Biological Soft Materials

Cucurbit[8]uril-based supramolecular theranostics

Different from most of the conventional platforms with dissatisfactory theranostic capabilities, supramolecular nanotheranostic systems have unparalleled advantages via the artful combination of supramolecular chemistry and nanotechnology. Benefiting from the tunable stimuli-responsiveness and compatible hierarchical organization, host-guest interactions have developed into the most popular mainstay for constructing supramolecular nanoplatforms. Characterized by the strong and diverse complexation property, cucurbit[8]uril (CB[8]) shows great potential as important building blocks for supramolecular theranostic systems. In this review, we summarize the recent progress of CB[8]-based supramolecular theranostics regarding the design, manufacture and theranostic mechanism. Meanwhile, the current limitations and corresponding reasonable solutions as well as the potential future development are also discussed.

Modeling the Temperature-Dependent Size Change of Polydisperse Nano-objects using a Deep Generative Model

Modern microscopy techniques can be used to investigate soft nano-objects at the nanometer scale. However, time-consuming microscopy measurements combined with low numbers of observable polydisperse objects often limit the statistics. We propose a method for identifying the most representative objects from their respective point clouds. These point cloud data are obtained, for example, through the localization of single emitters in super-resolution fluorescence microscopy. External stimuli, such as temperature, can cause changes in the shape and properties of adaptive objects. Due to the demanding and time-consuming nature of super-resolution microscopy experiments, only a limited number of temperature steps can be performed. Therefore, we propose a deep generative model that learns the underlying point distribution of temperature-dependent microgels, enabling the reliable generation of unlimited samples with an arbitrary number of localizations. Our method greatly cuts down the data collection effort across diverse experimental conditions, proving invaluable for soft condensed matter studies.

Regulated Self-Folding in Multi-Layered Hydrogels Considered with an Interfacial Layer

Multi-layered hydrogels consisting of bi- or tri-layers with different swelling ratios are designed to soft hydrogel actuators by self-folding. The successful use of multi-layered hydrogels in this application greatly relies on the precise design and fabrication of the curvature of self-folding. In general, however, the self-folding often results in an undesired mismatch with the expecting value. To address this issue, this study introduces an interfacial layer formed between each layered hydrogel, and this layer is evaluated to enhance the design and fabrication precision. By considering the interfacial layer, which forms through diffusion, as an additional layer in the multi-layered hydrogel, the degree of mismatch in the self-folding is significantly reduced. Experimental results show that as the thickness of the interfacial layer increases, the multi-layered hydrogel exhibits a 3.5-fold increase in its radius of curvature during the self-folding. In addition, the diffusion layer is crucial for creating robust systems by preventing the separation of layers in the muti-layered hydrogel during actuation, thereby ensuring the integrity of the system in operation. This new strategy for designing multi-layered hydrogels including an interfacial layer would greatly serve to fabricate precise and robust soft hydrogel actuators.

Statistics of carrier-cargo complexes

We explore the statistics of assembling soft-matter building blocks to investigate the uptake and encapsulation of cargo particles by carriers engulfing their load. While the such carrier-cargo complexes are important for many applications out of equilibrium, such as drug delivery and synthetic cell encapsulation, we uncover here the basic statistical physics in minimal hard-core-like models for particle uptake. Introducing an exactly solvable equilibrium model in one dimension, we demonstrate that the formation of carrier-cargo complexes can be largely tuned by both the cargo concentration and the carriers' interior size. These findings are intuitively explained by interpreting the internal free space (partition function) of the cargo inside a carrier as its engulfment strength, which can be mapped to an external control parameter (chemical potential) of an additional effective particle species. Assuming a hard carrier membrane, such a mapping can be exactly applied to account for multiple cargo uptake involving various carrier or cargo species and even attractive uptake mechanisms, while soft interactions require certain approximations. We further argue that the Boltzmann occupation law identified within our approach is broken when particle uptake is governed by nonequilibrium forces. Speculating on alternative occupation laws using effective parameters, we put forward a Bose-Einstein-like phase transition associated with polydisperse carrier properties.

Histidine-Containing Amphiphilic Peptide-Based Non-Cytotoxic Hydrogelator with Antibacterial Activity and Sustainable Drug Release

A histidine-based amphiphilic peptide (P) has been found to form an injectable transparent hydrogel in phosphate buffer solution over a pH range from 7.0 to 8.5 with an inherent antibacterial property. It also formed a hydrogel in water at pH = 6.7. The peptide self-assembles into a nanofibrillar network structure which is characterized by high-resolution transmission electron microscopy, field-emission scanning electron microscopy, atomic force microscopy, small-angle X-ray scattering, Fourier-transform infrared spectroscopy, and wide-angle powder X-ray diffraction. The hydrogel exhibits efficient antibacterial activity against both Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli). The minimum inhibitory concentration of the hydrogel ranges from 20 to 100 μg/mL. The hydrogel is capable of encapsulation of the drugs naproxen (a non-steroidal anti-inflammatory drug), amoxicillin (an antibiotic), and doxorubicin, (an anticancer drug), but, selectively and sustainably, the gel releases naproxen, 84% being released in 84 h and amoxicillin was released more or less in same manner with that of the naproxen. The hydrogel is biocompatible with HEK 293T cells as well as NIH (mouse fibroblast cell line) cells and thus has potential as a potent antibacterial and drug releasing agent. Another remarkable feature of this hydrogel is its magnification property like a convex lens.

Changes in the Secondary Structure and Assembly of Proteins on Fluoride Ceramic (CeF3) Nanoparticle Surfaces

Fluoride nanoparticles (NPs) are materials utilized in the biomedical field for applications including imaging of the brain. Their interactions with biological systems and molecules are being investigated, but the mechanism underlying these interactions remains unclear. We focused on possible changes in the secondary structure and aggregation state of proteins on the surface of NPs and investigated the principle underlying the changes using the amyloid β peptide (Aβ_16-20) based on infrared spectrometry. CeF₃ NPs (diameter 80 nm) were synthesized via thermal decomposition. Infrared spectrometry showed that the presence of CeF₃ NPs promotes the formation of the β-sheet structure of Aβ_16-20. This phenomenon was attributed to the hydrophobic interaction between NPs and Aβ peptides in aqueous environments, which causes the Aβ peptides to approach each other on the NP surface and form ordered hydrogen bonds. Because of the coexisting salts on the secondary structure and assembly of Aβ peptides, the formation of the β-sheet structure of Aβ peptides on the NP surface was suppressed in the presence of NH₄⁺ and NO₃^- ions, suggesting the possibility that Aβ peptides were adsorbed and bound to the NP surface. The formation of the β-sheet structure of Aβ peptides was promoted in the presence of NH₄⁺, whereas it was suppressed in the presence of NO₃^- because of the electrostatic interaction between the lysine residue of the Aβ peptide and the ions. Our findings will contribute to comparative studies on the effect of different NPs with different physicochemical properties on the molecular state of proteins.

Probing lipid membrane bending mechanics using gold nanorod tracking

Lipid bilayer membranes undergo rapid bending undulations with wavelengths from tens of nanometers to tens of microns due to thermal fluctuations. Here, we probe such undulations and the membranes' mechanics by measuring the time-varying orientation of single gold nanorods (GNRs) adhered to the membrane, using high-speed dark field microscopy. In a lipid vesicle, such measurements allow the determination of the membrane's viscosity, bending rigidity, and tension as well as the friction coefficient for sliding of the monolayers over one another. The in-plane rotation of the GNR is hindered by undulations in a tension dependent manner, consistent with simulations. The motion of single GNRs adhered to the plasma membrane of living cultured cells similarly reveals the membrane's complex physics and coupling to the cell's actomyosin cortex.

Biohybrid Nanocellulose-Lysozyme Amyloid Aerogels via Electrostatic Complexation

Modern science is increasingly turning to nature for inspiration to design sustainable biomaterials in a smart and effective way. Herein, we describe biohybrid aerogels based on electrostatic complexation between cellulose and proteins-two of the most abundant natural polymers on Earth. The effects of both particle surface charge and particle size are investigated with respect to aerogel properties including the morphology, surface area, stability, and mechanical strength. Specifically, negatively charged nanocellulose (cellulose nanocrystals and cellulose nanofibers) and positively charged lysozyme amyloid fibers (full-length and shortened via sonication) are investigated in the preparation of fibrillar aerogels, whereby the nanocellulose component was found to have the largest effect on the resulting aerogel properties. Although electrostatic interactions between these two classes of charged nanoparticles allow us to avoid the use of any cross-linking agents, the resulting aerogels demonstrate a simple additive performance as compared to their respective single-component aerogels. This lack of synergy indicates that although electrostatic complexation certainly leads to the formation of local aggregates, these interactions alone may not be strong enough to synergistically improve bulk aerogel properties. Nevertheless, the results reported herein represent a critical step toward a broader understanding of biohybrid materials based on cellulose and proteins.

Thermoresponsive Supramolecular Assemblies from Dendronized Amphiphiles To Form Fluorescent Spheres with Tunable Chirality

Balance between self-association of structural units and self-repulsion from crowding-induced steric hindrance accounts for the supramolecular assembly of the amphiphilic entities to form ordered structures, and solvation provides a toolbox to conveniently modulate the assemblies through differential interactions to various structural units. Here we report solvation-modulated supramolecular chiral assembly in aqueous solutions of amphiphilic dendronized tetraphenylethylenes (TPEs) with three-folded dendritic oligoethylene glycols (OEGs) through dipeptide Ala-Gly linkage. These dendronized amphiphiles can form supramolecular spheres with enhanced supramolecular chirality, which is tunable and dependent on solvation. These nanosized spherical aggregates exhibit thermoresponsive behavior, and their cloud point temperatures are dependent on mixed solvent of water and THF. The phase transition temperatures increase with water fractions due to water-driven shifting of OEG moieties from interiors of the aggregates to their peripheries. Furthermore, the thermally induced dehydration and collapse of OEG moieties mediate the reversible aggregation and deaggregation between the spheres, imparting tunable aggregation-induced fluorescent emission (AIE) and supramolecular chirality. Both experimental results and molecular dynamic simulations have highlighted that reversible chirality transformations of the amphiphilic dendronized assemblies mediated by solvation through change solvent quality or thermally dehydration are dependent on the balance between interactions of OEG dendrons with TPE moieties and with the solvent molecules.

Dynamic self-assembly of mannosylated-calix[4]arene into micelles for the delivery of hydrophobic drugs

Carbohydrate-lectin interactions and glycol-molecule-driven self-assembly are powerful yet challenging strategies to create supramolecular nanostructures for biomedical applications. Herein, we develop a modular approach of micellization with a small molecular mannosylated-calix[4]arene synthetic core, CA₄-Man3, to generate nano-micelles, CA₄-Man3-NPs, which can target cancer cell surface receptors and facilitate the delivery of hydrophobic cargo. The oligomeric nature of the calix[4]arene enables the dynamic self-assembly of calix[4]arene (CA₄), where an amphiphile, functionalized with mannose units (CA-glycoconjugates) in the upper rim and alkylated lower rim, afforded the CA₄-Man3-NPs in a controllable manner. The presence of thiourea units between calixarene and tri-mannose moiety facilitated the formation of a stable core with bidentate hydrogen bonds, which in turn promoted mannose receptor targeted uptake and helped in the intracellular pH-responsive release of antineoplastic doxorubicin (Dox). Physiochemical features including the stability of the nanomicelle could circumvent the undesirable leakage of the cargoes, ensuring maximum therapeutic output with minimum off-targeted toxicity. Most importantly, surface-enhanced Raman scattering (SERS) was utilized for the first time to evaluate the critical micelle concentration during the formation, cellular uptake and intracellular drug release. The present study not only provides an architectural design of a new class of organic small molecular nanomicelles but also unveils a robust self-assembly approach that paves the way for the delivery of a wide range of hydrophobic chemotherapeutic drugs.

Growth of Myelin Figures from Parent Multilamellar Vesicles

We examine the formation and growth of isolated myelin figures and microscale multilamellar tubules from isotropic micellar solutions of an anionic surfactant. Upon cooling, surfactant micelles transform into multilamellar vesicles (MLVs) whose contact is found to trigger the unidirectional growth of myelins. While the MLV diameter grows as d_MLV ∝ t^1/2, myelins grow linearly in time as L_M ∝ t¹, with a fixed diameter. Combining time-resolved small-angle neutron scattering (SANS) and optical microscopy, we demonstrate that the microscopic growth of spherical MLVs and cylindrical myelins stems from the same nanoscale molecular mechanism, namely, the surfactant exchange from micelles into curved lamellar structures at a constant volumetric rate. This mechanism successfully describes the growth rate of (nonequilibrium) myelin figures based on a population balance at thermodynamic equilibrium.

Protein-polymer mixtures in the colloid limit: Aggregation, sedimentation, and crystallization

While proteins have been treated as particles with a spherically symmetric interaction, of course in reality, the situation is rather more complex. A simple step toward higher complexity is to treat the proteins as non-spherical particles and that is the approach we pursue here. We investigate the phase behavior of the enhanced green fluorescent protein (eGFP) under the addition of a non-adsorbing polymer, polyethylene glycol. From small angle x-ray scattering, we infer that the eGFP undergoes dimerization and we treat the dimers as spherocylinders with aspect ratio L/D - 1 = 1.05. Despite the complex nature of the proteins, we find that the phase behavior is similar to that of hard spherocylinders with an ideal polymer depletant, exhibiting aggregation and, in a small region of the phase diagram, crystallization. By comparing our measurements of the onset of aggregation with predictions for hard colloids and ideal polymers [S. V. Savenko and M. Dijkstra, J. Chem. Phys. 124, 234902 (2006) and Lo Verso et al., Phys. Rev. E 73, 061407 (2006)], we find good agreement, which suggests that the behavior of the eGFP is consistent with that of hard spherocylinders and ideal polymers.

Self-shaping liquid crystal droplets by balancing bulk elasticity and interfacial tension

Liquid crystal (LC) research is rapidly expanding to include studies of curved and topologically nontrivial structures. Here, we explore the role of the bulk LC elasticity and interfacial free energy under weak thermal stimuli to achieve structural transformations in LC emulsions using two different surfactants. Our method is universal and could be used for any LC material or phase. A theoretical model for transforming LC emulsions into uniform fibers and vice versa is presented. We also show the self-shaping of smectic vesicle structures and monodispersed droplet formation at the nematic–smectic transition, utilizing the LC bulk elasticity. This work shows the potential to obtain the controllable shape of complex curved structures for a constant volume of different LCs and other soft materials.

The shape diversity and controlled reconfigurability of closed surfaces and filamentous structures, universally found in cellular colonies and living tissues, are challenging to reproduce. Here, we demonstrate a method for the self-shaping of liquid crystal (LC) droplets into anisotropic and three-dimensional superstructures, such as LC fibers, LC helices, and differently shaped LC vesicles. The method is based on two surfactants: one dissolved in the LC dispersed phase and the other in the aqueous continuous phase. We use thermal stimuli to tune the bulk LC elasticity and interfacial energy, thereby transforming an emulsion of polydispersed, spherical nematic droplets into numerous, uniform-diameter fibers with multiple branches and vice versa. Furthermore, when the nematic LC is cooled to the smectic-A LC phase, we produce monodispersed microdroplets with a tunable diameter dictated by the cooling rate. Utilizing this temperature-controlled self-shaping of LCs, we demonstrate life-like smectic LC vesicle structures analogous to the biomembranes in living systems. Our experimental findings are supported by a theoretical model of equilibrium interface shapes. The shape transformation is induced by negative interfacial energy, which promotes a spontaneous increase of the interfacial area at a fixed LC volume. The method was successfully applied to many different LC materials and phases, demonstrating a universal mechanism for shape transformation in complex fluids.

Protein morphology drives the structure and catalytic activity of bio-inorganic hybrids

Bio-hybrid materials have received a lot of attention in view of their bio-mimicking nature. One such biomimetic material with catalytic activity are the protein derived floral nanohybrid. Copper phosphate coordinated flakes can be curated to distinct floral morphology using proteins. Structurally two different proteins with similar size and with no known enzymatic activity are used to evaluate the role of protein structure and morphology, on the structure-activity relationship of the developed hybrid nanoflowers. Globular protein BSA and bacterial microcompartment domain protein PduBB' are selected. PduBB' because of self-assembling nature forms extended sheets, whereas BSA lacks specific assembly. The developed hybrid NFs differ in their morphology and also in their mimicry as a biological catalyst. The present investigation highlights the importance of the quaternary structure of proteins in tailoring the structure and function of the h-NFs. The results in this manuscript will motivate and guide designing, engineering and selection of glue material for fabricating biomacromolecule derived biohybrid material to mimic natural enzymes of potential industrial application.

Using reactive dissipative particle dynamics to understand local shape manipulation of polymer vesicles

Biological cells have long been of interest to researchers due to their capacity to actively control their shape. Accordingly, there is significant interest in generating simplified synthetic protocells that can alter their shape based on an externally or internally generated stimulus. To date, most progress has been made towards controlling the global shape of a protocell, whereas less is known about generating a local shape change. Here, we seek to better understand the possible mechanisms for producing local morphological changes in a popular protocell system, the block copolymer vesicle. Accordingly, we have combined Dissipative Particle Dynamics (DPD) and the Split Reactive Brownian Dynamics algorithm (SRBD) to produce a simulation tool that is capable of modeling the dynamics of self-assembled polymer structures as they undergo chemical reactions. Using this Reactive DPD or RDPD method, we investigate local morphological change driven by either the microinjection of a stimulus or an enzymatically-produced stimulus. We find that sub-vesicle-scale morphological change can be induced by either a solvent stimulus that swells the vesicle membrane, or by a reactant stimulus that alters the chemistry of the block polymer in the membrane corona. Notably, the latter method results in a more persistent local deformation than the former, which we attribute to the slower diffusion of polymer chains relative to the solvent. We quantify this deformation and show that it can be modulated by altering the interaction parameter of the parts of the polymer chain that are affected by the stimulus.

The Role of Amylogenic Fiber Aggregation on the Elasticity of a Lipid Membrane

This work presents a systematic study of the swelling behavior of a lecithin lamellar phase incorporating different amounts of the short peptide sequence diphenylalanine (FF). Small- and wide-angle X-ray scattering assays provide relevant information about the structure and elasticity of the lamellar stacking. These data show that important changes occur at the interface of the lipid membrane dependent not only on the peptide content but also on the hydration of the lamellar structure. Multilamellar-to-unilamellar transitions, previously observed for an increasing number of peptides, are now observed to be dependent on the hydration of the lamellar phase. Wide-angle X-ray scattering and electron microscopy observations (TEM) provide experimental evidence of peptide aggregation into long amylogenic fibers. We argue that aggregates that partition in water may become large enough to destabilize the lamellar structure. It is also shown that, for a given peptide concentration, the lamellar structure can be rendered more flexible or more rigid, by tuning the hydration.

DNA nanotweezers for stabilizing and dynamically lighting up a lipid raft on living cell membranes and the activation of T cells

Lipid rafts are generally considered as nanodomains on cell membranes and play important roles in signaling, viral infection, and membrane trafficking. However, the raft hypothesis is still debated with many inconsistencies because the nanoscale and transient heterogeneous raft structure creates difficulties in its location and functional analysis. In the present study, we report a DNA nanotweezer composed of a cholesterol-functionalized DNA duplex that stabilizes transient lipid rafts, which facilitate the further analysis of the raft component and its functions via other spectroscopy tools. The proposed DNA nanotweezer can induce clustering of raft-associated components (saturated lipids, membrane protein and possibly endogenous cholesterol), leading to the T cell proliferation through clustering of a T-cell antigen receptor (TCR). The flexibility of random sequence noncoding DNA provides versatile possibilities of manipulating lipid rafts and activating T cells, and thus opens new ways in a future T cell therapy.

We report a DNA nanotweezer that recruits raft-associated lipids, proteins and possibly endogenous cholesterol on living cell membrane. The DNA nanotweezers could activate T cell proliferation in a nonspecific activation manner.

DNA translocation to giant unilamellar vesicles during electroporation is independent of DNA size

Delivery of naked DNA molecules into living cells via physical disruption of the membrane under electric pulses has potential biomedical applications ranging from gene electro-transfer, electro-chemotherapy, to gene therapy, yet the mechanisms involved in DNA transport remain vague. To investigate the mechanism of DNA translocation across the cell membrane, giant unilamellar vesicles (GUVs) were electroporated in the presence of DNA molecules keeping the size of the DNA molecules as a variable parameter. We experimentally determined the translocation efficiency for each size of the DNA molecule, to compare the results with the existing and conflicting theories of the translocation mechanism i.e. stochastic threading and bulk electrophoresis. We observed that the translocation efficiency is independent of DNA size (ranging from 25-20 000 bp, bp = base pairs), implying that DNA molecules translocate freely across the electro-pores in the lipid membrane in their native polymer conformation, as opposed to unravelling and threading through the electro-pore. Bulk electrophoretic mobility determines the relationship between translocation efficiency and the size of the DNA molecule. This research provides experimental evidence of the mechanistic understanding of DNA translocation across lipid membranes which is essential for devising efficient and predictable protocols for electric field mediated naked DNA delivery.

Tuning the shape anisotropy of loosely bound colloid-like ionic clusters in solution

We characterize the influence of the ionic ratio on the dynamic self-assembly process involving a macrocyclic tetraimidazolium molecular box and small dianionic salts into highly defined, colloid-like ionic clusters in solution, called ionoids.

Phosphorescent cyclometalated iridium(iii) complexes: synthesis, photophysics, DNA interaction, cellular internalization, and cytotoxic activity

Phosphorescent cyclometalated quinoline-appended iridium(iii) complexes undergo rapid cellular internalization and accumulate throughout the cell.

Low Molecular Weight Supramolecular Gels Under Shear: Rheology as the Tool for Elucidating Structure-Function Correlation

Self-healing low molecular weight supramolecular gels (SMGs) represent an emerging class of smart materials, which can closely mimic the complex biological healing process, such as blood clotting, bone repair or wound healing. However, a lack of understanding of the structure-function correlation in the self-assembly process limits their molecular design and subsequent property tuning. The indispensability of a rheological study on supramolecular gels lies in direct transcription of the assembly property to the viscoelastic behavior of the material. This is similarly relevant to healable and non-healable systems. Thus, using rheology as a tool for elucidating structure-function relationships in self-assembled systems has huge potential. This review article will depict a general introduction of rheology in the field of soft matter including SMGs, followed by representative studies with interpretations, and discussion on future challenges. Altogether, this would be an effort, where an in-depth rheological study complemented with a real-time visualization with the help of microscopy, and introduction of other sophisticated real-time experiments, could be a step forward to capture the mystery of self-assembly process.

Structural behaviour and gene delivery in complexes formed between DNA and arginine-containing peptide amphiphiles

We describe in depth the structure of complexes formed between DNA and two classes of arginine-containing peptide amphiphiles, namely, the lipopeptide PRW-C₁₆ (P = proline, R = arginine, W = tryptophan, C₁₆ = C16 : 0 alkyl chain) and the bolaamphiphile RFL₄FR (R = arginine, F = phenylalanine, L = leucine). A combination of X-ray and neutron scattering provided unprecedented insights into the local structure of these complexes. Lipopeptide-based complexes self-assembled into layered structures with large-scale fractal features, hosting DNA in the interstices. Bola-amphiphile scaffolds were characterized by planar structures with DNA strands presumably sandwiched in-between peptide nanotapes. Importantly, complexation did not affect the structural integrity of DNA in either of the two complexes. The bolaamphiphile conjugates displayed high levels of molecular ordering in contrast to the liquid-crystalline features observed in lipopeptide assemblies. Peptide-DNA complexes were assessed for their potential as a means to deliver the reporter vector pEGFP-N1 into SW480 human colon carcinoma cells. Successfully transfected cells expressed green fluorescent protein. The potentiating effect of PRW-C₁₆ on the cellular uptake of ectopic DNA was found to be much greater than that observed with RFL₄FR. In contrast to the bolaamphiphile-based conjugate, the liquid-crystalline nature of the lipopeptide complex is likely to play a key role in DNA release and transfection efficiency since these weakly bound structures require lower energy expenditure during disassembly and load release.

Fluorescent zinc(ii) complexes for gene delivery and simultaneous monitoring of protein expression

Two new zinc(ii) complexes, [Zn(l-His)(NIP)]+(1) and [Zn(acac)2(NIP)](2) (where NIP is 2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, acac = acetyl acetone), have been synthesized and characterized by elemental analysis, UV-vis, fluorescence, IR, 1H NMR and electron spray ionization mass spectroscopies. Gel retardation assay, atomic force microscopy and dynamic light scattering studies show that 1 and 2 can induce the condensation of circular plasmid pBR322 DNA into nanometer size particles under ambient conditions. Treatment of 2 with 5 mM EDTA restored 30% of the supercoiled form of DNA, revealing partial reversibility of DNA condensation. The in vitro transfection experiment demonstrates that the complexes can be used to deliver pCMV-tdTomato-N1 plasmid which expresses red fluorescent protein. The confocal studies show that the fluorescent nature of complexes is advantageous for visualizing the intracellular delivery of metal complexes as well as transfection efficiency using two distinct emission windows.

Self-assembly of amphiphilic anionic calix[4]arenes and encapsulation of poorly soluble naproxen and flurbiprofen

The ability of an anionic calix[4]arene amphiphile to aggregate and to solubilize, as a result, the poorly water-soluble drugs naproxen and flurbiprofen is described.

Photoresponsive supramolecular complexes as efficient DNA regulator

Two supramolecular complexes of trans-1⊂CB[8] and trans-2⊂CB[8] were successfully achieved by the controlled selective complexation process of cucurbit[8]uril (CB[8]) with hetero-guest pair containing azobenzene and bispyridinium moieties in aqueous solution, exhibiting the reversibly light-driven movements of CB[8] upon the photocontrollable isomerization of azophenyl axle components. Significantly, the obtained bistable supramolecular complexes and their corresponding [2]pseudorotaxanes could act as a promising concentrator and cleavage agent to regulate the binding behaviors with DNA molecules.

Designing new symmetrical facial oligothiophene amphiphiles

In this study we designed a new class of symmetrical facial oligothiophene amphiphiles, which could be obtained in fewer steps than for previously reported analogues, but still possess the specific substituent sequence to control their backbone curvature. This novel design allows the late-stage introduction of hydrophilic groups, aiding both purification and ease of structure variation. Following the new synthetic scheme, symmetrical ter- and sexi-thiophenes were synthesized, analysed and their properties were compared to their non-symmetrical analogues. Surprisingly, the self-assembly behaviour in water, aggregate morphologies and photo-physical properties turned out to be significantly different despite the same ratio of hydrophilic and hydrophobic substituents. The new substitution pattern resulted in a drastic decrease of the critical aggregation concentration and an increase of the aggregate size. The symmetrical positioning of the substituents also heavily influenced the photo-physical properties. The changes were observed as large blue shifts in the absorption and emission spectra in water when compared to similar regio-regular oligothiophene amphiphiles.

Alternative FIB TEM sample preparation method for cross-sections of thin metal films deposited on polymer substrates

Transmission electron microscopy (TEM) and focused ion beam (FIB) are proven tools to produce site-specific samples in which to study devices from initial processing to causes for failure, as well as investigating the quality, defects, interface layers, etc. However, the use of polymer substrates presents new challenges, in the preparation of suitable site-specific TEM samples, which include sample warping, heating, charging, and melting. In addition to current options that address some of these problems such as cryo FIB, we add an alternative method and FIB sample geometry that address these challenges and produce viable samples suitable for TEM elemental analysis. The key feature to this approach is a larger than usual lift-out block into which small viewing windows are thinned. Significant largely unthinned regions of the block are left between and at the base of the thinned windows. These large unthinned regions supply structural support and thermal reservoirs during the thinning process. As proof-of-concept of this sample preparation method, we also present TEM elemental analysis of various thin metallic films deposited on patterned polycarbonate, lacquer, and poly-di-methyl-siloxane substrates where the pattern (from low- to high-aspect ratio) is preserved.

Regioisomeric control induced by DABCO coordination to rotatable self-assembled bis- and tetraporphyrin α,γ-cyclic octapeptide dimers

The design and synthesis of two α,γ-cyclic octapeptides decorated with one and two Zn-porphyrin units in their periphery is described. In nonpolar organic solvents the α,γ-cyclic octapeptides quantitatively self-assemble into Zn-bis- or -tetraporphyrin architectures that could act as molecular tweezers. The self-assembly process, however, is not regioselective and affords a mixture of different regioisomers that are involved in chemical exchange processes. The regioisomers with the Zn-porphyrin units positioned in register with respect to each other are proposed to be the less abundant species in the solution mixture. It has been demonstrated that the coordination of 1,4-diazabicyclo[2.2.2]octane (DABCO) to the supramolecular bis- or tetraporphyrin tweezers is an effective way to achieve regioisomeric control of the self-assembled mixture of dimers. Thus, DABCO functions as an external molecular trigger and, when used under strict stoichiometric control with respect to the Zn-porphyrin units, provokes the exclusive formation of self-assembled dimers with a cofacial arrangement of Zn-porphyrin units through the formation of sandwich-type complexes. The use of excess DABCO fragments the sandwich complexes and affords open dimers of high stoichiometry with DABCO molecules axially monocoordinated to the Zn-porphyrin units, probably as a regioisomeric mixture. In the case of Zn-tetraporphyrin tweezers, the ditopic coordination of DABCO at the two binding sites shows a moderate positive cooperativity factor, αP=5. These assemblies have potential applications as light-induced energy and electron-transfer switches regulated by DABCO coordination; such applications would require the introduction of additional chromophores in the cyclic peptide scaffold.