Direct ESR detection of pentadienyl radicals and peroxyl radicals in lipid peroxidation: mechanistic insight into regioselective oxygenation in lipoxygenases

Well-resolved ESR spectra of free pentadienyl radicals have been observed under photoirradiation of di-tert-butylperoxide (Bu(t)OOBu(t)) and polyunsaturated fatty acids in the absence of O(2), allowing us to determine the hfc values. The hfc values of linoleyl radical indicate that the spin density is the largest at the C-11 position. The linoleyl radical is readily trapped by O(2) to produce the peroxyl radical (11-HPO.) in which O(2) is added mainly at the C-11 position of the pentadienyl radical as indicated by the comparison of the ESR spectra of peroxyl radicals derived from linoleic acid and [11,11-(2)H(2)]linoleic acid. The peroxyl radical (13-HPO.), which is initially formed by the hydrogen abstraction from 13-(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid (13-HPOD) by Bu(t)O., is found to isomerize to 11-HPO. via removal of O(2) from 13-HPO. and addition of O(2) to linoleyl radical to produce 11-HPO. . This finding supports an idea of O(2) entering via a specific protein channel, which determines the stereo- and regiochemistry of the biradical combination between O(2) and linoleyl radical in lipoxygenases.     

Selective gas-chromatographic detection using an ion-selective electrode-II Selective detection of fluorine compounds

Components in samples are separated on a gas chromatography column using hydrogen as carrier gas. The individual components from the column are passed through a platinum tube heated at 1000 degrees , where they undergo hydrogenolysis, and fluorine compounds are converted into hydrogen fluoride. The hydrogen fluoride is dissolved in a slow stream of an absorption solution, and the fluoride ion concentration in the resulting solution is monitored in a flow-cell with a fluoride ion electrode. The potentiometric output of the cell is converted into a signal, which is proportional to the concentration of fluoride ion, by an antilogarithmic converter, and recorded. The response of the detector to fluorine compounds was about 10,000 times that to an equal quantity of other organic compounds, and 5 x 10(-11) mole of fluorobenzene could be detected.     

pH-selective synthesis and structures of alkynyl, acyl, and ketonyl intermediates in anti-Markovnikov and Markovnikov hydrations of a terminal alkyne with a water-soluble iridium aqua complex in water

Chemoselective synthesis and isolation of alkynyl [Cp*Ir(III)(bpy)CCPh]+ (2, Cp* = eta5-C5Me5, bpy = 2,2'-bipyridine), acyl [Cp*Ir(III)(bpy)C(O)CH2Ph]+ (3), and ketonyl [Cp*Ir(III)(bpy)CH2C(O)Ph]+ (4) intermediates in anti-Markovnikov and Markovnikov hydration of phenylacetylene in water have been achieved by changing the pH of the solution of a water-soluble aqua complex [Cp*Ir(III)(bpy)(H2O)]2+ (1) used as the same starting complex. The alkynyl complex [2]2.SO4 was synthesized at pH 8 in the reaction of 1.SO4 with H2O at 25 degrees C, and was isolated as a yellow powder of 2.X (X = CF3SO3 or PF6) by exchanging the counteranion at pH 8. The acyl complex [3]2.SO4 was synthesized by changing the pH of the aqueous solution of [2]2.SO4 from 8 to 1 at 25 degrees C, and was isolated as a red powder of 3.PF6 by exchanging the counteranion at pH 1. The hydration of phenylacetylene with 1.SO4 at pH 4 at 25 degrees C gave a mixture of [2]2.SO4 and [4]2.SO4. After the counteranion was exchanged from SO4(2-) to CF3SO3-, the ketonyl complex 4.CF3SO3 was separated from the mixture of 2.CF3SO3 and 4.CF3SO3 because of the difference in solubility at pH 4 in water. The structures of 2-4 were established by IR with 13C-labeled phenylacetylene (Ph12C13CH), electrospray ionization mass spectrometry (ESI-MS), and NMR studies including 1H, 13C, distortionless enhancement by polarization transfer (DEPT), and correlation spectroscopy (COSY) experiments. The structures of 2.PF6 and 3.PF6 were unequivocally determined by X-ray analysis. Protonation of 3 and 4 gave an aldehyde (phenylacetaldehyde) and a ketone (acetophenone), respectively. Mechanism of the pH-selective anti-Markovnikov vs Markovnikov hydration has been discussed based on the effect of pH on the formation of 2-4. The origins of the alkynyl, acyl, and ketonyl ligands of 2-4 were determined by isotopic labeling experiments with D2O and H2(18)O.     

C(2)-Symmetric bis-sulfoxide: A novel chiral auxiliary for asymmetric desymmetrization of cyclic meso-1,2-diols

A new heterocyclic compound, C(2)-symmetric bis-sulfoxide 1, has been found to be an efficient chiral auxiliary for asymmetric desymmetrization of cyclic meso-1,2-diols via diastereoselective acetal fission. Both (R,R)- and (S,S)-1 are readily synthesized with high optical purity via asymmetric oxidation of 1, 5-benzodithiepan-3-one (2). After acetalization of meso-1,2-diols 6a-e and a mono-TMS ether 6f with this chiral auxiliary 1, the resulting acetals 7a-f were subjected to base-promoted acetal fission upon treatment with potassium hexamethyldisilazide (KHMDS) followed by acetylation or benzylation to give the desymmetrized diol derivatives 8a-f with high diastereoselectivity. The chiral auxiliary 1 is readily removed by acid-promoted hydrolysis and can be recovered without a loss in enantiomeric excess.     

Photoinduced swing of a diarylethene thin broad sword shaped crystal: a study on the detailed mechanism

We report a swinging motion of photochromic thin broad sword shaped crystals upon continuous irradiation with UV light. By contrast in thick crystals, photosalient phenomena were observed. The bending and swinging mechanisms are in fact due to molecular size changes as well as phase transitions. The first slight bending away from the light source is due to photocyclization-induced surface expansion, and the second dramatic bending toward UV incidence is due to single-crystal-to-single-crystal (SCSC) phase transition from the original phase I to phase II_UV. Upon visible light irradiation, the crystal returned to phase I. A similar SCSC phase transition with a similar volume decrease occurred by lowering the temperature (phase III_temp). For both photoinduced and thermal SCSC phase transitions, the symmetry of the unit cell is lowered; in phase II_UV the twisting angle of disordered phenyl groups is different between two adjacent molecules, while in phase III_temp, the population of the phenyl rotamer is different between adjacent molecules. In the case of phase II_UV, we found thickness dependent photosalient phenomena. The thin broad sword shaped crystals with a 3 μm thickness showed no photosalient phenomena, whereas photoinduced SCSC phase transition occurred. In contrast, large crystals of several tens of μm thickness showed photosalient phenomena on the irradiated surface where SCSC phase transition occurred. The results indicated that the accumulated strain, between isomerized and non-isomerized layers, gave rise to the photosalient phenomenon.

We report a swinging motion of photochromic thin broad sword shaped crystals upon continuous irradiation with UV light.     

Substituent effects of beta-diketiminate ligands on the structure and physicochemical properties of copper(II) complexes

Substituent effects of beta-diketiminate ligands on the structure and physicochemical properties of the copper(II) complexes have been systematically investigated by using 3-iminopropenylamine derivatives R1LR3H, R3-N=CH-C(R1)=CH-NH-R3, where R1 is Me, H, CN, or NO2, and R3 is Ph, Mes (mesityl), Dep (2,6-diethylphenyl), Dipp (2,6-diisopropylphenyl), or Dtbp (3,5-di-tert-butylphenyl). When the ligands with R3=Ph or Dtbp were treated with CuII(OAc)2, bis(beta-diketiminate) copper(II) complexes exhibiting distorted tetrahedral geometries were obtained, the crystal structures of which were nearly the same as each other regardless of the alpha-substituent (R1); dihedral angles between the two beta-diketiminate coordination planes are 62.5 +/- 1.2 degrees, and the Cu-N bond lengths are 1.959 +/- 0.008 A. The distorted tetrahedral structures are maintained in solution, but the spectroscopic features, especially gII values of the ESR spectra and the d-d bands of the absorption spectra, as well as the electrochemical behaviors of the complexes, are significantly affected by the electronic nature of R1. The ligands with R3=Mes and Dep, on the other hand, gave di(mu-hydroxo)dicopper(II) complexes, and their crystal structures as well as spectroscopic and electrochemical features have also been explored. Furthermore, the ligand with the more sterically encumbered aromatic substituent (Dipp) provided a mononuclear four-coordinate square planar copper(II) complex supported by one beta-diketiminate ligand and one didentate acetate ion. Thus, the beta-diketiminate ligands with a variety of substituents (R1 and R3) have been explored to provide coordinatively unsaturated (four-coordinate) mononuclear and dinuclear copper(II) complexes with significantly different coordination geometry and properties.     

Study of photopolymers. XXX. Syntheses of new di(meth) acrylate oligomers by addition reactions of epoxy compounds with active esters

Some dimethacrylate oligomers were synthesized by new addition reactions of 2,2-(4-hydroxyphenyl)propane diglycidyl ether (BPGE) or glycidyl methacrylate (GMA) with phenyl methacrylates such as phenyl methacrylate (PMA), 4-nitrophenyl methacrylate (NPMA), 2,4-dichlorophenyl methacrylate (DCPMA), 4-methoxyphenyl methacrylate (MPMA), and (4-cinnamoyloxy)phenyl methacrylate (CIPMA) using tetrabutylammonium bromide as a catalyst at 120°C. The other new dimethacrylate or diacrylate oligomers were also prepared by the addition reactions of GMA or glycidyl acrylate with active esters such as di(S-phenyl)thioisophthalate (PTIP), di(4-nitrophenyl)isophthalate (NPIP), di(4-nitrophenyl)adipate (NPAD), and di(4-nitrophenyl)sebacate (NPSB) under similar reaction conditions. Furthermore, the rates of photochemical reaction of the obtained dimethacrylate oligomers were measured with 3 mol % of various photosensitizers such as benzoin iso-propyl ether (BIPE), 2-ethylanthraquinone (EAQ), and benzophenone (BP). The rate of photochemical reaction of BPGE-DCPMA oligomer was higher than those of BPGE-PMA, BPGE-NPMA, and BPGE-MPMA oligomers using BIPE as a photosensitizer. However, the photochemical reactivity of the unsensitized BPGE-CIPMA was almost the same as that of the sensitized BPGE-DCPMA. On the other hand, when EAQ was used as a photosensitizer, GMA-PTIP oligomer showed much higher reactivity than GMA-NPAD, GMA-NPSB, and GMA-NPIP oligomers. Also it was shown that the activity of EAQ as a sensitizer was higher than BIPE and BP in the photochemical reaction of BPGE-DCPMA oligomer.     

Cycloadditions of N-Aryl-C-(trifluoromethyl)nitrilimines with dimethyl fumarate and maleate

The cycloadditions of N-aryl-C-(trifluoromethyi)nitrilimines 1 , generated in situ from various precursors, with dimethyl fumarate and maleate are described. N-Aryltrifluoroacetohydrazonoyl bromides 2 reacted with fumarate in the presence of triethylamine to give the trans-4,5-dimethoxycarbonylpyrazolines 4 whereas the reactions with maleate afforded the 4,5 -dimethoxycarbonylpyrazoles 5 as well as 4. In the reactions with the chloride 6 under the more drastic conditions, both fumarate and maleate gave the pyrazole 5a. From thermolysis of the oxadiazaphosphole 8 , the trans-pyrazoline 4a was formed in both cases of fumarate and maleate. The preparation of the cis-pyrazoline 9 was attempted from 8 and maleic anhydride but 9 was found to be so unstable as to be epimerized under the mild conditions.     

The chemistry of zerumbone. Part 5: Structural transformation of the dimethylamine derivatives

Zerumbone (1) and its 6,7-epoxide (2) react with ammonia and dimethylamine regio- and stereospecifically, affording monoamines 3, 4, 7 and 8. All adducts have the same relative configuration at C2 and C3. The conjugate amination is thermodynamically controlled to arrive at a single diastereomer. At 15°C 7 reacts with cyanide to give aminonitrile 10 as the single product, while at 30°C, acyclic aminonitrile 11 is also formed. The reaction with 8 affords at 0°C bicyclic aminonitrile 12 of the asteriscane skeleton, while at 30°C or higher temperature, mixtures of 12 and tricyclic nitriles 13 and 13′ are obtained. Refluxing of 7, 8 and 10 in aqueous acetonitrile promotes scission of the zerumbone ring by retro-Mannich reaction to provide acyclic aldehydes 16-18, respectively. The dimethylamino group of 7, 8 and 10 is eliminated stereospecifically by Cope- and base-catalyzed eliminations to regenerate the zerumbone skeleton in the products 1, 2 and 21. Cope elimination of 12 results in a mixture of 13 and 13′ by deaminative transannular etherification.     

Ultrafast excitation relaxation dynamics of lutein in solution and in the light-harvesting complexes II isolated from Arabidopsis thaliana

Ultrafast excitation relaxation dynamics and energy-transfer processes in the light-harvesting complex II (LHC II) of Arabidopsis thaliana were examined at physiological temperature using femtosecond time-resolved fluorescence spectroscopy. Energy transfer from lutein to Chl a proceeded with a rate constant of k(ET) = 1.8-1.9 x 10(13) s(-1) and a yield of approximately Phi(ET) = 0.70, whereas that from neoxanthin to Chl a had a rate constant of k(ET) = 6.5 x 10(11) s(-1) and a yield at the most of Phi(ET) = 0.09. Fluorescence anisotropic decay of lutein in LHC II showed a value larger than 0.4 at the initial state and decayed to approximately 0.1 in 0.3 ps, indicating that two lutein molecules interact with each other in LHC II. In solution, anisotropy of lutein remained constant (0.38) independent of time, and thus a new excited state inferred between the S(2) (1B(u)) state and the S(1) (2A(g)) state was not applicable for lutein in solution. Energy migration processes among Chl a or Chl b molecules were clearly resolved by kinetic analysis. On the basis of these results, relaxation processes and energy-transfer kinetics in LHC II of A. thaliana are discussed.