Wilson Kevin R, Peterka Darcy S, Jimenez-Cruz Michael, Leone Stephen R, Ahmed Musahid
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Phys Chem Chem Phys. 2006 Apr 28;8(16):1884-90. doi: 10.1039/b517487b. Epub 2006 Mar 7.
The ionization energies of biological nanoparticles are determined using the velocity map photoelectron imaging technique. A beam of nanoparticles produced by aerosol methods is photoionized with tunable vacuum ultraviolet (VUV) synchrotron radiation. The resulting photoelectrons are detected and their angular and energy distributions are measured, yielding an angle-resolved photoelectron spectrum. The ionization energies of the nanoparticles are derived from plots of the photoelectron spectrum versus incident photon energy. The ionization energies of nanophase glycine and phenylalanine-glycine-glycine are 7.6 +/- 0.2 eV, and 7.5 +/- 0.2 eV, respectively. X-Ray powder diffraction studies on the glycine nanoparticles indicate that they are crystalline in nature. The reduced ionization energy when compared to gas phase results suggests that the polarization energy in the solid is significant. The difference in the ionization energy between the nano and gas phase reflects this polarization energy and is derived to be 1.7 +/- 0.2 eV and 1.6 +/- 0.2 eV for glycine and phenylalanine-glycine-glycine, respectively. Using these results the molecular polarizability of glycine is estimated to be 4.7 +/- 0.3 A3 (31.9 +/- 1.9 au).
利用速度映射光电子成像技术测定生物纳米颗粒的电离能。通过气溶胶方法产生的纳米颗粒束用可调谐真空紫外（VUV）同步辐射进行光电离。检测产生的光电子，并测量其角分布和能量分布，从而得到角分辨光电子能谱。纳米颗粒的电离能由光电子能谱与入射光子能量的关系图得出。纳米相甘氨酸和苯丙氨酸 - 甘氨酸 - 甘氨酸的电离能分别为7.6±0.2电子伏特和7.5±0.2电子伏特。对甘氨酸纳米颗粒的X射线粉末衍射研究表明它们本质上是晶体。与气相结果相比，电离能降低表明固体中的极化能很显著。纳米相和气相之间电离能的差异反映了这种极化能，甘氨酸和苯丙氨酸 - 甘氨酸 - 甘氨酸的极化能分别为1.7±0.2电子伏特和1.6±0.2电子伏特。利用这些结果，估计甘氨酸的分子极化率为4.7±0.3埃³（31.9±1.9原子单位）。
