Spin-label electron paramagnetic resonance characterization of heterogeneously functionalized dendrimers

Abstract

Dendrimers are roughly spherical macromolecular polymers that can provide a molecular framework for the attachment of various functionalities. The range of application can be vastly expanded when attached with a heterogeneous mix of functionalities tailored to meet a specific need. The effective application requires the acquisition of several new techniques. First, chemical control of the average ratio of functional groups and analytical methods to determine the ratio. Secondly, a determination of the distribution of ratios. And finally, a method whereby the spatial distribution is determined. The ratio and distribution of ratios were determined by MALDI-TOF Mass Spectrometry. The average ratio was easily controlled by using stoichiometric ratios of reactants and the distribution of ratios was found to follow a normal distribution. This was determined by the analysis of the MALDI spectral linewidths. The spatial distribution was determined by a Spin-Label Electron Paramagnetic Resonance technique. By adapting and combining mathematical and spectroscopic techniques from other related systems, it was found that the EPR spectrum was sensitive to the spatial distribution of spin-labels included as one of the attached functional groups. The dipolar interaction between spins lead to an increase in spectral line-broadening that could be compared to computer simulations of different spatial distributions. For all cases studied the distribution was found to be random.