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-d₄₀, polyethylene-d₄, and stearic acid-d₃₅. Six spectral indicators are identified: I[v_a(CD₂)₂₁₉₆]/ I[v_a(CD₂)₂₁₇₂], I[v(C-C)_G]/I[v(C-C) _T], I[v_s(CD₃)]/I[v_a(CD ₂)₂₁₇₂], I[v_s(CD₂)]/I[v _a(CD₂)₂₁₇₂], and the full width at half-maximum (fwhm) and frequency of the v_s(CD₂) mode. Among these indicators, the ratio of I[v_a-(CD₂)₂₁₉₆]/ I[v_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[v_a(CH ₂)]/I[v_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.