Pacific Northwest National Laboratory, Chemical and Materials Sciences Division, P.O. Box 999, K8-88, Richland, Washington 99352, USA.
Phys Chem Chem Phys. 2011 Apr 21;13(15):6936-46. doi: 10.1039/c1cp00029b. Epub 2011 Mar 8.
Interactions between quaternary amino or guanidino groups with anions are ubiquitous in nature and have been extensively studied phenomenologically. However, little is known about the binding energies in non-covalent complexes containing these functional groups. Here, we present a first study focused on quantifying such interactions using complexes of phosphorylated A(3)pXA(3)-NH(2) (X = S, T, Y) peptides with decamethonium (DCM) or diaguanidinodecane (DGD) ligands as model systems. Time- and collision energy-resolved surface-induced dissociation (SID) of the singly charged complexes was examined using a specially configured Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS). Dissociation thresholds and activation energies were obtained from RRKM modeling of the experimental data that has been described and carefully characterized in our previous studies. For systems examined in this study, covalent bond cleavages resulting in phosphate abstraction by the cationic ligand are characterized by low dissociation thresholds and relatively tight transition states. In contrast, high dissociation barriers and large positive activation entropies were obtained for cleavages of non-covalent bonds. Dissociation parameters obtained from the modeling of the experimental data are in excellent agreement with the results of density functional theory (DFT) calculations. Comparison between the experimental data and theoretical calculations indicate that phosphate abstraction by the ligand is rather localized and mainly affected by the identity of the phosphorylated side chain. The hydrogen bonding in the peptide and ligand properties play a minor role in determining the energetics and dynamics of the phosphate abstraction channel.
季铵或胍基与阴离子的相互作用在自然界中普遍存在，并已在现象学上得到广泛研究。然而，对于含有这些官能团的非共价复合物中的结合能知之甚少。在这里，我们首次进行了一项研究，使用带磷酸化 A(3)pXA(3)-NH(2)（X = S、T、Y）肽的与十甲基铵（DCM）或二胍基癸烷（DGD）配体的复合物作为模型系统，来定量这些相互作用。使用专门配置的傅里叶变换离子回旋共振质谱仪（FTICR-MS），通过考察单电荷复合物的时间和碰撞能分辨表面诱导解吸（SID），来研究这些相互作用。从 RRKM 对实验数据的建模中得到了离解阈值和活化能，这些数据在我们之前的研究中已经进行了描述和仔细的特征化。对于本研究中检查的系统，由阳离子配体引起的磷酸酯基团的共价键断裂具有低离解阈值和相对紧密的过渡态的特征。相比之下，非共价键的断裂获得了高的离解势垒和较大的正活化熵。从实验数据建模中获得的离解参数与密度泛函理论（DFT）计算的结果非常吻合。实验数据与理论计算的比较表明，配体对磷酸酯的抽取是相当局部化的，主要受磷酸化侧链的身份影响。氢键在肽和配体中的性质在决定磷酸酯抽取通道的能量学和动力学方面作用较小。
