摘要:

Aspen that bear a certain type of black gall have a lower incidence of heartwood rot (caused by the fungusPhellinustremulae) than do nearby non-gall trees. Efforts to determine the chemical nature of this black gall effect are described. The metabolites of some fungi associated with the black gall (Phomaetheridgei,Stachybotryscylindrospora), and of the rotting fungusPhellinustremulae, are described. Extracts of the black gall tissue have a very high concentration of benzoic acid and it is suggested that the benzoic acid may play a role in the protection of the galled trees.Keywords: fungal metabolites, aspen, benzoic acid, salicylic acid, black galls on aspen,Phellinustremulae.

ISSN:0008-4042    

DOI:10.1139/v95-061

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The1H NMR signals of the Ru(III) species present in solution are considerably broadened and shifted by paramagnetism, but they can be used to follow chloride displacement in thetrans-[RuCl4Im2]−ion. This anion remains predominant for several hours at room temperature in D2O, but its signals are progressively replaced by those of a monoaqua [RuCl3(D2O)Im2] complex. Over a period of days, two new sets of peaks appear, corresponding to two isomers of [RuCl2(D2O)2Im2]+. The same behaviour is observed for the 1-methyl-and 4-methylimidazole analogues. These reactions can be driven backwards by addition of KCl, but [RuCl4Im2]−is not quantitatively regenerated in solution even for 6 M NaCl. Within several months, the [RuCl2(D2O)2Im2]+isomers further aquate to a single species [RuCl(D2O)3Im2]2+. In CD3OD, displacement of the first chloride of [RuCl4Im2]−takes place faster, over several hours, but substitution stops at the [RuCl3(CD3OD)Im2] stage. In DMSO, substitution occurs very slowly. The [RuCl3(DMSO)Im2]:[RuCl4Im2]−mixture (1:2) obtained after 12 days starts to show very slow reduction to two Ru(II) species, one of which precipitates as yellow crystals. From X-ray diffraction work (monoclinic, P21/n,a = 9.951,b = 8.564,c = 10.527 Å, β = 92.95°,R = 0.033), the compound was identified as [RuCl2(DMSO-d6)2Im2], where the metal has atrans-trans-transcoordination and the DMSO ligands are S-bonded.Keywords: paramagnetic ruthenium anion, solvolysis, chloro complexes.

ISSN:0008-4042    

DOI:10.1139/v95-062

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Family-independent relationships between computed molecular surface properties and solute hydrogen bond acidity/basicity and solute-induced methanol O–H infrared frequency shifts are presented. The molecular surface quantities, computed at the ab initio HF/6-31G* level, are primarily related to the electrostatic potential of the molecule, but also include the average local ionization energy on its surface.Keywords: hydrogen bond acidity/basicity, O–H frequency shifts, molecular electrostatic potential.

ISSN:0008-4042    

DOI:10.1139/v95-063

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The role that histidyl, seryl, tyrosyl, and other side chains of small peptides play in the formation of vanadate complexes has been investigated using1H,13C, and51V nuclear magnetic resonance spectroscopy. Formation constants of product complexes in aqueous solution have been determined and the influence of pH on the equilibria established. The results revealed that, in histidine-containing compounds, the protonation state of the imidazole ring of the free ligand strongly influences product formation. The results unequivocally showed that no vanadium-to-imidazole bond was formed for any of the histidine-containing complexes studied. However, imidazole and other aromatic side-chain residues have an effect on product stability via their influence on the protonation state (pKa) of the products. Aliphatic side-chains, such as those in asparagine or glutamate, do not appear to play a significant role in the formation of products. This is not true, however, of serine or threonine where the side-chains readily generate vanadium–oxygen bonds.Keywords: vanadate, vanadium, 51-V NMR, peptides, complexes, aqueous equilibria.

ISSN:0008-4042    

DOI:10.1139/v95-064

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The X-ray crystal and molecular structures of the three benzodiazepine (BZD) receptor ligands are presented and the electronic character of inverse agonist ligands is probed through molecular orbital calculations. Two of the ligands have a 6-benzylamino substituent: 6-benzylamino-β-carboline-3-carboxylic acid methyl ester,1, which is a high affinity antagonist with IC50 = 10 nM, and 6-benzylamino-β-carboline,2, which is a moderate affinity inverse agonist with IC50 = 106 nM. The third compound, 3-ethoxy-β-carboline hydrochloride,3, displays partial inverse agonist activity with an IC50of 24 nM. Intermolecular interactions, including extensive hydrogen bonding involving both the pyridyl nitrogen atom and the indole N—H as well as π stacking of aromatic rings, are characteristic of β-carbolines and are found in these three structures. In addition, two of these compounds are protonated in the crystalline state, thereby providing a model for interactions in the absence of the 3-carboxylic acid ester function. Electronic calculations show that (1) the partial inverse agonist ligand has the highest charge on the N(2) atom and (2) high affinity β-carbolines possess two neighboring sites that have high electrostatic attraction for a hydrogen atom in an intermolecular interaction. These findings suggest that modifications to the 3-position side chain to enhance the charge on the pyridyl N atom and provide a hydrogen bond acceptor site will facilitate the development ofpartialinverse agonist ligands.Keywords: β-carbolines, benzodiazepine receptor, crystallography, structure–activity relationships.

ISSN:0008-4042    

DOI:10.1139/v95-065

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The crystal structures of hexakis(phenylthio)benzene (HPTB) and its CBr4clathrate have been determined by single crystal X-ray diffraction data collected atT = 18 °C and refined to finalRwof 0.036 and 0.047, respectively. Pure HPTB is triclinic, space group(No. 2), witha = 9.589(2) Å,b = 10.256(1) Å,c = 10.645(2) Å, α = 68.42(1)°, β = 76.92(2)°, γ = 65.52(1)°, andZ = 1. The CBr4clathrate of HPTB is rhombohedral, space group(No. 148), witha = 14.327(4) Å,b = 20.666(8) Å, andZ = 3. The host–guest mole ratio of HPTB–CBr4is 1:2. Neutron powder diffraction was carried out on powders of both compounds in the temperature range 25 K <T < 295 K. Thermal expansion coefficients were determined for HPTB and HPTB–CBr4over this temperature range.Keywords: thermal expansion, crystal structure, clathrate.

ISSN:0008-4042    

DOI:10.1139/v95-066

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The structure and reactivity of the radical cation of (+)-2-carene ((1S,6R)-3,7,7-trimethyl-cis-bicyclo[4.1.0]hept-2-ene (3)) have been studied. The radical cation was generated by photoinduced single electron transfer to the first electronically excited singlet state of 1,4-dicyanobenzene in acetonitrile–methanol (3:1). The 1:1:1 (methanol:2-carene:1,4-dicyanobenzene) adducts were formed:trans-3-(4-cyanophenyl)-4-(1-methoxy-1-methylethyl)-1-methylcyclohexene(14), andcis- (15) andtrans-3-(4-cyanophenyl)-6-(1-methoxy-1-methylethyl)-3-methylcyclohexene (16) in a combined yield of 80%. The efficiency of the reaction and the yield of products were increased by the addition of biphenyl, serving as a codonor. These photo-NOCAS adducts formally result from cleavage of the three-membered ring of the 2-carene radical cation, at the C1—C7 bond, forming the tertiary carbocation and allylic radical. Reaction of the cation with methanol and coupling of the allylic radical with the 1,4-dicyanobenzene radical anion at theipsoposition, followed by loss of cyanide ion, completes the sequence. There was no evidence for cleavage of the C1—C6 bond under these conditions; however, when the irradiation was carried out in acetonitrile (no methanol) the (+)-2-carene was partially racemized. Racemization is indicative of C1—C6 bond cleavage. The results ofabinitiomolecular orbital calculations (STO-3G) provide insight into the extent of C1—C7 bond cleavage in the radical cation. The calculated spin and charge distribution, on the 2-carene radical cation global minimum (3a+•), is consistent with the observed regiospecificity of adduct formation.Keywords: photoinduced electron transfer, radical ions, molecular orbital calculations, bond cleavage, 2-carene.

ISSN:0008-4042    

DOI:10.1139/v95-067

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Procedures were elaborated for the syntheses of the title compounds. The thermodynamic changes brought about by each methyl substitution were then determined quantitatively. In acetonitrile, the respective one-electron oxidation and one-electron reduction potentials of the NADH and NAD+analogues were obtained by means of direct and indirect (using ferrocene mediators) cyclic voltammetry. The redox potentials of formal hydride transfers were deduced from the studies of equilibrated reactions occurring between the analogues. The pKa's of the cation radicals ensued.Keywords: NADH/NAD+methylated analogues, one-electron transfers, hydride transfer, thermodynamics.

ISSN:0008-4042    

DOI:10.1139/v95-068

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Mesitylketene was generated flash photolytically in aqueous solution by the photo-Wolff reaction of 2,4,6-trimethyldiazoacetophenone and also by rearrangement of mesitylynol obtained through photodecarbonylation of mesitylhydroxycyclopropenone, and rates of hydration of this ketene were measured in dilute perchloric acid, sodium perchlorate, and sodium hydroxide solutions as well as in concentrated sodium perchlorate and perchloric acid solutions. In dilute solution only an uncatalyzed reaction and a sodium-hydroxide-catalyzed process were observed, both of which could be attributed to nucleophilic attack, by water and by hydroxide ion, respectively, at the ketene carbonyl carbon atom. In concentrated sodium perchlorate solutions, a mild decrease in reaction rate with increasing salt concentration was observed, as expected on the basis of decreasing water activity and a consequent slowing of the uncatalyzed reaction. A similar mild decrease was found in perchloric acid solutions up tobut this then gave way to a rate increase that became dominant aboveThis appearance of acid catalysis indicates a change in reaction mechanism from nucleophilic attack of water to an electrophilic process involving rate-determining protonation on the β-carbon atom of the ketene group. Analysis of the acid-catalyzed reaction rate by the Cox–Yates method gives the catalytic coefficientThis, when compared withfor ketene itself, shows that the mesityl group retards acid-catalyzed hydration by a factor of 2200, and consequently the acid-catalyzed reaction of this, and other aromatic ketenes as well, becomes apparent only under strongly acidic conditions.Keywords: mesitylketene, ketene hydration, acid catalysis, Cox–Yates excess acidity correlation.

ISSN:0008-4042    

DOI:10.1139/v95-069

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

SCF and Møller–Plesset calculations have been carried out for systems containing P—S and P—Npπ—pπ bonds: namely, the 1,3,2-dithiaphospholium cation, the 1,3,2-diazaphospholium cation, and the 1,3,2-azathiaphospholium cation. The computed geometries are reported, along with Mulliken atomic charges and selected vibrational frequencies. ΔH0values for heterolytic P—H bond dissociation and for isodesmic bond separation reactions provide information on the energetics and stabilization of the P—S and P—Npπ—pπ bonds.Keywords: SCF and MP2 calculations, third periodpπ—pπ bonding, bond separation reactions.

ISSN:0008-4042    

DOI:10.1139/v95-070

出版商:NRC Research Press    

年代:1995

数据来源: NRC