Masatoshi Kanesato

Reversible transformation between rings and coils in a dynamic hydrogen-bonded self-assembly.

Several proteins, such as tobacco mosaic virus coat protein and the beta protein of the bacteriophage lambda, are known to exhibit unique dynamic self-organization processes involving ring-shaped and extended helical nanostructures triggered by chemical stimuli. However, transformation of rings into coils as observed in biological assemblies has never been realized with synthetic molecular building blocks. Oligo(p-phenylenevinylene) functionalized on one end with barbituric acid and on the other end with aliphatic tails self-organizes in aliphatic solvents to form nanorings through hydrogen-bonding and pi-stacking interactions. Upon an increase in concentration, the nanorings transform into rodlike nanostructures, which are considered to be formed through helically coiled objects consisting of quasi-one-dimensional fibers.

Odd–even effect and metal induced structural convergence in self-assembled monolayers of bipyridine derivatives

Scanning tunneling microscopy (STM) observations reveal that bipyridine derivatives which exhibit various two-dimensional structures due to the odd-even chain length effect are converged into a lamellar structure upon metal coordination.

Bipyridine derivatives at a solid/liquid interface: effects of the number and length of peripheral alkyl chains.

Bipyridine derivatives (bpys) with various number and length of peripheral alkyl chains (with carbon numbers of n = 11-17) were synthesized, and their self-assembled monolayers were observed by scanning tunneling microscopy (STM) at a 1-phenyloctane/highly oriented pyrolytic graphite (HOPG) interface. The effects of the number, the substitution position, and the length of alkyl chains on the two-dimensional structures were systematically studied. Bpys substituted by a single alkyl chain in the p-position on each side adopted an almost linear form with zigzag-type alignment of the pi-conjugated unit, whereas, in the case of m-substitution, the bpys showed Z-shaped morphology with interdigitated alkyl chains. In both cases, no odd-even alkyl chain length effects were observed. The bpys with double alkyl chains at m- and p-positions displayed odd-even alkyl chain effects, suggesting that the formation of two-dimensional structure is dominated by the interactions between alkyl chains. Bpys with triple alkyl chains at o-, m-, and p-positions also showed odd-even alkyl chain effects, but only for the higher number of carbon atoms in the alkyl chain unit (n = 14-17). These results indicate that concerted intermolecular interactions of the alkyl chain unit introduce the odd-even chain length effect on the self-assembled two-dimensional structure. After coordination of PdCl(2), odd-even effects were quenched, and bpys were converged into the same lamellar structure, in which the molecules are almost linear. All the structural differences due to the odd-even alkyl chain length effect were explained in terms of intermolecular and molecule-substrate interactions.

Efficient biosensor interfaces based on space-controlled self-assembled monolayers.

In this paper we demonstrate control over the spacing of surface-modifying probe molecules through the use of labile dendron spacers. During this process, anchor molecules are first adsorbed to a surface, with dendron modifiers attached. Steric interactions of the bulky dendrons control the density of anchor molecules bound to the surface. The dendron branches are subsequently detached from the anchor molecules, and the anchors are chemically modified with probe molecules, resulting in a surface with controlled spacing between probe molecules. Control over this spacing is important when the probe size is small in comparison with the target molecule. This importance is demonstrated for the binding of protein (streptavidin) targets to the probe (biotin) surface. The effect of probe space control on the efficiency of target capture is evaluated by examining the binding of streptavidin to thiolated biotin for a series of mixed monolayers. Surface modification is monitored by Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS). The relative concentration of probe molecules at the surface is measured using X-ray photoelectron spectroscopy (XPS) measurements. Thiolated-biotin surfaces with optimized spacing show an increased capture efficiency for streptavidin relative to surfaces with nonoptimal or no control over probe spacing, as measured by surface plasmon resonance (SPR) spectroscopy. These results are of potential significance for the optimization and fabrication of micro- and nanoarrays used in chemical and biochemical measurements.

The architecture of dinuclear Ni and Cu complexes: twisted and parallel forms controlled by the self-assembly of Schiff base ligands

Novel dinuclear complexes were synthesized through the self-assembly of macrocyclic Schiff base ligands and either nickel(II) or copper(II) ions. X-Ray structural analysis revealed that the complexes had either a double helix (twisted) structure in which each atom had a distorted square-planar coordination or a non-helical (parallel) structure in which the metals had octahedral coordination. The helical complexes were rather unusual in that their helicity originated not in the coordination centre, but mainly in the linker moieties in the ligand. Several factors influencing the formation of the helical structure are discussed.

Effect of Phase Structure on Enzymatic Degradation in Poly(l-lactide)/Atactic Poly(3-hydroxybutyrate) Blends with Different Miscibility

Thin films of poly(L-lactide) (PLLA)/atactic poly(3-hydroxybutyrate) (ataPHB) blends with different miscibility were prepared and characterized by using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The DSC analysis suggested that the blend thin films exhibited different phase structures, such as miscible, partially miscible, and immiscible depending on the blending ratio as well as molecular weight of ataPHB component. The different miscibility was further confirmed by the surface morphological observation by AFM. Both the immiscible and partially miscible blends of PLLA/ataPHB revealed the formation of phase-separated morphology of PLLA and ataPHB components, whereas the homogeneous surface morphology was observed for the miscible blend. On the basis of the changes in the depth profile from the surface level of the thin films, the enzymatic degradation rates of the PLLA and ataPHB domains were determined in the presence of either PHB depolymerase or proteinase K, respectively. The erosion rate of PLLA/ataPHB blends was strongly dependent on the blend composition and the degree of dispersion of the two components. The enzymatic degradation behaviors were discussed in terms of phase structure, molecular mobility, and retardation effect of the components in the blends.

Interaction Force of Chitin-Binding Domains onto Chitin Surface

Interaction force of chitin-binding domains (ChBD1 and ChBD2) from a thermostable chitinase onto chitin surface was directly measured by atomic force microscopy (AFM) in a buffer solution. In the force curve measurement, multiple pull-off events were observed for the AFM tips functionalized with either ChBD1 or ChBD2, whereas the AFM tips terminated with nitrilotriacetic acid groups without ChBD showed no interaction peak, suggesting that the detected forces are derived from the binding functions of ChBDs onto the chitin surface. The force curve analyses indicate that the binding force of ChBD2 is stronger than that of ChBD1. This result suggests that ChBD1 and ChBD2 play different roles in adsorption onto chitin surface.

Synthesis and characterization of dinuclear lanthanide(III) and yttrium(III) cryptates of a hexavalent anionic polydentate ligand

Abstract Reaction of tris(2-aminomethyl)amine with bis(hydroxybenzaldehyde) (1) in presence of M(CF3SO3)3 (M=Y, Gd, Tb, Dy, Ho, Er, Tm) in methanol yielded the dinuclear lanthanide(III) and yttrium(III) cryptates [M2L] (2). The structure of [Y2L] was established by X-ray crystallography. Each yttrium ion is in a seven-coordinate environment composed of three imine nitrogen atoms, one apical nitrogen atom, and three oxygen atoms. The dinuclear complexes were found to be a host for Rb+ and Cs+.

Controlled Stacking and Unstacking of Peripheral Chlorophyll Units Drives the Spring‐Like Contraction and Expansion of a Semi‐Artificial Helical Polymer

Developing new strategies for controlling polymer conformations through precise molecular recognition can potentially generate a machine-like motion that is dependent on molecular information-an important process for the preparation of new intelligent nanomaterials (e.g., polymer-based nanomachines) in the field bordering between polymer chemistry and conventional supramolecular sciences. Herein, we propose a strategy to endow a helical polymer chain with dynamic spring-like (contraction/expansion) motion through the one-dimensional self-assembly (aggregation/disaggregation) of peripheral amphiphilic molecules. In this developing system, we employed a semi-artificial helical polysaccharide presenting peripheral amphiphilic chlorophyll units as a power device that undergoes contractive motion in aqueous media, driven by strong π-π interactions of its chlorophyll units or by cooperative molecular recognition of bipyridyl-type ligands through pairs of chlorophyll units, thereby converting molecular information into the regulated motion of a spring. In addition, this system also undergoes expansive motion through coordination of pyridine. We anticipate that this strategy will be applicable (when combined with the established wrapping chemistry of the helical polysaccharide) to the development of, for example, drug carriers (e.g., nano-syringes), actuators (stimuli-responsive films), and directional transporters (nano-railways), thereby extending the frontiers of supramolecular science.

[3]Rotaxane synthesized via covalent bond formation can recognize cations forming a sandwich structure

A novel [3]rotaxane composed of two 25-membered crownophanes and one axle molecule having two anthryl end groups was successfully synthesized via covalent bond formation followed by aminolysis, and can incorporate caesium ion into the space between the two macrocycles as a 1 : 1 sandwich-type complex, whereas it makes a 1 : 2 complex with lithium ion.