Roy Aritro Sinha, Srivastava Madhur
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA.
National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, NY 14853, USA.
Magnetochemistry. 2022 Mar;8(3). doi: 10.3390/magnetochemistry8030032. Epub 2022 Mar 8.
The objective of spectral analysis is to resolve and extract relevant features from experimental data in an optimal fashion. In continuous-wave (cw) electron spin resonance (ESR) spectroscopy, both values of a paramagnetic center and hyperfine splitting caused by its interaction with neighboring magnetic nuclei in a molecule provide important structural and electronic information. However, in the presence of - and/or -anisotropy and/or large number of resonance lines, spectral analysis becomes highly challenging. Either high-resolution experimental techniques are employed to resolve the spectra in those cases or a range of suitable ESR frequencies are used in combination with simulations to identify the corresponding and values. In this work, we present a wavelet transform technique in resolving both simulated and experimental cW-ESR spectra by separating the hyperfine and super-hyperfine components. We exploit the multiresolution property of wavelet transforms that allow the separation of distinct features of a spectrum based on simultaneous analysis of spectrum and its varying frequency. We retain the wavelet components that stored the hyperfine and/or super-hyperfine features, while eliminating the wavelet components representing the remaining spectrum. We tested the method on simulated cases of metal-ligand adducts at L-, S-, and X-band frequencies, and showed that extracted values, hyperfine and super-hyperfine coupling constants from simulated spectra, were in excellent agreement with the values of those parameters used in the simulations. For the experimental case of a copper(II) complex with distorted octahedral geometry, the method was able to extract and hyperfine coupling constant values, and revealed features that were buried in the overlapped spectra.
光谱分析的目的是以最佳方式从实验数据中解析并提取相关特征。在连续波（cw）电子自旋共振（ESR）光谱中，顺磁中心的参数值以及由其与分子中相邻磁性核相互作用引起的超精细分裂，都提供了重要的结构和电子信息。然而，在存在g-和/或A-各向异性和/或大量共振线的情况下，光谱分析极具挑战性。在这些情况下，要么采用高分辨率实验技术来解析光谱，要么结合一系列合适的ESR频率与模拟来确定相应的g和A值。在这项工作中，我们提出了一种小波变换技术，通过分离超精细和超超精细分量来解析模拟和实验cw-ESR光谱。我们利用小波变换的多分辨率特性，基于对光谱及其变化频率的同时分析，实现对光谱不同特征的分离。我们保留存储超精细和/或超超精细特征的小波分量，同时消除代表其余光谱的小波分量。我们在L-、S-和X波段频率下对金属-配体加合物的模拟案例测试了该方法，结果表明，从模拟光谱中提取的g值、超精细和超超精细耦合常数与模拟中使用的这些参数值高度吻合。对于具有扭曲八面体几何结构的铜（II）配合物的实验案例，该方法能够提取g和超精细耦合常数的值，并揭示了隐藏在重叠光谱中的特征。
