光谱法研究碳量子点与人血清白蛋白的相互作用

近年来，纳米材料对环境和人类健康的潜在风险已经引起了人们的广泛关注。纳米颗粒尺寸小、反应活性高，当其进入机体后很可能与体内的生物大分子相互作用，使其原来的理化性质发生改变，更容易被细胞识别、吞噬，进而对组织、器官等产生危害；作用过程中生物大分子也会受到纳米颗粒的影响，可能导致其生理结构受到损伤，并干扰其特定功能的正常执行；因此研究纳米材料与蛋白质的相互作用对探究其生物安全性具有重要意义。实验通过多种光谱手段研究了碳量子点（CQDs）对人血清白蛋白（HSA）结构与功能性质的影响以及两者的相互作用机制。荧光光谱与紫外-可见吸收光谱结果显示，CQDs通过与HSA结合形成复合物导致蛋白质荧光猝灭；结合常数K_A与结合位点数n的计算结果表明CQDs在HSA上只有一个结合位点，且同步荧光和位点竞争实验发现，这个结合位点接近HSA中ⅡA亚结构域上的色氨酸残基；根据Förster共振能量转移(FRET)理论计算出两者的作用距离r=2.89 nm<8 nm，表明HSA与CQDs之间通过非辐射能量转移导致蛋白质内源性荧光猝灭；根据Van’t Hoff方程计算得到HSA-CQDs体系的热力学参数，由热力学参数计算结果推断相互作用过程中主要有氢键和范德华力参与；根据共振光散射（RLS）、三维荧光光谱和圆二色光谱（CD）结果显示，相互作用会导致HSA的二级、三级结构发生改变，蛋白质中α-螺旋结构含量增加，HSA进一步卷曲折叠，使色氨酸残基所处微环境的疏水性增大；而结构变化还进一步影响着蛋白质的聚集状态和一些生理功能，使得相互作用后HSA的聚集程度和类酯酶活性降低，不利于蛋白质的团聚，自由基清除能力略有提高。该研究可为纳米材料的生物与环境安全评价提供参考依据，也为探究纳米颗粒-蛋白质相互作用提供了一套较为系统的光谱分析方法。

Study on the Interaction Between Carbon Quantum Dots and HumanSerum Albumin by Spectroscopic Methods

The potential risk of nanomaterials to the environment and human health has caused widespread concernin recent years.Because of their small size and high reactivity,nanoparticles are likely to interact with biological macromolecules in vivo when they enter into the organisms.Therefore their original physical and chemical properties will change.Then,they are easily recognized and phagocytized by cells,and further bring about harm to the tissues and organs.In the process of interaction,biomacromolecules are also affected by nanoparticles,which may cause damage to their structure and interfere with the normal performance of their specific functions.Therefore,the toxic effect of nanomaterials on biomacromolecules is an important theoretical basis for studying their biosafety.Structure and function changes of human serum albumin(HSA)when exposed to carbon quantum dots(CQDs)and the mechanism for their interaction were studied by a variety of spectroscopic methods.According to fluorescence spectra and UV-Vis absorption spectra,CQDs quenched the intrinsic fluorescence of HSA by forming non-fluorescence complexes.Calculation results of binding constant(K A)and the number of binding sites(n)showed that there was only one binding site for CQDs on HSA,and synchronous fluorescence spectrum and binding sites competition experiment revealed this binding site was close to the only tryptophan residuein HSA,which located inⅡA subdomain of protein.Based on Forster resonance energy transfer(FRET)theory,binding distancer between CQDs and HSA was calculated to be 2.89 nm,which is less than 8 nm,indicating that there was a high possibility of fluorescence quenching caused by non-radiative energy transfer between CQDs and HSA.From the calculated thermodynamic parameters,it can be inferred that hydrogen bonds and van der Waal’s force played an important role in the interaction of HSA with CQDs.According to the results of resonance light scattering(RLS)spectra,three-dimensional fluorescence spectra and circular dichroism(CD)spectra,CQDs could change the secondary and tertiary structure of HSA,causingα-helix conformation content of protein increase,promoting HSA further curling and folding,making hydrophobicity of microenvironment around tryptophan residue increase.Structural changes further affected the aggregation state and some physiological functions of protein,resulting in the decrease of the aggregation degree and esterase-like activity of HSA and a slight improvement of its free radical scavenging ability.This work can provide a reference for the evaluation of biological and environmental safety of nanomaterials,and it also provides a relatively systematic set of spectral analysis methods for exploring the interaction between nanoparticles and proteins.