Raman spectral conformational order indicators in perdeuterated alkyl chain systems

Conformational order indicators for perdeuterated alkyl chain systems are identified in the Raman spectra of nonadecane-d(40), polyethylene-d(4), and stearic acid-d(35). Six spectral indicators are identified: I[nu(a)(CD2)(2196)]/I[nu(a)(CD2)(2172)], I[nu(C-C)(G)]/I[nu(C-C)(T)], I[nu(s)(CD3)]/I[nu(a)(CD2)(2172)], I[nu(s)(CD2)]/I[nu(a)(CD2)(2172)], and the full width at half-maximum (fwhm) and frequency of the nu(s)(CD2) mode. Among these indicators, the ratio of I[nu(a)(CD2)(2196)]/I[nu(a)(CD2)(2172)] is considered a primary indicator of conformational order, since it responds to alkyl chain conformational changes in a manner similar to the I[nu(a)(CH2)]/I[nu(s)(CH2)] primary indicator for hydrogenated systems. Other indicators are correlated to this primary indicator to derive a better understanding of the effect of structural attributes on conformational order in perdeuterated alkyl chain systems. These Raman spectral order indicators are applicable to any perdeuterated alkyl-containing system including lipids, biological membranes, alkylsilane-based chromatographic stationary phases, and self-assembled monolayers.