Nanoscale Order Research Articles

How Peptide Molecular Structure and Charge Influence the Nanostructure of Lipid Bicontinuous Cubic Mesophases: Model Synthetic WALP Peptides Provide Insights

Nanostructured bicontinuous lipidic cubic phases are used for the encapsulation of proteins in a range of applications such as in meso crystallization of transmembrane proteins and as drug delivery vehicles. The retention of the nanoscale order of the cubic phases subsequent to protein incorporation, as well as retention of the protein structure and function, is essential for all of these applications. Herein synthetic peptides (WALP21, WALPS53, and WALPS73) with a common α-helical hydrophobic domain, but varying hydrophilic loop size, were designed to systematically examine the effect of peptide structure and charge on bicontinuous cubic phases. The effect of the cubic phases on the secondary structure of the peptides was also investigated. The incorporation of the WALP peptides in cubic phases formed by a range of lipids showed that hydrophobic mismatch of the peptides with the lipid bilayers, the hydrophilic domain size, and peptide charge were all significant factors determining the response of the lipid nanomaterial to protein insertion. As charge repulsion had the most significant effect on the phase transitions observed, we suggest that buffer pH and salt concentration must be carefully considered to ensure cubic mesophase retention. Importantly, the WALP peptides were found to have a different conformation depending on the local lipid environment. Such structural changes could potentially affect membrane protein function, which is crucial for both current and prospective applications.

Nanoscale order in the frustrated mixed conductor La5.6WO12−δ

This article reports a comprehensive investigation of the average and local structure of La5.6WO12−δ, which has excellent mixed proton, electron and oxide ion conduction suitable for device applications. Synchrotron X-ray and neutron powder diffraction show that a cubic fluorite supercell describes the average structure, with highly disordered lanthanum and oxide positions. On average, the tungsten sites are sixfold coordinated and a trace [3.7 (1.3)%] of anti-site disorder is detected. In addition to sharp Bragg reflections, strong diffuse neutron scattering is observed, which hints at short-range order. Plausible local configurations are considered and it is shown that the defect chemistry implies a simple `chemical exchange' interaction that favours ordered WO6octahedra. The local model is confirmed by synchrotron X-ray pair distribution function analysis and EXAFS experiments performed at the LaKand WL3edges. It is shown that ordered domains of ∼3.5 nm are found, implying that mixed conduction in La5.6WO12−δis associated with a defective glassy-like anion sublattice. The origins of this ground state are proposed to lie in the non-bipartite nature of the face-centred cubic lattice and the pairwise interactions which link the orientation of neighbouring octahedral WO6sites. This `function through frustration' could provide a means of designing new mixed conductors.

Stimulation of Odontogenesis and Angiogenesis via Bioactive Nanocomposite Calcium Phosphate Cements Through Integrin and VEGF Signaling Pathways.

Formulating self-setting calcium phosphate cements (CPCs) with secondary phases particularly in the nanoscale order holds great promise to improve biological properties. Here, we focus on the effect that bioactive glass nanoparticles (BGN) incorporated in CPC compositions can have on the proliferation, odontogenic differentiation, and angiogenic stimulation of stem cells derived from human dental pulp (HDPSCs). These odontogenic and angiogenic events are of special importance in the dentin-pulp regeneration processes. In comparison to pure CPCs, nanocomposite cements exhibit a significantly improved proliferation of HDPSCs, and the improvement is more significant as the BGN content increases. The nanocomposite cements substantially enhance the adhesion of cells, and significantly up-regulate odontogenic differentiation, including alkaline phosphatase (ALP) activity and the expressions of odontogenic genes (sialophosphoprotein, dentin matrix protein I, ALP, osteopontin and osteocalcin). Furthermore, the use of nanocomposite cements result in stimulation of angiogenic gene expression (VEGF, FGF-2, VEGFRs, PECAM-1, and VE-cadherin) and protein production (VEGF, VEGFR-1). The angiogenic stimulation by the HDPSCs significantly affects the endothelial cell behaviors, that is, the endothelial cell migration and the tubular network formation are substantially improved when treated with HDPSC-conditioned medium, particularly with the help of nanocomposite cements. The integrin and VEGF signaling pathways are reasoned for the stimulation of the odontogenesis and angiogenesis of cells, where the nanocomposite cements up-regulate the integrin subsets α1, α2, α3, and β1, and activate the integrin downstream signal pathways, such as p-FAK, p-Akt, p-paxillin, JNK, EK, and NF-κB, as well as other nuclear transcriptional factors, including CREB, STAT-3, and ELK-1. The current results indicate that the new formulation of the nanocomposite self-setting cements might provide some beneficial microenvironments for the regenerative processes of dentin-pulp complex tissues.

Cornucopia of Nanoscale Ordered Phases in Sphere-Forming Tetrablock Terpolymers.

We report the phase behavior of a series of poly(styrene)-b-poly(isoprene)-b-poly(styrene)'-b-poly(ethylene oxide) (SIS'O) tetrablock terpolymers. This study was motivated by self-consistent field theory (SCFT) calculations that anticipate a rich array of sphere-forming morphologies with variations in the molecular symmetry parameter τ = NS/(NS + NS'), where N is the block degree of polymerization and the volume fraction of O is less than about 0.22. Eight SIS'O samples, with τ ranging from 0.21 to 0.73, were synthesized and investigated using small-angle X-ray scattering and transmission electron microscopy, yielding evidence of nine different spherical phases: hexagonal, FCC, HCP, BCC, rhombohedral (tentative), liquid-like packing, dodecagonal quasicrystal, and Frank-Kasper σ and A15 phases. At temperatures close to the order-disorder transition, these tetrablocks behave as pseudo-[SIS']-O diblocks and form equilibrium morphologies mediated by facile chain exchange between micelles. Transition from equilibrium to nonequilibrium behavior occurs at a temperature (Terg) several tens of degrees below the order-disorder transition temperature, speculated to be coincident with the loss of ergodicity, as chain exchange is arrested due to increased segregation strength between the core (O) and corona (SIS') blocks. Nonequilibrium ordered structures form when T < Terg; these are interpreted using SCFT calculations to elucidate the free energy landscape driving ordering in the S and I block matrix. These experiments demonstrate a profound dependence on phase stability with variations in τ and temperature, providing insights into the formation of ordered phase symmetry in this class of asymmetric multiblock polymers.

Spontaneous structural transition and crystal formation in minimal supramolecular polymer model.

The association of building blocks into supramolecular polymers allows the fabrication of diverse functional architectures at the nanoscale. The use of minimal assembly units to explore polymer dynamics and phase transitions significantly contributes to the application of polymer physicochemical paradigms in the field of supramolecular polymers. We present a minimal model that displays spontaneous coordinated structural transitions between micro- and nanostructures, hydrogels with nanoscale order, and single crystals. The simple amphiphilic 9-fluorenylmethoxycarbonyl-3,4-dihydroxyphenylalanine (Fmoc-DOPA) modified amino acid undergoes a noninduced transition from spherical assemblies into nanofibrils followed by sol-gel transition, nanotube formation via intermediate assembly, and crystallization within the gel. Notably, the transition kinetics is slow enough to allow both multistage and multiscale characterization of the supramolecular arrangement using electron microscopy, vibrational and circular dichroism spectroscopies, nuclear magnetic resonance, and x-ray crystallography. This minimalistic system is the first comprehensive model for a complete spontaneous structural transition between diverse states governed by distinct molecular interactions.

Monte Carlo Modelling of Single-Crystal Diffuse Scattering from Intermetallics

Single-crystal diffuse scattering (SCDS) reveals detailed structural insights into materials. In particular, it is sensitive to two-body correlations, whereas traditional Bragg peak-based methods are sensitive to single-body correlations. This means that diffuse scattering is sensitive to ordering that persists for just a few unit cells: nanoscale order, sometimes referred to as “local structure”, which is often crucial for understanding a material and its function. Metals and alloys were early candidates for SCDS studies because of the availability of large single crystals. While great progress has been made in areas like ab initio modelling and molecular dynamics, a place remains for Monte Carlo modelling of model crystals because of its ability to model very large systems; important when correlations are relatively long (though still finite) in range. This paper briefly outlines, and gives examples of, some Monte Carlo methods appropriate for the modelling of SCDS from metallic compounds, and considers data collection as well as analysis. Even if the interest in the material is driven primarily by magnetism or transport behaviour, an understanding of the local structure can underpin such studies and give an indication of nanoscale inhomogeneity.

Self-assembled peptide-polymer hydrogels as a 3D nanofiber substrate for biomimetic hydroxyapatite mineralization

Event Abstract Back to Event Self-assembled peptide-polymer hydrogels as a 3D nanofiber substrate for biomimetic hydroxyapatite mineralization Elham Radvar1, C Remzi Becer1 and Helena S. Azevedo1 1 Institute of Bioengineering, Queen Mary University of London, School of Engineering and Materials Science, United Kingdom Introduction: Hard tissues in vertebrates, such as bones, are produced by controlled biomineralization of an organic matrix that regulates the growth of the inorganic phase. In bone, the fundamental subunit is a collagen fibril, formed by self-assembly of single tropocollagen molecules (triple helix), where hydroxyapatite nanocrystals grow with their crystallographic c-axes aligned with the fibril long axes. Molecular self-assembly offers the possibility to recreate the same degree of nanoscale order in synthetic biomaterials and promote epitaxial mineralization mediated by an organic matrix. The self-assembly between a negatively charged polymer and a peptide amphiphile (PA) of opposite charge was shown to result in the formation of sacs and membranes[1]. Inspired by this seminal work, here we investigate the use of the negatively charged synthetic polymer polystyrene sulfonate (PSS) with a positively charged PA to form self-assembling matrices and their ability to direct hydroxyapatite mineralization. Materials and Methods: PSS (1 MDa, Fig 1-A) was commercially available from Sigma. C15H31CONH-V3A3K3-CONH2 PA (Fig 1-A) was synthesized by solid phase and purified as described elsewhere[2]. PSS/PA hydrogels were obtained by self-assembly combining aqueous solutions of PSS (2% w/v) and PA (2% w/v). Mineralization studies were performed by incubating the PSS/PA hydrogels in a simulated body fluid (SBF[3]) solution at 37°C for several days. Then, the gels were washed with distilled water and prepared for surface analysis by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results and Discussion: Conversely to previous work reporting the self-assembly between PAs and oppositely charged polysaccharides, combining an aqueous PSS solution with a positively charged PA resulted in the formation of a self-supporting gel (Fig 1-B) exhibiting a random nanofibrilar network (Fig 1-C). PSS has been shown to direct the nucleation and growth of calcium carbonate mineral by binding to calcium ions[4]. Thus, we hypothesize that these nanofiber PSS/PA gels could be used as a 3D matrix to drive the nucleation of hydroxyapatite and create a mineralized matrix resembling the structure of natural bone. The formation of hydroxyapatite mineral on the surface of hydrogels after 14 days of incubation in SBF was confirmed by SEM (Fig 1-D, E) and EDS (Fig 1-F) analysis which show a typical morphology of hydroxyapatite crystals and the presence of calcium and phosphorus, respectively. Conclusions: While further studies are necessary to characterize the formed mineral, these self-assembled PSS/PA gels present an interesting approach to develop new biomaterials for bone regeneration considering the potential for further functionalization of the peptide segment with bioactive sequences. I would like to acknowledge the help of Dr. Daniela Ferreira and Sofia Ribeiro in peptide synthesis and SBF preparation, respectively. This work is supported by School of Engineering and Materials Science (SEMS)

Early aggregation preceding the nucleation of insulin amyloid fibrils as monitored by small angle X-ray scattering.

The nucleation event of amyloid fibrils is one of the most crucial processes that dictate the timing and rate of the pathology of diseases; however, information regarding how protein molecules associate to produce fibril nuclei is currently limited. In order to explore this issue in more detail, we performed time-resolved small angle X-ray scattering (SAXS) measurements on insulin fibrillation, in combination with additional multidirectional analyses of thioflavin T fluorescence, FTIR spectroscopy, light scattering, and light transmittance, during the fibrillation process of bovine insulin. SAXS monitoring revealed that insulin molecules associated into rod-like prefibrillar aggregates in the very early stage of the reaction. After the formation of these early aggregates, they appeared to further coalesce mutually to form larger clusters, and the SAXS profiles subsequently showed the further time evolution of conformational development towards mature amyloid fibrils. Distinct types of structural units in terms of shape in a nano-scale order, cross-β content, and thioflavin T fluorescence intensity were observed in a manner that was dependent on the fibrillation pathways. These results suggest the presence of diverse substructures that characterize various fibrillation pathways, and eventually, manifest polymorphisms in mature amyloid fibrils.

Understanding nanoscale order in amorphous pharmaceuticals

Understanding nanoscale order in amorphous pharmaceuticals

Nanoscale Order and Crystallization in POSS–PCL Shape Memory Molecular Networks

The angstrom- and nanometer-scale crystallization and long-range ordering behavior of polyhedral oligosilsesquioxane–poly(e-caprolactone) (POSS–PCL) shape memory nanocomposites under thermomechanical shape memory cycles and uniaxial stretching were studied by simultaneous wide-angle and small-angle X-ray scattering (WAXS/SAXS). POSS/PCL cross-linked molecular networks featuring a single POSS moiety centered between two PCL network chains, previously reported [Alvarado-Tenorio Macromolecules 2011, 44, 5682−5692], with molecular weight of 2600 g/mol and exhibiting shape memory behavior, were synthesized with variation of cross-linking molar ratio (POSS–PCL diacrylate/tetrathiol cross-linker, 2:1, 2:1.5, and 2:2). The photocured networks exhibited a morphology consisting of POSS crystals embedded in an amorphous PCL matrix, and the POSS crystals were ordered in a cubic nanostructure. However, under tensile stress afforded by a shape memory cycle, the networks yielded a double-induced orientation (90° and 180...

Direct Observation of Active Nickel Oxide Cluster in Nickel–Borate Electrocatalyst for Water Oxidation by In Situ O K-Edge X-ray Absorption Spectroscopy

In situ O K-edge X-ray absorption fine structure (XAFS) spectroscopy was applied to investigate the electronic and structural change in the nickel–borate (Ni–Bi) electrocatalyst during the oxygen evolution reaction (OER). An absorption peak was observed around 528.7 eV at 1.0 V versus Ag/AgCl in a potassium borate aqueous solution, which relates with the formation of nanoscale order domains of edge-sharing NiO6 octahedra in the Ni–Bi electrocatalyst. XAFS spectra were measured with variation of the electrode potential from 0.3 up to 1.0 V. The measured absorption peaks suggest that the quantity of NiO6 octahedra increased in correlation with the OER current; however, when the potential was changed downward, the XAFS absorption peak assigned to NiO6 octahedra remained constant, even at the electrode potential for no OER current. This difference implies that the water oxidation catalysis proceeds at the domain edge of NiO6 octahedra. The XAFS technique provides the first successful direct probing of the act...

Block Copolymer Response to Photothermal Stress Fields

Block copolymer materials can be aligned using shear forces; in order to fully exploit this phenomenon for controlling nanoscale order, the coupling between applied forces and molecular properties must be elucidated. We use a photothermal method to generate extreme and controllable thermal and stress fields in thin films of cylinder-forming block copolymers. By studying morphological ordering as a function of time, shear rate, polymer material, molecular weight, and film thickness, we elucidate the critical parameters with respect to efficient ordering. We find that ordering efficiency depends weakly on the block copolymer interaction parameter and strongly on the difference in mechanical response of the two phases. Morphologies can be aligned only when the inverse shear rate is smaller than the material’s relaxation time. Overall, photothermal shear alignment provides an efficient means of ordering and aligning nanoscale morphologies over macroscopic areas, using a surprisingly short (subsecond) shear pulse.

Decoupling Substrate Surface Interactions in Block Polymer Thin Film Self-Assembly

We report a highly predictive approach to capturing the major substrate–polymer interactions that can dominate nanoscale ordering and orientation in block polymer (BP) thin films. Our approach allows one to create designer BP thin films on modified substrates while minimizing the need for extensive parameter space exploration. Herein, we systematically and quantitatively examined the influence of substrate surface energy components (dispersive and polar interactions) on thin film self-assembly, and our analysis demonstrates that although total surface energy plays a dominant role in substrate wetting, individual contributions from the dispersive and polar components of the surface energy influence the composite through-film behavior. Additionally, long-range forces as described by the Hamaker constant are under-recognized factors in thin film assembly and can alter expected wetting behavior by affecting thermodynamic stability. This more inclusive interpretation of surface energy effects, including the Hamaker constant, on BP thin films was supported by studies of interfacial and through-film behavior as gleaned from temporal island/hole measurements via in situ optical microscopy during thermal annealing. The formalism correctly predicted experimental wetting and hole formation sizes over a wide range of substrate surface energies when employing the appropriate relationships based on decoupled dispersive and polar components. Our results indicate a promising and more universal approach for matching desired BP thin film self-assembly with chemically tailored substrate modifications.

Nanoscale Atomic Displacements Ordering for Enhanced Piezoelectric Properties in Lead-Free ABO3 Ferroelectrics.

In situ synchrotron X-ray diffuse scattering and inelastic neutron scattering measurements from a prototype ABO3 ferroelectric single-crystal are used to elucidate how electric fields along a nonpolar direction can enhance its piezoelectric properties. The central mechanism is found to be a nanoscale ordering of B atom displacements, which induces increased lattice instability and therefore a greater susceptibility to electric-field-induced mechanical deformation.

Synthesis and thin-film self-assembly of radical-containing diblock copolymers

Abstract

Spectral Investigations on Cu2+-doped Li2CaAl4(PO4)4F4 Phosphors

Cu2+-doped Li2CaAl4(PO4)4F4 nanophosphor has been synthesized using solid-state reaction method at room temperature. The prepared phosphor is characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), optical absorption, photoluminescence (PL), electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) techniques. From powder XRD pattern, the evaluated average crystallite size is in the order of nanoscale. Morphological studies of prepared sample were analyzed using SEM and TEM. The optical absorption spectrum reveals that Cu2+ enters into the tetragonally distorted octahedral site in the host lattice. Spin-Hamiltonian, crystal field and bonding parameters are evaluated from the EPR spectrum. The PL spectrum of Cu2+-doped Li2CaAl4(PO4)4F4 phosphor gives emission peaks in the UV and blue region. The FT-IR spectrum exhibited bands which are attributed to vibrations of phosphate ions, P–O–H and water molecules.

(Invited) Surface-Mediated Molecular Assembly of Organic Semiconductors for High-Performance Organic Electronics

Microstructure in organic semiconductor thin films has been regarded as the key factor determining the performance of the organic electronics. In case of bottom-contact organic field effect transistors (OFETs) and organic photovoltaics (OPVs), the control of the surface characteristics of the underlying substrates can govern the mesoscale and/or nanoscale ordering of the semiconductor assembled on them. Here, we present various approaches for controlling the growth of organic semiconductors on the gate dielectrics and electrodes to achieve high performance OFETs and OPVs.

Degradation of external quantum efficiency of AlGaN UV LEDs grown by hydride vapor phase epitaxy

AbstractA comparative study of the degradation of HVPE‐grown 360 nm AlGaN/GaN UV and commercially available InGaN/GaN blue LED chips was performed. The common feature of the degradation of these two types of LEDs was found to be the increase of the conductivity of shunt paths under current injection. The paths (shunts) are localized in the extended defects system (EDS). It is proposed that the conductivity increase is due to defect formation under multiphonon carriers recombination in a part of the EDS enriched by Ga or In atoms. This process is accompanied by a local overheating and migration of Ga or In atoms. To increase the lifetime of the AlGaN/GaN UV LEDs to more than 2000 h it is necessary to improve their nano‐structural and nanoscale AlGaN composition ordering. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A Process for Modelling Diffuse Scattering from Disordered Molecular Crystals, Illustrated by Application to Monoclinic 9-Chloro-10-methylanthracene

Diffuse scattering from a crystal contains valuable information about the two-body correlations (related to the nanoscale order) in the material. Despite years of development, the detailed analysis of single crystal diffuse scattering (SCDS) has yet to become part of the everyday toolbox of the structural scientist. Recent decades have seen the pair distribution function approach to diffuse scattering (in fact, total scattering) from powders become a relatively routine tool. However, analysing the detailed, complex, and often highly anisotropic three-dimensional distribution of SCDS remains valuable yet rare because there is no routine method for undertaking the analysis. At present, analysis requires significant investment of time to develop specialist expertise, which means that the analysis of diffuse scattering, which has much to offer, is not incorporated thorough studies of many compounds even though it has the potential to be a very useful adjunct to existing techniques. This article endeavours to outline in some detail how the diffuse scattering from a molecular crystal can be modelled relatively quickly and largely using existing software tools. It is hoped this will provide a template for other studies. To enable this, the entire simulation is included as deposited material.

Nanoscale order and crystallization in nitrogen-alloyed amorphous GeTe

The nanoscale order in amorphous GeTe thin films is measured using fluctuation transmission electron microscopy (FTEM). The order increases upon annealing at 145 °C, which indicates a coarsening of subcritical nuclei. This correlates with a reduction in the nucleation delay time in laser crystallization. A shift in the FTEM peak positions may indicate a transformation in local bonding. In samples alloyed with 12 at. % nitrogen, the order does not change upon annealing, the peak does not shift, and the nucleation time is longer. The FTEM data indicate that nitrogen suppresses the structural evolution necessary for the nucleation process and increases the thermal stability of the material.