Rozenberg M, Shoham G
Department of Inorganic and Analytical Chemistry, The Hebrew University of Jerusalem, Jerusalem, Givat Ram 91904, Israel.
Biophys Chem. 2007 Jan;125(1):166-71. doi: 10.1016/j.bpc.2006.07.008. Epub 2006 Jul 25.
Three bands at 3270 cm(-1), 3200 cm(-1) and 3030 cm(-1) are found in the IR stretching proton (nu(1)) mode spectral range in spectra of solid poly-l-lysine (PLL). Strong quantitative changes of these bands are observed in samples dried from water solutions with different pH. The narrow band at 3270 cm(-1), which is strong in the spectrum of PLL precipitated from pH=12 alkaline medium, is assigned to the nu(1) peptide proton mode of NH-CO (amide A) of the beta-sheet structure type. The band at 3200 cm(-1), which is intensified in PLL precipitated from pH=1 acidic medium, relates to the nu(1) peptide mode in the random coil structure. The band at 3030 cm(-1), whose peak intensity increases two-fold in going from alkaline to acidic medium, is assigned to the nu(1) modes of protonated NH(3)(+) side chain groups. The frequencies of all bands were used for estimating H-bond energy relying on an empirical correlation between this property and the red shift of the nu(1) band. The enthalpy of the secondary structure transition from beta-sheet to the random coil, which is observed in PLL at the change of pH from 11 to 1 amounts to 4.7 kJ mol(-1).
在固体聚-L-赖氨酸（PLL）的红外伸缩质子（ν₁）模式光谱范围内，发现了位于3270 cm⁻¹、3200 cm⁻¹和3030 cm⁻¹处的三条谱带。在从不同pH值的水溶液中干燥得到的样品中，观察到了这些谱带的强烈定量变化。在从pH = 12碱性介质中沉淀出的PLL光谱中较强的3270 cm⁻¹处的窄带，被归属于β-折叠结构类型的NH-CO（酰胺A）的ν₁肽质子模式。在从pH = 1酸性介质中沉淀出的PLL中增强的3200 cm⁻¹处的谱带，与无规卷曲结构中的ν₁肽模式有关。在从碱性介质到酸性介质转变过程中峰值强度增加两倍的3030 cm⁻¹处的谱带，被归属于质子化的NH₃⁺侧链基团的ν₁模式。所有谱带的频率都用于依据该性质与ν₁谱带红移之间的经验相关性来估算氢键能量。在PLL中，当pH从11变为1时观察到的从β-折叠到无规卷曲的二级结构转变的焓为4.7 kJ mol⁻¹。
