Several aspects of pyrene fluorescence were applied to gain an insight into the nature of the microdomains in hydrophobically modified starch nanoparticles (HM-SNPs), prepared by reacting SNPs with propionic and hexanoic anhydride to yield C3- and C6-SNPs, respectively. The fluorescence experiments took advantage of the inherent hydrophobicity of pyrene to bind onto the hydrophobic domains generated by the HM-SNPs, and its specific response to the polarity of its environment, to probe its accessibility to quenchers such as oxygen or nitromethane dissolved in water. The equilibrium constant K for the binding of pyrene onto HM-SNPs, the ratio ( I/ I) describing the relative hydrophobicity of the microenvironment experienced by pyrene, its lifetime (τ), and the rate constant of quenching of pyrene bound to the HM-SNPs by water-soluble nitromethane ( k) were determined as a function of the degree of substitution and weight fraction (wt %) of the hydrophobic modifier. The C3- and C6-SNPs yielded similar parameters at low levels of hydrophobic modification, indicating higher hydrophobicity of the modified SNPs with increasing modification level. However, SNPs modified with more than 5 wt % of hexanoyl pendants all displayed enhanced hydrophobicity for the C6-SNPs relative to the C3-SNPs. This substantial enhancement is attributed to the formation of larger hydrophobic microdomains by the hexanoyl pendants of the C6-SNPs above the 5 wt % C6-modification threshold, which did not occur with the C3-SNPs. Finally, the size of the SNPs did not appear to influence their relative hydrophobicity. These experiments demonstrate how the fluorescence of pyrene can be harnessed to provide information about the relative hydrophobicity of HM-SNPs.
The conjugation of dendrons having varying peripheral functionalities to polymer vesicles, commonly referred to as polymersomes, provides an opportunity to significantly alter the polymersome surface chemistry in a single step while leaving intact the block copolymers responsible for assembly. In this work, polymersomes with surface azide groups were prepared from poly(1,2-butadiene)-poly(ethylene oxide) (PBD-PEO) and poly(3-caprolactone)-PEO (PCL-PEO) block copolymers and were functionalized with polyester dendrons having focal point alkyne moieties and peripheral hydroxyls, amines, or guanidines. The release rates of a small molecule rhodamine B and a rhodamine B-labeled protein from naked and functionalized polymersomes were investigated and the presence of dendritic groups was found to have a minimal effect. All of the naked and functionalized polymersomes were found to be nontoxic at all concentrations tested, except for the guanidine functionalized polymersomes which did impart some toxicity at the highest concentrations tested. The cell uptake of the different polymersomes was compared and it was found that the guanidine functionalized polymersomes exhibited increased cell uptake relative to all other materials. Further studies of this phenomenon suggested that the uptake is mediated by endocytosis and possibly direct translocation across the membrane.
Theoretical calculations illustrate that organometallic macromolecules with piano stool coordination repeating units (Fe-acyl complex) adopt linear chain configuration with a P-Fe-C backbone surrounded by aromatic groups. The macromolecules show molecular weight-dependent and temperature stimulated solution behaviour in DMSO.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.