摘要:

The intramolecular photocycloaddition of cytosine (Cyt) to 5-methoxyuracil (mo5U) in Cyt-(CH2)3-mo5Ura, a dinucleotide model compound, occurs upon irradiation with near ultraviolet light (λ > 300 nm) with the formation of an unstable cyclobutane dimer. The dimer undergoes spontaneous dark deamination with a rate constantk = 9.0 × 10−5 s−1andt1/2 = 128 min, to give a related uracil derivative.

ISSN:0008-4042    

DOI:10.1139/v88-170

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

If R = CH3, an increase in the bulk of the R groups of the amides R′CONR2provokes an increase in the complexation constants with iodine. Conversely, if R is an alkyl group (but not a CH3), the constants decrease up to a critical size for the bulkiness of R and R′. Above these limits, an abrupt increase of the constants is observed. This behaviour is rationalized in terms of a change in the point of fixation of the iodine. While the basic site of theN,N-disubstituted amides is the oxygen of the carbonyl, steric hindrance reduces the conjugation of the CO and NR2groups and hence the basicity of the oxygen; above the critical size and due to steric hindrance, the basicity of the nitrogen atom becomes similar to that of amines. This explanation is confirmed by the position of the charge transfer band and by a comparison with the formation constants of the complexes iodine–amines and iodine–α-amino carbonyl compounds. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v88-171

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Hemispherical microelectrodes prepared by electroplating of mercury on platinum microelectrodes were used in studies of fast charge transfer processes under convolutive voltammetry conditions. The algorithm used in the convolutive transformation was modified to account for spherical symmetry of diffusion. The sweep rate was varied from 0.1 to 220 V/s. Low sweep rate experiments were used to test the symmetry of the mass transport. It was found that the mass transport to (and inside) the electrodes can be described with good accuracy by the spherical symmetry diffusion. It was shown that the spherical convolution can be used to determine from cyclic voltammetric data the diffusion coefficient of a depolarizer and the number of electrons transfered to (or from) the depolarizer molecule in the electrode process.At high sweep rates the technique was found useful in studies of fast electrode reactions. The technique was tested in the determination of kinetic parameters for Cd2+reduction in aqueous solutions andp-dicyanobenzene reduction in DMF solutions. In both cases good agreement with values reported in literature was found. Properties of Hg/Pt microelectrodes were also studied using the ac impedance techniques. The ac impedance measurements were carried out at various frequencies (0.1 Hz to 100 kHz) in solutions containing 0.1 to 10−5 Mof the supporting electrolyte.

ISSN:0008-4042    

DOI:10.1139/v88-172

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Numerous studies have shown the particular usefulness of dielectric methods for observing low energy specific molecular interactions in solution. Before applying these methods, it is necessary to evaluate the non-specific interactions between species in solution (in this paper, these interactions are termed the "normal" effect of the solvent). However, in the particular case of halogenated derivatives of ethane, which can exist in solution as several conformers of different polarities, this possibility was not available. The object of our work has been to study all the procedures that might be acceptable in evaluating this solvent effect. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v88-173

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The effect of adsorbed propargyltriphenyl- and vinyltriphenylphosphonium cations on the discharge of Cd2+and Zn2+at dropping mercury electrode is studied by direct current polarographic measurements. Adsorption characteristics are determined by capacitance measurements. The size parameters of the activated complex and the surfactant particles are derived and an elucidation of the mechanism of the inhibited reaction is attempted.

ISSN:0008-4042    

DOI:10.1139/v88-174

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Treatment of 4-neopentoxyphthalonitrile with hydrogen sulfide gas yielded 1-imino-6-neopentoxy-3-thioisoindoline and 1-imino-5-neopentoxy-3-thioisoindoline, which on alkylation with iodomethane gave 1-imino-3-methylthio-6-neopentoxyiso-indolenine and 1-imino-3-methylthio-5-neopentoxyisoindolenine. The methylthioisoindolenines readily condensed at room temperature to a mixture of tetrasubstituted phthalocyanines and a series of linear open-chained purple compounds characteristic of isoindigos, while condensation at −20 °C in the presence of zinc acetate gave, in at least one experiment, 2,9,16,23-tetraneo-pentoxyphthalocyanine as a pure isomer. The low temperature formation of phthalocyanines is remarkable and the syntheses described herein provide guidelines for the synthesis of pure isomers of 2,9,16,23-tetrasubstituted phthalocyanines. The purple and red compounds are shown to have isoindigo structures rather than a ring-opened phthalocyanine structure as previously reported.

ISSN:0008-4042    

DOI:10.1139/v88-175

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The mechanism of the electrodeposition of CdSe from selenosulfite and cadmium–NTA complex has been studied by analysis of the Tafel regions of linear sweep voltammograms. The Tafel plots were linear for up to 20% of the peak height, and were used to calculate the dependence of the reduction rate on the concentration of each of the reactants. The electron transfer process was found to be first order with respect toand zero order with respect to each of the other reactants. These results are consistent with a two-step reduction ofto Se2−, followed by precipitation of CdSe. The reduction of Cd(NTA)−to cadmium metal appears to be blocked or inhibited in the presence of, resulting in CdSe films of nearly perfect stoichiometry to be deposited.

ISSN:0008-4042    

DOI:10.1139/v88-176

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The mononuclear complexes [Rh(η2-(Ph2P)3CH)2]X, [Ir(CO)(η2-(Ph2P)3CH)2]X, [Pd(η2-(Ph2P)3CH)2]X2, and [Pt(η2-(Ph2P)3CH)2]X2,are synthesized and fully characterized by31P{1H} nmr and infrared spectroscopy. The complex [Pt(η2-(Ph2P)3CH)2][BF4]2was further characterized by a single crystal X-ray diffraction study. Crystals are triclinic,a = 12.514(6) Å,b = 13.289(7) Å,c = 12.609(9) Å, α = 120.63(4)°, β = 104.51(5)°, γ = 99.45(4)°,Z = 1, space group. The structure was solved by conventional heavy atom methods and refined by full-matrix least-squares procedures toR(%) = 6.87 andRw(%) = 7.28 for 2995 reflections with. The Rh, Pd, and Pt complexes are square planar and shown by31P{1H} nmr to exist in solution as a mixture ofsynandantiisomers. The structure of [Pt(η2-(Ph2P)3CH)2][BF4]2shows theantiisomer exists in the solid state for this complex. Both thesynandantiisomers of the complex [Rh(η2-(Ph2P)3CH)2][BF4] react with HX (X = Cl, Br) to give a single octahedral Rh(III) producttrans-[RhX(H)(η2-(Ph2P)3CH)2)][BF4] characterized by31P{1H} and1H nmr.

ISSN:0008-4042    

DOI:10.1139/v88-177

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Acetone reacts with cyclohexane-1,2-dione, on refluxing in the presence of potassium carbonate, to give the crossed-aldol product, 2-hydroxy-2-acetonylcyclohexanone,2(R=CH3). Other methyl ketones react similarly with cyclohexane-1,2-dione. This is believed to be a consequence of unfavorable dipole interaction in the 1,2-dione. The product, on reaction with liquid ammonia, afforded the 5-amino-4-hydroxy-1-pyrroline derivative,5, which was reduced with lithium aluminum hydride to the 3-hydroxy-1-pyrroline,7.

ISSN:0008-4042    

DOI:10.1139/v88-178

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The structure of traversianal, a tricyclic diterpenoid fungal metabolite ofCercosporatraversiana, has been elucidated through detailed1H and13C magnetic resonance studies, including homo- and heteronuclear correlation spectra of the natural product and examination of13C-labelled material obtained by [1,2-13C2]acetate incorporation experiments. Its stereochemistry was established from a series of nuclear Overhauser effect difference spectra. The tricyclic carbon skeleton of traversianal is that of the fusicoccin/cotylenin and ophiobolane terpenes although the oxygenation pattern closely resembles the latter. Incorporation experiments with [2,2,2-2H3, 1-13C1]acetate revealed that traversianal arises by a sequence that differs substantially from that established for the fusicoccanes but rather resembles that previously shown for the ophiobolanes, in the retention of hydride at C-2, -10, and -14. However, the opposite configuration of the methyl group at C-3 suggests that the route to traversianal involves a terminaltrans-geranylgeranyl unit instead of thecisunit implicated in ophiobolin generation.

ISSN:0008-4042    

DOI:10.1139/v88-179

出版商:NRC Research Press    

年代:1988

数据来源: NRC