HR MAS

Schlafli HR, MA Weiss, T Leisinger, AM Cook (1994) Terephthalate 1,2-dioxygenase system from Comamonas testosteroni T-2 purification and some properties of the oxygenase component. J Bacteriol 176 6644-6652. 

TLC plates are of particular interest as substrates for spectroscopy (i) as a storage device for offline spectroscopic analysis (ii) for efficient in situ detection and identification and (iii) for exploitation of spectroscopic techniques that cannot be used in HPLC. Thin-layer chromatography combined with HR MAS (NMR) can be used for compound identification without the need for elution from the stationary phase [413]. Recently also TLC-XRF was found suitable for in situ TLC imaging of elements [414]. The combination... 

Time, t (hr) mA (lb) mB (lb) Total mass (lb) Fraction of input A that remains unconverted... 

Figure 8.3 Illustration of HR-MAS techniques applied to a resin-bound trisaccharide (a) static XH spectrum of the solvent swollen sample (b) XH spectrum with magic-angle spinning at 3.5 kHz (c) H spectrum with MAS and spin echo pulse sequence.

In addition to well-resolved one-dimensional (ID) 1H and 13C spectra, which are usually sufficient for monitoring synthetic steps, HR-MAS techniques can be applied to two-dimensional (2D) homonuclear and heteronuclear experiments, which allow a wealth of structural information to be obtained. H,13C HMQC (heteronuclear multiple quantum coherence) spectra are particularly useful in the analysis of solid support-bound oligosaccharides, since the anomeric protons exhibit characteristic resonances. Such a spectrum of a polymer-bound trisaccharide glycal is shown in Figure 8.4. 

Figure 8.4 Example of an HR-MAS HMQC spectrum of a resin-bound trisaccharide glycal.20...

We have characterized a resin-bound pentasaccharide by HR-MAS techniques. A comparison of the solution spectrum of the resin-cleaved pentasaccharide with the HR-MAS spectrum of the resin-bound pentasaccharide is shown in Figure 8.5. It is immediately obvious that the HR-MAS technique provides data of a quality similar to that of the solution technique, but in both cases, only four of the five anomeric protons are visible. However, a 2D homonuclear total correlation spectroscopy (TOCSY) spectrum (Fig. 8.6) of the resin-bound pentasaccharide allowed us to clearly observe the overlapped anomeric protons (demonstrating a resolution of 4.4 Hz). 

The power of the HR-MAS method for on-resin analysis has been further underscored in the development of new linkers. Without this method, only indirect analytical data after removal from the resin was available. Direct assessment of the resin-bound linker greatly facilitated the introduction of a 4,5-dibromo octane- 1,8-diol linker that was converted into an octane-1,8-diol linker cleavable by olefin metathesis at the end of the synthesis.6 The disappearance and reappearance of the olefinic protons as well as the growing oligosaccharide chain was clearly visible in the H spectrum (Fig. 8.7).7... 

Figure 8.7 HR-MAS spectra of resin-bound intermediates in the solid-phase synthesis of a trisaccharide using thiodonors. Traces a and b have been recorded using spin echo pulse sequences to suppress resonances of the resin. Traces c and d have been recorded using a standard proton experiment.

Another, yet completely different access to macroscopic binding strengths of selectands on CSPs has been described by Hellriegel et al. [65] employing suspended-state NMR spectroscopy. Thus, HR-MAS 2D transfer-nuclear Overhauser effect spectroscopy (NOESY) was utilized to distinguish solutes strongly binding to the... 

Resin loadings can be determined using either gel-phase 19F NMR, [222, 223] MAS NMR (in a conventional soHd-state probe) [187, 224] or using H HR-MAS... 

Fig. 1.25 Gel-phase H HR-MAS NMR spectrum of resin containing pyridyl ligand (3) and the enol ether side-product (13).

NMR spectroscopy [225]. The measurement of enantiomeric excesses of supported substrates has also been achieved by HR-MAS NMR [226]. 

P. Rousselot-Pailley, D. Maux, J. M. Wieruszeski, J. L. Aubagnac, J. Martinez and G. Lippens, Impurity detection in solid-phase organic chemistry Scope and limits of HR MAS NMR,... 

J. S. Fruchart, G. Lippens, C. Kuhn, H. Gras-Masse and O. Melnyk, Solid-phase enolate chemistry investigated using HR-MAS NMR spectroscopy, J. Org. Chem., 2002,67, 526-532. 

B. Combourieu, J. Inacio, A. M. Delort and C. Forano, Differentiation of mobile and immobile pesticides on anionic clays by 1H HR MAS NMR spectroscopy, Chemical Communications, 2001, 2214-2215. 

A. J. Simpson, W. L. Kingery, D. R. Shaw, M. Spraul, E. Humpfer and P. Dvortsak, The application of H HR-MAS NMR spectroscopy for the study of structures and associations of organic components at the solid-aqueous interface of a whole soil, Environ. 

S. J. Barton, F. A. Howe, A. M. Tomlins, S. A. Cudlip, J. K. Nicholson, B. A. Bell and J. R. Griffiths, Comparison of in vivo H MRS of human brain tumors with ll HR-MAS spectroscopy of intact biopsy samples in vitro, Magnetic Resonance Materials in Physics, Biology and Medicine, 1999, 8, 121-128. 

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