Showing papers on "Benzophenone published in 1996"

Benzene, pyridine, naphtalene or benzophenone derivatives as inhibitors of squalene synthetase and protein farnesyltransferase

Abstract: The present invention provides a compound of formula (I), (II), (III) or (IV), processes for the preparation of the compounds of the invention, intermediates useful in these processes, a pharmaceutical composition, and methods of using the compounds of the invention.

Total Synthesis of (-)- and (+)-Balanol(1).

Abstract: Two total syntheses of the potent protein kinase C inhibitory fungal metabolite balanol are described In the first approach, the core aminohydroxyazepane subunit was prepared in racemic form by stereospecific functionalization of N-benzyl-e-caprolactam Resolution prior to coupling to the benzophenone subunit provided access to both enantiomers of balanol In the second approach, an efficient silicon-mediated cyclization of (2S,3R)-3-hydroxylysine followed by reduction provided the azepane subunit in enantiomerically pure form The sterically congested benzophenone subunit was assembled from two highly substituted aromatic precursors by way of an anionic homo-Fries rearrangement

Reactions of a Silanediyl with Carbon−Oxygen and Carbon−Nitrogen Double Bonds

Abstract: Silanediyl 2 (generated by thermolysis of cyclotrisilane 1) reacts with benzophenone, tetracyclone, and fluorenone to yield products, which may originate from highly reactive siloxiranes as intermediates. However, using adamantanone as ketone, stable siloxirane 24 is obtained. The interaction of 2 with benzophenone anil or 36 gives heterocyclic compounds 31 and 37, respectively. The involvement of silaziridines in these reactions, as well as in the reactions of 1 with 1,4-diaza-1,3-butadienes 41a and b, which yield the expected formal [4 + 1] cycloaddition products, remains questionable.

The Effect of High Magnetic Field on the Crystal Growth of Benzophenone

Abstract: The crystal growth of benzophenone was observed under high magnetic fields. In the presence of a magnetic field (8 T) the benzophenone crystal, which was diamagnetic, aligned in such a way that its crystal c-axis was perpendicular to the direction of the magnetic field. This phenomenon seemed attributable to the anisotropic diamagnetic susceptibility of the crystal.

Photosensitized cationic polymerization using allyl sulfonium salt

Abstract: The cationic polymerization of cyclic ethers such as cyclohexane oxide (CHO) and vinyl monomers such as butyl vinyl ether (BVE) and N-vinylcarbazole (NVC) is initiated upon irradiation at λ 380 nm in CH 2 CI 2 solution containing an allylic sulfonium salt, namely, 2-ethoxycarbonyl-2-propenylthiophenium hexafluoroantimonate (1) (EMT + SbF 6 - ), and one of the following compounds : benzophenone, anthracene, thioxanthone, perylene or phenothiazine. Electron transfer and hydrogen abstraction mechanisms were proposed for the initiation step. Stable cation radicals of phenothiazine were also prepared, and the cationic polymerization of butyl vinyl ether was initiated by these cation radicals.

Photooxidation of 8-Oxo-7,8-dihydro-2‘-deoxyguanosine by Thermally Generated Triplet-Excited Ketones from 3-(Hydroxymethyl)-3,4,4-trimethyl-1,2-dioxetane and Comparison with Type I and Type II Photosensitizers

Abstract: Calf thymus DNA and 8-oxo-7,8-dihydro-2‘-deoxyguanosine (8-oxodGuo) were photooxidized in the dark by triplet-excited ketones generated in the thermal decomposition of 3-(hydroxymethyl)-3,4,4-trimethyl-1,2-dioxetane (HTMD). The oxidation of DNA led to 8-oxodGuo and the type I photooxidation product 2,2-diamino[2-deoxy-β-d-erythro-pentofuranosyl)-4-amino]-5(2H)-oxazolone (oxazolone). While the yield of oxazolone progressively increased, 8-oxodGuo was substantially consumed in DNA on successive exposure to HTMD. The oxidation of authentic 8-oxodGuo by HTMD and established photosensitizers such as benzophenone (mainly type I) and Rose Bengal (predominantly type II) was studied in detail in regard to the concentration and time dependence and the influence of D2O versus H2O. The singlet-oxygen-derived 4R* and 4S* diastereomers of 4-hydroxy-8-oxo-4,8-dihydro-2‘-deoxyguanosine (4-HO-8-oxodGuo) and oxazolone were the major products. A substantial kinetic D2O effect (ca. 10-fold) in the Rose Bengal-photosensitized...

Photoionization of Benzophenone Carboxylic Acids in Aqueous Solution. A FT EPR and Optical Spectroscopy Study of Radical Cation Decay

Abstract: Benzophenone and some of its carboxylic acid derivatives were photoionized by a biphotonic process in aqueous solution. For all substances studied, the EPR spectra of the hydrated electrons eaq- and of radicals produced by the decay of the benzophenone radical cation could be detected on the nanosecond and microsecond time scale. Time-resolved optical measurements revealed additional reaction channels for the benzophenone radical cation decay. In general three different reaction channels were found, namely, the reaction of the radical cation with nucleophilic OH- under cyclohexadienyl radical formation, the generation of aryl radicals by β-scission, and the generation of aryl radicals by CO2 elimination.

Hydrogen-Bonding-Induced Electron Transfer from Triplet N,N-Dialkyl-1-naphthylamines to Benzophenone via Triplet Exciplexes1

Abstract: Laser flash photolysis studies at 355-nm on the photoreactions of the benzophenone (BP) and N,N-dialkyl-1-naphthylamine, DANA (N,N-dimethyl-1-naphthylamine, DMNA, and N,N-diethyl-1-naphthylamine, DENA) system have been carried out with and without H2O and methanol in acetonitrile (ACN) at 295 K. In the nanosecond time scale, triplet energy transfer from triplet BP (3BP*) to DANA occurs with the efficiency φTET (0.74 for DMNA and 0.61 for DENA) regardless of the presence of H2O and methanol. After the formation of triplet DANA (3DANA*), the triplet exciplex 3(DANA···BP)* with weak charge-transfer character is produced with the equilibrium constant K1 (10 M-1 for DMNA and 9 M-1 for DENA) between 3DANA* and BP. The mechanism for the formation of 3(DANA···BP)* is shown in Scheme 1. In the presence of H2O and methanol, it is found that the intraexciplex electron transfer takes place to give the BP anion (BP•-) and DANA cation (DANA•+) radicals in the hydrogen-bonded triplet exciplex 3(DANA···BP)*HB by H2O or m...

Polyphosphazene membranes. I. Solid‐state photocrosslinking of poly[(4‐ethylphenoxy)‐(phenoxy)phosphazene]

Abstract: : Dense films of poly((4-ethylphenoxy)(phenoxy)phosphazene), PEPP, a potentially attractive ion-exchange membrane material, were crosslinked to varying degrees using UV light and a photoinitiator. This polymer contained two kinds of substituents: phenoxy groups to be used for possible functionalization (e.g. , sulfonation) and ethylphenoxy sidechains for photocrosslinking, where hydrogens at the benzylic carbons could be abstracted by a photoinitiator leaving macroradicals that after recombination formed covalent bonds. The polyphosphazene polymer was synthesized, mixed with a photoinitiator, shaped into a thin film by solvent casting, and irradiated with UV light for a specified period of time. Benzophenone, BP, was selected as the photoinitiator because it was miscible with polyphosphazene, had the highest rate of hydrogen abstraction and absorbed UV light of 365 nm wavelength. The half-life of benzophenone in 50 micrometers thick irradiated films was determined to be 20 min. When the BP-PEPP molar ratio was increased from 0 to 0.5 the glass transition temperature increased after irradiation from -8.8 to 53.5 deg C. At the same time the equilibrium swelling in dimethylacetamide, at 25 deg C, decreased from infinity to 0.31. Tensile strength tests of the crosslinked films revealed a nonlinear dependence on BP-PEPP molar ratio. jg p2

Photoinduced Inter- and Intra-Ion-Pair Electron Transfer Reactions in N-(p-Benzoylbenzyl)-N,N,N-tri-n-butylammonium Triphenyl-n-butylborate and -Gallate Salts

Abstract: The photoreduction of N-(p-benzoylbenzyl)-N,N,N-tri-n-butylammonium triphenyl-n-butylborate (1) and gallate (2) was studied using nano- and picosecond laser flash photolysis. An electron transfer reaction from the borate or the gallate counteranion to the excited triplet state of the benzophenone moiety (BP*3) was demonstrated. This reaction leads to the formation of benzophenone radical anion (6) and the boranyl radical, the latter of which dissociates rapidly to form butyl radical. The electron transfer rate was found to depend on the polarity of the solvent. In neat benzene, the short lifetime of the triplet obtained (300 ± 150 ps) indicates an intramolecular process and that the compounds exist as tight ion pairs. The addition of 1% MeCN increases the triplet lifetime up to 1.2 ns. The formation of a solvent-separated ion pair was suggested in this solvent mixture. However, in the polar solvent MeCN, 1 and 2 exist partially as free ions as determined by their dissociation constants. A diffusion-contro...

Synthesis and Characterization of a Novel Polymeric System Bearing a Benzophenone Borate Salt as a New Photoinitiator for UV Curing1

Abstract: Polymeric photoinitiators bearing benzophenone triphenylbutyl borate salt as the side chain have been synthesized and characterized and their activity measured in the photoinitiated polymerization of a bifunctional monomer, diethylene glycol diacrylate. The results were compared with a low-molecular weight model compound. At lower concentrations of the requisite benzophenone moiety, the highest activity was observed for the model compound, while at higher concentrations the homopolymer was superior. For both cases, the lowest photoinitiation activity was observed with significant induction period for copolymers with methyl methacrylate when compared to the homopolymer. The results are discussed in light of the microenvironment of the initiator fragments in the polymeric systems.

Magnetic field effects on the hydrogen abstraction reactions of triplet benzophenone with thiophenol in nonviscous homogeneous solutions

Abstract: The hydrogen abstraction reaction of triplet benzophenone with thiophenol at room temperature was investigated in several nonviscous homogeneous solutions (η = 0.29−3.33 cP) by means of a nanosecond laser flash photolysis technique under magnetic fields of 0−10 T. The escape yield of the benzophenone ketyl radical decreased with increasing magnetic field strength from 0 to 10 T. In 2-methyl-1-propanol (η = 3.33 cP), the yield at 10 T reduced to 80 ± 2% of that at 0 T. The observed magnetic field effects can be interpreted by the Δg mechanism when the geminate recombination process is faster than or comparable to the escape one.

Benzophenone-Initiated Photoisomerization of the Norbornadiene Group in a Benzophenone−Steroid−Norbornadiene System via Long-Distance Intramolecular Triplet Energy Transfer

Abstract: Bichromophoric compound 3β-((2-(methoxycarbonyl)bicyclo[2.2.1]hepta-2,5-diene-3-yl)carboxy)androst-5-en-17β-yl benzophenone-4-carboxylate (NBD-S-BP) was synthesized, and its photochemistry was examined. The phosphorescence of the benzophenone (BP, donor) chromophore is efficiently quenched by the remote norbornadiene (NBD, acceptor) group. Time-resolved spectroscopic measurements indicate that the lifetime of the triplet state of the BP chromophore is shortened by the NBD group. Selective excitation of the BP chromophore results in isomerization of the NBD group to quadricyclane. All these observations suggest that a long-distance intramolecular triplet energy transfer occurs in the NBD-S-BP molecule. The efficiency and rate constant for this triplet energy transfer were determined to be ca. 22% and 1.5 × 105 s-1, respectively, by steady-state photolysis and laser flash photolysis. This long-distance intramolecular triplet energy transfer is proposed to proceed via a through-bond exchange mechanism.

On the yield of intermediates formed in the photoreduction of benzophenone

Abstract: The production of intermediates (light absorbing transients, LAT) has been examined in the photoreduction of benzophenone by different hydrogen donors in inert solvents (acetonitrile and benzene). For 2-propanol in acetonitrile, a branching ratio of 0.3 for the coupling reaction between dimethyl- and diphenylketyl radicals was extracted by computer model simulations considering inner filter effects and the quenching of triplet benzophenone by LAT. Experimental evidence is presented that indicates that LAT could be an efficient H-donor. Steady-state quantum yields for LAT production, Φ LAT , and benzophenone conversion, − Φ Ph2CO , were determined for the donors 2-propanol, n- and c-hexane, benzhydrol and tetrahydrofuran. The relative quantum yield, − Φ LAT / Φ Ph2CO , which indicates the differential partitioning of the products, shows that 2-propanol and tetrahydrofuran are nearly ten times more efficient than alkanes. From the analysis of the mechanism we derived an upper limit for the rate constant for the coupling reaction of two diphenylketyl radicals to yield LAT: k 6d ⩽ 5 × 10 5 M −1 s −1 .

Dynamic Spectral Shift of Benzophenone Radical Anion Caused by the Solvent Molecule Reorientation. Semiempirical PM3-MO and Classical Trajectory Studies

Abstract: The spectral shifts for the first electronic transition of the benzophenone anion radical (Bp-) caused by solvent geometrical reorientation have been investigated by means of semiempirical PM3-MO a...

Photoreduction of organic dyes in ketone amine systems

Abstract: Nucleophilic radicals, such as α-amino and ketyl radicals, produced by reaction of benzophenone triplets with amines and alcohols respectively, react efficiently by electron transfer with cationic organic dyes, such as phenosafranine, thiopyronine, methylene blue, and crystal violet. Time-resolved laser flash photolysis studies reveal a high reactivity of α-amino radicals toward these cationic dyes; in contrast, ketyl radicals are less reactive. The electron transfer rate constants for the reaction between the α-amino radical of triethanol amine and these dyes range from 2.7 × 109 M−1 s−1 (phenosafranine) to 7.5 × 109 M−1 s−1 (methylene blue). In contrast, rate constants ranging from 1.1 × 108 M−1 s−1 (phenosafranine) to 1.2 × 109 M−1 s−1 (methylene blue) were measured for the reaction of the dyes with the diphenyl ketyl radical. In dye mixtures used in conjunction with ketone-amine systems, stepwise electron transfer from an initially formed semireduced dye to a molecule of another dye occurs. For example, the primarily formed crystal violet radical reacts very rapidly (k = 2 × 109 M−1 s−1) with phenosafranine, thus forming the semireduced phenosafranine and regenerating crystal violet.

Observation of dielectric enrichment upon the formation of benzophenone radical anion in a binary solvent mixture

Abstract: In this paper we present results about the non-linear solvatochromic shift of the benzophenone radical anion absorption maximum in dimethyl sulfoxide–1,2-dichloroethane mixtures as a function of solvent mole fraction. Because of the non-hydrogen bonding character of the solvents, the observed absorption shift is attributed to dielectric enrichment only. The mathematical model which was developed for neutral dipolar solutes is extended to ionic species of charge q and molecular radius r; the preferential solvation index is proportional to q2r–4. In the present case its value is larger than those observed in most cases of dipolar solutes.

Molecularly Imprinted Anisotropic Polymer Monoliths

Abstract: Anisotropic materials with selective binding properties may have potential as active components in optical sensors. A novel route for the synthesis of such materials is described and the validity of the concept has been demonstrated. To this end free radical polymerization of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol trimethacrylate (TRIM) in the presence of a template molecule [4,4‘-bis(dimethylamino)benzophenone (Michler's ketone)] and binding sites [2-(acrylamido)-2-methylpropanesulfonic acid (AMPSA) or methacrylic acid (MAA)] led to molecularly imprinted polymer monoliths. Upon irradiation using linearly polarized light, the template molecules reacted with the polymer networks to form transparent and anisotropic polymer monoliths. The origin of the dichroism is discussed and is believed to result from the incorporation of reactive template molecular species (radicals) into the polymer network. That the polymers are indeed imprinted was confirmed using competitive binding studies. The polymers are size...

Horseradish Peroxidase-Catalyzed Generation of Acetophenone and Benzophenone in the Triplet State*

Abstract: Horseradish peroxidase catalyzes the aerobic oxidation of 2-phenylpropanal and diphenylacetaldehyde at physiological pH to yield acetophenone and benzophenone partly in the triplet state, respectively. These excited products plus formic acid are expected from the thermolysis of dioxetane intermediates. The presence of acetophenone was demonstrated spectrophotometr-ically and the chemiluminescence spectrum (δmax - 430 nm) was consistent with its triplet state. Energy transfer to 9,10-dibromoanthracene-2-sulfonate ion, a triplet carbonyl counter, but not to anthracene-2-sulfonate ion, a singlet carbonyl acceptor, occurred, confirming the triplet nature of the main emitter. In the case of the diphenylacetaldehydelperoxidase system, benzophenone could also be detected spectrophotometrically but the corresponding chemiluminescence spectrum showed only red emission (δmax - 630 nm), which was tentatively attributed to singlet oxygen formed by triplet-triplet energy transfer to ground state oxygen. Horseradish peroxidase can be replaced by other he-meproteins such as myoglobin, hemoglobin and micro-peroxidase as catalyst of the chemiluminescent reaction. The distinct emission spectra achieved with different hemeproteins suggest a role of the microenvi-ronment in totally or partly protecting the excited species from oxygen collisions, resulting in emission maxima around 430 nm, 630 nm or both.