论文标题

糖构象的能量景观控制自组装的Bola糖胶质水凝胶中的Sol-Gel转变

Energy Landscape of Sugar Conformation Controls the Sol-to-Gel Transition in Self-assembled Bola Glycolipid Hydrogels

论文作者

Poirier, Alexandre, Griel, Patrick Le, Zinn, Thomas, Pernot, Petra, Roelants, Sophie, Soetaert, Wim, Baccile, Niki

论文摘要

自组装的原纤维网络(SAFIN)水凝胶和有机凝胶通常是通过结晶过程获得的,该过程是由温度或pH(例如温度或pH)引起的纤维。凝胶到溶质到凝胶的转变通常很容易可逆,刺激的变化速率决定了凝胶的纤维均匀性和最终弹性特性。然而,最近的工作表明,在某些特定情况下,对于给定的分子构象而发生纤颤,而溶胶 - 凝胶转变取决于一种构型的相对能量稳定性,而不是另一个构型的相对能量稳定性,而不是刺激的变化速率。我们在一类Bolaform糖脂上观察到这种现象,类似于众所周知的Sophorolipid生物表面活性剂,但由两个对称的Sophorose单位组成。振荡性流变学,小角度X射线散射(SAXS)低温传递电子显微镜(Cryo-TEM)和使用同步辐射的原位Rheo-Saxs的组合表明,低于14 $^\ circ $ c,扭曲的纳米纤维是热力学相。在14 $^\ Circ $ C和大约33 $^\ CIRC $ C之间,纳米纤维与胶束和强凝胶形式共存,在此温度范围内,Sol-to-Gel过渡很容易可逆。但是,高于大约40 $^\ Circ $ c的退火温度,胶束形态在数小时内会被动力捕获,即使在冷却后,无论速率以哪一为4 $^\ circt $ c。 A combination of solution and solid-state nuclear magnetic resonance (NMR) suggests two different conformations of the 1'', 1' and 2' carbon stereocenters of sophorose, precisely at the $β(1,2)$ glycosidic bond, for which several combinations of the dihedral angles are known to provide at least three energetic minima of comparable magnitude and each corresponding to a given sophorose conformation.

Self-assembled fibrillar network (SAFIN) hydrogels and organogels are commonly obtained by a crystallization process into fibers induced by external stimuli like temperature or pH. The gel-to-sol-to-gel transition is generally readily reversible and the change rate of the stimulus determines the fiber homogeneity and eventual elastic properties of the gels. However, recent work shows that in some specific cases, fibrillation occurs for a given molecular conformation and the sol-to-gel transition depends on the relative energetic stability of one conformation over the other, and not on the rate of change of the stimuli. We observe such a phenomenon on a class of bolaform glycolipids, sophorosides, similar to the well-known sophorolipid biosurfactants, but composed of two symmetric sophorose units. A combination of oscillatory rheology, small-angle X-ray scattering (SAXS) cryogenic transmission electron microscopy (cryo-TEM) and in situ rheo-SAXS using synchrotron radiation shows that below 14$^\circ$C, twisted nanofibers are the thermodynamic phase. Between 14$^\circ$C and about 33$^\circ$C, nanofibers coexist with micelles and a strong hydrogel forms, the sol-to-gel transition being readily reversible in this temperature range. However, above the annealing temperature of about 40$^\circ$C, the micelle morphology becomes kinetically-trapped over hours, even upon cooling, whichever the rate, to 4$^\circ$C. A combination of solution and solid-state nuclear magnetic resonance (NMR) suggests two different conformations of the 1'', 1' and 2' carbon stereocenters of sophorose, precisely at the $β(1,2)$ glycosidic bond, for which several combinations of the dihedral angles are known to provide at least three energetic minima of comparable magnitude and each corresponding to a given sophorose conformation.

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