Preparation of copper ion complexes of sterically congested diaryldiazomethanes having a pyridine ligand and characterization of their photoproducts

To realize fairly stable high-spin polycarbenes by utilizing heterospin systems comprising 2p spins of organic radicals and 3d spins of magnetic metal ions, we prepared dianthryldiazomethanes having two pyridyl groups at the 2,2'- or 2,7-positions, that is, bis[10-(4-tert-butyl-2,6-dimethylphenyl)-2-(4-pyridyl)-9-anthryl]diazomethane (2,2'-DPy-1-N(2)) and [10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl][(10-(4-tert-butyl-2,6-dimethylphenyl)-2,7-di(4-pyridyl)-9-anthryl]diazomethane (2,7-DPy-1-N(2)). The triplet carbene DPy-(3)1 generated by photolysis of DPy-1-N(2) was characterized by ESR and UV-vis spectroscopy in a matrix at low temperature as well as by time-resolved UV-vis in solution at room temperature. The results showed that the triplet carbene DPy-(3)1 was destabilized to some extent as opposed to the parent triplet carbene before pyridination, but it was still fairly persistent, having a half-life of more than 30 min in solution at room temperature. Photoproducts from the complex between DPy-1-N(2) and Cu(hfac)(2) were characterized in a similar manner, and the results suggested that the generated carbene centers interacted magnetically with the Cu(II) ion to form a high-spin species with significant thermal stability. The fact that no significant signals due to the isolated triplet carbene DPy-(3)1 were observed suggested that the pyridine moiety binds with Cu(hfac)(2) in a nearly quantitative manner under these cryogenic conditions. Magnetic measurements of the photoproduct using a superconducting quantum interference device (SQUID) magneto/susceptometer were performed to determine the spin state of the complex. The temperature dependence of the molar paramagnetic susceptibility indicated the presence of ferromagnetic interaction. The field dependences of magnetization for the complexes, expressed using M versus H/T plots, were analyzed in terms of the two-component Brillouin function to be S = 3.18 (F = 0.66) and S = 0.02 (F = 0.23) for the 1:1 complex of 2,7-DPy-1 and Cu(hfac)(2) and S = 2.70 (F = 0.33) and S = 0.49 (F = 0.11) for the 1:1 complex of 2,2'-DPy-1 and Cu(hfac)(2).     

Preparation of sterically congested diphenyldiazomethanes having a pyridine ligand and magnetic characterization of photoproducts of their 2:1 copper complexes

[structure: see text] To confirm whether high-spin species can be generated as a result of ferromagnetic interaction between the 3d spin of metal ions and the 2p spins of triplet carbene through the pyridyl group located remote from the carbene center, [2,6-dibromo-4-(3- and 4-pyridyl)phenyl](4-tert-butyl-2,6-dimethylphenyl)diazomethanes were prepared and the corresponding carbenes were generated either in the absence or presence of Cu(hfac)2. These were characterized by ESR and UV/vis in a matrix at low temperature, and by laser flash photolysis in solution at room temperature. These studies indicated that although both carbenes generated a fairly stable complex with copper ions, the 4-pyridyl isomer formed a high-spin species as a result of ferromagnetic interaction between the 3d spin of metal ions and the 2p spins of triplet carbene. Such an interaction in the corresponding 3-isomer is likely to be antiferromagnetic. This is further confirmed by magnetic measurements using a Superconducting Quantum Interference Device (SQUID). The results demonstrate that extension of this method will enable stable high-spin polycarbenes to be obtained.     

A new carotenoid,halocynthiaxanthin from the sea squirt, halocynthiaroretzi

A new carotenoid, halocynthiaxanthin (5,6-epoxy-3,3′-dihydroxy-7′,8′-didehydro-5,6,7,8-tetrahydro-β,β-caroten-8-one) has been isolated from the Japanese sea squirt, $\text{Halocynthia}$ roretzi.     

Reactions of 3-substituted pyrazolin-5-ones with isocyanates

The reaction sites of 3-substituted pyrazolin-5-ones and their O- and N-blocked analogues toward various isocyanates were investigated. 3-Methyl and 3-ethoxycarbonylpyrazolin-5-ones gave the corresponding 1-carbamoylpyrazolinones, whereas the O-alkylpyrazoles afforded 2-carbamoylpyrazoles. On the other hand, the N-alkylpyrazolinones were carbamoylated at 4-position under drastic conditions.     

New quinone sulfates from the crinoids Tropiometra afra macrodiscus and Oxycomanthus japonicus

Quinone pigments in the crinoids were investigated. New quinone sulfates 1 and 3 were isolated from Tropiometra afra macrodiscus and Oxycomanthus japonicus, respectively. The structures 1 and 3 were determined to be 1,6,8-trihydroxy-3-propylanthraquinone-2-carboxylic acid 6-O-sulfate (ptilometric acid 6-O-sulfate) and 2-butanoyl-3,6,8-trihydroxy-1,4-naphtoquinone 6-O-sulfate, respectively, by chemical and spectroscopic analysis. Ptilometric acid 6-O-sulfate (1) showed an antifeedant activity on fish.     

Structure and photophysical properties of porphyrin-modified metal nanoclusters with different chain lengths

Three-dimensional porphyrin-monolayer-protected gold clusters with different chain lengths (MPCs) have been prepared to examine the structure and photophysical properties, in comparison with self-assembled monolayers (SAMs) of the porphyrins on a flat gold surface. The three-dimensional porphyrin MPCs exhibit electrochemical and photophysical properties that are much closer to those of a porphyrin reference compound in solution than those of two-dimensional porphyrin SAMs on the flat gold surface. The three-dimensional architectures of porphyrin MPCs with large surface area have improved the light-harvesting efficiency relative to the corresponding porphyrin SAM on the two-dimensional flat gold surface. Time-resolved single photon counting fluorescence and transient absorption spectroscopic studies have demonstrated that undesirable quenching of the porphyrin excited singlet state via energy transfer to the gold surface of the three-dimensional MPCs is much suppressed, as compared to the quenching of the porphyrin SAMs on the two-dimensional flat gold surface. Both the quenching rate constants of the porphyrin excited singlet state by the surfaces of bulk gold and gold nanoclusters reveal weak chain length dependence of the energy transfer quenching.     

Photografting of 2-methacryloyloxyethyl phosphorylcholine from polydimethylsiloxane: tunable protein repellency and lubrication property

The phosphorylcholine group functional methacrylate monomer, 2-methacryloyloxyethyl phosphorylcholine (MPC), was graft polymerized from the polydimethylsiloxane (PDMS) substrate using ultraviolet irradiation and using benzophenone as a photoinitiator. The varying monomer concentrations and irradiation times were investigated in order to verify the relationships between graft density and protein resistance under specific biological conditions. The ellipsometry analysis revealed that the layer thickness of the grafted polymer depended on the monomer concentrations after the irradiation for 1 min, however, it stabilized thereafter in all the specified conditions. The curve fitting of the C1s spectrum obtained by X-ray photoelectron spectroscopy analysis showed that the amount of grafted polymer increased with an increase in both monomer concentration and irradiation time. Atomic force microscopic images revealed that the terminations among the graft chains became dominant due to magnified chain mobility followed by growth of their length. In vitro albumin and fibrinogen adsorption results indicated that the resistance to protein adsorption was easily tuned by the specified conditions due to the controlled graft density. Lubrication was dramatically enhanced by the grafting and it was further promoted by an increase in the graft density in good solvents, indicating that the interactions between the graft chains and the solvents resulted in the lubrication system. These basic findings regarding the grafted PDMS surface are important for versatile applications, including its use as a biomaterial and microfluidic device.     

Unbiased Rotational Motions of an Ellipsoidal Guest in a Tight Yet Pliable Host

In the design of machinery such as steel bearings, a fundamental understanding of material characteristics provides an indispensable basis for the design. Although hydrocarbon cycloarylenes have started to be used for providing unique supramolecular bearings with anomalous dynamic behaviors, their fundamental understanding is immature. A unique property of the cycloarylene host is now reported: the cyclic host is so pliable that it tracks the orientational changes of the ellipsoidal guest, that is, C₇₀ fullerene. Unique structures of the complex were revealed by spectroscopic and crystallographic analyses, and additional theoretical investigations deepened our understanding by revealing the structural changes associated with unbiased rotational motions.     

Retarded Solid‐State Rotations of an Oval‐Shaped Guest in a Deformed Cylinder with CH–π Arrays

Upon encapsulating an oval‐shaped hydrocarbon guest, a cylindrical host deforms its shape to maximize intermolecular contacts. Structure–assembly relationship studies with a series of hydrocarbon guests disclosed the importance of molecular shapes and CH–π contacts. Multiple contacts and weak CH–π hydrogen bonds resulted in an optimal assembly; however, the shape deformation resulted in severe retardation of rotational motions in the crystal. Thus, unlike a circular guest, the oval‐shaped guest did not change its orientation in the host. Unexpectedly, the planar guest did not affect the packing structure to form a double helix in intertwined host arrays.