Enhanced Enantioselectivity in the Synthesis of Mercury Sulfide Nanoparticles through Ostwald Ripening

Chirality in nanoparticles (NPs) has recently emerged as an active area of research owing to its wide range of potential applications. NPs with intrinsic chirality in their inorganic core are of particular interest owing to their giant optical activity. Mercury sulfide (HgS) NPs with intrinsic chirality in their core crystalline structure were prepared in the presence of a chiral thiol, penicillamine (Pen), as a capping ligand, leading to the preferential formation of NPs with an enantiomeric core. The synthesis of chiral HgS NPs proceeded via the transient formation of NPs with an achiral metacinnabar phase, which was transformed into a chiral cinnabar phase along with the growth of NPs of size over 5.5 nm. The reaction temperature had an effect on the optical activity of HgS NPs, which was enhanced by 75% compared to that obtained in the first report, giving the highest optical activity for the semiconductor NPs reported so far. This enhancement was discussed in conjunction with the evolution of NPs possessing a combination of crystal handedness and surface ligand coordination pattern. The Pen ligand was considered to afford two chiral bidentate coordination modes with opposite handedness using a pair of thiol and either carboxylate or amine. These two coordination modes selectively stabilize the HgS crystal core with opposite handedness to each other to give NPs with different thermodynamic stability. The less stable NPs disappeared in accord with the growth of more stable NPs with opposite handedness through the Ostwald ripening process, resulting in the enhancement of NPs' enantiopurity.

纳米粒子（NPs）的手性由于其广泛的潜在应用，最近已成为一个活跃的研究领域。由于其巨大的光学活性，无机核具有固有手性的纳米粒子尤其受到关注。在一种手性硫醇——青霉胺（Pen）作为封端配体存在的情况下，制备了其核心晶体结构具有固有手性的硫化汞（HgS）纳米粒子，这导致优先形成具有对映体核心的纳米粒子。手性HgS纳米粒子的合成是通过瞬间形成具有非手性黑辰砂相的纳米粒子进行的，当纳米粒子尺寸增长到超过5.5 nm时，该相转变为手性辰砂相。反应温度对HgS纳米粒子的光学活性有影响，与首次报道相比，其光学活性提高了75%，这是迄今为止所报道的半导体纳米粒子中光学活性最高的。结合具有晶体手性和表面配体配位模式组合的纳米粒子的演变对这种增强进行了讨论。Pen配体被认为可以利用一对硫醇以及羧酸盐或胺提供两种具有相反手性的双齿配位模式。这两种配位模式选择性地稳定具有相反手性的HgS晶体核心，从而得到具有不同热力学稳定性的纳米粒子。不太稳定的纳米粒子通过奥斯特瓦尔德熟化过程随着更稳定的具有相反手性的纳米粒子的生长而消失，从而提高了纳米粒子的对映体纯度。