The Phenomenon of Vibrational Circular Dichroism Enhancement: A Systematic Survey of Literature Data.

While the intensity of vibrational circular dichroism (VCD) signals is commonly 10-10 times smaller than that of corresponding IR signals, several kinds of systems display enhanced VCD spectra with -values (VCD/IR intensity ratio) above 10 and even reaching 5 × 10 in some exceptional cases. These systems include transition metal and lanthanide complexes, protein and peptide fibrils, short oligopeptide gels, crystalline compounds, gels and solution aggregates of organic compounds. We review the literature on VCD enhancement, focusing on collecting and analyzing data on enhanced -values. Special attention is given to the mechanisms proposed to produce these effects.