"Clickable" polymersomes

Polymersomes, composed of amphiphilic polystyrene-block-poly(acrylic acid) (PS-b-PAA), with the periphery being covered with azide groups, were used for further functionalization using "click" chemistry.     

Cascade Reactions in Multicompartmentalized Polymersomes

Enzyme‐filled polystyrene‐b‐poly(3‐(isocyano‐L ‐alanyl‐aminoethyl)thiophene) (PS‐b‐PIAT) nanoreactors are encapsulated together with free enzymes and substrates in a larger polybutadiene‐b‐poly(ethylene oxide) (PB‐b‐PEO) polymersome, forming a multicompartmentalized structure, which shows structural resemblance to the cell and its organelles. An original cofactor‐dependent three‐enzyme cascade reaction is performed, using either compatible or incompatible enzymes, which takes place across multiple compartments.     

Drug-like inhibitors of protein-protein interactions: a structural examination of effective protein mimicry

Protein-protein interactions represent targets for drug discovery that are highly relevant in a biological sense, but have proven difficult in a practical sense. Nevertheless, there have been recent successes in discovering drug-like small molecule inhibitors of protein-protein systems. To build on this progress, it is worth analyzing successful cases to understand at a molecular level the strategies by which these compounds effectively interfere with protein-protein pairing. A commonly observed situation is one wherein the small molecule acts as a direct mimic of one of the protein partners. This review focuses exclusively on cases where this strategy is employed, and examines the structural characteristics of the binding sites and the conformational attributes of the small molecule ligands. Common traits shared among these successful examples are identified, and formulated into potentially useful guidance for drug discovery efforts within this target class.     

Recognition-induced polymersomes: structure and mechanism of formation

Random polystyrene copolymers grafted with complementary recognition elements were combined in chloroform producing vesicular aggregates, that is, recognition-induced polymersomes (RIPs). Reflection interference contrast microscopy (RICM) in solution, coupled with optical microscopy (OM) and atomic force microscopy (AFM) on solid substrates, were used to determine the wall thickness of the RIPs. Rather than a conventional mono- or bilayer structure (approximately 10 or approximately 20 nm, respectively) the RIP membrane was 43+/-7 nm thick. Structural arrangement of the polymer chains on the RIP wall were characterized by using angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The interior portion of the vesicle membrane was found to be more polar, containing more recognition units, than the exterior part. This gradient suggests that a rapid self-sorting of polymers takes place during the formation of RIPs, providing the likely mechanism for vesicle self-assembly.     

Synthetic polyion-counterion transport systems in polymersomes and gels

Transport across the membranes of polymersomes remains difficult in part due to the great thickness of the polymer bilayers. Here, we report that dynamic polyion-counterion transport systems are active in fluorogenic polymersomes composed of poly(dimethylsiloxane)-b-poly(2-methyloxazoline) (PDMS-PMOXA). These results suggest that counterion-activated calf-thymus DNA can act as cation carrier that moves not only across lipid bilayer and bulk chloroform membranes but also across the "plastic" membranes of polymersomes. Compared to egg yolk phosophatidylcholine (EYPC) lipsosomes, activities and activator scope in PDMS-PMOXA polymersomes are clearly reduced. Embedded in agar gel matrices, fluorogenic PDMS-PMOXA polymersomes respond reliably to polyion-counterion transporters, with high contrast, high stability and preserved selectivity. Compared to standard EYPC liposomes, it cannot be said that PDMS-PMOXA polymersomes are better. However, they are different, and this difference could be interesting for the development of sensing devices.     

Biocompatible functionalization of polymersome surfaces: a new approach to surface immobilization and cell targeting using polymersomes

Vesicles assembled from amphiphilic block copolymers represent promising nanomaterials for applications that include drug delivery and surface functionalization. One essential requirement to guide such polymersomes to a desired site in vivo is conjugation of active, targeting ligands to the surface of preformed self-assemblies. Such conjugation chemistry must fulfill criteria of efficiency and selectivity, stability of the resulting bond, and biocompatibility. We have here developed a new system that achieves these criteria by simple conjugation of 4-formylbenzoate (4FB) functionalized polymersomes with 6-hydrazinonicotinate acetone hydrazone (HyNic) functionalized antibodies in aqueous buffer. The number of available amino groups on the surface of polymersomes composed of poly(dimethylsiloxane)-block-poly(2-methyloxazoline) diblock copolymers was investigated by reacting hydrophilic succinimidyl-activated fluorescent dye with polymersomes and evaluating the resulting emission intensity. To prove attachment of biomolecules to polymersomes, HyNic functionalized enhanced yellow fluorescent protein (eYFP) was attached to 4FB functionalized polymersomes, resulting in an average number of 5 eYFP molecules per polymersome. Two different polymersome-antibody conjugates were produced using either antibiotin IgG or trastuzumab. They showed specific targeting toward biotin-patterned surfaces and breast cancer cells. Overall, the polymersome-ligand platform appears promising for therapeutic and diagnostic use.     

Polymersomes with ionic liquid interiors dispersed in water

We describe polymersomes with ionic liquid interiors dispersed in water. The vesicles are prepared via a simple and spontaneous migration of poly(butadiene-b-ethylene oxide) (PB-PEO) block copolymer vesicles from a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), to water at room temperature. As PB is insoluble in both water and [EMIM][TFSI] and PEO is well solvated in both media, the vesicles feature a PB membrane with PEO brushes forming both interior and exterior coronas. The robust and stable PB-PEO vesicles migrate across the liquid-liquid interface with their ionic liquid interiors intact and form a stabilized aqueous dispersion of vesicles enclosing microscopic ionic liquid pools. The nanostructure of the vesicles with ionic liquid interiors dispersed in water is characterized by direct visualization using cryogenic transmission electron microscopy. Upon heating, the vesicles can be quantitatively transferred back to [EMIM][TFSI], thus enabling facile recovery. The reversible transport capability of the shuttle system is demonstrated by the use of distinct hydrophobic dyes, which are selectively and simultaneously loaded in the vesicle membrane and interior. Furthermore, the fluorescence of the loaded dyes in the vesicles enables probing of the microenvironment of the vesicular ionic liquid interior through solvatochromism and direct imaging of the vesicles using laser scanning confocal microscopy. This vesicle system is of particular interest as a nanocarrier or nanoreactor for reactions, catalysis, and separations using ionic liquids.     

Action of phorbol esters in cell culture: mimicry of transformation, altered differentiation, and effects on cell membranes.

The carcinogenic process is usually multifactor in its causation and multistep in its evolution. It is likely that entirely different molecular mechanisms underlie the many steps in this process. In contrast to initiating carcinogens, the action of the tumor-promoting phorbol esters does not appear to involve covalent binding to cellular DNA and they are not mutagenic. Recent studies in cell culture have revealed two interesting biologic effects of the phorbol esters and related macrocyclic plant diterpenes. The first is that at nanomolar concentrations they induce several changes that resemble those seen in cells transformed by chemical carcinogens or tumor viruses. These include altered morphology and increased saturation density, altered cell surface fucose-glycopeptides, decrease in the LETS protein, increased transport of deoxyglucose, and increased levels of plasminogen activator and ornithine decarboxylase. In transformed cells exposed to phorbol esters the expression of these features is further accentuated. Phorbol esters do not induce normal cells to grow in agar but they do enhance the growth in agar of certain transformed cells. The second effect of the phorbol esters is inhibition of terminal differentiation. This effect extends to a variety of programs of differentiation and is reversible when the agent is removed. With certain cell culture systems induction of differentiation, rather than inhibition, is observed. Both the transformation mimetic and the differentiation effects are exerted by plant diterpenes that have tumor-promoting activity but not by congeners that lack such activity. The primary target of phorbol esters appears to be the cell membrane. Early membrane-related effects include enhanced uptake of 2-deoxyglucose and other nutrients, altered cell adhesion, induction of arachidonic acid release and prostaglandin synthesis, inhibition of the binding of epidermal growth factor to cell surface receptors, altered lipid metabolism, and modifications in the activities of other cell surface receptors. A model of "two stage" carcinogenesis encompassing the known molecular and cellular effects of initiating carcinogens and tumor promoters is presented. According to this model, initiating carcinogens induce stable alterations in the cellular genome but these are not manifested until tumor promoters modulate programs of gene expression and induce the clonal outgrowth of the initiated cell.     

Porphyrin Containing Polymersomes with Enhanced ROS Generation Efficiency: In Vitro Evaluation

Porphyrins are molecules possessing unique photophysical properties making them suitable for application in photodynamic therapy. The incorporation of porphyrins into natural or synthetic nano‐assemblies such as polymersomes is a strategy to improve and prolong their therapeutic capacities and to overcome their limitations as therapeutic and diagnostic agents. Here, 5,10,15,20‐tetrakis(1‐(6‐ethoxy‐6‐oxohexyl)‐4‐pyridin‐1‐io)‐21H,23H‐porphyrin tetrabromide porphyrin is inserted into polymersomes in order to demonstrate that the encapsulation enhances its ability to generate highly reactive singlet oxygen (¹O₂) upon irradiation in vitro. The photoactivation of the free and polymersome‐encapsulated porphyrin is evaluated by electron spin resonance and cell viability assays on three different mammalian cell lines. The results indicate that by encapsulating the porphyrin, a controlled ROS delivery within the cells is achieved, at the same time avoiding side effects such as dark toxicity, non‐specific porphyrin release and over time decreased activity in vitro. This work focuses on showing a not‐toxic model system for modern therapeutic nanomedicine, which works under mild irradiation and dosage conditions.     

Protein-based materials,toward a new level of structural control

Through billions of years of evolution nature has created and refined structural proteins for a wide variety of specific purposes. Amino acid sequences and their associated folding patterns combine to create elastic, rigid or tough materials. In many respects, nature's intricately designed products provide challenging examples for materials scientists, but translation of natural structural concepts into bio-inspired materials requires a level of control of macromolecular architecture far higher than that afforded by conventional polymerization processes. An increasingly important approach to this problem has been to use biological systems for production of materials. Through protein engineering, artificial genes can be developed that encode protein-based materials with desired features. Structural elements found in nature, such as beta-sheets and alpha-helices, can be combined with great flexibility, and can be outfitted with functional elements such as cell binding sites or enzymatic domains. The possibility of incorporating non-natural amino acids increases the versatility of protein engineering still further. It is expected that such methods will have large impact in the field of materials science, and especially in biomedical materials science, in the future.     

Challenge toward structural complexity using asymmetric catalysis: target-oriented development of catalytic enantioselective Diels-Alder reaction

A new method for the catalytic enantioselective Diels-Alder reaction using polysubstituted silyl enol ethers as dienes is described. High enantioselectivity (up to 92% ee) was produced using a catalyst generated from FeBr(3) and AgSbF(6) in a 1:2 ratio and aryl-pybox (aryl = Ph or p-ethoxyphenyl). This reaction should facilitate the enantioselective synthesis of polycyclic acylphloroglucinols such as hyperforin or garsubellin A, which are currently of interest from synthetic and medicinal points of view.     

Insulated copper(I) "wires": structural variations and photoluminescence

An unprecedented "molecular wire" type of structure for the copper(I) carboxylate family has been synthesized by utilizing copper-copper interactions and controllable switch of copper-oxygen interactions. Several modifications of the same complex, copper(I) 2,4,6-triisopropylbenzoate, have been isolated to allow evaluation of the structural variation effects on photoluminescent behavior.     

Mastering a double emulsion in a simple co-flow microfluidic to generate complex polymersomes

We show that the production and the geometrical shape of complex polymersomes can be predicted by varying the flow rates of a simple microdevice using an empirical law which predicts the droplet size. This device is constituted of fused silica capillaries associated with adjusted tubing sleeves and T-junctions. Studying the effect of several experimental parameters, double emulsions containing a controlled number of droplets were fabricated. First, this study examines the stability of a jet in a simple confined microfluidic system, probing the conditions required for droplets production. Then, multicompartmental polymersomes were formed, controlling flow velocities. In this work, poly(dimethylsiloxane)-graft-poly(ethylene oxide) (PDMS-g-PEO) and poly(butadiene)-block-poly(ethyleneoxide) (PBut-b-PEO) amphiphilic copolymers were used and dissolved in chloroform/cyclohexane mixture. The ratio of these two solvents was adjusted in order to stabilize the double emulsion formation. The aqueous suspension contained poly(vinyl alcohol) (PVA), limiting the coalescence of the droplets. This work constitutes major progress in the control of double emulsion formation in microfluidic devices and shows that complex structures can be obtained using such a process.     

Stabilizing heteroatom-centered 16-vertex group 11 tetrahedral architectures: Bonding and structural considerations toward versatile endohedral species

Density functional theory (DFT) calculations were carried out on a series of clusters made of a centered tetrahedral 16-atom superatomic cage having 20 or 18 jellium electrons (je) and structurally related to [Au₂₀], namely [X@M₁₆] (M = group 11; X = group 2, 4, 12, 14 element). Such species provide further information of how two different electron counts offer a more preferred endohedral situation for specific group elements. Calculations show that the encapsulated atom provides supplementary orbitals to stabilize the bonding M₁₆ MO's. Different favored electron counts are found depending on the nature of the encapsulated atom, as observed by the formation of 20-je species when encapsulating a group 14 element and 18-je species when encapsulating a group 2 element. In addition, the capabilities to enable reactive sites along the cage structure are found via the formation of σ holes at the coinage-metal edges, as shown by their electrostatic potential surface. Such naked species, which constitute an interesting addition to libraries of examples as small models for doped M(111) surfaces of fcc metals, reveal that different superatomic electronic configurations can favor the encapsulation of certain group elements. These results can guide further design of endohedral species.     

Cyanine Polymersomes Inbreathe Gas Signaling Molecule: SO2-Driven Bilayer Tubular Deformation for Transmembrane Traffic Regulation

Fabricating nanoscale assemblies that can respond to gas signaling molecules has emerged as a field of growing interest owing to their unique biomedical applications in gas-guided delivery and gas therapeutics. Yet, among a variety of endogenous gaseous biosignals, exploiting sulfur dioxide (SO₂) as a cue for controllable self-assembly remains elusive, despite its crucial two-sided roles both in physiology and pathology. Here we show a SO₂-responsive polymersome system assembled from a novel class of cyanine-containing block copolymers. By intake of SO₂ gas, the tautomerism of cyanine drives such vesicles to continuously deform, and change into long nanotubes through axial stretching and anisotropic extrusion of the membranes. Unexpectedly, during this order-to-order phase transition, their membranes manifest well SO₂-dose-dependent permselectivity, which allows the cargos of different sizes loaded therein to be selectively transferred across the bilayers. This study would inspire us to better understand and mimic the function of gas signaling molecules in shifting biomembrane shape and managing transmembrane traffic.     

Structural change in Li and Na aluminophosphate glasses: evidence of a "structural mixed alkali effect"

The short- and long-range structure of a series of single and mixed aluminophosphate glasses with the general composition [xNa(2)O (46 - x)Li(2)O], [yAl(2)O(3) (54 - y)P(2)O(5)] is analyzed using (31)P and (27)Al magic-angle spinning (MAS) NMR as well as small-angle X-ray scattering. These series of glasses allow analyzing both the effect of alumina incorporation in these glasses, for small alumina content (y = 0, 4, 8), and the structural changes associated with the so-called mixed alkali effect (x = 0, 11.5, 23, 34.5, 46). Our results indicate that aluminum is mainly octahedrally coordinated in these glasses and that there is most likely some segregation of the Al(OP)(6) species. In the pure phosphate glasses, we observe a "classical" continuous variation of the structural properties with the relative alkali content, but in the aluminophosphate, both local and long-range structural results reveal for the first time some nonlinear change as a function of the relative alkali content.     

A structural remedy toward bright dipolar fluorophores in aqueous media

The donor–acceptor (D–A) type dipolar fluorophores, an important class of luminescent dyes with two-photon absorption behaviour, generally emit strongly in organic solvents but poorly in aqueous media. To understand and enhance the poor emission behaviour of dipolar dyes in aqueous media, we undertake a rational approach that includes a systematic structure variation of the donor, amino substituent of acedan, an important two-photon dye. We identify several factors that influence the emission behaviour of the dipolar dyes in aqueous media through computational and photophysical studies on new acedan derivatives. As a result, we can make acedan dyes emit bright fluorescence under one- and two-photon excitation in aqueous media by suppressing the liable factors for poor emission: 1,3-allylic strain, rotational freedom, and hydrogen bonding with water. We also validate that these findings can be generally extended to other dipolar fluorophores, as demonstrated for naphthalimide, coumarin and (4-nitro-2,1,3-benzoxadiazol-7-yl)amine (NBD) dyes. The new acedan and naphthalimide dyes thus allow us to obtain much brighter two-photon fluorescent images in cells and tissues than in their conventional forms. As an application of these findings, a thiol probe is synthesized based on a new naphthalimide dye, which shows greatly enhanced fluorescence from the widely used N,N-dimethyl analogue. The results disclosed here provide essential guidelines for the development of efficient dipolar dyes and fluorescence probes for studying biological systems, particularly by two-photon microscopy.