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PubMed2001

The epigenetic toxicity of pyrene and related ozonation byproducts containing an aldehyde functional group.

Gap junction intercellular communication (GJIC) was used to assess the epigenetic toxicity of pyrene, pure byproducts of pyrene ozonation, and other compounds similar in chemical structure. Byproduct mixtures collected from HPLC were also evaluated using GJIC. Of the 11 pure compounds studied, five inhibited GJIC completely. Two inhibiting compounds contained four rings and were the only compounds studied with greater than three rings. The remaining three compounds contained either two or three rings, and all three contained an aldehyde group. Toxicological evaluation and GC/MS of impure byproduct mixtures showed that two common compounds were found in inhibiting fractions. These common compounds contained both a bay region and at least one aldehyde group.

Aldehydes↗
PubMed2004

Optimization of the peroxy acid treatment of alpha-methylnaphthalene and benzo[a]pyrene in sandy and silty-clay sediments.

The majority of polycyclic aromatic hydrocarbons (PAHs) released to the environment come from anthropogenic sources involving the incomplete combustion of organic compounds. Several techniques are available for the degradation of PAHs. Among the abiotic/biotic processes used to degrade PAHs, an alternative strategy utilizing a primary chemical oxidative step to be combined with a biological was created. The degradation of alpha-methylnaphthalene and benzo[a]pyrene using an advanced oxidation process was optimized over a period of 24 h by varying the ratio of acetic acid to hydrogen peroxide, the compounds that form peroxy acids. The optimization process was performed using sandy and silty-clay sediment types. Gas chromatography equipped with a flame ionization detector was used to determine the varied rates of degradation depending on acetic acid:hydrogen peroxide ratios and the characteristics of the sediment sample. Reduction of 20-90% of alpha-methylnaphthalene and benzo[a]pyrene was observed when 2-5 mL of hydrogen peroxide was used, respectively. A peracetic acid solution (e.g., a commercial form of acetic acid and hydrogen peroxide) was used to compare the results from the peroxy acid experiments. In all the experiments, peracetic acid was more reactive than the combination of acetic acid and hydrogen peroxide. Acetic acid, deionized water, and hydrogen peroxide served as controls and demonstrated minimal degradation over the time course study. Therefore, the use of a peroxy acid process to target electron dense pollutants may have a great utility.

Aluminum Silicates↗
PubMed2001

New insights on the mechanisms of the pH-independent reactions of benzo[a]pyrenes 7,8-diol 9,10-epoxides.

The rates and products of the reactions of (+/-)-7beta,8alpha-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (1) and (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (2) in water and dioxane-water mixtures have been determined over a pH range wider than that of earlier studies. This study provides additional insight on the mechanisms of the pH-independent reactions of 1 and 2. The rate profile for reaction of 1 shows acid-catalyzed hydrolysis at pH <5, a rate plateau at pH 5-9.5, a negative inflection at pH 10-11.5, and a rate increase at pH >11.5. The rate decrease between pH 10 and pH 11.5 is accompanied by a decrease in the yield of tetrols from 60% (pH 8) to 29% (pH 11.2) and is interpreted to be the result of a partial change in mechanism brought about by attack of hydroxide ion acting as a base to deprotonate a carbocation intermediate and regenerate 1 at pH >10, thus reducing the contribution of the pathway for tetrol formation in which water attacks the carbocation. The rate profile for the reaction of 2 exhibits only a single rate plateau at intermediate pH, along with increases in rate at low and high pH because of second-order reactions of 2 with H+ and HO-, respectively. The lack of a rate depression at pH >10 and the product studies for the reaction of 2 in dilute sodium azide solutions suggest that the tetrol-forming reactions of the pH-independent reaction of 2 are concerted or near-concerted.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2003

Novel peptides bearing pyrene and coumarin units with or without beta-cyclodextrin in their side chains exhibit intramolecular fluorescence resonance energy transfer.

Novel peptides bearing the pyrene/coumarin FRET pair in their side chains have been designed and synthesized. Peptide 1 having endogenous beta-cyclodextrin (beta-CD) in the side chain exhibits FRET in aqueous solution, indicating that coumarin, being accommodated into the CD cavity, is separated from pyrene. Guest-induced quenching of the fluorophores in 1 indicates that coumarin, being excluded from the CD cavity, comes into close contact with pyrene. Peptide 2 shows FRET only after addition of external beta-CD that again reflects the idea that beta-CD surely caps the coumarin unit in its hydrophobic cavity, and, therefore, quenching of the fluorophores can be prevented in FRET peptide probes. With this strategy, various peptide-based FRET probes can be developed that would be useful for studying biological phenomena in living cells.

Circular Dichroism↗
PubMed2005

Receptor for anionic pyrene derivatives provides the basis for new biomembrane assays.

This study describes a new receptor cyclen 1 capable of strong selective binding of pyrene-based anionic dyes under near-physiological conditions. This receptor comprises four naphthylthiourea groups tethered to a cyclen core via an ester linkage. The complexation behavior of cyclen 1 receptor is characterized by a series of (1)H NMR, microcalorimetry, UV-vis, and fluorometry experiments. The relevance of structural features of this receptor to its recognition function is assessed using control compounds that lack some of the groups found in cyclen 1. The specificity of cyclen 1 toward pyrene-based dyes is assessed through experiments using dyes with different molecular organization. The most important finding was the ability of cyclen 1 to bind efficiently to a pH-sensitive dye pyranine, a dye that is commonly used in various biomembrane assays. The high affinity of cyclen 1 to pyranine, its impermeability to the lipid bilayer membrane, fast kinetics of binding, and ability to quench the pyranine's fluorescence were used as a basis for a new membrane leakage assay. This membrane leakage assay is fully compatible with the commonly applied pH-stat transport assay, and therefore it allows for differentiation of the ion transport and nonselective leakage mechanisms within a single set of experiments. The ability of cyclen 1 to quench the fluorescence of pyranine also finds limited applicability to the detection of endovesiculation.

Anions↗
PubMed2007

Highly diastereoselective synthesis of nucleoside adducts from the carcinogenic benzo[a]pyrene diol epoxide and a computational analysis.

A diastereoselective synthesis of the nucleoside adducts corresponding to a cis ring-opening of the carcinogen (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP DE-2) by 2'-deoxyadenosine and 2'-deoxyguanosine is described. The key intermediate (+/-)-10alpha-amino-7beta,8alpha,9alpha-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene was synthesized by a highly diastereoselective dihydroxylation wherein phenylboronic acid was a water surrogate. The resulting boronate ester was converted to a tetraol derivative in which two of the four hydroxyl groups (trans 7, 8) were protected as benzoate esters while the remaining two (cis 9, 10) were free. The cis glycol entity was then subjected to a reaction with 1-chlorocarbonyl-1-methylethylacetate to yield an intermediate chloro monoacetoxy dibenzoate. Displacement of the halide with azide, complete cleavage of the esters, and catalytic reduction of the azide yielded the requisite amino triol. Fluoride displacement from appropriately protected nucleoside derivatives, 6-fluoropurine 2'-deoxyribonucleoside and 2-fluoro-2'-deoxyinosine, by the amino triol then yielded diastereomeric pairs of diol epoxide-adducted 2'-deoxyadenosine (dA) and 2'-deoxyguanosine (dG) nucleosides. Small aliquots of these adducts were separated for characterization purposes. The present approach provides the first diastereoselective synthesis of the cis adducts of BaP DE-2 with 2'-deoxyguanosine as well as the first synthesis of both dA and dG adducts from a common intermediate. An informative analysis of the 1H NMR spectra of the cis adducts synthesized and comparisons to the trans adducts are reported. To gain insight into the diastereoselectivity in the key dihydroxylation step, a computational analysis, including molecular mechanics (MMFF94) and semiempirical AM1 geometry optimizations, yielded results that are in fairly good agreement with the experimental observations.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2000

New and highly efficient synthesis of cis- and trans-opened Benzo[a]pyrene 7,8-diol 9,10-epoxide adducts at the exocyclic N(2)-amino group of deoxyguanosine.

We describe a new and facile method for the synthesis of both cis- and trans-opened N(2)-deoxyguanosine (dG) adducts of (+/-)-7alpha, 8beta-dihydoxy-9beta,10beta-epoxy-7,8,9,10-tetra hydrobenzo[a]pyrene and (+/-)-7alpha,8beta-dihydoxy-9alpha,10alpha -epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene at C-10. The key step in our approach is the direct coupling of O(6)-allyl-3', 5'-di-O-(tert-butyldimethylsilyl)-2'-deoxyguanosine with these epoxides followed by the separation of the mixtures of cis- and trans-diastereomers produced. Overall coupling yields ranged from 45 to 65%. Stereochemistry of addition of the N(2)-exocyclic amino group of dG (cis-trans, approximately 1:1) was assigned by NMR, and the absolute configuration of the dG adducts was unequivocally assigned by CD spectroscopy after separation of each individual diastereomer and cleavage of the allyl protecting group. A strong CD band at 279 nm in the O(6)-protected adduct was found to be diagnostic for configuration at C-10, with a negative band correlating with 10R configuration. The synthetic methodology described allows easy access to cis- and trans-opened N(2)-dG adducts which are valuable building blocks for the synthesis of adduct-containing oligonucleotides for physical and biochemical studies.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2003

Evaluation of the enantiomeric resolution of 7,8-dihydroxy-7,8-dihydrobenzo[a]-pyrene and its 6-fluoro and 6-bromo derivatives on polysaccharide-derived stationary phases.

The enantiomeric resolution and the elution order of (+/-)-trans-7,8-dihydrodiols of benzo[a]pyrene and its 6-fluoro and 6-bromo derivatives were analyzed on three polysaccharide-based columns: Daicel Chiralcel CA-I (cellulose triacetate), OF, and OG [cellulose tris(4-chloro- and 4-methylphenylcarbamate)]. For comparison, the separation of (+/-)-1,1'-bi-2-naphthol was evaluated on the OG and OF columns. Possibly similar interactions of (S)-1,1'-bi-2-naphthol and (7S,8S)-isomers of 6-halo-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene with the chiral sorbent are suggested.

Hydrocarbons, Brominated↗
PubMed2004

Synthesis and hydrolysis of a cis-chlorohydrin derived from a benzo[a]pyrene 7,8-diol 9,10-epoxide.

(+/-)-7beta,8alpha-Dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (DE-1) undergoes reaction with anhydrous HCl in dioxane to yield predominantly ( approximately 94%) a single chlorohydrin. This chlorohydrin was assigned structure 9, in which the chloro goup at C-10 is located cis to the C-9 hydroxyl group, on the basis of its (1)H NMR spectrum. This result is in contrast to the reaction of a diastereomeric benzo[a]pyrene 7,8-diol 9,10-epoxide (DE-2) with HCl, which yields only trans-chlorohydrin 8. The hydrolysis of cis-chlorohydrin 9 in 10:90 dioxane-water solutions yields the same ratio of tetrols ( approximately 89% cis/11% trans) as that formed by acid-catalyzed hydrolysis of DE-1. This result again contrasts with the hydrolysis of trans-chlorohydrin 8, which undergoes hydrolysis to give tetrols in a ratio different from that from acid-catalyzed hydrolysis of DE-2. A marked common ion rate depression in the hydrolysis of cis-chlorohydrin 9 is observed, which shows that hydrolysis proceeds via an intermediate carbocation that has a sufficient lifetime to be trapped by external chloride ion. The observation that DE-1 reacts with HCl to give mainly the cis-chlorohydrin is rationalized by quantum chemical calculations that suggest that the cis-chlorohydrin is more stable than the epimeric trans-chlorohydrin.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2004

Chiral morphologies and interfacial electronic structure of naphtho[2,3-a]pyrene on Au(111).

The adsorption of the two-dimensionally chiral naphtho[2,3-a]pyrene molecule has been studied on Au(111). Both structural and electronic properties of the naphtho[2,3-a]pyrene (NP)/Au(111) interface have been measured. Ultraviolet and X-ray photoelectron spectroscopy have been employed to measure the energies of the molecular orbitals of the NP film with respect to the gold Fermi level. A Schottky junction with a large interface dipole (0.99 eV) is formed between Au(111) and NP. Temperature-programmed desorption was used to determine that adsorbed NP has a binding energy of 102.2 kJ/mol. Chiral domains have been observed with scanning tunneling microscopy due to the spontaneous phase separation of the 2-D enantiomers. Two distinct structural polymorphs have been observed, one of which has homochiral paired molecular rows. Models of the 2D structure are proposed that are in excellent agreement with experimental measurements.

Electrons↗
PubMed1999

Umbelliferone analogues and their potential to inhibit Benzo(a)pyrene- and hydrogen peroxide-induced mutations.

Following the natural product lead, farneciferol-D (kopetdaghin, 8), some ether analogues of umbelliferone were synthesized and assayed for their potential to be antimutagenic/anticarcinogenic against mutations induced by benzo(a)pyrene, a potent mutagen/carcinogen, and hydrogen peroxide, and for their ability to function as free radical scavengers. The "true" antimutagenic effect of these compounds was determined at half the nontoxic concentration in Salmonella typhimurium strains utilizing a modified Ames test protocol, and their free radical-scavenging ability was assayed utilizing a nonenzymatic phenazine methosulfate (PMS)-NADH system. Umbelliferone analogues 4 and 5 demonstrated good potential in preventing mutations induced by benzo(a)pyrene and hydrogen peroxide and also exhibited good superoxide scavenging ability in the PMS-NADH assay, suggesting that the antimutagenic activity of these analogues may be linked to their antioxidative properties.

Antimutagenic Agents↗
PubMed2003

Synthesis of new, pyrene-containing, metal-chelating lipids and sensing of cupric ions.

The syntheses of several saturated, pyrene-containing, metal-chelating lipids are described. These lipids are capable of strongly binding to transition metal ions employing the metal-chelating headgroup. The excimer-to-monomer ratio of the pyrene groups changes with addition of cupric ions to the liposomes. Three other transition metal ions (Zn(2+), Ni(2+), and Hg(2+)) did not cause any appreciable changes in the excimer-to-monomer ratio. [reaction--see text]

Chelating Agents↗
PubMed2005

A fluoride-selective PCT chemosensor based on formation of a static pyrene excimer.

[reaction: see text] Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized. Complexation of F(-) by 1 causes a red shift of its absorption band to 400 nm (Deltalambda = 54 nm) and a blue shift of the excimer emission to 470 nm (Deltalambda = 12 nm) together with enhanced fluorescence intensity. The blue-shifted excimer emission is attributed to a pyrene dimer formed in the ground state, a so-called static excimer.

Calixarenes↗
PubMedDate not supplied

Modulation of benzo[a]pyrene-DNA adducts in hamster cheek pouch by chronic ethanol consumption.

The effects of chronic ethanol consumption by hamsters on the binding of [3H]benzo[a]pyrene (BaP) metabolites to the DNA of cheek pouch and liver have been examined. Thirty hamsters were fed control liquid diet, and another 30 hamsters were given 6.6% v/v, 190 proof ethanol-containing diet for 28 days. Twenty-four hours after topical application of [3H]BaP to the cheek pouches, the hamsters were killed and DNA was isolated from epithelial sheets of the cheek pouches and from the liver. Two major deoxyribonucleoside adducts were detected in the hamster cheek pouch; one was identified as the N2-deoxyguanosine adduct of (+)-[3H]-7 alpha,8 beta-dihydroxy-9 beta,10 beta-epoxy-7,8,9,10-tetrahydro- BaP [(+)-anti-BPDE-dG]. The other has not yet been characterized. It was named adduct A and cochromatographed with the major adduct derived from (+)-[3H]-trans-7,8-dihydroxy-7,8- dihydrobenzo[a]pyrene [(+)-BaP-7,8-diol] in mouse skin. Chronic ethanol consumption by hamsters had no statistically significant effect on the (+)-anti-BPDE-dG adduct whereas it increased the level of adduct A by 80%. Binding of BaP metabolites to liver DNA was minor and was not influenced by ethanol. This study suggests that chronic ethanol consumption by hamsters either enhances the formation of the (+)-BaP-7,8-diol from BaP or increases oxidation of this diol and its binding to the DNA of the hamster's cheek pouch.

Alcoholism↗
PubMedDate not supplied

Direct synthesis and identification of benzo[a]pyrene diol epoxide-deoxyguanosine binding sites in modified oligodeoxynucleotides.

Adducts derived from the reaction of the benzo[a]pyrene metabolite model compound (+)-anti-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene [(+)-BPDE] with the single-stranded oligodeoxynucleotide 5'-d(TATGCGTAT) were obtained according to direct synthesis techniques described earlier [Cosman, M., Ibanez, V., Geacintov, N. E., and Harvey, R. G. (1990) Carcinogenesis 11, 1667-1672]. Four major adducts, involving trans and cis addition (trans/cis adduct ratio approximately 4.5) of (+)-BPDE to the exocyclic amino groups of guanines G4 and G6 (the numbers denote the positions of the guanines counted from the 5'-side) were obtained. These adducts can be separated from one another by reverse-phase high-performance liquid chromatography methods. The site of BPDE binding on either G4 or G6 can be determined from the electrophoresis band patterns on 20% polyacrylamide gels of the BPDE-modified oligonucleotides subjected to the G+A and G Maxam-Gilbert strand cleavage reactions [Maxam, A. M., and Gilbert, W. (1980) Methods. Enzymol. 65, 499-560]. The electrophoresis gel band patterns are different for unmodified DNA and the two different BPDE-modified oligonucleotides because (1) the strand cleavage fragments bearing BPDE residues migrate slower than the corresponding fragments derived from the unmodified oligonucleotide and (2) strand cleavage tends to be inhibited on the 5'-sides of BPDE-modified guanines in the G+A, but not the G reaction.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMedDate not supplied

Identification and quantitation of benzo[a]pyrene-DNA adducts formed in mouse skin.

The DNA adducts of benzo[a]pyrene (BP) formed in vitro were previously identified and quantitated. In this paper, we report the identification and quantitation of the depurination adducts of BP, 8-(benzo[a]pyren-6-yl)guanine (BP-6-C8Gua), BP-6-N7Gua, and BP-6-N7Ade, formed in mouse skin by one-electron oxidation, as well as the major stable adduct formed via the diolepoxide pathway, BP diolepoxide bound at C-10 to the 2-amino of dG (BPDE-10-N2dG). Identification of the depurination adducts was achieved by HPLC and fluorescence line narrowing spectroscopy. The depurination adducts, BP-6-C8Gua (34%), BP-6-N7Gua (10%), and BP-6-N7Ade (30%), constituted 74% of the adducts found in mouse skin 4 h after treatment with BP. The stable adduct BPDE-10-N2dG accounted for 22% of the adducts. Treatment of the skin with BP-7,8-dihydrodiol or BP diolepoxide yielded almost exclusively the stable adduct BPDE-10-N2dG. When BP or BP-7,8-dihydrodiol was bound to RNA or denatured DNA in reactions catalyzed by rat liver microsomes, no depurination adducts were detected. The profiles of stable adducts were similar both qualitatively and quantitatively with native or denatured DNA. With activation of BP by horseradish peroxidase, the profiles of stable adducts differed with native and denatured DNA. The total amount of adducts with denatured DNA was only 25% of the amount detected with native DNA. No depurination adducts were detected with denatured DNA or RNA in the peroxidase system.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Topical↗
PubMedDate not supplied

Characterization of benzo[a]pyrene anti-diol epoxide adducts to human histones.

Nuclei from human lymphoblast cells grown in culture were treated with [7-14C]-(+/-)-r-7,t-8-dihydroxy-t-9,t-10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (anti-BPDE), and the nucleosomal core histones were isolated for adduct studies by cryogenic fluorescence line narrowing spectroscopy. The four core histones H2A, H2B, H3, and H4 were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which yielded each histone free of contamination by the others. Further purification of histones H2A, H2B, and H4 by reversed-phase HPLC also yielded a tetrahydrotetrol of benzo[a]pyrene, indicating that these three histones had some labile adducts. No tetrol was observed upon purification of histone H3. Fluorescence emission spectra of the HPLC-purified histones recorded at 4K after vibronic excitation into the S1 state were generally similar. Fluorescence line-narrowed spectra of model compounds formed by reaction of anti-BPDE with acetic acid, ethylenediamine, cysteamine, and histidine were also recorded. Only the spectra of the ethylenediamine adduct model matched consistently, at different excitation wavelengths, the spectra of the adducted histones. From this it is concluded that the stable human histone adducts of anti-BPDE are formed by reaction with lysine residues and/or the amino groups of the N-termini.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMedDate not supplied

Laser pulse-induced photochemical strand cleavage of site-specifically and covalently modified (+)-anti-benzo[a]pyrene diol epoxide-oligonucleotide adducts.

The specificity of the laser pulse-induced photocleavage method [Boles, T. C., and Hogan, M. E. (1986) Biochemistry 25, 3039] for detecting the sites of covalent binding of benzo[a]pyrene diol epoxide in DNA was investigated using site-specifically modified oligonucleotide duplexes d(CTCACAT[G*]TACACTCT).d(GAGAGTGTACATGTGA), where [G*] is the adducted guanine residue (+)-trans-anti-BPDE-N2-dG (anti-BPDE = 7 beta,8 alpha- dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene). The appropriate oligonucleotide strands were 32P-end-labeled, and the duplexes were irradiated with a pulse train of 355 nm Nd:YAG laser pulses (approximately 300 mW/cm2). The products of the photocleavage reaction were analyzed by denaturing gel electrophoresis. The major observed products included the intact oligonucleotide strand that had lost the BPDE residue, and shorter oligonucleotide fragments arising from strand scission at the BPDE-modified guanine residue and at nearby flanking bases. Photocleavage at the BPDE-modified G is dominant (approximately 50 +/- 5% of the sum of all of the shorter oligonucleotide fragments), and cleavage extends to at least 4 bases on the 5'-side, and 7 bases on the 3'-side of the BPDE-modified G residue; the probability of cleavage diminishes with increasing distance from the modified G residue. On the unmodified complementary strand, nonspecific strand cleavage is also observed, but the probability of cleavage is > or = 20 times smaller than at the BPDE-modified G residue on the modified strand. The photocleavage method thus preferentially causes strand scission at the sites of BPDE modification, but the occurrence of strand cleavage with lower probabilities at neighboring sites is also significant.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗