Mechanism of charge-transfer polymerization. V. Photopolymerization and photocyclodimerization of N-vinylcarbazole in the N-vinylcarbazole–oxygen–solvent system

Photochemical reactions of N-vinylcarbazole (VCZ), studied in various solvents, were profoundly influenced by the atmosphere. In the deaerated system radical polymerization of VCZ occurred in various solvents, e.g., tetrahydrofuran, acetone, ethyl methyl ketone, acetonitrile, methanol, sulfolane, N,N-dimethylformamide (DMF), or dimethyl sulfoxide (DMSO). By contrast, when dissolved oxygen was present, cyclodimerization of VCZ occurred exclusively to give trans-1,2-dicarbazole-9-yl-cyclobutane in such polar, basic solvents as acetone, ethyl methyl ketone, acetonitrile or methanol. In stronger basic solvents, i.e., sulfolane, DMF, or DMSO, simultaneous radical polymerization and cyclodimerization of VCZ proceeded, the ratio of the cyclodimerization to the radical polymerization decreasing in the order, sulfolane > DMF > DMSO. In dichloromethane, on the other hand, cationic polymerization of VCZ occurred irrespective of the atmosphere. It is suggested that oxygen acts as an electron acceptor to the excited VCZ, electron transfer occurring in polar solvents from the excited VCZ to oxygen to give transient VCZ cation radical. The effect of solvent basicity on the photocyclodimerization of VCZ is discussed.     

In situ scanning tunneling microscopy of molecular assemblies of cobalt(II)- and copper(II)-coordinated tetraphenyl porphine and phthalocyanine on Au(100)

Molecules of copper(II) and cobalt(II) 5,10,15,20-tetraphenyl-21H,23H-porphine (CuTPP and CoTPP) and cobalt(II) phthalocyanine (CoPc) are spontaneously adsorbed onto reconstructed Au(100) substrate from a benzene solution containing each individual complex. In situ scanning tunneling microscopy (STM) was used to examine the real-space arrangement and the internal molecular structure of each of the individual molecules in 0.1 M HClO4 under potential control. The adsorption of CuTPP and CoTPP produced the same highly ordered square array with an intermolecular spacing of 1.44 nm on a reconstructed Au(100) surface. These molecular superlattices and the underlying reconstructed Au(100) predominated between 0 and 0.9 V, but lifting of the reconstructed Au(100) surface and elimination of the ordered adlayers occurred at more positive potentials. Molecular resolution STM revealed propeller-shaped admolecule with its center imaged as a protrusion for Co(II) and a depression for Cu(II). In contrast, the spontaneous adsorption of CoPc molecules resulted in a rapid phase transition from the reconstructed Au(100) surface to the (1 x 1) phase, coupled with the production of locally ordered, square-shaped arrays with an intermolecular distance of 1.65 nm. This molecular adlayer and the Au(100)-(1 x 1) remained unchanged when the potential was modulated between 0 and 1.0 V. These results indicate that the subtle variation in the molecular structure of adsorbate influenced not only its spatial arrangement but also the structure of the underlying Au(100) substrate.     

Furopyridines. IV. Unexpected dimerization of 5-methyl-4,5,6,7-tetrahydrofuro[3,2-c]- and 6-methyl-4,5,6,7-tetrahydrofuro[2,3-c]pyridine by acidic hydrolysis

Reaction of 5-methyl-4,5,6,7-tetrahydrofuro[3,2-c]- ( 1 ) and 6-methyl-4,5,6,7-tetrahydrofuro[2,3-c]pyridine ( 2 ) with hydrochloric acid gave novel dimerized compounds 3a-d and 4a-d , respectively. The structures of 3a, 3b, 4a and 4b were determined by spectroscopic method, and 3c, 3d, 4c and 4d by single crystal X-ray analysis. The reaction courses for the formation of these compounds are proposed.     

The influence of basis sets on wave function tails

Wave function tails are analyzed quantitatively by investigating the dependence of exterior electron density (EED ) on basis sets; the EED is defined as the integrated electron density outside the repulsive molecular surface. Ab initio MO calculations with large scale basis sets were performed to establish the benchmark order of EED values for valence orbitals of some simple molecules. It is found that very popular basis sets, such as 4-31G, which are determined by energy optimization, are inferior in describing the wave function tails to some similar size basis sets, such as MIDI -4, which are obtained by least-squares fit to near Hartree-Fock atomic functions. Further the EED values for atomic 2s functions are shown to be unfavorably smaller than those for atomic 2p functions when the same value is used for the exponent α in the GTO basis sets. This indicates that the frequently used constraint α_s = α_p is not appropriate for describing wave function tails with medium-size basis sets. Deficiencies in the energy-optimized basis sets are found to become more serious for molecules including heavier atoms.     

Anodic modification of proline derivatives using a lithium perchlorate/nitromethane electrolyte solution

[reaction: see text] N-Acyliminium cation of prolines was efficiently generated to accumulate in an undivided cell at 0 degrees C by an anodic oxidation of N-acylprolines or alpha'-phenylsulfanylated N-acylproline derivatives in a lithium perchlorate/nitromethane solution. The iminium cation intermediates gave modified prolines by a reaction with nucleophiles under mild conditions.     

Theory of electric field-induced optical second harmonic generation in semiconductors

The nonlinear optical coefficientd _ij(kl) (2, 0,, ) for electric field-induced optical second harmonic generation in semiconductors is calculated by means of a perturbation treatment. The result is given directly as a Brillouin zone integral over a resonant energy denominator. A simplified energy band structure model is used to carry out the Brillouin zone integral. The analytic closed-form expression ford _ij(kl) (2, 0,, ) thus obtained permits the calculation of the absolute value of its spectrum from available energy band parameters. The dispersion ofd ₁₁₍₁₁₎ (2, 0,, ) of Ge is numerically calculated, second harmonic photon energies being close to theE ₀ andE ₁ gaps. The results show pronounced resonant behaviours.     

Simultaneous determination of thiols and disulfides by high-performance liquid chromatography with fluorescence detection

The proposed simultaneous determination of thiols and disulfides requires 4- (aminosulfonyl)- 7-fluor-2,1,3,-benzoxadiazole (ABD-F) as the pre-column derivatization reagent for thiols and ammonium 7-fluoro-2,1,3,-benzoxadiazole-4-sulfonate (SBD-F) for disulfides followed by chromatography. The thiols and disulfides in solution are treated with ABD-F at 60°C for 5 min in pH 9.3 borate buffer containing 1 nM disodium-EDTA. After removal of excess of ABD-F with ethyl acetate, the remaining disulfides in the aqueous phase are treated with SBD-F at 60°C for 20 min in the presence of tri-n-butylphosphine, a reducing agent. The ABD-thiols and SBD-thiols thus produced are separated by reversed-phase chromatography and detected by fluorimetry (380- nm excitation, 510 - nm emission). SBD-cystein, SBD-homocystein, ABD-homocysteine, ABD-cysteine, SBD-glu- tathione, ABD-homocystein, SBD-N-acetylcystein, ABD-glutatione and ABD-N-acetylcysteine are well separated by linear gradient elution from 0.15 M H₃PO₄/CH₃CN (96:4) to 0.15 M H₃PO₄/CH₃CN (85:15) over 30 min followed by isocratic elution with 0.15 M H₃PO₄/CH₃CN (85:15) fro 10 min. The detection limits for the derivatives are in the range 0.09–0.9 pmol. When the method was applied to the determination of thiols and disulfides in rat tissues, cystein (0.75 μmol g^-1) and cystine (0.62 μmol g^-1) were obtained in kidney and reduced glutathione (1.4–3.4 μmol g^-1) was observed in liver, spleen, heart and testicle.     

Effect of adlayer structure on the host-guest recognition between calcium and crown-ether-substituted phthalocyanine arrays on Au single-crystal surfaces.

Adlayers of 15-crown-5-ether-substituted cobalt(II) phthalocyanine (CoCRPc) were prepared by immersion of either Au(111) or Au(100) substrate into benzene-ethanol (9:1 v/v) mixed solutions containing CoCRPc. In situ STM imaging was carried out after transferring the CoCRPc-modified Au crystals into aqueous HClO(4) solution. The packing arrangement of the CoCRPc array on Au(111) was determined to be p(8 x 4 radical 3R - 30 degrees ), and the internal structure was clearly observed by high-resolution STM. Two adlayer structures of CoCRPc, (8 x 9) and (4 radical 5 x 4 radical 5)R26.7 degrees, were found on the Au(100)-(1 x 1) terrace. In the presence of 1 mM Ca(2+), two Ca(2+) ions were trapped in two diagonally located 15-crown-5-ether moieties of each CoCRPc molecule on Au(111), whereas encapsulation of Ca(2+) ions was not seen in the CoCRPc arrays on the Au(100)-(1 x 1) surface. The present study demonstrates that the relationship between crown moieties of CRPc and the underlying Au lattice is important in the trapping of Ca(2+) ions in crown rings.