Translating a Low‐Molecular‐Weight MRI Probe Sensitive to Amino Acid Neurotransmitters into a PAMAM Dendrimer Conjugate: The Impact of Conjugation

Abstract A novel nano‐sized MRI probe sensitive to zwitterionic amino acid neurotransmitters (ZNTs) was prepared by the conjugation of bismacrocyclic ZNT‐responsive units to a generation 4 (G4) polyamidoamine (PAMAM) dendrimer. In vitro evaluation through ¹H NMR relaxometric titrations provided binding profiles revealing a surface morphology‐dependent interaction with the ZNTs. The positively charged dendrimeric periphery gave higher initial relaxivities and a milder decrease upon interaction with the target molecules. To improve solubility under physiologically relevant conditions, polyethylene glycol (PEG) units were additionally conjugated to the dendrimeric surface. The PEGylated conjugate displayed discrimination towards acetylcholine and a slightly increased binding affinity towards glutamate over the massively abundant competitive metabolite hydrogencarbonate.