chromatographic results. They show that even hexane can be quantitatively analyzed in 250 μl of a pentane solution. Injection of a volume of 250 μl by vaporizer/precolumn solvent splitting was used in the analysis of gasoline in drinking water. Conditions for the transfer of a 1000 μl volume can easily be adjusted through detection of the front end of the flooded zone by a thermocouple mounted on the outer wall of the precolumn.     

3D-PTV measurements in a plane Couette flow

Genuine plane Couette flow is hard to realize experimentally, and no applications of modern spatially resolving measurement techniques have been reported for this flow so far. In order to resolve this shortcoming, we designed and built a new experimental facility and present our first results here. Our setup enables us to access the flow via 3D particle tracking velocimetry and therefore to obtain truly three-dimensional flow fields for the first time experimentally in plane Couette flow. Results are analyzed in terms of basic flow properties, and a clear distinction of flow regimes (laminar for Re < 320, transitional for 320 < Re < 400, and turbulent when Re > 400) could be made. Comparison with DNS data shows good agreement in the turbulent regime and builds trust in our data. Furthermore, vortical coherent structures are studied in detail with the additional help of kalliroscope imaging, and the typical vortex spacing is determined to be roughly one gap width. As a noteworthy result, we find that the onset of the turbulent regime coincides with the range of Reynolds numbers at which a distance of 100 wall units is comparable to the gap width.     

Pre-organization of the core structure of E-selectin antagonists

A new class of N-acetyl-D-glucosamine (GlcNAc) mimics for E-selectin antagonists was designed and synthesized. The mimic consists of a cyclohexane ring substituted with alkyl substituents adjacent to the linking position of the fucose moiety. Incorporation into E-selectin antagonists led to the test compounds 8 and the 2'-benzoylated analogues 21, which exhibit affinities in the low micromolar range. By using saturation transfer difference (STD)-NMR it could be shown that the increase in affinity does not result from an additional hydrophobic contact of the alkyl substituent with the target protein E-selectin, but rather from a steric effect stabilizing the antagonist in its bioactive conformation. The loss of affinity found for antagonists 10 and 35 containing a methyl substituent in a remote position (and therefore unable to support to the stabilization of the core) further supports this hypothesis. Finally, when a GlcNAc mimetic containing two methyl substituents (52 and 53) was used, in which one methyl was positioned adjacent to the fucose linking position and the other was in a remote position, the affinity was regained.     

Development and validation of a HPAE-PAD method for the quantification of CGP69669A, a sialyl Lewis(x) mimetic, in skin permeation studies

A simple, rapid, precise and specific isocratic HPAE‐PAD method for quantification of CGP69669A was developed and validated. CGP69669A is a glycomimetic of sialyl Lewis^x and an antagonist of E‐selectin with potential application in the treatment of inflammatory skin disease. Quantification was performed using a Dionex CarboPac^TM PA‐200 anion‐exchange column (3 × 250 mm) with 100 mm NaOH solution as mobile phase, a flow rate of 0.50 mL/min and an injection volume of 10 μL. A quadruple potential waveform was used to detect the carbohydrate (+0.1 V from 0.00 to 0.40 s, ?2.0 V from 0.41 to 0.42 s, +0.6 V at 0.43 s and ?0.1 V from 0.44 to 0.50 s with current integrated between 0.20 and 0.40 s for detection) and rafinose was employed as an internal standard. The optimized conditions enabled rapid elution of CGP69669A (at 3.0 min) without interference from solvent peaks or substances present in the skin. The method showed good intra‐ and inter‐day precision and accuracy and the response was linear from 1.0 to 25 µg/mL. This is the first validated direct method for the quantification of CGP69669A. It will now be employed in studies investigating the topical and transdermal delivery of CGP69669A in vitro and in vivo and it should also be of use for other applications of this molecule. Copyright © 2011 John Wiley & Sons, Ltd.     

Ionic-liquid-based MS probes for the chemo-enzymatic synthesis of oligosaccharides

A new N-benzenesulfonyl-based ionic-liquid mass spectroscopy label (I-Tag2) for covalent attachment to substrates has been prepared. I-Tag2 was used to monitor oligosaccharide elongation and serve as a purification handle. Starting from chemically synthesized I-Tag2-labelled N-acetyl glucosamine (GlcNAc) 1, I-Tag2-LacNAc (Galβ(1-4)GlcNAc) 2 and I-Tag2-Lewis(X) (Galβ(1-4)[Fucα(1-3)]GlcNAc) 3, which are oligosaccharides of biological relevance, were enzymatically prepared. The apparent kinetic parameters for the enzyme catalysed transformations with β-1,4-galactosyltransferase (β-1,4-GalT) and fucosyltransferase VI (FucT VI) were measured by LC-MS demonstrating the applicability and versatility of the new I-Tags in enzymatic transformations with glycosyltransferases.