Experimental and Theoretical Investigations into the Paratropic Ring Current of a Porphyrin Sheet

Anomalous induced magnetic effects were observed in a directly fused square‐planar porphyrin sheet 1 , in that the protons above the center of the tetraporphyrin core were characteristically shifted downfield in the ¹H NMR spectrum. These observations suggest a rare paratropic ring‐current effect around the planar cyclooctatetraene (COT) core of 1 . To examine the spatial distribution of the induced magnetic effect, face‐to‐face dimeric complexes of porphyrin sheet 1 with bipyridyl‐type guest molecules ( G1 – G3 ) were prepared, which provided complexation‐induced shifts (CISs) of the guest molecules as a neat experimental guide to the distance dependence of the induced magnetic effects in 1 . Nucleus‐independent chemical shift (NICS) values of 1 were calculated by varying the distance of the probe from the plane of 1 . Whereas a simple bell‐type profile was estimated for the complex ( 1 )₂–( G1 )₄, the distance profiles of the CIS became increasingly flat for ( 1 )₂–( G2 )₄ and ( 1 )₂–( G3 )₄. Finally, we investigated the paratropic ring‐current effect just above the COT core of the complex 1 –( G4 )₂, which agrees well with the theoretically estimated distance‐dependent induced magnetic effect. Consequently, both experimental and theoretical studies on the complexes of porphyrin sheets with guest molecules revealed for the first time a unique distance dependence of the paratropic ring current.     

Photoinduced charge separation and charge recombination in the [60]fullerene-diphenylbenzothiadiazole-triphenylamine triad: role of diphenylbenzothiadiazole as bridge

Photoinduced electron-transfer processes of the newly synthesized [60]fullerene-diphenylbenzothiadiazole-triphenylamine (C60-PBTDP-TPA) triad in polar and nonpolar solvents have been studied by using time-resolved transient absorption and fluorescence measurements from picosecond to microsecond regions. By fluorescence lifetime measurements in picosecond time regions, excitation of the charge-transfer transition of the PBTDP-TPA moiety in C60-PBTDP-TPA induces energy transfer to the C60 moiety generating 1C60*-PBTDP-TPA, competitively with charge separation generating C60*--PBTDP-TPA*+. From 1C60*-PBTDP-TPA, which is generated directly and indirectly, charge separation occurs generating C60*--PBTDP-TPA*+ in polar solvents. The C60*--PBTDP-TPA*+ formed via the singlet excited states decayed within a few nanoseconds as revealed by the picosecond transient absorption spectra. In the nanosecond time region, C60*--PBTDP-TPA*+ is produced slowly, probably via 3C60*-PBTDP-TPA. Lifetimes of such slowly generated C60*--PBTDP-TPA*+ were longer than 1 micros, which are the longest values among the C60-bridge-TPA triad systems reported hitherto at room temperature. Roles of the PBTDP-TPA moiety with twisted intermolecular charge-transfer character playing as energy donor and electron donor in addition to the bridge have been disclosed.     

Study of photoinduced electron transfer between [60]fullerene and proton-sponge by laser flash photolysis: addition effects of organic acid

Photoinduced electron-transfer processes between fullerene (C60) and 1,8-bis(dimethylamino)naphthalene, which is called a proton-sponge (PS), have been investigated by means of laser flash photolysis in the presence and absence of CF3CO2H. For a mixture of C60 and PS, the transient absorption spectra showed the rise of the C60 radical anion with concomitant decay of the C60 triplet (3C60), suggesting that photoinduced intermolecular electron transfer occurs via 3C60 in high efficiency in polar solvent. For a covalently bonded C60-PS dyad, photoinduced intramolecular charge-separation process takes place via the excited singlet state of the C60 moiety, although charge recombination occurs within 10 ns. For both systems, electron-transfer rates were largely decelerated by addition of a small amount of CF3CO2H, leaving the long-lived 3C60. These observations indicate that the energy levels for charge-separated states of the protonated PS and C60 become higher than the energy level of the 3C60 moiety, showing low donor ability of the protonated PS. Thus, intermolecular electron-transfer process via 3C60 for C60-PS mixture and intramolecular charge-separation process via 1C60-PS for C60-PS dyad were successfully controlled by the combination of the light irradiation with a small amount of acid.     

Synthesis of cyclotetrapeptides,am-toxin analogs,containing α-hydroxyalanine

Condensation of amide with α-keto acid to yield a α-hydroxyalanine (α-Hyala) or dehydroalanine residue was applied to syntheses of analogs of AM-toxins, cyclotetradepsipeptides. Cyclo(-α-Hyala-L-Ala-L-Val-L-Phe-), cyclo(-α-Hyala-L-Ala-L-Hmb-L-Phe-) and cyclo(-α-Hyala-L-Ala-L-Hmb-L-Tyr-) (Hmb, 2-hydroxy-3-methylbutanoic acid) were obtained from the corresponding pyruvyl-tripeptide amides in good yields by the treatment of anhydrous hydrogen fluoride.     

Studies on the syntheses of heterocyclic compounds. Part DCXXXII. The formation of the benzimidazo[2,1-a]isoquinoline by reaction of the 1,2,3,4-tetrahydro-1-(2-nitrophenethyl)isoquinoline with triethyl phosphite

Reductive cyclization of 1,2,3,4-tetrahydro-6,7-dimethoxy-1-(4,5-dimethoxy-2-nitrophen-ethyl)isoquinoline (V) with triethyl phosphite gave 5,6-dihydro-2,3,9,10-tetramethoxybenzimidazo[2,1-a]isoquinoline (IX), whose structure was identified by the spectroscopic analyses by an alternative synthesis.     

Features of the energy surface in Dirac-Fock discrete basis description as applied to the Be atom

The features of the Be atom's energy surface as a function of basis set exponents in the Slater-type basis have been examined for both “balanced” and “unbalanced” basis sets. The results clearly show that the “balanced” basis guarantees a minimum energy which is an upper bound to the numerical Dirac-Fock limit. The “unbalanced” basis, however, gives a minimum energy which is much lower than the numerical limit.     

Catalytic Effects of Metal-loaded Membrane-like Alumina Tubes on Ammonia Synthesis in Atmospheric Pressure Plasma by Dielectric Barrier Discharge

Plasma synthesis of ammonia was studied at atmospheric pressure using a dielectric-barrier-discharge-plasma reactor equipped with a metal-loaded membrane-like alumina tube as a catalyst between the electrodes. Introducing the pure alumina into N₂–H₂ plasma resulted in an increase in the ammonia yield and the further improvement was achieved by loading the alumina with Ru, Pt, Ni, and Fe. These results clearly demonstrate the catalytic effects of the alumina and the metals in the plasma reaction. Temperature-programmed desorption and isotope exchange reaction of nitrogen revealed that plasma-excited N₂ molecules were subjected to dissociative adsorptions mainly on the alumina to form atomic N(a) (The suffix “(a)” denotes adsorbed species) species, which were converted into ammonia by H₂ plasma. A role of the metals is considered to be acceleration of ammonia formation by the reaction of the alumina-adsorbed N(a) atoms with plasma-activated hydrogen species.     

Sequence distribution of 1,4 and 3,4 units in polyisoprenes

The ¹³C-NMR spectra of hydrogenated polyisoprenes were investigated. Polyisoprenes containing various ratios of 1,4 and 3,4 units were prepared with n-BuLi/Et₂O and were hydrogenated by using p-toluenesulfonylhydrazide. ¹³C-NMR signals of the hydrogenated polymers were assigned for the triad sequences arising respectively from the 1, 4 and 3, 4 units of polyisoprenes. On the basis of these assignments it was confirmed that 1,4 and 3,4 units were randomly distributed in the polyisoprenes prepared with n-BuLi and that these polymers did not contain appreciable amounts of head-to-head or tail-to-tail 1,4 linkages.     

Effect of separators on the self-discharge reaction in nickel-metal hydride batteries

The effects of separators on the self-discharge behavior and the suppression of self-discharge by a sulfonated polyolefin separator were investigated with test cells. The experimental results indicate that a sulfonated polyolefin separator effectively suppresses the self-discharge reaction in nickel-metal hydride batteries. It is also found that a sulfonated polyolefin sheet does not necessarily need to be sandwiched by positive and negative electrodes to act as a separator; it can be placed anywhere within a cell to suppress the self-discharge reaction. The self-discharge reaction is considered to be suppressed by trapping redox shuttle substances, especially nitrogen-containing compounds, by the separator.     

A novel and useful oxidative intramolecular coupling reaction of phenol ether derivatives on treatment with a combination of hypervalent iodine(III) reagent and heteropoly acid

The oxidative intramolecular coupling reaction of phenol ether derivatives (nonphenolic derivatives) on treatment with a novel combination of a hypervalent iodine(III) reagent, phenyliodine bis(trifluoroacetate) (PIFA), and heteropoly acid (HPA) was studied. Biaryl compounds were obtained in excellent yields on treatment of highly substituted phenol ethers. On the other hand, spirodienones were specifically formed when one of the preferred arylic coupling sites was substituted with a methoxy group in the para position.