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PubMed2004

Products and mechanism of the reaction of OH radicals with 2,3,4-trimethylpentane in the presence of NO.

Alkanes are important constituents of gasoline fuel and vehicle exhaust, with branched alkanes comprising a significant fraction of the total alkanes observed in urban areas. Using a relative rate method, a rate constant for the reaction of OH radicals with 2,3,4-trimethylpentane of (6.84+/-0.12) x 10(-12) cm3 molecule(-1) s(-1) at 298+/-2 K was measured, where the indicated error is two least-squares standard deviations and does not include the uncertainty in the rate constant for the n-octane reference compound. Products of the gas-phase reaction of OH radicals with 2,3,4-trimethylpentane in the presence of NO at 298+/-2 K and atmospheric pressure of air have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatographymass spectrometry (GC-MS), and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). Products identified and quantified by GC-FID and GC-MS were (molar yields given in parentheses): acetaldehyde (47+/-6%), acetone (76+/-11%), 3-methyl-2-butanone (41+/-5%), 3-methyl-2-butyl nitrate (1.6+/-0.2%), and 2-propyl nitrate (6.2+/-0.8%). These compounds account for 69+/-6% of the reaction products, as carbon. Additional products observed by API-MS analyses using positive and negative ion modes were C5- and C8-hydroxynitrates and a C8-hydroxycarbonyl, which, together with the predicted formation of octyl nitrates, account for some or all of the remaining products. The product distribution is compared to those for the linear and branched C8-alkanes n-octane and 2,2,4-trimethylpentane.

Air Pollutants↗
PubMed2001

Carborane-containing liquid crystals: synthesis and structural, conformational, thermal, and spectroscopic characterization of diheptyl and diheptynyl derivatives of p-carboranes.

Molecular and electronic structures for four p-carborane derivatives were studied in the context of their liquid crystalline properties. Thus molecular and crystal structures of diheptyl and diheptynyl derivatives of 10- and 12-vertex bi-p-carboranes were determined by X-ray crystallography and compared to the results of ab initio calculations at the HF/6-31G level of theory. Experimentally observed significant positional disorder of one of the substituents in the 10-vertex derivatives, 2[2]a and 2[2]b, was related to conformational properties of the alkyl-carborane bond. Experimental and theoretical studies of the electronic structures were conducted for the four compounds using UV and NMR spectroscopies. The nature of the unique long wavelength absorption band at 232 nm in the diheptynyl derivative 2[2]b was explained using INDO/2//HF/6-31G analysis. The complete assignment of the (13)C signals was accomplished using a long-range coupling technique and was supported by the calculated (HF/6-31G) isotropic shielding tensors. Analysis of absorption spectra, NMR substituent effects, and trends in bond lengths shows generally strong cage-acetylene electronic interactions for the 10-vertex p-carborane, while the 12-vertex p-carborane remains largely electronically isolated. Ab initio calculations revealed that 12-vertex p-carborane has significantly larger electronic polarizability and quadrupole moments than the 10-vertex analogues, which are larger than those for bicyclo[2.2.2]octane compounds. All these results on packing, conformational, and electronic properties form the basis for the discussion of thermal behavior of the four carborane compounds, bicyclo[2.2.2]octane analogues, and some related compounds.

Journal Article↗
PubMed1997

Intraligand Charge Transfer in Pt(qol)(2). Characterization of Electronic States by High-Resolution Shpol'skii Spectroscopy.

Pt(qol)(2) (qol(-) = 8-quinolinolato-O,N) is investigated in the Shpol'skii matrices n-heptane, n-octane-h(18), n-octane-d(18), n-nonane, and n-decane, respectively. For the first time, highly resolved triplet phosphorescence as well as triplet and singlet excitation spectra are obtained at T = 1.2 K by site-selective spectroscopy. This permits the detailed characterization of the low-lying singlet and triplet states which are assigned to result mainly from intraligand charge transfer (ILCT) transitions. The electronic origin corresponding to the (3)ILCT lies at 15 426 cm(-)(1) (FWHM approximately 3 cm(-)(1)) exhibiting a zero-field splitting smaller than 1 cm(-)(1), which shows that the metal d-orbital contribution to the (3)ILCT is small. At T = 1.2 K, the three triplet sublevels emit independently due to slow spin-lattice relaxation (slr) processes. Therefore, the phosphorescence decays triexponentially with components of 4.5, 13, and 60 &mgr;s. Interestingly, two of the sublevels can be excited selectively, which leads to a distinct spin polarization manifested by a biexponential decay. At T = 20 K, the decay becomes monoexponential with tau = 10 &mgr;s due to a fast slr between the triplet sublevels. From the Zeeman splitting of the (3)ILCT the g-factor is determined to be 2.0 as expected for a relatively pure spin triplet. The (1)ILCT has its electronic origin at 18 767 cm(-)(1) and exhibits a homogeneous line width of about 12 cm(-)(1). This feature allows us to estimate a singlet-triplet intersystem crossing rate of about 2 x 10(12) s(-)(1). This relatively large rate compared to values found for closed shell metal M(qol)(n)() compounds displays the importance of spin-orbit coupling induced by the heavy metal ion. Moreover, this small admixture leads to the relatively short emission decay times. All spectra show highly resolved vibrational satellite structures. These patterns provide information about vibrational energies (which are in good accordance with Raman data) and shifts of equilibrium positions between ground and excited states. These shifts are different in the (1)ILCT and (3)ILCT states. The vibrational satellite structures support the assignment of ILCT character to the lowest excited states.

Journal Article↗
PubMed2006

Synthesis and reactivity of azapalladacyclobutanes.

N-Sulfonyl aziridines undergo oxidative addition to palladium(0) complexes generated in situ from mixtures of Pd2(dba)3 and 1,10-phenanthroline. The resulting azapalladacyclobutane complexes undergo intramolecular carbopalladation in the presence of copper(I) iodide to afford azapalladabicyclo[3.2.1]octanes. A deuterium-labeling experiment indicates that the oxidative addition proceeds via SN2-type attack of palladium(0) on the less-hindered carbon of the aziridine ring and that alkene insertion occurs in a syn fashion. The azapalladabicyclo[3.2.1]octane complexes undergo oxidative palladium-carbon bond functionalization in the presence of copper(II) bromide.

Journal Article↗
PubMed2003

Novel antioxidative metabolites in rat liver with ingested sesamin.

Sesamin, a major lignan in sesame oil, is known to have many biological activities, especially protective effects against oxidative damage in the liver. As sesamin itself has no antioxidative properties in vitro, to elucidate the mechanism of its antioxidative effects, the reaction products of sesamin in rat liver homogenate were analyzed. The methylenedioxyphenyl moiety in the structure of sesamin was shown to be changed into a dihydrophenyl (catechol) moiety. The enzymatic reaction products in vitro were identified as (1R,2S,5R,6S)-6-(3,4-dihydroxyphenyl)-2-(3,4-methylenedioxyphenyl)-3,7-dioxabicyclo[3,3,0]octane and (1R,2S,5R,6S)-2,6-bis(3,4-dihydroxyphenyl)-3,7-dioxabicyclo[3,3,0]octane, which showed strong radical scavenging activities; the latter was a novel compound. The same metabolites were found as glucuronic acid and/or sulfic acid conjugates in substantial amounts in rat bile after oral administration of sesamin. It is suggested that sesamin is a prodrug and the metabolites containing the catechol moieties in their structures are responsible for the protective effects of sesamin against oxidative damage in the liver.

Animals↗
PubMed2006

Amine degradation by 4,5-epoxy-2-decenal in model systems.

The reactions of 4,5-epoxy-2-decenal with octylamine, benzylamine, and 2-phenylglycine methyl ester were studied to investigate if amines may suffer a Strecker type degradation by epoxyalkenals analogously to amino acids. In addition to other reactions, the studied amines were converted into their corresponding Strecker aldehydes (octanal, benzaldehyde, and methyl 2-oxo-2-phenylacetate, respectively) to an extent that depended on the pH, the temperature, the amount of epoxyalkenal, and the amine involved. Each amine exhibited an optimum pH for the reaction, but the corresponding Strecker aldehydes were produced to a significant extent within a broad pH range. In addition, the temperature mostly influenced the reaction rate, which was increased between 6.5 and 9.5 times when the reaction was carried out at 60 degrees C than when it took place at 37 degrees C. Furthermore, Strecker aldehyde formation was linearly correlated with the amount of the epoxyalkenal present in the reaction mixture. Nevertheless, the reaction yield mostly depended on the amine involved. Thus, octylamine only produced trace amounts of octanal, benzylamine was converted into benzaldehyde with a yield of 4.3%, and 2-phenylglycine methyl ester was converted into methyl 2-oxo-2-phenylacetate with a reaction yield of 49%. All of these results suggest that suitable amines can be degraded by epoxyalkenals to their corresponding Strecker aldehydes to a significant extent.

Aldehydes↗
PubMed2006

Changes induced by UV radiation during virgin olive oil storage.

The effects of UV radiation on the chemical and sensory characteristics of virgin olive oils (cv. Arbequina and Picual) were assessed. Even small doses of UV radiation induced oxidation of the virgin olive oil samples. Total phenols and fatty acids contents decreased during the process as well as the intensity of the bitter and fruity sensory attributes, while the intensity of the rancid sensory attribute notably increased. Acetaldehyde, 2-butenal, 2-pentenal, octane, octanal, hexanal, nonanal, and 2-decenal were the volatile compounds most affected, showing an important increase during the irradiation process. Nonanal, hexanal, and pentanal showed high correlation with the rancid sensory attribute (90%, 86%, and 86%, respectively). 2-Decenal and nonanal concentrations allowed us to predict the alteration level of the samples by mean of multiple Ridge regression.

Chromatography, Gas↗
PubMed1999

Enantiomeric purity and odor characteristics of 2- and 3-acetoxy-1, 8-cineoles in the rhizomes of Alpinia galanga willd.

(S)-(+)-O-methylmandelate esters of trans- and cis-1,3, 3-trimethyl-2-oxabicyclo[2.2.2]octan-5- and 6-ols (2- and 3-hydroxy-1,8-cineoles) were prepared, and eight diastereomers were separated. The absolute configuration of the asymmetric carbons of the cineole moiety of each diastereomer was determined by (1)H NMR data according to the Mosher theory. Each mandelate was reduced with LiAlH(4) to obtain optically pure hydroxy-1,8-cineoles, this being followed by acetylation to afford optically pure acetoxy-1, 8-cineoles. These acetates were subjected to chiral GC, using a cyclodextrin column, and the enantiomeric purity of trans- and cis-1, 3,3-trimethyl-2-oxabicyclo[2.2.2]octan-5- and 6-yl acetates in the aroma concentrate from the rhizomes of Alpinia galanga was determined as 93.9 (5S), 19.4 (5R), 63.5 (6R), and 100 (6R) % ee, respectively. The aroma character of each enantiomer was also evaluated by GC-sniffing.

Aluminum Compounds↗
PubMed2000

Effects of the sniffing port air makeup in gas chromatography-olfactometry.

A time-intensity gas chromatography-olfactometry (GCO) apparatus was developed to study some aerodynamic parameters that may influence odor detection and intensity measurements by the subjects. The addition of humidified air at the elution place of the compounds is generally recommended for several reasons (essentially to prevent nasal mucosa dehydration and to improve chromatographic effluent carriage out of the column), but clues about these effects are yet to be published. This question is studied through two complementary experiments using synthetic solutions of 3-methyl-1-butanethiol, hexan-2-one, octanal, nonanal, furfural, citronellal, benzaldehyde, octan-1-ol, 2-phenylethyl acetate, guaiacol, 2-phenylethanol, and vanillin. This work demonstrates the need for an air makeup to increase odor detection frequency and intensity rating. With the conditions tested, a minimum makeup air flow rate of 50 L.min(-)(1) is necessary. On the contrary, humidification of the makeup is useless for the sniffers comfort and to improve the quantitative GCO results.

Adult↗
PubMed1992

Synthesis of carbon-11 labeled iodinated cocaine derivatives and their distribution in baboon brain measured using positron emission tomography.

Three iodine-substituted derivatives of cocaine, methyl esters of 3-[(2'-, 3'-, and 4'-iodobenzoyl)oxy]-8-methyl-[1R-(exo,exo)]-8- azabicyclo[3.2.1]octane-2 carboxylic acid (2a-c), were synthesized and subjected to N-demethylation to give the corresponding noriodococaines 3-[(2'-,3'-, and 4'-iodobenzoyl)oxy]-[1R-(exo,exo)]-8- azabicyclo[3.2.1]-octane-2-carboxylic acid (3a-c). These were remethylated with [11C]CH3I to give the [N-11C-methyl]iodococaines 4a-c which were examined in baboon brain in vivo using positron emission tomography (PET). Compared to [N-11C]cocaine itself the regional distributions were changed from a highly specific localization in the corpus striatum to more diffuse patterns which included the cerebellum and cortex. Peak brain uptakes and clearance kinetics were also changed. [N-11C]-o-Iodococaine (4a) had a peak uptake in the striatum at 4-5 min after injection of only 17% that of cocaine in the same animal. The peak uptake of [N-11C]-p-iodococaine (4c) was 60% of that of [N-11C]cocaine and a clearance half-time of approximately 55 min, twice that of [N-11C]cocaine. [N-11C]-m-Iodococaine (4b) displayed half the uptake of [N-11C]cocaine, buts its clearance was similar to that of the parent molecule. The fractions of unmetabolized tracer in blood plasma at 1-30 min were higher for 4a-c than for [N-11C]cocaine. Plasma protein binding experiments showed 10%, 0.3%, 1.6%, and 6% as the free fraction for cocaine and o-, m-, and p-iodococaines respectively, consistent with the low brain uptake observed for the ortho isomer, and implicated alpha 1-acid glycoprotein as responsible for the low free fraction of o-iodococaine. The potencies of 2a-c to displace tritiated cocaine from striatal membranes were p-iodo approximately cocaine greater than m-iodo approximately o-iodo.

Animals↗
PubMed1990

Synthesis of 3-arylecgonine analogues as inhibitors of cocaine binding and dopamine uptake.

3-Arylecgonine analogues were synthesized and characterized by 1H and 13C NMR, IR, and MS. The compounds were synthesized as racemates from cycloheptatriene-7-carboxylic acid or enantiomerically from (-)-cocaine. These analogues were tested for their ability to inhibit [3H]cocaine binding to bovine striatal tissue and to inhibit [3H]dopamine uptake into striatal synaptosomes. Methyl (1RS-2-exo-3-exo)-8-methyl-3-phenyl-8-azabicyclo[3.2.1]octane-2-ca rboxylate was the most potent analogue. IC50 values for inhibition of cocaine binding and dopamine uptake were 20 and 100 nM, respectively. The racemates and the 1R isomers were equally potent inhibitors of binding and uptake. Methyl (1RS-2-endo-3-exo)-3-(2,4-dinitrophenyl)-8-methyl-8-azabicyclo[3.2 .1]octane- 2-carboxylate was the least potent. IC50 for inhibition of both binding and uptake was 40 microM.

Animals↗
PubMed1976

Potential antitumor agents. 18. Bisquaternary ammonium heterocycles.

It was earlier proposed that a close approach to overall planarity was a structural prerequisite for antileukemic activity (L1210) in bisquaternary ammonium heterocycles. The preparation of L1210 active 3,3'-[bicyclo[2.2.2]octane-1,4-dicarbonylbis(mino-p-phenylenecarbonylimino)bis(1-alkylpyridinium) salts, containing a nonplanar bridged ring system, negates this view. A replacement proposal is that a relatively rigid molecular framework in necessary to maintain the spacing and positioning of the quaternary functions, thereby ensuring correct site selection. Replacement of a terephthaloyl drug component by a bicyclo[2.2.2]octane-1,4-dicarbonyl residue lowers DNA binding. A terephthaloyl unit confers necessary molecular rigidity, greater DNA binding, and higher L1210 activity.

Animals↗
PubMed1985

Synthesis and antifertility activity of zoapatanol analogues.

The synthesis of and guinea pig contragestational screening data for several oxepane and 3,8-dioxabicyclo[3.2.1]octane analogues of zoapatanol (1) are described and their structure-activity relationships discussed. Conversion of the 5-keto group on the nonenyl side chain of 1 into a hydroxyl function enhanced the potency. Further significant enhancement in the potency was realized with the transformation of several oxepanes into the 3,8-dioxabicyclo-[3.2.1]octane-1-acetic acid derivatives. Detailed, comparative contragestational evaluation of the three most potent compounds 9, 33, and 37 is presented, which led to the selection of 33 (ORF 13811) for further biological evaluation.

Abortifacient Agents↗
PubMed2003

A study into the possible homoaromatic nature of some related carbene and cationic intermediates with the potential for transannular interaction.

A comparison of the aromatic nature of the cations and carbenes centered at the 8-position of tricyclo[3.2.1.0(2,4)]octane, the 9-position of pentacyclo[4.3.0.0(2,4).0(3,8).0(5,7)]nonane, the 6-position of tricyclo[3.1.1.0(2,4)]heptane, and the 4-position of tetracyclo[3.3.0.0(2,8).0(3,6)]octane has been undertaken. Hybrid density functional theory calculations have been used to examine the geometric, energetic, and magnetic characteristics of each cation, singlet carbene, and triplet carbene. The results shed light on the flexibility of the polycycles to achieve stable intermediates and on the breadth of homoaromaticity.

Bridged-Ring Compounds↗
PubMed2005

Cubane, cuneane, and their carboxylates: a calorimetric, crystallographic, calculational, and conceptual coinvestigation.

[reaction: see text] This study is a multinational, multidisciplinary contribution to the thermochemistry of dimethyl1,4-cubanedicarboxylate and the corresponding isomeric, cuneane derivative and provides both structural and thermochemical information regarding the rearrangement of dimethyl 1,4-cubanedicarboxylate to dimethyl 2,6-cuneanedicarboxylate. The enthalpies of formation in the condensed phase at T = 298.15 K of dimethyl 1,4-cubanedicarboxylate (dimethyl pentacyclo[4.2.0.0.(2,5)0.(3,8)0(4,7)]octane-1,4-dicarboxylate) and dimethyl 2,6-cuneanedicarboxylate (dimethyl pentacyclo[3.3.0.0.(2,4)0.(3,7)0(6,8)]octane-2,6-dicarboxylate) have been determined by combustion calorimetry, delta(f) H(o)m (cr)/kJ x mol(-1) = -232.62 +/- 5.84 and -413.02 +/- 5.16, respectively. The enthalpies of sublimation have been evaluated by combining vaporization enthalpies evaluated by correlation-gas chromatography and fusion enthalpies measured by differential scanning calorimetry and adjusted to T = 298.15 K, delta(cr) (g)Hm (298.15 K)/kJ x mol(-1) = 117.2 +/- 3.9 and 106.8 +/- 3.0, respectively. Combination of these two enthalpies resulted in delta(f) H(o)m (g., 298.15 K)/kJ x mol(-1) of -115.4 +/- 7.0 for dimethyl 1,4-cubanedicarboxylate and -306.2 +/- 6.0 for dimethyl 2,6-cuneanedicarboxylate. These measurements, accompanied by quantum chemical calculations, resulted in values of delta(f) Hm (g, 298.15 K) = 613.0 +/- 9.5 kJ x mol(-1) for cubane and 436.4 +/- 8.8 kJ x mol(-1) for cuneane. From these enthalpies of formation, strain enthalpies of 681.0 +/- 9.8 and 504.4 +/- 9.1 kJ x mol(-1) were calculated for cubane and cuneane by means of isodesmic reactions, respectively. Crystals of dimethyl 2,6-cuneanedicarboxylate are disordered; the substitution pattern and structure have been confirmed by determination of the X-ray crystal structure of the corresponding diacid.

Journal Article↗
PubMed1997

Synthesis of Linear and Angular Triquinane Skeletons by O-Stannyl Ketyl-Promoted Fragmentation-Cyclization Reactions of alpha-Keto Cyclopropanes.

Several investigations of rigid alpha-keto cyclopropane cleavage by O-stannyl ketyls are summarized herein. Tricyclo[3.3.0.0(2,8)]octan-3-one ring systems were treated with nBu(3)SnH, which produced different ring-cleavage products depending on the location and type of substituent present. An examination of both radical-stabilizing substituents and stereoelectronic factors was initiated to understand what factors bias bond cleavage in a configurationally restricted alpha-ketocyclopropane via O-stannyl ketyls. A preference for cleavage of the cyclopropane bond with the best orbital overlap with the ketyl radical sp(2)-orbital even in the presence of radical stabilizing groups is indicated by these results. An O-stannyl ketyl ring scission-cyclization resulted in the novel synthesis of either a linear or an angular triquinane skeleton depending on the length and location an alkene tether on the tricyclo[3.3.0.0(2,8)]octan-3-one precursor.

Journal Article↗
PubMed1997

Microbiological Oxygenation of Bridgehead Azabicycloalkanes.

A series of N-substituted bridgehead azabicycloalkanes has been prepared and examined as substrates for microbiological oxygenation using the fungi Beauveria bassiana, Rhizopus nigricans, Aspergillus ochraceus, and Rhizopus arrhizus. Oxygenation using B. bassiana of N-tosyl-7-azabicyclo[2.2.1]heptane gave N-[p-(hydroxymethyl)benzenesulfonyl]-7-azabicyclo[2.2.1]heptane (56% yield), of N-(phenyloxycarbonyl)-7-azabicyclo[2.2.1]heptane gave the 2-endo-ol (56% yield, 51% ee), of N-BOC-7-azabicyclo[2.2.1]heptane gave the 2-endo-ol (10% yield), of N-Cbz-7-azabicyclo[2.2.1]heptane gave the 2-endo-ol (28%), of N-(phenyloxycarbonyl)-8-azabicyclo[3.2.1]octane gave the 3-endo-ol, and of N-(phenyloxycarbonyl)-9-azabicyclo[3.3.1]nonane gave the 3-exo-ol (30%) and 3-one (16%). Oxygenation using R. nigricans of N-BOC-7-azabicyclo[2.2.1]heptane gave the 2-endo-ol (62% yield, 28% ee) and the 2-exo-ol (27% yield, 42% ee). Oxidation of the N-BOC-7-azabicyclo[2.2.1]heptan-2-ols gives the 2-ketone, a synthetic intermediate useful for conversion to the natural product, epibatidine. Oxygenation of N-(phenyloxycarbonyl)-7-azabicyclo[2.2.1]heptane using R. arrhizus gives the 2-endo-ol (5% yield, 31% ee) and the 2-exo-ol (18% yield, 22% ee). Oxygenation of N-(phenyloxycarbonyl)-8-azabicyclo[3.2.1]octane using A. ochraceous gives the 3-endo-ol (36%) and the 3-one (4%).

Journal Article↗
PubMed1999

Directed, DDQ-Promoted Benzylic Oxygenations of Tetrahydronaphthalenes.

Positional preferences for para benzylic oxygenation of tetrahydronaphthalenes by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-aqueous dioxane were investigated by comparing the tetralone products from 6-hydroxy-7-methoxy- and 6-acetoxy-7-methoxy-1,2,3,4-tetrahydronaphthalene. The directing influence by an aromatic substituent on para benzylic oxygenation was in the order OH > OMe > OAc. Consistent with this finding were results obtained from lignan analogues. Treatment of (+)-beta-conidendryl alcohol with DDQ in dry dioxane resulted in the intramolecular bridging by one of two primary hydroxy groups to the benzylic position, giving an oxabicyclo[3.2.1]octane. Similar treatment of (+)-dimethyl-beta-conidendryl alcohol resulted in bridging by the alternate primary hydroxyl group to the benzhydrylic carbon giving an isomeric oxabicyclo[3.2.1]octane.

Journal Article↗