Aggregation-induced enhanced fluorescence emission of chiral Zn(II) complexes coordinated by Schiff-base type binaphthyl ligands.

A pair of novel chiral Zn(II) complexes coordinated by Schiff-base type ligands derived from BINOL (1,1'-bi-2-naphthol), R-/S-Zn, were synthesized. X-ray crystallography revealed the presence of two crystallographically independent complexes; one has a distorted trigonal-bipyramidal structure coordinated by two binaphthyl ligands and one disordered methanol molecule (molecule A), while the other has a distorted tetrahedral structure coordinated by two binaphthyl ligands (molecule B). Numerous CH⋯π and CH⋯O interactions were identified, contributing to the formation of a 3-dimensional rigid network structure. Both R-/S-Zn exhibited fluorescence in both CH2Cl2 solutions and powder samples, with the photoluminescence quantum yields (PLQYs) of powder samples being twice as large as those in solutions, indicating aggregation-induced enhanced emission (AIEE). The AIEE properties were attributed to the restraint of the molecular motion arising from the 3-dimensional intermolecular interactions. CD and CPL spectra were observed for R-/S-Zn in both solutions and powders. The dissymmetry factors, gabs and gCPL values, were within the order of 10-3 to 10-4 magnitudes, comparable to those reported for chiral Zn(II) complexes in previous studies.

Synthesis and Characterization of Quinone Compounds Derived from Doubly and Triply Linked Diporphyrins and Tuning of Their Absorption Properties.

Porphyrins are attracting increasing attention in materials science and photochemistry owing to their unique properties and diverse applications. This study focuses on modifying and tuning the absorption properties of porphyrins, specifically those of quinoidal porphyrins, to extend their spectral range into the near-infrared (NIR) region. We report the synthesis and structural and physical properties of quinone compounds derived from doubly and triply linked diporphyrins and their metal complexes. Doubly linked diporphyrinquinone exhibits broad panchromatic absorption properties in solution owing to its low symmetry. Metal complexation markedly extends its absorption range into the near-infrared region. In contrast, the metal complexes of the triply linked diporphyrinquinones exhibit sharp and strong absorption bands in the visible to near-infrared region owing to their higher symmetry. The longest absorption wavelength of the triply linked diporphyrinquinones was approximately 1500 nm, which was significantly more red-shifted than that of the doubly linked ones.

Structurally well-defined conjugated meso-aminoporphyrin oligomers analogous to polyanilines.

Polyaniline, which is formed by the oxidative polymerization of aniline, is a widely explored conducting polymer with several stable oxidation states, and can be applied in advanced materials, including sensing devices and electrochemical catalysts. The marriage of polyanilines with the diverse chemistry of porphyrins is expected to confer new properties, including a combination of electrical, optical, magnetic and chemical properties. Herein, we demonstrate that meso-aminodiarylporphyrin, a porphyrin analogue of aniline, undergoes oxidative oligomerization in an acidic solution under an oxygen atmosphere to yield stable oligomeric products that are analogous to fully oxidized polyanilines. The so-formed oligomers are composed of the same number of electron-rich porphyrinoid and electron-deficient quinoid moieties, and they exhibit a broad electronic absorption band in the near infrared (NIR) region, which is attributable to intramolecular charge transfer (ICT) transition from electron-rich porphyrinoid moieties to electron-deficient quinoid ones. The quinoid moieties in the oligomers could be reversibly reduced using sodium ascorbate to obtain all-porphyrinoid oligomers that resemble fully reduced polyanilines. The fully reduced oligomers do not exhibit the NIR ICT band. Furthermore, three types of partially reduced tetramers consisting of a single quinoid moiety were also obtained, among which two interconverted in solution. Their interconversion was significantly accelerated in the presence of a protic solvent. This result is consistent with the high electron conductivity of partially oxidized polyanilines following their protonation.

Aggregation-induced circularly polarized phosphorescence of Pt(II) complexes with an axially chiral BINOL ligand.

A pair of chiral Pt(II) complexes coordinated by simple BINOL and bipyridine ligands displaying aggregation-induced phosphorescence and circularly polarized luminescence were characterized by X-ray crystallography and absorption and emission spectroscopies. The emission of the powder sample was reddish whereas the thin film dispersed in PMMA (fPf = 1 wt%) exhibited a white emission.

[2.2]Paracyclophane-Based Chiral Platforms for Circularly Polarized Luminescence Fluorophores and Their Chiroptical Properties: Past and Future.

Quality of CPL fluorophore is defined by the vectors of electric dipole transition moment and imaginary magnetic dipole transition moment. The aim of this review is to introduce readers to a chiral moiety applicable to CPL studies focusing on chiral cyclophanes because the rigid cyclophanes are able to hold the vector directions of electric dipole transition moment and imaginary magnetic dipole transition moment.

Synthesis of Porphyrinquinone and Doubly-Fused Diporphyrin Quinone Through Oxidation of Diarylporphyrins Using a Hypervalent Iodine Compound.

Treatment of a meso-diarylporphyrin with PhI(OAc)2 in the presence of BF3 ⋅ OEt2 and propionic acid affords the corresponding porphyrinquinone in a high yield (91%). A novel quinone derived from meso-meso ß-ß doubly-fused diporphyrin was obtained as the sole byproduct (16% yield), which exhibits strong panchromatic absorption between 300 and 1000 nm. It has a low HOMO-LUMO gap owing to expanded and low-symmetry π-planes.

Metal-Free Synthesis of meso-Aminoporphyrins through Reduction of meso-Azidoporphyrins Generated in Situ by Nucleophilic Substitution Reactions of meso-Bromoporphyrins.

A facile and metal-free method for the preparation of free base meso-aminodiarylporphyrins from readily available meso-bromodiarylporphyrins is described. Simple treatment of meso-bromoporphyrins with sodium azide and sodium ascorbate in DMF affords the corresponding meso-aminoporphyrins in very good yields. This method involves the aromatic nucleophilic substitution (SNAr) of a bromo group with an azido group and the subsequent in situ reduction of the introduced azido group by sodium ascorbate. This amination reaction can be scaled up to gram scale without any decrease of the product yield. The amination reaction of free base meso-dibromoporphyrin affords a monoaminated product selectively, whereas that of the Ni(II) complex furnishes a diaminated product that is oxidized by air under ambient conditions but isolable as a trifluoroacetyl ester. Metal-insertion reactions of the obtained free base aminoporphyrins afford the corresponding metal complexes (Ni(II), Cu(II), Zn(II), and Pd(II)) all in good yields except the Pd(II) complex. Synthetic methods for the preparation of N-mono- or dialkylaminoporphyrins from the free base meso-aminoporphyrins have been also established.

Molecular Design and Syntheses of Tetracyano-5,10-porphyrinquinodimethane Showing Stabilized LUMO.

An isomer of tetracyanoporphyrinquinodimethane (TCPQ), 5,10-TCPQ, was designed, synthesized, and structurally characterized, and its basic properties were discussed with emphasis on comparison with those of reported 5,15-TCPQ. The title compound was synthesized by a convenient cascade reaction involving a catalyst-free aromatic nucleophilic substitution reaction and the Uno-Takahashi reaction. The obtained π-expanded redox molecule acted as a Wurster-type redox molecule that underwent not only reduction but also oxidation processes. Furthermore, its absorption spectrum showed a large bathochromic shift that extended to the near-IR region, approximately 1150 nm.

Galectin LEC-1 plays a defensive role against damage due to oxidative stress in Caenorhabditis elegans.

LEC-1 is a major galectin in Caenorhabditis elegans and contains two carbohydrate recognition domains (CRDs), N-CRD and C-CRD. To determine the role of LEC-1, we examined the phenotypes of a mutant C. elegans strain lacking lec-1. We observed negligible differences in embryogenesis, morphogenesis and egg laying at 20 °C between the mutant and the wild-type. Furthermore, the life spans of the mutant and the wild-type were equivalent at either 20 °C or 25 °C. However, the lec-1 mutant showed a greater susceptibility to H2O2 and paraquat than the wild-type. This result suggests an increased susceptibility to oxidative stress, with the phenotypes being similar to those of lec-10 deletion mutants as previously described. To understand the molecular mechanism underlying this phenotype, C. elegans proteins bound by either the LEC-1 N-CRD or C-CRD were isolated and identified using a nano liquid chromatography-tandem mass spectrometry technique. MIG-6 was identified as a major binding partner of LEC-1 with both N- and C-CRD. From these results and previous reports, we speculate that interaction of LEC-1 and MIG-6 in the pharynx may affect susceptibility to paraquat and that LEC-10 has different functions from LEC-1 in regulating H2O2 and paraquat resistance in the intestine.

Catalyst-free aromatic nucleophilic substitution of meso-bromoporphyrins with azide anion: efficient synthesis and structural analyses of meso-azidoporphyrins.

meso-Mono- or diazidoporphyrins were readily obtained in high yields by the catalyst-free aromatic nucleophilic reaction of the corresponding bromoporphyrins with azide anions under mild conditions. The molecular structures of the obtained azides were unambiguously determined by X-ray crystallographic analysis.

Sugar-binding properties of the two lectin domains of LEC-1 with respect to the Galß1-4Fuc disaccharide unit present in protostomia glycoconjugates.

Galß1-4Fuc disaccharide unit was recently reported to be the endogenous structure recognized by the galectin LEC-6 isolated from the nematode Caenorhabditis elegans. LEC-1, which is another major galectin from this organism, is a tandem repeat-type galectin that contains two carbohydrate recognition domains, the N-terminal lectin domain (LEC-1Nh) and the C-terminal lectin domain (LEC-1Ch), and was also found to have an affinity for the Galß1-4Fuc disaccharide unit. In the present study, we compared the binding strengths of LEC-1, LEC-1Nh, and LEC-1Ch to Galß1-4Fuc, Galß1-3Fuc, and Galß1-4GlcNAc units as well as to LEC-6-ligand N-glycans by using frontal affinity chromatography (FAC) analysis. The two lectin domains of LEC-1 exhibited the highest affinity for Galß1-4Fuc, though sugar-binding properties differed somewhat between LEC-1Nh and LEC-1Ch. Furthermore, these two domains had significantly lower affinities for the LEC-6-binding glycans. These results suggest that the endogenous recognition unit of LEC-1 is likely to be Galß1-4Fuc, and that the endogenous ligands for LEC-1 are different from those for LEC-6.

Superexchange mediated energy transfer in zinc(II) porphyrin-free base porphyrin dimers: comparison of m- and p-bis(phenylethynyl) phenylene linked dimers.

The singlet-singlet energy transfer rate in a new zinc(II) porphyrin-free base porphyrin dimer, having a m-bis(phenylethynyl)phenylene bridge, was found to be slower than that in the corresponding p-bis(phenylethynyl)phenylene-bridged dimer, despite the shorter donor-acceptor distance and pathway. The slower rate is interpreted as evidence for a major contribution of the superexchange mechanism.

ß-galactosidases from jack bean and Streptococcus have different cleaving abilities towards fucose-containing sugars.

We examined the sugar-cleaving abilities of ß-galactosidases from jack bean and Streptococcus towards sugars containing fucose residues, and found that jack bean ß-galactosidase has an ability to cleave the ß1-3 linkage between galactose (Gal) and fucose (Fuc) residues, but not ß1-4 linkage. On the other hand, streptococcal ß-galactosidase was found to cleave the linkage in both Galß1-4Fuc and Galß1-3Fuc disaccharide units. Such a difference in sugar-cleaving abilities between these 2 ß-galactosidases will be useful for structural analysis of glycans, especially those from species belonging to Protostomia, such as Caenorhabditis elegans.

Manipulating double-decker molecules at the liquid-solid interface.

We have used a scanning tunneling microscope (STM) to manipulate heteroleptic phthalocyaninato, naphthalocyaninato, and porphyrinato double-decker (DD) molecules at the liquid-solid interface between 1-phenyloctane solvent and graphite. We employed nanografting of phthalocyanines with eight octyl chains to place these molecules into a matrix of heteroleptic DD molecules; the overlayer structure is epitaxial on graphite. We have also used nanografting to place DD molecules in matrices of single-layer phthalocyanines with octyl chains. Rectangular scans with a STM at low bias voltage resulted in the removal of the adsorbed DD molecular layer and substituted the DD molecules with bilayer-stacked phthalocyanines from phenyloctane solution. Single heteroleptic DD molecules with lutetium sandwiched between naphthalocyanine and octaethylporphyrin were decomposed with voltage pulses from the probe tip; the top octaethylporphyrin ligand was removed, and the bottom naphthalocyanine ligand remained on the surface. A domain of decomposed molecules was formed within the DD molecular domain, and the boundary of the decomposed molecular domain self-cured to become rectangular. We demonstrated a molecular "sliding block puzzle" with cascades of DD molecules on the graphite surface.

Caenorhabditis elegans galectins LEC-6 and LEC-1 recognize a chemically synthesized Galbeta1-4Fuc disaccharide unit which is present in Protostomia glycoconjugates.

Galbeta1-4GlcNAc is thought to be a common disaccharide unit preferentially recognized by vertebrate galectins. Eight-amino-acid residues conserved in proteins belonging to the galectin family have been suggested to be responsible for recognition. Meanwhile, we isolated and analyzed endogenous N-glycans of Caenorhabditis elegans that were captured by a C. elegans galectin LEC-6 and demonstrated that the unit of recognition for LEC-6 is a Gal-Fuc disaccharide, though the linkage between these residues was not confirmed. In the present study, we chemically synthesized Galbeta1-4Fuc and Galbeta1-3Fuc labeled with 2-aminopyridine (PA) and demonstrated that LEC-6 interacts with PA-Galbeta1-4Fuc more strongly than PA-Galbeta1-3Fuc by frontal affinity chromatography (FAC). Galbeta1-4Fuc also inhibited hemagglutination caused by LEC-6 more strongly than Galbeta1-3Fuc. FAC analysis using LEC-6 point mutants revealed that some of the conserved amino acid residues which have proven to be important for the recognition of Galbeta1-4GlcNAc are not necessary for the binding to Galbeta1-4Fuc. Another major C. elegans galectin, LEC-1, also showed preferential binding to Galbeta1-4Fuc. These results suggest that Galbeta1-4Fuc is the endogenous unit structure recognized by C. elegans galectins, which implies that C. elegans glycans and galectins may have co-evolved through an alteration in the structures of C. elegans glycans and a subsequent conversion in the sugar-binding mechanism of galectins. Furthermore, since glycans containing the Galbeta1-4Fuc disaccharide unit have been found in organisms belonging to Protostomia, this unit might be a common glyco-epitope recognized by galectins in these organisms.

A C-type lectin of Caenorhabditis elegans: its sugar-binding property revealed by glycoconjugate microarray analysis.

C-type lectins are a family of proteins with an affinity to carbohydrates in the presence of Ca(2+). In the genome of Caenorhabditis elegans, almost 300 genes encoding proteins containing C-type lectin-like domains (CTLDs) have been assigned. However, none of their products has ever been shown to have carbohydrate-binding activity. In the present study, we selected 6 potential C-type lectin genes and prepared corresponding recombinant proteins. One of them encoded by clec-79 was found to have sugar-binding activity by using a newly developed glycoconjugate microarray based on evanescent-field excited fluorescence. CLEC-79 exhibited affinity to sugars containing galactose at the non-reducing terminal, especially to the Galbeta1-3GalNAc structure, in the presence of Ca(2+). Combined with structural information of the glycans of C. elegans, these results suggest that CLEC-79 preferentially binds to O-glycans in vivo.

Unusual regioselective mercuration of metalloporphyrins and its potential applications.

The reaction of Hg(CF3CO2)2 with metalloporphyrins produces mercurated porphyrins regioselectively, the reaction, surprisingly occurring at the most hindered betaB-position; this behavior is in marked contrast to the usual electrophilic substitution reactions of porphyrins, whose reactions produce meso-substituted porphyrins; the obtained mercurated porphyrins are active to transition metal-catalyzed coupling reactions, such as the Mizoroki-Heck reaction.

Metal-insulator transition of charge-transfer salts based on unsymmetrical donor DMET and metal halide anions (DMET)4(MCl4)(TCE)2 (M = Mn, Co, Cu, Zn; TCE = 1,1,2-trichloroethane).

New charge-transfer salts based on an unsymmetrical donor DMET [dimethyl(ethylenedithio)diselenadithiafulvalene] and metal halide anions (DMET)4MIICl4(TCE)2 (M = Mn, Co, Cu, Zn; TCE = 1,1,2-trichloroethane) have been synthesized and characterized by transport and magnetic measurements. The crystal structures of the DMET salts are isostructural, consisting of a quasi-one-dimensional stack of DMET and insulating layers containing metal halide anions and TCE. Semimetallic band structures are calculated by the tight-binding approximation. Metal-insulator transitions are observed at TMI = 25, 15, 5-20, and 13 K for M = Mn, Co, Cu, and Zn, respectively. The M = Cu salt exhibits anisotropic conduction at ambient pressure, being semiconducting in the intralayer current direction but metallic for the interplane current direction, down to T(MI). The metal-insulator transitions are suppressed under pressure. In the M = Co and Zn salts, large magnetoresistances with hysteresis are observed at low temperatures, on which Shubnikov-de Haas oscillations are superposed above 30 T. In the M = Cu salt, no hysteresis is observed but clear Shubnikov-de Haas oscillations are observed. The magnetoresistance is small and monotonic in the M = Mn salt. Paramagnetic susceptibilities of the spins of the magnetic ions are observed for the M = Mn, Co, and Cu salts with small negative Weiss temperatures of approximately 1 K. In the nonmagnetic M = Zn salt, Pauli-like pi-electron susceptibility that vanishes at TMI is observed. The ground state of the pi-electron system is understood as being a spin density wave state caused by imperfect nesting of the Fermi surfaces. In this pi-electron system, the magnetic ions of the M = Mn, Co, and Cu salts interact differently, exhibiting a variety of transport behaviors.

Single-chain magnet behavior in an alternated one-dimensional assembly of a Mn(III) Schiff-base complex and a TCNQ radical.

An alternated 1:1 chain compound of a Mn(III) salen derivative and the TCNQ monoradical was synthesized: [Mn(5-TMAMsaltmen)(TCNQ)](ClO(4))(2) (1) (TCNQ=tetracyano-p-quinodimethane; 5-TMAMsaltmen=N,N'-(1,1,2,2-tetramethylethylene) bis(5-trimethylammoniomethylsalicylideneiminato)). Compound 1 has a zigzag chain structure packed with adjacent chains with an interchain MnMn distance of over 8 Angatrom. As compound 1 contains no crystallization solvent, the void spaces between chains are occupied only by ClO(4) (-) counter ions. Compound 1 has a structure reminiscent of what has been observed in the family of Mn(III)(porphyrin)-TCNE or -TCNQ compounds reported previously by Miller and co-workers and we demonstrate herein its unique single-chain magnet behavior among this family of compounds. The direct current (dc) magnetic measurements established the one-dimensional nature of compound 1 with an antiferromagnetic exchange coupling, J/k(B) approximately -96 K, between the Mn(III) ion and TCNQ radical and with an activated correlation length (Delta(xi)=26.5 K) at low temperatures (50-15 K). The slow relaxation of the magnetization was shown in compound 1 by the field hysteresis of the magnetization observed below 3.5 K (with a coercive field up to 14 kOe at 1.8 K). Single-crystal magnetization measurements demonstrated the uniaxial symmetry of this compound and allowed an estimation of the anisotropy field, H(a) approximately 97 kOe. The absence of magnetic ordered phase or spin-glass behavior was established by heat-capacity calorimetry measurements that exhibit no abnormality of C(p) between 0.5 K and 10 K. The study of the magnetization relaxation by combined ac (alternating current) and dc techniques showed that compound 1 possesses a single relaxation time (tau). As the consequence of the finite size of the chain, the temperature dependence of tau presents two activated regimes above and below 4.5 K with tau(01)=2.1 x 10(-10) s, Delta(tau1)=94.1 K and tau(02)=6.8 x 10(-8) s and Delta(tau2)=67.7 K, respectively. The detailed analysis of these dynamics properties together with the correlation length, allows an unambiguous demonstration of the single-chain magnet behavior in 1.