Supramolecular dye inclusion single crystals created from 2,3,6-trimethyl-β-cyclodextrin and porphyrins

In Nature, chromophoric groups play various roles, such as oxygen carriers, electron donors, light sensitizers, which are achieved in many cases by control of their aggregation modes in proteins. Host-guest chemistry between cyclodextrins and porphyrins has attracted great interest from supramolecular chemists because of their unique structures and functions that mimic those of proteins with chromophoric prosthetic groups. To mimic Nature's contrivances, the host-guest systems between cyclodextrins and porphyrins have frequently been studied. It is really surprising, however, that to date no detailed structural information of these complexes has been obtained from single-crystal analysis. In 2011, we reported the first successful isolation of a dye inclusion single crystal (DISC) between 2,3,6-trimethyl-β-cyclodextrin (TMβCD) and 5,10,15,20-tetrapyridylporphyrin (TPyP), and analyzed its X-ray crystal structure. The crystal structure revealed not only the real complex mode but also the attractive orientation of TPyP in the DISC. Herein, we present new strategies to prepare DISCs of TMβCD for several porphyrins and provide crystal structures, details of the complex modes, and optical properties. We believe that the present study has various important implications not only for the basic crystal analysis of inclusion complexes but also for potential applications that use these single crystals.     

Quantum Dots Arrangement and Energy Transfer Control via Charge‐Transfer Complex Achieved on Poly(Phenylene Ethynylene)/Schizophyllan Nanowires

Assemblies of organic and inorganic compounds in the nanoscale region have contributed to the development of novel functional materials toward future applications, including sensors and opto‐electronics. We succeed in fabricating hybrid nanowires composed of a conjugated polymer and semiconductor quantum dots (QDs) by a supramolecular assembly technique. The 1‐D fashion of the nanowire structure is obtained by the polymer wrapping of cationic poly(phenylene ethynylene) (PPE) with helix‐forming polysaccharide schizophyllan (SPG). The electrostatic interaction between cationic PPE and anionic QDs affords the nanowires decorated with QDs. Upon addition of an acceptor molecule, tetranitrofluorenone (TNF), the charge‐transfer (CT) complex between PPE and TNF is formed, resulting in energy transfer from the QDs to PPE arising from the induced spectral overlap. Furthermore, the employment of the conjugated polymer allows highly sensitive quenching of the QD’s emission by raising the transmission efficiency to the CT complexed electron deficient sites along the polymer backbone.     

Simultaneous determination of a pyridine-triphenylborane anti-fouling agent and its estimated degradation products using capillary zone electrophoresis

A commercial organoborane compound, pyridine-triphenylborane (PTPB), is often applied to ship hulls as an anti-fouling agent. We developed capillary zone electrophoresis (CZE) with direct UV detection for the simultaneous determination of PTPB and its estimated degradation products: diphenylborinic acid (DPB), phenylboronic acid (MPB), and phenol. The limits of detection (LODs) for PTPB, DPB, MPB, and phenol were, respectively, 25, 30, 50, and 29 μg/l at a signal-to-noise ratio of three. At concentrations of 0.5 mg/l, values of the relative standard deviation (RSD, n = 6, intra-day) of peak area were obtained, respectively, for PTPB, DPB, MPB, and phenol, as 4.1, 4.1, 4.7, and 3.4% for peak heights 3.6, 3.2, 1.7, and 1.4%, and for migration times 1.1, 1.1, 1.0, and 0.73%. The analytes were detected within 14 min. Simple photodegradation experiments were conducted to verify the usefulness of the proposed method for additional PTPB degradation investigations.     

Charge-order driven proton arrangement in a hydrogen-bonded charge-transfer complex based on a pyridyl-substituted TTF derivative

A unique N(+)-HN hydrogen-bonded (H-bonded) dimer motif based on partially oxidized pyridyl-substituted TTF was constructed in the charge-transfer complex. The charge ordering in the TTF column by the charge disproportionation in the dimer regulates the arrangement of the H-bonded proton, evidencing the proton-electron coupled state.     

High-performance liquid chromatography of aromatic compounds with photochemical decomposition and tris(2,2'-bipyridine)ruthenium(III) chemiluminescence detection

A novel high-performance liquid chromatographic method for the determination of aromatic compounds based on the on-line photochemical degradation and subsequent tris(2,2'-bipyridine)ruthenium(III) chemiluminescence detection has been developed. Chemiluminescence intensity depended upon the number of aromatic rings, UV irradiation time, and variety of substituted functional groups. One of the decomposition products of aromatic compounds by UV irradiation was identified as oxalic acid. As one application of this methodology, determination of catechins in tea has been shown. Calibration graphs, based on standard (-)-epicatechin and (-)-epigallocatechin gallate solutions, were linear over the range of 0.1-50 microM. The detection limits (signal-to-noise ratio=3) were 0.8 pmol for (-)-epigallocatechin gallate and 1.2 pmol for (-)-epicatechin. The high-performance liquid chromatography-chemiluminescence (HPLC-CL) detection method with a post-column photochemical reactor can be applied to the sensitive and selective determination of catechins in tea.     

Synthesis and optical resolution of aminophosphines with axially chiral C(aryl)-N(amine) bonds for use as ligands in asymmetric catalysis

N-Aryl indoline-type aminophosphines 1a-c were obtained in good yields by a nucleophilic aromatic substitution (S(N)Ar) reaction followed by silane reduction. Aminophosphine 1d was also prepared from 2,3-difluorobenzaldehyde (4) via dimethylhydrazone. Optical resolution of C(aryl)-N(amine) bond atropisomers was achieved using (S)-(+)-di-mu-chlorobis[2-[(dimethylamino)ethyl]phenyl-C(2),N]dipalladium(II) ((S)-10). The determination of absolute configuration and the investigation of the rotation barrier for C(aryl)-N(amine) bond axial stability of an aminophosphine 1 are described. Finally, the ability of the chiral phosphine ligand 1 is demonstrated in a catalytic asymmetric reaction, such as a palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate (up to 95% ee).     

Modulation structure in the STM images of the non-metallic misfit-layer compound (PbS)1.12VS2

This paper presents the scanning tunneling microscopy (STM) results of the misfit-layer compound (PbS)_1.12VS₂, which is constructed of alternately stacking of PbS (Q) and VS₂ (H) layers. Temperature dependent resistivity measurements show a semiconducting behavior with small activation energies. Unlike the metallic 1Q/1H type of compounds we have succeeded to take both the STM images of a Q layer and a H layer, because electron tunneling from the underlying H layer is suppressed when intermediate positive bias voltage (V_b) is applied to a tip. At V_b = 0.15 V the image shows pseudo-tetragonal arrays of bright spots, although it is obscure with decreasing bias voltage and disappears at less than 10 mV. A modulation structure is found on the H layer of a stepped surface on which surface atoms are undulated in a period being twice the V-V interatomic distance in the [1 0]_H or the [1 1]_H direction.     

Structure–Property Relationship of Supramolecular Ferroelectric [H‐66dmbp][Hca] Accompanied by High Polarization,Competing Structural Phases,and Polymorphs

Three polymorphic forms of 6,6′‐dimethyl‐2,2′‐bipyridinium chloranilate crystals were characterized to understand the origin of polarization properties and the thermal stability of ferroelectricity. According to the temperature‐dependent permittivity, differential scanning calorimetry, and X‐ray diffraction, structural phase transitions were found in all polymorphs. Notably, the ferroelectric α‐form crystal, which has the longest hydrogen bond (2.95 Å) among the organic acid/base‐type supramolecular ferroelectrics, transformed from a polar structure (space group, P2₁) into an anti‐polar structure (space group, P2₁/c) at 378 K. The non‐ferroelectric β‐ and γ‐form crystals also exhibited structural rearrangements around hydrogen bonds. The hydrogen‐bonded geometry and ferroelectric properties were compared with other supramolecular ferroelectrics. A positive relationship between the phase‐transition temperature (T_C) and hydrogen‐bond length (<d>) was observed, and was attributed to the potential barrier height for proton off‐centering or order/disorder phenomena. The optimized spontaneous polarization (P_s) agreed well with the results of the first‐principles calculations, and could be amplified by separating the two equilibrium positions of protons with increasing <d>. These data consistently demonstrated that stretching <d> is a promising way to enhance the polarization performance and thermal stability of hydrogen‐bonded organic ferroelectrics.