A strong preference for a salt-bridge structure in the gas phase: reactions of deprotonated amino acids with borane.
A strong preference for a salt-bridge structure in the gas phase: reactions of deprotonated amino acids with borane.
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对气相盐桥结构的强烈偏好：去质子化氨基酸与硼烷的反应。
DOI：
10.1021/ja010966q
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发表时间：
2001
影响因子：
15
通讯作者：
Huang,R
中科院分区：
文献类型：
--
作者：
Gronert,S;Huang,R
近年来，人们对气相中盐桥型结构的存在越来越感兴趣，这些结构往往与多肽的裂解途径有关。1-12虽然氨基酸似乎更喜欢常规结构(而不是溶液中的两性离子)，但有证据表明，脯氨酸和精氨酸的金属盐在气相中更喜欢采用盐桥结构(即，金属与氨基酸两性离子络合)。6，8，9，13我们最近发现，硼烷是一种潜在的有用的反应物，用于表征气相生物分子，14在目前的通信中，我们报告了由硼烷与去质子化的甘氨酸反应生成的产物中盐桥结构的显著偏好。此外，我们还提供了在与其他氨基酸的反应和反应产物的碰撞激活解离(CAD)中形成异常的硼杂环的证据。使用改进的Finnigan LCQ四极离子陷阱质谱仪，15甘氨酸中的M-1阴离子与BH3的二甲硫络合物(DMS-BH3)发生反应。快速反应产生几个产物，但与BH3加成并失去H2相对应的离子占主导地位(等式1)。合乎逻辑的产物是环状硼氢化物，其中来自硼的氢化物和来自氮的质子的结合导致H2损失并塌陷为五元环。16，17在两个标记实验中证实了参与H2损失的氢的身份。从H_2NCD_2CO_2~-开始，与硼烷的反应完全导致H_2的损失。样本光谱如图1a所示。相反，D2NCH2CO2-与BH3反应，得到与HD损失相对应的产物。我们的第一个想法是，BH3会加到羧酸盐上，然后利用最初加成的放热，排出一个氢化物离子(H-)，它会使胺去质子化，最终导致环关闭(方案1)。为了更好地了解反应机理，我们在MP2/6-31+G(d，p)//MP2/6-31+G(D)水平上对该反应进行了从头算计算。表1总结了数据。在失去DMS的情况下，在羧酸盐上的加成仅放热约17千卡/摩尔，这远远不足以为氢的排放过程提供燃料。过渡态II大于40千卡/摩尔
In recent years there has been a growing interest in the existence of salt-bridge-type structures in the gas phase, and they often have been implicated in the fragmentation pathways of peptides. 1-12 Although it appears that amino acids prefer conventional structures (rather than the zwitterions found in solution), there is evidence that metal salts of proline and arginine prefer to adopt salt-bridge structures in the gas phase (ie, metal complexed to the amino acid zwitterion). 6, 8, 9, 13 We have recently found that borane is a potentially useful reactant for characterizing gas-phase biomolecules, 14 and in the present communication, we report a remarkably large preference for a salt-bridge structure in the product from the reaction of borane with deprotonated glycine. In addition, we provide evidence for the formation of unusual boron heterocycles in reactions with other amino acids and in the collisionactivated dissociation (CAD) of the reaction products. Using a modified Finnigan LCQ quadrupole ion trap mass spectrometer, 15 the M-1 anion from glycine was allowed to react with the dimethyl sulfide complex of BH3 (DMS-BH3). A rapid reaction leads to several products, but an ion corresponding to the addition of BH3 with loss of H2 dominates (eq 1).A logical product is a cyclic borohydride where the combination of a hydride from the boron and proton from the nitrogen leads to H2 loss and collapse to a five-membered ring. 16, 17 The identity of the hydrogens involved in the H2 loss was confirmed in two labelleing experiments. Starting with H2NCD2CO2-, the reaction with the borane leads exclusively to H2 loss. A sample spectrum is shown in Figure 1a. Conversely, D2NCH2CO2-reacts with BH3 to give a product corresponding to HD loss. Our first thought was that the BH3 would add to the carboxylate and then using the exothermicity of the initial addition, expel a hydride ion (H-) which would deprotonate the amine eventually leading to ring closure (Scheme 1). To gain a better understanding of the mechanism, we have completed ab initio calculations on this reaction at the MP2/6-31+ G (d, p)//MP2/6-31+ G (d) level. 18 The data are summarized in Table 1. The addition at the carboxylate with loss of DMS is only exothermic by about 17 kcal/mol which is not nearly enough energy to fuel the H2 expulsion process. The transition state, II, is over 40 kcal/mol
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表面光滑度和与磷酸盐粘合投资的边际配合。
DOI：
10.1016/0022-3913(79)90038-6
发表时间：
1979
期刊：
The Journal of prosthetic dentistry
影响因子：
--
作者：
J. Cooney;T. M. Doyle;A. Caputo
通讯作者：
A. Caputo
全瓷面缘陶瓷金属冠边缘适应性分析。
DOI：
10.1016/0022-3913(86)90005-3
发表时间：
1986
期刊：
The Journal of prosthetic dentistry
影响因子：
--
作者：
D. J. Wanserski;K. Sobczak;J. Monaco;G. McGivney
通讯作者：
G. McGivney
影响因子：
2
作者：
K. D. Jørgensen
通讯作者：
K. D. Jørgensen
影响因子：
4.6
作者：
BUCHANAN, WT;SVARE, CW;TURNER, KA
通讯作者：
TURNER, KA
使用肩部准备评估 45 度唇斜面。
DOI：
10.1016/0022-3913(86)90136-8
发表时间：
1986
期刊：
The Journal of prosthetic dentistry
影响因子：
--
作者：
F. V. Panno;F. Vahidi;I. Gulker;K. Ghalili
通讯作者：
K. Ghalili