Reactions of 9-substituted guanines with bromomalondialdehyde in aqueous solution predominantly yield glyoxal-derived adducts

Reactions of 9-ethylguanine, 2'-deoxyguanosine and guanosine with bromomalondialdehyde in aqueous buffers over a wide pH-range were studied. The main products were isolated and characterized by (1)H and (13)C NMR and mass spectroscopy. The final products formed under acidic and basic conditions were different, but they shared the common feature of being derived from glyoxal. Among the 1 : 1 adducts, 1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (6) predominated at pH < 6 and N(2)-carboxymethylguanine adduct (10a,b) at pH > 7. In addition to these, an N(2)-(4,5-dihydroxy-1,3-dioxolan-2-yl)methylene adduct (11a,b) and an N(2)-carboxymethyl-1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (12) were obtained at pH 10. The results of kinetic experiments suggest that bromomalondialdehyde is significantly decomposed to formic acid and glycolaldehyde under the conditions required to obtain guanine adducts. Glycolaldehyde is oxidized to glyoxal, which then modifies the guanine base more readily than bromomalondialdehyde. Besides the glyoxal-derived adducts, 1,N(2)-ethenoguanine (5a-c) and N(2),3-ethenoguanine adducts (4a-c) were formed as minor products, and a transient accumulation of two unstable intermediates, tentatively identified as 1,N(2)-(1,2,2,3-tetrahydroxypropano)(8) and 1,N(2)-(2-formyl-1,2,3-trihydroxypropano)(9) adducts, was observed.     

Muon spin rotation in superconductors

By means of the muon spin rotation technique (⁺SR), the temperature dependence of the magnetic field inside the normal-conducting domains of high-purity tantalum crystals in the intermediate state has been measured in the temperature range 2.36K+SR. Possible applications of these findings to the study of long-range diffusion of positive muons at low temperatures are indicated.     

On the theory of diffusion of light interstitials in metals

Using a nonlinear-screening approach the potential energy of positively charged light interstitials in Cu and lattice distortions around these particles have been determined numerically. The calculations predict a marked isotope effect for the lattice distortions around positive muons and protons at octahedral interstitial sites. They indicate that in Cu the diffusion mechanisms for positive muons and for hydrogen isotopes may be different.     

Validated capillary electrophoretic method for the analysis of ivermectin in plasma after intragastric administration in pigs and horses

A capillary electrophoretic (CE) method has been developed for the determination of ivermectin (CAS 70288-86-7), a new generation drug with antiparasitic activity, in pig and horse plasma. The method was statistically validated for its linearity, accuracy, precision and selectivity. The linear range was from 1 to 30 ng mL(-1) with correlation coefficients greater than 0.999. The limit of detection was 0.3 ng mL(-1), while the quantitative limit was 1 ng mL(-1), using a 0.5 mL sample size. The validated procedure was used to determination of pharmacokinetic parameters of ivermectin after ingestion of 0.1 mg for pigs and 0.2 mg dose per kg body weight for horses, respectively. Studies were performed on a group of eight pigs and six horses. There were no significant differences between pigs and horses in any of the estimated pharmacokinetic parameters.     

Carbene-carbene rearrangements as a route to 1,5-dihydropentalene

1,5-Dihydropentalene (4) is formed as the main product on treatment of trans-1,2-bis(2,2-dibromocyclo-propyl)ethene 3 with methyllithium at −40°. In addition the reaction affords 1- and 2-propadienylcyclopentadienes (5a) and (5b), and trans-1,2,4,6,7-octapentaene (6), new C₈H₈ isomers. Diels-Alder adducts of 4, 5a and 5b were obt in the reaction with perfluorobut-2-yne. The formation of 1,5-dihydropentalene 4 is explained by a double ring expansion sequence involving consecutive carbene-carbene rearrangements with 1,3-carbon and subsequent 1,2-hydrogen shifts, supported by the reaction of double labelled (¹³C-depleted) 3. From readily available 3 at low temperatures formation and fusion of two 5-membered rings are achieved in one step.     

Attempts for the chromatographic separation of D- and L-penicillamine enantiomers

Summary The chromatographic characteristics of the thiazolidine carboxylic acids formed by the reaction of D- and L-penicillamine with various substituted benzaldehydes and heterocyclic aldehydes have been studied on Chiralplate layers. It has been found that the nature and position of substituents strongly affect the R_F values and resolution factors (R_S) of the isomers. An unambiguous relationship has been established between the R_S values of the L- and D-enantiomers and the dipole moment of the aldehydes. The transformation to thiazolidine carboxylic acids with benzaldehyde and substituted benzaldehydes, however, is not complete, thus the reaction with formaldehyde is still more suitable for quantitative determination of penicillamine isomers.     

Ammonium hydroxide detoxification of spruce acid hydrolysates

When dilute-acid hydrolysates from spruce are fermented to produce ethanol, detoxification is required to make the hydrolysates fermentable at reasonable rates. Treatment with alkali, usually by overliming, is one of the most efficient approaches. Several nutrients, such as ammonium and phosphate, are added to the hydrolysates prior to fermentation. We investigated the use of NH₄OH for simultaneous detoxification and addition of nitrogen source. Treatment with NH₄OH compared favorably with Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, and NaOH to improve fermentability using Saccharomyces cerevisiae. Analysis of monosaccharides, furan aldehydes, phenols, and aliphatic acids was performed after the different treatments. The NH₄OH treatments, performed at pH 10.0, resulted in a substantial decrease in the concentrations of furfural and hydroxymethylfurfural. Under the conditions studied, NH₄OH treatments gave better results than Ca(OH)₂ treatments. The addition of an extra nitrogen source in the form of NH₄Cl at pH 5.5 did not result in any improvement in fermentability that was comparable to NH₄OH treatments at alkaline conditions. The addition of CaCl₂ or NH₄Cl at pH 5.5 after treatment with NH₄OH or Ca(OH)₂ resulted in poorer fermentability, and the negative effects were attributed to salt stress. The results strongly suggest that the highly positive effects of NH₄OH treatments are owing to chemical conversions rather than stimulation of the yeast cells by ammonium ions during the fermentation.     

Neue Koordinationsverbindungen aus Triorganylzinn(IV)-dimesylamiden und Neutralliganden: Einkern- und Mehrkernkomplexe mit molekularer oder ionischer Kristallstruktur

Polysulfonylamines. CII. New Coordination Compounds Derived from Triorganyltin(IV) Dimesylamides and Uncharged Ligands: Mononuclear and Polynuclear Complexes with Molecular or Ionic Crystal Structures The purpose of this report is to draw attention to the remarkable versatility of the dimesylamides R₃SnA [A^– = (MeSO₂)₂N^–; R = Me ( 1 a ) or Ph ( 1 b )] as precursors for pentacoordinate triorganyltin(IV) complexes belonging to four distinct structural types. Representative complexes were prepared by treating 1 a or 1 b in the appropriate molar ratios with unidentate thiourea or urea-type ligands or with the bidentate ligand [Ph₂P(O)CH₂]₂ (DPPOE). The following compounds were characterized by X-ray analysis: [Me₃Sn(A)(thiourea)] ( 2 a ; monoclinic, space group P2₁/n), [Ph₃Sn(A)(tetramethylthiourea)] ( 2 b ; monoclinic, P2₁, two independent formula units), [Me₃Sn(1-methylurea)₂]⁺ · A^– ( 3 a ; monoclinic, P2₁/c), [Ph₃Sn(1,1-dimethylurea)₂]⁺ · A^– ( 3 c ; triclinic, P1), [{Ph₃Sn(A)}₂(μ-dppoe)] ( 4 ; triclinic, P1), [Ph₃Sn(μ-dppoe)]_nⁿ⁺ · n A^– · n MeCN ( 5 ; monoclinic, P2₁/c). The lattices of 2 a , 2 b and 4 contain discrete uncharged formula units which are mononuclear for 2 a and 2 b or dinuclear for 4 , whereas 3 a , 3 c and 5 have ionic structures featuring mononuclear cations for 3 a and 3 c or an infinite linear-polymeric cation for 5 . In all the structures, the tin atoms adopt trigonal-bipyramidal geometries, the apical positions being occupied in 2 a and 2 b by the S atom of the thiourea and one O atom of A^–, in 3 a and 3 c by the O atoms of two urea-type ligands, in 4 by an O atom of the bridging DPPOE molecule and one O atom of A^–, and in 5 by two phosphoryl O atoms from different bridging DPPOE ligands. In the structures of 2 a , 3 a and 3 c , the (thio)urea NH functions are connected to A^– via intermolecular or interionic N–H … O and N–H … N hydrogen bonds. Crystals of [{Me₃Sn(bipyH⁺ … A^–)}₂(μ-bipy)]²⁺ · 2 A^– ( 6 ; monoclinic, C2/c) formed adventitiously in a reaction mixture containing 1 a and 4,4′-bipyridine. The rod-like supramolecular cation of 6 (length ca. 4 nm) is built up from two Me₃Sn⁺ units bridged through bipy and unidentally coordinated by a monoprotonated bipy (= bipyH⁺), resulting in a trigonal-bipyramidal geometry around tin (N atoms apical); each of the terminal bipyH⁺ ligands forms an ⁺N–H … N^– hydrogen bond with one A^–.     

Selectivity of 1-O-Propargyl-d-Mannose Preparations

Thanks to their ability to bind to specific biological receptors, mannosylated structures are examined in biomedical applications. One of the most common ways of linking a functional moiety to a structure is to use an azide-alkyne click reaction. Therefore, it is necessary to prepare and isolate a propargylated mannose derivative of high purity to maintain its bioactivity. Three known preparations of propargyl-α-mannopyranoside were revisited, and products were analysed by NMR spectroscopy. The preparations were shown to yield by-products that have not been described in the literature yet. Our experiments showed that one-step procedures could not provide pure propargyl-α-mannopyranoside, while a three-step procedure yielded the desired compound of high purity.     

Iron-Mediated Amination of Hydrocarbons in the Gas Phase

FeNH⁺ is chosen as a model system to probe the transition-metal-mediated transfer of imine groups in the gas phase by mass-spectrometric means. Ab initio calculations at the MR-ACPF level predict FeNH⁺ to have a linear sextet ground state (⁶Σ⁺); a bent quartet state (⁴A′) and a linear doublet state (²Δ) are higher in energy by 0.14 eV and 0.51 eV, respectively. The bond-dissociation energy is determined to D(Fe⁺−NH)=69±2 kcal mol⁻¹ using ion-molecule reactions. Charge-stripping experiments combined with ab initio calculations yield an ionization energy of IE(FeNH⁺)=15.7±0.5 eV. The chemical behavior of FeNH⁺ towards oxygen, water, hydrogen, aliphatic hydrocarbons, benzene, and toluene reveals an intrinsically high reactivity of FeNH⁺. Because a transfer of the 〈NH〉 fragment to the substrate is feasible in most cases, attractive amination reactions like methane→methylamine, benzene→aniline, or toluene→benzylidenamine can be afforded by FeNH⁺.