摘要:

The nature of complex formation between aromatic amino acids and some of their components with NAD+(nicotinamide adenine dinucleotide) have been studied by spectrophotometric methods. A comparison of the stability of these complexes with that of the complexes of the same donors with a model compound of NAD+i.e.N-methyl-3-carboxamide pyridinium chloride (MCP) has been carried out by examining the type of complexes formed and their geometry. Simple molecular orbital calculations have been done to determine the quantity of charge transfer δQand stabilization energy δEand to show the significance of mutual orientation of donor and acceptor in determining the stability. The enhanced stability of tryptophan–NAD+complex in comparison to indole–NAD+complex has also been explained.

ISSN:0008-4042    

DOI:10.1139/v76-011

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The decomposition of butyl dixanthogen in the presence of cetyl trimethylammonium bromide (CTA) at pH10.5 is studied. CTA micelles strongly catalyze the decomposition. A great difference is also found between freshly prepared dixanthogen and that stored pure or dissolved in dioxane for more than one month. A general mechanism is proposed to account for the results obtained.

ISSN:0008-4042    

DOI:10.1139/v76-012

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The contribution to the circular dichroism ofL-Ala-L-Ala,L-Nva-L-Nva,L-Val-L-Val,L-Leu-L-Leu,L-Ile-L-Ile,L-Cys(Me)-L-Cys(Me),L-Met-L-Met, andL-Phe-L-Phe internal peptide chromophores in 1,1,1,3,3,3-hexafluoropropan-2-ol were calculated by subtracting the total molar ellipticity values of N- and C-protected homo-trimers from those of the pertinent protected homo-tetramers.The circular dichroism of the internal peptide chromophore of aliphatic hydrocarbon- and sulfur-containing peptides, each of theL-configuration, show a negative band at 2l5–230 nm accompanied by a more intense negative band near 200 nm. A structured weak and negative band near 260 nm along with bands at 240 nm (negative), 222 nm (positive), and 210.5 nm (negative) of progressively increasing intensity are apparent in the circular dichroic spectrum ofL-Phe-L-Phe internal peptide chromophore. The effect of solvent polarity is discussed in the case ofL-Val-L-Val andL-Ala-L-Ala internal peptide chromophores.Among the protected homo-trimers and tetramers only those ofL-alanine are soluble in aqueous solution; consequently, the effect of water as a function of temperature, urea, and guanidinium chloride on theL-Ala-L-Ala internal peptide chromophore circular dichroism was established.

ISSN:0008-4042    

DOI:10.1139/v76-013

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The triplet cadmium photosensitized decomposition of cyclopentane in the vapor phase has been studied at 355 °C and has been shown to give rise to cyclopentyl radicals and hydrogen atoms with close to unit efficiency in the primary process. Subsequent reactions of these species, including an important contribution from unimolecular decomposition of cyclopentyl radicals, yield the observed volatile products, hydrogen, methane, ethylene, ethane, propylene, and cyclopentene. As a result of significant olefin scavenging of H-atoms product yields are strongly time dependent. The system has been shown to be unaffected by addends. The temperature dependence of the rate of product formation is consistent with the known energetics of cyclopentyl radical decomposition.

ISSN:0008-4042    

DOI:10.1139/v76-014

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The preparation of some complexes of benzoxazole-2-thione with halides of cobalt(II) and nickel(II) is reported. The complexes of cobalt(II) and nickel(II) are tetrahedral of the type ML2X2with the exception of NiLBr2. The complexes have been studied by means of magnetic susceptibility measurements, infrared and far ir spectra, electronic spectra, and conductivity measurements. The ligand behaves as monodentateN-bonded. The various ligand field parameters,Dq,B′, and β show about 60 and 80% of covalency in the cobalt(II) and nickel(II) complexes respectively and suggest a medium strong ligand field. The spectroscopy parameters of cobalt and nickel derivatives confirm the presence of CoN2X2and NiN2X2chromophores.

ISSN:0008-4042    

DOI:10.1139/v76-015

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The acetone-initiated photochemical addition of formamide to 2,3,4,6-tetra-O-acetyl-1-deoxy-D-arabino-hex-1-enopyranose (1) afforded 3,4,5,7-tetra-O-acetyl-2,6-anhydro-D-glycero-D-ido-heptonamide (2), 3,4,5,7-tetra-O-acetyl-2,6-anhydro-D-glycero-D-talo-heptonamide (3), and 4,5,6,8-tetra-O-acetyl-3,7-anhydro-1-deoxy-2-methyl-D-glycero-D-talo-octitol (4), in 55, 7, and 23% yields, respectively. Reduction of2with diborane followed by acetylation yielded 1-acetamido-3,4,5,7-tetra-O-acetyl-2,6-anhydro-1-deoxy-D-glycero-D-ido-heptitol (7) in 70% yield. Deacetylation of2and3with sodium methoxide yielded the unsubstituted heptonamides5and6.Photoamidation of (Z)-3-deoxy-3-C-(methoxycarbonyl)methylene-1,2:5,6,-di-O-isopropylidene-α-D-ribo-hexofuranose (8) yielded 3-C-[RandS-carbamoyl(methoxycarbonyl)methyl]-3-deoxy-1,2:5,6-di-O-isopropylidene- α-D-allofuranose (9) and (10).

ISSN:0008-4042    

DOI:10.1139/v76-016

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A stereoselective synthesis of ormosanine (1), identical in all respects with the naturally occurring racemic alkaloid ofO.jamaicensis, has been accomplished. Subsequent transformation of synthetic ormosanine into racemic piptanthine (2) and intod,l-panamine (3) is described. 18-Epiormosanine (22) has also been prepared by total synthesis. Some unusual stereochemical effects allowing the control of configuration at C6, C11, and C18are discussed.

ISSN:0008-4042    

DOI:10.1139/v76-017

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The ir and laser Raman spectra of η5-C5H5Mn(CO)2(CS) and η5-C5H5Mn(CO)(CS)2have been investigated. In the case of the monothiocarbonyl complex, vapor phase, solution, and solid-state measurements were made, while for the dithiocarbonyl, only solid-state data were obtained. The vibrational spectra of both complexes have been assigned satisfactorily in terms of theC5vandCslocal symmetries of the η5-C5H5—Mn and Mn(CO)2(CS) (or Mn(CO)(CS)2) moieties, respectively. The effect of change of state on the spectra of the monothiocarbonyl complex is discussed.

ISSN:0008-4042    

DOI:10.1139/v76-018

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The effects of different heteroatoms in the α position to the thiocarbonyl group on nucleophilic behavior of sulfur atom have been studied. Three symmetrical environments have been considered: nitrogen, sulfur, and oxygen atoms.The theoretical treatment by the CNDO/2 method and the analysis of orbitals interactions show a frontier orbital control for the reaction studied.

ISSN:0008-4042    

DOI:10.1139/v76-019

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The13C magnetic resonance spectra of a series of methyl and phenyl substituted morpholines, their hydrochlorides, and methiodides have been determined. The effects of methyl substitution adjacent to oxygen and nitrogen are reasonably equivalent and substituent induced chemical shift parameters derived for the series show favorable agreement with those previously observed in both alicyclic and heterocyclic systems. Results for thecisandtransisomers of phendimetrazine (3,4-dimethyl-2-phenylmorpholine), confirm the preferred chair conformations and configurationscis-3-CH3,cis-2-phenyl (cis) andtrans-3-CH3,cis-2-phenyl (trans) for these isomers. The preferred course of quaternization of nitrogen in these systems was determined as axial, using deuteriomethyliodide as a label. This13C–2H technique relies on the observation of the γ-syn-axial effect and is clearly unambiguous and superior to other methods used in evaluating this mechanism. Product ratios and consequently free energies of this reaction were measured from proton and deuterium nmr spectra.

ISSN:0008-4042    

DOI:10.1139/v76-020

出版商:NRC Research Press    

年代:1976

数据来源: NRC