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Abstract
Nano-sized amylopectin fragments (NAFs), prepared by extrusion of waxy corn starch, were investigated by viscometry, dynamic light scattering (DLS), and pyrene excimer fluorescence (PEF). NAF57, with a hydrodynamic diameter of 57 nm, was treated with nitric acid to yield three degraded NAFs, which appeared to share the same interior and structural features as amylopectin based on their measured intrinsic viscosity and hydrodynamic diameter. This conclusion was further supported by comparing the efficiency of forming excimer between an excited and a ground-state pyrenyl label covalently attached to the NAFs (Py-NAFs) using their IE/IM ratio of the fluorescence intensity of the excimer (IE) to that of the monomer (IM). The overlapping trends obtained for all Py-NAFs and the pyrene-labeled amylopectin samples by plotting the IE/IM ratio as a function of pyrene content provided further evidence that the interior of NAFs and amylopectin shared the same structural features and contained a similar amount of free volume as predicted by the Solution-Cluster (Sol-CL) model. The presence of free volume was validated by adding linear poly(ethylene glycol) (PEG) chains that could not penetrate the interior of Py-NAFs, thus subjecting the Py-NAFs to increased osmotic pressure, which induced their compression and resulted in an increase in IE/IM.
Highlights
Starch nanoparticles (SNPs) can be employed as substitutes of petroleum-based latex used in the paper coating industry, and their potential as food additives or drug carriers is being actively researched [1]
To be most effective, these chemical modifications require the characterization of SNPs from a viewpoint pertaining to synthetic polymer particles, based on their hydrodynamic diameter (Dh )
The global Fluorescence Blob Model (FBM) analysis of the pyrene monomer and excimer fluorescence decays acquired with Py-nano-sized amylopectin fragments (NAFs) dispersions in dimethyl sulfoxide (DMSO) has been described earlier in detail [15] and are presented in the Supplementary Materials
Summary
Starch nanoparticles (SNPs) can be employed as substitutes of petroleum-based latex used in the paper coating industry, and their potential as food additives or drug carriers is being actively researched [1]. Changes in the IE /IM ratio of a polysaccharide fluorescently labeled with PyBA indicate changes in [Py]loc , and in the local concentration of the oligosaccharide side chains onto which PyBA is covalently attached These concepts were implemented in the present study that provides additional evidence in support of the Sol-CL model introduced earlier [15] and affords a better understanding of the arrangement of oligosaccharide side chains inside NAFs. The experiments described in this paper used the same. This study on Py-NAFs confirmed the existence of oligosaccharide-rich clusters inside NAFs separated by the excluded volume generated by linear oligosaccharide segments bridging the clusters of helices This study represents another example of the use of PEF in the characterization of polysaccharides in solution
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