Principal component analysis of hemoglobin redox reaction in spectroelectrochemical cell

The redox reaction of hemoglobin (Hb) is studied by spectroelectrochemistry. Fifteen absorption spectra are measured at different electrode potentials in the range from +0.4 V to -0.3 V. The spectra are collected in a matrix, X, with each spectrum representing one column. The method of Principal component analysis (PCA) is applied by the aid of the scikit library of the Python programing language. X is decomposed and presented as the matrix multiplication product of two matrices, the Scores matrix, S, and the Loadings matrix, L. In such presentation S contains the “abstract” spectra of the principal components (PC), and L contains the coefficients used to reconstruct all original spectra as linear combinations of the PC. The results show that the original spectra can be presented as combination of two PC. The Loading values of the two components can be directly used to estimate the ratio of the oxidized to the reduced form of Hb in each spectrum and to construct the Nernst plot of the redox reaction. Two Nernst plot were obtained, one for each PC. The redox potentials estimated from these plots differ by only ±2.5 mV from the value obtained by the original absorbances, and the slopes coincide to 98.82% for the first PC and to 99.88% for the second PC.