Reconsideration of the conformation of methyl cellulose and hydroxypropyl methyl cellulose ethers in aqueous solution.
Reconsideration of the conformation of methyl cellulose and hydroxypropyl methyl cellulose ethers in aqueous solution.
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基于使用小角和广角中子散射（S-WANS）技术在0.05至100 nm−1的散射矢量（q）范围内获得的实验结果，详细重新考虑了在25 °C下溶解在稀水（D2 O）溶液中的甲基纤维素（MC）和羟丙基甲基纤维素（HpMC）醚样品的结构和构象。MC样品表现出每个葡萄糖单元的甲基平均取代度（DS）= 1.8，重均摩尔质量Mw = 37 × 103和79 × 103 g mol−1。另一方面，HpMC样品具有每个葡萄糖单元的羟丙基的平均摩尔取代数（MS）= 0.25，DS = 1.9，并且Mw = 50 × 103和71 × 103 g mol−1。收集到相同样品物质溶液曲线中的浓度换算散射强度数据清楚地证明了在0.05至2.0 nm−1的q范围内I（q）c−1 <$q−1的关系，并且在所有检查的样品溶液中，在q <$7和17 nm−1处发现了小的干扰峰。这些观察结果有力地揭示了MC和HpMC样品的形状因子与平均直径分别为0.8和0.9 nm的长的刚性棒状颗粒的形状因子以及具有特征平均间距约为0.5 nm的内部结构的形状因子完美地描述。0.9和0.37 nm，而与化学改性条件和摩尔质量无关。提出了MC和HpMC在水溶液中溶解的合理推测结构模型。由甲基纤维素醚和羟丙基甲基纤维素醚在水溶液中构建了具有一次折叠高度延伸的发夹状构象的棒状结构。
The structure and conformation of methyl cellulose (MC) and hydroxypropyl methyl cellulose (HpMC) ether samples dissolved in dilute aqueous (D2O) solutions at a temperature of 25 °C were reconsidered in detail based on the experimental results obtained using small- and wide-angle neutron scattering (S-WANS) techniques in a range of scattering vectors (q) from 0.05 to 100 nm−1. MC samples exhibited an average degree of substitution (DS) by methyl groups per glucose unit of DS = 1.8 and the weight average molar mass of Mw = 37 × 103 and 79 × 103 g mol−1. On the other hand, HpMC samples possessed the average molar substitution number (MS) by hydroxypropyl groups per glucose unit of MS = 0.25, DS = 1.9, and Mw = 50 × 103 and 71 × 103 g mol−1. The concentration-reduced scattering intensity data gathered into a curve for the solutions of identical sample species clearly demonstrated the relationship I(q)c−1 ∝ q−1 in a q range from 0.05 to 2.0 nm−1, and small interference peaks were found at q ∼ 7 and 17 nm−1 for all examined sample solutions. These observations strongly revealed that form factors for both the MC and HpMC samples were perfectly described with that for long, rigid rod particles with average diameters of 0.8 and 0.9 nm, respectively, and with an inner structure with characteristic mean spacing distances of ca. 0.9 and 0.37 nm, respectively, regardless of the chemically modified conditions and molar masses. A rationally speculated structure model for the MC and HpMC samples dissolved in aqueous solution was proposed. A rod-like structure with once-folded highly extended hairpin-like conformation is constructed from methyl and hydroxypropyl methyl cellulose ethers in aqueous solution.
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