Acrylic Acid “Reversed” PolyHIPEs

Summary: An oil‐in‐water high internal phase emulsion consisting of acrylic acid, water, and a crosslinker (N,N′‐methylene bisacrylamide) as the water phase, and toluene as the oil phase was successfully stabilised to sustain thermal initiation of radical polymerisation resulting in porous open‐cellular monolithic material. The type of initiator used influenced the average pore size ranging from approx. 708 nm to approx. 1 087 nm, as determined by mercury porosimetry.

Schematic of the preparation of an oil‐in‐water‐type polyHIPE (high internal phase emulsion).     

Distorted Fivefold‐Diamond Structure of 4,4‐Bis(2‐carboxyethyl)pimelic Acid (‘Methanetetrapropionic Acid’)

The molecules of 4,4‐bis(2‐carboxyethyl)pimelic acid (=4,4‐bis(2‐carboxyethyl)heptanedioic acid; 1 ) assemble to build up hollow, five‐fold interpenetrating diamond‐like networks in tetragonal crystals via standard pairwise H‐bonds between the carboxy groups. In keeping with the flat, extended molecular conformation of 1 of approximate D_2d symmetry, the supramolecular diamondoid networks are tetragonally compressed. Their mode of interpenetration is unusual and corresponds to that of adamantane‐1,3,5,7‐tetracarboxylic acid, which has an undistorted five‐fold diamond structure. Both the degree and the mode of interpenetration of 1 differ from those of the lower homologue 3,3‐bis(carboxymethyl)glutaric acid ( 2 ), which adopts a more‐common tetragonally elongated triple‐diamond architecture in the solid state.     

Applications of “Hot” and “Cold” Bis(thiosemicarbazonato) Metal Complexes in Multimodal Imaging

The applications of coordination chemistry to molecular imaging has become a matter of intense research over the past 10 years. In particular, the applications of bis(thiosemicarbazonato) metal complexes in molecular imaging have mainly been focused on compounds with aliphatic backbones due to the in vivo imaging success of hypoxic tumors with PET (positron emission tomography) using ⁶⁴CuATSM [copper (diacetyl‐bis(N4‐methylthiosemicarbazone))]. This compound entered clinical trials in the US and the UK during the first decade of the 21^st century for imaging hypoxia in head and neck tumors. The replacement of the ligand backbone to aromatic groups, coupled with the exocyclic N's functionalization during the synthesis of bis(thiosemicarbazones) opens the possibility to use the corresponding metal complexes as multimodal imaging agents of use, both in vitro for optical detection, and in vivo when radiolabeled with several different metallic species. The greater kinetic stability of acenaphthenequinone bis(thiosemicarbazonato) metal complexes, with respect to that of the corresponding aliphatic ATSM complexes, allows the stabilization of a number of imaging probes, with special interest in “cold” and “hot” Cu(II) and Ga(III) derivatives for PET applications and ¹¹¹In(III) derivatives for SPECT (single‐photon emission computed tomography) applications, whilst Zn(II) derivatives display optical imaging properties in cells, with enhanced fluorescence emission and lifetime with respect to the free ligands. Preliminary studies have shown that gallium‐based acenaphthenequinone bis(thiosemicarbazonato) complexes are also hypoxia selective in vitro, thus increasing the interest in them as new generation imaging agents for in vitro and in vivo applications.