Approximately 5 mg of each sample was dissolved in a solution of DMSO-d6 (1.0 mL, 0.03% TMS) and D2O (0.2 mL, 35% DCl), before measurement at room temperature on a Bruker Advance III HD 500 MHz spectrometer at the Department of Chemistry, University of Cambridge. TMS was used as a standard and data processing and analysis was carried out using TopSpin software version 4.1.1. Optical microscopy. A Leica MZ95 microscope and a Optika C-B10 camera with a 10 megapixels CMOS sensor was used to obtain optical images of all samples.