FT-IR microspectroscopy: a powerful tool for spatially resolved studies on supports for solid phase organic synthesis
published: Jan. 18, 2008, recorded: October 2007, views: 5340
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Solid Phase Organic Synthesis (SPOS) is an efficient technique for the synthesis of fine chemicals and for the development of compounds libraries through combinatorial approaches. SOPS performances can be optimized carefully tuning the chemo-physical properties of polymeric supports, usually porous beads, with particular reference to the distribution of the reaction products into the beads, which gives information on the pore accessibility, on the efficiency of the reactant’s diffusion process into pores and on the load capacity of the bead. Differently from optical transparent polymers, for which all parameters of interest can be quantified by two-photon microscopy, opaque supports are difficult to characterize by conventional analytical techniques. We propose a new method to systematically study parameters affecting performance of opaque supports for SPOS, based on FT-IR microspectroscopy on thin bead slides in transmission mode (All data collected with Bruker VERTEX 70 interferometer coupled with Hyperion 3000 IR microscope). Opaque amino-methacrylate beads with different pore diameters, Synbeads by Resindion s.r.l (Mitsubishi Chem. Corp., Milan, Italy), are acylated via chemical coupling with 3-nitropropionic acid at different reactions times. Functionalized and non-functionalized beads, cut in 5 microns slices, are chemically imaged with Focal Plane Array detector (FPA, 64X64 pixel) coupled with a IR conventional source, allowing a fast chemical imaging of the nitro functional group presence and distribution within the bead. In order to achieve a better S/N ratio and then more accurate details on nitro-group distribution, selected bead sections are also mapped at 5 microns spatial resolution along their diameter using a Mercury-Cadmium-Telluride (MCT) single-point detector operated with Synchrotron Radiation (SR). The combined approached proposed has the main advantage to be useful for each type of SPOS support material and allows, by FT-IR imaging, an easy and fast access to data as bead functionalization and functional group distribution. More accurate quantitative relations between bead polymer type, its degree of polymerization, bead pore dimension and mean porosity, supported reaction and synthesis condition can be achieved exploiting the high brightness of SR source and the major sensitivity of MCT detector.
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