Klassen J S, Schnier P D, Williams E R
Department of Chemistry, University of California, Berkeley 94720-1460, USA.
J Am Soc Mass Spectrom. 1998 Nov;9(11):1117-24. doi: 10.1016/S1044-0305(98)00098-1.
The dissociation kinetics of a series of doubly deprotonated oligonucleotide 7-mers [d(A)7(2-), d(AATTAAT)2-, d(TTAATTA)2-, and d(CCGGCCG)2-] were measured using blackbody infrared radiative dissociation in a Fourier-transform mass spectrometer. The oligonucleotides dissociate first by cleavage at the glycosidic bond leading to the loss of a neutral nucleobase, followed by cleavage at the adjacent (5') phosphodiester bond to produce structurally informative a-base and w type ions. From the temperature dependence of the unimolecular dissociation rate constants, Arrhenius activation parameters in the zero-pressure limit are obtained for the loss of base. The measured Arrhenius parameters are dependent on the identity of the nucleobase. The process involving the loss of an adenine base from the dianions, d(A)7(2-), d(AATTAAT)2-, and d(TTAATTA)2- has an average activation energy (Ea) of approximately 1.0 eV and a preexponential factor (A) of 10(10) s-1. Both guanine and cytosine base loss occurs for d(CCGGCCG)2-. The average Arrhenius parameters for the loss of cytosine and guanine are Ea = 1.32 +/- 0.03 eV and A = 10(13.3 +/- 0.3) s-1. No loss of thymine was observed for mixed adenine-thymine oligonucleotides. Neither base loss nor any other fragmentation reactions occur for d(T)7(2-) over a 600 s reaction delay at 207 degrees C, a temperature close to the upper limit accessible with our instrument. The Arrhenius parameters indicate that the preferred cleavage sites for mixed oligonucleotides of similar mass-to-charge ratio will be strongly dependent on the internal energy of the precursor ions. At low internal energies (effective temperatures below 475 K), loss of adenine and subsequent cleavage of the adjacent phosphoester bonds will dominate, whereas at higher energies, preferential cleavage at C and G residues will occur. The magnitude of the A factors < or = 10(13) s-1 measured for the loss of the three nucleobases (A, G, and C) is indicative of an entropically neutral or disfavored process as the rate limiting step for this reaction.
在傅里叶变换质谱仪中，使用黑体红外辐射解离法测量了一系列双去质子化的7聚体寡核苷酸[d(A)7(2-), d(AATTAAT)2-, d(TTAATTA)2-, 以及d(CCGGCCG)2-]的解离动力学。寡核苷酸首先通过糖苷键断裂解离，导致一个中性核碱基的丢失，随后在相邻的（5'）磷酸二酯键处断裂，产生具有结构信息的α-碱基和ω型离子。根据单分子解离速率常数的温度依赖性，得到了零压力极限下碱基丢失的阿伦尼乌斯活化参数。所测得的阿伦尼乌斯参数取决于核碱基的种类。从二价阴离子d(A)7(2-), d(AATTAAT)2-, 以及d(TTAATTA)2-中丢失腺嘌呤碱基的过程，平均活化能（Ea）约为1.0 eV，指前因子（A）为10(10) s-1。d(CCGGCCG)2-会发生鸟嘌呤和胞嘧啶碱基的丢失。胞嘧啶和鸟嘌呤丢失的平均阿伦尼乌斯参数为Ea = 1.32 ± 0.03 eV，A = 10(13.3 ± 0.3) s-1。对于腺嘌呤 - 胸腺嘧啶混合寡核苷酸，未观察到胸腺嘧啶的丢失。在207℃、600 s的反应延迟时间内，d(T)7(2-)既没有碱基丢失，也没有发生任何其他碎片化反应，该温度接近我们仪器可达到的上限。阿伦尼乌斯参数表明，对于质荷比相似的混合寡核苷酸，其优先裂解位点将强烈依赖于前体离子的内能。在低内能（有效温度低于475 K）时，腺嘌呤的丢失以及随后相邻磷酸酯键的断裂将占主导，而在较高能量时，将优先在C和G残基处裂解。对于三种核碱基（A、G和C）丢失所测得的A因子大小≤10(13) s-1，表明作为该反应速率限制步骤的过程在熵上是中性的或不利的。
