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At least 307 records · Page 17Linked to original sources
PubMed1997

High Stabilities of Di(1-azulenyl)(4-hydroxyphenyl)methyl Hexafluorophosphates and Polarized Properties of alpha,alpha-Di(1-azulenyl)-1,4-benzoquinone Methides.

Acid-catalyzed condensation of azulenes 8a-c with 4-hydroxy- and 3,5-di-tert-butyl-4-hydroxybenzaldehyde leads to substituted di(1-azulenyl)(4-hydroxy- and 3,5-di-tert-butyl-4-hydroxyphenyl)methanes 7a- f, which are easily converted into substituted di(1-azulenyl)(4-hydroxy- and 3,5-di-tert-butyl-4-hydroxyphenyl)methyl cations 5a-f by oxidation with DDQ. The spectroscopic data are consistent with the protonated cationic structures of 5a-f. The electrochemical reduction of 5a-f showed a reversible wave at -0.74 to -0.86 V (V vs Ag/Ag(+)) upon cyclic voltammetry (CV), although 5d and 5e showed an irreversible wave at -0.79 V. The relatively high reduction potentials of 5a-f, compared with those of di(1-azulenyl)phenylmethyl cations 2a-c, exhibit the stabilization by 4-hydroxy substituents on the phenyl groups. These salts (5a-f.PF(6)(-)) bearing 4-hydroxyl groups on the phenyl rings have been converted by treatment with bases to alpha,alpha-di(1-azulenyl)-1,4-benzoquinone methides 6a-f, which revert to 5a-f.PF(6)(-) upon reprotonation with HPF(6). These quinone methides (6a-f) are highly polarized by the extreme-electrodonating properties of 1-azulenyl groups. The highly polarized properties of 6a-f reflected to the high pK(a) values of their conjugate acids (5a-c, 6.5-7.1, and 5d-f, 3.4-3.8). The strong solvatochromic effects also provide strong evidence of a large contribution of dipolar forms (6') in the ground state. The relatively low oxidation potentials of 6a-f (+0.35 to +0.47 V vs Ag/Ag(+)) reflected facile formation of phenoxy radical cations, stabilized by two 1-azulenyl groups.

Journal Article↗
PubMed1999

Aza[10]annulene: Next Higher Aromatic Analogue of Pyridine.

The aza[10]annulene isomers (CH)(9)N derived from "twist", "heart", "naphthalene-like", and "azulene-like" [10]annulenes by replacement of a CH group by nitrogen were investigated at the CCSD(T)/DZd//B3LYP/6-311+G level of theory. Except for the twist structure, all aza[10]annulenes studied were found to be aromatic. As the transannular repulsion is reduced in the aza[10]annulenes, the aromatic isomers become competitive energetically with the twist form.

Journal Article↗
PubMed2006

Kinetically controlled selective ionization study on the efficient collisional energy transfer in the deactivation of highly vibrationally excited trans-stilbene.

Direct measurements of the gas-phase collisional energy transfer parameters are reported for the deactivation of highly vibrationally excited trans-stilbene molecules, initially prepared with an average energy of about 40 000 cm(-1), in the bath gases argon, CO2, and n-heptane. The method of kinetically controlled selective ionization (KCSI) has been used. Complete experimental collisional transition probability density functions P(E',E) are determined, which are represented by a monoexponential form with a parametric exponent in the argument, P(E',E) proportional to exp[-{(E - E')/(C0 + C1E)}Y] (for downward collisions), well established from earlier KCSI studies. A comparison of the first moments of energy transfer rate constants, kE,1, or of resulting first moments of energy transfer, , for trans-stilbene with those for azulene and toluene clearly shows the considerably more efficient deactivation of trans-stilbene for all bath gases, presumably due to the much greater number of very low-frequency modes of trans-stilbene. However, on a relative scale this gain in deactivation rate of excited trans-stilbene is clearly collider dependent and decreases distinctly with the growing collision efficiency of the larger bath gas molecules.

Journal Article↗
PubMed1999

The versatility of polysorbate 80 (Tween 80) as an ionophore.

A number of experiments were performed to illustrate the unusual versatility of Polysorbate 80 (Tween 80) as an ionophore. New ions shown to be transported by it from and to water layers through a model membrane (CH2Cl2) include H3O+, Li+, Pb2+, Co2+, piperidinium ion, guanidinium ion, and Paraquat, while two complex ions resisted transport under the conditions used. "Reverse" transport of lipophilic guests (azobenzene, azulene, ferrocene) from and to organic solvents through water was also promoted by Tween 80, but C60 was not carried. Three water molecules were transported per molecule of KSCN by the Tween.

Excipients↗
PubMedDate not supplied

New proazulene guaianolides from Thapsia villosa.

Four new guaianolides 2-5 possessing the terpenoid skeleton of archangelolide [6] were isolated from a specimen of Thapsia villosa [chromosome number 2n = 66 (= 6x)]. Attempts to hydrolyze the natural products 2-6 yielded azulenes, mainly 7-acetyl-1,4-dimethylazulene [9].

Animals↗
PubMed2003

The first fully characterized 1,3-polyazulene: high electrical conductivity resulting from cation radicals and polycations generated upon protonation.

[reaction: see text] 1,3-Polyazulene prepared by the chemical polymerization of 1,3-dibromoazulene with Ni(COD)(2) was aptly characterized by spectroscopic analysis. The azulene units remain intact in the isolated polymer. Protonation of 1,3-polyazulene by trifluoroacetic acid was found to exhibit high conductivity and paramagnetic properties via the formation of cation radicals and di- and polycations.

Journal Article↗
PubMed2005

Synthesis of meso-azulenylporphyrins.

[reaction: see text] meso-Azulenylporphyrins 1-4 were prepared by Suzuki-Miyaura coupling or the Ziegler-Hafner method. 1-Azulenyl and 6-azulenyl groups are indeed acting as electron-donating and electron-accepting substituents toward Zn(II) porphyrin. Fluorescence of Zn(II) porphyrin in the dyads is strongly quenched depending upon substitution position of azulene in order of 2 > 1 > 4 > 3.

Journal Article↗
PubMed2004

Autofluorescence of developing plant vegetative microspores studied by confocal microscopy and microspectrofluorimetry.

Phenomenon of autofluorescence from vegetative microspores of spore-breding plant Equisetum arvense has been studied by methods of laser-scanning confocal microscopy (LSCM) and microspectrofluorimetry during the development of the cells. The microspores have demonstrated a difference between structures: blue-fluorescing cover and red-fluorescing chloroplasts. The fluorescence spectra of the studied cells was also measured by original microspectrofluorimeter. The character of the spectra and the color of fluorescence was changed during the microspores germination. The red fluorescence of the microspores was, mainly, due to the presence of chlorophyll and azulenes. The unicellular microspores may be recommended as natural probes of cellular viability and development.

Equisetum↗
PubMed2004

Vitamin B12 as an allosteric cofactor; dual fluorescence, hysteresis, oscillations and the selection of corrin over porphyrin.

Studies of the emission spectra of four Co(III) cobinamides (diaquo-, aquohydroxo-, dihydroxo- and dicyano-) show (1) that the excited states corresponding to the alphabeta and epsilon absorption bands behave like the S(1) and S(2) levels in the non-alternant hydrocarbon azulene (with emission from S(2)>> S(1) in violation of Kasha's rule) and (2) that the excited states include a TICT (twisted intramolecular charge transfer) mechanism, as in the simpler cyanines, but where the TICT state gives rise to dual fluorescence instead of cis-trans isomerisation. Combined with the previously reported dual fluorescence from the S(1) level in synthetic metal corrinoids and in the naturally-occurring metal-free corrin, this provides evidence that the existence of an additional (metastable) ground state with a significantly different vibronic splitting and nuclear configuration is an intrinsic property of the basic corrin ligand (irrespective of the nature of the side-chains and the metal ion or even the absence of a metal) which distinguishes it from porphyrin. The occurrence of hysteresis (and its associated oscillations) in redox reactions of the cobinamides involving both the Co(III/II) and Co(II/I) couples indicates that the corrin ligand also has an intrinsic ability to exist in different conformations or "allosteric" forms with differing redox potential, which further distinguishes it from the porphyrin ligand. Possible links between the existence of an additional metastable ground state and of allosteric changes and the likely reasons for the selection of corrin over a porphyrin for the vitamin B(12)-dependent enzymes are discussed.

Allosteric Regulation↗
PubMed2005

Corannulene and corazulene tiling of nanostructures.

Tiling modification in nanostructure modeling can be achieved by map operations, as well as the well-known Stone-Wales bond rotation. In this respect, sequences of classical operations, or single generalized operations, were used to obtain corannulenic flowers and corannulene-like azulenic patterns. The first "corazulenic" tessellation is reported. The aromaticity of some cages tessellated by the above supra-faces is discussed in terms of several different criteria. The covering was given as a pi-electron partition within some Kekulé valence structures.The well-known geometric index of aromaticity HOMA (harmonic oscillator model of aromaticity) enabled the evaluation of local aromaticity of the discussed supra-faces and brought evidence for several dominant Kekulé valence structures. The most intriguing is the "Kekulé-Dewar" valence structure of the cage C(192) having a disjoint corazulenic tessellation.

Chemical Phenomena↗
PubMed2006

Laboratory measurements of the recombination of PAH ions with electrons: implications for the PAH charge state in interstellar clouds.

Laboratory measurements of the recombination of polycyclic aromatic hydrocarbon (PAH) ions with electrons are presented. Experimental data have been obtained at room temperature for azulene (C10H8) and acenaphthene (C12H10) cations by the Flowing Afterglow with PhotoIons method. The results confirm that the recombination of PAH ions is fast although well below the geometrical limit. The set of our recent and present measurements reveal a definite trend of increasing rate with the number of carbon atoms of the PAH. This behaviour that needs further characterization is potentially of great interest for charge state models as recombination is a dominant mechanism of PAH ion destruction in the interstellar medium. The design of experiments to measure the recombination of larger PAHs and their temperature dependence is discussed.

Journal Article↗
PubMed2003

Torilin from Torilis japonica, as a new inhibitor of testosterone 5 alpha-reductase.

The methanolic extract of the fruits of Torilis japonica showed a potent inhibition against 5 alpha-reductase activity in vitro. Bioassay-guided fractionation of the methanol extract of the fruits followed by repeated silica gel chromatography led to the isolation of an active principle and its structure was identified as torilin on the basis of spectroscopic data. Torilin (IC50 = 31.7 +/- 4.23 microM) showed a stronger inhibition of 5 alpha-reductase than alpha-linolenic acid (IC50 = 160.3 +/- 24.62 microM) but was weaker than finasteride. (IC50 = 0.38 +/- 0.06 microM). Simple guaiane-type compounds, such as (-)-guaiol and guaiazulene showed weak inhibitory effects on the 5 alpha-reductase activity with IC50 values of f 81.6 microM and 100.8 microM, respectively, while azulene was not active. These results suggest that both degrees of unsaturation and the side-chain in the guaiane skeleton are important for the manifestation of 5 alpha-reductase inhibition.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed2005

Acetophenone derivatives and sesquiterpene from Euphorbia ebracteolata.

Two new acetophenone derivatives and a new sesquiterpene, along with four known acetophenone compounds, were isolated from the roots of Euphorbia ebracteolata. The structures of the new compounds were identified as 2,2',4,4'-tetrahydroxy-6,6'-dimethoxy-3,3'-dimethyl-7,5'-bisacetophenone, 2,4-dihydroxy-6-methoxy-3-methylacetophenone 4-O-alpha-L-arabinofuranosyl-(1-->6)-beta- D-glucopyranoside and decahydro-1a,4a,7,7-tetramethyl-1H-cycloprop[e]azulene-2,5-diol (1a R,2 R,4a S,5 S,7a R,7b R) using 1D and 2D NMR spectroscopy and X-ray crystallography.

Acetophenones↗
PubMed2004

Vibrational energy relaxation of naphthalene in the S(1) state in various gases.

Time-resolved fluorescence spectra of naphthalene in the S(1) state have been measured in various gases below 10(2) kPa. The band shape of the fluorescence changed in an earlier time region after the photoexcitation when an excess energy (3300 cm(-1)) above the 0-0 transition energy was given. The excitation energy dependence of the fluorescence band shape of an isolated naphthalene molecule was measured separately, and the time dependence of the fluorescence band shape in gases was found to be due to the vibrational energy relaxation in the S(1) state. We have succeeded in determining the transient excess vibrational energy by comparing the time-resolved fluorescence band shape with the excitation energy dependence of the fluorescence band shape. The excess vibrational energy decayed almost exponentially. From the slope of the decay rate against the buffer gas pressure, we have determined the collisional decay rate of the excess vibrational energy in various gases. The dependence of the vibrational energy relaxation rate on the buffer gas species was similar to the case of azulene. The comparisons with the results in the low temperature argon and the energy relaxation rate in the S(0) state in nitrogen were also discussed.

Journal Article↗
PubMed2004

Combined coupled-cluster and many-body perturbation theories.

Various approximations combining coupled-cluster (CC) and many-body perturbation theories have been derived and implemented into the parallel execution programs that take into account the spin, spatial (real Abelian), and permutation symmetries and that are applicable to closed- and open-shell molecules. The implemented models range from the CCSD(T), CCSD[T], CCSD(2)(T), CCSD(2)(TQ), and CCSDT(2)(Q) methods to the completely renormalized (CR) CCSD(T) and CCSD[T] approaches, where CCSD (CCSDT) stands for the CC method with connected single and double (single, double, and triple) cluster operators, and subscripted or parenthesized 2, T, and Q indicate the perturbation order or the excitation ranks of the cluster operators included in the corrections. The derivation and computer implementation have been automated by the algebraic and symbolic manipulation program TENSOR CONTRACTION ENGINE (TCE). The TCE-synthesized subroutines generate the tensors with the highest excitation rank in a blockwise manner so that they need not be stored in their entirety, while enabling the efficient reuse of other precalculated intermediate tensors defined by prioritizing the memory optimization as well as operation minimization. Consequently, the overall storage requirements for the corrections due to connected triple and quadruple cluster operators scale as O(n(4)) and O(n(6)), respectively (n being a measure of the system size). For systems with modest multireference character of their wave functions, we found that the order of accuracy is CCSD<CR-CCSD(T) approximately CCSD(2)(T) approximately CCSD(T)<CCSDT approximately CCSD(2)(TQ)<CCSDT(2)(Q), whereas CR-CCSD(T) is more effective in cases of larger quasidegeneracy. The operation costs of the TCE-generated CCSD(2)(TQ) and CCSDT(2)(Q) codes scale as rather steep O(n(9)), while the TCE-generated CCSD(T), CCSD(2)(T), and CR-CCSD(T) codes are near operation minimum [a noniterative O(n(7))]. The perturbative correction part of the CCSD(T)/cc-pVDZ calculations for azulene exhibited a 45-fold speedup upon a 64-fold increase in the number of processors from 8 to 512.

Journal Article↗
PubMed2005

Supercollisions and energy transfer of highly vibrationally excited molecules.

Collisional energy-transfer probability distribution functions of highly vibrationally excited molecules and the existence of supercollisions remain as the outstanding questions in the field of intermolecular energy transfer. In this investigation, collisional interactions between ground state Kr atoms and highly vibrationally excited azulene molecules (4.66 eV internal energy) were examined at a collision energy of 410 cm-1 using a crossed molecular beam apparatus and time-sliced ion imaging techniques. A large amount of energy transfer (1000-5000 cm-1) in the backward direction was observed. We report the experimental measurement for the shape of the energy-transfer probability distribution function along with a direct observation of supercollisions.

Journal Article↗
PubMed2006

One-electron properties and electrostatic interaction energies from the expectation value expression and wave function of singles and doubles coupled cluster theory.

One-electron density matrices resulting from the explicitly connected commutator expansion of the expectation value were implemented at the singles and doubles coupled cluster (CCSD) level. In the proposed approach the one-electron density matrix is obtained at a little extra cost in comparison to the calculation of the CCSD correlation energy. Therefore, in terms of the computational time the new method is significantly less demanding than the conventional linear-response CCSD theory which requires additionally an expensive calculation of the left-hand solution of the CCSD equations. The quality of the new density matrices was investigated by computing a set of one-electron properties for a series of molecules of varying sizes and comparing the results with data obtained using the full configuration interaction method or higher level coupled cluster theory. It has been found that the results obtained using the new approach are of the same quality as those predicted by the linear-response CCSD method. The novel one-electron density matrices have also been applied to study the energy of the electrostatic interaction for a number of van der Waals complexes, including the benzene and azulene dimers.

Journal Article↗