Odd-even effect in two dimensions induced by the bicomponent blends of isobutenyl compounds.

Scanning tunneling microscopy (STM) investigation was performed for the blends of isobutenyl compounds, in which the long alkyl chains were connected with ester or carbamoyl linkages. Each component by itself did not show the odd-even effect of alkyl chain length, whereas after blending them, the 2D structures drastically changed and modulated to exhibit odd-even effect. Star, lozenge, twist-like, and linear structures were found, dependent on the blend ratio and alkyl chain length. The blend ratio dependence of 2D structures was explained in terms of homogeneous and heterogeneous dimerization due to the interdigitation of alkyl chains.

Effects of alkyl chain length, solvent and tandem Claisen rearrangement on two-dimensional structures of noncyclic isobutenyl compounds: scanning tunnelling microscopic study.

A series of isobutenyl compounds possessing various alkyl chain lengths (C(n)-1) with a carbon number of n = 14-21 were synthesized and their two-dimensional (2D) structures were systematically studied using scanning tunnelling microscopy (STM) at a highly oriented pyrolytic graphite (HOPG)/solvent interface. Two kinds of solvent, such as 1-phenyloctane (PO) and 1-phenylnonane (PN), were selected to examine the 2D structures by changing the alkyl chain length of the isobutenyl compounds. At the HOPG/PO interface, C(n)-1 molecules with shorter alkyl chains (n = 14-17) showed the same zig-zag shaped 2D structure regardless of the alkyl chain length, whereas an odd-even effect was recognized in C(n)-1 compounds with longer alkyl chains (n = 18-21) displaying the wavy and tripod structures, alternately. This odd-even effect was also observed at the HOPG/PN interface rather more distinctly. These results suggest that there is a specific alkyl chain length range that shows the odd-even effect in the present 2D system. After a tandem Claisen rearrangement (TCR), the 2D structures of all the C(n)-2 compounds formed were converged into the same linear structure, i.e. the odd-even effect was cancelled by the conformational limitation induced by the TCR.

Well-organised two-dimensional self-assembly controlled by in situ formation of a Cu(II)-coordinated rufigallol derivative: a scanning tunnelling microscopy study.

The two-dimensional self-assembly of rufigallol derivatives and their metal coordination were studied by scanning tunnelling microscopy. Ex situ Cu(II)-coordinated rufigallol derivatives exhibited columnar structures with some defects, whereas regular and linear structures were formed upon in situ metal coordination at solid/liquid interfaces.

A mild conversion from 3-vinyl- to 3-formyl-chlorophyll derivatives.

The C3-vinyl group of a chlorophyll derivative, methyl pyropheophorbide-a, was converted into the formyl group by a novel one-pot reaction with thiophenol at room temperature. The mild reaction can provide insight into development of 'green' catalysts displacing OsO(4) or O(3), and into elucidation of unknown biosynthetic processes of chlorophyll-d.

Dynamic host-guest behavior in halogen-bonded two-dimensional molecular networks investigated by scanning tunneling microscopy at the solid/liquid interface.

The fabrication of supramolecularly engineered two-dimensional (2D) networks using simple molecular building blocks is an effective means for studying host-guest chemistry at surfaces toward the potential application of such systems in nanoelectronics and molecular devices. In this study, halogen-bonded molecular networks were constructed by the combination of linear halogen-bond donor and acceptor ligands, and their 2D structures at the highly oriented pyrolytic graphite/1-phenyloctane interface were studied by scanning tunneling microscopy. The bi-component blend of the molecular building blocks possessing tetradecyloxy chains formed a lozenge structure via halogen bonding. Upon the introduction of an appropriate guest molecule (e.g., coronene) into the system, the 2D structure transformed into a hexagonal array, and the central pore of this array was occupied by the guest molecules. Remarkably, the halogen bonding of the original structure was maintained after the introduction of the guest molecule. Thus, the halogen-bonded molecular networks are applicable for assembling guest species on the substrate without the requirement of the conventional rigid molecular building blocks with C 3 symmetry.

Hexagonal array formation by intermolecular halogen bonding using a binary blend of linear building blocks: STM study.

Hexagonal arrays were fabricated via intermolecular halogen bonding between two linear molecular building blocks in a bicomponent blend. The substitution position of the pyridine N atom involved in the halogen bond plays an important role in the formation of the hexagonal structures.

Preparation of 2D Carbon Materials by Chemical Carbonization of Cellulosic Materials to Avoid Thermal Decomposition.

Cellulosic materials, including regenerated cellulose, are promising precursors for a variety of carbon materials. However, thermal decomposition, typically accompanying carbonization at high temperatures, hinders cellulosic materials from being efficiently carbonized (i.e., very low carbon yields). Herein, this study presents a new and efficient method for the preparation of porous 2D carbon materials from sheet-like cellulosic materials, such as papers and fabrics, involving a catalyzed chemical reaction at high temperatures without thermal decomposition. Thus, cellulosic materials are treated with sulfonic acid solutions and significantly dehydrated at high temperatures via evaporation of water. As a result, black materials are obtained at a weight near the theoretical carbon content of cellulose and remain in the carbonized materials. The as-obtained porous 2D carbon materials are flexible and suitable for a wide range of applications such as in electrodes and gas absorbents.

Chiral sensing for amino acid derivative based on a [2]rotaxane composed of an asymmetric rotor and an asymmetric axle.

A racemic [2]rotaxane, composed of an asymmetric rotor and an asymmetric axle, formed a diastereomer with an amino acid derivative, and showed an optical response for the chiral recognition.

Phosphate anion-selective recognition by boron complex having plural hydrogen bonding sites.

A boron complex having plural proton donors (OH, amide NH) and proton acceptors (quinoline) acted as a selective chromo-ionophore toward phosphate anions in CH3CN.

[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.

A novel synthesis of chiral rotaxanes via covalent bond formation.

Chiral rotaxanes composed of the asymmetric crownophane incorporating two hydroxy groups as a rotor moiety and the asymmetric axis were effectively synthesized via covalent bond formation, i.e. tandem Claisen rearrangement, esterification, and aminolysis.

Self-assembly of double stranded dinuclear titanium(IV)-Schiff base complexes and formation of intramolecular mu-oxo bridges.

The reaction of titanium isopropoxide with a Schiff base ligand containing an isobutenyl linker leads to double stranded dinuclear titanium(IV)-Schiff base complexes through self-assembly with concomitant formation of intramolecular mu-oxo bridges upon hydrolysis.

A novel crownophane trapping CO2 as carbonic acid at room temperature.

A 25 membered crownophane with two hydroxy and two amide groups around the cavity has been reported for the first time to be able to include carbonic acid formed from both carbon dioxide and water molecules to give a stable 1:1 complex at room temperature.

Bicomponent blend-directed amplification of the alkyl chain effect on the 2D structures.

Only one methylene unit difference in the long alkyl group of isobutenyl ether compounds is amplified by blending, resulting in the diversification of 2D structures, although each component formed individual 2D patterns, regardless of alkyl chain lengths. The 2D structures were revealed by using scanning tunneling microscopy at the solid/liquid interface.

Fabrication and transformation of novel two-dimensional tripod structures: structural modulation by alkyl chain length and tandem Claisen rearrangement.

Novel two-dimensional C3 symmetric (tripod) structures are fabricated from isobutenyl compounds possessing long alkyl chains. Alteration from tripod to wavy structures is accomplished by odd-even effect, and tandem Claisen rearrangement allows the transformation to the linear structures.

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 tandem Claisen rearrangement in the construction of building blocks for supramolecular chemistry.

The tandem Claisen rearrangement is a simple but highly efficient reaction to synthesize useful building blocks for supramolecular chemistry. It provides in one step two new C-C bonds in very high yield. The scope and limits of this reaction will be discussed in this review and it will be shown, how macrocyclic compounds as well as rotaxanes or helicates can be formed by use of butenylidene bridged aromatic compounds obtained after the rearrangement reaction. Special aspects will cover the search for new receptors and sensors or for energy transfer properties. The contents of this tutorial review are within the field of preparative organic synthesis but in addition cover aspects of inorganic and supramolecular chemistry.

Structural and electrochemical studies of novel bis(mu-methoxo)diiron complexes: observation of Fe(III)Fe(IV) and Fe(IV)Fe(IV) states resonating with phenoxyl radicals.

Novel diiron complexes with an Fe2(mu-OMe)2 core were studied as models of the active site of nonheme iron-containing enzymes. X-ray crystal structures of the complexes showed the existence of two types of ligand folding-parallel and twisted-both of which have four virtually equivalent phenolato groups sticking out from the Fe2O2 rhombic plane. Cyclic voltammetry measurements revealed two or more distinct redox waves in a region of relatively high potential, in addition to known Fe(II)/Fe(III) redox waves in a region of lower potential. These new peaks were assigned to the high-valence state of iron atoms, that is, Fe(III)Fe(IV) and Fe(IV)Fe(IV), resonating with the phenoxyl radical(s). The split width of the redox waves ranged from 0.14 to 0.20 eV, which may be a measure of the electronic interaction of the phenolate groups through the Fe2(mu-OMe)2 core.

Adjustment of twist angles in pseudo-helical lanthanide complexes by the size of metal ions.

Control of self-assembled nanostructures is a promising technique for nanotechnology. We have examined as to whether nanostructures could be controlled by the size of the central metal ion. Lanthanides are a natural choice for such a study as the size of their trivalent ions changes with atomic number gradually. For this investigation, a series of rare earth complexes ([LaL(1)], [CeL(1)], [SmL(1)], [TbL(1)], [YL(1)], and [LuL(1)]) with a tripodal heptadentate ligand L(1) were synthesized, and their X-ray crystallographic analysis was performed. Although the structures of the ligand (H(3)L(1)) and of the metal complex ([ML(1)]) were quite different, all complexes were almost isostructural pseudohelices. The result of the crystallographic studies demonstrated that the twist angles of helices in the complexes depend on the ionic size of the central metal. A detailed analysis helped determine which portion of the helical strand contributed to the total helicity, and the major cause for the difference in helicity among the lanthanides is discussed. Moreover, this result is the first example showing that La(I) (II) and Lu(I) (II) complexes with the same tripodal heptadentate ligand are isostractural.

Synthesis of [1]rotaxane via covalent bond formation and its unique fluorescent response by energy transfer in the presence of lithium ion.

Although there have been a lot of reports on the synthesis and properties of [n]rotaxanes (mainly n = 2), only a few reports on the synthesis of [1]rotaxane has been published by Vögtle's group and others (see ref 5). Generally speaking, [1]rotaxane might be expected to exhibit properties different from other rotaxanes, because the rotor and the axle in the [1]rotaxane is bound covalently and closely. We report on a novel method to make [1]rotaxanes via covalent bond formation from a macrocyclic compound. That is, we first prepared a bicyclic compound from macrocycle and then proceeded to [1]rotaxane by aminolysis. This is the first synthetic example of preparation of [1]rotaxane via covalent bond formation, not utilizing weak interactions such as hydrogen bonding, charge transfer, via metal complexation, etc. This method might provide a powerful and new tool for construction of [1]rotaxane as a new supramolecular system. In addition, we investigated energy transfer from rotor to axle using [1]rotaxane that we prepared. Energy transfer occurred perfectly from the naphthalene ring of the rotor to the anthracene ring of the axle. We found also that only lithium ion among alkali ions can drastically enhance the fluorescence intensity. This finding could be applicable to ion-sensing systems, switching devices, and so on.