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外文期刊>The Journal of Chemical Physics
>Effects of counterion valency on the damping of phonons propagating along the axial direction of liquid-crystalline DNA
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Effects of counterion valency on the damping of phonons propagating along the axial direction of liquid-crystalline DNA
The phonon propagation and damping along the axial direction of films of aligned 40 wt % calf-thymus DNA rods are studied by inelastic x-ray scattering (IXS).The IXS spectra are analyzed with the generalized three effective eigenmode theory,from which we extract the dynamic structure factor S(Q,E) as a function of transferred energy E=h omega,and the magnitude of the transferred wave vector Q.S(Q,E) of a DNA sample typically consists of three peaks,one central Rayleigh scattering peak,and two symmetric Stokes and anti-Stokes Brillouin side peaks.By analyzing the Brillouin peaks,the phonon excitation energy and damping can be extracted at different Q values from about 4 to 30 nm~(-1).A high-frequency sound speed is obtained from the initial slope of the linear portion of the dispersion relation below Q=4 nm~(-1).The high-frequency sound speed obtained in this Q range is 3100 m/s,which is about twice faster than the ultrasound speed of 1800 m/s,measured by Brillouin light scattering at Q approx 0.01 nm~(-1) at the similar hydration level.Our observations provide further evidence of the strong coupling between the internal dynamics of a DNA molecule and the dynamics of the solvent.The effect on damping and propagation of phonons along the axial direction of DNA rods due to divalent and trivalent counterions has been studied.It is found that the added multivalent counterions introduce stronger phonon damping.The phonons at the range between approx 12.5 and approx 22.5 nm~(-1) are overdamped by the added counterions according to our model analyses.The intermediate scattering function is extracted and it shows a clear two-step relaxation with the fast relaxation time ranging from 0.1 to 4 ps.
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机译：通过非弹性X射线散射（IXS）研究了对准的40 wt％小牛胸腺DNA棒沿膜轴向的声子传播和阻尼。利用广义三有效本征模理论分析了IXS光谱，从中提取动态结构因子S（Q，E）与传递能量E = hΩ的函数关系，DNA样品的传递波矢量QS（Q，E）的大小通常由三个峰组成，一个中心瑞利散射峰，以及两个对称的斯托克斯和反斯托克斯布里渊边峰。通过分析布里渊峰，可以在大约4至30 nm〜（-1）的不同Q值下提取声子激发能和阻尼。高频声速从Q = 4 nm〜（-1）以下的色散关系线性部分的初始斜率获得。在此Q范围内获得的高频声速为3100 m / s，比超声快约两倍通过布里渊光散射在Q处测量的速度为1800 m / s在相似的水合作用水平下约为0.01 nm〜（-1）。我们的观察结果进一步证明了DNA分子内部动力学与溶剂动力学之间的强耦合。对声子沿轴向阻尼和传播的影响研究了二价和三价抗衡离子对DNA杆的影响，发现添加的多价抗衡离子会引入更强的声子阻尼。在约12.5至约22.5 nm〜（-1）范围内的声子被添加的抗衡离子过度阻尼。提取了中间散射函数，它显示了清晰的两步弛豫，快速弛豫时间为0.1到4 ps。
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