Chromatic response of cationic polydiacetylene vesicles induced by permeation of target compound

Structure and stability of polydiacetylene membrane systems: Molecular dynamics simulation studies

We have performed full atomistic molecular dynamics (MD) simulations to investigate structure and stability of bilayer membrane systems consisting of monomeric or polymeric 10,12-pentacosadiynoic acid (PCDA) units connected with lysine groups by amide bonds. The PCDA monomer molecules show a twisted three-rod-domain structure with two kinks but upon polymerization, they possess more elongated conformation. The resulting polydiacetylene (PDA) membrane systems have stable membrane structures at room temperature, which is similar to biological lipid bilayer membranes and maintain their gel-like membrane integrity even up to as high as 370 K. Structural properties such as area per monomer, membrane thickness, density profile, 2D pair distribution function, and orientational correlation function are also calculated to understand the membrane structure and check its stability upon thermal fluctuation with atomistic resolution. This study is expected to provide the understanding about PDA membrane systems in atomistic details as well as significant insights into designing new novel PDA sensors.

Alkali Metal Salts of 10,12-Pentacosadiynoic Acid and Their Dosimetry Applications

Wide-dose-range 2D radiochromic films for radiotherapy, such as GAFchromic EBT, are based on the lithium salt of 10,12-pentacosadiynoic acid (Li-PCDA) as the photosensitive component. We show that there are two solid forms of Li-PCDA-a monohydrated form A and an anhydrous form B. The form used in commercial GAFchromic films is form A due to its short needle-shaped crystals, which provide favorable coating properties. Form B provides an enhanced photoresponse compared to that of form A, but adopts a long needle crystal morphology, which is difficult to process. The two forms were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, CP-MAS ¹³C solid-state NMR spectroscopy, and thermogravimetric analysis. In sum, these data suggest a chelating bridging bidentate coordination mode for the lithium ions. The sodium salt of PCDA (Na-PCDA) is also reported, which is an ionic cocrystal with a formula of Na⁺PCDA^-·3PCDA. The PCDA and PCDA^- ligands display monodentate and bridging bidentate coordination to the sodium ion in contrast to the coordination sphere of the Li-PCDA forms. In contrast to its lithium analogues, Na-PCDA is photostable.