The potential energy surfaces for the cycloaddition reaction Me2X:+C60-->Me2X(C60) (X=C, Si, Ge, Sn, and Pb) have been studied at the B3LYP/LANL2DZ level of theory. It has been found that there are two competing pathways in these reactions, which can be classified as a [6,5]-attack (path 1) and a [6,6]-attack (path 2). It was found that, given the same reaction conditions, the cycloaddition reaction of C60 via a [6,6]-attack is more favorable than that via a [6,5]-attack, both kinetically and thermodynamically. A qualitative model that is based on the theory of Pross and Shaik has been used to develop an explanation for the reaction barrier heights. As a result, our theoretical investigations suggest that the singlet-triplet splitting DeltaEst(=Etriplet-Esinglet) of the 6 valence electron Me2X: and C60 species can be used as a guide to predict their reactivity toward cycloaddition reactions. Our model results demonstrate that the reactivity of heavy carbene cycloaddition to C60 decreases in the order Me2C:>Me2Si:>Me2Ge>Me2Sn:>Me2Pb:. As a consequence, we show that electronic effects play a decisive role in determining the energy barriers as well as the reaction enthalpy.
Protein kinases are involved in many important cellular signaling pathways. Development of activitybased probes targeting this enzyme family would be of great contemporary values. In this study, we established a synthetic route that allows parallel synthesis for the preparation of a 2´2 probe library. The probes feature a reactive fluorosulfonylbenzoyl moiety on an adenosine framework to investigate the effect of two structural variables on the labeling performance toward kinases. Preliminary labeling results indicated that probe 3, which is the best candidate in the probe library, is indeed an activity-based probe for kinases. The results also revealed that the ester linkage between the fluorosulfonylbenzoyl moiety and the sugar plays an important role in the labeling ability of the probes, and the meta-substituted sulfonyl fluoride could help improving the target specificity. The valuable information obtained in this study could be applied for probe improvement in the future.
The potential energy surfaces for the abstraction reactions of heavy cyclopropenes with alcohol have been characterized in detail using density functional theory (B3LYP/LANL2DZdp), including zero-point corrections. Five heavy cyclopropene species including cyclopropene, cyclotrisilene, cyclotrigermene, cyclotritinene, and cyclotrileadene, have been chosen in this work as model reactants. All the interactions involve a hydrogen shift via a two-center transition state. The activation barriers and enthalpies of the reactions were compared in order to determine the relative reactivity of the heavy cyclopropenes. The present theoretical investigations suggest that the relative heavy cyclopropene reactivity increases in the order cyclopropene < cyclotrisilene < cyclotrigermene < cyclotritinene < cyclotrileadene. That is, for alcohol dehydrogenations there is a very clear trend toward lower activation barriers and less endothermic reactions on going from C to Pb. Besides this, our theoretical findings indicate that the final abstraction-addition products should adopt the anti geometry, rather than the syn geometry, from a thermodynamic viewpoint. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.
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