Phototaxis of Oil Droplets Comprising a Caged Fatty Acid Tightly Linked to Internal Convection.

We found that novel sub-millimeter-sized photoactive oil droplets of oleic acid bearing a photolabile protecting group, 2-nitrobenzyl oleate (NBO), in basic water exhibited unidirectional motion toward a UV light source. This unidirectional motion can be explained by anisotropic photolysis on a surface of the NBO droplet with low permeability for UV light. Time-dependent changes of the movement under UV irradiation occurred in a cascade manner (still-standing, induction, and active stages). The velocity of the UV-irradiated droplet in the induction stage was small, but it was accelerated sixteen times by the presence of an inner convection structure, which was created by continued photolysis. This characteristic dynamics, which is derived from a supramolecular machinery system towards the external stimulus, may be similar to the phototaxis of a living cell.

Structure and growth behavior of centimeter-sized helical oleate assemblies formed with assistance of medium-length carboxylic acids.

The nonequilibrium organization of self-assemblies from small building-block molecules offers an attractive and essential means to develop advanced functional materials and to understand the intrinsic nature of life systems. Fatty acids are well-known amphiphiles that form self-assemblies of several shapes. Here, we found that the lengths of helical structures of oleic acid formed in a buffered aqueous solution are dramatically different by the presence or absence of certain amphiphilic carboxylic acids. For example, under the coexistence of a small amount of N-decanoyl-l-alanine, we observed the formation of over 1 centimeter-long helical assemblies of oleate with a regular pitch and radius, whereas mainly less than 100 µm-long helices formed without this additive. Such long helical assemblies are unique in terms of their highly dimensional helical structure and growth dynamics. Results from the real-time observation of self-assembly formation, site-selective small-angle X-ray scattering, high-performance liquid chromatography analysis, and pH titration experiments suggested that the coexisting carboxylates assist in elongation by supplying oleate molecules to a scaffold for oleate helical assembly.

Local electronic properties at organic-metal interfaces: thiophene derivatives on Pt(111).

The valence electronic states of thiophene (TP), 2-thiophenethiol (TT), 2,2'-bithiophene (BTP), and 2,2'-bithiophene-5-thiol (BTT) on Pt(111) were measured by ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) to elucidate how the local electronic properties at the organic-metal interface are altered by the extent of π-conjugation and substituent effects. First-principles calculations using density functional theory (DFT) were used to assign the observed spectra. TP and BTP chemisorb weakly on Pt(111), whereas TT and BTT are strongly bound to Pt(111) through the S atom with the cleavage of the S-H bond, forming a thiolate. In the MAES spectra, weak emission just below the Fermi level (E(F)) was attributed to a chemisorption-induced gap state (CIGS) produced by orbital mixing between the organic species and Pt(111). The formation of CIGS is responsible for a metallic structure at the organic-metal interface. The relative intensities of CIGSs at E(F) were in the order of TP (flat-lying configuration) > TT > TP (inclined configuration), indicating that the spatial distribution of CIGSs is drastically altered by the strength of the organic-metal bond and the adsorption geometry. In other words, TP (flat-lying geometry) and TT serve as good mediators of the extension of the metal wave function at E(F), which would be closely related to charge transport at organic-metal interfaces.

Interplay between magnetism and conductivity derived from spin-polarized donor radicals.

Tutorial review: to achieve molecule-based spintronic devices, an organic conducting magnet that exhibits both conductivity and magnetism in a cooperative manner must be constructed. As a building block for such new materials, a spin-polarized donor radical, which serves as a molecular "spin-filter" in its singly oxidized state, was designed and synthesized. The resistivity of ion radical salts of selenium-substituted, tetrathiafulvalene-based spin-polarized donor radicals decreased substantially in the presence of a magnetic field, thus indicating cooperative conductivity and magnetism.

Evolution of Proliferative Model Protocells Highly Responsive to the Environment.

In this review, we discuss various methods of reproducing life dynamics using a constructive approach. An increase in the structural complexity of a model protocell is accompanied by an increase in the stage of reproduction of a compartment (giant vesicle; GV) from simple reproduction to linked reproduction with the replication of information molecules (DNA), and eventually to recursive proliferation of a model protocell. An encounter between a plural protic catalyst (C) and DNA within a GV membrane containing a plural cationic lipid (V) spontaneously forms a supramolecular catalyst (C@DNA) that catalyzes the production of cationic membrane lipid V. The local formation of V causes budding deformation of the GV and equivolume divisions. The length of the DNA strand influences the frequency of proliferation, associated with the emergence of a primitive information flow that induces phenotypic plasticity in response to environmental conditions. A predominant protocell appears from the competitive proliferation of protocells containing DNA with different strand lengths, leading to an evolvable model protocell. Recently, peptides of amino acid thioesters have been used to construct peptide droplets through liquid-liquid phase separation. These droplets grew, owing to the supply of nutrients, and were divided repeatedly under a physical stimulus. This proposed chemical system demonstrates a new perspective of the origins of membraneless protocells, i.e., the "droplet world" hypothesis. Proliferative model protocells can be regarded as autonomous supramolecular machines. This concept of this review may open new horizons of "evolution" for intelligent supramolecular machines and robotics.

Dependence of single-molecule conductance on molecule junction symmetry.

The symmetry of a molecule junction has been shown to play a significant role in determining the conductance of the molecule, but the details of how conductance changes with symmetry have heretofore been unknown. Herein, we investigate a naphthalenedithiol single-molecule system in which sulfur atoms from the molecule are anchored to two facing gold electrodes. In the studied system, the highest single-molecule conductance, for a molecule junction of 1,4-symmetry, is 110 times larger than the lowest single-molecule conductance, for a molecule junction of 2,7-symmetry. We demonstrate clearly that the measured dependence of molecule junction symmetry for single-molecule junctions agrees with theoretical predictions.

Multitude of morphological dynamics of giant multilamellar vesicles in regulated nonequilibrium environments.

Lipid giant vesicles (GVs) exhibit biologically relevant morphological dynamics such as growth and division under certain conditions without any sophisticated molecular machineries employed by the current organisms. Nonequilibrium conditions are essential for the emergence of dynamic behaviors, which are normally generated by the addition of stimulating materials or by the change of some physical conditions. Therefore, an experimental method that allows flexible control of external conditions is desirable. Here we report a new and simple perfusion device for light microscopy observation that simultaneously realizes such control and tracking of individual phospholipid GVs for the long-term. We apply this device to the study of the morphological dynamics of POPC-based giant multilamellar vesicles (GMVs) under a monotonic and gradual increase of surfactant concentration; thereby we reveal the existence of multiple pathways in the slow solubilization processes, whose frequencies depend on the compositions of GMVs. This perfusion device would offer an unprecedented control of external conditions in the studies of GVs and might help us characterize the physicochemical origins of rich morphological dynamics of living cells.

Colocalization Analysis of Lipo-Deoxyribozyme Consisting of DNA and Protic Catalysts in a Vesicle-Based Protocellular Membrane Investigated by Confocal Microscopy.

The linkage between the self-reproduction of compartments and the replication of DNA in a compartment is a crucial requirement for cellular life. In our giant vesicle (GV)-based model protocell, this linkage is achieved through the action of a supramolecular catalyst composed of membrane-intruded DNA and amphiphilic acid catalysts (C@DNA) in a GV membrane. In this study, we examined colocalization analysis for the formation of the supramolecular catalyst using a confocal laser scanning fluorescence microscope with high sensitivity and resolution. Red fluorescence spots emitted from DNA tagged with Texas Red (Texas Red-DNA) were observed in a GV membrane stained with phospholipid tagged with BODIPY (BODIPY-HPC). To our knowledge, this is the first direct observation of DNA embedded in a GV-based model protocellular membrane containing cationic lipids. Colocalization analysis based on a histogram of frequencies of "normalized mean deviation product" revealed that the frequencies of positively correlated [lipophilic catalyst tagged with BODIPY (BODIPY-C) and Texas Red-DNA] were significantly higher than those of [BODIPY-HPC and Texas Red-DNA]. This result demonstrates the spontaneous formation of C@DNA in the GV membrane, which serves as a lipo-deoxyribozyme for producing membrane lipids from its precursor.

Influence of magnetic field upon the conductance of a unicomponent crystal of a tetrathiafulvalene-based nitronyl nitroxide.

A spin-polarized donor, BTBN, which is a dibromotetrathiafulvalene derivative containing a nitronyl nitroxide group in a cross-conjugated manner, was prepared. Upon hole injection from an electrode, the neutral microcrystals of BTBN exhibited nonlinear I-V characteristics that were interpreted in terms of the space-charge-limited conduction (SCLC) mechanism. Moreover, the resistance of BTBN decreased upon application of a magnetic field below 30 K and exhibited a giant negative magnetoresistance of (R(H) - R(0))/R(0) = -76% at 2 K under 5 T. These results show that the transport of carriers in the neutral unicomponent radical crystal can be controlled by the external magnetic field. These findings are important as a basis for developing molecule-based spin electronic devices.

Direct observation of arylnitrene formation in the photoreaction of arylazide crystals.

Seven crystal structures of arylazides, 2-azidobiphenyl (2), 4-(4-azidophenyl)butanoic acid (3), 3-azidobenzoic acid (4), N-(4-azidophenyl)acetamide (5), 2,4,6-trichlorophenyl azide (6), 2,5-dibromophenyl azide (7) and 2,4,6-tribromophenyl azide (8), have been analyzed by X-rays. When the crystals were irradiated with UV light at ≃ 80 K, only 2-azidobiphenyl gradually changed its cell dimensions with the retention of the single-crystal form. The crystal structure after photo-irradiation was analyzed by X-rays under the same conditions as those before photo-irradiation. Approximately 20% of the 2-azidobiphenyl molecule was converted to the triplet 2-biphenylnitrene and dinitrogen molecules. The existence of the triplet nitrene was confirmed by ESR and IR measurements. Although the structure of dinitrogen was clearly determined, the nitrene structure was obscure because the nitrene produced was almost superimposed on the original 2-azidobiphenyl. The other six crystals were non-reactive or easily broken when they were exposed to UV light. The different reactivity between 2-azidobiphenyl and the other compounds was successfully explained by the reaction cavity of the azido group.

Environment-Sensitive Intelligent Self-Reproducing Artificial Cell with a Modification-Active Lipo-Deoxyribozyme.

As a supramolecular micromachine with information flow, a giant vesicle (GV)-based artificial cell that exhibits a linked proliferation between GV reproduction and internal DNA amplification has been explored in this study. The linked proliferation is controlled by a complex consisting of GV membrane-intruded DNA with acidic amphiphilic catalysts, working overall as a lipo-deoxyribozyme. Here, we investigated how a GV-based artificial cell containing this lipo-deoxyribozyme responds to diverse external and internal environments, changing its proliferative dynamics. We observed morphological changes (phenotypic expression) in GVs induced by the addition of membrane precursors with different intervals of addition (starvation periods). First, we focused on a new phenotype, the "multiple tubulated" form, which emerged after a long starvation period. Compared to other forms, the multiple tubulated form is characterized by a larger membrane surface with a heavily cationic charge. A second consideration is the effect of the chain length of encapsulated DNA on competitive proliferation. The competitive proliferation among three different species of artificial cells containing different lengths of DNA was investigated. The results clearly showed a distinct intervention in the proliferation dynamics of the artificial cells with each other. In this sense, our GV-based artificial cell can be regarded as an intelligent supramolecular machine responding to external and internal environments, providing a new concept for developing molecular machines and robotics.

Self-propelled oil droplets consuming "fuel" surfactant.

A micrometer-sized oil droplet of 4-octylaniline containing 5 mol % of an amphiphilic catalyst exhibited a self-propelled motion, producing tiny oil droplets, in an aqueous dispersion of an amphiphilic precursor of 4-octylaniline. The tiny droplets on the surface of the self-propelled droplet were conveyed to the posterior surface and released to the aqueous solution. Thus the persistent movement becomes possible in this chemical system, because the processing of chemical energy to mechanical movement proceeds by consuming exogenous fuel, not consuming the oil droplet itself. The mechanism of the unidirectional motion is hypothesized in terms of an asymmetric interfacial tension around the surface of the oil droplet.

Heat-resistant DNA tile arrays constructed by template-directed photoligation through 5-carboxyvinyl-2'-deoxyuridine.

Template-directed DNA photoligation has been applied to a method to construct heat-resistant two-dimensional (2D) DNA arrays that can work as scaffolds in bottom-up assembly of functional biomolecules and nano-electronic components. DNA double-crossover AB-staggered (DXAB) tiles were covalently connected by enzyme-free template-directed photoligation, which enables a specific ligation reaction in an extremely tight space and under buffer conditions where no enzymes work efficiently. DNA nanostructures created by self-assembly of the DXAB tiles before and after photoligation have been visualized by high-resolution, tapping mode atomic force microscopy in buffer. The improvement of the heat tolerance of 2D DNA arrays was confirmed by heating and visualizing the DNA nanostructures. The heat-resistant DNA arrays may expand the potential of DNA as functional materials in biotechnology and nanotechnology.

A sustainable self-reproducing liposome consisting of a synthetic phospholipid.

A novel phosphoric membrane lipid (phospholipid) bearing an oleyl group as one of the hydrophobic chains formed a liposome with a thin lamella in water. Since the anionic membrane of pre-existing liposomes acted as a catalytic surface in phosphate buffer, membrane lipids could be generated from their precursor in an autocatalytic manner without the inclusion of catalytic amphiphiles in the liposome. The morphological changes of this anionic liposome were monitored both by flow cytometry and optical microscopy, and it was found that the liposomes deformed into a budding shape, followed by division, after the addition of a membrane precursor. Hence, this anionic monocomponent liposome could be regarded as a sustainable self-reproducing system. This liposome was also able to provide a reaction cavity for enzymatic reactions, such as DNA amplification by a polymerase chain reaction.

DNA Length-dependent Division of a Giant Vesicle-based Model Protocell.

DNA is an essential carrier of sequence-based genetic information for all life today. However, the chemical and physical properties of DNA may also affect the structure and dynamics of a vesicle-based model protocell in which it is encapsulated. To test these effects, we constructed a polyethylene glycol-grafted giant vesicle system capable of undergoing growth and division. The system incorporates a specific interaction between DNA and lipophilic catalysts as well as components of PCR. We found that vesicle division depends on the length of the encapsulated DNA, and the self-assembly of an internal supramolecular catalyst possibly leads to the direct causal relationship between DNA length and the capacity of the vesicle to self-reproduce. These results may help elucidate how nucleic acids could have functioned in the division of prebiotic protocells.

Generation of a triplet diradical from a donor-acceptor cross conjugate upon acid-induced electron transfer.

Enhancement of the electron acceptor ability of a para-quinodiimine unit by double protonation leads to the proton-induced intramolecular electron transfer from the donor unit to the cross-conjugated acceptor, giving rise to ground state triplet diradical reversibly.

Observations of cellular responses to diamagnetic forces acting on cell components.

The magnetooptical measurements of the properties of living cells have a potentially large impact on cellular engineering and biotechnology because the noninvasive approach to applying magnetic fields on cells enables the detection of the dynamics of intracellular components under natural conditions. In this study, we examine a magnetooptical response in smooth muscle cells exposed to a vertical magnetic field of 5 T. The time course of the linearly polarized light transmittance of cells showed both a gradual decrease and fluctuations during exposure at 5 T. Real-time observations of smooth muscle cells and giant rodlike vesicles revealed that magnetic fields cause morphological changes in the cells and vesicles. In addition, results of the optical transmittance measurement of a fish scale indicate that cellular or tissue components are diamagnetically reoriented by magnetic fields.

Photo-triggered recognition between host and guest compounds in a giant vesicle encapsulating photo-pierceable vesicles.

Here, we used centrifugal precipitation to construct a giant vesicle (GV) encapsulating smaller giant vesicles (GV-in-GV) which comprises a photo-resistant outer GV and a photo-pierceable inner GV; the outer GV contained a fluorescent probe (SYBR Green I) in its inner water pool, and the inner GV contained double-stranded DNA (dsDNA) in its inner water pool. The phospholipid membrane of the inner GV was made photo-pierceable by inclusion of ca. 15mol% of a caged phospholipid in its membrane. Immediately after exposure of the GV-in-GVs to UV irradiation, strong fluorescence was detected in the inner water pool of the outer GV, indicating that dsDNA had been released from the inner GV and had complexed with the fluorescent probe. These dynamics can be recognized as a macroscopic representation of the molecular level function of a caged compound.

Study on structural changes in supramolecular assemblies composed of amphiphilic nicotinamide and its dihydronicotinamide derivative by flow cytometry.

Flow cytometric analysis revealed that the redistribution of components of a hybrid vesicular system composed of amphiphilic nicotinamide and its reduced form occurred associated with the emergence of nonlamellar aggregates that emitted an enhanced blue emission together with a green emission due to exciplex formation.

DNA polymerization on the inner surface of a giant liposome for synthesizing an artificial cell model.

We have designed a new artificial cell model consisting of a giant liposome, an enzyme, and DNA conjugated with a cholesterol tag by a poly(ethylene glycol) spacer to characterize the model system. The cholesterol tag of the conjugated molecule was anchored to the inner surface of the giant liposome and the single-stranded DNA unit hybridized with a 100-mer template DNA that was added to the water pool inside the liposome. We found that the DNA unit acted as a primer, DNA polymerization proceeded on the inner surface of the liposome. This reaction was a key step of our cell model. Production of a full-length strand was proved by selective cleavage of the polymerized DNA by a restriction enzyme.