Petrova Rositza I, Swift Jennifer A
Department of Chemistry, Georgetown University, 37th and "O" Streets NW, Washington, DC 20057-1227, USA.
J Am Chem Soc. 2004 Feb 4;126(4):1168-73. doi: 10.1021/ja0392263.
The crystallization of sodium chlorate (NaClO3) is a classic example of spontaneous chirality, since it is achiral in solution but adopts a chiral form in the solid state. While crystal growth of NaClO3 from pure aqueous solutions yields a 50:50 statistical distribution of d- and l-crystals, large enantiomeric excesses of either d- and l-crystals can be achieved by crystal growth in agarose gel, a naturally occurring chiral polysaccharide. The influence of gel density (0.1-0.75 wt %), temperature, and the diffusion of cosolvents on crystal distribution was discerned from statistical data obtained from 752 gel-mediated crystallization experiments yielding 12,384 individual crystals. These studies demonstrate that the magnitude and direction of the bias can be selectively engineered toward either d- or l-forms by changing the gelation conditions. Aqueous agarose gels infused with 48 wt % NaClO3 at 6 degrees C, favored the growth of d-NaClO3 crystals, with ee's reaching 22% at the highest gel concentrations. Crystal growth under methanol diffusion favored deposition of the opposite enantiomorph, l-NaClO3. The bias in the crystal distribution is enhanced at higher temperatures. Aqueous gels at 24 degrees C infused with methanol cosolvent favored l-NaClO3, with ee's reaching 53%. The changing magnitude and direction of the enantiomorph bias can be ascribed to differences in the agarose conformation and intermolecular interactions between the gel and crystal surfaces that inhibit the formation of the two enantiomers to different extents.
氯酸钠（NaClO₃）的结晶是自发手性的一个经典例子，因为它在溶液中是非手性的，但在固态时会呈现出手性形式。虽然从纯水溶液中生长NaClO₃晶体时，d型和l型晶体的统计分布为50:50，但通过在琼脂糖凝胶（一种天然存在的手性多糖）中进行晶体生长，可以实现d型或l型晶体的大量对映体过量。从752次凝胶介导的结晶实验获得的统计数据（产生了12384个单晶）中，识别出了凝胶密度（0.1 - 0.75 wt%）、温度和助溶剂扩散对晶体分布的影响。这些研究表明，通过改变凝胶化条件，可以选择性地设计偏向d型或l型的偏差大小和方向。在6℃下注入48 wt% NaClO₃的水琼脂糖凝胶有利于d - NaClO₃晶体的生长，在最高凝胶浓度下对映体过量达到22%。在甲醇扩散下的晶体生长有利于相反的对映体l - NaClO₃的沉积。在较高温度下，晶体分布的偏差会增强。在24℃下注入甲醇助溶剂的水凝胶有利于l - NaClO₃，对映体过量达到53%。对映体偏差大小和方向的变化可归因于琼脂糖构象以及凝胶与晶体表面之间分子间相互作用的差异，这些差异在不同程度上抑制了两种对映体的形成。
