Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
Photosynth Res. 2018 Mar;135(1-3):309-317. doi: 10.1007/s11120-017-0413-8. Epub 2017 Jun 22.
Zinc 3-hydroxymethyl-13-oxo-chlorins bearing a variety of primary alkyl groups at the 20-position were prepared as models of bacteriochlorophyll-c by chemical modification of naturally occurring chlorophyll-a. The synthetic chlorophyll-a derivatives self-aggregated in an aqueous Triton X-100 solution to afford large oligomers whose Soret and Qy bands were red-shifted and broadened, compared with the bands of their monomers in tetrahydrofuran. The oligomeric bands are similar to those of bacteriochlorophyll-c self-aggregates in chlorosomes, the main light-harvesting antennae of photosynthetic green bacteria. The 20-alkylation led to bathochromic shifts of the visible Soret maxima in J-type self-aggregates of the synthetic models, while elongation of the 20-alkyl group decreased the chlorosomal Qy maxima due to an increase in steric hindrance. Considering the light-harvesting and energy-transferring processes in a chlorosome, the 20-methylation in bacteriochlorophyll-c would be more suitable for efficient culturing of green bacteria than the 20-ethylation and propylation as well as the 20-unsubstitution in bacteriochlorophyll-d.
锌 3-羟甲基-13-氧代氯代物在 20 位带有各种伯烷基，通过对天然叶绿素-a 的化学修饰制备，作为细菌叶绿素-c 的模型。合成的叶绿素-a 衍生物在 Triton X-100 水溶液中自组装，形成大的寡聚物，其 Soret 和 Qy 带与它们在四氢呋喃中的单体相比发生红移和展宽。寡聚物带类似于在叶绿素体中的细菌叶绿素-c 自组装体，叶绿素体是光合作用绿细菌的主要光捕获天线。20-烷基化导致合成模型 J 型自组装体中可见 Soret 最大值的红移，而 20-烷基链的延长由于空间位阻的增加而降低了叶绿素体 Qy 最大值。考虑到叶绿素体中的光捕获和能量转移过程，与细菌叶绿素-d 的 20-乙基化、丙基化和未取代相比，细菌叶绿素-c 的 20-甲基化更适合绿细菌的高效培养。
