Department of Physics, Campus Las Lagunillas, University of Jaén, 23071 Jaén, Spain.
J Colloid Interface Sci. 2010 Apr 1;344(1):144-9. doi: 10.1016/j.jcis.2009.11.061. Epub 2009 Dec 3.
The synthesis of nanoparticles consisting of a magnetite core coated with one or more layers of amino acid (L-arginine, L-lysine, glycine, and L-glutamine) is described in this paper. For all the amino acids it is found that adsorption increases with concentration in solution in the range 0.5-10 mg/mL. The adsorption, however, differs substantially from one amino acid to another, depending on the length of the hydrocarbon chain and the polarity and charge of the side group. Thus, for given concentration and pH, adsorption is found to increase in the order L-arginine < L-lysine < L-glutamine < glycine. This order corresponds roughly to amino acids with decreasing chain length; in addition, the presence of the less polarizable guanidine group in the arginine molecule may explain why this amino acid is slightly less adsorbed than lysine. The pH dependence of the adsorption of each amino acid is reasonably explained considering the surface charge of magnetite and the charge of the amino acid molecules for different pHs, indicating a significant role of electrostatics in adsorption. This is further checked by means of determinations of the electrophoretic mobility of amino acid-coated magnetite as a function of pH: the results indicate a shift of the isoelectric point of the raw magnetite toward more basic pHs, an indication of adsorption of positive species, as confirmed by the tendency of the mobility of amino acid-coated magnetite toward more positive values below neutral pH. The electrophoretic mobility of coated particles was also measured as a function of the concentration of amino acid, and it was found that for low concentrations the four amino acids provoke charge inversion and overcharging of the magnetite surface at pH 6. Finally, the dependence of the electrophoretic mobility on the ionic strength indicated that from an electrophoretic point of view, the functionalized magnetite-amino acid particles do not behave as soft particles, and that the amino acid coating should be very compact.
本文描述了由磁铁矿核组成的纳米粒子的合成，这些纳米粒子表面覆盖有一层或多层氨基酸（L-精氨酸、L-赖氨酸、甘氨酸和 L-谷氨酰胺）。对于所有的氨基酸，都发现其吸附量随溶液浓度在 0.5-10mg/mL 范围内增加。然而，吸附量因氨基酸而异，这取决于烃链的长度以及侧基的极性和电荷。因此，在给定的浓度和 pH 值下，吸附量按 L-精氨酸<L-赖氨酸<L-谷氨酰胺<甘氨酸的顺序增加。这个顺序大致对应于氨基酸链长逐渐变短；此外，精氨酸分子中胍基的极化率较低，这可能解释了为什么这种氨基酸的吸附量略低于赖氨酸。考虑到磁铁矿的表面电荷和不同 pH 值下氨基酸分子的电荷，可以合理地解释每种氨基酸吸附的 pH 依赖性，这表明静电在吸附中起着重要作用。通过测定作为 pH 函数的氨基酸包覆磁铁矿的电泳迁移率来进一步检查这一点：结果表明原始磁铁矿的等电点向更碱性 pH 值移动，这表明吸附了带正电的物质，这一点被氨基酸包覆磁铁矿的迁移率在中性 pH 以下向更正值移动的趋势所证实。还测量了包覆颗粒的电泳迁移率作为氨基酸浓度的函数，发现对于低浓度，四种氨基酸在 pH6 下会引起磁铁矿表面的电荷反转和过充电。最后，电泳迁移率对离子强度的依赖性表明，从电泳的角度来看，功能化的磁铁矿-氨基酸颗粒的行为不像软颗粒，并且氨基酸涂层应该非常紧密。
