Optical spectroscopy of cryogenic metalated flavins: The O2(+) isomers of M+lumiflavin (M=Li–Cs)
Optical spectroscopy of cryogenic metalated flavins: The O2(+) isomers of M+lumiflavin (M=Li–Cs)
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低温金属化黄素的光谱：M 发光黄素 (M=LiâCs) 的 O2( ) 异构体
DOI：
10.1016/j.jpap.2020.100009
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发表时间：
2020
影响因子：
--
通讯作者：
O. Dopfer
中科院分区：
文献类型：
--
作者：
D. Müller;O. Dopfer
黄素复合物在自然界中用于许多光生物学过程，因为它们在可见光范围内的光化学反应可以受到环境的强烈调节。本文报道了光黄素（LF）与碱金属离子（M=Li-Cs）的质量选择性金属配合物在低温（T<20 K）下在可见光范围内通过光解离（VISPD）记录的光谱。VISPD光谱在耦合到低温离子阱和电喷雾电离源的串联质谱仪中测量。在420-450 nm范围内获得的振动分辨VISPD光谱通过与时间相关的密度泛函理论计算（PBE 0/cc-pVDZ）耦合多维Franck-Condon（FC）模拟的比较被分配给M+LF的O2（+）异构体的S 0 ←S1（ππ*）跃迁。优选的结合基序和相互作用强度强烈依赖于M+的大小。具有较小M+离子（M=Li和Na）的M+LF的光谱归因于最稳定的O2+异构体，其特征在于N1-M-O2螯合物结合基序，其中M+可以与LF的N1和O2的孤对相互作用。由于与N10处的CH 3基团的空间相互作用，三环芳环轻微弯曲，并且VISPD光谱具有LF的低频面外弯曲模式。这样的O2+结构对于较大的M+离子（M=Rb和Cs）是空间排斥的，其反而形成具有几乎线性C2-O2-M键的平面O2最小值。它们的VISPD谱由描述M+... LF相互作用的低频面内弯曲模（β）表征。K+LF与中等大小的K+离子的VISPD谱是更复杂的，其特征是非常低频的模式，这是由于一个非常浅的电位沿着O2参与O2+异构化坐标，这不能很好地描述谐波FC模拟。电子S1激发稍微减弱了M+... LF相互作用（6-9%），这是从O2（+）结合位点金属化后的小Δ S1蓝移推断的，与从ππ* 激发中涉及的分子轨道推断的电荷重组一致。总的来说，LF的O2（+）络合效应与先前研究的O 4+异构体的效应有很大的不同，O 4+异构体的特征是基于LF发色团的相同ππ* 激发下M+... LF相互作用的强烈增加（高达20%）的大Δ S1红移。O2（+）和O 4+异构体的电子物理响应的剧烈的位置特异性变化主要来自于电子激发对M+... LF键强度的不同影响，而不是来自于金属引起的负责ππ* 激发的LF的电子结构和分子轨道的变化。
Flavin complexes are used by nature in many photobiological processes, because their photochemical response in the visible range can be strongly modulated by their environment. Herein, we report optical spectra of mass-selected metal complexes of lumiflavin (LF) with alkali metal ions (M=Li–Cs) recorded in the visible range by photodissociation (VISPD) at cryogenic temperatures (T<20 K). VISPD spectra are measured in a tandem mass spectrometer coupled to a cryogenic ion trap and an electrospray ionization source. The vibrationally-resolved VISPD spectra obtained in the 420–450 nm range are assigned to the S0←S1(ππ*) transition of the O2(+) isomers of M+LF by comparison to time-dependent density functional theory calculations (PBE0/cc-pVDZ) coupled to multidimensional Franck–Condon (FC) simulations. The preferred binding motif and interaction strength strongly depend on the size of M+. The spectra of M+LF with the smaller M+ions (M=Li and Na) are attributed to the most stable O2+ isomers characterized by a N1–M–O2 chelate binding motif in which M+can interact with the lone pairs of both N1 and O2 of LF. Because of steric interaction with the CH3group at N10, the tricyclic aromatic ring is slightly bent and the VISPD spectra feature low-frequency out-of-plane bending modes of LF. Such an O2+ structure is sterically repulsive for the larger M+ions (M=Rb and Cs), which instead form planar O2 minima with nearly linear C2–O2–M bonds. Their VISPD spectra are characterized by low-frequency in-plane bending modes (β) describing the M+…LF interaction. The VISPD spectrum of K+LF with the intermediate-size K+ion is more complex and features very low-frequency modes resulting from a very shallow potential along the O2↔O2+ isomerization coordinate, which cannot be described well by harmonic FC simulations. Electronic S1excitation slightly weakens the M+…LF interaction (6–9%), as deduced from the small ΔS1blueshifts upon metalation at the O2(+) binding site, consistent with the charge reorganization deduced from the molecular orbitals involved in ππ* excitation. Overall, the effects of O2(+) complexation of LF are drastically different from those of the previously studied O4+ isomers, which are characterized by large ΔS1redshifts based on the strong increase in the M+…LF interaction (up to 20%) upon the same ππ* excitation of the LF chromophor. The drastic site-specific variation in the photophysical response of the O2(+) and O4+ isomers arises mainly from the different effect of electronic excitation on the M+…LF bond strength rather than from the metal-induced change of the electronic structure and molecular orbitals of LF responsible for ππ* excitation.
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DOI：
10.1039/c8cp05368e
发表时间：
2018
期刊：
Physical chemistry chemical physics : PCCP
影响因子：
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作者：
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期刊：
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影响因子：
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10.1039/c4cp01524j
发表时间：
2014-06
期刊：
Physical chemistry chemical physics : PCCP
影响因子：
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影响因子：
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