Two-dimensional IR spectroscopy can be designed to eliminate the diagonal peaks and expose only the crosspeaks needed for structure determination

The power of two-dimensional (2D) IR spectroscopy as a structural method with unprecedented time resolution is greatly improved by the introduction of IR polarization conditions that completely eliminate diagonal peaks from the spectra and leave only the crosspeaks needed for structure determination. This approach represents a key step forward in the applications of 2D IR to proteins, peptides, and other complex molecules where crosspeaks are often obscured by diagonal peaks. The technique is verified on the model compound 1,3-cyclohexanedione and subsequently used to clarify the distribution of structures that the acetylproline-NH(2) dipeptide adopts in chloroform. In both cases, crosspeaks are revealed that were not observed before, which, in the case of the dipeptide, has led to additional information about the structure of the amino group end of the peptide.

二维红外（two-dimensional IR, 2D IR）光谱作为一种时间分辨率空前的结构表征手段，其应用潜力因红外极化条件的引入而得到极大提升——该条件可完全消除光谱中的对角峰，仅保留结构解析所需的交叉峰。该方法为二维红外光谱在蛋白质、多肽及其他复杂分子的研究应用迈出了关键一步，此前这类体系中的交叉峰常被对角峰所掩盖。本技术以模式化合物1,3-环己二酮完成验证，随后被用于阐明乙酰脯氨酸-NH(2)二肽在氯仿溶液中所采取的结构分布。在上述两个案例中，均发现了此前未被观测到的交叉峰；就该二肽而言，这一发现进一步揭示了多肽氨基端的结构信息。