Single-molecule force spectroscopic study on chiral recognition of cysteine derivatives immobilized on a gold substrate by using AFM tips chemically modified with optically active crown ethers

Nakahara, Yoshio; Mitani, Hitoshi; Kado, Shinpei; Kimura, Kazuhiro

doi:10.1039/c4ra10553b

Cited by 6 publications

(1 citation statement)

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“…Interestingly, the FJC as well as the WLC model fits the experimental data very well when Kuhn length and contour length are used as free fitting parameters (see Supporting Information). On the one hand, this explains why the WLC model is commonly used to fit experimental PEG stretching data. − On the other hand, this demonstrates that the short coming of standard polymer stretching models is only revealed when the fundamental polymer length scales b and L are determined independently, as is the case in Figure a. These results for PEG are different from the classical example of DNA stretching, where the FJC model fails but the WLC chain model correctly describes the DNA stretching data over the entire force range .…”

Section: Results and Discussionmentioning

confidence: 97%

Hydration Effects Turn a Highly Stretched Polymer from an Entropic into an Energetic Spring

Liese¹,

et al. 2016

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Polyethylene glycol (PEG) is a structurally simple and nontoxic water-soluble polymer that is widely used in medical and pharmaceutical applications as molecular linker and spacer. In such applications, PEG's elastic response against conformational deformations is key to its function. According to text-book knowledge, a polymer reacts to the stretching of its end-to-end separation by a decrease in entropy that is due to the reduction of available conformations, which is why polymers are commonly called entropic springs. By a combination of single-molecule force spectroscopy experiments with molecular dynamics simulations in explicit water, we show that entropic hydration effects almost exactly compensate the chain conformational entropy loss at high stretching. Our simulations reveal that this entropic compensation is due to the stretching-induced release of water molecules that in the relaxed state form double hydrogen bonds with PEG. As a consequence, the stretching response of PEG is predominantly of energetic, not of entropic, origin at high forces and caused by hydration effects, while PEG backbone deformations only play a minor role. These findings demonstrate the importance of hydration for the mechanics of macromolecules and constitute a case example that sheds light on the antagonistic interplay of conformational and hydration degrees of freedom.

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