Chung Hoi Sung, Khalil Munira, Smith Adam W, Tokmakoff Andrei
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Rev Sci Instrum. 2007 Jun;78(6):063101. doi: 10.1063/1.2743168.
We have developed a Fourier transform two-dimensional infrared (2D IR) spectrometer to probe chemical reactions and biophysical processes triggered by a nanosecond temperature jump (T jump). The technical challenges for such a spectrometer involve (1) synchronization of a nanosecond T-jump laser and femtosecond laser system, (2) overcoming the decreased signal-to-noise ratio from low repetition rate data acquisition, and (3) performing an interferometric measurement through a sample with a density and index of refraction that varies with time delay after the T jump. The first challenge was overcome by synchronizing the two lasers to a clock derived from the Ti:sapphire oscillator, leading to timing accuracy of 2 ns for delays up to 50 ms. The data collection time is reduced by using undersampling with the improved signal-to-noise ratio obtained from a balanced detection scheme with a dual stripe array detector. Transient dispersed vibrational echo and 2D IR spectroscopy are applied to N-methylacetamide and ubiquitin, as examples, and the spectral responses by a temperature elevation and by structural changes of the protein are compared. The synchronization of 2D IR spectroscopy with a nanosecond temperature jump without losing its sensitivity at a low repetition rate opens a new applicability of the nonlinear spectroscopy to probe a variety of molecular structure changes induced by a nanosecond perturbation.
我们开发了一种傅里叶变换二维红外（2D IR）光谱仪，用于探测由纳秒级温度跃升（T跃变）引发的化学反应和生物物理过程。这种光谱仪面临的技术挑战包括：（1）纳秒级T跃变激光器与飞秒激光系统的同步；（2）克服低重复率数据采集导致的信噪比降低问题；（3）通过T跃变后密度和折射率随时间延迟而变化的样品进行干涉测量。通过将两台激光器与源自钛宝石振荡器的时钟同步，克服了第一个挑战，对于长达50 ms的延迟，定时精度达到2 ns。使用欠采样技术，并借助双条纹阵列探测器的平衡检测方案获得的更高信噪比，减少了数据采集时间。以N-甲基乙酰胺和泛素为例，应用瞬态色散振动回波和二维红外光谱，比较了温度升高和蛋白质结构变化引起的光谱响应。二维红外光谱与纳秒级温度跃升的同步，且在低重复率下不损失灵敏度，为非线性光谱开辟了新的应用领域，可用于探测由纳秒级扰动引起的各种分子结构变化。
