Positron annihilation in alpha- and beta-cyclodextrin

Hsu, F. H.; Yang, Meek; Yang, Chuanlu

doi:10.1007/bf00896895

Cited by 9 publications

(2 citation statements)

References 7 publications

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“…Notably, the free-volume size of the CD glass was approximately the same as the corresponding polyrotaxane glass. Evacuated, unmodified, crystalline α-CD is known to have a relatively long lifetime (∼4 ns), which corresponds to the size of the inclusion cavity size, whereas the cavity can be occupied with adsorbed water to shorten the lifetime (∼2 ns). , Both the CD glass also exhibited ∼2 ns lifetimes, suggesting that the observed free volume was not located in the inclusion cavity but outside the interspace between CD molecules. It is consistent with the observed coincidence of the free-volume size independent of the presence of the threading PEG chains.…”

Section: Resultsmentioning

confidence: 99%

Effects of Ring Size on the Dynamics of Polyrotaxane Glass

et al. 2020

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The dynamics of two polyrotaxanes with different ring component sizes were compared through viscoelastic measurements. An improved polyrotaxane synthesis was used to develop a glass-forming polyrotaxane composed of γ-cyclodextrin (γ-CD), which is a larger cyclic molecule than α-cyclodextrin (α-CD)a component of a comparative polyrotaxane. In the glass state, both polyrotaxanes exhibited a large secondary relaxation attributed to the confined motion of the threading polyethylene glycol as the main chain, and their dynamics were not affected by the ring size. However, the glass-transition dynamics were clearly steepened by the enlargement of rings. The analysis of the glass-transition dynamics revealed that the segment motion of polyrotaxane, which is the translation of the threading polymer with several rings threaded cooperatively, was released near the glass-transition temperature determined by differential scanning calorimetry, T g(d), in the case of polyrotaxane with γ-CD, whereas the release was relatively delayed in the case of α-CD. This finding suggests that the enlargement of the rings weakens the topological constraints that prolong the onset of the segment motion of polyrotaxanes. Positron annihilation lifetime measurements showed a negligible difference in the free volume of polyrotaxane glasses with different ring sizes. This finding indicates that the larger ring did not provide an additional space for the segment motion but probably an undetectable small gap between the inner wall of the ring and the threading polymer to facilitate the ring-chain cooperative motion.

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Section: Resultsmentioning

confidence: 99%

Effects of Ring Size on the Dynamics of Polyrotaxane Glass

et al. 2020

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“…For a reason unknown to the author, the research on biological membranes stopped in mid 80's and further development on positron studies or theory on biological membranes has not occurred until know. In addition, several studies are published in related materials, ranging from studies on micelles [32] to porous chemical structures such as cyclodextrines [33]. Different approaches and examples over the years can also be found in the proceedings of both International…”

Section: -Experimental Techniques For Biophysical Researchmentioning

confidence: 99%

Probing The Microstructure Of Biomaterials With Positrons

Sane¹,

Tuomisto²,

Vattulainen³

et al. 2009

Biophysical Journal

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Voids in biological membranes are vital to the diffusion characteristics of the membranes and as such information gained from e.g. void sizes elucidates the understanding of the functionality of the membrane. In this thesis the focus is on lipid bilayers, a type of membrane that exists in almost all organisms as a diffusion barrier surrounding the cells. The lipid bilayer consists of hydrophilic and hydrophobic parts that can form the bilayer structure in aqueous solution and the structural properties of the inner core of the bilayer (aka. hydrocarbon tail area) have a strong effect on the diffusion of particles through the bilayer. One of the key elements in the bilayer structure is the distribution and size of the free volume pockets, voids. The size of the voids depend both on the lipid type, but as well as the structural parameters of the bilayer, so called phase behaviour of the bilayer structure. Positron annihilation lifetime spectroscopy is a widely used tool to characterize atomic-scale structural properties of both solid state and soft matter and as such the correlation with positron (or to be specific positronium, the bound state of positron and electron) lifetime and the size of voids in e.g. polymers has been observed. In this thesis positron annihilation lifetime spectroscopy has been applied to probe the voids in lipid bilayers in several manners: Firstly as a proof-of-concept-type of experiment reveals the feasibility of positron annihilation lifetime spectroscopy as a tool to detect subtle differences in the void sizes depending on the lipid concentration in aqueous solution, secondly it is found possible to characterize the phase transition temperature by observing the change of void sizes below and above the phase transition temperature. In addition, the effect of dopants, namely cholesterol, on the bilayer structure is studied as a function of cholesterol concentration. The feasibility of positron annihilation lifetime spectroscopy to study intact tissues in-situ is also presented in a study where the temperature-induced structural transition of mammalian lens is observed and traced down to the lipids the lens strongly consists of.

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Positron Annihilation Spectroscopy

Schmidt¹

2002

Handbook of Porous Solids

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Positron annihilation in alpha- and beta-cyclodextrin

Cited by 9 publications

References 7 publications

Effects of Ring Size on the Dynamics of Polyrotaxane Glass

Effects of Ring Size on the Dynamics of Polyrotaxane Glass

Probing The Microstructure Of Biomaterials With Positrons

Positron Annihilation Spectroscopy

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