明胶/Fe2S3纳米生物复合物形成反应的热力学及明胶构象变化

在pH=7.40条件下,采用一锅化学反应法制得水溶性明胶/Fe₂S₃纳米生物复合物,扫描电镜照片显示Fe₂S₃颗粒为棒状.根据吸光度与Fe₂S₃浓度关系,由Benesi-Hildebrand方程计算了不同温度下反应的形成常数K (293 K: 14.47×10² L·mol^-1; 297 K: 9.24×10² L·mol^-1; 309 K: 1.70×10² L·mol^-1)及对应温度下反应的热力学参数(Δ_rG_m = -17.88/-16.68/-13.09 kJ·mol^-1; Δ_rH_m = -105.57 kJ·mol^-1; Δ_rS_m = -299.28 J·K^-1·mol^-1),结果表明明胶/Fe₂S₃纳米生物复合物的形成反应是自发的放热过程,且为焓驱动.傅里叶变换红外光谱表明,Fe₂S₃主要与明胶大分子肽链中的酰胺键结合;对红外光谱进行去卷积拟合,结果表明:明胶蛋白质的 α-螺旋含量减少,β-折叠含量明显增加.结合紫外和红外光谱测试结果对复合物的形成机理作了初步的推测:首先Fe³⁺与明胶大分子中的酰胺键结合形成明胶/Fe³⁺复合物,然后S^2-与明胶/Fe³⁺中的Fe³⁺形成明胶/Fe₂S₃复合物.

The Thermodynamics of Gelatin/Fe2S3 Bionanocomposites Formation and Gelatin Conformational Change

The gelatin/Fe₂S₃ bionanocomposite was synthesized via a facile one-pot chemical route at pH=7.40. The SEM image showed that the shapes of the bionanocomposites were rod-like. Based on the relationship between the absorbance data of system and the concentration of Fe₂S₃, the Benesi Hildebrand equation was used to calculate the formation constants K(293 K: 14.47 10² L·mol^-1; 297 K: 9.24 10² L·mol^-1; 309 K: 1.70 10² L·mol^-1) at three different temperatures. Thermodynamic parameters were also determined (Δ_rG_m =-17.88/-16.68/-13.09 kJ·mol^-1; Δ_rH_m =-105.57 kJ·mol^-1; Δ_rS_m =-299.28 J·K^-1·mol^-1). The results indicated the formation process was spontaneous, exothermic and enthalpy-driven. FT-IR data indicated that the amide linkage in gelatin polypeptide chain can be especially active sites for the nucleation and growth of Fe₂S₃. The effect of Fe³⁺ and Fe₂S₃ on the conformations of gelatin macromolecule had also been analyzed by means of UV-vis and FT-IR spectra. The results showed that there was less α-helix content and more β-sheet structures due to integration of them. By integrating the information of the UV-vis and FT-IR analyses of the synthesized samples, a most plausible formation mechanism of the gelatin/Fe₂S₃ bionanocomposites was given: Fe³⁺ coordinated with amide linkage in gelatin macromolecule to form gelatin/Fe³⁺ complex, then S^2- combined with Fe³⁺ cooperated by gelatin to form gelatin/Fe₂S₃.