Salens, as chelating, double Schiff base ligands, are an important group utilized in transition metal catalysis. They have been used to build interesting functional metal-organic frameworks (MOFs). However, salens interacting with amino acids have also found applications in receptors. Here, we intended to form a “green” glycine-derived salen fragment, but the available literature data were contradictory. Therefore, we optimized the synthetic conditions and obtained the desired product as two different crystallographic polymorphs (orthorhombic Pcca and monoclinic P21/c space groups). Their structures differ in conformation at the glycine moiety, and the monoclinic form contains additional, disordered water molecules. Despite the high stability of Schiff bases, these newly obtained compounds hydrolyze in aqueous media, the process being accelerated by metal cations. These studies, accompanied by mechanistic considerations and solid-state moisture and thermal analysis, clarify the structure and behavior of this amino acid Schiff base and shed new light on the role of water in its stability.

Recently, the demand for hybrid PET/MRI imaging techniques has increased significantly, which has sparked the investigation into new ways to simultaneously track multiple molecular targets and improve the localization and expression of biochemical markers. Multimodal imaging probes have recently emerged as powerful tools for improving the detection sensitivity and accuracy—both important factors in disease diagnosis and treatment; however, only a limited number of bimodal probes have been investigated in preclinical models. Herein, we briefly describe the strengths and limitations of PET and MRI modalities and highlight the need for the development of multimodal molecularly-targeted agents. We have tried to thoroughly summarize data on bimodal probes available on PubMed. Emphasis was placed on their design, safety profiles, pharmacokinetics, and clearance properties. The challenges in PET/MR probe development using a number of illustrative examples are also discussed, along with future research directions for these novel conjugates.

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Aminophenols are an important class of N,O-ligands, particularly for the coordination of first-row transition metals. While their structural and electronic character and the additional possibility of bioactivation are well appreciated in coordination chemistry, particularly of responsive systems, the synthesis of the more branched and structurally demanding models is still a challenge. Therefore, the synthesis of bulky bis(hydroxybenzyl)-N'-(aminopyridyl)propanamines is described here. It consists of the Mannich reaction of 2,4disubstituted phenols with 3-aminopropan-1-ol and paraformaldehyde to N,N-bis(2hydroxybenzyl)-3-aminopropan-1-ol. Substitution of the hydroxyl group with chlorine followed by amination with 2-(aminomethyl)pyridine results in bulky pentadentate N,Oligands with a free site on the nitrogen atom for further functionalization. The method features good yields and high selectivity, and the products are well identified by spectroscopic methods.

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