Yuzo Yamazaki1, Shuuichi Nakaya1, Kozo Ito2, Kazuaki Kato2
- Global Application Development Center, Analytical & Measuring Instruments Division, Shimadzu Corporation, 1, Nishinokyo-Kuwabaracho, Nakagyo-ku, Kyoto 604-8511, Japan
- Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
Polyrotaxane (PR) is a necklace-like supramolecule composed of cyclic components, such as cyclodextrin (CD), and a threading polymer capped with bulky end groups. PR exhibits peculiar mechanical properties attributed to the intermolecular cross-links with CD. Various CD molecules threaded on a linear PEG chain are often modified with chemical groups to add specific physicochemical properties. In general, the stoichiometry between CD and the PEG chain is a significant parameter that defines the unique physical properties of CD-based polyrotaxane (CD-PR). To date, mass spectrometry (MS) has been applied to investigate the molecular distribution of CD-PR, modifications of CD, and the threaded ratio of CD. However, only molecular weights (MWs) up to several 10s of kDa can be subjected to such analysis, whereas the MW of CD-PR used as industrial materials is much greater. Herein, we applied two ionic liquid matrices composed of 3-aminoquinoline and a high mass detector to analyze PRs using MALDI-TOF-MS. High to very high MW PRs in the range of 90–700 kDa were successfully analyzed using this method. The threaded ratio of CD was estimated from a single MW of CD, PEG, and PR. The ratios obtained were consistent with that obtained using 1H NMR. Furthermore, a single-stranded form of PR in γ-cyclodextrin threaded PR (γCD-PR) was clearly distinguished from a double-stranded form, which is only possible in γCD -PR because of its large host cavity.
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The physical properties of cyclodextrin (CD) based polyrotaxane (PR) were analyzed in this article by understanding the stoichiometry between CD and the polyethylene glycol (PEG) chain using the high and very high molecular weights (MW) of CD-PR ranges of 90-700 kDa. Five different CD-PRs were analyzed which include APR20 and APR35 that were dissolved in ACS grade dimethyl sulfoxide (DMSO) at 20 mg/mL, Gamma-PRs that were dissolved in DMSO at 5 mg/mL, and SH2400 & SH3400 were dissolved in two kinds of solvents: HPLC grade tetrahydrofuran (THF) and DMSO containing 20 mM LiBr at 20 mg/mL. 0.5 to 1.0 μL of the dissolved PRs were mixed with the same volume of the ionic liquid matrices (ILM) matrix solution on a stainless MALDI plate. These solutions were analyzed using MALDI-TOF-MS containing 337 nm nitrogen laser along with CovalX’s HM3 highmass detection system. From a single MW of CD, PEG and PR obtained from MS results, the threaded ratios of CD were estimated and came out consistent with what is obtained using 1H-NMR.