Attenuated Total Reflection synthesis

The photocatalytic oxidation of alcohols constitutes a novel approach for the synthesis of aldehydes and acid from alcohols. Modification of Ti02 catalyst with Pt and Nafion could block the catalyst active sites for the oxidation of ethanol to CO2. Incorporation of Pt resulted in enhanced selectivity towards formate (HCOO ad)-Blocking of active sites by Nafion resulted in formation of significantly smaller amounts of intermediate species, CO2 and H2O, and accumulation of photogenerated electrons. The IR experimental teclmique has been extended to Attenuated Total Reflectance (ATR), enabling the study of liquid phase photocatalytic systems. 

To shed light on the mechanism of formation of silsesquioxane a7b3, to identify the species formed during the process, and to try to explain the high selectivity towards structure a7b3 of the optimised synthetic method described above (64% yield in 18 h), the synthesis of cyclopentyl silsesquioxane a7b3 was monitored by electrospray ionisation mass spectrometry (ESI MS) [50-52] and in situ attenuated total reflection Fourier-transform infrared (ATR FTIR) spectroscopy [53, 54]. Spectroscopic data from the latter were analysed using chemometric methods to identify the pure component spectra and relative concentration profiles. 

Important to quality control are the comparison and confirmation of drug substance identity, excipients, and packaging components. Techniques such as Fourier transform IR (FTIR), attenuated total reflectance (ATR), NIR, Raman spectroscopy are used with increased regularity. The detection of foreign metal contaminants is essential with inductively coupled plasma spectroscopy (ICP), atomic absorption (AA), and X-ray fluorescence. Also notable is the increased attention to analysis of chiral compounds, as in the synthesis of drug substances. Optical rotation, ORD, and CD are currently the preferred instruments for this practice. The analytical techniques commonly used in the preformulation study are discussed in the following. 

Other reactions analysed by IR-techniques are typically CO hydrogenation,29 and methanol synthesis,159 while more recently ATR (attenuated total reflection) has been employed for the study of the... 

Solution-phase reactions can be followed conveniently by simple means such as TLC, conventional NMR or UV, whereas solid-phase synthesis requires either prior cleavage from the support or special equipment, e.g. ATR (attenuated total reflection)-IR or MAS (magic angle spinning)-NMR. This difference affects primarily the development of new reactions but may also be relevant for the actual library synthesis, e.g., checking completion of a reaction or the quality of intermediates. 

Parallel to the synthesis of library compounds on solid supports, the direct analysis (i.e. on-bead ) is an attractive concept. Leaving aside the methods of on-bead-infrared-spec-troscopy [41] using attenuated total reflection (ATR) and gel-phase NMR-techniques [42, 43], we wish to consider the use of on-bead analysis in mass spectrometry. The requirements of the ionization process restrict on-bead analysis to the MALD1 technique. However, also for MALDI-analysis, in so-called direct monitoring studies [44-46], the compounds are cleaved from the bead before the actual ionization. True on-bead analysis under MALDI conditions is only possible with photolytically cleavable linkers, and this technique has been dealt with in several publications [28,29] in which the compounds are both cleaved and ionized simultaneously within the MALDI source with a single laser shot. The wavelength of the MALDI-laser must however correspond with the wavelength required to cleave the compounds from the resin. Therefore, on-bead analysis represents a method for special analytical problems which is limited to MALDI. 

Vibrational spectroscopy is a molecule-specific analytical method that probes the vibrations of molecules and solids. Fourier transform infrared (FTIR) and Raman spectroscopies are widely used in situ techniques in the analysis of chemical reactions. However, in the case of silicalite-1 synthesis, they have not yet been used [35]. Attenuated total reflectance infrared (ATR-IR) spectroscopy has however been used to study soluble silicates and shown to be able to characterize various structures [25, 35-37]. It is likely only a matter of time before we see ATR-IR used under in situ conditions. 

Brandstetter, M. (2009). Ultrasonically enhanced in-line Attenuated Total Reflection (ATR) infrared absorption spectroscopy of suspensions. Diploma Thesis, Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna Braunshier, C. Hametner, C. Froehlich, J. Schnoeller, J. Hutter, H. (2008). Novel monodisperse PEG-grafted polystyrene resins synthesis and application in gel-phase 13C NMR spectroscopy. Tetrahedron Letters Vol.49, pp. 7103-7105, ISSN 0040-4039... 

Convenient multigram synthesis of monodisperse oligo(ethylene glycols) effective reaction monitoring by infrared spectroscopy using an attenuated total reflection fibre optic ptrobe. Tetrahedron Letters Vol.50, pp. 6469-6471, ISSN 0040-4039... 

Sahre K, Elrehim MHA, Eichhom K-J, Voit B. Monitoring of the synthesis of hyperbranched poly(urea-urethane)s by real-time Attenuated Total Reflection (ATR)-FT-IR Spectroscopy. Macromol Mat Eng 2006 291 470 76. 

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