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Two-Photon Excited Fluorescence Dynamics in NADH in Water–Methanol Solutions: The Role of Conformation States
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2020-11-11 , DOI: 10.1021/acs.jpcb.0c07620 Ioanna A. Gorbunova 1 , Maxim E. Sasin 1 , Jesus Rubayo-Soneira 2 , Andrey G. Smolin 1 , Oleg S. Vasyutinskii 1
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2020-11-11 , DOI: 10.1021/acs.jpcb.0c07620 Ioanna A. Gorbunova 1 , Maxim E. Sasin 1 , Jesus Rubayo-Soneira 2 , Andrey G. Smolin 1 , Oleg S. Vasyutinskii 1
Affiliation
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The dynamics of polarized fluorescence in reduced nicotinamide adenine dinucleotide (NADH) at 460 nm under two-photon excitation at 720 nm by femtosecond laser pulses in water–methanol solutions has been studied experimentally and theoretically as a function of methanol concentration. A number of fluorescence parameters have been determined from experiment by means of the global fit procedure and then compared with the results reported by other authors. A comprehensive analysis of experimental errors was made. Ab initio calculations of the structure of NADH in water and methanol and of β-nicotinamide mononucleotide (NMNH) in vacuum have been carried out for clarifying the role of decay time heterogeneity. The main results obtained are as follows. An explanation of the heterogeneity in the measured fluorescence decay times in NADH has been suggested based on the influence of the internal molecular electric field in the nicotinamide ring on nonradiative decay rates. We suggest that different charge distributions in the cis and trans configurations result in different internal electrostatic field distributions that lead to the decay time heterogeneity. A slight but noticeable rise of the fluorescence decay times τ1 and τ2 with methanol concentration was observed and treated as a minor effect of a nonradiative relaxation slowing due to the decrease in solution polarity. Relative concentrations of the folded and unfolded NADH conformations in solutions have been determined using a new method of analysis of the rotational diffusion time τr as a function of methanol concentration on the basis of the Stokes–Einstein–Debye equation. The analysis of the fluorescence anisotropy parameters obtained under linearly and circularly polarized excitation and the parameter Ω has been carried out and resulted in the determination of the two-photon excitation tensor components and suggested the existence of two excitation channels with comparable intensities. These were the longitudinal excitation channel dominated by the diagonal tensor component Szz and the mixed excitation channel dominated by the off-diagonal tensor components |Sxz2 + Syz2|1/2.
中文翻译：
NADH在水-甲醇溶液中的两光子激发荧光动力学：构象态的作用
在水-甲醇溶液中，通过飞秒激光脉冲在720 nm的双光子激发下，在720 nm的两光子激发下，在460 nm的还原烟酰胺腺嘌呤二核苷酸（NADH）中的偏振荧光动力学已通过实验和理论方法研究了甲醇浓度的函数。已经通过整体拟合程序从实验中确定了许多荧光参数，然后将其与其他作者报告的结果进行了比较。对实验误差进行了综合分析。从头算为了阐明衰减时间异质性的作用，已经对水和甲醇中的NADH以及真空中的β-烟酰胺单核苷酸（NMNH）的结构进行了计算。获得的主要结果如下。根据烟酰胺环内部分子电场对非辐射衰变速率的影响，已经提出了对NADH中所测量的荧光衰变时间中的异质性的解释。我们建议顺式和反式构型的不同电荷分布导致不同的内部静电场分布，从而导致衰减时间异质性。荧光衰变时间的轻微但明显的上升τ 1和τ 2由于溶液极性的降低，观察到并用甲醇浓度的H 2 O 3处理作为非辐射弛豫减缓的次要作用。溶液中的折叠和非折叠构象NADH的相对浓度已经使用旋转扩散时间τ的分析的新方法来确定ř根据Stokes–Einstein–Debye方程，它是甲醇浓度的函数。进行了线偏振和圆偏振激发下获得的荧光各向异性参数以及参数Ω的分析，并确定了两个光子激发张量分量，并暗示了存在两个强度相当的激发通道。这些是由对角张量分量S zz占主导的纵向激励通道和由非对角张量分量S |占主导的混合激励通道。S xz 2 + S yz 2 | 1/2。
更新日期：2020-11-25
中文翻译：
NADH在水-甲醇溶液中的两光子激发荧光动力学：构象态的作用
在水-甲醇溶液中，通过飞秒激光脉冲在720 nm的双光子激发下，在720 nm的两光子激发下，在460 nm的还原烟酰胺腺嘌呤二核苷酸（NADH）中的偏振荧光动力学已通过实验和理论方法研究了甲醇浓度的函数。已经通过整体拟合程序从实验中确定了许多荧光参数，然后将其与其他作者报告的结果进行了比较。对实验误差进行了综合分析。从头算为了阐明衰减时间异质性的作用，已经对水和甲醇中的NADH以及真空中的β-烟酰胺单核苷酸（NMNH）的结构进行了计算。获得的主要结果如下。根据烟酰胺环内部分子电场对非辐射衰变速率的影响，已经提出了对NADH中所测量的荧光衰变时间中的异质性的解释。我们建议顺式和反式构型的不同电荷分布导致不同的内部静电场分布，从而导致衰减时间异质性。荧光衰变时间的轻微但明显的上升τ 1和τ 2由于溶液极性的降低，观察到并用甲醇浓度的H 2 O 3处理作为非辐射弛豫减缓的次要作用。溶液中的折叠和非折叠构象NADH的相对浓度已经使用旋转扩散时间τ的分析的新方法来确定ř根据Stokes–Einstein–Debye方程，它是甲醇浓度的函数。进行了线偏振和圆偏振激发下获得的荧光各向异性参数以及参数Ω的分析，并确定了两个光子激发张量分量，并暗示了存在两个强度相当的激发通道。这些是由对角张量分量S zz占主导的纵向激励通道和由非对角张量分量S |占主导的混合激励通道。S xz 2 + S yz 2 | 1/2。
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