Heats of formation and singlet-triplet separations of hydroxymethylene and 1-hydroxyethylidene

Thermochemical parameters of hydroxymethylene (HC:OH) and 1-hydroxyethylidene (CH3C:OH) were evaluated by using coupled-cluster, CCSD(T), theory, in conjunction with the augmented correlation consistent, aug-cc-pVnZ, basis sets, with n = D, T, Q, and 5, extrapolated to the complete basis set limit. The predicted value at 298 K for Delta Hf(CH2O) is -26.0 +/- 1 kcal/mol, as compared to an experimental value of -25.98 +/- 0.01 kcal/mol, and for Delta Hf(CH:OH) it is 26.1 +/- 1 kcal/mol. The hydroxymethylene-formaldehyde energy gap is 52.1 +/- 0.5 kcal/mol, the singlet-triplet separation of hydroxymethylene is Delta E(ST)(HC:OH) = 25.3 +/- 0.5 kcal/mol, the proton affinity is PA(HC:OH) = 222.5 +/- 0.5 kcal/mol, and the ionization energy is IEa(HC:OH) = 8.91 +/- 0.04 eV. The predicted value at 298 K for Delta Hf(CH3CHO) is -39.1 +/- 1 kcal/mol as compared to an experimental value of -40.80 +/- 0.35 kcal/mol, and for Delta Hf(CH3C:OH) it is 11.2 +/- 1 kcal/mol. The hydroxyethylidene-acetaldehyde energy gap is 50.6 +/- 0.5 kcal/mol, the singlet-triplet separation of 1-hydroxyethylidene is Delta E(ST)(CH3C:OH) = 30.5 +/- 0.5 kcal/mol, the proton affinity is PA(CH3C:OH) = 234.7 +/- 0.5 kcal/mol, and the ionization energy is IEa(CH3C:OH) = 8.18 +/- 0.04 eV. The calculated energy differences between the carbene and aldehyde isomers, and, thus, the heats of formation of the carbenes, differ from the experimental values by 2.5 kcal/mol.     

Identification and quantification of molecular species of diacyl glyceryl ether by reversed-phase high-performance liquid chromatography with refractive index detection and mass spectrometry

We have developed a method to identify and quantify the molecular species of diacyl glyceryl ether (DAGE) using high-performance liquid chromatography (HPLC) equipped with a refractive index detector and an electrospray ionization and time of flight mass spectrometer (LC-RI-MS). An octadecyl silica column with a mixture of acetonitrile and dichloromethane (65:35, v/v) as an eluant was used for the HPLC. When the LC-RI-MS method was applied to a mixture of synthetic DAGEs; 1-O-hexadecyl-2,3-dioleoylglycerol (O-16:0-18:1-18:18:1), 1-O-octadecyl-2,3-dioleoylglycerol (O-18:0-18:1-18:1), 1-O-octadecenyl-2,3-dioleoylglycerol (O-18:1-18:1-18:1), 1-O-octadecyl-2,3-didocodahexaenoylglycerol (O-18:0-22:6-22:6), and 1-O-octadecenyl-2,3-didocosahexaenoylglycerol (O-18:1-22:6-22:6), good separation and quantification were obtained on the refractive index chromatogram. A pseudo-molecular ion [M+NH4]+ and a monoacyl glyceryl ether ion [M-RCO2] + were observed for all synthetic DAGEs on the mass spectrum. It was found that the fatty acids and glyceryl ether in DAGE could be easily identified by these mass spectra. When this LC-RI-MS method was applied to the DAGEs extracted from muscle of Stromateus stellatus, approximately 18 peaks were observed on LC-RI-MS chromatograms and the major molecular species of DAGEs were identified as O-16:0-18:1-18:1.     

Ab initio SCF study of the interaction between L-serine phosphate and ammonia

The possible conformational changes of L -serine phosphate due to the interaction with ammonia are investigated by means of ab initio MO-LCAO-SCF calculations, using a supermolecule approach and an STO -3G basis set. The most favorable conformation of a four-hydrated L -serine phosphate anion is found to be changed by the binding of an ammonium ion. Cointeraction of ammonia and NH suggests another conformational change through the displacement of the bridging water molecule of the polyhydrated L -serine phosphate anion.     

A spectroscopic study of the inclusion of azulene by beta- and gamma-cyclodextrins

The inclusion of azulene (AZ) inside the cavities of beta-cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD) was studied using absorption, fluorescence and induced-circular dichroism spectroscopy. The inclusion of AZ into the cavity of beta-CD has a stoichiometry of 1:1, whereas that of AZ/gamma-CD complex is 1:2. The equilibrium constants for the formation of the two complexes were calculated to be 780+/-150 M(-1) for AZ:beta-CD and (4.5+/-0.86)x10(5) M(-2) for AZ:(gamma-CD)(2). The latter is due to a stepwise equilibrium mechanism in which a 1:1 complex is formed with a binding constant of 775 M(-1), followed by the formation of a 1:2 complex with a binding constant of 580 M(-1). The difference between the two binding constant values is slight, indicating an almost equal contribution from each of the gamma-CD molecules to the overall binding in AZ:(gamma-CD)(2). From the induced-circular dichroism spectra, the inclusion of AZ was found to be axial in AZ:beta-CD and nearly axial in AZ:(gamma-CD)(2).     

Convergent synthesis and preliminary biological evaluations of the stilbenolignan (+/-)-aiphanol and various congeners

Treatment of an equimolar mixture of stilbene 7 and cinnamyl alcohol 8 with silver carbonate in acetone-benzene afforded a ca. 2:1:2:1 mixture of the stilbenolignan (+/-)-aiphanol (1) and congeners 2-4 each of which show significant anti-angiogenic and COX-2 inhibitory properties.     

Sensitive and selective determination of metabolically formed trans-dihydrodiols and phenols of benzo[a]pyrene in water and urine samples by HPLC with amperometric detection

A method has been developed to separate hydroxylated metabolites of the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene, i. e. trans-4,5-, 7,8-, 9,10-dihydrodiol and 1-, 3-, 7-, and 9-phenol, by HPLC with amperometric detection employing an isocratic methanol/water eluent (70:30, v/v) containing 0.5 g/L sulfuric acid and 1 g/L lithium perchlorate. Compared with the usually applied fluorescence (λ_ex = 265 nm, λ_em = 460 nm) and ultraviolet (λ = 265 nm) detection, the amperometric technique is about 2–12 times more sensitive for the determination of all metabolites investigated. The method was applied to the determination of the seven metabolites of benzo[a]pyrene in different water samples and in urine after solid-phase extraction (SPE). The results obtained by HPLC with amperometric detection after SPE enrichment from an aqueous extract of a soil sample and from the urine of a rat intragastrically treated with benzo[a]pyrene agreed well with the values determined with fluorescence and/or UV detection. Received: 20 December 1996 / Revised: 10 March 1997 / Accepted: 30 April 1997     

Ligand substitution and nucleophilic reactivity of tricarbonyl(1–3:5,6-η-cyclooctadienylium)ruthenium cation and its derivatives

Nucleophilic attack of triphenylphosphine on tricarbonyl(1–3:5,6-η-cyclooctadienylium)ruthenium cation initially gives a phosphonium ion, which, during three weeks isomerizes to the dicarbonyl(4–6-η,1-σ-cyclooctenediyl)triphenylphosphineruthenium cation. (This species was also obtained by two other routes.) Nucleophilic attack on the latter of I^? gives dicarbonyl(4–6-η,1-σ-cyclooctadienylium)iodoruthenium, which with AgPF₆ gives the coordinatively unsaturated dicarbonyl(1–3:5,6-η-cyclooctadienylium)ruthenium cation as an intermediate. Reactions of this cation with triphenylphosphine and with hydride ion give rise, respectively, to dicarbonyl(1–3:5,6-η-cyclooctadienylium)triphenylphosphineruthenium hexafluorophosphate and the metallic hydride dicarbonyl(4–6-η,1-σ-cyclooctadienylium)hydrideruthenium.     

Spectrophotometric determination of cobalt(II) and cyanocobalamin with vanillilfluorone and its applications

Spectrophotometric determination of cobalt(II) was accomplished with vanillilfluorone (VF) in the presence of dimethylbenzyltetradecylammonium chloride (Zephiramine, Zep). In the determination of cobalt(II), Beer's law was obeyed in the range of 24-470 ng/ml, with an effective molar absorption coefficient (at 575 nm) and relative standard deviation of 1.35×10(5) l mol(-1) cm(-1) and 0.66% (n=5), respectively. The composition ratio of the colored complex was determined by the mole ratio and continuous variation methods, and it was found to be Co(II) : VF : Zep=1 : 2 : 4. Analysis of cyanocobalamin by the same procedure showed that cyanocobalamin could be determined in the concentration range of 0.5-0.11 μg/ml using the proposed method.     

Small-angle X-ray and neutron scattering studies of the morphology of ionomers

Preliminary small-angle neutron scattering (SANS) studies have been made of different ionomers in the dry state and after saturation with water. Scattering from the dry samples arises from differences in the neutron scattering cross sections of the ionic and nonionic units in the polymer. The SANS technique is complementary to previous small-angle x-ray scattering (SAXS) studies since the SANS contrast differences are generally quite different than those for SAXS. A quantitative comparison is made of SANS and SAXS intensities for a dry cesium salt of an ethylene-methacrylic acid (E-MAA) copolymer. For water-saturated samples the technique of isotopic replacement can be used in conjunction with SANS since saturation can be effected with either H₂O or D₂O. In this case information about the chemical composition of the phases is obtained from an analysis of the intensity ratio I/I. Results are consistent with the presence of a separate phase containing water molecules and ions in a matrix of the nonionic units. A Guinier analysis gives a radius of gyration of 17 Å for a water-saturated cesium salt of an E-MAA copolymer.     

Hydrogen isotope effects and mechanism of aqueous ozone and peroxone decompositions

Hydrogen peroxide exalts the reactivity of aqueous ozone by reasons that remain obscure. Should H2O2 enhance free radical production, as it is generally believed, a chain mechanism propagated by (.OH/.O2-) species would account for O3 decomposition rates in neat H2O, HR-O3, and in peroxone (O3 + H2O2) solutions, HPR-O3. We found, however, that: (1) the radical mechanism correctly predicts HR-O3 but vastly overestimates HPR-O3, (2) solvent deuteration experiments preclude radical products from the (O3 + HO2-) reaction. The modest kinetic isotope effect (KIE) we measure in H2O/D2O: HR-O3/DR-O3 = 1.5 +/- 0.3, is compatible with a chain process driven by electron- and/or O-atom transfer processes. But the large KIE found in peroxone: HPR-O3/DPR-O3 = 19.6 +/- 4.0, is due to an elementary (O3 + HO2-) reaction involving H-O2- bond cleavage. Since the KIE for the hypothetical H-atom transfer: O3 + HO2- HO3. +.O2-, would emerge as a KIE1/2 factor in the rates of the ensuing radical chain, the magnitude of the observed KIE must be associated with the hydride transfer reaction that yields a diamagnetic species: O3 + HO2- HO3- + O2. HO3-/H2O3 may be the bactericidal trioxide recently identified in the antibody-catalyzed addition of O2(1Deltag) to H2O.     

Enantioselective syntheses of (+)-xylarenal A and ent-xylarenal A

[reaction: see text] The total synthesis of the sesquiterpenoid xylarenal A is reported. This first synthetic entry to an eremophilane terpenoid with an exocyclic vinyl aldehyde unit involves the use of the bicyclic enone (+)-3, which after a gamma-oxidation and alpha'-allylation leads to the formation of the ketone (+)-8. After its acylation, an oxidative cleavage of the allyl side chain followed by alpha-methylenation of the resulting aldehyde gives (+)-xylarenal A (1). The synthesis of (-)-xylarenal A from (-)-3 is also reported. Moreover, the first total synthesis of the trinoreremophilane (+)-1alpha-hydroxyisoondetianone (5) is described.     

Development and validation of spectrophotometric, TLC and HPLC methods for the determination of lamotrigine in presence of its impurity

Three reliable, rapid and selective methods have been developed and validated for the determination of lamotrigine in the presence of its impurity, 2,3-dichlorobenzoic acid. The first method is spectrophotometric method using p-chloranilic acid forming a colored product with lambda(max) 519+/-2 nm. All variables affecting the reaction have been investigated and the conditions were optimized. Beer's law was obeyed over a concentration range of 10-200 microg ml(-1) with mean accuracy 100.13+/-0.44%. The molar ratio of the formed ion-association complex is found to be 1 : 1 as deduced by Job's method. The conditional stability constant (K(f)), standard free energy (DeltaG), molar absorptivity(epsilon), and sensitivity index were evaluated. The second method is based on TLC separation of the cited drug (Rf=0.75+/-0.01) from its impurity (Rf=0.23+/-0.01) followed by densitometric measurement of the intact drug spots at 275 nm. The separation was carried on silica gel plates using ethyl acetate : methanol : ammonia 35% (17 : 2 : 1 v/v/v) as a mobile phase. The linearity range was 0.5-10 microg/spot with mean accuracy 99.99+/-1.33%. The third method is accurate and sensitive stability-indicating HPLC method based on separation of lamotrigine from its impurity on a reversed phase C(18) column, using a mobile phase of acetonitrile : methanol : 0.01 M potassium orthophosphate (pH 6.7+/-0.1) (30 : 20 : 50 v/v/v) at ambient temperature 25+/-5 degrees C and UV detection at 275 nm in an overall analysis time of about 6 min., based on peak area. The injection repeatability, intraday and interday repeatability were calculated. The procedure provided a linear response over the concentration range 1-12 microg ml(-1) with mean accuracy of 99.50+/-1.30%. The proposed methods were successfully applied for the determination of lamotrigine in bulk powder, in dosage form and in presence of its impurity. The results obtained were analyzed by ANOVA to assess that no significant difference between each of the three methods and the reported one. The validation was performed according to USP guidelines.     

Schiff碱型和仲胺型双冠醚的合成和配位性能

由水杨醛与α,ω-二溴代烷或二(对-甲苯磺酸)三甘醇酯反应,制成相应的二醛化合物。再与4′-氨基苯并-15-冠-5反应生成5种Schiff碱型双冠醚,经LiAlH_4还原可生成5种仲胺型双冠醚。电导率测量结果表明可与KCl(Rb)盐生成2:1(冠醚单元:金属离子)的夹心型配合物。而与钠离子形成1:1配合物。用双冠醚制成PVC膜钾离子选择电极,并测量了电极的线性范围和选择系数。     

Cuprous Complexes and Dioxygen. Part 12.. Rate law and mechanism of the copper-catalyzed oxidation of ascorbic acid in aqueous acetonitrile

The copper-catalyzed oxidation of ascorbic acid (AscH₂) has been studied with a Clark electrode in aqueous MeCN. Cu^I or Cu^II may be equally used as the source of metal ion, without influence on the rate law. At sufficiently high [MeCN], the rate of the overall reaction is essentially given by the rate of Cu^I autoxidation: the reaction is of first order with respect to [Cu] and [O₂] and shows an inverse-square dependence on [MeCN] as observed for the autoxidation of Cu. The pH dependence is complicated by the combination of the intrinsic pH effect on autoxidation with an additional term in the rate law which is directly proportional to [AscH^?]. The latter term is explained by direct oxidation of the organic substrate by the primary dioxygen adduct of Cu^I, CuO. For [MeCN] < 0.7M , a gradual and pH-dependent transformation of this rate law and deviation from the first-order dependence on [O₂] is indicated.     

Intramolecular ene reaction of epoxyallylsilanes: synthesis of allyl- and vinylsilane-functionalized cyclohexanols

[reaction: see text] Epoxyallylsilanes bearing the bulky tert-butyldiphenylsilyl group undergo an uncommon tandem rearrangement-cyclization process upon treatment with Lewis acids. Two pathways for the carbonyl ene reaction are observed: one leading to allylsilane-cyclohexanols when the epoxyallylsilane (28-31) is nonsubstituted, 2-, or 4-monosubstituted and other leading to vinylsilane-cyclohexanols when the epoxyallylsilane (24-27) is 2,4-disubstituted or trisubstituted. An explanation for the observed regio- and stereoselectivity is advanced and a reliable mechanism proposed.     

Configurational studies of complexes of various tea catechins and caffeine in crystal state

Crystals of the complexes of (+)-catechin (CA) of non-galloylated catechin and (-)-catechin-3-O-gallate (Cg) of galloylated catechin with caffeine were prepared, and their stereochemical structures and intermolecular interactions were determined by X-ray crystallographic analysis. CA formed a 1 : 1 complex with caffeine by intermolecular hydrogen bonds, whereas Cg formed a 1 : 2 complex with caffeine, which was formed by face-to-face and offset π-π interactions and intermolecular hydrogen bonds. A solution of two kinds of non-galloylated catechin, CA and (-)-epicatechin (EC), and caffeine (molar ratio 1 : 1 : 2) in water afforded a 1 : 1 : 2 complex, the crystal structure of which had two layers, one layer in which CA and caffeine formed alternate lines and an other layer in which EC and caffeine formed alternate lines. The 1 : 1 : 2 complex was formed by offset π-π and CH-π interactions and intermolecular hydrogen bonds.     

Structure and viscoelasticity of matched asymmetric diblock and triblock copolymers in the cylinder and sphere microstructures

A polystyrene–polyisoprene (PS–PI) diblock copolymer (10,000–50,000 g/mol) and a matched PS&ndashPI–PS triblock (10,000–100,000–10,000 g/mol) were employed to study the effect of chain architecture on the rheological response of ordered block copolymer melts. Both samples adopt hexagonal microstructures with PS cylinders embedded in a PI matrix; on further heating, an order–order transition (OOT) into a cubic array of spheres takes place prior to the order–disorder transition. Each morphology was verified by SAXS and TEM. Interestingly, at the OOT the low-frequency elastic modulus of the diblock increased abruptly, whereas that of the triblock decreased. In contrast, the modulus of the cubic phase was roughly independent of chain architecture. Chain relaxation parallel and perpendicular to the cylinders was probed by measuring the elastic modulus of a macroscopically aligned sample in directions parallel G and perpendicular (G) to the cylinder orientation. For both materials G < G < G where G is the elastic modulus of a randomly oriented sample. This result is attributed to the ability of the unentangled PS blocks to move along the direction of the cylinder axis, and thus relax the stress in the PI matrix in the parallel alignment. In each of the three cylindrical orientations the triblock had a larger modulus than the diblock, which is attributed to the presence of bridging PI blocks that connect distinct PS domains. About 20° below the OOT G showed a distinct change in its temperature dependence, which, coupled with SAXS measurements, is indicative of the onset of an undulation in the cylinder diameter that presages the pinching off of cylinders into spheres, as recently predicted by theory. The use of oriented samples also permitted SAXS confirmation of an approximate epitaxial relationship between the cylinder and the sphere unit cells, although a distinct change in the location of the structure factor maximum, q^*, is noted at the OOT. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2811–2823, 1997     

Determination of N-desmethyl- and N-bisdesmethyl metabolites of Sibutramine in doping control analysis using liquid chromatography-tandem mass spectrometry

Since January 2006, the list of prohibited substances established by the World Anti-Doping Agency includes the antidepressant / anti-obesity drug Sibutramine. Due to its rapid degradation to its active metabolites N-desmethyl and N-bisdesmethyl Sibutramine, reference compounds were synthesized and included into an existing screening assay to allow the unambiguous determination of these metabolic products in human urine using liquid-liquid extraction followed by liquid chromatography/tandem mass spectrometry. Characteristic product ions, obtained after electrospray ionization and collision-induced dissociation, were elucidated using high resolution/high accuracy mass measurements with a hybrid linear ion trap/orbitrap mass analyzer. Based on diagnostic product ions, the extended screening procedure was validated for both Sibutramine metabolites using a triple quadrupole mass spectrometer. Items such as lower limits of detection (6-40 ng mL(-1)), recoveries (39-42%), intraday precision (low: 5.5-10.6%, medium: 4.9-5.9%), high: 12.8-16.4%) and interday precision (low: 15.0-22.8%, medium: 17.7-18.6%), high: 16.5-25.6%) were evaluated, and a clinical spot urine sample was analyzed to demonstrate the applicability of the developed assay in sports drug testing.     

Highly sensitive colour-reaction of nickel with a new chromogenic reagent benzothiaxolyldiazoaminoazobenzene and its application

The synthesis of benzothiaxolyldiazoaminoazobenzene (BTDAB) is described, and a simple, rapid and sensitive procedure for spectrophotometric determination of nickel has been developed. At pH 9.4, in the presence of emulsifier p-octylpolyethyleneglycol phenylether (OP), the reagent reacts with nickel to form a red 1:3 (metal:ligand) complex. The nickel-BTDAB complex exhibit an adsorption maximum at 550 nm with an apparent molar absorptivity of 1.96 x 10(5) 1 mol(-1) cm(-1), Beer's law is obeyed for nickel in the range 0-7 mug per 25 ml. The proposed method has been applied to the determination of nickel in aluminum alloy with satisfactory results.     

Stepwise and one-pot syntheses of Ir(III) complexes with imidazolium-based carbene ligands

We report the preparation, crystal structure, electrochemistry, and emission properties of Ir(Cinsertion markC:)3, where Cinsertion markC: is an N-heterocyclic carbene ligand. Two synthetic approaches are introduced for generating Ir(III) complexes bearing imidazolium-based carbene ligands whose precursors are [pypiH2][Cl] (1a) (pyridyl[1,2-a]{2-phenylimidazol}-3-ylidene chloride) and [pympiH2][Cl] (1b) (pyridyl[1,2-a-{2-(p-methoxy)phenylimidazol}-3-ylidene chloride). The first method is a stepwise reaction: treatment of [Ir(mu-Cl)(COD)]2, where COD is 1,5-cyclooctadiene, with 4 equiv. of the corresponding carbene (Cinsertion markC:) ligands in the presence of an excess amount of sodium methoxide affords Ir(III) dimers [Ir(mu-Cl)(Cinsertion markC:)2]2 (2a, Cinsertion markC: = pypi(-); 2b, Cinsertion markC: = pympi(-)). These chloro-bridged dimers 2a and 2b react with the corresponding carbene (Cinsertion markC:) ligands to form the desired homoleptic compounds Ir(Cinsertion markC:)3 (3a, Cinsertion markC: = pypi(-); 3b, Cinsertion markC: = pympi(-)). The second method, using a one-pot reaction of [Ir(mu-Cl)(COD)]2 with 6 equiv. of the corresponding carbene (Cinsertion markC:) ligands 1a and 1b in the presence of excess amounts of Ag2O, affords Ir(Cinsertion markC:)3. The two methods are convenient and reproducible procedures for the synthesis of Ir(Cinsertion markC:)3. Complexes 3a and 3b are obtained as mixtures of meridional and facial isomers, which can be separated by recrystallization or flash column chromatography.