Unprecedented Water Effect as a Key Element in Salicyl-Glycine Schiff Base Synthesis

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

Surprising Solid-State ESIPT Emission from Apparently Ordinary Salicyliden Glycinates Schiff Bases

Excited-State Intramolecular Photon Transfer (ESIPT) is known for the geometry-related phenolic and imine groups. The Schiff bases formed upon condensation of salicyl aldehyde and glycine led to the formation of ESIPT models. A series of alkali metal salicyliden glycinates were analyzed by X-ray diffraction of their monocrystals and spectroscopy measurements. The X-ray analysis revealed varied hydration levels between the salts. They adapted trans geometry on the imine groups and mostly anticlinal conformation with the neighboring atoms, which is different from the other structurally-related compounds in literature. Fluorescence of these compounds was found for the crystalline forms only. Protonation of the imine nitrogen atom and further proton distribution was consistent with the ESIPT theory, which also explained the observed fluorescence with the highest Stokes shift of 10,181 cm−1 and 10.1% of fluorescence quantum yield for the sodium salt

Doping Engineering of Single-Walled Carbon Nanotubes by Nitrogen Compounds Using Basicity and Alignment.

Charge transport properties in single-walled carbon nanotubes (SWCNTs) can be significantly modified through doping, tuning their electrical and thermoelectric properties. In our study, we used more than 40 nitrogen-bearing compounds as dopants and determined their impact on the material's electrical conductivity. The application of nitrogen compounds of diverse structures and electronic configurations enabled us to determine how the dopant nature affects the SWCNTs. The results reveal that the impact of these dopants can often be anticipated by considering their Hammett's constants and pKa values. Furthermore, the empirical observations supported by first-principles calculations indicate that the doping level can be tuned not only by changing the type and the concentration of dopants but also by varying the orientation of nitrogen compounds around SWCNTs