Zubarev Roman A
Division of Ion Physics and Laboratory for Biological and Medical Mass Spectrometry, Uppsala University, Sweden.
Mass Spectrom Rev. 2003 Jan-Feb;22(1):57-77. doi: 10.1002/mas.10042.
Reactions of electrons in the energy range below 70 eV with polypeptide cations and anions are reviewed, as well as their applications for the structural analysis of polypeptides. At very low energies (</= 0.1 eV), the major outcome is electron-capture dissociation (ECD) of S-S and backbone N-C(alpha) bonds, leading to c' and z. fragments. ECD is useful in sequencing and characterization of post-translational modifications (PTMs), because c', z. fragmentation is abundant and the fragments usually retain labile groups. Electron capture at higher energies (3-13 eV) induces secondary fragmentation in radical z. fragments; this hot ECD (HECD) allows one to distinguish between the isomeric leucine and isoleucine residues. If a hot electron is not captured, then the induced electronic excitation converts internally into vibrational energy, resulting in fragmentation of the C(O)bond;N backbone bond (so-called EIEIO process). Above 9-10 eV, further ionization of n-charged cations occurs. If the formed (n + 1)+. cations capture electrons, then the C(alpha)bond;C backbone bond is usually broken. For anions that collide with approximately 20 eV electrons, the ejection of an electron leads to the creation of a radical positive charge (hole) that recombines internally with a negative charge. Such recombination leads to various backbone bond cleavages. This electron-detachment dissociation (EDD) is analogous to ECD for negative ions.
综述了能量低于70 eV的电子与多肽阳离子和阴离子的反应，以及它们在多肽结构分析中的应用。在非常低的能量（≤0.1 eV）下，主要结果是S-S键和主链N-C(α)键的电子捕获解离（ECD），产生c'和z.碎片。ECD在翻译后修饰（PTM）的测序和表征中很有用，因为c'、z.碎片丰富，且碎片通常保留不稳定基团。在较高能量（3-13 eV）下的电子捕获会在自由基z.碎片中诱导二次碎片化；这种热电子捕获解离（HECD）能让人区分异亮氨酸和亮氨酸的异构体残基。如果没有捕获热电子，那么诱导的电子激发会在内部转化为振动能量，导致C(O)键；N主链键断裂（所谓的EIEIO过程）。在9-10 eV以上，n价阳离子会进一步电离。如果形成的(n + 1)+.阳离子捕获电子，那么C(α)键；C主链键通常会断裂。对于与能量约为20 eV的电子碰撞的阴离子，电子的射出会导致产生一个自由基正电荷（空穴），该正电荷会在内部与一个负电荷重新结合。这种重新结合会导致各种主链键的断裂。这种电子脱离解离（EDD）类似于阴离子的ECD。
