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

Amy V Hall,Osama M Musa,David K Hood,Dmitry S Yufit,Jonathan W Steed,David C Apperley

doi:10.1021/acs.cgd.1c00031

Amy V Hall, Osama M Musa + Show 4 more

Open Access

https://doi.org/10.1021/acs.cgd.1c00031

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Abstract

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.

Highlights

Radiochromic films are commercially important materials, especially in medical physics, and provide reliable and accurate dose assessments
The lithium salt of PCDA is synthesized by dissolving PCDA in a basic solution at elevated temperatures.[32]
We have examined the differences between the two crystal morphologies of lithium salt of PCDA (Li-PCDA) by powder X-ray diffraction (PXRD), which revealed that the two different morphologies represent two different crystalline forms

Summary

■ INTRODUCTION

Radiochromic films are commercially important materials, especially in medical physics, and provide reliable and accurate dose assessments. The proposed coordination environment of the lithium ion in form B is displayed, while the water molecule is likely in form B) is indicative of triclinic or hexagonal packing,[42] with triclinic being the most likely crystal system;[43,44] this is in agreement with the P1 space group of the related Agdocosanoate and long-chain lithium alkanoates.[38,41] if the methylene band is split (as observed in form A), a monoclinic or orthorhombic crystal system is suggested, such as the P21/c space group of short-chain lithium alkanoates.[38,42] While it is the monohydrated Li-PCDA (form A) material that is currently used in GAFchromic EBT3 films, it can be assumed that both form A and form B must conform to the topochemical postulate for photoreactivity, since both display radiation sensitivity. Characterization of the irradiated powder provided no evidence of photopolymerization or photodegradation, which was evident by the lack of alkene peaks in the region of 130−100 ppm in the ssNMR spectra

■ CONCLUSION

■ ACKNOWLEDGMENTS

■ REFERENCES