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Anisotropic robustness of talc particles after surface modifications probed by atomic force microscopy force spectroscopy

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Particuology 2021年第5期19卷 308-315页

作者： Vipada Dokmai Kitiphat Sinthiptharakoon Witchukorn Phuthong Varong Pavarajarn Center of Excellence in Particle and Materials Processing Technology Department of Chemical EngineeringFaculty of EngineeringChulalongkorn UniversityBangkok 10330Thailand National Nanotechnology Center(NANOTEC) National Science and Technology Development Agency(NSTDA)111 Thailand Science ParkPhahonyothin RoadKhlong NuengKhlong LuangPhathum Thani 12120Thailand Department of Physics Faculty of ScienceKasetsart UniversityLadyaoChatuchakBangkok 10900Thailand

As a versatile mineral,the crystalline hydrated magnesium silicate talcum,or talc,has been widely used in numerous industries from pharmaceutical formulations to composite material *** efficient application as filler/additives incorporates the improvement in concomitant properties within materials,e.g.,strength,which involves interactions between talc particles and aqueous/nonaqueous *** property enhancement imposes ideal mixing and homogenous adhesion within a talc particle,but they are limited by the coexistence of face and edge surfaces of talc,which exhibit different level of ***,using atomic force microscopy force spectroscopy,we showed that although hydrophilic talc particles obtained from acid treatment or aminosilanization better adhered with materials representing a matrix,the anisotropic characters of the two surface types ***,the degree of talc’s surface anisotropy reduced with the surface hydrophobization by aliphatic methylsilanization,but followed by the decrease in *** ten-fold difference in Hamaker constants of the probe/talc surface interacting pairs,we showed that the adhesions resulted from van der Waals interactions that suggested the influence of surface *** insight from this work would provide grounds for strategies to modulate talc’s adhesion,hydrophobicity and surface uniformity.

关键词： Talc Atomic force microscopy force spectroscopy Adhesion Surface

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Protein folding mechanism revealed by single-molecule force spectroscopy experiments

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Biophysics Reports 2021年第5期7卷 399-412页

作者： Hao Sun Zilong Guo Haiyan Hong Ping Yu Zhenyong Xue Hu Chen Research Institute for Biomimetics and Soft Matter Fujian Provincial Key Lab for Soft Functional Materials Research Department of Physics Xiamen University Center of Biomedical Physics Wenzhou Institute University of Chinese Academy of Sciences Oujiang Laboratory

force spectroscopy experiments use mechanical force as a control factor to regulate the folding and unfolding process of proteins. Atomic force microscopy has been widely used to study the mechanical stability of proteins, and obtained unfolding forces and unfolding distance of different proteins, while recently, more low force folding and unfolding measurements were done by optical tweezers and magnetic tweezers. Due to the relatively small distortion of the free energy landscape, low force measurements give the free energy landscape information over bigger conformational space. In this review, we summarize the results of force spectroscopy experiments on different proteins. The unfolding distance obtained at high forces by atomic force microscopy are mostly smaller than 2 nm, while the unfolding distances at low forces distribute over a larger range: from a negative value to more than 6 nm. The sizes of the transition states at low force are ～4 nm for most compact two-state globular proteins,which indicates that this transition state might be the general free energy barrier separating the unfolded state and the theoretically predicated molten globule state. Up to now, only a limited number of proteins has been studied at low forces. We expect that more and more proteins with different conformations will be studied at low forces to reveal the general protein folding mechanism.

关键词： Protein folding Free energy landscape force spectroscopy Molten globule state Transition state

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Unfolding rates of 1:1 and 2:1 complex of CX-5461 and c-MYC promoter G-quadruplexes revealed by single-molecule force spectroscopy

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Biophysics Reports 2024年第3期10卷 180-189页

作者： Hui Peng Yashuo Zhang Qun Luo Xinyu Wang Huijuan You Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation School of Pharmacy Tongji Medical College Huazhong University of Science and Technology College of Physics Science and Technology Yangzhou University

CX-5461, also known as pidnarulex, is a strong G4 stabilizer and has received FDA fast-track designation for BRCA1-and BRCA2-mutated cancers. However, quantitative measurements of the unfolding rates of CX-5461-G4 complexes which are important for the regulation function of G4s, remain ***, we employ single-molecule magnetic tweezers to measure the unfolding force distributions of c-MYC G4s in the presence of different concentrations of CX-5461. The unfolding force distributions exhibit three discrete levels of unfolding force peaks, corresponding to three binding modes. In combination with a fluorescent quenching assay and molecular docking to previously reported ligand-c-MYC G4 structure, we assigned the ～69 pN peak corresponding to the 1:1（ligand:G4） complex where CX-5461binds at the G4's 5'-end. The ～84 p N peak is attributed to the 2:1 complex where CX-5461 occupies both the 5' and 3'. Furthermore, using the Bell-Arrhenius model to fit the unfolding force distributions,we determined the zero-force unfolding rates of 1:1, and 2:1 complexes to be（2.4 ± 0.9） × 10-8s-1and（1.4 ± 1.0） × 10-9s-1respectively. These findings provide valuable insights for the development of G4-targeted ligands to combat c-MYC-driven cancers.

关键词： Single-molecule G-quadruplex Magnetic tweezers Stoichiometry force spectroscopy Pidnarulex

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Effect of small peptide(P-15) on HJMSCs adhesion to hydroxyap-atite

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Science China(Physics,Mechanics & Astronomy) 2016年第2期59卷 102-107,109-112页

作者： Wei Cheng Xin Tong Qin Gang Hu Yong Bin Mou Hai Yan Qin Nanjing Stomatological Hospital Medical School of Nanjing University Central Laboratory of Stomatology Nanjing Stomatological Hospital

P-15, a synthetic peptide of 15-amino acids, has been tested in clinical trials to enhance cell adhesion and promote osseointe-gration. This feature of P-15 has also inspired the development of designing new bone substitute materials. Despite the increasing applications of P-15 in bone graft alternatives, few studies focus on the mechanism of cell adhesion promoted by P-15 and the mechanical property changes of the cells interacting with P-15. In this article, we used atomic force microscope(AFM) based single cell indentation force spectroscopy to study the impact of P-15 on the stiffness and the adhesion ability of human jaw bone mesenchymal stem cells(HJMSCs) to hydroxyapatite(HA). We found that the stiffness of HJMSCs increases as the concentration of P-15 grows in short culture intervals and that the adhesion forces between HJMSCs and HA particles in both the presence and absence of P-15 are all around 30 p N. Moreover, by calculating the binding energy of HJMSCs to HA particles mixed with and without P-15, we proved that P-15 could increase the adhesion energy by nearly four times. Scanning electron microscope(SEM) was also exploited to study the morphology of HJMSCs cultured in the presence and absence of P-15 on HA disc surface for a short term. Apparent morphological differences were observed between the cells cultured with and without P-15. These results explain the probable underlying adhesion mechanism of HJMSC promoted by P-15 and can serve as the bases for the design of bone graft substitute materials.

关键词： atomic force microscopy (AFM) cell stiffness force spectroscopy

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Re-evaluation of the Widely Applied force-Frequency Relation for Frequency-Modulation AFM Under Solution

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Journal of Shanghai Jiaotong university(Science) 2014年第5期19卷 612-616页

作者：何健锋胡钧孙洁林 CZAJKOWSKY Daniel M School of Biomedical Engineering Shanghai Jiaotong University Laboratory of Physical Biology Shanghai Institute of Applied PhysicsChinese Academy of Sciences Key Laboratory of Systems Biomedicine Shanghai Jiaotong University

Frequency-modulation atomic force microscopy(FM-AFM) is a highly versatile tool for surface *** imaging surfaces, FM-AFM is capable of measuring interactions between the AFM probe and the surface with high sensitivity, which can provide chemical information at sub-nanometer resolution. This is achieved by deconvoluting the frequency shift, which is directly measured in experiments, into the force between the probe and sample. At present, the widely used method to perform this deconvolution has been shown to be accurate under high quality(high-Q) factor vacuum conditions. However, under low quality(low-Q) factor conditions, such as in solution, it is not clear if this method is valid. A previous study apparently verified this relation for experiments in solution by comparing the force calculated by this equation with that obtained in separate experiments using the surface force apparatus(SFA). Here we show that, in solution, a more direct comparison of the force calculated by this relation with that directly measured by the cantilever deflection in AFM reveals significant differences,both qualitative and quantitative. However, we also find that there are complications that hinder this ***, while contact with the surface is clear in the direct measurements(including the SFA data), it is less certain in the FM-AFM case. Hence, it is not clear if the two methods are measuring the same tip-sample distance regimes. Thus, our results suggest that a more thorough verification of this relation is required, as application of this formulation for experiments in solution may not be valid.

关键词： frequency-modulation atomic force microscopy(FM-AFM) chemical mapping frequency-force relationship force spectroscopy

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Measuring the elasticity of liquid–liquid phase separation droplets with biomembrane force probe

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Biophysics Reports 2022年第2期8卷 68-79页

作者： Min Sun Hui Chen Qinghua Ji Jianhui Xiao Yanzhe Hou Jizhong Lou Key Laboratory of RNA Biology CAS Center for Excellence in Biomacromolecules Institute of Biophysics Chinese Academy of Sciences University of Chinese Academy of Sciences School of Basic Medical Pharmacology Lanzhou University

Numerous biomacromolecules undergo liquid–liquid phase separation(LLPS) inside living cells and LLPS plays important roles in their functions. The droplets formed by LLPS molecules are complex fluids and their behavior follows fluid mechanics, thus studies on rheological and material properties are required to gain full insight into the biophysical mechanism of these droplets. Biophysical force spectroscopy techniques are particularly useful in this aspect. Indeed, atomic force microscopy and optical tweezers have been used to quantify the elasticity and the viscoelasticity of LLPS droplets. The Biomembrane force Probe(BFP) is a single-molecule technique designed to investigate liquid-like objects and is more suitable to quantify the material properties of LLPS droplets, but its usage on LLPS droplets is not yet described. Here we present an experimental protocol to measure the Young's modulus of LLPS droplets using BFP, we believe that the application of BFP on phase separation studies can be expanded and will be very helpful in deciphering the underlying principles of LLPS.

关键词： Phase separation force spectroscopy Young’s modulus

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Harvesting Mechanical Work From Folding-Based Protein Engines: From Single-Molecule Mechanochemical Cycles to Macroscopic Devices

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CCS Chemistry 2019年第1期1卷 138-147页

作者： Linglan Fu Han Wang Hongbin Li Department of Chemistry University of British ColumbiaVancouverBC V6T 1Z1Canada

Mechanochemical coupling cycles underlie the work-generation mechanisms of biological systems and are realized by highly regulated conformational changes of the protein ***,it has been challenging to utilize protein conformational changes to do mechanical work at the macroscopic level in biomaterials,and it remains elusive to con-struct macroscopic mechanochemical devices based on molecular-level mechanochemical coupling ***,the authors demonstrate that protein folding can be utilized to realize protein’s mechano-chemical cycles at both single-molecule and macro-scopic levels.

关键词： protein hydrogel protein folding actu-ation force spectroscopy single molecule

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