title: An insight into sequential order in two-dimensional correlation spectroscopy.
abstract: Determination of the sequential order of events is a very important feature of generalized two-dimensional correlation spectroscopy (2D-COS). Recently, queries have been put forward on the actual effectiveness of this method when changes are non-periodic, particularly in the presence of local sequential order. Consequently, it brings an urgent necessity to understand the true connotation of the sequential order parameter derived from 2D-COS analysis. This article presents an attempt to address these questions based on the analysis of simulated spectra by assuming the band intensity changes in a logarithmic, exponential, hyperbolic, or polynomial manner. It is concluded that for two events changing monotonically and without local sequential orders, one event occurring prior to the other as determined using 2D-COS means in most cases that the former has both a shorter half-time and a greater half-intensity. As a rule of thumb, intensity versus the perturbation factor should be plotted before performing the 2D-COS analysis to determine the sequential order of the involved events. In the presence of obvious local sequential order, 2D-COS analysis is unnecessary. Otherwise, sequential order can be determined quite reliably based on 2D-COS analysis.
authors.affiliation: Key Laboratory of Bioorganic Phosphorous Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Jia
authors.forename: Nan-Nan
authors.initials: NN
authors.lastname: Wang
authors.forename: Zhi-Wu
authors.initials: ZW
authors.lastname: Yu
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D008956:Models, Chemical; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods*