Li Xinmeng, Buda Francesco, de Groot Huub J M, Sevink G J Agur
Leiden University, Leiden Institute of Chemistry, Einsteinweg 55, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
J Phys Chem C Nanomater Interfaces. 2018 Jul 5;122(26):14877-14888. doi: 10.1021/acs.jpcc.8b01790. Epub 2018 May 30.
Chlorosome antennae form an interesting class of materials for studying the role of structural motifs and dynamics in nonadiabatic energy transfer. They perform robust and highly quantum-efficient transfer of excitonic energy while allowing for compositional variation and completely lacking the usual regulatory proteins. Here, we first cast the geometrical analysis for ideal tubular scaffolding models into a formal framework, to relate effective helical properties of the assembly structures to established characterization data for various types of chlorosomes. This analysis shows that helicity is uniquely defined for chlorosomes composed of bacteriochlorophyll (BChl) and that three chiral angles are consistent with the nuclear magnetic resonance (NMR) and electron microscope data for BChl , including two novel ones that are at variance with current interpretations of optical data based on perfect cylindrical symmetry. We use this information as a starting point for investigating dynamic and static heterogeneity at the molecular level by unconstrained molecular dynamics. We first identify a rotational degree of freedom, along the Mg-OH coordination bond, that alternates along the syn-anti stacks and underlies the (flexible) curvature on a larger scale. Because rotation directly relates to the formation or breaking of interstack hydrogen bonds of the O-H···O=C structural motif along the syn-anti stacks, we analyzed the relative fractions of hydrogen-bonded and the nonbonded regions, forming stripe domains in otherwise spectroscopically homogeneous curved slabs. The ratios 7:3 for BChl and 9:1 for BChl for the two distinct structural components agree well with the signal intensities determined by NMR. In addition, rotation with curvature-independent formation of stripe domains offers a viable explanation for the localization and dispersion of exciton states over two fractions, as observed in single chlorosome fluorescence decay studies.
叶绿体天线构成了一类有趣的材料，可用于研究结构基序和动力学在非绝热能量转移中的作用。它们能高效且高量子效率地进行激子能量转移，同时允许成分变化且完全缺乏常见的调节蛋白。在此，我们首先将理想管状支架模型的几何分析纳入一个形式框架，以便将组装结构的有效螺旋特性与各种类型叶绿体的既定表征数据联系起来。该分析表明，由细菌叶绿素（BChl）组成的叶绿体具有独特定义的螺旋度，并且三个手性角与BChl的核磁共振（NMR）和电子显微镜数据一致，其中包括两个与基于完美圆柱对称的当前光学数据解释不同的新角度。我们以此信息为起点，通过无约束分子动力学研究分子水平上的动态和静态异质性。我们首先确定了一个沿着Mg - OH配位键的旋转自由度，它沿着顺 - 反堆叠交替出现，并在更大尺度上构成（灵活的）曲率基础。由于旋转直接关系到沿着顺 - 反堆叠的O - H···O = C结构基序的堆叠间氢键的形成或断裂，我们分析了氢键结合区域和非结合区域的相对比例，这些区域在其他方面光谱均匀的弯曲平板中形成条纹域。两种不同结构成分的BChl比例为7:3，BChl比例为9:1，这与NMR确定的信号强度非常吻合。此外，与曲率无关的条纹域形成的旋转为激子态在两个部分上的定位和分散提供了一个可行的解释，这在单个叶绿体荧光衰减研究中有所观察。
