Artie McFerrin Department of Chemical Engineering, Texas A&M University, 3122 TAMU, College Station, TX 77843-3122, USA.
J Colloid Interface Sci. 2012 Oct 1;383(1):19-27. doi: 10.1016/j.jcis.2012.06.009. Epub 2012 Jun 15.
The formation process of silica nanoparticles in lysine-silica mixtures was studied using dynamic light scattering (DLS) and pulsed-field gradient (PFG) NMR measurements. (1)H NMR shows line broadening of the lysine resonances during TEOS hydrolysis/nanoparticle formation. Analysis of the TEOS hydrolysis kinetics show that TEOS hydrolysis is the rate-limiting step in particle formation, and has an activation energy of 20.5 kJ/mol. Transverse relaxation measurements show a corresponding decrease in T(2) with TEOS hydrolysis, indicating a reduction in the lysine mobility due to lysine-silica interactions. PFG NMR results indicate a systemic decrease in the self-diffusion coefficient of lysine as particle formation proceeds. The results obtained can be described using a two-state model wherein lysine is either free in solution or bound to the nanoparticles. Analysis of the PFG data of samples made at various temperatures show that lysine coverage upon complete hydrolysis is between 2.5 and 2.8 mmol lysine/kg solution, and insensitive to the heating temperature. PFG NMR shows a linear increase in the amount of bound lysine with increasing lysine content, indicating an increase in the surface area present, i.e. more and smaller particles, with increased lysine content. The PFG NMR results presented give quantitative insights that indicate that while pH is likely the primary driver for the rate of particle formation and particle size, lysine is critical for stabilization of the nanoparticles.
使用动态光散射（DLS）和脉冲梯度（PFG）NMR 测量研究了赖氨酸-硅混合物中二氧化硅纳米颗粒的形成过程。（1）H NMR 显示在 TEOS 水解/纳米颗粒形成过程中赖氨酸共振线的展宽。对 TEOS 水解动力学的分析表明，TEOS 水解是颗粒形成的限速步骤，其活化能为 20.5 kJ/mol。横向弛豫测量表明，随着 TEOS 水解，T（2）相应减小，表明由于赖氨酸-硅相互作用，赖氨酸的流动性降低。PFG NMR 结果表明，随着颗粒形成的进行，赖氨酸的自扩散系数呈系统性降低。所得结果可以用两种状态模型来描述，其中赖氨酸要么在溶液中自由存在，要么与纳米颗粒结合。对在不同温度下制备的样品的 PFG 数据进行分析表明，完全水解时赖氨酸的覆盖率在 2.5 至 2.8 mmol 赖氨酸/kg 溶液之间，并且不随加热温度而变化。PFG NMR 表明，随着赖氨酸含量的增加，结合的赖氨酸量呈线性增加，表明存在的表面积增加，即随着赖氨酸含量的增加，出现更多且更小的颗粒。所提出的 PFG NMR 结果提供了定量的见解，表明虽然 pH 值可能是颗粒形成速率和颗粒尺寸的主要驱动因素，但赖氨酸对于纳米颗粒的稳定至关重要。
