Bingqian Xu - Academia.edu (original) (raw)

Papers by Bingqian Xu

ACS Nano, 2018

One of the promising approaches to meet the urgent demand for further device miniaturization is t... more One of the promising approaches to meet the urgent demand for further device miniaturization is to create functional devices using single molecules. Although various single-molecule electronic devices have been demonstrated recently, single-molecule optical devices which use external stimulations to control the optical response of a single molecule have rarely been reported. Here, we propose and demonstrate a field-effect Raman scattering (FERS) device with a single molecule, an optical counterpart to fieldeffect transistors (a key component of modern electronics). With our devices, the gap size between electrodes can be precisely adjusted at subangstrom accuracy to form single molecular junctions as well as to reach the maximum performance of Raman scattering via plasmonic enhancement. Based on this maximum performance, we demonstrated that the intensity of Raman scattering can be further enhanced by an additional ∼40% if the orbitals of the molecules bridged two electrodes were shifted by a gating voltage. This finding not only provides a method to increase the sensitivity of Raman scattering beyond the limit of plasmonic enhancement, but also makes it feasible to realize addressable functional FERS devices with a gate electrode array.

Nanoscale, 2019

Characterization of the stiffness of thin DNA strands remains difficult.

Soft Matter, 2012

Using analytical techniques and Langevin dynamics simulations, we investigate the dynamics of pol... more Using analytical techniques and Langevin dynamics simulations, we investigate the dynamics of polymer translocation through a nanochannel embedded in two dimensions under an applied external field. We examine the translocation time for various ratio of the channel length L to the polymer length N. For short channels L ≪ N , the translocation time τ ∼ N 1+ν under weak driving force F , while τ ∼ F −1 L for long channels L ≫ N , independent of the chain length N. Moreover, we observe a minimum of translocation time as a function of L/N for different driving forces and channel widths. These results are interpreted by the waiting time of a single segment.

Nano Letters, 2009

We functionalized double-walled carbon nanotubes (DWCNTs) as artificial water channel proteins. F... more We functionalized double-walled carbon nanotubes (DWCNTs) as artificial water channel proteins. For the first time, molecular dynamics simulations show that the bilayer structure of DWCNTs is advantageous for carbon nanotube based transmembrane channels. The shielding of the amphiphilic outer layer could guarantee biocompatibility of the synthetic channel and protect the inner tube (functional part) from disturbance of the membrane environment. This novel design could promote more sophisticated nanobiodevices which could function in a bioenvironment with high biocompatibility.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2014

We develop a transition model to interpret single-molecule ricin-aptamer interactions with multip... more We develop a transition model to interpret single-molecule ricin-aptamer interactions with multiple unbinding pathways and energy barriers measured by atomic force microscopy dynamic force spectroscopy. Molecular simulations establish the relationship between binding conformations and the corresponding unbinding pathways. Each unbinding pathway follows a Bell-Evans multiple-barrier model. Markov-type transition matrices are developed to analyze the redistribution of unbinding events among the pathways under different loading rates. Our study provides detailed information about complex behaviors in ricin-aptamer unbinding events.

Chemical Science, 2014

Single DNA conductance measurements with increasing MgCl2 concentrations unambiguously revealed t... more Single DNA conductance measurements with increasing MgCl2 concentrations unambiguously revealed two DNA (B and Z) conformations and the B–Z transition process.

Physical chemistry chemical physics : PCCP, Jan 18, 2016

An advanced understanding of the molecule-electrode contact interfaces of single-molecule junctio... more An advanced understanding of the molecule-electrode contact interfaces of single-molecule junctions is a necessity for real world application of future single-molecule devices. This study aims to elucidate the change in the contact tunnelling barrier induced by junction extension and how this change affects the resulting junction conductance. The contact barrier of Au-octanedithiol/octanediamine-Au junctions was studied under triangle (TRI) mechanical modulations using the modified scanning tunneling microscopy (STM) break junction technique. The experimental results reveal that as the junction separation extends, the contact barrier of octanedithiol follows a unique trend, a linear increase followed by a plateau in barrier height, which is in contrast to that of octanediamine, a nearly rectangle barrier. We propose a modified contact barrier model for the unique barrier shape of octanedithiol, based on which the calculation agrees well with the experimental data. This study shows u...

Science China Materials, 2021

The assembly of monomicelles along onedimension (1D) to construct tubular or fibrous mesostructur... more The assembly of monomicelles along onedimension (1D) to construct tubular or fibrous mesostructures is greatly desired but still challenging. Herein, we have demonstrated a facile strategy to synthesize 1D bimodal mesoporous metal oxides (e.g., WO 3 , WO 3 /Pd, WO 3 /PdCu, TiO 2 , and ZrO 2) nanofibers (NFs) through assembling the organic-inorganic composite monomicelles in a beam stream generated via an electrospinning technique. This facile and repeatable methodology relies on the preparation of copolymer@metal-complex monomicelles in an anisotropic solution and oriented assembly of them in the beam stream by the selective evaporation of solvent. WO 3 and its derivatives are chosen as the demo, which show a uniform continuous fibrous structure with dual mesopore sizes (~4.0 and 7.6 nm) and large surface area (~93.1 m 2 g −1). Benefitting from the unique textual structure, gas sensors made by Pd-decorated mesoporous WO 3 NFs display outstanding comprehensive sensing performance to ethylbenzene, including a high sensitivity (52.5), an ultralow detection limit (50 ppb), and fast response/ recovery kinetics (11/16 s) as well as an outstanding selectivity, which render them promising for rapid environmental monitoring.

Light: Science & Applications, 2019

Electronic switches with nanoscale dimensions satisfy an urgent demand for further device miniatu... more Electronic switches with nanoscale dimensions satisfy an urgent demand for further device miniaturization. A recent heavily investigated approach for nanoswitches is the use of molecular junctions that employ photochromic molecules that toggle between two distinct isoforms. In contrast to the reports on this approach, we demonstrate that the conductance switch behavior can be realized with only a bare metallic contact without any molecules under light illumination. We demonstrate that the conductance of bare metallic quantum contacts can be reversibly switched over eight orders of magnitude, which substantially exceeds the performance of molecular switches. After the switch process, the gap size between two electrodes can be precisely adjusted with subangstrom accuracy by controlling the light intensity or polarization. Supported by simulations, we reveal a more general and straightforward mechanism for nanoswitching behavior, i.e., atomic switches can be realized by the expansion of nanoelectrodes due to plasmonic heating.

Journal of the American Chemical Society, Jan 5, 2018

In the seeking of molecular expression of fractal geometry, chemists have endeavored in the const... more In the seeking of molecular expression of fractal geometry, chemists have endeavored in the construction of molecules and supramolecules during the past few years, while only a few examples were reported, especially for the discrete architectures. We herein designed and constructed five generations of supramolecular fractals (G1-G5) based on the coordination-driven self-assembly of terpyridine ligands. All the ligands were synthesized from triphenylamine motif, which played a central role in geometry control. Different approaches based on direct Sonogashira coupling and/or ⟨tpy-Ru(II)-tpy⟩ connectivity were employed to prepare complex Ru(II)-organic building blocks. Fractals G1-G5 were obtained in high yields by precise coordination of organic or Ru(II)-organic building blocks with Zn(II) ions. Characterization of those architectures were accomplished by 1D and 2D NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), traveling-wave ion mobility mass spectrometry (TWI...

Nature communications, Jan 8, 2018

Nested concentric structures widely exist in nature and designed systems with circles, polygons, ... more Nested concentric structures widely exist in nature and designed systems with circles, polygons, polyhedra, and spheres sharing the same center or axis. It still remains challenging to construct discrete nested architecture at (supra)molecular level. Herein, three generations (G2-G4) of giant nested supramolecules, or Kandinsky circles, have been designed and assembled with molecular weight 17,964, 27,713 and 38,352 Da, respectively. In the ligand preparation, consecutive condensation between precursors with primary amines and pyrylium salts is applied to modularize the synthesis. These discrete nested supramolecules are prone to assemble into tubular nanostructures through hierarchical self-assembly. Furthermore, nested supramolecules display high antimicrobial activity against Gram-positive pathogen methicillin-resistant Staphylococcus aureus (MRSA), and negligible toxicity to eukaryotic cells, while the corresponding ligands do not show potent antimicrobial activity.

Journal of the American Chemical Society, Jun 8, 2017

With the goal of increasing the complexity of metallo-supramolecules, two rhombus star-shaped sup... more With the goal of increasing the complexity of metallo-supramolecules, two rhombus star-shaped supramolecular architectures, namely, supersnowflakes, were designed and assembled using multiple 2,2':6',2″-terpyridine (tpy) ligands in a stepwise manner. In the design of multicomponent self-assembly, ditopic and tritopic ligands were bridged through Ru(II) with strong coordination to form metal-organic ligands for the subsequent self-assembly with a hexatopic ligand and Zn(II). The combination of Ru(II)-organic ligands with high stability and Zn(II) ions with weak coordination played a key role in the self-assembly of giant heteroleptic supersnowflakes, which encompassed three types of tpy-based organic ligands and two metal ions. With such a stepwise strategy, the self-sorting of individual building blocks was prevented from forming the undesired assemblies, e.g., small macrocycles and coordination polymers. Furthermore, the intra- and intermolecular dynamic exchange study of t...

Nature communications, May 19, 2017

Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves ... more Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves and so on. These star-shaped patterns are also frequently used in both functional and artistic man-made architectures. Here following a stepwise synthesis and self-assembly approach, pentagonal and hexagonal metallosupramolecules possessing star-shaped motifs were prepared based on the careful design of metallo-organic ligands (MOLs). In the MOL design and preparation, robust ruthenium-terpyridyl complexes were employed to construct brominated metallo-organic intermediates, followed by a Suzuki coupling reaction to achieve the required ensemble. Ligand LA (VRu(2+)X, V=bisterpyridine, X=tetraterpyridine, Ru=Ruthenium) was initially used for the self-assembly of an anticipated hexagram upon reaction with Cd(2+) or Fe(2+); however, unexpected pentagonal structures were formed, that is, [Cd5LA5](30+) and [Fe5LA5](30+). In our redesign, LB [V(Ru(2+)X)2] was synthesized and treated with 60° V-...

Biotechnology for biofuels, 2016

The main challenges of large-scale biochemical conversion involve the high costs of cellulolytic ... more The main challenges of large-scale biochemical conversion involve the high costs of cellulolytic enzymes and the inefficiency in enzymatic deconstruction of polysaccharides embedded in the complex structure of the plant cell wall, leading to ongoing interests in studying the predominant mode of enzymatic hydrolysis. In this study, complete enzymatic hydrolysis of pretreated biomass substrates was visualized in situ and in real time by atomic force microscopy (AFM) topography and recognition imaging. Throughout the entire hydrolytic process, a hydrolysis mode for exoglucanase (CBH I) consisting of a peeling action, wherein cellulose microfibrils are peeled from sites on the pretreated cellulose substrate that have cracks sufficiently large for CBH I to immobilize. We quantitatively monitored the complete hydrolytic process on pretreated cellulose. The synergetic effect among the different enzymes can accelerate the cellulose hydrolysis rate dramatically. However, the combination of C...

Journal of the American Chemical Society, Jul 5, 2016

In an effort to exert more precise control over structural features of supramolecules, a series o... more In an effort to exert more precise control over structural features of supramolecules, a series of giant concentric hexagons were assembled as discrete structures using tetratopic terpyridine (tpy) ligands. In preparation of tetratopic ligand, pyrylium and pyridinium salts chemistry significantly facilitated synthesis. The key compounds were obtained by condensation reactions of pyrylium salts with corresponding primary amine derivatives in good yields. These discrete metallo-supramolecular concentric hexagons were fully characterized by NMR, ESI-MS, TWIM-MS and TEM, establishing their hexagon-in-hexagon architectures. The combination of different tetratopic ligands also assembled hybrid concentric hexagons with increasing diversity and complexity. Furthermore, these concentric hexagon supramolecules with precisely controlled shapes and sizes were utilized as building blocks to hierarchically self-assemble supramolecular metal-organic nanoribbons (SMON) at solid-liquid interfaces. A...

The Journal of Physical Chemistry B, 2016

The health risk associated with high cholesterol levels in the human body has motivated intensive... more The health risk associated with high cholesterol levels in the human body has motivated intensive efforts to lower them by using specialized drugs. However, little research has been reported on utilizing nanomaterials to extract extra cholesterol from living tissues. Graphene possesses great potential for cholesterol extraction from cell membranes due to its distinct porous structure and outstanding surface adhesion. Here we employ dissipative dynamic simulations to explore pathways for cholesterol extraction from a cell membrane by a sheet of graphene using a coarse-grained graphene nanosheets (CGGN) model. We first demonstrate that the self-assembly process among a single layer of graphene and a group of randomly distributed cholesterol molecules in the aqueous environment, which provides a firm foundation for graphene−cholesterol interactions and the dynamic cholesterol extraction process from the cell membrane. Simulations results show that graphene is capable of removing cholesterol molecules from the bilayer membrane. The interaction between graphene and cholesterol molecules plays an important role in determining the amount of extracted cholesterol molecules from the cell membrane. Our findings open up a promising avenue to exploit the capability of graphene for biomedical applications.

Chemical Science, 2014

Giant metallo-supramolecular cubes were assembled by using tritopic terpyridine ligands as corner... more Giant metallo-supramolecular cubes were assembled by using tritopic terpyridine ligands as corners and metal ions as edges.

Biotechnology for biofuels, Jan 11, 2013

Enzymatic hydrolysis of lignocellulosic biomass (mainly plant cell walls) is a critical process f... more Enzymatic hydrolysis of lignocellulosic biomass (mainly plant cell walls) is a critical process for biofuel production. This process is greatly hindered by the natural complexity of plant cell walls and limited accessibility of surface cellulose by enzymes. Little is known about the plant cell wall structural and molecular level component changes after pretreatments, especially on the outer surface. Therefore, a more profound understanding of surface cellulose distributions before and after pretreatments at single-molecule level is in great need. In this study, we determined the structural changes, specifically on crystalline cellulose, of natural, dilute sulfuric acid pretreated and delignified cell wall surfaces of poplar, switchgrass, and corn stover using single molecular atomic force microscopy (AFM) recognition imaging. The AFM tip was first functionalized by a family 3 carbohydrate-binding module (CBM3a) (Clostridium thermocellum Scaffoldin) which specifically recognizes crys...

Recent Patents on DNA & Gene Sequences, 2010

DNA sequencing techniques witnessed fast development in the last decades, primarily driven by the... more DNA sequencing techniques witnessed fast development in the last decades, primarily driven by the Human Genome Project. Among the proposed new techniques, Nanopore was considered as a suitable candidate for the single DNA sequencing with ultrahigh speed and very low cost. Several fabrication and modification techniques have been developed to produce robust and well-defined nanopore devices. Many efforts have also been done to apply nanopore to analyze the properties of DNA molecules. By comparing with traditional sequencing techniques, nanopore has demonstrated its distinctive superiorities in main practical issues, such as sample preparation, sequencing speed, cost-effective and read-length. Although challenges still remain, recent researches in improving the capabilities of nanopore have shed a light to achieve its ultimate goal: Sequence individual DNA strand at single nucleotide level. This patent review briefly highlights recent developments and technological achievements for DNA analysis and sequencing at single molecule level, focusing on nanopore based methods.

The Journal of Physical Chemistry B, 2012

The affinitive interaction between a carbohydratebinding module (CBM3a) and natural crystalline c... more The affinitive interaction between a carbohydratebinding module (CBM3a) and natural crystalline cellulose was visualized and measured at the single-molecule level. Noncontact high resolution imaging by atomic force microscopy (AFM) was used to follow the binding process, in real time, of CBM3a-functionalized 6 nm gold nanoparticles (GNPs) to the cell wall polymers on poplar stem sections. The GNP−CBM3a complexes were found to bind to the cellulose surface, closely aligning along the cellulose fibril axis. The binding details were further confirmed and studied by single-molecule recognition imaging and AFM single-molecule dynamic force spectroscopy (SMDFS) using a CBM3a-functionalized AFM tip. The unbinding force was measured to be 44.96 ± 18.80 pN under a loading rate of 67.2 nN/s. This research provides a radical method for the study of single-molecule affinity between CBM and cellulose that is critical to the engineering of novel cellulolytic enzymes.

ACS Nano, 2018

One of the promising approaches to meet the urgent demand for further device miniaturization is t... more One of the promising approaches to meet the urgent demand for further device miniaturization is to create functional devices using single molecules. Although various single-molecule electronic devices have been demonstrated recently, single-molecule optical devices which use external stimulations to control the optical response of a single molecule have rarely been reported. Here, we propose and demonstrate a field-effect Raman scattering (FERS) device with a single molecule, an optical counterpart to fieldeffect transistors (a key component of modern electronics). With our devices, the gap size between electrodes can be precisely adjusted at subangstrom accuracy to form single molecular junctions as well as to reach the maximum performance of Raman scattering via plasmonic enhancement. Based on this maximum performance, we demonstrated that the intensity of Raman scattering can be further enhanced by an additional ∼40% if the orbitals of the molecules bridged two electrodes were shifted by a gating voltage. This finding not only provides a method to increase the sensitivity of Raman scattering beyond the limit of plasmonic enhancement, but also makes it feasible to realize addressable functional FERS devices with a gate electrode array.

Nanoscale, 2019

Characterization of the stiffness of thin DNA strands remains difficult.

Soft Matter, 2012

Using analytical techniques and Langevin dynamics simulations, we investigate the dynamics of pol... more Using analytical techniques and Langevin dynamics simulations, we investigate the dynamics of polymer translocation through a nanochannel embedded in two dimensions under an applied external field. We examine the translocation time for various ratio of the channel length L to the polymer length N. For short channels L ≪ N , the translocation time τ ∼ N 1+ν under weak driving force F , while τ ∼ F −1 L for long channels L ≫ N , independent of the chain length N. Moreover, we observe a minimum of translocation time as a function of L/N for different driving forces and channel widths. These results are interpreted by the waiting time of a single segment.

Nano Letters, 2009

We functionalized double-walled carbon nanotubes (DWCNTs) as artificial water channel proteins. F... more We functionalized double-walled carbon nanotubes (DWCNTs) as artificial water channel proteins. For the first time, molecular dynamics simulations show that the bilayer structure of DWCNTs is advantageous for carbon nanotube based transmembrane channels. The shielding of the amphiphilic outer layer could guarantee biocompatibility of the synthetic channel and protect the inner tube (functional part) from disturbance of the membrane environment. This novel design could promote more sophisticated nanobiodevices which could function in a bioenvironment with high biocompatibility.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2014

We develop a transition model to interpret single-molecule ricin-aptamer interactions with multip... more We develop a transition model to interpret single-molecule ricin-aptamer interactions with multiple unbinding pathways and energy barriers measured by atomic force microscopy dynamic force spectroscopy. Molecular simulations establish the relationship between binding conformations and the corresponding unbinding pathways. Each unbinding pathway follows a Bell-Evans multiple-barrier model. Markov-type transition matrices are developed to analyze the redistribution of unbinding events among the pathways under different loading rates. Our study provides detailed information about complex behaviors in ricin-aptamer unbinding events.

Chemical Science, 2014

Single DNA conductance measurements with increasing MgCl2 concentrations unambiguously revealed t... more Single DNA conductance measurements with increasing MgCl2 concentrations unambiguously revealed two DNA (B and Z) conformations and the B–Z transition process.

Physical chemistry chemical physics : PCCP, Jan 18, 2016

An advanced understanding of the molecule-electrode contact interfaces of single-molecule junctio... more An advanced understanding of the molecule-electrode contact interfaces of single-molecule junctions is a necessity for real world application of future single-molecule devices. This study aims to elucidate the change in the contact tunnelling barrier induced by junction extension and how this change affects the resulting junction conductance. The contact barrier of Au-octanedithiol/octanediamine-Au junctions was studied under triangle (TRI) mechanical modulations using the modified scanning tunneling microscopy (STM) break junction technique. The experimental results reveal that as the junction separation extends, the contact barrier of octanedithiol follows a unique trend, a linear increase followed by a plateau in barrier height, which is in contrast to that of octanediamine, a nearly rectangle barrier. We propose a modified contact barrier model for the unique barrier shape of octanedithiol, based on which the calculation agrees well with the experimental data. This study shows u...

Science China Materials, 2021

The assembly of monomicelles along onedimension (1D) to construct tubular or fibrous mesostructur... more The assembly of monomicelles along onedimension (1D) to construct tubular or fibrous mesostructures is greatly desired but still challenging. Herein, we have demonstrated a facile strategy to synthesize 1D bimodal mesoporous metal oxides (e.g., WO 3 , WO 3 /Pd, WO 3 /PdCu, TiO 2 , and ZrO 2) nanofibers (NFs) through assembling the organic-inorganic composite monomicelles in a beam stream generated via an electrospinning technique. This facile and repeatable methodology relies on the preparation of copolymer@metal-complex monomicelles in an anisotropic solution and oriented assembly of them in the beam stream by the selective evaporation of solvent. WO 3 and its derivatives are chosen as the demo, which show a uniform continuous fibrous structure with dual mesopore sizes (~4.0 and 7.6 nm) and large surface area (~93.1 m 2 g −1). Benefitting from the unique textual structure, gas sensors made by Pd-decorated mesoporous WO 3 NFs display outstanding comprehensive sensing performance to ethylbenzene, including a high sensitivity (52.5), an ultralow detection limit (50 ppb), and fast response/ recovery kinetics (11/16 s) as well as an outstanding selectivity, which render them promising for rapid environmental monitoring.

Light: Science & Applications, 2019

Electronic switches with nanoscale dimensions satisfy an urgent demand for further device miniatu... more Electronic switches with nanoscale dimensions satisfy an urgent demand for further device miniaturization. A recent heavily investigated approach for nanoswitches is the use of molecular junctions that employ photochromic molecules that toggle between two distinct isoforms. In contrast to the reports on this approach, we demonstrate that the conductance switch behavior can be realized with only a bare metallic contact without any molecules under light illumination. We demonstrate that the conductance of bare metallic quantum contacts can be reversibly switched over eight orders of magnitude, which substantially exceeds the performance of molecular switches. After the switch process, the gap size between two electrodes can be precisely adjusted with subangstrom accuracy by controlling the light intensity or polarization. Supported by simulations, we reveal a more general and straightforward mechanism for nanoswitching behavior, i.e., atomic switches can be realized by the expansion of nanoelectrodes due to plasmonic heating.

Journal of the American Chemical Society, Jan 5, 2018

In the seeking of molecular expression of fractal geometry, chemists have endeavored in the const... more In the seeking of molecular expression of fractal geometry, chemists have endeavored in the construction of molecules and supramolecules during the past few years, while only a few examples were reported, especially for the discrete architectures. We herein designed and constructed five generations of supramolecular fractals (G1-G5) based on the coordination-driven self-assembly of terpyridine ligands. All the ligands were synthesized from triphenylamine motif, which played a central role in geometry control. Different approaches based on direct Sonogashira coupling and/or ⟨tpy-Ru(II)-tpy⟩ connectivity were employed to prepare complex Ru(II)-organic building blocks. Fractals G1-G5 were obtained in high yields by precise coordination of organic or Ru(II)-organic building blocks with Zn(II) ions. Characterization of those architectures were accomplished by 1D and 2D NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), traveling-wave ion mobility mass spectrometry (TWI...

Nature communications, Jan 8, 2018

Nested concentric structures widely exist in nature and designed systems with circles, polygons, ... more Nested concentric structures widely exist in nature and designed systems with circles, polygons, polyhedra, and spheres sharing the same center or axis. It still remains challenging to construct discrete nested architecture at (supra)molecular level. Herein, three generations (G2-G4) of giant nested supramolecules, or Kandinsky circles, have been designed and assembled with molecular weight 17,964, 27,713 and 38,352 Da, respectively. In the ligand preparation, consecutive condensation between precursors with primary amines and pyrylium salts is applied to modularize the synthesis. These discrete nested supramolecules are prone to assemble into tubular nanostructures through hierarchical self-assembly. Furthermore, nested supramolecules display high antimicrobial activity against Gram-positive pathogen methicillin-resistant Staphylococcus aureus (MRSA), and negligible toxicity to eukaryotic cells, while the corresponding ligands do not show potent antimicrobial activity.

Journal of the American Chemical Society, Jun 8, 2017

With the goal of increasing the complexity of metallo-supramolecules, two rhombus star-shaped sup... more With the goal of increasing the complexity of metallo-supramolecules, two rhombus star-shaped supramolecular architectures, namely, supersnowflakes, were designed and assembled using multiple 2,2':6',2″-terpyridine (tpy) ligands in a stepwise manner. In the design of multicomponent self-assembly, ditopic and tritopic ligands were bridged through Ru(II) with strong coordination to form metal-organic ligands for the subsequent self-assembly with a hexatopic ligand and Zn(II). The combination of Ru(II)-organic ligands with high stability and Zn(II) ions with weak coordination played a key role in the self-assembly of giant heteroleptic supersnowflakes, which encompassed three types of tpy-based organic ligands and two metal ions. With such a stepwise strategy, the self-sorting of individual building blocks was prevented from forming the undesired assemblies, e.g., small macrocycles and coordination polymers. Furthermore, the intra- and intermolecular dynamic exchange study of t...

Nature communications, May 19, 2017

Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves ... more Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves and so on. These star-shaped patterns are also frequently used in both functional and artistic man-made architectures. Here following a stepwise synthesis and self-assembly approach, pentagonal and hexagonal metallosupramolecules possessing star-shaped motifs were prepared based on the careful design of metallo-organic ligands (MOLs). In the MOL design and preparation, robust ruthenium-terpyridyl complexes were employed to construct brominated metallo-organic intermediates, followed by a Suzuki coupling reaction to achieve the required ensemble. Ligand LA (VRu(2+)X, V=bisterpyridine, X=tetraterpyridine, Ru=Ruthenium) was initially used for the self-assembly of an anticipated hexagram upon reaction with Cd(2+) or Fe(2+); however, unexpected pentagonal structures were formed, that is, [Cd5LA5](30+) and [Fe5LA5](30+). In our redesign, LB [V(Ru(2+)X)2] was synthesized and treated with 60° V-...

Biotechnology for biofuels, 2016

The main challenges of large-scale biochemical conversion involve the high costs of cellulolytic ... more The main challenges of large-scale biochemical conversion involve the high costs of cellulolytic enzymes and the inefficiency in enzymatic deconstruction of polysaccharides embedded in the complex structure of the plant cell wall, leading to ongoing interests in studying the predominant mode of enzymatic hydrolysis. In this study, complete enzymatic hydrolysis of pretreated biomass substrates was visualized in situ and in real time by atomic force microscopy (AFM) topography and recognition imaging. Throughout the entire hydrolytic process, a hydrolysis mode for exoglucanase (CBH I) consisting of a peeling action, wherein cellulose microfibrils are peeled from sites on the pretreated cellulose substrate that have cracks sufficiently large for CBH I to immobilize. We quantitatively monitored the complete hydrolytic process on pretreated cellulose. The synergetic effect among the different enzymes can accelerate the cellulose hydrolysis rate dramatically. However, the combination of C...

Journal of the American Chemical Society, Jul 5, 2016

In an effort to exert more precise control over structural features of supramolecules, a series o... more In an effort to exert more precise control over structural features of supramolecules, a series of giant concentric hexagons were assembled as discrete structures using tetratopic terpyridine (tpy) ligands. In preparation of tetratopic ligand, pyrylium and pyridinium salts chemistry significantly facilitated synthesis. The key compounds were obtained by condensation reactions of pyrylium salts with corresponding primary amine derivatives in good yields. These discrete metallo-supramolecular concentric hexagons were fully characterized by NMR, ESI-MS, TWIM-MS and TEM, establishing their hexagon-in-hexagon architectures. The combination of different tetratopic ligands also assembled hybrid concentric hexagons with increasing diversity and complexity. Furthermore, these concentric hexagon supramolecules with precisely controlled shapes and sizes were utilized as building blocks to hierarchically self-assemble supramolecular metal-organic nanoribbons (SMON) at solid-liquid interfaces. A...

The Journal of Physical Chemistry B, 2016

The health risk associated with high cholesterol levels in the human body has motivated intensive... more The health risk associated with high cholesterol levels in the human body has motivated intensive efforts to lower them by using specialized drugs. However, little research has been reported on utilizing nanomaterials to extract extra cholesterol from living tissues. Graphene possesses great potential for cholesterol extraction from cell membranes due to its distinct porous structure and outstanding surface adhesion. Here we employ dissipative dynamic simulations to explore pathways for cholesterol extraction from a cell membrane by a sheet of graphene using a coarse-grained graphene nanosheets (CGGN) model. We first demonstrate that the self-assembly process among a single layer of graphene and a group of randomly distributed cholesterol molecules in the aqueous environment, which provides a firm foundation for graphene−cholesterol interactions and the dynamic cholesterol extraction process from the cell membrane. Simulations results show that graphene is capable of removing cholesterol molecules from the bilayer membrane. The interaction between graphene and cholesterol molecules plays an important role in determining the amount of extracted cholesterol molecules from the cell membrane. Our findings open up a promising avenue to exploit the capability of graphene for biomedical applications.

Chemical Science, 2014

Giant metallo-supramolecular cubes were assembled by using tritopic terpyridine ligands as corner... more Giant metallo-supramolecular cubes were assembled by using tritopic terpyridine ligands as corners and metal ions as edges.

Biotechnology for biofuels, Jan 11, 2013

Enzymatic hydrolysis of lignocellulosic biomass (mainly plant cell walls) is a critical process f... more Enzymatic hydrolysis of lignocellulosic biomass (mainly plant cell walls) is a critical process for biofuel production. This process is greatly hindered by the natural complexity of plant cell walls and limited accessibility of surface cellulose by enzymes. Little is known about the plant cell wall structural and molecular level component changes after pretreatments, especially on the outer surface. Therefore, a more profound understanding of surface cellulose distributions before and after pretreatments at single-molecule level is in great need. In this study, we determined the structural changes, specifically on crystalline cellulose, of natural, dilute sulfuric acid pretreated and delignified cell wall surfaces of poplar, switchgrass, and corn stover using single molecular atomic force microscopy (AFM) recognition imaging. The AFM tip was first functionalized by a family 3 carbohydrate-binding module (CBM3a) (Clostridium thermocellum Scaffoldin) which specifically recognizes crys...

Recent Patents on DNA & Gene Sequences, 2010

DNA sequencing techniques witnessed fast development in the last decades, primarily driven by the... more DNA sequencing techniques witnessed fast development in the last decades, primarily driven by the Human Genome Project. Among the proposed new techniques, Nanopore was considered as a suitable candidate for the single DNA sequencing with ultrahigh speed and very low cost. Several fabrication and modification techniques have been developed to produce robust and well-defined nanopore devices. Many efforts have also been done to apply nanopore to analyze the properties of DNA molecules. By comparing with traditional sequencing techniques, nanopore has demonstrated its distinctive superiorities in main practical issues, such as sample preparation, sequencing speed, cost-effective and read-length. Although challenges still remain, recent researches in improving the capabilities of nanopore have shed a light to achieve its ultimate goal: Sequence individual DNA strand at single nucleotide level. This patent review briefly highlights recent developments and technological achievements for DNA analysis and sequencing at single molecule level, focusing on nanopore based methods.

The Journal of Physical Chemistry B, 2012

The affinitive interaction between a carbohydratebinding module (CBM3a) and natural crystalline c... more The affinitive interaction between a carbohydratebinding module (CBM3a) and natural crystalline cellulose was visualized and measured at the single-molecule level. Noncontact high resolution imaging by atomic force microscopy (AFM) was used to follow the binding process, in real time, of CBM3a-functionalized 6 nm gold nanoparticles (GNPs) to the cell wall polymers on poplar stem sections. The GNP−CBM3a complexes were found to bind to the cellulose surface, closely aligning along the cellulose fibril axis. The binding details were further confirmed and studied by single-molecule recognition imaging and AFM single-molecule dynamic force spectroscopy (SMDFS) using a CBM3a-functionalized AFM tip. The unbinding force was measured to be 44.96 ± 18.80 pN under a loading rate of 67.2 nN/s. This research provides a radical method for the study of single-molecule affinity between CBM and cellulose that is critical to the engineering of novel cellulolytic enzymes.