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Crowding effect on helix-coil transition: Beyond entropic stabilization
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10.1063/1.4723871
/content/aip/journal/jcp/136/21/10.1063/1.4723871
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/21/10.1063/1.4723871

Figures

Image of FIG. 1.
FIG. 1.

Coherent differential scattering cross section per unit volume and unit of PEG volume fraction IPEG vs. scattering vector q for PEG solutions at T = 20 °C. Lines are best fits following Eq. (2).

Image of FIG. 2.
FIG. 2.

Mean short distance, ξ/a, and curvilinear distance, g = m(ξ)/m a , between neighboring PEG chains vs. volume fraction ϕPEG, measured at T = 20 °C, with m a the molar mass of the monomer and a its length from Ref. 15. Straight lines are best power law fits corresponding to and , respectively.

Image of FIG. 3.
FIG. 3.

Molar ellipticity θ at 222 nm per amino acid of poly(L-glutamic acid) solutions vs. temperature for different pH. The horizontal dashed line has an ordinate θ1/2 corresponding to the helix fraction 1/2.

Image of FIG. 4.
FIG. 4.

Ellipticity θ at 222 nm per amino acid of poly(L-glutamic acid) solutions at pH = 3.75 vs. temperature for different volume fractions of PEG. Full and open symbols correspond to rising and decreasing temperature curves, respectively. The horizontal line has an ordinate θ1/2 corresponding to the helix fraction x h = 1/2.

Image of FIG. 5.
FIG. 5.

Helix fraction x h of poly(L-glutamic acid) solutions at pH = 3.75 vs. reduced temperature T/T* for different volume fractions of PEG.

Image of FIG. 6.
FIG. 6.

Reverse transition temperature 1/T* vs. logarithm of the accessible volume fraction ln (1 − ϕPEG). Straight lines are guides for the eyes with slopes equal to 1/560 K (Ref. 30) for fully protonated (dashed lines) and 1/317 K (Ref. 31) for fully dissociated (full lines) glutamic acid monomers, respectively. Full symbols: present work (pH = 3.75). Open symbols: from Fig. 5 in Ref. 5 (pH = 5.8). At this latter pH, T*(0) (intercept of dashed and full lines) is not accessible. It has been arbitrary set to 235 K in order the green dashed line fits the data points of Ref. 5.

Image of FIG. 7.
FIG. 7.

(Top) Reverse correlation length L h (T*) of helices at the transition vs. reverse mesh size ξ of the PEG network. (Bottom) Average number N h (T*) of amino acid per helix at the transition vs. the ratio L h (T*)/ξ. The close symbol at x-coordinate equal to 0 corresponds to ϕPEG = 0 (i.e., ξ → ∞). Either ξ measured at 20 °C (circles) or ξ(T*) (squares) calculated from Eq. (3) and Ref. 16 are used to compute the x-coordinate.

Tables

Generic image for table
Table I.

Summary of the results obtained by circular dichroism measurements: transition temperature T*; Zimm-Bragg parameter σ deduced from the slope at T* of θ(T); extent N h and correlation length L h of helical domains at the transition.

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/content/aip/journal/jcp/136/21/10.1063/1.4723871
2012-06-04
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Crowding effect on helix-coil transition: Beyond entropic stabilization
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/21/10.1063/1.4723871
10.1063/1.4723871
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