Wang Yixuan, Ai Hongqi
Department of Natural Science, Albany State University, Albany, GA 31705, USA.
J Phys Chem B. 2009 Jul 16;113(28):9620-7. doi: 10.1021/jp903315n.
Adsorptions of nine tripeptides GXG, ranging from negatively (D) and positively (K) charged, to hydrophilic (N and S), and to hydrophobic (G, V, F, W, and Y) residues, on the two cluster models (C(54)H(18) and C(54)) of (10,0) single-walled carbon nanotubes (SWCNTs) are systemically investigated with the MPWB1K and MP2 methods. The solvent effects are taken into account with the implicit CPCM model. The objective is to provide novel insights into the interaction mechanism between proteins and SWCNTs. Results reveal that the adsorption strength of two charged tripeptides is greatly affected by the solvent effect and the hydrogen saturability of the SWCNT models. In the gas phase, on the surface of C(54)H(18), GKG has the strongest adsorption (adsorption energy (AE): -29.3 kcal/mol at the MP2 level), whereas the adsorption of the negatively charged GDG is the strongest on C(54) (AE: -30.4 kcal/mol with MP2). However, because of strong solvation, the adsorptions of the charged residues (D and K) on both C(54)H(18) and C(54) surfaces in aqueous solution are either rather weak or even unbound. The two neutral hydrophilic residues (N and S) exhibit adsorptions on C(54)H(18) in the gas phase (AE: -3.3 and -4.2 kcal/mol), yet are unable to adsorb on SWCNTs in aqueous solution (AE: +0.3 kcal/mol at MP2+CPCM). The five hydrophobic residues present relatively strong adsorption on SWCNTs, especially for the three aromatic residues (GFG, GYG, and GWG), regardless of the CNT model and whether they are in the gas phase or solution. These results indicate that in general the aromatic groups of proteins would play a very important role on functionalizing CNTs, which basically supports the relevant experimental observations. In addition, the electron correlation is essential for adsorptions of GXG on pristine SWCNTs, and the three aromatic residues have the highest electron correlation effects. The present investigation provides strong evidence that for the functionalization of CNTs via proteins it is most likely that hydrophobic interaction and van der Waals are the dominant driving forces.
采用MPWB1K和MP2方法，系统研究了9种三肽GXG（从带负电荷（D）和正电荷（K），到亲水性（N和S），再到疏水性（G、V、F、W和Y）残基）在（10,0）单壁碳纳米管（SWCNT）的两种簇模型（C(54)H(18)和C(54)）上的吸附情况。采用隐式CPCM模型考虑溶剂效应。目的是为蛋白质与SWCNT之间的相互作用机制提供新的见解。结果表明，两种带电三肽的吸附强度受溶剂效应和SWCNT模型的氢饱和性的显著影响。在气相中，在C(54)H(18)表面，GKG的吸附最强（在MP2水平下吸附能（AE）：-29.3 kcal/mol），而带负电荷的GDG在C(54)上的吸附最强（MP2计算的AE：-30.4 kcal/mol）。然而，由于强烈的溶剂化作用，在水溶液中，带电荷残基（D和K）在C(54)H(18)和C(54)表面的吸附都相当弱甚至没有吸附。两个中性亲水性残基（N和S）在气相中对C(54)H(18)有吸附（AE：-3.3和-4.2 kcal/mol），但在水溶液中不能吸附在SWCNT上（MP2+CPCM计算的AE：+0.3 kcal/mol）。五个疏水性残基在SWCNT上表现出相对较强的吸附，特别是对于三个芳香族残基（GFG、GYG和GWG），无论CNT模型如何以及它们是在气相还是溶液中。这些结果表明，一般来说，蛋白质的芳香基团在碳纳米管功能化中起着非常重要的作用，这基本支持了相关的实验观察。此外，电子相关对于GXG在原始SWCNT上的吸附至关重要，并且三个芳香族残基具有最高的电子相关效应。本研究提供了有力证据，表明通过蛋白质对碳纳米管进行功能化时，疏水相互作用和范德华力很可能是主要驱动力。
