含硫/硒动态共价键强弱的测定

Measuring the Strength of S/Se Based Dynamic Covalent Bonds

含硫、硒元素的化学键是重要的光响应动态共价键,本文试图从分子作用力的角度研究它们为何具有不同灵敏度的动态特征,采用基于原子力显微镜的单分子力谱(AFM-SMFS)对含硫、硒元素的动态共价键进行研究,揭示了其兼具稳定性与响应性的内在原因.用化学方法在石英基底上修饰了二硫键或二硒键,通过前述3种化学键的光控动态交换过程,分别得到了含有单个二硫键、硒硫键或二硒键的高分子修饰的石英基底.利用单分子力谱测量了这3组动态共价键的断裂力值,在200 nm/s的拉伸速度下,二硒键的断裂力为(1100±300)pN,硒硫键的断裂力为(1320±330)pN,二硫键的断裂力值为(1450±300)pN,它们的强度从大到小依次为SS>SSe>SeSe.单分子力谱结果表明动态共价键的强度介于非共价相互作用与传统意义上的稳定共价键(如C―C键)之间,这是它们兼具响应性和稳定性的原因之一.

Sulfur,selenium-containing bonds,including disufide bond(SS),diselenide bond(SeSe),and selenide-sulfide bond(SeS),are an important type of light responsive dynamic covalent bonds.Among them,SS and SeS bonds can undergo exchange reaction with the irridiation of UV light,while SeSe bond only requires visible light due to its weaker bond energy.The purpose of this research is to use atomic force microscope-based single molecule force spectroscopy(AFM-SMFS)measurement to reveal the reasons behind the responsiveness and stability of S/Se related dynamic covalent bonds.In this study,quartz substrates modified by SS or SeSe bond were prepared via surface modification.Specifically,the quartz substrates were first washed with a mixture of sulfuric acid and hydrogen peroxide(volume ratio is 7:3),and then processed with oxygen plasma to obtain a hydrophilic surface.The surface then reacted with 3-aminopropyltriethoxysilane to form amino groups at the top,which further reacted with disulfide or diselenide containing diacid to afford SS or SeSe bond-modified substrates.The structures of the surfaces were comfirmed by water contact angle(WCA),atomic force microscopy,X-ray photoelectron spectroscopy(XPS),and time of flight secondary ion mass spectrometry.Based on the light induced exchange reaction,wettabilities of the substrates were able to adjusted and were characterized by WCA and XPS.By exchanging with thiol or diselenide containing polymer,the polymer chain-attached substrates linked by a single bond of either SS,SeS,or SeSe could be obtained.The rupture forces of the three bonds were measured by SMFS.At a pulling speed of 200 nm/s,the rupture forces of SeSe,SeS and SS bonds were(1100±300),(1320±330),and(1450±300)pN,respectively,indicating their strengths decreased as SS>SeS>SeSe.This result was consistent with the thermodynamic stability ranking of the three bonds.SMFS results illustrated that the strength of the dynamic covalent bond is between that of non-covalent interaction and that of robust covalent bond(e.g.C―C bond),which accounts for its balance of responsiveness and stability.