Pulsed‐Laser Polymerization in Compartmentalized Liquids, 2. Miniemulsions

The propagation rate coefficient (k_p) of methyl methacrylate has been measured in miniemulsions. The molecular weight distributions show many higher order peaks, which seems to be specific for pulsed initiation polymerization in compartmentalized liquids. The k_p values are very similar to bulk values although a frequency dependence is observed. This frequency dependence, which was overlooked in earlier research, is also present in pulsed laser experiments in bulk.     

Unprecedented Relaxivity Gap in pH-Responsive FeIII-Based MRI Probes

Two mononuclear ferric complexes are reported that respond to a pH change with a 27- and 71-fold jump, respectively, in their capacity to accelerate the longitudinal relaxation rate of water-hydrogen nuclei, and this starting from a negligible base value of only 0.06. This unprecedented performance bodes well for tackling the sensitivity issues hampering the development of Molecular MRI. The two chelates also excel in the fully reversible and fatigue-less nature of this phenomenon. The structural reasons for this performance reside in the macrocyclic nature of the hexa-dentate ligand, as well as the presence of a single pendant arm displaying a five-membered lactam or carbamate which show (perturbed) pK_a values of 3.5 in the context of this N6 N5O1 coordination motif.