Department of Chemical and Biomolecular Engineering, Colburn Laboratory, University of Delaware, 150 Academy Street, Newark, Delaware 19716, United States.
Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, United States.
J Phys Chem B. 2020 Apr 2;124(13):2702-2714. doi: 10.1021/acs.jpcb.0c00226. Epub 2020 Mar 24.
Synthetic melanin nanoparticles that exhibit properties analogous to naturally found allomelanin can be formed by assembly of dimers/oligomers of the synthetic precursor of allomelanin, 1,8-dihydroxy naphthalene (DHN). To link the nanostructure within these assembled melanin nanoparticles to DHN dimer structure, we use explicit-solvent atomistic molecular dynamics (MD) simulations to study assembly of DHN dimers (2-2', 2-4', and 4-4' and their mixture) into nanoparticles in aqueous solutions. We analyze how the dimer structure and mixture composition impact the molecular interactions that drive assembly, as well as the assembled nanostructure, both internally and on the surface. We find that, prominently, hydrogen-bonding interactions drive the assembly of like-dimers, whereas unlike-dimer stacking interactions play a role in the assembly of dimer mixtures. The aggregate/nanoparticle assembled from 2-2' dimers assumes a spherical morphology as opposed to 4-4' dimers that adopt an anisotropic shape. The surface of the aggregate formed by 2-2' dimers is primarily hydrophobic, while the surface of aggregates formed by 2-4' dimers, 4-4' dimers, and their mixtures is amphiphilic. We also find that the addition of linear poly(ethylene glycol) (PEG) chains to the assembled particle does not alter the aggregate structure formed by a single dimer type. However, the PEG chains prefer to interact with 4-4' dimers more than with 2-2' and 2-4'. In aggregates formed by mixtures of dimers, PEG chains interact preferentially with 2-4' dimers than with 4-4' and 2-2' dimers.
合成黑色素纳米粒子可以通过组装天然存在的黑色素的合成前体，即 1,8-二羟基萘（DHN）的二聚体/低聚物来形成，这些纳米粒子表现出类似于天然黑色素的特性。为了将这些组装的黑色素纳米粒子中的纳米结构与 DHN 二聚体结构连接起来，我们使用显式溶剂原子分子动力学（MD）模拟来研究 DHN 二聚体（2-2'、2-4'和 4-4'及其混合物）在水溶液中组装成纳米粒子的过程。我们分析了二聚体结构和混合物组成如何影响驱动组装的分子相互作用，以及组装的纳米结构，包括内部和表面。我们发现，氢键相互作用显著地驱动了同二聚体的组装，而不同二聚体的堆积相互作用在二聚体混合物的组装中起作用。由 2-2'二聚体组装而成的聚集体/纳米粒子呈现出球形形态，而 4-4'二聚体则呈现出各向异性形状。由 2-2'二聚体形成的聚集体的表面主要是疏水性的，而由 2-4'二聚体、4-4'二聚体及其混合物形成的聚集体的表面是两亲性的。我们还发现，将线性聚乙二醇（PEG）链添加到组装的粒子中不会改变由单个二聚体类型形成的聚集体结构。然而，PEG 链更倾向于与 4-4'二聚体而不是 2-2'和 2-4'二聚体相互作用。在由二聚体混合物形成的聚集体中，PEG 链优先与 2-4'二聚体相互作用，而不是与 4-4'和 2-2'二聚体相互作用。
