Fluorescence and Laser photolysis studies on 1,2,4,5-tetracy anobenzene CT complexes in micellar solutions

CT complexes of 1,2,4,5-tetracyanobenzene were formed in the inner part of neutral micelles and in the surface region of ionic ones. The excitation of the CT absorption band of these complexes gives broad and structureless CT fluorescence spectra, their lifetimes being relatively short (≈10 ns). Micellar effect upon ionic photodissociation was observed, and their quantum yeild is smaller than that obtained in acetonitrile. These results are quite different from those on another typical excited CT system of pyrene and N,N-dimethylaniline.     

A novel method for preparation of 2-(methyl- or phehnylthio)alkanoic esters

Ethyl 2-acetylalkanoate gave ethyl 2-(methyl- or phenylthio)alkanoate in high yield on treatment wiht CH₃SSO₂CH₃, PhSSO₂Ph, or PhSSPh in the presence of small excess of EtONa in EtOH. Application of the present method to synthesis of pellitorine and the queen substance is also described.     

Computer simulation for the cooligomerization system

In order to clarify the kinetic features of the styrene (A)–methyl methacrylate (B)–CCl₄(S) cooligomerization system, a computer simulation was carried out. The experimental data on the degree of polymerization and the deviation of the cooligomer composition from the statistical steady-state composition were comparatively well explained by calculations based on the kinetic equations derived from the assumed reaction scheme and the values of the velocity coefficients, although the values of the four velocity coefficients in the initiation step and the velocity coefficient of the termination by the coupling of two solvent radicals were estimated. The results of the calculation of the rate of each component reaction show that the following two reactions are the most important in the initiation and in the transfer and termination steps when the [S]/([A] + [B]) ratio is large: where, A, A*, and P are styrene, polystyryl radical, and the cooligomer, respectively. Moreover, it was concluded that the deviation of the cooligomer composition from the statistical steady-state composition was caused by these two reactions.     

Protective effects of small amounts of bis(2-ethylhexyl)sulfosuccinate on the helical structures of human and bovine serum albumins in their thermal denaturations

The protective effect of an anionic double-tailed surfactant, sodium bis(2-ethylhexyl)sulfosuccinate (AOT), on the structures of human serum albumin (HSA) and bovine serum albumin (BSA) in their thermal denaturations was examined by means of circular dichroism measurements. The structural changes of these albumins were reversible in the thermal denaturation below 50 degrees C, but became partially irreversible above this temperature. The effect was observed in the thermal denaturation above 50 degrees C. Although the helicity of HSA decreased from 66% to 44% at 65 degrees C in the absence of the surfactant, the decrement of it was restrained in the coexistence of AOT of extremely low concentrations. When the HSA concentration was 10 muM, the maximal protective effect appeared at 0.15 mM AOT. In the coexistence of the surfactant of this concentration, the helicity was maintained at 58% at 65 degrees C, increasing to the original value upon cooling to 25 degrees C. Beyond 0.15 mM AOT, the helicity sharply decreased until 3 mM AOT. A particular AOT concentration required to induce the maximal protective effect ([AOT]REQ) was examined at different HSA concentrations. [AOT]REQ shifted to higher values with an increase of the protein concentration. From the protein concentration dependences of [AOT]REQ, the maximal protection was estimated to require 8.0 and 5.0 AOT ions per a molecule of HSA and BSA, respectively. The AOT concentration, where the protective effect was observed, was too low to form its micelle-like aggregate. Then the protein structures might be stabilized by a cross-linking of surfactant monomers bound to specific sites. These specific sites might exist between a group of nonpolar residues and a positively charged residue located on several sets of amphiphilic helical rods in the proteins. Such a unique function of the double-tailed ionic surfactant is first presented by its characteristic nature as an amphiphilic material.     

Polymerization of allyl esters of unsaturated acids. VII. Copolymerization of methyl allyl maleate and fumarate with styrene

Radical copolymerizations of methyl allyl maleate (MAM) and methyl allyl fumarate (MAF) with styrene (St) are carried out in bulk using AIBN as an initiator at 60°C, and their copolymerization behaviors are compared in detail. The different rate features are observed with each other; thus in the MAF-St copolymerization the rate was quite enhanced and, also, the maximum rate was found at the molar ratio of 1:1 in the monomer feed, whereas no maximum phenomenon of the rate was apparent for the MAM—St copolymerization. The copolymerizability of MAF with St was quite high, whereas that of MAM was very poor. The cyclization of MAM or MAF was hindered by the highly reactive St monomer. These results are discussed in terms of the formation of the charge—transfer complex between MAF and St and, furthermore, the cyclocopolymerization kinetics involving the 17 elementary reactions as the propagation reactions.     

Polymerization of allyl esters of unsaturated acids. V. Cyclopolymerization of methyl allyl fumarate

The kinetics of radical polymerization of methyl allyl fumarate (MAF) is discussed in terms of cyclopolymerization and compared with the polymerization results of methyl allyl maleate (MAM) as a cis isomer. In the polymerization of MAF, the rate and degree of polymerization were quite enhanced compared with MAM, and gelation occurred at low conversion. The content of the unreacted allylic double bonds of the MAF polymer was quite large; whereas those of the unreacted fumaric double bonds and the cyclic structural units showed reverse tendencies. Only a slight presence of a five-membered ring was observed in the MAF polymer. The cyclization constants K_A and K_V, the ratios of the rate constants of the unimolecular cyclization reaction to those of the bimolecular propagation reaction of the uncyclized allylic and fumaric radicals, were estimated to be 2.73 and 1.48 mole/liter, respectively. These values suggest the great difference in the cyclopolymerization behavior between two isomeric monomers. These results are discussed in detail in connection with the high reactivity of the fumaric double bond compared to the maleic double bond. In addition, the formation mode and the sequence distribution of the structural units of the polymer produced are discussed on the basis of these analytical results. Thus, for the MAF polymer obtained in the bulk polymerization, about 60% of the cyclic structure can be formed via the intramolecular attack of the uncyclized fumaric radical on the allylic double bond, as opposed to the case of MAM via the predominant intramolecular attack (ca. 90%) of the uncyclized allylic radical on the maleic double bond; these results and the low probability for the succession of cyclic structures and the rather high probability of a vinyl-to-vinyl addition are presented.     

Comparison of PAMAM-Au and PPI-Au nanocomposites and their catalytic activity for reduction of 4-nitrophenol

Dendrimer-Au nanocomposites are prepared in aqueous solutions using poly(amidoammine)dendrimers (PAMAM) (generation 2, 3, and 5) and poly(propyleneimine)dendrimers (PPI)(generation 2, 3, and 4) by wet chemical NaBH(4) method. The Au nanoparticles thus obtained are 2-4 nm in diameter for both dendrimers and no generation dependence on the particle size is observed, whereas the generations of the dendrimers are increased as stabilization of Au-nanoparticles is achieved with lower dendrimer concentrations. Studies of the reduction reaction of 4-nitrophenol using these nanocomposites show that the rate constants for the PAMAM dendrimers (generations 2 and 3) are higher than those for the PPI dendrimers (generations 2 and 3), while a distinct difference in the rate constants is not seen for the PAMAM dendrimer (generation 5) or the PPI dendrimer (generation 4). In addition, the rate constants for the reduction of 4-nitrophenol involving all the dendrimers decrease with increases in dendrimer concentrations.     

Synthetic studies on (+)-aplasmomycin. 1. Stereoselective synthesis of the C-12˜C-17 segment

The C-12˜C-17 segment of (+)-aplasmomycin ( ) was synthesized stereoselectively starting from (−)-malic acid based on the stereoselective ketone reduction.     

A new method of constructing dearomatized compounds using triazene

We are reporting on a new method of constructing dearomatized compounds from α-substituted aryltriazenes. Deprotonation occurs at C atom α to N3. Nucleophilic attack of generated anion at the ortho-position of aryl group forms a new carbon-carbon bond. A stereoselective reaction was observed when the substituents on the C α to N3 are tied together in either a pyrrolidine or a piperidine. The product of this reaction possessed an interesting dearomatized tetrahydrobenzotriazine framework.     

Molecular structure of 3-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 3-methylthiophene

has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: r_g(S---C₂) = 1.719(2) Å, r_g(C₂=C₃) = 1.370(3) Å, r_g(C₃---C₆) = 1.497(6) Å, r_g(C₂---H) = 1.101(5) Å, CSC = 91.6(2)°, SC₂C₃ = 113.3(5)°, SC₅C₄ = 111.3(3)°, C₂C₃C₆ = 123.2(11)° and C₃C₆H = 112(2)°. The values of r(S---C₂) − r(S---C₅) and r(C₂=C₃) − r(C₄=C₅) were fixed at the 3–21G* value of 0.002Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit.