Molecular Self-assembly Process Research Articles

Intentions and actions in molecular self-assembly: perspectives on students’ language use

ABSTRACTLearning to talk science is an important aspect of learning to do science. Given that scientists' language frequently includes intentions and purposes in explanations of unobservable objects and events, teachers must interpret whether learners’ use of such language reflects a scientific understanding or inaccurate anthropomorphism and teleology. In the present study, a framework consisting of three ‘stances’ (Dennett, 1987) – intentional, design and physical – is presented as a powerful tool for analysing students’ language use. The aim was to investigate how the framework can be differentiated and used analytically for interpreting students’ talk about a molecular process. Semi-structured group discussions and individual interviews about the molecular self-assembly process were conducted with engineering biology/chemistry (n = 15) and biology/chemistry teacher students (n = 6). Qualitative content analysis of transcripts showed that all three stances were employed by students. The analysis also identified subcategories for each stance, and revealed that intentional language with respect to molecular movement and assumptions about design requirements may be potentially problematic areas. Students’ exclusion of physical stance explanations may indicate literal anthropomorphic interpretations. Implications for practice include providing teachers with a tool for scaffolding their use of metaphorical language and for supporting students’ metacognitive development as scientific language users.

Chemical and entropic control on the molecular self-assembly process

Molecular self-assembly refers to the spontaneous assembly of molecules into larger structures. In order to exploit molecular self-assembly for the bottom-up synthesis of nanomaterials, the effects of chemical control (strength of the directionality in the intermolecular interaction) and entropic control (temperature) on the self-assembly process should be clarified. Here we present a theoretical methodology that unambiguously distinguishes the effects of chemical and entropic control on the self-assembly of molecules adsorbed to metal surfaces. While chemical control simply increases the formation probability of ordered structures, entropic control induces a variety of effects. These effects range from fine structure modulation of ordered structures, through to degrading large, amorphous structures into short, chain-shaped structures. Counterintuitively, the latter effect shows that entropic control can improve molecular ordering. By identifying appropriate levels of chemical and entropic control, our methodology can, therefore, identify strategies for optimizing the yield of desired nanostructures from the molecular self-assembly process.

Synthesis and characterization of a new hydrogen bonded side chain liquid crystal block copolymer and investigation of electrical properties

Abstract A new PEG-containing liquid crystalline side chain block copolymer HBC-PEG550 was prepared from poly(ethylene glycol)-b-poly(2-(diethylamino) ethyl methacrylate copolymer (BC-PEG550) and 8-(4-cyanobiphenyl-4′-oxy) octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between amine group of HBC-PEG550 and hydroxyl group of the LC8. The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the HBC-PEG550 was investigated by differential scanning calorimeter (DSC) and polarized optical microscopy. Dielectric properties of HBC-PEG550 and HBC-PEG550 has been studied by impedance spectroscopy. Real and imaginary parts of complex dielectric constant, impedance, and energy loss tangent factor for HBC-PEG550 and HBC-PEG550 have been characterized in the frequency range of 100 Hz–15 MHz.

Exfoliation of Reduced Graphene Oxide with Self-Assembled π-Gelators for Improved Electrochemical Performance.

Among several methodologies to improve the solution processing of graphene-based materials, noncovalent functionalization has been considered as the simplest and nondestructive method. Herein, we show that molecular self-assembly process can be used as a useful tool to exfoliate reduced graphene oxide (RGO), resulting in hybrid materials with improved physical properties. Upon interacting with a π-gelator, the dispersing ability of the RGO increased significantly in most of nonpolar and polar aprotic solvents when compared to the bare one. The amount of RGO dispersed was 1.7-1.8 mg mL-1 in solvents such as toluene, o-dichlorobenzene (ODCB) and tetrahydrofuran (THF). Morphological studies revealed that aggregation of π-gelator over RGO helps to exfoliate graphene layers to remain as individual sheets with higher surface area. Experimental studies revealed enhanced surface area (250 m2 g-1) and better conductivity (3.7 S m-1) of the hybrid materials with 30% of RGO content resulting in excellent electrochemical performance (specific capacitance of 181 F g-1) as electrodes for supercapacitors.

Macroscopic and Fluorescent Discrimination of Adenosine Triphosphate via Selective Metallo-hydrogel Formation: A Visual, Practical, and Reliable Rehearsal toward Cellular Imaging.

With use of simple terpyridine zinc nitrate complexes, intriguing visual recognition of adenosine triphosphate (ATP) via selective coordination assembly leading to two-component metallo-hydrogel formation has been realized. With intensive fluorescent study and density functional theory calculations, it may be inferred, besides the selective metal-ligand interaction between Zn center and phosphate groups, the intramolecular π-stacking between the planar nucleobases of ATP and the metal-hybrid aromatic ring of pincer complex strongly affected the geometry of the coordinated adducts and possible molecular self-assembly process, which constitute a completely new sensing strategy in comparison with the conventional approaches. Furthermore, in light of extreme sensitivity of pincer zinc complexes toward ATP at micromolar scale (1.85 μM) and remarkable fluorescent enhancement (ca. 44-fold) upon ATP addition, the feasibility of the low cytotoxicity pincer zinc complexes in monitoring ATP in HeLa cells has been fulfilled with confocal fluorescence microscopy.

Probing amyloid protein aggregation with optical superresolution methods: from the test tube to models of disease.

The misfolding and self-assembly of intrinsically disordered proteins into insoluble amyloid structures are central to many neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Optical imaging of this self-assembly process in vitro and in cells is revolutionizing our understanding of the molecular mechanisms behind these devastating conditions. In contrast to conventional biophysical methods, optical imaging and, in particular, optical superresolution imaging, permits the dynamic investigation of the molecular self-assembly process in vitro and in cells, at molecular-level resolution. In this article, current state-of-the-art imaging methods are reviewed and discussed in the context of research into neurodegeneration.

Heterogeneous Epitaxy: Designed Peptides Scale Graphene’s Surface

To the capable climber, a sheer mountain face on close inspection presents tenuous finger- and toe-holds that allow scaling of its vertical surface. Just as assumptions about scale influence our perceptions of everyday objects, similar questions arise regarding appropriate length scales for describing molecular recognition or self-assembly processes. Such is the case with targeting graphene—on one scale, this two-dimensional (2D) allotrope of carbon is only a few Angstroms thick and exceptionally flat in the facial dimension.

Preparation of the anatase/TiO2(B) TiO2 by self-assembly process and the high photodegradable performance on RhB

The TiO2 samples, synthesized with different addition amount of titanium source, have been prepared by a bottom-up method employing inverse lamellar micelles as the template in a surfactant molecular self-assembly process. The products were characterized by X-ray diffraction (XRD), Raman, Field-emission scanning electron microscope (FESEM), Transmission scanning electron microscopy (TEM), X-ray photoelectron Spectroscopy (XPS), Nitrogen adsorption-desorption isotherms, Photoluminescence spectra (PL), UV–vis diffuse reflectance (DRS) and photodegradable tests. The results show that all samples are biphases TiO2 (anatase and TiO2(B)). In addition, with the increment of titanium source, the microstructure of three samples have changed from small 3D aggregates to big 3D aggregates composed of 2D nanosheets, and the proportion of the anatase phase in three products and the specific surface area (BET) of the samples gradually increased, which not only can suppress the recombination of photogenerated electrons and holes, and can also enhance the photodegradable performance and the adsorption performance of three products on organic pollutants RhB. The 2.5-TiO2 Ss exhibited the best photodegradable performance among three samples. Meanwhile, the 2.5-TiO2 Ss also had a good cycle stability and low performance loss (8%).

Synthesis and electrical properties of hydrogen bonded liquid crystal polymer

In this study, a new polystyrene based side chain liquid crystalline polymer (EP-PS-LC11)) has been prepared from polystyrene having ethylpiperazine moiety as a hydrogen bond acceptor polymer and 11-(4-cyanobiphenyl-4(-oxy)undekan-1-ol (LC11) as a bond donor by molecular self-assembly processes via hydrogen bond formation between nitrogen of ethylpiperazine on polymer chain and hydroxyl group of the LC11. The formation of hydrogen bond has been confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the EP-PS-LC11 has been investigated by a differential scanning calorimeter (DSC) and polarized optical microscopy. The thermal behaviors of the H-bonded liquid crystalline polymer have been investigated by DSC measurements. The dielectric properties and ac conductivity mechanism of EP-PS-LC11 have also been investigated by impedance spectroscopy within the frequency interval of 5Hz–15MHz. The dielectric relaxation type of EP-PS-LC11 has been analyzed by fitting dispersion curves of ε′-ω. The system obeys nearly Debye and non-Debye type relaxations for the low and high frequency regions. In addition, it has been revealed that since the dielectric strength decreases by increasing frequency, the LC composite molecules can align more easily at high frequency. Moreover, the variation of imaginary component of dielectric constant with frequency shows two relaxation peaks. While the low frequency relaxation peak corresponds to molecular vibration, the high frequency relaxation peak is attributed to molecular orientation. The frequency dependence of ac conductivity has also been analyzed by means of frequency exponent, s. Depending on the frequency deal with, the system exhibit nearly dc, correlated barrier hopping (CBH) and super linear power law (SLPL) behaviors.

Experimental Insights into the Nanostructure of the Cores of Topological Defects in Liquid Crystals.

The nanoscopic structure of the cores of topological defects in anisotropic condensed matter is an unresolved issue, although a number of theoretical predictions have been reported. In the experimental study reported in this Letter, we template the assembly of amphiphilic molecules from the cores of defects in liquid crystals and thereby provide the first experimental evidence that the cores of singular defects that appear optically to be points (with strength m=+1) are nanometer-sized closed-loop, disclination lines. We also analyze this result in the context of a model that describes the influence of amphiphilic assemblies on the free energy and stability of the defects. Overall, our experimental results and theoretical predictions reveal that the cores of defects with opposite strengths (e.g., m=+1 vs m=-1) differ in ways that profoundly influence processes of molecular self-assembly.

ChemInform Abstract: What Do We Learn from the Molecular Self‐Assembly Process

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An electrochemical platform for localized pH control on demand.

Solution pH is a powerful tool for regulating many kinds of chemical activity, but is generally treated as a static property defined by a pre-selected buffer. Introducing dynamic control of pH in space, time, and magnitude can enable richer and more efficient chemistries, but is not feasible with traditional methods of titration or buffer exchange. Recent reports have featured electrochemical strategies for modifying bulk pH in constrained volumes, but only demonstrate switching between two preset values and omit spatial control entirely. Here, we use a combination of solution-borne quinones and galvanostatic excitation to enable quantitative control of pH environments that are highly localized to an electrode surface. We demonstrate highly reproducible acidification and alkalinization with up to 0.1 pH s(-1) (±0.002 pH s(-1)) rate of change across the dynamic range of our pH sensor (pH 4.5 to 7.5) in buffered solutions. Using dynamic current control, we generate and sustain 3 distinct pH microenvironments simultaneously to within ±0.04 pH for 13 minutes in a single solution, and we leverage these microenvironments to demonstrate spatially-resolved, pH-driven control of enzymatic activity. In addition to straightforward applications of spatio-temporal pH control (e.g. efficiently studying pH-dependencies of chemical interactions), the technique opens completely new avenues for implementing complex systems through dynamic control of enzyme activation, protein binding affinity, chemical reactivity, chemical release, molecular self-assembly, and many more pH-controlled processes.

Co-effects of matrix low elasticity and aligned topography on stem cell neurogenic differentiation and rapid neurite outgrowth

The development of novel biomaterials that deliver precise regulatory signals to direct stem cell fate for nerve regeneration is the focus of current intensive research efforts. In this study, a hierarchically aligned fibrillar fibrin hydrogel (AFG) that was fabricated through electrospinning and the concurrent molecular self-assembly process mimics both the soft and oriented features of nerve tissue, thus providing hybrid biophysical cues to instruct cell behavior in vitro and in vivo. The electrospun hydrogels were examined by scanning electron microscopy (SEM), polarized light microscopy, small angle X-ray scattering assay and atomic force microscopy (AFM), showing a hierarchically linear-ordered structure from the nanoscale to the macroscale with a soft elastic character (elasticity ∼1 kPa). We found that this low elasticity and aligned topography of AFG exhibit co-effects on promoting the neurogenic differentiation of human umbilical cord mesenchymal stem cells (hUMSCs) in comparison to random fibrin hydrogel (RFG) and tissue culture plate (TCP) control after two week cell culture in growth medium lacking supplementation with soluble neurogenic induction factors. In addition, AFG also induces dorsal root ganglion (DRG) neurons to rapidly project numerous long neurite outgrowths longitudinally along the AFG fibers for a total neurite extension distance of 1.96 mm in three days in the absence of neurotrophic factor supplementation. Moreover, the AFG implanted in a rat T9 dorsal hemisection spinal cord injury model was found to promote endogenous neural cell fast migration and axonal invasion along AFG fibers, resulting in aligned tissue cables in vivo. Our results suggest that matrix stiffness and aligned topography may instruct stem cell neurogenic differentiation and rapid neurite outgrowth, providing great promise for biomaterial design for applications in nerve regeneration.

Hierarchically aligned fibrillar fibrin hydrogel designed for spinal cord injury repair

Event Abstract Back to Event Hierarchically aligned fibrillar fibrin hydrogel designed for spinal cord injury repair Xiumei Wang1* and Shenglian Yao1* 1 Tsinghua University, School of Materials Science and Engineering, China Biomaterial-based strategies for nerve regeneration have attracted extensive attentions in recent years. In this study, a hierarchical aligned fibrillar fibrin hydrogel was prepared through electrospinning technique and the concurrent molecular self-assembly process at the moment of collection. The aligned fibrin hydrogel that simulated the elasticity and oriented structures of nerve tissue simultaneously provided biomimetically biophysical cues to direct in vivo or in vitro cells thus constructing nerve-like microtissues rapidly. In vitro studies showed that human umbilical cord mesenchymal stem cells could “feel” the cues afforded by aligned fibrin gels and extend along the long axis of the fibers soon after cell attachment and undergo strong neural differentiation after two weeks cell culture in regular growth medium without any soluble growth factors. More interestingly, the rat dorsal root ganglion neurons also could follow the fiber structure in a highly oriented longitudinal manner with three-dimensionally neurite elongation to total 3.92 mm just in 3 days basic culture. In rat T9 dorsal hemisection spinal cord injury. the host neural cells with β-tubulin III-positive migrated into the aligned fibrin hydrogels very quickly. And the axon reconstruction and locomotor performance was improved starting from 2 weeks after the surgery in the aligned fibrin hydrogel group. Our study suggested that the hierarchically aligned fibrillar fibrin hydrogels will not only have great promising for directing stem cells towards nerve lineage, but also may have great potential applications in spinal cord regeneration. Tsinghua University Initiative Scientific Research Program (20121087982, 20131089199); 973 Program (No. 2011CB606205)

The role of solvent in the self-assembly of m-aminobenzoic acid: a density functional theory and molecular dynamics study

Solvent can have significant effects on the solution thermodynamics and crystallisation kinetics of organic compounds from solution. In the present work, the early stages of aggregation of the organic molecule m-aminobenzoic (mABA) in two different solvents, dimethyl sulfoxide (DMSO) and water were studied using a combination of quantum chemistry, molecular dynamics and metadynamics simulations. Density functional theory (B97-D and M06-2X) calculations with the continuum solvation SMD model were used to probe the potential energy surface of molecular clusters of m-aminobenzoic acid, (mABA)n (n = 2–4), locate their low-lying energy structures, and compute the Gibbs free energies of (mABA)n in solution. Starting from a large number of randomly generated candidate structures and by imposing the condition of minimum free energy in solution for the isomers of (mABA)n, we proved that the most stable dimer and tetramer in solution correspond to the classic carboxylic dimer π–π stacking synthon found in the crystalline form-II of mABA. Molecular dynamics simulations of mABA solutions at different concentrations reveal a significant solvent-dependent aggregation behaviour for mABA: in water, even at low concentrations, mABA molecules spontaneously form H-bonded π–π stacking molecular clusters, whereas in organosulfur solutions the molecules of mABA are in a more solvated state. Metadynamics simulations and microsolvation density functional theory calculations rationalize the low level of mABA aggregation in DMSO in terms of the energetic barrier for the desolvation of mABA molecules and formation of dimers, and the strength of mABA-solvent interactions, which are both larger in DMSO compared with water. This work shows that the solvent and its specific interaction with the organic solute molecules influences both the thermodynamics and kinetics of the molecular self-assembly process.

Problems, successes and challenges for the application of dispersion-corrected density-functional theory combined with dispersion-based implicit solvent models to large-scale hydrophobic self-assembly and polymorphism

The recent advent of dispersion-corrected density-functional theory (DFT) methods allows for quantitative modelling of molecular self-assembly processes, and we consider what is required to develop applications to the formation of large self-assembled monolayers (SAMs) on hydrophobic surfaces from organic solution. Focus is on application of the D3 dispersion correction of Grimme combined with the solvent dispersion model of Floris, Tomasi and Pascual–Ahuir to simulate observed scanning-tunnelling microscopy (STM) images of various polymorphs of tetraalkylporphyrin SAMs on highly oriented pyrolytic graphite surfaces. The most significant problem is identified as the need to treat SAM structures that are incommensurate with those of the substrate, providing a challenge to the use of traditional periodic-imaging boundary techniques. Using nearby commensurate lattices introduces non-systematic errors into calculated lattice constants and free energies of SAM formation that are larger than experimental uncertainties and polymorph differences. Developing non-periodic methods for polymorph interface simulation also remains a challenge. Despite these problems, existing methods can be used to interpret STM images and SAM atomic structures, distinguishing between multiple feasible polymorph types. They also provide critical insight into the factors controlling polymorphism. All this stems from a delicate balance that the intermolecular D3 and solvent Floris, Tomasi and Pascual–Ahuir corrections provide. Combined optimised treatments should yield fully quantitative approaches in the future.

Topological defects in liquid crystals as templates for molecular self-assembly.

Topological defects in liquid crystals (LCs) have been widely used to organize colloidal dispersions and template polymerization, leading to a range of assemblies, elastomers and gels. However, little is understood about molecular-level assembly processes within defects. Here, we report that nanoscopic environments defined by LC topological defects can selectively trigger processes of molecular self-assembly. By using fluorescence microscopy, cryogenic transmission electron microscopy and super-resolution optical microscopy, we observed signatures of molecular self-assembly of amphiphilic molecules in topological defects, including cooperativity, reversibility and controlled growth. We also show that nanoscopic o-rings synthesized from Saturn-ring disclinations and other molecular assemblies templated by defects can be preserved by using photocrosslinkable amphiphiles. Our results reveal that, in analogy to other classes of macromolecular templates such as polymer-surfactant complexes, topological defects in LCs are a versatile class of three-dimensional, dynamic and reconfigurable templates that can direct processes of molecular self-assembly.

<i>In Situ</i> Studies of Molecular Self-Assembling during the Formation of Ion-Conducting Membranes for Fuel Cells

In present work a new setup for in situ studies of molecular self-assembling process for fabrication of ion-conducting membranes for “green” fuel cells was developed. Due to compactness, this unique setup can be used on the synchrotron beamlines. The GISAXS and optical microscopy data have shown the effectiveness of the control of molecular architecture by impact of high temperature, UV-irradiation and solvent vapors.

What Do We Learn from the Molecular Self-Assembly Process?

What Do We Learn from the Molecular Self-Assembly Process?

Effect of incubation temperature on the self-assembly of regenerated silk fibroin: A study using AFM

Understanding effect of temperature on the molecular self-assembly process will be helpful to unravel the structure–function relationship of biomolecule and to provide important information for the bottom-up approach to nanotechnology. In this work, the effect of incubation temperature on the secondary structures and morphological structures of regenerated silk fibroin (RSF) was systematically studied using atomic force microscopy and Fourier Transform infrared spectroscopy. The effect of incubation temperature on RSF self-assembly was dependent on RSF concentration. For the RSF solution with relatively low concentrations (15μg/mL and 60μg/mL), the increase of the incubation temperature mainly accelerated the formation and aggregation of antiparallel β-sheet protofibrils and decreased the formation of random coil protofilaments/globule-like molecules. For the RSF solution with relatively high concentrations (300μg/mL and 1.5mg/mL), the increase of the incubation temperature mainly accelerated the formation and aggregation of antiparallel β-sheet RSF features (protofibrils and globule-like features) and decreased the formation of random coil bead-like features. This work implies that the morphology and conformation of biomacromolecules could be tuned by controlling the incubation temperature. Further, it will be beneficial to basic understanding of the nanoscale structure formation in different silk-based biomaterials.