Structure and chain dynamics of alkanethiol-capped gold colloids
Structure and chain dynamics of alkanethiol-capped gold colloids
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DOI：
10.1021/la9510487
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发表时间：
1996-03-06
期刊：
影响因子：
3.9
通讯作者：
Reven, L
中科院分区：
文献类型：
--
作者：
Badia, A;Gao, W;Reven, L
利用变温固体~（13）C NMR研究了短链和长链烷基硫醇CH_3（CH_2）（7）SH和CH_3（CH）（17）SH以及羟基烷基硫醇HO（CH_2）（16）SH在金纳米粒子上的吸附结构和动力学行为。在溶液和固体状态下，与硫头基相邻的前三个碳的共振在与金结合时消失，表明与表面的强相互作用。C-13富集的样品，CH 3（CH 2）（12）* CH 2SH/金，对于硫头基旁边的碳显示出以42 ppm为中心的宽共振。而CH 3（CH 2）（7）SH/金的固态C-13位移基本上与溶液中相同，CH 3（CH 2）（17）SH和HO（CH 2）（16）SH/金的亚甲基碳在固态下向低场位移4.5 ppm，表明链结晶成扩展的全反式构象。高构象顺序，沿着与减少亚甲基质子线宽度在CH 3（CH）（17）SH/金样品，表明链正在经历大幅度运动围绕其长轴。分子的流动性增加对未结合的结束，有一个较高的人口gauche构象。弛豫测量表明，在室温下，在CH 3（CH 2）（17）SH/金中，运动受限的全反式链和较小数量的液态构象无序链共存。这两种类型的链被认为是由于金胶体球的紧密堆积而产生的，从而导致相邻胶体的链可以相互交叉以产生有序域的间隙空间和区域。的硫醇封端的金纳米晶体，这是通过差示扫描量热法检测的相变，涉及可逆的无序的烷基链。
The structure and dynamical behavior of short and long chain alkanethiols, CH3(CH2)(7)SH and CH3(CH)(17)SH, and of a hydroxyalkanethiol, HO(CH2)(16)SH, adsorbed onto gold nanoparticles were studied by variable temperature solid-state C-13 NMR spectroscopy. In both the solution and solid state, the resonances of the first three carbons next to the sulfur headgroup disappear upon binding to the gold, indicating a strong interaction with the surface. A C-13-enriched sample, CH3(CH2)(12)*CH2SH/gold, displays a broad resonance centered at 42 ppm for the carbon next to the sulfur headgroup. Whereas the solid-state C-13 shifts of CH3(CH2)(7)SH/gold are essentially the same as in solution, the methylene carbons of CH3(CH2)(17)SH and HO(CH2)(16)SH/gold shift, downfield by 4.5 ppm in the solid state, indicating that the chains crystallize into an extended all-trans conformation. The high conformational order, along with reduced methylene proton line widths in the CH3(CH)(17)SH/gold sample, indicates that the chains are undergoing large-amplitude motions about their long axes. Molecular mobility increases toward the unbound ends which have a higher population of gauche conformers. Relaxation measurements show the coexistence of motionally restricted all-trans chains and a smaller population of liquid-like conformationally disordered chains in CH3(CH2)(17)SH/gold at room temperature. The two types of chains are proposed to arise from close packing of the gold colloidal spheres, resulting in interstitial spaces and regions where chains of neighboring colloids can interdigitate to produce ordered domains. Phase transitions of the thiol-capped gold nanocrystals, which are detected by differential scanning calorimetry, are shown to involve a reversible disordering of the alkyl chains.