Showing papers on "Benzophenone published in 1994"

Benzophenone photophores in biochemistry

Abstract: The photoactivatable aryl ketone derivatives have been rediscovered as biochemical probes in the last 5 years. The expanding use of benzophenone (BP) photoprobes can be attributed to three distinct chemical and biochemical advantages. First, BPs are chemically more stable than diazo esters, aryl azides, and diazirines. Second, BPs can be manipulated in ambient light and can be activated at 350-360 nm, avoiding protein-damaging wavelengths. Third, BPs react preferentially with unreactive C-H bonds, even in the presence of solvent water and bulk nucleophiles. These three properties combine to produce highly efficient covalent modifications of macromolecules, frequently with remarkable site specificity. This Perspectives includes a brief review of BP photochemistry and a selection of specific applications of these photoprobes, which address questions in protein, nucleic acid, and lipid biochemistry.

Photochemical and photobiological properties of ketoprofen associated with the benzophenone chromophore

Abstract: Irradiation of ketoprofen in neutral aqueous medium gave rise to 3-ethylbenzophenone as the major photoproduct. Its formation is justified via protonation of a benzylic carbanion or hydrogen abstraction by a benzylic radical. Minor amounts of eight additional compounds were isolated. Four of them are derived from the benzylic radical: 3-(1-hydroperoxyethyl)benzophenone, 3-(1-hydroxyethyl)benzophenone, 3-acetylbenzophenone and 2,3-bis-(3-benzoylphenyl)butane. The other four products involve initial hydrogen abstraction by the excited benzophenone chromophore of ketoprofen: 1,2-bis-(3-ethylphenyl)-1,2-diphenyl-1,2-ethanediol, 2-(3-benzoylphenyl)-1-(3-ethylphenyl)-1-phenylpropan-1-ol, alpha-(3-ethylphenyl)phenylmethanol, 1,2-bis-[3-(2-hydroxycarbonylethyl) phenyl]-1,2-diphenyl-1,2-ethanediol. The latter process was found to mediate the photoperoxidation of linoleic acid through a type I mechanism, as evidenced by the inhibition produced by the radical scavengers butylated hydroxyanisole and reduced glutathione. The major photoproduct, which contains the benzophenone moiety but lacks the propionic acid side chain, also photosensitized linoleic acid peroxidation. Because lipid peroxidation is indicative of cell membrane lysis, the above findings are highly relevant to explain the photobiological properties of ketoprofen.

UV-visible absorbance spectroscopy of organic probes in supercritical water

Abstract: UV-visible spectra of organic probes are reported in supercritical water (SCW) for the first time up to 440 o C and 5000 psia. Solvatochromic shifts in the π-π * absorbance band of benzophenone are compared with those of the n-π * and of acetone to characterize the dipolarity, polarizability, and hydrogen bond donor strength of water. In the near-critical region (0.5<ρ r <1.5), physical and hydrogen-bonding interactions augment the density of water about each probe, relative to the bulk density. At 380 o C, hydrogen bonding persists at a density of only 0.1 g/mL but rapidly disappears at lower densities. Spectroscopic measurements of interactions between SCW and organic solutes at the molecular level provide new insights into solvent effects on chemical reactions in SCW

Photosensitive compositions useful in three-dimensional part-building and having improved photospeed

Abstract: A method useful for stereolithography that yields enhanced photospeed, as well as a photocurable polymer composition well adapted for use with same, are disclosed A preferred combination includes 1,2-dimethoxy-2-phenyl acetophenone, benzophenone, and triphenyl phosphine combined with a polyurethane (meth)acrylate oligomer

Polyimides with alicyclic diamines. II. Hydrogen abstraction and photocrosslinking reactions of benzophenone-type polyimides

Abstract: Photosensitive polyimides with alicyclic diamines and benzophenone moiety were prepared by reactions of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) with diamines in aprotic solvents, followed by thermal or chemical imidizations. Among them the polyimide from BTDA and bis (4-amino-3-methylcyclohexyl)methane (DMDHM) can be dissolved in common organic solvents. In order to compare properties of the polyimides with alicyclic diamines with those of corresponding aromatic polyimides, the UV absorption spectra and fluorescence spectra of these polyimides and their model compounds were investigated

Isomeric Poly(benzophenone)s: Synthesis of Highly Crystalline Poly(4,4′-benzophenone) and Amorphous Poly(2,5-benzophenone), a Soluble Poly(p-phenylene) Derivative

Abstract: : Nickel-catalyzed polymerization which employs the coupling of isomeric dichlorobenzophenones is described The polymerization utilizes inexpensive readily available monomers, 4,4'-dichlorobenzophenone (4,4'-DCBP) and 2,5-dichlorobenzophenone (2,5-DCBP) The poly(4,4'-benzophenone) can be derivatized to be soluble during the synthesis by the use of a ketimine precursor that is subsequently hydrolyzed to give the target material The polymerization of 2,5-dichlorobenzophenone yields a soluble derivative of poly(p-phenylene) The resulting polymers were characterized to confirm the composition, molar mass, and thermal properties The Ni(O) catalyzed route proves to be facile and economically feasible and opens the way to a large variety of heterocyclic and phenyl-based homo- and copolymers 4,4'- dichlorobenzophenone, Hydrolyzed, Molar mass, Thermal

Chromatographic selectivity for amino acid esters and alkali metal ions on a silica bonded calix[4]arene tetraester stationary phase

Abstract: A silica bonded tetrameric calix[4]arene ester stationary phase has been used in the chromatographic separation of alkali metal ions and amino acid esters. Under reversed phase conditions, baseline resolution of a standard test mixture of benzamide, benzophenone and biphenyl was achieved using an MeOH—H2O mobile phase. In the chromatography of the amino acid ester hydrochlorides, retention appears to be related to the hydrophobicity of the esters studied, with tryptophan methyl ester being the longest retained.

A reinvestigation of the mechanism of photoreduction of benzophenones by alkyl sulfides

Abstract: The photoreduction of benzophenone and 4-carboxybenzophenone by dimethyl sulfide was examined in aqueous, mixed water—acetonitrile (1:1v/v) and acetonitrile solutions by the use of nanosecond laser photolysis. Bimolecular quenching rate constants were determined and were found to be in the range (1.5–4.6)×109 M−1s−1. Electron transfer from the sulfur atom to the triplet state of the benzophenones was found to be a primary photochemical step. This was established by the large values of quenching rate constants and by the observation of free radical ions, i.e. ketyl radical anions and (S∴S)+ radical cations of dimethyl sulfide in aqueous and mixed water-acetonitrile solutions. The overall quantum yields of photoproducts (ketyl radicals and ketyl radical anions) are low (Φtotalketyl=0.26 in aqueous solutions, are in the range 0.16–0.20 in mixed water-acetonitrile solutions, and decrease to less than or equal to 0.01 in pure acetonitrile), suggesting that back electron transfer within the charge-transfer complex to regenerate the reactants is the dominant process.

Photochemical Formation of Colloidal Silver in the Presence of Benzophenone

Abstract: An aqueous silver perchlorate–sodium dodecylsulfate (SDS)–benzophenone (BP) solution was photolyzed with either UV or near-UV light. Irradiation with 253.7 nm light, which was absorbed by both BP and silver ions, brought about the formation of collidal silver and the photobleach of BP. Peptization of colloidal silver agglomerates after prolonged irradiation was ascribed to electron injection from the benzophenone ketyl radical (BPK). The formation of colloidal silver and the photobleach of BP were also caused by irradiation with 365 nm light, which was absorbed solely by BP (sensitized reaction). A simple reaction scheme was introduced and the initial rates for the sensitized photoreduction of silver ions and the photobleach of BP were expressed in closed forms. Suitable combinations of the kinetics parameters and the extinction coefficient of colloidal silver were proposed in order to interpret the dependences of the initial rates on the reactant concentrations.

Isolation, structure and reaction of selenobenzophenones. X-Ray molecular structure of 4,4′-dimethoxyselenobenzophenone and of 4,4-biphenyl-2,3-diselenabicyclo[3.3.0]oct-7-ene

Abstract: 4,4′-Dimethoxy-1a and 4,4′-dimethyl-selenobenzophenone 1b could be isolated in moderate yields by the reaction of the corresponding ylides 3 with elemental selenium in benzene at 80 °C. Their spectral data are described. Attempted isolation of unsubstituted selenobenzophenone afforded only its dimer 5. Compound 1a crystallizes in space group P21/n with unit-cell parameters a= 7.191(3), b= 7.505(4), c= 24.856(4)A, β= 90.32(1)°, Z= 4, R= 0.055. The oxidation and thiation of 4,4′-dimethoxyselenobenzophenone 1a afforded the corresponding benzophenone and thiobenzophenone in good yields. The reaction of compound 1 with cyclopentadiene afforded the corresponding cycloadducts 7(3,3-diaryl-2-selenabicyclo[2.2.1] hept-5-enes), whereas bicyclic diselenides 8(4,4-diaryl-2, 3-diselenabicyclo[3.3.0]oct-7-enes) were obtained by using an excess of selenium and a higher temperature. Oxidation of compound 8c gave the corresponding diol 12, aldehyde 13, and diphenylfulvene 11. The reaction of compound 1a with benzenediazonium carboxylate afforded 2,2- bis-(4-methoxyphenyl)-4H-3,1 -benzooxaselenin -4-one 17.

Protonation at the aromatic ring of samarium benzophenone dianion species. Isolation and structural characterization of a samarium(III) enolate complex

Abstract: The reduction of aromatic compounds into their dihydro derivatives by dissolving metal/alcohol systems (the Birch reduction) is a useful methodology in organic synthesis. Of particular importance is the reduction of aromatic carbonyl compounds such as aromatic acids, esters, amides, and monoaryl ketones, which usually generates in situ useful metal enolate intermediates that upon further reaction with electrophiles yield a variety of cyclohexadiene derivatives. One of the possible processes to generate these metal enolate intermediates is thought to be the monoprotonation of dianionic species at the para position of the aromatic rings. On the other hand, the reduction of diaryl ketones by alkali metals in liquid ammonia or by lanthanide metals in THF/HMPA or DME has been well known to afford the corresponding ketone dianions. The first X-ray structure of metal ketone dianion complexes, [Yb([mu]-[eta][sup 1],[eta][sup 2]-OCPh[sub 2]) (HMPA)[sub 2]][sub 2], has been recently determined in this laboratory. Protonation of this complex with ArOH or CpMo(CO)[sub 3]H also occurred at the carbonyl unit to release benzhydrol. In striking contrast to these results, when the analogous samarium benzophenone dianion species was aallowed to react with ArOH, the protonation occurred at the aromatic ring to give a samarium(III) enolate complex. 15 refs., 1more » fig.« less

BENZOPHENONE PHOTOSENSITIZATION OF 2′‐DEOXYGUANOSINE: CHARACTERIZATION OF THE 2R AND 2s DIASTEREOISOMERS OF 1‐(2‐DEOXY‐β‐D‐erythoW‐PENTOFURANOSYL)‐2‐METHOXY‐4,5‐IMIDAZOLIDINEDIONE. A MODEL SYSTEM FOR THE INVESTIGATION OF PHOTOSENSITIZED FORMATION OF DNA‐PROTEIN CROSSLINKS

Abstract: Benzophenone-mediated photosensitization of 2'-deoxyguanosine and its 3',5'-di-O-acetyl derivative, used as DNA model compounds, in oxygen-saturated water-methanol (1:1) solution results in the nucleophilic addition of methanol to the guanine base. The resulting modified nucleosides have been isolated by reverse-phase high-performance liquid chromatography and characterized by extensive spectroscopic measurements including 13C and 1H nuclear magnetic resonance, fast atom bombardment mass spectrometry and circular dichroism as the 2R and 2S diastereoisomers of 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-2-methoxy-4,5-imidazolinedione and their related 3',5'-di-O-acetyl derivates. Information concerning the absolute configuration of the two pairs of diastereoisomers was inferred from detailed nuclear Overhauser effect experiments. A reaction mechanism, involving guanine radical intermediates, is proposed to explain the generation of these new guanine photoproducts.

Coupled benzotriazole and benzophenone UV absorbers

Abstract: Provided are ultraviolet stabilizers which are diphenylmethane compounds of the formula: ##STR1## wherein: R1 and R2 are independently C1 to C8 alkyl, cyclopentyl, cyclohexyl or cumyl; and X is selected from the group consisting of hydrogen, halogen, C1 to C12 alkyl and C1 to C12 alkoxy. The invention also pertains to a process for their preparation and stabilized polymer blends containing the stabilizers.

Indoline formation by regioselective aryl radical cyclization to azomethine bond

Abstract: Aryl radical-initiated cyclization of the ketimines derived from acetophenone and benzophenone occurred exclusively at the nitrogen end of the azomethine bond in an exo-5 mode to yield the corresponding indoline derivatives

Ionic chiral handle-induced asymmetric synthesis in a solid state Norrish type II photoreaction

Abstract: Irradiation of crystals of salts formed between 4-(2,4,6-triisopropylbenzoyl)benzoic acid ( 1a ) and various optically active amines is shown to lead to optically active Norrish type II photoproducts in low to moderate enantiomeric excesses, a process in which the ammonium ion has acted as an “ionic chiral handle.” X-ray crystallography reveals that the salts crystallize with two independent, mirror image-related molecules of the benzophenone moiety in the asymmetric unit, and this is suggested to be the source of the low ee s observed.

Synthesis and Characterization of Surface-Functionalized 1,2-Polybutadiene Bearing Hydroxyl or Carboxylic Acid Groups

Abstract: We have modified the surface of 1,2-polybutadiene (PBD), without severe etching, via oxidation with aqueous potassium permanganate. The primary functionality introduced, either hydroxyl or carboxylic acid groups, depends upon the concentration and temperature of the oxidizing solution. An alternative and more selective method for introducing hydroxyl or carboxylic acid moieties at this surface is the photolytic addition of 3-mercapto-1,2-propanediol or mercaptoacetic acid, using benzophenone as an initiator and light (350 nm). On the polymer surfaces containing carboxylic acid groups, contact angles varied with the pH of the contacting drop of water, consistent with the presence of ionizable functionality.

Photochemistry and photocuring activity of novel 1-halogeno-4-propoxythioxanthones

Abstract: The photochemical and photopolymerisation properties of 1-fluoro-4-propoxythioxanthone (FPTX), 1-chloro-4-propoxythioxanthone (CPTX) and 1-bromo-4-propoxythioxanthone (BPTX) have been determined and compared with the corresponding activity of 2-propoxythioxanthone (ITX). Both CPTX and BPTX exhibit high photoinitiation activity when used alone and in conjunction with a tertiary amine cosynergist and benzophenone. The ITX and FPTX are active only when used with a tertiary amine cosynergist and/or benzophenone. Absorption and luminescence spectra indicate that the lowest excited states possess mixed ππ*/nπ* character with the BPTX exhibiting the highest phosphorescence quantum yield probably due to heavy-atom spin–orbit coupling by the Br atom. Photolysis/photoreduction quantum yields are higher in a reductive solvent such as propan-2-ol than in non-reductive acetonitrile for the three halogenated derivatives. They are enhanced further in the presence of a tertiary amine. These data contrast with that for ITX where photolysis/photoreduction is observed only in reductive propan-2-ol, in the absence and presence of a tertiary amine. Ketyl radical formation, with a wavelength maximum at 390 nm on microsecond flash photolysis, is similar for all the thioxanthones and is virtually insensitive to oxygen except for the BPTX derivative. The three halogenated derivatives give strong triplet–triplet absorptions on nanosecond laser flash photolysis in propan-2-ol and acetonitrile, similar to those for ITX. Quenching of the triplet state by a tertiary amine is found to increase with increasing amine concentration, with ITX being the most sensitive initiator. This quenching is consistent with their behaviour as photopolymerisation initiators. Bimolecular triplet quenching by naphthalene gives rate constants for ITX and FTPX which are similar to that of benzophenone while that for CPTX is an order of magnitude less. From these data we have determined that the molar absorption coefficients of the triplet–triplet absorptions for FPTX and CPTX are half that of ITX with all three being greater than that of benzophenone. The FPTX is also found to exhibit a significantly lower yield of intersystem crossing compared with CPTX and ITX. The latter two initiators exhibit rates of intersystem crossing which are almost comparable with that of benzophenone. Values of molar absorption coefficients and rates of intersystem crossing for BPTX could not be measured since the laser flash studies indicated the formation of a charge-transfer complex with triplet quenchers such as naphthalene. Solution photolysis studies indicated an additional reaction involving subsequent scission of the halogen–thioxanthone bond in the case of BPTX and CPTX but the FPTX gave no such reaction. Various mechanisms are discussed to account for the effective photoinitiation activity of BPTX and CPTX including their potential role as hybrid initiators.

Stereoselective radical addition of carbon-centred radicals to the dehydroalanine moiety of the chiral nickel(II) complex of the Schiff′s base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone and dehydroalanine

Abstract: A new approach to the asymmetric synthesis of β-substituted α-aminopropanoic acids by 2,2′-azoisobutyronitrile (AIBN) and Bu3SnH-initiated radical addition of Etl, PriBr, ButBr, and PhCH2Br to the dehydroalanine moiety of the NiII complex 1 of a Schiff′s base derived from (S)-o-[N-(N′-benzylprolyl)amino]benzophenone (BPB) and dehydroalanine is described. The radical addition produced a mixture of diastereoisomeric complexes 4a–d with a 40–90% excess of (S,S)diastereoisomers over the (S,R)-ones, giving the reaction products in almost quantitative yields. The diastereoselectivity of the reaction depended on the size of the entering radicals, the most effective asymmetric induction being achieved for the But radical addition. Enantiomerically pure ‘(S)-2-amino3-(tert-butyl)propanoic acid’[(S)-γ-methylleucine] and the chiral auxiliary BPB were recovered from compound 4d after its decomposition with HCl. The reactivities of the carbon–centred radicals towards the carbon-carbon double bond in the amino acid moiety of the complex 1 was quantitatively established by using ESR spectroscopy in the spin-trap technique.

Photoinduoed molecular transformations. Part 146. Photoacylation and photoalkylation of 2-arylamino- and 2-alkylamino-1,4-naphthoquinones

Abstract: The photoacylation of 2-arylamino- or 2-alkylamino-1,4-naphthoquinones with aromatic or aliphatic aldehydes can be achieved in high yields when a solution of N-substituted 2-amino-1,4-naphthoquinones and an aldehyde in benzene is irradiated in the presence of benzophenone. Irradiation of 2-anilino-1,4-naphthoquinones and cyclic ethers, such as tetrahydrofuran or dioxane, in the presence of benzophenone led to analogous photoalkylation products, 3-alkyl-2-anilino-1,4-naphthoquinones, in high yield. 1,4-Dihydroxy-2-diphenylamino-3-propionylnaphthalene, characterized as the diacetate, could be isolated from the photoacylation of 2-diphenylamino-1,4-naphthoquinones with propanal. The photoacylation thus involves hydroquinone derivatives as intermediates. Radical processes involving the formation of acyl or alkyl radicals from aldehydes or cyclic ethers by hydrogen abstraction with excited benzophenone for these photoacylations and photoalkylations are proposed.

Benzophenone derivative, and ultraviolet light absorbent and an endermic liniment

Abstract: A silicone-type benzophenone derivative represented by Formula 1 below, an ultraviolet light absorbent and an endermic liniment which contains it. ##STR1## The silicone-type benzophenone derivative of the present invention exhibits a superior ability to absorb UV-A and UV-B and is compatible with silicone-type bases.

Energy transfer processes in the quenching of triplet states of organic compounds by 1,3-diketonates of lanthanides(III) and magnesium(II) in acetonitrile solution. Laser flash photolysis studies

Abstract: Quenching of the triplet states of nine different organic compounds by 1,3-diketonates of lanthanides was studied by laser flash photolysis in acetonitrile solution. Five different lanthanides were used, but terbium(III) and gadolinium(III) were investigated in detail. For comparison, two 1,3-diketonates of magnesium(II) were also studied. Observed correlations between the quenching rate constants (log kq) and the free energy change for energy transfer processes (ΔGen) allowed a distinction to be made between the energy transfer to the ligand-localized triplet states and energy transfer to the ff* states of the complexes used. The observation of sensitized emission of Tb(III) and a correlation of the donor triplet decay with the rise time of Tb(III) emission gave direct evidence for an energy transfer mechanism of quenching. The quantitative evaluation of the log kqvs. ΔGen correlation led to very small values of the transmission coefficients (κen in the region of 10−6) for energy transfer to the metal-centered ff* states of the lanthanide complexes. These transmission coefficients are from one to three orders of magnitude lower than those obtained for energy transfer to ligand-localized triplet states or to excited dd states of transition metal 1,3-diketonates. An additional quenching process, i.e. electron transfer from the acetylacetonate ligand to the benzophenone triplet state, was observed for benzophenone derivatives as donors.

Solvent dependence of interactions between triplet benzophenone and N,N-dimethylaminonaphthalene studied by laser flash photolysis

Abstract: It is found by nanosecond laser flash photolysis at 355 nm that triplet energy transfer from triplet benzophenone ( 3 BP * ) to N,N-dimethylaminonaphthalene (RNMe 2 ) occurs to yield triplet RNMe 2 with an efficiency of 0.58 in acetonitrile (ACN) whereas electron transfer from RNMe 2 to 3 BP * takes place to produce the benzophenone anion and RNMe 2 cation radicals with an efficiency of 1.0 in ACH:H 2 O (4:1 v/v) at 295 K. A possible mechanism for electron transfer of the BP-RNMe 2 system in the presence of H 2 O is discussed.