Structure and dynamics in alkanethiolate monolayers self-assembled on gold nanoparticles: A DSC, FT-IR, and deuterium NMR study
Structure and dynamics in alkanethiolate monolayers self-assembled on gold nanoparticles: A DSC, FT-IR, and deuterium NMR study
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DOI：
10.1021/ja963571t
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发表时间：
1997-03-19
影响因子：
15
通讯作者：
Lennox, RB
中科院分区：
文献类型：
--
作者：
Badia, A;Cuccia, L;Lennox, RB
纳米金颗粒, cn.直径为 30 埃，已用专门氘化（位置 1 和位置 10 至 13）和全氘化（位置 2 至 18）十八烷硫醇 (C18SH) 衍生化。通过差示扫描量热法 (DSC) 表征了化学吸附在胶体 Sold 表面上的十八烷硫醇单层的相行为。 DSC 热分析图显示，C18SH 衍生的金纳米粒子经历了明显的相变，这可能与烷基链的可逆无序有关。尽管这些金颗粒具有高度弯曲的几何形状，但链烷硫醇链中存在显着程度的构象顺序，并且硫醇修饰的金纳米颗粒的热致行为与传统的平面自组装单层非常相似。与 DSC 转变相关的峰值最高温度和焓与等效链长的 n-二酰基磷脂酰胆碱脂质双层膜的凝胶到液晶转变的那些非常相似。由于硫头基团与金表面的共价键合而导致的链移动性受限，不会影响转变在转变温度和焓方面的协同性。使用变温固态氘核磁共振光谱和透射傅里叶变换红外光谱探测了氘化 C18S/Au 纳米粒子的局部链有序和动力学。对称 CD2 伸缩频率的温度依赖性已证实 DSC 检测到的相变涉及热诱导的从主要全反式构象到链无序状态的变化。 d(35)-C18S/Au 和 10,10, II, II, IZ, 12, 13, 13-d(8)-C18S/Au 的热行为比较表明，无序起源于链末端区域，并随着温度升高向链中部传播。I,1-d(2)-C18S/Au 的研究表明，无序不会延伸到链末端区域。束缚硫头基团。氘核磁共振波谱明确表明，链熔化是由于链烷硫醇链中高斯键频率的增加而引起的。 H-2 NMR 谱线形状进一步表明，束缚的烷硫醇链正在经历快速的反式高斯键异构化和轴向链旋转。
Gold nanoparticles, cn. 30 Angstrom in diameter, have been derivatized with specifically deuterated (position 1 and positions 10 to 13) and perdeuterated (positions 2 to 18) octadecanethiols (C18SH). The phase behavior of the octadecanethiolate monolayers chemisorbed onto the colloidal Sold surface was characterized by differential scanning calorimetry(DSC). The DSC thermograms show that the C18SH-derivatized Au nanoparticles undergo distinct phase transitions which can be associated with the reversible disordering of the alkyl chains. Despite the highly curved geometry of these Au particles, there is a remarkable degree of conformational order in the alkanethiolate chains and the thermotropic behavior of the thiol-modified gold nanoparticles is very similar to that of conventional, planar self-assembled monolayers. Both the peak maximum temperature and the enthalpy associated with the DSC transition strongly parallel those of the gel-to-liquid crystalline transition of n-diacylphosphatidylcholine lipid bilayer membranes of equivalent chain length. Restricted chain mobility due to covalent bonding of the sulfur head group to the gold surface does not affect the cooperativity of the transition in terms of the transition temperature and enthalpy. Local chain ordering and dynamics in the deuterated C18S/Au nanoparticles have been probed using variable-temperature solid-state deuterium NMR spectroscopy and transmission FT-IR spectroscopy. The temperature dependence of the symmetric CD2 stretching frequency has confirmed that the DSC-detected phase transition involves a thermally-induced change from a predominantly all-trans conformation to a chain disordered state. A comparison of the thermal behavior of d(35)-C18S/Au and 10,10, II, II, IZ, 12, 13, 13-d(8)-C18S/Au shows that disordering originates in the chain terminus region and propagates toward the middle of the chain as the temperature increases, Studies of I,1-d(2)-C18S/Au show that the disorder does not extend to the tethered sulfur head group. Deuterium NMR spectroscopy specifically establishes that chain melting arises from an increased frequency of gauche bonds in the alkanethiolate chains. The H-2 NMR line shapes further indicate that the tethered alkanethiolate chains are undergoing rapid trans-gauche bond isomerization and axial chain rotation.