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Biotin-dendrimer conjugates (such as biotin-PAMAMs-NH2) are important macromolecules in the field of host-guest chemistry and widely used systems for delivery. The similar chemical structures of the inner and outer layers of PAMAM-NH2 make it difficult to illuminate the interaction and the binding affinity of biotin-PAMAMs-NH2. By utilizing NMR techniques including 1H NMR titration, CSSF-TOCSY, STDD methods, and 2D DOSY analysis, we demonstrate a method to sort out these interactions. The methylene protons of the inner and outer layers of PAMAM-NH2 are successfully identified and accurately positioned so that the carboxylic acid groups of biotins are having ionic interactions with the outermost amine groups of PAMAM-NH2. The inner PAMAM-NH2 is protonated when reaching the isoelectric point of PAMAM-NH2, increasing the hydrodynamic radius. On the basis of the NMR experiments, a model is proposed, where the carboxylic acid groups and heterocyclic skeleton of biotin arched over the outer layers of PAMAM-NH2 like a bridge. Furthermore, using STDD epitope mapping, the binding affinity between biotin and PAMAM-NH2 was quantified. The diffusion behavior of biotin-G5 PAMAM-NH2 complex is more complicated than that of biotin-G3 PAMAM-NH2 complex due to steric hindrance. The results provide a theoretical basis for understanding these complicated drug delivery systems.

Parasitism usually causes considerable changes in lipids and fatty acids by redirecting the development of the host. In this study, changes in weight and in free fatty acid content of cotton aphids were recorded after aphids had been parasitized. Results showed that the weight of parasitized Aphis gossypii was increased compared to nonparasitized aphids, and significantly increased weights were detected at 1, 2, and 3 instars after parasitization by Lysiphlebia japonica. Free fatty acid test kits and GC-MS showed that the fatty acid content increased in the early stage of parasitization but decreased after 3 days of parasitization. Seven genes related to the fatty acid synthesis pathway were significantly upregulated in the parasitized aphids, where they were 1.96-10.97 times greater. Our data described the change that occurs in the fatty acid content of parasitized A. gossypii.