摘要:

The2H nuclear magnetic resonance spectrum of mollisin from cultures of the fungusMollisiacaesiasupplemented with [2-2H3]acetate was consistent with biosynthesis of the metabolite via a single-chain polyketide. The presumption that chain scission accompanies dichlorination of a reactive methylene group in such a polyketide was supported by the detection of chloroperoxidase activity with monochlorodimedone as a substrate, and failure to detect chlorinating activity when the substrate was acetoacetyl coenzyme A. However, a decisive choice between single-chain and two-chain polyketide intermediates cannot be made with information provided by the techniques used so far.Keywords: biosynthesis, mollisin, deuterium labelling and NMR; deuterium labelling and NMR, mollisin biosynthesis; labeling of mollisin by deuterium, NMR analysis; mollisin biosynthesis, deuterium, labeling and NMR; NMR deuterium, mollisin biosynthesis.

ISSN:0008-4042    

DOI:10.1139/v90-001

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The behavior of tin and thallium has been studied in water–HF mixtures. The formation of thallium fluoride complexes was not observed. Tin Sn2+forms two complexes, SnF2and SnF+, in mixtures containing less than 60% in HF. SnF2is strong enough to prevent the formation of chloride complexes. SnF62−and SnF5−have been determined for Sn4+in the same solutions. The relatively high strength of the tin fluoride complexes is reflected in theR0(M) function. In fact, all the metals studied, Sn, Cd, Pb, and Tl, are less solvated in water–HF mixtures than in water, except for the case where the fluoride complex is strong, i.e., tin. HF2−seems to be the complexing species at high HF concentrations.Keywords: polarography, thallium, tin, cadmium, lead, hydrogen fluoride. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v90-002

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The isolation and characterization of a novel triterpene glycoside from the sea cucumberCucumariafrondosa, collected from the Gulf of St. Lawrence, are described. Physico-chemical data obtained on the underivatized saponin are presented in support of structure1for frondoside A. The structure is characterized by the presence of a branched oligosaccharidic chain composed of five units. The holostane-type aglycone features an endocyclic double bond at position C-7,8 and a β-acetoxy group at C-16.Keywords: triterpene glycoside;Cucumariafrondosasaponins; saponins, triterpene from holothurians; holothurian saponins; echinoderm triterpene saponins.

ISSN:0008-4042    

DOI:10.1139/v90-003

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The total sporidesmolide fraction from cultures ofPithomyceschartarumcontains at least five cyclodepsipeptides. Four of these are known compounds but the fifth, cyclo-2-oxyisovaleryl-D-alloisoleucyl-D-leucyl-2-oxyisocaproyl-L-valyl-L-N-methylleucyl, appears to be new. Its isolation, physical properties, and structure determination are reported.Keywords:Pithomyceschartarum, sporidesmolide II, sporidesmolide V, sporidesmolic acid D.

ISSN:0008-4042    

DOI:10.1139/v90-004

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Isodomoic acids E and F, two new geometrical isomers of the neurotoxin domoic acid, have been found to occur with domoic acid and isodomoic acid D in extracts of toxic mussels. The entire set of geometrical isomers can be prepared in the laboratory by photolysis.Keywords: amnesic shellfish toxin, domoic acid, isodomoic acid, neurotoxin.

ISSN:0008-4042    

DOI:10.1139/v90-005

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The charge densities of acrylamide/acrylate copolymers can be determined using tensammetry. The tensammograms were run using 20 ppm solutions of polymer in 0.1 Mtetraethylammonium chloride. A standard curve of desorption peak height versus mol% anionicity was useful in the range 10–50%. A second standard curve of the potential at which the capacitive current measured 1 μA versus mol% anionicity allowed the determination of charge density in the range 0–15%.Keywords: tensammetry, polyaerylamide, charge density, tetraethylammonium, desortion peaks.

ISSN:0008-4042    

DOI:10.1139/v90-006

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The oxidation of lactic acid by chromic acid was studied at high concentrations of HClO4, HNO3, and H2SO4. It was observed that the reaction rate depends not only on the acidity of the medium, but also on the nature of the mineral acid. The use of the Bunnett and Bunnett–Olsen criteria and the excess acidity concept allows us to propose a reaction mechanism of the A-2 type, the rate-determining step being a bimolecular process in which water participates as a nucleophile. The enthalpy and entropy of activation were determined; the decrease of the magnitude of these parameters when the acidity of the medium was increased suggests the existence of a compensation effect.Keywords: chromic acid, oxidation, lactic acid, acidic media.

ISSN:0008-4042    

DOI:10.1139/v90-007

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Ternary interdiffusion coefficients have been measured for ten compositions of the system sodium dodecylsulfate (NaDS) + 1-butanol (BuOH) + water at 25 °C. The diffusivity of BuOH in this system is lower than in pure water because about one half of the alcohol is solubilized in the slowly-diffusing NaDS micelles. Yet, surprisingly, diffusion of the NaDS component transports only minor amounts of BuOH. Diffusion of the BuOH component, however, produces a substantial coupled flow of NaDS. Although added BuOH increases the solution viscosity and the size of the micelles, the diffusivity of the NaDS component does not change significantly. The Harned restricted diffusion method for the determination of electrolyte diffusivities is extended to electrolyte + nonelectrolyte solutes.Keywords: micelles, ionic; solubilization; diffusion, coupled.

ISSN:0008-4042    

DOI:10.1139/v90-008

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Polymer compounds including both antimony and molybdenum were formed by mixing freshly prepared solutions of antimonic and molybdic acid. These acids were formed through an ion exchange process. When antimony is in excess, molybdenum is included in the high polymers having the ccp structure of β antimonic acid. When molybdic acid is in excess in the starting mixture, molybdenum-rich polymers with a larger molecular weight than molybdic acid were formed. In GPC experiments the behaviour of the compounds is related to their Mo and Sb content. The elution volume is only related to the molecular weight of the compound when Sb is the main component and imposes its structure.Keywords: molybdoantimonic acids, inorganic polymers, ultracentrifugation, GPC.

ISSN:0008-4042    

DOI:10.1139/v90-009

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The bimetallic complexes (η6-1,4-C6H4XFp)Cr(CO)3(where X = H, Me, Cl, or OMe; Fp = (η5-C5H5)Fe(CO)2) were synthesized in 32–80% yields by the reaction of NaFp with (η6-1,4-C6H4XF)Cr(CO)3(where X = H, Me, or OMe) or (η6-1,4-C6H4Cl2)Cr(CO)3. They were fully characterized by conventional spectroscopic techniques. In these complexes, the arenes are σ bound to the Fp group and π bound to the Cr(CO)3group. The13C NMR data suggest that a synergic substituent–arene–Fp π interaction is occurring. Cyclic voltammetric studies of these complexes in CH2Cl2show that they are oxidized reversibly to give stable radical cations, and confirm that the Fp substituents are strong net electron donors to the Cr(CO)3fragments.Keywords: bimetallic, iron, chromium, arene, oxidation.

ISSN:0008-4042    

DOI:10.1139/v90-010

出版商:NRC Research Press    

年代:1990

数据来源: NRC