Formation of 8-nitroguanine and 8-oxoguanine due to reactions of peroxynitrite with guanine

Reactions of peroxynitrite with guanine were investigated using density functional theory (B3LYP) employing 6-31G** and AUG-cc-pVDZ basis sets. Single point energy calculations were performed at the MP2/AUG-cc-pVDZ level. Genuineness of the calculated transition states (TS) was tested by visually examining the vibrational modes corresponding to the imaginary vibrational frequencies and applying the criterion that the TS properly connected the reactant and product complexes (PC). Genuineness of all the calculated TS was further ensured by intrinsic reaction coordinate (IRC) calculations. Effects of aqueous media were investigated by solvating all the species involved in the reactions using the polarizable continuum model (PCM). The calculations reveal that the most stable nitro-product complex involving the anion of 8-nitroguanine and a water molecule i.e. 8NO(2)G(-) + H(2)O can be formed according to one reaction mechanism while there are two possible reaction mechanisms for the formation of the oxo-product complex involving 8-oxoguanine and anion of the NO(2) group i.e. 8OG + NO(2)(-). The calculated relative stabilities of the PC, barrier energies of the reactions and the corresponding enthalpy changes suggest that formation of the complex 8OG + NO(2)(-) would be somewhat preferred over that of the complex 8NO(2)G(-) + H(2)O. The possible biological implications of this result are discussed.     

Investigation of solution‐grown,chain‐folded lamellar crystals of the even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12

Chain‐folded lamellar crystals of the ten even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy, both imaging and diffraction. Sedimented mats were examined using X‐ray diffraction. The solution‐grown crystals are lath‐shaped lamellae and diffraction from these crystals, at room temperature, reveals that three crystalline forms are present in differing ratios. The crystals are composed of chain‐folded, hydrogen‐bonded sheets, the linear hydrogen bonds within which generate a progressive shear of the chains (p‐sheets). The sheets are found to stack in two different ways. Some p‐sheets stack with a progressive shear, to form the “α_p structure”; others sheets stack with an alternate stagger, to form the “β_p structure”. Both the α_p and β_p structures give two strong diffraction signals at spacings of 0.44 nm and 0.37 nm; these signals represent a projected intrasheet interchain distance (actual value 0.48 nm) and the intersheet spacing, respectively. Preparations of nylons 6 6, 8 6, 8 8, 12 6, and 12 8 consisted almost entirely of α_p‐structure material, with only a trace of β_p‐structure material being present. In contrast, nylons 10 6, 10 8, 10 10, 12 10, and 12 12 contained substantial quantities of both α_p‐ and β_p‐structure material, with α_p‐structure material always being in the majority. Preparations of nylons 10 8, 12 10, and 12 12 also showed an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudohexagonal (high temperature) structure. The melting temperature of solution‐grown lamellae of these even‐even nylons decreases with decreasing linear amide density. On heating, the strong diffraction signals (0.44 nm and 0.37 nm) gradually moved together and merge at the Brill temperature to form a single diffraction signal (0.42 nm), characteristic of the pseudohexagonal structure. This single diffraction signal remained until melting. For nylons 6 6, 8 6, 8 8, 10 6, and 12 6, the Brill temperatures were substantially below the respective melting temperatures and the single 0.42 nm diffraction signal was stable over temperature ranges of 14 °C to 56 °C, depending on the nylon. Conversely, nylons 10 8, 10 10, 12 8, 12 10, and 12 12 had coincident melting and extrapolated Brill temperatures. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1209–1221, 2000     

The supramolecular helical architecture of 8-oxoinosine and 8-oxoguanosine derivatives

The 8-oxoguanosine derivative 1 and the 8-oxoinosine derivative 2 b, with appropriate substituents on their ribose moieties, form hexagonal lyotropic mesophases in hydrocarbon solvents. Small-angle X-ray scattering analysis of a film of 1 and of the mesophase of 2 b, and NMR and CD spectra of isotropic solutions of 2 b, indicate that in both cases the supramolecular structures adopted are continuous helices formed by a hydrogen-bond network between the heterocyclic bases. Notably, while derivative 2 b, which bears large substituents on its ribose moiety, undergoes self-assembly and mesophase formation, oxoinosine 2 a, with only decanoyl groups on its ribose moiety, does not. This may be ascribed to the reduced amphiphilic properties of the latter and the absence of aromatic groups.     

Lewis Acid Mediated Tandem Reaction of Propargylic Alcohols to Tetrazoles Involving CO‐ and CC‐Bond Cleavage Reactions and a CN‐Bond Formation

A novel and direct synthesis of 1‐aryl‐5‐arylvinyl‐tetrazoles from easily prepared propargylic alcohols and TMSN₃ is developed in the presence of TMSCl under mild conditions (TMS=trimethylsilyl). The process involves an allenylazide intermediate, followed by a C?C‐bond cleavage and C?N‐bond formation to afford the desired products. Moreover, this method offers a good functional‐group applicability and can be scaled‐up to grams (yield up to 85 %).     

Complexes of Diquat with Dibenzo-24-Crown-8

The complexation between dibenzo‐24‐crown‐8 ( 1 ) and diquat ( 2 ) was investigated in detail by NMR, MS and X‐ray analysis. It was found that dibenzo‐24‐crown‐8 and diquat formed a 1:1 complex 1 · 2 in acetone with K_a=2.0×10² L·mol^?1, but, as shown by X‐ray analysis, a crystalline 2:1 host:guest inclusion complex 1 ₂· 2 was isolated, in which a single molecule of diquat is enclosed in the concave cavity provided by two dibenzo‐24‐crown‐8 host molecules. Both results are different from the previously assumed stoichiometry of the complexation between dibenzo‐24‐crown‐8 and diquat. This result enriches the range of host‐guest complexes based on dibenzo‐24‐ crown‐8 and provides new opportunities for developing more complicated structures and chemosensors for diquat.     

Selenoketene (H2CCSe)+• and selenoketyl cumulene (HCCSe)+ ions and their neutral counterparts: a tandem mass spectrometric and computational study

Dissociative electron ionization (70eV) of selenophene (C₄H₄Se) generates m/z 106 ions of composition [H₂, C₂, ⁸⁰Se]^+? and m/z 105 ions of [H, C₂, ⁸⁰Se]⁺. From tandem mass spectrometric experiments, Density Functional Theory (DFT) and ab initio calculations, it is concluded that these ions have the structure of selenoketene H₂C?C?Se^+? (1a^+? )and selenoketyl HC?C?Se⁺ (2a⁺) ions respectively. The calculations predict that selenoketene ion 1a^+? is separated by high energy barriers from its isomers selenirene (H e)^+? 1b^+?, ethyne selenol (HCCSeH)^+? 1c^+?, (CCHSeH)^+? 1d^+? and (CCSeH₂)^+? 1e^+?. The selenoketyl ion 2a⁺ is separated by high barriers from its isomers (CCHSe)⁺ 2b⁺, and (CCSeH)⁺ 2c⁺. Neutralization‐reionization mass spectra (NRMS) of these structurally characterized ions confirmed that the corresponding neutral analogues, selenoketene H₂CCSe 1a and selenoketyl radical HCCSe 2a^? are stable in the rarefied gas phase. The relative, dissociation, and isomerization energies for selenoketene and selenoketyl ions and neutrals studied at B3LYP/6–31G(d,p) and G2/G2(MP2) levels are used to support and interpret the experimental results. Copyright © 2005 John Wiley & Sons, Ltd.     

Capillary electrophoresis with end-column amperometric detection of urinary 8-hydroxy-2'-deoxyguanosine

Urinary 8-hydroxy-2'-deoxyguanosine (8OHdG) is an excellent marker of oxidative DNA damage. Until now, urinary 8OHdG has been measured by high-performance liquid chromatography with electrochemical detection. A simple and sensitive method for the analysis of urinary 8OHdG by capillary electrophoresis with end-column amperometric detection has been developed in our laboratory. A single-step solid-phase extraction procedure was optimized and used for extracting 8OHdG from human urine. To improve the sensitivity of this method, a new focusing technique based on a dynamic pH junction was used. The limit of detection was 20 nM (signal-to-noise ratio S/N = 3), the linear range was 50 nM-10 microM, and the correlation coefficient was better than 0.999. The relative standard deviation (RSD) was found to be 0.57% for migration time, and 4.79% for peak current. To show the usefulness of the method, the urinary concentration of 8OHdG in nine healthy persons and ten cancer patients was determined. The urinary concentration of 8OHdG in cancer patients was significantly higher than that in healthy persons.     

Nickel‐Catalyzed Enantioselective CC Bond Formation through CO Cleavage in Aryl Esters

We report the first enantioselective C? C bond formation through C? O bond cleavage using aryl ester counterparts. This method is characterized by its wide substrate scope and results in the formation of quaternary stereogenic centers with high yields and asymmetric induction.     

Metal‐Mediated Production of Isocyanates,R3ENCO from Dinitrogen,Carbon Dioxide,and R3ECl

A highly efficient and versatile chemical cycle has been developed for the production of isocyanates through the molecular fixation of N₂, CO₂ and R₃ECl (E=C, Si, and Ge). Key steps include a ‘one‐pot’ photolytic N? N bond cleavage of a Group 6 dinuclear dinitrogen complex with in situ trapping by R₃ECl to provide a metal terminal imido complex that can engage in simultaneous nitrene‐group transfer and oxygen‐atom transfer to generate an intermediate metal terminal oxo complex with release of the isocyanate product. Reaction of the oxo complex with additional equivalents of R₃ECl regenerates a metal dichloride that is the precursor for dinuclear dinitrogen starting material.     

Verbindungen mit Schichtstrukturen in den Systemen CuGa5S8/CuIn5S8 und AgGa5S8/AgIn5S8

Compounds with Layered Structures in the Systems CuGa₅S₈/CuIn₅S₈ and AgGa₅S₈/AgIn₅S₈ The title systems have been investigated by single crystal and powder X‐ray diffraction methods on quenched samples. In the system AgGa_xIn_5–xS₈ spinel type phases are formed up to x < 2. A compound crystallising with a hexagonal layered structure is obtained for 2 < x ≤ 3. The crystal structure of this layered phase has been solved on a single crystal of composition AgGa₃In₂S₈: space group P6₃mc, Z = 2, a = 380.80 and c = 3076.4 pm. The structure is isotypic to the Zn₂In₂S₅ (II a) type. The sample AgGa₄InS₈ crystallises in a Wurtzite like structure with a = 377.25 and c = 616.1 pm. In the system CuGa_xIn_5–xS₈ a new compound with layered structure has been detected for 1 ≤ x ≤ 2 which crystallises hexagonally with a = 380.28 and c = 3073.4 pm (x = 2). For the spinel CuIn₅S₈ an exchange of In by Ga is not detected.     

A Comparative Study of 8‐Hydroxyquinoline and 8‐Hydroxyquinoline‐5‐sulfonic Acid for Antimony(III) Determination by AdSV. Substituent Effect on Sensitivity II

A sensitive and selective method for the determination of Sb³⁺ based on the formation of its complexes with 8‐hydroxyquinoline (HQ) and 8‐hydroxyquinoline‐5‐sulfonic acid (HQS) is proposed. The best analytical conditions are: pH 5.4 and 2.2 for HQ and HQS, respectively; C_HQ from 15.0 to 25.0 µmol L^?1 and C_HQS from 70.0 to 200.0 µmol L^?1. The detection limits are 100.0 and 14.0 ng L^?1 (t_acc=30 s) for Sb³⁺ with HQ and HQS, respectively. The method using HQS as ligand has a 2.2‐fold higher sensitivity than that with HQ and the former was chosen for Sb³⁺ determination.     

Resolution of 8-aminonaphthalene-1,3,6-trisulfonic acid-labeled glucose oligomers in polyacrylamide gel electrophoresis at low gel concentration

A discontinuous Tris-Cl/acetate (OAc) buffer system, unprecedently containing OAc as the trailing constituent, and operative in polyacrylamide gel electrophoresis (PAGE) at low polyacrylamide concentration (T = 4.8%) is described in the paper. The characteristics of the electrophoretic system are illustrated by the resolution of fluorescent 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS)-labeled malto-oligosaccharides and dextran homopolymers. In this buffer system, the resolving phase is constituted by Tris-OAc behind a moving boundary formed between the leading chloride ion of Tris-HCl gel buffer and the trailing OAc ion provided by a catholyte of NH(4)OAc. In contrast with the results obtained with Tris-CI/glycinate buffer commonly used in electrophoresis, or with Tris-CI/borate, the best resolution of the glucose oligomers containing 1-4 glucose units in Tris-OAc, pH 8.8, ionic strength of 0.08, was obtained at 4.8% polyacrylamide concentration, using 0.5 M NH(4)OAc, pH 9.5 as the catholyte. Under those conditions, the ANTS-glucose oligomers were separated with mobilities decreasing from glucose to maltohexaose. The linear Ferguson plots (log relative mobility, R(f), vs.%T) of the glucose oligomers show that the surface net charge of those oligomers is inversely related to their sizes, given by the slopes, K(R), of the plots. The molecular weight of the oligomers is directly but nonlinearly related to K(R). The novel electrophoretic system illustrated here for separation of short ANTS-saccharides can be potentially applied to the resolution of other biomolecules such as rapidly migrating DNA, peptides or proteins.     

Monitoring of 8-oxo-7,8-dihydro-2'-deoxyguanosine in urine by high-performance liquid chromatography after pre-column derivatization with glyoxal reagents

A new, simple and sensitive pre-column fluorescence derivatization high-performance liquid chromatographic method for the determination of the oxidative DNA stress marker, 8-oxo-7,8-dihydro-2'-deoxyguanosine, was developed. Solid-phase extraction using an Oasis HLB cartridge avoided troublesome sample preparation steps, interference from charged species and frequent and essential electrode maintenance in electrochemical procedures. 8-Oxo-7,8-dihydro-2'-deoxyguanosine and other guanine compounds were selectively derivatized with glyoxal reagents (phenylglyoxal, 3,4-methylenedioxyglyoxal, 2-naphtylglyoxal and 6-methoxynaphthylglyoxal) at 40-60 degrees C. Derivatization with 6-methoxynaphthylglyoxal at 40 degrees C for 30 min gave the strongest fluorescence product. The fluorescence derivatives from reaction with 6-methoxynaphthylglyoxal were separated on a Capcell Pak C18 SG 120A column (4.6 mm i.d. x 150 mm, 5 microm) with acetonitrile-5 mM phosphate buffer (pH 6.0; 3:7, v/v) as mobile phase. The detection wavelength of the fluorescence derivative of 8-oxo-7,8-dihydro-2'-deoxyguanosine was lambda(ex) 400 nm and lambda(em) 510 nm. The detection limit of 8-oxo-7,8-dihydro-2'-deoxyguanosine was 1 ng/mL using 50 mL of urine. The calibration graphs were linear up to 30 microg/mL for 8-oxo-7,8-dihydro-2'-deoxyguanosine. The relative standard deviation of 20 ng/mL of 8-oxo-7,8-dihydro-2'-deoxyguanosine was 7.0%. The proposed method was compared with the enzymatic ELISA 8-oxo-7,8-dihydro-2'-deoxyguanosine analysis method (8-OH-dG Check, JaICA, Shizuoka, Japan). The correlation coefficient was 0.79 (n = 20) and y = 0.85x + 5.34. The proposed method was applied to the monitoring of 8-oxo-7,8-dihydro-2'-deoxyguanosine in urine from male heavy smokers.     

The First Lutetacyclopentadienes: Synthesis,Structure, and Diversified Insertion/CH Activation Reactivity

The first well‐defined lutetacyclopentadienes are synthesised from pentamethylcyclopentadienyl lithium (Cp*Li), 1,4‐dilithio‐1,3‐butadienes, and LuCl₃. The lutetacyclopentadiene shows excellent reactivity towards some small molecules, such as pivalaldehyde, Se, carbon dioxide, and isonitrile to efficiently construct 3‐, 5‐, 7‐, 8‐, and 9‐membered rare‐earth metallacycles. Both monoinsertion and double‐insertion of two Lu?C bonds are observed. Specially, the reaction between lutetacyclopentadiene and isonitrile afforded [3,5,5]‐fused metallacycles. The distinguished reactivity can be attributed to the highly ionic character and the cooperative reactivity of two Lu?C bonds.