Alternative synthesis and novel oxidizing ability of 6,9-disubstituted cyclohepta[b]pyrimido[5,4-d]pyrrole-8(6H),10(9H)-dione derivatives

Synthesis of 6,9-disubstituted cyclohepta[b]pyrimido[5,4-d]pyrrole-8(6H),10(9H)-diones 7a-g was accomplished by ring opening and ring closure sequences of 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8,10(9H)-dione derivatives induced by several amines. Furthermore, alternative synthetic methodology for compounds 7a-e was also accomplished by single-step reaction of 2-chlorotropone with 6-aminouracil derivatives under mild conditions. X-ray crystal analysis of 7a was carried out to clarify the structural characteristics. The properties of 7a-e were studied by the UV-vis spectra and reduction potentials (−1.24 to −1.39 V vs Ag/AgNO₃). Novel photo-induced oxidation reaction of 7a-d toward some amines under aerobic conditions was carried out to give the corresponding imines in more than 100% yield [based on compounds 7a-d], suggesting the oxidation reaction occurs in an autorecycling process.     

Novel synthesis and oxidizing ability of tropylium ions annulated with two 2,4-dimethylfuro[2,3-d]pyrimidine-1(2H),3(4H)-diones

Convenient preparation of novel tropylium ions annulated with two 2,4-dimethylfuro[2,3-d]pyrimidine-1(2H),3(4H)-diones, 12a(+).BF(4)(-) and 12b(+)().BF(4)(-), consists of a reaction of 2-methoxytropone with dimethylbarbituric acid to give 7,9-dimethyl-3-[1',3'-dimethyl-2'(1'H),4'(3'H),6'(5'H)-trioxopyrimidin-5'-ylidene]cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dione 8 and the following oxidative cyclization by using DDQ or photoirradiation under aerobic conditions. On the basis of the MO calculations, the selectivity of two types of oxidative cyclization reactions of 8 was rationalized. X-ray crystal analyses and MO calculations were carried out to clarify the structural characteristics of 12a(+). BF(4)(-) and 12b(+).BF(4)(-). The stability of cations 12a(+) and 12b(+) is expressed by the pK(R) + values which were determined spectrophotometrically as 8.8 and 8.6. The electrochemical reduction of 12a(+) and 12b(+) exhibited reduction potential at -0.63 and -0.62 (V vs Ag/AgNO(3)), respectively. Reactions of 12a(+)().BF(4)(-) and 12b(+)().BF(4)(-) with some nucleophiles, hydride and diethylamine, were carried out to clarify that the reactivity of 12a(+)().BF(4)(-) and 12b(+).BF(4)(-) was substantially dependent on the annulating position. The oxidizing ability of 12a(+).BF(4)(-) and 12b(+).BF(4)(-) toward alcohols and amines in the autorecycling process was demonstrated as well.     

Application and details of photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones and related compounds

As novel methodology for synthesizing the furan ring, a photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones (7a-c) and related compounds 9a-c was accomplished to give 5,10-methanocycloundeca[4,5]furo[2,3-d]pyrimidine-2,4(1,3H)-dionylium tetrafluoroborates (8a-c⁺·BF₄⁻) and related compounds 2a-c⁺·BF₄⁻, respectively. In the photoinduced oxidative cyclization, the molecular oxygen in air is used as oxidant and the reaction proceeds under mild conditions to give desired products without byproducts, and thus, it is interesting from the viewpoint of the green chemistry. On the reactions of the mono-substituted derivatives 7d,e and 9e,f, the selectivity of the photoinduced cyclizations were reversed as compared with those of the DDQ-promoted oxidative cyclizations. By the NMR monitoring of the reactions of 7a and deuterated compound 7a-D₂ under degassed conditions, the details of the reaction pathway were clarified and rationalized on the basis of the MO calculation by the 6-31G^∗ basis set of the MP2 levels as well.     

Activation of C-H and C-Br bonds in cyclopalladation reactions of Schiff base ligands: Influence of the benzylidene ring substituents

Reaction of Pd(AcO)₂ with the Schiff base ligands 2-Br-4,5-(OCH₂O)C₆H₂C(H)N(Cy) (a) and 4,5-(OCH₂CH₂)C₆H₃C(H)N(Cy) (b) leads to the cyclometallated compounds [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)N(Cy)-C6,N}(μ-O₂CMe)]₂ (1a) and [Pd{4,5-(OCH₂CH₂)C₆H₂C(H)N(Cy)-C6,N}(μ-O₂CMe)]₂ (1b), respectively, via C-H activation. Treatment of a with Pd₂(dba)₃ gave [Pd{4,5-(OCH₂O)C₆H₂C(H)N(Cy)-C2,N}(μ-Br)]₂ (6a), via C-Br activation. The metathesis reaction of 1a and 1b with aqueous sodium chloride gave the corresponding cyclopalladated dimers with bridging chloride ligands, 2a and 2b, respectively. Treatment of the halogen-bridged compounds with tertiary tri- and diphosphines in the appropriate molar ratio gave the mono and dinuclear compounds 3a-5a, 7a-9a and 3b-5b. The structure of compounds 3a, 4a, 5a, 8a, 2b, 3b and 5b has been determined by X-ray diffraction analysis.     

Estimating the reversing and non‐reversing heat flow from standard DSC curves in the glass transition region

A mathematical model for the total heat flow obtained in differential scanning calorimetry (DSC) experiments from polymers with enthalpic relaxation is proposed. It is limited to the glass transition and enthalpic relaxation range of temperature and to the cases where the enthalpic relaxation is the only non‐reversing process taking place. The model consists of a mixture of functions representing the heat capacity heat flow of the glassy and non‐glassy fractions, the glass transition progress and the enthalpic relaxation heat flow. Optimal fittings of the model were performed on the experimental total heat flow data, obtained from two thermoplastics with different aging times. Considering which functions of the mixture represent reversing and non‐reversing processes, the reversing and non‐reversing heat flows were also estimated. The estimated reversing and non‐reversing signals were compared with the ones obtained by modulation. On the whole a good match was found, which was even better considering that the estimates are not affected by the frequency effect of the modulated temperature DSC (MTDSC) measurements. The model assumes linear trends for the heat capacity heat flow of the glassy and non‐glassy structures. The glass transition progress is represented by a generalized logistic function and the enthalpic relaxation heat flow by the first derivative of another generalized logistic. It brings about a new approach to these phenomena, where the parameters of these functions represent the temperature at which each event is centered, the change of heat capacity (C_p) at the glass transition and the energy involved in the enthalpic recovery. Copyright © 2011 John Wiley & Sons, Ltd.     

TOF-SIMS imaging of halide/thiocyanate anions and hydrogen sulfide in mouse kidney sections using silver-deposited plates

In vivo imaging of reactive small molecule metabolites with high spatial resolution and specificity could give clues to understanding pathophysiology of various diseases. We herein applied time of flight-secondary ion mass spectrometry (TOF-SIMS) to newly developed silver-deposited plates that were stamped on mouse tissues, and succeeded in visualization of halide (Cl⁻, Br⁻, and I⁻) and pseudohalide thiocyanate (SCN⁻) anions, a class of substrates for neutrophils/eosinophil peroxidases to produce hypohalous acids (HOX/OX⁻ mixture; X: (pseudo)halides), as well as hydrogen sulfide (H₂S). Forty-micrometer frozen mouse kidney sections on cover glasses were attached to 37 °C preheated silver-deposited plates and incubated at −10 °C for 1 h. After sputter cleaning to remove surface contaminants, the plates were analyzed by TOF-SIMS to identify distribution of Br⁻, AgBr₂⁻, I⁻, AgI₂⁻, SCN⁻, as well as S²⁻ and AgS⁻ as products of tissue-derived H₂S. Br⁻, AgBr₂⁻, I⁻, and SCN⁻ anions were mainly distributed in core regions including the inner medulla and inner stripe of the outer medulla (except for I⁻), rather than outer regions such as the cortex and outer stripe of the outer medulla. AgI₂⁻ anion was spread over the whole kidney, although its levels were relatively low. In contrast, S²⁻ and AgS⁻ anions were mainly present in the outer regions. To our knowledge, this is the first imaging study to reveal the distribution of (pseudo)halides and H₂S in animal tissue sections.     

TMDSC phase angle for a better nanocomposite interphase identification

The present study suggests a new approach, based on the utilization of temperature modulated differential scanning calorimetry (TMDSC) technique, for identifying and characterizing the organic?Cinorganic interphase of two materials: an epoxy?Cfumed silica nanocomposite and a thermoplastic polyurethane (TPU)?Cmultiwalled nanotube (MWNT) composite. The approach used here makes use of TMDSC data and basically consists of using the phase angle or the derivative of the reversing heat flow instead of the reversing heat flow curve itself. In the case of epoxy?Cfumed silica composites, two glass transition regions were identified. The glass transition temperature (T _g) of the composite was observed to vary as a consequence of the filler content. This study shows that the T _g variation is due to the formation of an organic?Cinorganic interphase, with its own glass transition temperature, which is different from the epoxy matrix T _g. In the case of TPU?CMWNT composites, two relaxations and an additional first order transition were observed: the first relaxation corresponds to the hard segment, the second is related to an interaction between filler and matrix and the third process may be connected to the partial melting of the hard segment. The addition of 0.5?wt% MWNT causes a small reduction in T _g of the TPU. A major nanotube addition, 10?wt%, induces the appearance of a new relaxation that may be associated with the existence of an interface. In general, a better separation between the matrix and interphase glass transitions was obtained by the TMDSC phase angle signal.     

Synthesis, properties, and NAD+-NADH-type redox ability of 14-substituted 1,3-dimethyl-5,10-methanocycloundeca[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3h)-dionylium tetrafluoroborates and their hydride adducts

A synthesis of 14-substituted 1,3-dimethyl-5,10-methanocycloundeca[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium tetrafluoroborates 11a,b(+).BF4- was accomplished by the methylation of 5,10-methanocycloundeca[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dione derivatives with MeI and following anion-exchange reaction by treatment with 42% aq HBF(4). Compound 11b(+).BF4- was synthesized alternatively by the reaction of 1,6-methano[11]annulenylium tetrafluoroborate with 6-phenylamino-1,3-dimethyluracil and following oxidative cyclization reaction. Remarkable structural characteristics of 11a,b(+)were clarified on inspection of the UV-vis and NMR spectral data as well as X-ray crystal analyses. The stability of cations 11a,b(+)() is expressed by the pK(R+) values which were determined spectrophotometrically as 9.8 and 9.7, which are smaller by 1.4 and 1.2 pH units than those of the corresponding seven-membered ring cations, respectively; however, the values are larger by 3.6 and 3.5 pH units than that of the parent 1,6-methano[11]annulenylium ion (pK(R+) = 6.2). The feature is rationalized on the basis of the perturbation derived from the bond fixation of the parent cation and the electron-donating ability of pyrrolopyrimidine. The electrochemical reduction of 11a,b(+).BF4- exhibited reduction potential at -0.58 and -0.52 (V vs Ag/AgNO3) upon cyclic voltammetry (CV). Reaction of 11a(+).BF4- with hydride afforded mixures of the C13- and C11-adducts in a ratio with hydride afforded, on the other hand, the C13-adduct as a single product. In both cations, the methano-bridge seemed to control the nucleophilic attack to the C13 favorably with exo-selectivity. The photoinduced autorecycling oxidation reactions of 11a,b(+).BF4- toward some amines under aerobic conditions were carried out to give the corresponding imines (isolated by converting to the corresponding 2,4-dinitrophenylhydrazones) with the recycling number of 1.1 to 32.2. Furthermore, as an example of the NAD+-NADH models, the reduction of a pyruvate analogue and some carbonyl compounds with the hydride adducts of 11a,b+.BF4- was accomplished for the first time to give the corresponding alcohol derivatives.     

Visible‐Light‐Induced Electron Transport from Small to Large Nanoparticles in Bimodal Gold Nanoparticle‐Loaded Titanium(IV) Oxide

A key to realizing the sustainable society is to develop highly active photocatalysts for selective organic synthesis effectively using sunlight as the energy source. Recently, metal‐oxide‐supported gold nanoparticles (NPs) have emerged as a new type of visible‐light photocatalysts driven by the excitation of localized surface plasmon resonance of Au NPs. Here we show that visible‐light irradiation (λ>430 nm) of TiO₂‐supported Au NPs with a bimodal size distribution (BM‐Au/TiO₂) gives rise to the long‐range (>40 nm) electron transport from about 14 small (ca. 2 nm) Au NPs to one large (ca. 9 nm) Au NP through the conduction band of TiO₂. As a result of the enhancement of charge separation, BM‐Au/TiO₂ exhibits a high level of visible‐light activity for the one‐step synthesis of azobenzenes from nitrobenzenes at 25 °C with a yield greater than 95 % and a selectivity greater than 99 %, whereas unimodal Au/TiO₂ (UM‐Au/TiO₂) is photocatalytically inactive.     

Mathematical analysis of a viscoelastic problem with temperature‐dependent coefficients—Part II: Regularity

In this paper, we study local regularity properties of the stress solution of a quasistatic thermoviscoelastic problem whose behaviour law is of the Maxwell–Norton type with temperature‐dependent coefficients. Copyright © 2007 John Wiley & Sons, Ltd.