Nanoarchitectonics of Nanocellulose Filament Electrodes by Femtosecond Pulse Laser Deposition of ZnO and <i>In Situ</i> Conjugation of Conductive Polymers

Electroactive filament electrodes were synthesized by wet-spinning of cellulose nanofibrils (CNF) followed by femtosecond pulse laser deposition of ZnO (CNF@ZnO). A layer of conducting conjugated polymers was further adsorbed by in situ polymerization of either pyrrole or aniline, yielding systems optimized for electron conduction. The resultant hybrid filaments were thoroughly characterized by imaging, spectroscopy, electrochemical impedance, and small- and wide-angle X-ray scattering. For the filaments using polyaniline, the measured conductivity was a result of the synergy between the inorganic and organic layers, while the contribution was additive in the case of the systems containing polypyrrole. This observation is rationalized by the occurrence of charge transfer between ZnO and polyaniline but not that with polypyrrole. The introduced conductive hybrid filaments displayed a performance that competes with that of metallic counterparts, offering great promise for next-generation filament electrodes based on renewable nanocellulose

Structure of the Electrostatic Complex of DNA with Cationic Dendrimer of Intermediate Generation: The Role of Counterion Entropy

Polyamidoamine (PAMAM) dednrimer bearing a well-defined number of amine groups can be protonated under physiological or acidic condition to generate the macrocations capable of forming electrostatic complex (called “dendriplex”) with DNA for gene delivery. Using small-angle X-ray scattering (SAXS) and small angle neutron scattering (SANS), here we constructed the morphological map of the complex of DNA with PAMAM dendrimer of generation four (G4) in terms of the dendrimer charge density and the nominal N/P ratio given by the feed molar ratio of dendrimer amine group to DNA phosphate group. With the increase of dendrimer charge density under a given nominal N/P ratio, the structure was found to transform from square columnar phase (in which the DNA chains packed in square lattice were locally straightened) to hexagonally-packed DNA superhelices (in which the DNA chains organizing in a hexagonal lattice twisted moderately into superhelices) and finally to beads-on-string structure (in which DNA wrapped around the dendrimer to form nuclesome-like array). The phase transition sequence was understood from the balance between the bending energy of DNA and the free energy of charge matching governed by the entropic gain from counterion release. Decreasing the nominal N/P ratio under fixed dendrimer charge density was found to exert the same effect as increasing dendrimer charge density; that is, the structure with higher DNA curvature tended to form at a lower nominal N/P ratio, in particular for the dendriplex with low dendrimer charge density. The effect of the N/P ratio was attributed to the tendency of the system to increase the translational entropy of the counterions released to the bulk solution by reducing the concentration of free DNA or dendrimer remained in the solution. The experimental results presented here thus demonstrated the crucial role of counterion entropy in the structural formation of DNA–dendrimer complexes, and this entropic contribution was governed by the dendrimer charge density, the nominal N/P ratio, and the initial concentrations of DNA and dendrimer used for complex preparation

Supramolecular Nanostructure Formation of Coassembled Amyloid Inspired Peptides

Characterization of amyloid-like aggregates through converging approaches can yield deeper understanding of their complex self-assembly mechanisms and the nature of their strong mechanical stability, which may in turn contribute to the design of novel supramolecular peptide nanostructures as functional materials. In this study, we investigated the coassembly kinetics of oppositely charged short amyloid-inspired peptides (AIPs) into supramolecular nanostructures by using confocal fluorescence imaging of thioflavin T binding, turbidity assay and in situ small-angle X-ray scattering (SAXS) analysis. We showed that coassembly kinetics of the AIP nanostructures were consistent with nucleation-dependent amyloid-like aggregation, and aggregation behavior of the AIPs was affected by the initial monomer concentration and sonication. Moreover, SAXS analysis was performed to gain structural information on the size, shape, electron density, and internal organization of the coassembled AIP nanostructures. The scattering data of the coassembled AIP nanostructures were best fitted into to a combination of polydisperse core–shell cylinder (PCSC) and decoupling flexible cylinder (FCPR) models, and the structural parameters were estimated based on the fitting results of the scattering data. The stability of the coassembled AIP nanostructures in both fiber organization and bulk viscoelastic properties was also revealed via temperature-dependent SAXS analysis and oscillatory rheology measurements, respectively

Elucidating the DNA–Histone Interaction in Nucleosome from the DNA–Dendrimer Complex

The electrostatic complex of DNA with poly­(amidoamine) G6 dendrimer (called “dendriplex”) is used as a model system to resolve if pure electrostatic interaction can lead to the key structural features of nucleosome. Both dendrimer and histone octamer (HO) are found to attract DNA to wrap helically around them with comparable pitch lengths; however, the superhelical trajectory in the dendriplex is loose and fluctuating, whereas that in nucleosome is tight and rigid. The DNA-wrapped dendrimer particles are closely spaced along the dendriplex fiber, while the nucleosome core particles (NCPs) in the nucleosome array are separated by relatively long linker DNA. The clear contrast in structural features attests that DNA–HO interaction is beyond electrostatics, as additional specific interactions exist to fix DNA superhelical trajectory and to select the favored DNA sequence for constituting the NCP

Distribution of Crystalline Polymer and Fullerene Clusters in Both Horizontal and Vertical Directions of High-Efficiency Bulk Heterojunction Solar Cells

In this study, we used (i) synchrotron grazing-incidence small-/wide-angle X-ray scattering to elucidate the crystallinity of the polymer PBTC₁₂TPD and the sizes of the clusters of the fullerenes PC₆₁BM and ThC₆₁BM and (ii) transmission electron microscopy/electron energy loss spectroscopy to decipher both horizontal and vertical distributions of fullerenes in PBTC₁₂TPD/fullerene films processed with chloroform, chlorobenzene and dichlorobezene. We found that the crystallinity of the polymer and the sizes along with the distributions of the fullerene clusters were critically dependent on the solubility of the polymer in the processing solvent when the solubility of fullerenes is much higher than that of the polymer in the solvent. In particular, with chloroform (CF) as the processing solvent, the polymer and fullerene units in the PBTC₁₂TPD/ThC₆₁BM layer not only give rise to higher crystallinity and a more uniform and finer fullerene cluster dispersion but also formed nanometer scale interpenetrating network structures and presented a gradient in the distribution of the fullerene clusters and polymer, with a higher polymer density near the anode and a higher fullerene density near the cathode. As a result of combined contributions from the enhanced polymer crystallinity, finer and more uniform fullerene dispersion and gradient distributions, both the short current density and the fill factor for the device incorporating the CF-processed active layer increase substantially over that of the device incorporating a dichlorobenzene-processed active layer; the resulting power conversion efficiency of the device incorporating the CF-processed active layer was enhanced by 46% relative to that of the device incorporating a dichlorobenzene-processed active layer

Tracing the Surfactant-Mediated Nucleation, Growth, and Superpacking of Gold Supercrystals Using Time and Spatially Resolved X‑ray Scattering

The nucleation and growth process of gold supercrystals in a surfactant diffusion approach is followed by simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS), supplemented with scanning electron microscopy. The results indicate that supercrystal nucleation can be activated efficiently upon placing a concentrated surfactant solution of a nematic phase on top of a gold nanocrystal solution droplet trapped in the middle of a vertically oriented capillary tube. Supercrystal nuclei comprised of tens of gold nanocubes are observed nearly instantaneously in the broadened liquid–liquid interface zone of a steep gradient of surfactant concentration, revealing a diffusion-kinetics-controlled nucleation process. Once formed, the nuclei can sediment into the naoncrystal zone below, and grow efficiently into cubic or tetragonal supercrystals of ∼1 μm size within ∼100 min. Supercrystals matured during sedimentation in the capillary can accumulate and face-to-face align at the bottom liquid–air interface of the nanocrystal droplet. This is followed by superpacking of the supercrystals into highly oriented hierarchical sheets, with a huge number of gold nanocubes aligned for largely coherent crystallographic orientations

Probing the Acid-Induced Packing Structure Changes of the Molten Globule Domains of a Protein near Equilibrium Unfolding

Using simultaneously scanning small-angle X-ray scattering (SAXS) and UV–vis absorption with integrated online size exclusion chromatography, supplemental with molecular dynamics simulations, we unveil the long-postulated global structure evolution of a model multidomain protein bovine serum albumin (BSA) during acid-induced unfolding. Our results differentiate three global packing structures of the three molten globule domains of BSA, forming three intermediates <b>I</b>_<b>1</b>, <b>I</b>_<b>2</b>, and <b>E</b> along the unfolding pathway. The <b>I</b>_<b>1</b>–<b>I</b>_<b>2</b> transition, overlooked in all previous studies, involves mainly coordinated reorientations across interconnected molten globule subdomains, and the transition activates a critical pivot domain opening of the protein for entering into the <b>E</b> form, with an unexpectedly large unfolding free energy change of −9.5 kcal mol^–1, extracted based on the observed packing structural changes. The revealed local packing flexibility and rigidity of the molten globule domains in the <b>E</b> form elucidate how collective motions of the molten globule domains profoundly influence the folding–unfolding pathway of a multidomain protein

Directing the Interfacial Morphology of Hierarchical Structures of Dendron-Jacketed Block Copolymers via Liquid Crystalline Phases

Interfacial morphologies of hierarchically phase-separated domains in supramolecular dendron-jacketed block copolymers (DJBCP) are directed via liquid-crystalline (LC) phases of the dendronized blocks. The DJBCP is formed with a dendron 4′-(3,4,5-trioctyloxybenzoyloxy)­benzoic acid (TOB), selectively incorporated into the P4VP block of poly­(styrene)-<i>block</i>-poly­(4-vinylpyridine) (PS-<i>b</i>-P4VP). Revealed from small- and wide-angle X-ray scattering as well as transmission electron microscopy, the hexagonally packed columnar LC phase (HEX_col) of the dendronized blocks P4VP­(TOB) can substantially decrease the curvature of the intermaterial dividing surfaces (IMDS) of the DJBCP. Consequently formed are hierarchically structured DJBCP with hexagonally packed hexagon PS cylinders. As the locally two-dimensionally (2D)-ordered HEX_col phase reduces to 1D ordered smectic (Sm) phase with weakened LC packing strength, the planar IMDS of the DJBCP relaxes into curved IMDS for circular PS cylinders. IMDS flattening effect imposed by the columnar LC phase is further strengthened via a triblock DJBCP of P4VP­(TOB)_<i>x</i>-<i>b</i>-PS-<i>b</i>-P4VP­(TOB)_<i>x</i>, leading to a highly oriented honeycomb structure with an ordering length up to sub-millimeter. The LC-controlled IMDS morphology of the DJBCP might facilitate fabrication of templates toward nanoperiodic arrays with sharp channel edges for lithography applications

Interactive Crystallization Kinetics in Double-Crystalline Block Copolymer

The crystallization kinetics and crystallization-induced morphological formation of an asymmetric double-crystalline block copolymer, syndiotactic polypropylene-<i>block</i>-poly­(ε-caprolactone) (sPP-<i>b</i>-PCL), have been investigated by time-resolved simultaneous small-angle and wide-angle X-ray scattering (SAXS/WAXS). The sPP-<i>b</i>-PCL under study exhibited hexagonally packed cylinder morphology in the melt state, where the minority sPP block formed the cylindrical microdomains dispersed in the PCL matrix. The crystallization behavior was studied by imposing two types of crystallization histories: (1) two-stage crystallization, where the diblock was first cooled to the temperature <i>T</i>_c^sPP situating between the melting points of the two components (<i>T</i>_m^PCL < <i>T</i>_c^sPP < <i>T</i>_m^sPP) to allow sPP crystallization to saturation followed by cooling to <i>T</i>_c^PCL < <i>T</i>_m^PCL to induce PCL crystallization; (2) one-stage crystallization, where the system was cooled directly to <i>T</i>_c < <i>T</i>_m^PCL to allow the two components to crystallize competitively. In both cases, the crystallization of sPP block was in general able to disrupt the melt structure and transformed it into a crystalline lamellar morphology. For the two-stage crystallization process, the PCL block was found to exhibit a faster crystallization at a given <i>T</i>_c^PCL when the sPP block was precrystallized at higher <i>T</i>_c^sPP. This “interactive crystallization kinetics” was attributed to the mediation of the stretching of PCL blocks by the thickness of sPP crystalline domains which depended on <i>T</i>_c^sPP. In the one-stage process, the crystallization events of the two blocks became more competitive with decreasing <i>T</i>_c. The morphological perturbation induced by crystallization was also more hindered at lower <i>T</i>_c, such that a significant portion of sPP blocks remained confined within the cylindrical microdomains so as to suppress the sPP crystallinity

Membrane Charging and Swelling upon Calcium Adsorption as Revealed by Phospholipid Nanodiscs

Direct binding of calcium ions (Ca²⁺) to phospholipid membranes is an unclarified yet critical signaling pathway in diverse Ca²⁺-regulated cellular phenomena. Here, high-pressure-liquid-chromatography, small-angle X-ray scattering (SAXS), UV–vis absorption, and differential refractive index detections are integrated to probe Ca²⁺-binding to the zwitterionic lipid membranes in nanodiscs. The responses of the membranes upon Ca²⁺-binding, in composition and conformation, are quantified through integrated data analysis. The results indicate that Ca²⁺ binds specifically into the phospholipid headgroup zone, resulting in membrane charging and membrane swelling, with a saturated Ca²⁺-lipid binding ratio of 1:8. A Ca²⁺-binding isotherm to the nanodisc is further established and yields an unexpectedly high binding constant <i>K</i> = 4260 M^–1 and a leaflet potential of ca. 100 mV based on a modified Gouy–Chapman model. The calcium-lipid binding ratio, however, drops to 40% when the nanodisc undergoes a gel-to-fluid phase transition, leading to an effective charge capacity of a few μF/cm²