Spectral and microscopic study of self-assembly of novel cationic spermine amides of betulinic acid.

Abstract Supramolecular characteristics of two spermine amides of betulinic acid ( 1 and 2 ) were studied by measuring and evaluating their UV–VIS-NIR spectra in aqueous acetonitrile and DOSY-NMR spectra in tetradeuteromethanol, accompanied by atomic force microscopy (AFM) images, scanning electron microscopy (SEM) micrographs, and transmission electron microscopy (TEM) micrographs. Fibrous supramolecular self-assembly of 1 and 2 was observed by AFM images, as well as by the SEM and TEM micrographs. Bathochromic shifts of the absorbance maximum at 870 nm to 1015–970 nm in the UV–VIS-NIR spectra were observed with increasing water content in the acetonitrile/water systems, indicating formation of fibrous J -type aggregates. Variable temperature DOSY-NMR spectral measurement showed non-linear dependence that also suggests self-assembly behavior of the studied systems. Chiral supramolecular structures were formed by self-assembling due to the chirality of the monomeric molecules. Application of aqueous media during self-assembly procedures is an important factor in the development of targeted drug delivery systems.