Electronic transition dipole moment directions of reduced anionic flavin in stretched poly(vinyl alcohol) films
Electronic transition dipole moment directions of reduced anionic flavin in stretched poly(vinyl alcohol) films
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DOI：
10.1021/jp075830e
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发表时间：
2008-01-10
影响因子：
3.3
通讯作者：
Stanley, Robert J.
中科院分区：
文献类型：
--
作者：
Salim, M.;Siddiqui, U.;Stanley, Robert J.
在聚乙烯醇（PVA）薄膜中，测定了部分取向的还原阴离子黄素单核苷酸（FMNH-）的红外和紫外/可见线性二向色光谱，以确定主要电子跃迁偶极矩的方向。在1750-1350 cm（-1）区域测量了红外线性二色性（LD），以提供拉伸膜中FMNH-的整体分子取向。利用B3LYP泛函的时变密度泛函理论计算了还原光黄素的正模和跃迁偶极矩。计算出的正模有助于红外波段分配和确定红外跃迁偶极矩方向，这是确定PVA薄膜中FMNH-取向参数所必需的。在200-700 nm范围内测量了紫外/可见LD光谱，并将其分解为三个pi - pi*跃迁的贡献。转变方向为：在440 nm处90度+/- 4度，在350 nm处79度+/- 4度，在290 nm处93度+/- 4度，相对于N-5-N-10轴逆时针旋转。通过比较计算和实验确定的跃迁偶极矩，可以精确地确定跃迁偶极矩的方向。据我们所知，这是第一个实验证据，证明350-450纳米的吸收是由两个独特的转变产生的。值得注意的是，FMNH-的两个最低能量跃迁偶极矩几乎与之前氧化黄酮和半醌黄酮的研究结果平行。
The IR and UV/vis linear dichroic spectra of reduced anionic flavin mononucleotide (FMNH-) partially oriented in poly(vinyl alcohol) (PVA) films have been measured to determine the direction of the major electronic transition dipole moments. The IR linear dichroism (LD) was measured in the 1750-1350 cm(-1) region to provide the overall molecular orientation of the FMNH- in the stretched films. Time-dependent density functional theory using the B3LYP functional was used to calculate the normal modes and the transition dipole moments of reduced lumiflavin. The calculated normal modes assisted in IR band assignments and in the determination of the IR transition dipole moment directions which were required for the determination of the orientation parameters for FMNH- in PVA films. The UV/vis LD spectrum was measured over the 200-700 nm region and was resolved into contributions from three pi - pi* transitions. The directions of the transitions are 90 degrees +/- 4 degrees at 440 nm, 79 degrees +/- 4 degrees at 350 nm, and 93 degrees +/- 4 degrees at 290 nm with counterclockwise rotations with respect to the N-5-N-10 axis. Comparison of the calculated and experimentally determined transition dipole moments allowed for refined assignment of the transition dipole moment directions. To our knowledge, this is the first experimental evidence that the 350-450 nm absorption arises from two unique transitions. Remarkably, the two lowest energy transition dipole moments for FMNH- are nearly parallel to those obtained in prior studies for both oxidized and semiquinone flavin.