Force applied to a single molecule at a single nanogate molecule filter

We have investigated the origin of molecule filtering system based on a chemical potential barrier produced by thermodynamically driven molecular flow in a nanoscopic space at nanogates. Single molecule tracking experiments prove that the highly localized potential barrier allows for selective manipulation of the target molecule. We propose the presence of a force, a few fN per molecule, to decelerate the molecule's movement at the nanogate, which is comparable to or larger than the force applied by conventional electrophoretic operation. The present force can be tuned by changing the nanogate width at the nanometre level. These findings allow us to propose an accurate design of novel devices for molecular manipulation on an ultra small scale using a very small number of molecules without any external biases.     

One-dimensional supramolecular assembly of an Mn12 single molecule magnet by ligand interactions

A new Mn₁₂ complex was synthesized using ligand substitution reaction of Mn₁₂–OAc with 4-(thiophen-3-yl)benzoic acid and complex’s structural and magnetic properties were analysed. [Mn₁₂O₁₂(O₂CC₆H₄C₄H₃S)₁₆(H₂O)₃]·14CH₂Cl₂ (1) crystallized in the P2₁/c space group. Intermolecular π–π interactions between phenyl and thiophene rings of two adjacent Mn₁₂ molecules result in one-dimensional supramolecular assembly of 1 in the crystal. On the other hand, steric repulsion between the neighbouring molecules causes unusual ligand arrangement and coordination geometry of Mn(III) ion with five coordination. The ac magnetic study of 1 gives U_eff = 69.98 K and 1/τ₀ = 1.456 × 10⁸ s^?1 and dc reduced magnetization measurement gives S = 10, g = 1.95 and D = ?0.425 cm^?1 showing that outer ligand distortion has little effect on the magnetic properties.     

A ferrocene-based multi-signaling sensor molecule functions as a molecular switch

A multi-channel signaling cation sensor R had been achieved by covalently connecting ferrocene unit to the nitrogen (CN) containing binding site. Ferrocene-based sensor R was synthesized and characterized by spectroscopic methods and single crystal XRD. The chromogenic, flourogenic and electrochemical sensor study of R in CH₃CN shows selective binding of Cu²⁺ ion. Inherently molecule R performs as molecular switch beyond the sensing role.     

化学分子创造美好生活——访美利肯化工部亚太区市场经理蔡美德先生

美利肯公司于1865年建厂,是世界上最大的私人纺织和化工产品制造商之一。从1957年起,美利肯公司开始涉及化工产品,不仅提供高端的化工产品,还为客户提供卓越的技术支持,     

Detecting a single molecule using a micropore-nanopore hybrid chip

Nanopore-based DNA sequencing and biomolecule sensing have attracted more and more attention. In this work, novel sensing devices were built on the basis of the chips containing nanopore arrays in polycarbonate (PC) membranes and micropores in Si₃N₄ films. Using the integrated chips, the transmembrane ionic current induced by biomolecule''s translocation was recorded and analyzed, which suggested that the detected current did not change linearly as commonly expected with increasing biomolecule concentration. On the other hand, detailed translocation information (such as translocation gesture) was also extracted from the discrete current blockages in basic current curves. These results indicated that the nanofluidic device based on the chips integrated by micropores and nanopores possessed comparative potentials in biomolecule sensing.     

Synthesis and characterization of thermo-responsive supramolecular diblock copolymers

In this paper, we report the synthesis and characterization of a new thermo-responsive supramolecular amphiphiles diblock copolymer, methoxy poly (ethylene glycol)-block-Poly(N-isopropylacrylamide) (mPEG-b-PNIPAM). The mPEG with β-cyclodextrin (β-CD) group and the PNIPAM with adamantine (AD) group were synthesized, respectively, and mPEG-b-PNIPAM was then obtained by the host-guest inclusion between AD and β-CD. The structure and molecular weight of mPEG-b-PNIPAM was confirmed by ¹H NMR and GPC measurements. At low temperature (T?<?33 °C), the PNIPAM block is hydrophilic. With increasing temperature, the hydrophobicity the of PNIPAM block increases. This molecular feature leads to interesting aggregation behavior of micelles in aqueous solutions at different temperatures. The self-assembly was revealed by UV, DLS measurements, and TEM observations.     

超高分子质量聚碳硅烷的合成与表征

从常压合成得到的中低分子量PCS出发进行热压合成制备超高分子质量的PCS,并对其结构和性能进行了表征。研究表明控制热压反应温度在460~470℃、预加压力1~2 MPa、反应6h时得到先驱体PCS的Mw为6 400~8 500;热压合成后制得的超高分子质量PCS的Si—H含量和支化度有所降低;通过控制热压反应时间可以较好的调控超高分子PCS的重均分子质量的大小。     

Exploring the complexity of supramolecular interactions for patterning at the liquid-solid interface

The use of self-assembly to fabricate surface-confined adsorbed layers (adlayers) from molecular components provides a simple means of producing complex functional surfaces. The molecular self-assembly process relies on supramolecular interactions sustained by noncovalent forces such as van der Waals, electrostatic, dipole-dipole, and hydrogen bonding interactions. Researchers have exploited these noncovalent bonding motifs to construct well-defined two-dimensional (2D) architectures at the liquid-solid interface. Despite myriad examples of 2D molecular assembly, most of these early findings were serendipitous because the intermolecular interactions involved in the process are often numerous, subtle, cooperative, and multifaceted. As a consequence, the ability to tailor supramolecular patterns has evolved slowly. Insight gained from various studies over the years has contributed significantly to the knowledge of supramolecular interactions, and the stage is now set to systematically engineer the 2D supramolecular networks in a "preprogrammed" fashion. The control over 2D self-assembly of molecules has many important implications. Through appropriate manipulation of supramolecular interactions, one can "encode" the information at the molecular level via structural features such as functional groups, substitution patterns, and chiral centers which could then be retrieved, transferred, or amplified at the supramolecular level through well-defined molecular recognition processes. This ability allows for precise control over the nanoscale structure and function of patterned surfaces. A clearer understanding and effective use of these interactions could lead to the development of functional surfaces with potential applications in molecular electronics, chiral separations, sensors based on host-guest systems, and thin film materials for lubrication. In this Account, we portray our various attempts to achieve rational design of self-assembled adlayers by exploiting the aforementioned complex interactions at the liquid-solid interface. The liquid-solid interface presents a unique medium to construct flawless networks of surface confined molecules. The presence of substrate and solvent provides an additional handle for steering the self-assembly of molecules. Scanning tunneling microscopy (STM) was used for probing these molecular layers, a technique that serves not only as a visualization tool but could also be employed for active manipulation of molecules. The supramolecular systems described here are only weakly adsorbed on a substrate, which is typically highly oriented pyrolytic graphite (HOPG). Starting with fundamental studies of substrate and solvent influence on molecular self-assembly, this Account describes progressively complex aspects such as multicomponent self-assembly via 2D crystal engineering, emergence, and induction of chirality and stimulus responsive supramolecular systems.     

Thermodynamics of DNA interactions from single molecule stretching experiments

On the basis of our analysis of detailed measurements of the dependence of the overstretching transition of double-stranded DNA (dsDNA) on temperature, pH, and ionic strength, we have demonstrated that a model of force-induced melting accurately describes the thermodynamics of DNA overstretching. Measurements of this transition allow us to determine the stability of dsDNA and obtain information similar to that obtained in thermal melting studies. This single-molecule technique has the advantage that it can be used to measure DNA stability at any temperature. We discuss the use of this technique to study the nucleic acid chaperone activity of the HIV-1 nucleocapsid protein.     

Selectivity of heavy metal ions at acidic supramolecular surfaces

Langmuir monolayers containing surface carboxylic acid head groups were examined in order to characterize their selectivity to metal ion adsorption. Experimental data of ion adsorption obtained by surface isotherms and FTIR spectroscopy were analyzed using a thermodynamic-and-electrochemical model. Among bivalent ions examined (Cr²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, Ca²⁺, Ni²⁺, and Ba²⁺), Langmuir monolayers showed the highest selectivity to chromium ions. In addition, it was found that adsorption constants of the surface ions are quite different from binding constants of the bulk ions. The results show important implications to sensing and separating metal ions by the use of acidic supramolecular materials.     

亲和层析介质非特异性吸附的定量表征研究

针对亲和层析介质的非特异性吸附,基于脉冲响应法,建立了定量表征方法。以牛血清白蛋白、酵母发酵液和CHO细胞培养液作为典型杂质,考察了四种蛋白A亲和层析介质和两种基质微球,在不同pH和盐浓度条件下非特异性吸附。发现介质和基质对杂质均有不同程度的吸附,在酸性条件下非特异性吸附相对较强。对于不同料液,存在不同的杂质吸附机制,可通过静电、疏水作用或两者共同作用结合。两种介质和基质的比较结果表明,琼脂糖基介质的非特异性吸附主要依赖其基质微球与杂质间相互作用,而聚甲基丙烯酸酯基介质对杂质的吸附作用强于其基质微球。结果表明,本文建立的非特异性吸附定量表征方法切实可行,可用于量化表征介质非特异性吸附,探究相关作用机制,为介质研发提供新的分析方法和依据。     

无油润滑空压机导向环不正常磨损的分析及处理

我厂使用的５L－７５／２．５型空压机是无锡压缩机厂１９９１年的产品，１９９３年投入运行，为无油润滑空压机，分为双一级缸同时向外供气，容积流量为７５m３／min，排气压力为０．２４５MPa，实际工作压力为０．２５MPa，轴功率２４０kW，配备同步电动机。该机活塞环、导向环和填料函部分为聚四氟乙烯（TPFE）工程塑料。活塞环为整环无开口环，每个活塞上有２个活塞环和２个导向环。２０００年１１月之前，活塞环和导向环曾经因磨损更换过几次，每次可使用２～３年，但在２０００年１１月更换了立、卧缸的活塞环和导向环后，只运行…     

Greek key jellyroll protein motif design: expression and characterization of a first-generation molecule

A protein designed de novo to fold into the Greek key jellyrollstructural motif has been studied. Theoretical analyses haveindicated that the designed sequence should adopt the ß-strandarrangement of the Greek key jellyroll rather than any otherarrangement. A synthetic gene was constructed and the proteinexpressed in Escherichia coli. Circular dichroism spectroscopyis consistent with the protein folding into the designed conformationand also suggests the presence of tertiary structure. Fluorescencespectroscopy showed the single tryptophan to be partially buried,while denaturation studies showed changes in fluorescence toprecede alterations in secondary structure.     

Catching a molecule at the air-water interface: Dynamic pore array for molecular recognition

As a soft and flexible porous structure, a pore array of a steroid cyclophane SC(OH), which consists of the rigid 1,6,20,25-tetraaza[6.1.6.1]paracyclophane ring connected to four steroid moieties (cholic acid) through flexible L-lysine spacers, was prepared at the air-water interface. As confirmed by surface pressure (π)-molecular area (A) isotherms, transition between open conformation and cavity conformation of the SC(OH) molecule was reversibly induced upon repeated compression and expansion of its monolayer at pH 11 where amino groups of the lysine residues are not fully deprotonated. Capture and release of an aqueous fluorescent guest (TNS) by SC(OH) was observed upon dynamic cavity formation through surface fluorescence spectroscopy. At pH 12, dynamic cavity formation of SC(OH) was sufficiently suppressed, and the capture and release of an aqueous TNS by the monolayer was not virtually observed. Lessened electrostatic repulsion between the SC(OH) molecules due to conversion of ammonium to free amine may prevent the cavity from reopening. The importance of dynamic nature of cavity formation on the guest binding was also proved by control experiments using SC(H), which cannot form cavity conformation at any surface pressures at both pH 11 and 12.     

The study of single anticancer peptides interacting with HeLa cell membranes by single molecule force spectroscopy

To determine the effects of biophysical parameters (e.g. charge, hydrophobicity, helicity) of peptides on the mechanism of anticancer activity, we applied a single molecule technique-force spectroscopy based on atomic force microscope (AFM)-to study the interaction force at the single molecule level. The activity of the peptide and analogs against HeLa cells exhibited a strong correlation with the hydrophobicity of peptides. Our results indicated that the action mode between α-helical peptides and cancer cells was largely hydrophobicity-dependent.     

Catching a molecule at the air-water interface: Dynamic pore array for molecular recognition

As a soft and flexible porous structure, a pore array of a steroid cyclophane SC(OH), which consists of the rigid 1,6,20,25-tetraaza[6.1.6.1]paracyclophane ring connected to four steroid moieties (cholic acid) through flexible L-lysine spacers, was prepared at the air-water interface. As confirmed by surface pressure (π)-molecular area (A) isotherms, transition between open conformation and cavity conformation of the SC(OH) molecule was reversibly induced upon repeated compression and expansion of its monolayer at pH 11 where amino groups of the lysine residues are not fully deprotonated. Capture and release of an aqueous fluorescent guest (TNS) by SC(OH) was observed upon dynamic cavity formation through surface fluorescence spectroscopy. At pH 12, dynamic cavity formation of SC(OH) was sufficiently suppressed, and the capture and release of an aqueous TNS by the monolayer was not virtually observed. Lessened electrostatic repulsion between the SC(OH) molecules due to conversion of ammonium to free amine may prevent the cavity from reopening. The importance of dynamic nature of cavity formation on the guest binding was also proved by control experiments using SC(H), which cannot form cavity conformation at any surface pressures at both pH 11 and 12.