Synthesis, spectroscopy, and electrochemistry of tetra-tert-butylated tetraazaporphyrins, phthalocyanines, naphthalocyanines, and anthracocyanines, together with molecular orbital calculations

Tetraazaporphyrins (TAPs), phthalocyanines (Pcs), naphthalocyanines (Ncs), and anthracocyanines (Acs) with four tert-butyl groups attached at similar positions have been synthesized, and their electronic absorption, magnetic circular dichroism (MCD), IR, and voltammetric properties were studied and interpreted with the help of quantum-mechanical calculations. Through the preparation of a series of compounds with the same number of the same substituent, the effects of the increase in the size of the ring system were clearly derived. The main results may be summarized as follows. 1) The Q band shifts to longer wavelength and its intensity increases, but with decreasing degree of change with increasing molecular size. If the size of the effect of benzene directly fused to the TAP skeleton is set at unity, the effects of the second and third benzene units are roughly 0.8 and 0.5, respectively. 2) The splitting of the Q bands in metal-free compounds decreases with increasing molecular size, so that the Q bands of H2Nc and H2Ac appear as single bands. 3) The magnitude of the orbital angular momentum of the excited state of the ligand decreases with increasing molecular size. 4) Interestingly, the ring current, as judged from the positions of pyrrole proton signals in the 1H NMR spectrum, appears to decrease with increasing molecular size. 5) The first reduction potential becomes less negative, but only slightly, whereas the first oxidation potential shows a marked shift to less positive values with increasing molecular size, indicating that the HOMO destabilizes significantly as the molecule becomes larger. 6) In 5), the extent of the HOMO destabilization with molecular size differs depending on the central metal, so metals producing smaller destabilization effects can allow larger macrocycles. Of the metals studied, the most effective is cobalt, and the practical size limit is represented by the Acs. 7) The IR spectra become simpler the larger the molecule, and the main bands were assigned by DFT calculations. 8) The trend in experimentally determined redox potentials and electronic absorption and MCD spectra were reasonably reproduced by MO calculations using the ZINDO/S Hamiltonian. 9) EPR data for several metallocomplexes are also reported.     

The first samarium(II)-mediated stereoselective spirocyclization onto an aromatic ring

The first samarium(II)-mediated spirocyclisation onto an aromatic ring was achieved by the reaction of methyl 4-(4-oxoalkyl)benzoates with SmI2 in the presence of i-PrOH and HMPA, yielding methyl 1-alkyl-1-hydroxyspiro-[4.5]dec-6-ene-8-carboxylates in moderate to high yields.     

Double-stranded helical polymers consisting of complementary homopolymers

Two complementary homopolymers of chiral amidines and achiral carboxylic acids with m-terphenyl-based backbones were synthesized by the copolymerization of a p-diiodobenzene derivative with the diethynyl monomers bearing a chiral amidine group and a carboxyl group using the Sonogashira reaction, respectively. Upon mixing in THF, the homopolymer strands assembled into a preferred-handed double helix through interstrand amidinium-carboxylate salt bridges, as evidenced by its absorption, circular dichroism, and IR spectra. In contrast, when mixed in less polar solvents, such as chloroform, the complementary strands kinetically formed an interpolymer complex with an imperfect double helical structure containing a randomly hybridized cross-linked structure, probably because of strong salt bridge formations. This primary complex was rearranged into the fully double helical structure by treatment with a strong acid followed by neutralization with an amine. High-resolution atomic force microscopy revealed the double-stranded helical structure and enabled the determination of the helical sense.     

Solid-state molecular rotators of anilinium and adamantylammonium in [Ni(dmit)2](-) salts with diverse magnetic properties

Supramolecular rotators of hydrogen-bonding assemblies between anilinium (Ph-NH 3 (+)) or adamantylammonium (AD-NH 3 (+)) and dibenzo[18]crown-6 (DB[18]crown-6) or meso-dicyclohexano[18]crown-6 (DCH[18]crown-6) were introduced into [Ni(dmit) 2] salts (dmit (2-) is 2-thioxo-1,3-dithiole-4,5-dithiolate). The ammonium moieties of Ph-NH 3 (+) and AD-NH 3 (+) cations were interacted through N-H (+) approximately O hydrogen bonding with the six oxygen atoms of crown ethers, forming 1:1 supramolecular rotator-stator structures. X-ray crystal-structure analyses revealed a jackknife-shaped conformation of DB[18]crown-6, in which two benzene rings were twisted along the same direction, in (Ph-NH 3 (+))(DB[18]crown-6)[Ni(dmit) 2] (-) ( 1) and (AD-NH 3 (+))(DB[18]crown-6)[Ni(dmit) 2] (-) ( 3), whereas the conformational flexibility of two dicyclohexyl rings was observed in (Ph-NH 3 (+))(DCH[18]crown-6)[Ni(dmit) 2] (-) ( 2) and (AD-NH 3 (+))(DCH[18]crown-6)[Ni(dmit) 2] (-) ( 4). Sufficient space for the molecular rotation of the adamantyl group was achieved in the crystals of salts 3 and 4, whereas the rotation of the phenyl group in salts 1 and 2 was rather restricted by the nearest neighboring molecules. The rotation of the adamantyl group in salts 3 and 4 was evidenced from the temperature-dependent wide-line (1)H NMR spectra, dielectric properties, and X-ray crystal structure analysis. ab initio calculations showed that the potential energy barriers for the rotations of adamantyl groups in salts 3 (Delta E approximately 18 kJmol (-1)) and 4 (Delta E approximately 15 kJmol (-1)) were similar to those of ethane ( approximately 12 kJmol (-1)) and butane (17-25 kJmol (-1)) around the C-C single bond, which were 1 order of magnitude smaller than those of phenyl groups in salts 1 (Delta E approximately 180 kJmol (-1)) and 2 (Delta E approximately 340 kJmol (-1)). 1D or 2D [Ni(dmit) 2] (-) anion arrangements were observed in the crystals according to the shape of crown ether derivatives. The 2D weak intermolecular interactions between [Ni(dmit) 2] (-) anions in salts 1 and 3 led to Curie-Weiss behavior with weak antiferromagnetic interaction, whereas 1D interactions through lateral sulfur-sulfur atomic contacts between [Ni(dmit) 2] (-) anions were observed in salts 2 and 4, whose magnetic behaviors were dictated by ferromagnetic (salt 2) and singlet-triplet (salt 4) intermolecular magnetic interactions, respectively.     

LCST-type liquid-liquid phase separation behaviour of poly(ethylene oxide) derivatives in an ionic liquid

We present a new series of polymer-ionic liquid solutions exhibiting LCST-type liquid-liquid phase separation behaviour, and reveal their phase behaviour and intermolecular interactions based on phase diagrams and NMR analysis.     

Photoresponsive rolling and bending of thin crystals of chiral diarylethenes

Dithienylhexafluorocyclopentene with (R)- or (S)-N-phenylethylamide substituents formed rod-like and 0.2-1.0 microm-thick platelike crystals by sublimation; upon UV irradiation, the crystals bent concavely to the incident light and finally rolled crystals were obtained; the bent crystals were reconverted to flat crystals by visible light irradiation.     

Nanoparticles of iron(II) spin-crossover

We report the synthesis of spin crossover 69 nm spherical nanoparticles of [Fe(NH(2)-trz)(3)](Br)(2).3H(2)O.0.03(surfactant) (NH(2)trz = 4-amino-1,2,4-triazole, surfactant = Lauropal), prepared by the reverse micelle technique, which exhibit at room temperature a thermal hysteresis characterized by magnetic, diffuse reflectivity and Raman studies.     

Fullerene nanowires: self-assembled structures of a low-molecular-weight organogelator fabricated by the Langmuir-Blodgett method

Fullerene derivative C60TT, which is substituted with the low-molecular-weight organogelator tris(dodecyloxy)benzamide, formed nanowire structures on application of the Langmuir-Blodgett (LB) method. The surface morphology of the C60TT LB film was dependent on the holding time before deposition at a surface pressure of 5 mN m(-1); it changed from a homogeneous monolayer to a bilayer fibrous structure via a fibrous monolayer structure, which was estimated to have dimensions of 1.2 nm in height, 8 nm in width, and 5-10 microm in length. From the structural and spectroscopic data, it is inferred that close packing of the fullerene moiety occurs along with intermolecular hydrogen bonding within the monolayer fibrous structure. The morphological changes in the LB film are explained kinetically by the Avrami theory, based on the decrease in the surface area of the monolayer at the air/water interface. The growth of the quasi-one-dimensional fibrous monolayer structures at holding times from 0 to 0.2 h is considered to be an interface-controlled process, whereas the growth of the quasi-one-dimensional bilayer fibrous structures from 0.2 to 18 h is thought to be a diffusion-controlled process.     

Sonodynamic effect of erythrosin B on sarcoma 180 cells in vitro

The ultrasonically induced cytotoxic effect of erythrosin B (EB) on isolated sarcoma 180 cells was investigated. The tumor cells were suspended in an air-saturated phosphate buffered saline and exposed to ultrasound at 1.93 MHz in a standing-wave mode for up to 60 s in the presence and absence of EB. The rate of cell damage induction by ultrasound was enhanced by 4-5 times with 160-microM EB, while no cell damage was observed with EB alone. This enhancement was significantly inhibited by histidine. Sonochemical generation of active oxygen species in the presence of EB, measured by ESR spectroscopy, was also inhibited by histidine. These results indicate the involvement of a sonochemical mechanism.     

Soluble polyphenol

Soluble polyphenol was synthesized for the first time by enzymatic oxidative polymerization of phenol using peroxidase and hydrogen peroxide as catalyst and oxidizing agent, respectively. A mixed solvent of alcohol and buffer improved the polymer solubility toward N,N-dimethylformamide (DMF). The resulting polymer was composed of a mixture of phenylene and oxyphenylene units. Changing the solvent composition could control the molecular weight and regioselectivity of the polymer. The polymer was found to possess relatively high thermal stability.