Site distribution in resin beads as determined by confocal Raman spectroscopy

Investigation of Parameters that Affect Resin Swelling in Green Solvents

The influence of various physical and chemical factors on the swelling of polystyrene and PEG based resins in greener organic solvents has been systematically investigated. In general, chemical factors: the nature of the functionality/linker and the degree of loading were found to have a far larger influence on the swelling of the resins than physical parameters such as bead size. The results are interpreted in terms of Hansen solubility parameters for the solvents and there is evidence that some solvents interact with the polymeric core of a resin whilst others interact with the functionality. The results are extended to a study of the changes in resin swelling observed during both deprotection and chain elongation reactions during solid phase peptide synthesis.

Real-Time Imaging of Protease Action on Substrates Covalently Immobilised to Polymer Supports

We report for the first time single bead spatially resolved activity measurements of solid-phase biocatalytic systems followed in real-time. Trypsin cleavage of Bz-Arg-OH and subtilisin cleavage of Z-Gly-Gly-Leu-OH each liberate a free amino group on aminocoumarin covalently immobilised to PEGA(1900) beads [a co-polymer of poly(ethylene glycol) with molecular mass of 1900 cross-linked with acrylamide]. This restores fluorescence which is imaged in optical sections by two-photon microscopy. For trypsin cleavage, fluorescence is restricted initially to surface regions, with more than 1 hour needed before reaction is fully underway in the bead centre, presumably reflecting slow enzyme diffusion. In contrast, for subtilisin cleavage fluorescence develops throughout the bead more quickly.

Understanding Supported Reactions in Spherical Compartments: A General Algorithm To Model and Determine Rate Constants, Diffusion Coefficients, and Spatial Product Distributions

A general algorithm allowing the numerical modeling of the time and space dependence of product formation in spherical reaction volumes is described. The algorithm is described by the complete set of mass balance equations. On the basis of these equations, the effects of the diffusion coefficient, reaction rate, bead size, reagent excess, and packing density of the resin beads on the overall reaction rates are determined for second-order reactions. Experimental data of reaction progress are employed to calculate reaction rates and diffusion coefficients in polymer-supported reactions. In addition, the conditions for shell-like product formation are determined, and various strategies for the radial patterning of resin beads are compared. The effect of diffusion on polymer-supported enzyme-catalyzed reactions of the Michaelis-Menten type is treated, as well. Finally, the effects of typical nonideal solid-phase phenomena, namely, the inhomogeneity of rate constants and the concentration dependence of diffusion coefficients, on overall rates are discussed.

Resin Bead Micro-UV−Visible Absorption Spectroscopy

The construction and design of a microscope coupled with a miniature UV-vis spectrometer is described. This was applied to the study of dyes linked to solid supports and displayed good correlation in spectral shape and lambda(max) values when compared to the dyes in solution, as well as showing a linear relationship between dye loading and UV-vis absorbance. The spectral profiles of these dyes at various pH's were measured and used to determine the pK(a) of the dyes on the beads, which were compared with the pK(a) values of the dyes in solution, thus enabling the dye-loaded beads to act as pH sensors.

Determination of Site−Site Distance and Site Concentration within Polymer Beads: A Combined Swelling-Electron Paramagnetic Resonance Study

This work proposes a combined swelling-electron paramagnetic resonance (EPR) approach aiming at determining some unusual polymer solvation parameters relevant for chemical processes occurring inside beads. Batches of benzhydrylamine-resin (BHAR), a copolymer of styrene-1% divinylbenzene containing phenylmethylamine groups were, labeled with the paramagnetic amino acid 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amine-4-carboxylic acid (TOAC), and their swelling properties and EPR spectra were examined in DCM and DMF. By taking into account the BHARs labeling degrees, the corresponding swelling values, and some polymer structural characteristics, it was possible to calculate polymer swelling parameters, among them, the volume and the number of sites per bead, site-site distances and site concentration. The latter values ranged from 17 to 170 A and from 0.4 to 550 mM, respectively. EPR spectroscopy was applied to validate the multistep calculation strategy of these swelling parameters. Spin-spin interaction was detected in the labeled resins at site-site distances less than approximately 60 A or probe concentrations higher than approximately 1 x 10(-2) M, in close agreement with the values obtained for the spin probe free in solution. Complementarily, the yield of coupling reactions in different resins indicated that the greater the inter-site distance or the lower the site concentration, the faster the reaction. The results suggested that the model and the experimental measurements developed for the determination of solvation parameters represent a relevant step forward for the deeper understanding and improvement of polymer-related processes.

Getting more from IR-microscopy of resin-bound libraries

A linear pixel-array detector was employed to create spatially resolved multi-layered IR-images of a large collection of polymer beads supporting carbonyl and nitrile monomers. The feasibility of creating multi-layered IR-images with nitrile IR-band separation of 4 cm(-1) was demonstrated, an important issue when considering that many monomers used to develop combinatorial libraries are structurally analogous and therefore occupy very similar positions in the IR-spectrum. Strategies for obtaining high quality spectral data from both imaging and mapping IR-microscopes without compromising on sample area, analysis time, or spatial resolution are also described.

Microscopic infrared mapping of chloromethylated polystyrene resin beads

In solid-phase combinatorial chemistry, analyses are performed using a wide range of analytical techniques ranging from gel-phase nuclear magnetic resonance (NMR) to colorimetric tests to elemental analysis. However, these techniques cannot be used to interrogate functional group distribution at the single-bead level. This paper explores the feasibility of using Fourier transform infrared (FT-IR) microscopy to examine site distribution on chloromethylated polystyrene resin beads and to quantify the loading after coupling with 4-cyanophenol, an IR tagging agent. FT-IR microscopy also provides a unique opportunity to better understand the reactivity of highly cross-linked polymer beads under a range of chemical conditions.

Fluorometric Monitoring Of Organic Reactions On Solid Phase

The direct monitoring of reaction progress on solid supports by fluorescence spectroscopy is described. An immobilized fluorescent tracer molecule (dansyl chloride) is used to monitor the reaction on OH resins (Argopore Wang, PS Wang, and Argogel Wang), both in batch and in parallel chemistry. Fluorescence measurements were obtained directly on solid phase. The method demonstrated to be a valuable tool for the quantitative determination of resin-bound hydroxyl groups, to study reaction kinetics and for continuously monitoring the progress of the conversion of the hydroxyl resins into the chlorinated ones. The procedure proposed is highly sensitive compared to the traditional ones. The system can be extended to monitor a variety of reactions on solid supports, and in conjunction with a well-established technique such as flow analysis, basic studies on solid-phase become possible.

Understanding the effects of the polymer support on reaction rates and kinetics: knowledge toward efficient synthetic design

Solid-phase organic synthesis (SPOS) has an ever-expanding role in the field of organic synthesis. Partially out of difficulty, and partially from the rapid speed of progress, few basic studies on the role of the physical structure of the resin have been undertaken, and the dissemination of the existing knowledge has been slow. Major advances have been made in the understanding of the many factors that govern a SPOS reaction's performance as a function of the choice of solid support.

Ligand distributions in agarose particles as determined by confocal Raman spectroscopy and confocal scanning laser microscopy

Confocal Raman spectroscopy and confocal scanning laser microscopy have been used to analyze ligand distributions within individual chromatographic adsorbent particles. Three different types of particles have been investigated. The first type was synthesized to have a uniform distribution of allyl groups, whereas the two others were designed to have a surface layer of sulphopropyl groups and cores containing allyl groups and dextran, respectively. With confocal Raman spectroscopy it was possible to follow the distribution of both the surface layer and the interior. The distribution of sulphopropyl groups was evaluated with both confocal scanning laser microscopy and confocal Raman spectroscopy, whereas the distributions of allyl groups and dextran were evaluated only with the latter method. The results from the confocal measurements showed the expected result with a uniform distribution of allyl groups in the first type of particle and surface layers of sulphopropyl groups and cores with dextran or allyl groups for the two others.

Which sites react first? Functional site distribution and kinetics on solid supports investigated using confocal Raman and fluorescence microscopy

Fluorescence microscopy is a powerful technique for analyzing beads with very low loadings of fluorophores; however, the method is flawed when looking at more highly loaded beads as a result of severe problems with absorption. To probe distributions at higher loading levels, Raman spectroscopy avoids many of these issues. These studies show that there is a uniform distribution of reactive sites throughout the beads but that the spatial distribution of reacted sites depends on the polymer type, with a fine balance between reaction and diffusion rate.

Single-bead analysis in combinatorial chemistry

Notable limitations have previously prevented the wide application of split synthesis. However, recent developments in highly condensed and miniaturized biological screening and single-bead analysis methods have argued for a revival of split combinatorial synthesis. Although there are still many challenges, we are now in a much better position to accomplish high-throughput analysis and screening of one-bead-one-compound libraries.

Solid supports for combinatorial chemistry

Over the past year, numerous techniques have been used to study the resins commonly utilised in solid-phase synthesis to allow a greater understanding of the chemical nature and the physical properties of the supports. In addition, to overcome some of the drawbacks of existing materials, several new resins and new methods of handling solid supports have been developed. New methodologies have also been introduced to simplify the preparation of solid supports.