SEARCH · PubMed Health

Results for “Benzophenones”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24Linked to original sources

PubMed2003

Monitoring the formation and decay of transient photosensitized intermediates using pump-probe UV resonance Raman spectroscopy. I: Self-modeling curve resolution.

Resolution of transient excited-state Raman scattering from ground-state and solvent bands is a challenging spectroscopic measurement since excited-state spectral features are often of low intensity, overlapping the dominant ground-state and solvent bands. The Raman spectra of these intermediates can be resolved, however, by acquiring time-resolved data and using multidimensional data analysis methods. In the absence of a physical model describing the kinetic behavior of a reaction, resolution of the pure-component spectra from these data can be accomplished using self-modeling curve resolution, a factor analysis technique that relies on the correlation in the data along a changing composition dimension to resolve the component spectra. A two-laser UV pump-probe resonance-enhanced Raman instrument was utilized to monitor the kinetics of amine quenching of excited-triplet states of benzophenone. The formation and decay of transient intermediates were monitored over time, from 15 ns to 100 micros. Factor analysis of the time-resolved spectral data identified three significant components in the data. The time-resolved intensities at each Raman wavenumber shift were projected onto the three significant eigenvectors, and least-squares criteria were developed to find the common plane in the space of the eigenvectors that includes the observed data. Within that plane, the three pure-component spectra were resolved using geometric criteria of convex hull analysis. The resolved spectra were found to arise from benzophenone excited-triplet states, diphenylketyl radicals, and the solvent and ground-state benzophenone.

Algorithms↗

PubMed2002

New photoactivators for multiphoton excited three-dimensional submicron cross-linking of proteins: bovine serum albumin and type 1 collagen.

We report the synthesis and optical characterization of two new photoactivators and demonstrate their use for multiphoton excited three-dimensional free-form fabrication with proteins. These reagents were developed with the goal of cross-linking Type 1 collagen. This cross-linking process produces structures on the micron and submicron size scales. A rose bengal diisopropyl amine derivative combines the classic photoactivator and co-initiator system into one molecule, reducing the reaction kinetics and increasing cross-linking efficiency. This derivative was successful at producing stable structures from collagen, whereas rose bengal alone was not effective. A benzophenone dimer connected by a flexible diamine tether was also synthesized. This activator has two photochemically reactive groups and is highly efficient in cross-linking bovine serum albumin and Type 1 collagen to form stable, robust structures. This approach is more flexible in terms of cross-linking a variety of proteins than by traditional benzophenone photochemistry. The photophysical properties vary greatly from that of benzophenone, with the appearance of a new, lower energy absorption band (lambda max approximately 370 nm in water) and broad, visible emission band (approximately 500 nm maximum). This absorption band is highly solvatochromic, suggesting it arises, at least in part, from a charge transfer interaction. Collagens are typically difficult to cross-link photochemically, and the results here suggest that these two new activators will be suitable for cross-linking other forms of collagen and additional proteins for biomedical applications such as the de novo assembly of biomimetic tissue scaffolds.

Benzophenones↗

PubMedDate not supplied

Substituted pyridines: nonsteroidal inhibitors of human placental aromatase cytochrome P-450.

The binding to human placental aromatase cytochrome P-450 and resulting extent of inhibition was examined for pyridine, pyridines substituted at the 2-, 3-, or 4-positions with phenyl or benzoyl groups, and the nonpyridinic structural analogs biphenyl and benzophenone. Spectral binding studies with partially purified aromatase indicated that pyridine, 3- and 4-phenylpyridines, and 3- and 4-benzoylpyridines interact at the active site via ligation of the pyridinic nitrogen to heme iron, as judged by the type II difference spectra. The apparent dissociation constants for these compounds are 2.1, 0.11, 0.09, 2.6, and 0.27 mM, respectively. Biphenyl, benzophenone, and 2-benzoylpyridine show exclusively a hydrophobic interaction in the presence of the substrate, androst-4-ene-3,17-dione, to give reverse type I difference spectra, with apparent spectral dissociation constants of 0.14, 0.42, and 1.8 mM, respectively. 2-Phenylpyridine shows a unique spectrum, previously not observed with cytochrome P-450, that has components of both type I and type II spectra. As measured by tritium ion release from [1 beta-3H]androst-4-ene-3,17-dione, competitive inhibition of human microsomal aromatase activity was observed with pyridine, 2-, 3-, and 4-phenylpyridines, biphenyl, and benzophenone, with Ki values of 320, 62, 1.48, 0.36, 750, and 130 microM, respectively. In contrast, 2-, 3-, and 4-benzoylpyridines exhibited complex kinetic behavior from which inhibition constants could not be obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Aromatase Inhibitors↗

PubMed1988

Site-specific derivatives of wheat germ calmodulin. Interactions with troponin and sarcoplasmic reticulum.

Wheat germ calmodulin (CaM) was derivatized at its single cysteine (Cys27) with either the fluorescent reagent, N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonic acid (I-EDANS) or the photoactivable cross-linker benzophenone-4-maleimide. Comparison of the native and derivatized wheat germ CaMs with native bovine testis CaM indicates that the concentrations of these proteins required for half-maximal stimulation of either erythrocyte membrane Ca2+-ATPase activity or cardiac sarcoplasmic reticulum phosphorylation are very similar. Affinity labeling of troponin subunits with 125I- and benzophenone-4-maleimide-labeled CaM demonstrates CaM binding to troponin I (TnI) and troponin T (TnT) in binary complexes, as well as to both subunits in the CaM.TnI.TnT ternary complex. This suggests that both subunits are within 10 A of Cys27 of calmodulin. Affinity labeling of cardiac sarcoplasmic reticulum vesicles with 125I- and benzophenone-4-maleimide-labeled CaM exhibits a Ca2+- and Mg2+-dependent labeling of phospholamban, as shown previously with bovine calmodulin (Louis, C.F., and Jarvis, B. (1982) J. Biol. Chem. 257, 15187-15191). Thus, it appears that Ca2+-binding site I of calmodulin is at or near binding sites of calmodulin for TnI, TnT, and phospholamban. Analysis of the time-resolved fluorescence decay curves of I-EDANS-labeled calmodulin indicates a major component with a lifetime of 11.9 ns (+Ca2+), which accounts for 81% of the total fluorescence. The lifetime decreases slightly to 11.3 ns in the absence of Ca2+. Fluorescence anisotropy experiments indicate that I-EDANS-labeled CaM binds TnI with Kd = 6 x 10(-8) M in the presence of Ca2+. This study suggests that these single-site derivatives will be useful for characterizing a variety of calmodulin-receptor interactions because they lack ambiguities inherent in less specific labeling methods.

Animals↗

PubMed1998

[Estimation of the binding site of drugs by means of new types of photoactive ligands].

Photoaffinity labeling is a powerful technique to identify ligand-binding proteins in a crude mixture and localize their binding-site. Benzophenone photophore has several favorable features compared with the classical photoreactive unit, aromatic azides, that is why its application is expanding. Benzophenone can easily be attached to biologically active ligands by using a tritiated heterobifunctional crosslinker reagent: [3H]-BZDC-NHS or a photoreactive amino acid; [3H]-4-benzoyl-L-phenylalanine. Tethered inositol polyphosphates and antimitotic agents were prepared first and reacted with the high specific activity photocrosslinker reagent in microscale. The photoactivatable ligands obtained were used for studying IP3 receptor, alpha-Trinozitol receptor, PLC delta enzime, beta-tubullin and glycoprotein P. Thrombin receptor was investigated by a short peptide antagonist containing the photoactivatable amino acid. The results demonstrate the versatility of photoaffinity labeling and prove that this technique has a potential providing much more information about the receptor and mechanism than simply identifying a single polypeptide: it contributed to solve the 3D structure of the IP3 binding domain and to reveal a unique activation of the PLC delta. The results confirmed the superiority of benzophenone. Using that photophore glycoprotein P, which is responsible for the MDR, and thrombin receptor were labelled at the first time.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

Protein fishing with chiral molecular baits.

Chirality plays a central role in various biological recognition processes. Here a methodology was developed to utilize chiral recognition processes for the selective biotinylation of proteins in crude cell lysates. Two pairs of diastereomeric probes containing benzophenone and biotin were prepared through solid-phase synthesis. Protein-binding selectivity of each probe was examined by photo-cross-linking of cell lysates, followed by SDS-PAGE and Western blot. The study revealed that our approach permits selective labeling of benzophenone-binding proteins in complex proteomes. In addition, it was found that the selectivity depends largely on a single chiral center and substitutions in the vicinity of benzophenone. Taken together, the current work demonstrates that chiral recognition process can be employed to selectively label proteins in complex proteomes. Thus the study opens up the possibility to expand the scope of chemical proteomics research for various applications, including biomarker discovery, drug screening and development.

Biotin↗

PubMed1983

Kinetics and equilibrium of the reversible alprazolam ring-opening reaction.

Alprazolam underwent a facile 1,4-benzodiazepine ring-opening reaction in an acidic aqueous solution to form a benzophenone compound. The reaction was demonstrated by means of UV, IR, and 1H- and 13C-NMR spectroscopy. Its reverse cyclization reaction to alprazolam occurred when an acidic solution was neutralized. Both the ring-opening and the cyclization rate constants were obtained from the overall rate constant measured at 25 degrees over a pH range of 0.5--8.0; the latter was measured by monitoring the UV spectral change of the reaction. Although the equilibrium was favored for the benzophenone compound in acidic solutions, it was possible to directly measure the cyclization rate at three acidic pH values by providing a sink condition for the product, alprazolam, using a biphasic reaction system. The bell-shaped cyclization rate pH profile was interpreted in terms of a change in the rate-determining step. The pH profile of the ring-opening rate showed an inflection point indicating a different reactivity of mono- and dicationic alprazolam. The apparent equilibrium between alprazolam and the benzophenone compound at a given pH was estimated from the rate constants for the ring-opening and cyclization reactions. The results agree with the apparent pKa measured by a conventional UV spectrophotometry and a titration technique. The pKa of monocationic alprazolam, the reactive species for the covalent hydration, was determined from the pH dependence of the initial absorbance when an alprazolam solution is acidified.

Alprazolam↗

PubMed2004

Chemical analysis and genotoxicological safety assessment of paper and paperboard used for food packaging.

This study presents the research on the chemical analysis and genotoxicity of 28 virgin/recycled paper products in food-contact use. In the chemical analysis, paper products were extracted by reflux with ethanol, and analyzed by gas chromatography/mass spectrometry. 4,4'-bis(dimethylamino)benzophenone (Michler's ketone: MK), 4,4'-bis(diethylamino)benzophenone (DEAB), 4-(dimethylamino)benzophenone (DMAB) and bisphenol A (BPA) were found characteristically in recycled products. Seventy-five percent of the recycled paper products contained MK (1.7-12 microg/g), 67% contained DEAB (0.64-10 micro g/g), 33% contained DMAB (0.68-0.9 microg/g) and 67% contained BPA (0.19-26 microg/g). Although, BPA was also detected in virgin paper products, the detection levels in the recycled products were ten or more times higher than those in the virgin products. The genotoxicity of paper and paperboard extracts and compounds found in them were investigated by Rec-assay and comet assay. Of the 28 products tested by Rec-assay using Bacillus subtilis, 13 possessed DNA-damaging activity. More recycled than virgin products (75% against 25%) exhibited such activity, which, of the compounds, was observed in BPA, 1,2-benzisothiazoline-3-one (BIT), 2-(thiocyanomethylthio)benzothiazole, 2,4,5,6-tetrachloro-isophthalonitrile, 2,4,6-trichlorophenol (TCP), and pentachlorophenol. The critical toxicant in one virgin paper product was concluded to be BIT. Eight samples with DNA-damaging activity were also tested by comet assay using HL-60 cells; six induced comet cells significantly (five times or higher than the control) without a decrease of viable cells. TCP, BZ, DEAB, and BIT also caused a slight increase in comet cells. In conclusion, we showed that most recycled paper products contain chemicals such as MK, DEAB, DMAB, and BPA, and possess genotoxicity. However, the levels of the chemicals in the recycled products could not explain their genotoxic effects.

Apoptosis↗

PubMed1997

Alternative pathways of xanthone biosynthesis in cell cultures of Hypericum androsaemum L.

The biosynthesis of xanthones was studied in cell cultures of Hypericum androsaemum L. We have detected a new benzophenone synthase, for which the preferred substrate is benzoyl-CoA, itself supplied by 3-hydroxybenzoate:coenzyme A ligase. The stepwise condensation of benzoyl-CoA with three molecules of malonyl-CoA, catalyzed by benzophenone synthase, yields 2,4,6-trihydroxybenzophenone. This intermediate is subsequently converted by benzophenone 3'-hydroxylase, a cytochrome P450 monooxygenase. These biosynthetic steps, leading to the formation of 2,3',4,6-tetrahydroxybenzophenone, represent an alternative pathway to that recently proposed for cell cultures of Centaurium erythraea [Peters et al., Planta (1997) in press].

Acyl Coenzyme A↗

PubMed2004

Tuning emissive states in electrogenerated chemiluminescence.

Electrogenerated chemiluminescence (ECL) arising from the reaction of radical ions has previously be shown to arise from a variety of states including excited singlets, triplets, excimers, and exciplexes. In this work we describe two systems that form emissive states in ECL with different properties than those when formed with photoluminescence. The first system involves the reaction of the anthracene radical anion with the radical cation of 4,N,N-trimethylaniline. ECL from this system exhibited an exciplex whose energy and intensity relative to the emission from the anthracene singlet could be tuned by adjusting the solvent permittivity and ionic strength. Under conditions considered extreme for electrochemical experiments, no added electrolyte in dimethoxyethane, the relative intensity of the anthracene-related exciplex, formed from the encounter complex, was 8 times greater and red-shifted from that generated by photoluminescence in the same solution with 100-fold exciplex partner added. In the second system examined, the benzophenone radical anion reacted with the radical cation of either phenoxathiin or 4-methoxythioanisole; the ECL emission was from the benzophenone triplet state and an excimer. The excimer, a species not seen with photoluminescence, predominated as the benzophenone concentration was elevated into the low millimolar range. The results from these two simple systems clearly demonstrate that the radical ion annihilation pathway of ECL can generate different emissive states than those formed following photoexcitation.

Journal Article↗

PubMed2003

Catalytic asymmetric Mannich reactions of glycine derivatives with imines. A new approach to optically active alpha,beta-diamino acid derivatives.

Imines of glycine alkyl esters react with imines in a diastereo- and highly enantioselective Mannich reaction in the presence of chiral copper(I) complexes as the catalyst to give optically active alpha,beta-diamino acid derivatives. A series of imines of glycine esters derived from glycine and aromatic carbonyl compounds has been screened as substrates for the Mannich reaction with different imines in the presence of various combinations of metal salts and chiral ligands. The benzophenone imine of glycine esters was found to react with N-protected imines in a diastereoselective fashion giving functionalized alpha,beta-diamino acid esters with excellent enantioselectivities. The most effective chiral catalysts are chiral copper(I) complexes having phosphino-oxazoline (P,N)-ligands, and among these ligands, those derived from (1R,2S)-dihydroxy-1,2,3,4-tetrahydronaphthalene gave the best results. The scope of this new catalytic asymmetric reaction of the benzophenone imine glycine esters is demonstrated for the reaction with different N-protected-C-aryl and C-alkyl imines giving the Mannich adducts with excellent optical purity. Furthermore, the synthetic aspects of the reaction are presented by converting the Mannich adducts into alpha,beta-diamino acid derivatives. The relative and absolute configuration of the Mannich adduct have been determined and based on the stereochemical outcome of the reaction a tetrahedral chiral-copper(I)-imino glycine alkyl ester intermediate is proposed. In this intermediate the Re-face of the benzophenone imine glycine ester is shielded by the chiral ligand leaving the Si-face available for approach of the Si-face of the imine. A series of semiempirical calculations has been performed to support the structure of the tetrahedral chiral-copper(I) complex and to account for the influence of the substituents in the chiral phosphino-oxazoline ligands.

Amino Acids↗

PubMed2000

Use of competition kinetics with fast reactions of grignard reagents

Competition kinetics are useful for estimation of the reactivities of Grignard reagents if the reaction rates do not differ widely and if exact rates are not needed. If the rate of mixing is slower than the rate of reaction, the ratios between the rates of fast and slow reagents are found to be too small. This is concluded from experiments in which results obtained by competition kinetics are compared with results obtained directly by flow stream procedures. A clearer picture of the reactivity ratios is obtained when the highly reactive reagent is highly diluted with its competitor. A fast reagent may account for almost all the product even when present as only 1 part in 100 parts of the competing agent. In this way allylmagnesium bromide is estimated to react with acetone, benzophenone, benzaldehyde, and diethylacetaldehyde ca. 1.5 x 10(5) times faster than does butylmagnesium bromide. The rates found for the four substrates do not differ significantly, and it seems possible that there is a ceiling over the rate of reaction of this reagent, for example, caused by diffusion control. This may explain that competition kinetics using allylmagnesium bromide have failed to show kinetic isotope effects or effects of polar substituents with isotopically or otherwise substituted benzophenones. A recently reported alpha-deuterium secondary kinetic isotope effect for the reaction of benzaldehyde with allylmagnesium bromide was observed at -78 degrees C, but was absent at room temperature. It is suggested that the reaction of benzophenone and benzaldehyde with allylmagnesium bromide has a radical-concerted mechanism since no radical-type products are produced and since no color from an intermediate ketyl is observed even at -78 degrees C.

Journal Article↗

PubMed2005

Sulfonated poly(ether ether ketone)/poly(vinyl alcohol) sensitizing system for solution photogeneration of small Ag, Au, and Cu crystallites.

Illumination of air-free aqueous solutions containing sulfonated poly(ether ether ketone) and poly(vinyl alcohol) with 350 nm light results in benzophenone ketyl radicals of the polyketone. The polymer radicals form with a quantum yield 0.02 and decay with a second-order rate constant 6 orders of magnitude lower than that of typical alpha-hydroxy radicals. Evidence is presented that the polymeric benzophenone ketyl radicals reduce Ag+, Cu2+, and AuCl4- to metal particles of nanometer dimensions. Decreases in the reduction rates with increasing Ag(I), Cu(II), and Au(III) concentrations are explained using a kinetic model in which the metal ions quench the excited state of the polymeric benzophenone groups, which forms the macromolecular radicals. Quenching is fastest for Ag+, whereas Cu2+ and AuCl4- exhibit similar rate constants. Particle formation becomes more complex as the number of equivalents needed to reduce the metal ions increases; the Au(III) system is an extreme case where the radical reactions operate in parallel with secondary light-initiated and thermal reduction channels. For each metal ion, the polymer-initiated photoreactions produce crystallites possessing distinct properties, such as a very strong plasmon in the Ag case or the narrow size distribution exhibited by Au particles.

Journal Article↗

PubMed2004

The stereoselectivity of the Paternò-Büchi reaction between tertiary 2-furylmethanol derivatives and aromatic carbonyl compounds: on the nature of the hydroxy directing effect.

The photochemical reaction of 1-(2-furyl)-1-phenylethanol with benzaldehyde gave a mixture of regioisomeric products. The adduct obtained on the more hindered side of the molecule was obtained with complete diastereoselectivity. The same substrate with benzophenone gave only one product with a diastereoisomeric excess of 48%. The reaction of 2-(2-furyl)-3,3-dimethylbutan-2-ol with benzaldehyde and benzophenone gave the corresponding adducts on the more hindered side of the molecule with diastereoisomeric excesses of 42 and 71%, respectively. These results, and also those obtained using 2-furylphenylmethanol with benzophenone and acetone (complete diastereoselectivity and absence of diastereoselectivity, respectively), were explained assuming the attack of the excited carbonyl compound on the same side as the hydroxy group, through the formation of a hydrogen bond or of a complex. This type of attack gave the biradical intermediate in preferential conformations. The relative energies of these conformers account for the observed diastereoselectivity.

Benzaldehydes↗

PubMed2000

Immobilizing the moving parts of voltage-gated ion channels.

Voltage-gated ion channels have at least two classes of moving parts, voltage sensors that respond to changes in the transmembrane potential and gates that create or deny permeant ions access to the conduction pathway. To explore the coupling between voltage sensors and gates, we have systematically immobilized each using a bifunctional photoactivatable cross-linker, benzophenone-4-carboxamidocysteine methanethiosulfonate, that can be tethered to cysteines introduced into the channel protein by mutagenesis. To validate the method, we first tested it on the inactivation gate of the sodium channel. The benzophenone-labeled inactivation gate of the sodium channel can be trapped selectively either in an open or closed state by ultraviolet irradiation at either a hyperpolarized or depolarized voltage, respectively. To verify that ultraviolet light can immobilize S4 segments, we examined its relative effects on ionic and gating currents in Shaker potassium channels, labeled at residue 359 at the extracellular end of the S4 segment. As predicted by the tetrameric stoichiometry of these potassium channels, ultraviolet irradiation reduces ionic current by approximately the fourth power of the gating current reduction, suggesting little cooperativity between the movements of individual S4 segments. Photocross-linking occurs preferably at hyperpolarized voltages after labeling residue 359, suggesting that depolarization moves the benzophenone adduct out of a restricted environment. Immobilization of the S4 segment of the second domain of sodium channels prevents channels from opening. By contrast, photocross-linking the S4 segment of the fourth domain of the sodium channel has effects on both activation and inactivation. Our results indicate that specific voltage sensors of the sodium channel play unique roles in gating, and suggest that movement of one voltage sensor, the S4 segment of domain 4, is at least a two-step process, each step coupled to a different gate.

Base Sequence↗

PubMed2000

Prolonged photosensitivity following contact photoallergy to ketoprofen.

We report the third case of prolonged photosensitivity secondary to contact photoallergy to topical ketoprofen, a 2-arylpropionic acid derivative. The patient suffered from persistent photosensitivity for more than 1 year after the withdrawal of ketoprofen with recurrent eruptions on sun-exposed skin areas. This photosensitivity was associated with a persistent decrease in polychromatic and UVA minimal erythemal doses. Photobiological testing revealed cross-reactivity with fenofibrate and benzophenones. Photoallergy to ketoprofen is due to the benzophenone structure or to the very similar thiophene phenylketone of tiaprofenic acid, but not to the arylpropionic function. Thus, fenofibrate, tiaprofenic acid and benzophenones should be avoided by patients with a positive history of photocontact dermatitis to ketoprofen.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2004

New phenolic principles from Hypericum sampsonii.

Using the anti-hepatitis B virus (HBV)-producing cell line MS-G2 in vitro cultural system-guided screening was performed, and two new benzophenones, 2,6-dihydroxy-4-[(E)-5-hydroxy-3,7-dimethylocta-2,7-dienyloxy]benzophenone (1) and 2,6-dihydroxy-4-[(E)-7-hydroxy-3,7-dimethylocta-2-enyloxy]benzophenone (2), a new xanthone, hyperxanthone (3), a new bisanthraquinone glycoside, R-(-)-skyrin-6-O-beta-D-xylopyranoside (4), and 2-caffeoyloxy-3-hydroxy-3-(3,4-dihydroxyphenyl)propyl alcohol (5), and 16 known compounds were isolated from the anti-HBV active fraction of the whole herbs of Hypericum sampsonii. Their structures were elucidated using spectroscopic methods, mainly 2D NMR and MS spectrometry. Circular dichroism was used to determine the stereochemistry of bisanthraquinone glycosides.

Hypericum↗

PubMed1976

Simplified fluorometric assay for diphenylhydantoin in plasma.

The fluorometric benzophenone procedure for diphenylhydantoin has been simplified by eliminating the need for preliminary extraction of plasma with an organic solvent. Assays are done directly on 0.2 ml of plasma by treating it with alkaline permanganate to form benzophenone, extracting the benzophenone with heptane, and then shaking the heptane layer with sulfuric acid and measuring the fluorescence of the acid layer. The assay is highly reproducible, and adequately sensitive to detect 1 mug of the drug per milliliter of plasma. Fluorometric and gas-liquid chromatographic assays of 154 plasmas gave results that were not significantly different, even in the presence of phenobarbital, other barbiturates and anticonvulsant drugs, or of various tranquilizers and other commonly used drugs. The assay is rapid, the unit cost per assay low.

Chromatography, Gas↗