摘要:

Fast Atom Bombardment mass spectrometry is shown to be a useful tool in the investigation of strongly hydrogen bonded complexes of imidazole with various electron donors.

ISSN:0008-4042    

DOI:10.1139/v86-211

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The properties and reactivity of the bis(imidazole)bis-(dimethylglyoximato)iron(II) complex have been studied based on spectroelectrochemistry, cyclic voltammetry, and stopped-flow kinetics in aqueous solution. The autoxidation reaction was found to be inhibited by the imidazole ligand in excess but susceptible to copper(II) catalysis. In this case a mechanism has been proposed, consisting of a rapid electron transfer followed by the reoxidation of the resulting Cu(I) species by O2.

ISSN:0008-4042    

DOI:10.1139/v86-212

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Since Monte-Carlo studies on freely oriented dipoles suggest that at zero external field the dipoles are oriented preferentially in-plane in ordered configurations, an attempt is made here to incorporate dipole in-plane interactions in the multi-state model of the inner layer. It is found that the predictions of the model become unsatisfactory as ordered structures are taken into consideration. Polarization catastrophe and concentration dependent adsorption maxima are the main problems. Analysis of the polarization behaviour of the inner layer at the adsorption maximum of an adsorbate suggests that in aqueous interfaces and possibly in other real interfaces the dipole in-plane interactions should be quite weak. This is attributed to rotational barriers leading to an almost random distribution of the dipoles in the monolayer.

ISSN:0008-4042    

DOI:10.1139/v86-213

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The photolysis of α-methoxy acetophenones1a–1eadsorbed on silica gel show a significant deviation from the course of reaction in methanol. The results are discussed in terms of conformational control and restricted movement of the radical through adsorption on silica gel. Factors affecting the efficiency of modification of photochemical reactivity on silica gel surface have been examined.

ISSN:0008-4042    

DOI:10.1139/v86-214

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The four diones derived from benzo[a]pyrene oxidation have been characterized by high-field nuclear magnetic resonance techniques including 2-D COSY and selective nuclear Overhauser enhancement. All the proton chemical shifts for these four quinones have been uneqivocally assigned. The direct photoxidation of benzo[a]pyrene gives a product distribution very similar to the TPP photosensitized oxygenation, suggesting singlet oxygen is involved in the former. A major product, which was characterized as the 6-seco derivative6and not previously reported, was detected in the singlet oxygen reaction. The presence of this product suggests a possible mechanism for quinone formation in the singlet oxygen reaction. One-electron oxidations of benzo[a]pyrene were carried out using tris(p-bromophenyl)aminium hexachloroantimonate and quenching of the radical cation with superoxide or water. The product distribution in this case was quite different from that obtained in the direct photooxidation.

ISSN:0008-4042    

DOI:10.1139/v86-215

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The title compounds were synthesized by the reactions of NaNC4H2Me2with the appropriate complex metal chloride in THF. The crystal structures have been determined from X-ray data measured by counter methods. (η5-C5H5)2Zr(η1-NC4H2Me2)2crystallizes in the orthorhombic space group Pbca with cell dimensionsa = 15.797(6),b = 14.327(5),c = 16.417(6) Å, and ρcalcd = 1.46 g cm−3forZ = 8. Full-matrix least-squares refinement led to a finalRfactor of 0.041 based on 536 observed reflections. Zr(η1-NC4H2Me2)4belongs to the monoclinic space groupP21/nwitha = 14.065(5),b = 10.717(4),c = 15.733(6) Å, β = 90.61(4)°, and ρcalcd = 1.31 g cm−3forZ = 4. A finalRvalue of 0.029 resulted from the refinement on the basis of 2649 observed reflections. The dicyclopentadienyl derivative exhibits two features of importance. The Zr—N—centroid angles are 159 and 168°, and the Zr—N bond lengths are 2.24(2) Å. In the homoleptic complex the corresponding values are 164–169° and 2.069(3)–2.090(3) Å. In both cases the bonding parameters are indicative of a substantial amount of π overlap between the zirconium atom and the pyrrolyl nitrogen atom.

ISSN:0008-4042    

DOI:10.1139/v86-216

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

An isolate ofFusariumroseum"Graminearum" obtained from overwintered oats in Alaska produced toxic cultures when grown on rice. The toxic principle called fusarochromanone isolated from these cultures reproduced the signs of tibial dyschondroplasia in poultry and also reduced hatchability of fertile eggs. Spectroscopic data (nmr, ir, and ms) indicated the mycotoxin to be a chromanone derivative. The chromanone ring structure was also confirmed by single crystal X-ray.

ISSN:0008-4042    

DOI:10.1139/v86-217

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Methylene chloride extracts of the bryozoanFlustrafoliaceaeshow strong antimicrobial activity. Chemical investigation of the metabolites has led to the identification of a series of new bromoalkaloids belonging to the physostigmine class, which are responsible for this activity.

ISSN:0008-4042    

DOI:10.1139/v86-218

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Lanthanide induced shifts by Lu3+, Yb3+, Tm3+, Er3+, Ho3+, and Dy3+in NAcAsp (0.14 Min D2O, pH 5) are observed for ten magnetic sites (1H and13C). The averaged binding constant for 1:1 complexes is 72 M−1(for chloride solutions of ca. 0.05 M). Determination of the pseudo-contact geometrical factors (under axial symmetry approximation) requires taking into account a contact term and discarding the Tm3+results. Data from the Asp residue are in agreement with 6 structures of this residue such that chelation occurs through the two carboxylates. Oβ−… Cα′ length seems to be the main factor while COOα−orientation is a minor one. The entire set of results is consistent with only three structures where the nitrogen atom is far from the carboxylates, and the Cα—N rotamers have extended conformations. Three oxygen atoms (two from the COOβ−group) appear to be involved in the chelation. However, the data do not exclude another minor conformational species.

ISSN:0008-4042    

DOI:10.1139/v86-219

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Comprehensive equations for the thermodynamic properties of aqueous NaI, CsF, CsCl, CsI, NaIO3, KIO3, CsIO3, KClO4, and HCl are generated by combining the heat capacity and density measurements reported by the first author with literature data for the enthalpy and Gibbs energy, or activity, as a function of molality at 298 K. The composition dependence is represented by the equations of Pitzer, which combine a theoretical form and Debye–Hückel terms with empirically evaluated parameters for short-range ion interactions. Temperature dependencies are represented by simple empirical equations, which should be reliable to 413 K or a little higher.

ISSN:0008-4042    

DOI:10.1139/v86-220

出版商:NRC Research Press    

年代:1986

数据来源: NRC