摘要:

The13C NMR spectra of a series ofN-acyl six-member ring nitrogen heterocycles have been measured as a function of temperature and the results interpreted in terms of restricted amide rotation and ring inversion. Slow rotation is observed on the NMR time scale around the N-CO bond whilst the ring inversion is fast at ambient temperature. High temperature experiments have been undertaken to investigate the free energy of activation for the amide rotation and low temperature NMR experiments were used to probe the ring inversion process. The experimental results have been compared with theoretical calculations using molecular orbital, molecular mechanics and molecular dynamics approaches and good agreement is observed in all cases.

ISSN:0038-7010    

DOI:10.1080/00387019808003251

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The investigation of iron using off - line energy dispersive X-ray fluorescence, in iron ore dressing process, is presented. Techniques have been developed to determine the quality control of grinding, homogenization, separation, classification processes and residue material in dry basis of iron deposit. The laboratory trials on a wide variety of iron ores indicated that the range of ore grades is from 28–40 % Fe and maximum value is to be found 70 % Fe for processed ore. The results obtained increased the knowledge and performance of the dressing process which is of basic importance for its improvement and future automation.

ISSN:0038-7010    

DOI:10.1080/00387019808003252

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The near-infrared absorption spectra of open-chain secondary amides and smallring lactams have revealed the sensitivity of certain NH combination bands to conformation of the amide grouping1,3more specifically to thecisandtransconformations of the secondary amide grouping2. Some near-infrared characteristics of the peptide groups have been reported a long time ago4,5but despite their biological interest, no data are available for N-tertiobutoxycarbonyl amino acids. In this work, the near infiared spectra of the following molecules have been investigated in the solid state and in carbon tetrachloride solution.

ISSN:0038-7010    

DOI:10.1080/00387019808003253

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In3+-thenoyltrifluoroacetone In3+(TTA)3 Complex has been prepared by reaction of In(SO4)3.2H2O and thenoyltrifluoroacetone ligand in presence of acetate buffer. The complex has been investigated by conventional chemical and physical methods of analysis. Micro analytical data of the investigated complex showed the formula of the complex to be In(TTA)3formula. Trials to prepare mixed ligand complexes starting with In(TTA)3using neutral co-ligand were un successful. The complex is soluble in ethanol and could be of potential use in clinical studies.

ISSN:0038-7010    

DOI:10.1080/00387019808003254

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An asymmetric hetero-Diels-Alder cycloid duct (III) is synthesized and isolated. The1H-1H distance between a proton on the C12chiral center and an ortho phenyl proton is measured by NMR spectral studies (ROSEY, NOESY, TOCSY) of the reaction product of 2,4-penanedienoic acid -(-)-menthol ester with 4,4′-dimethoxy-diphenythione. The experimentally determined value is compared to the distance computed by molecular modeling software (Sybyl). The agreement between experiment and computation is only fair indicating that the use of such measurements for small molecules of uncertain geometry must be approached with care. The results indicate that the distance of closest approach between two protons in a molecule is more consistent with the NMR determined distance than is the equilibrium, lowest energy form of the molecule.

ISSN:0038-7010    

DOI:10.1080/00387019808003255

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Raman and IR. spectra of solid diamminediiodidezinc (II) with15N and2H isotopic substitution have been measured. The spectra have been interpreted assuming C2vsymmetry for the Zn(NH3)2I2complex structure. The skeletal stretching metal-ligand modes vs(ZnN), vas(ZnN), vs(ZnI), vas(ZnI) as well as the three bending modes δ(NZnN), δ(IZnI) and δ(IZnN) were assigned by comparison with the spectra of Zn(NH3)2C12and Zn(NH3)2Br2, and by the observed isotopic shifts of the frequencies. A normal coordinate analysis for the whole complex was carried out using the Local Symmetry Force Field Model.

ISSN:0038-7010    

DOI:10.1080/00387019808003256

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Electronic absorption spectroscopy was employed to study the aerial oxidation of catechol (1,2-benzenediol) in alkaline aqueous solution containing an excess of Mg(II) ions. Graphical analysis by the matrix method of UV spectra recorded at regular time intervals gave a good fit for two absorbing species in solution. Based on this result and our earlier ESR spectroscopic investigations we concluded that two main absorbing species in this system are Mg(II)-spin stabilizedo-benzosemiquinone anion radical and C-C dimer formed by the nucleophilic attack of catecholate anion ono-benzoquinone. Although the formation of 1,2,4-benzenetriol during the catechol oxidation has been detected in some ESR studies its presence was not indicated by this analysis probably because of the low and/or stable steady state concentration throughout the experiment.

ISSN:0038-7010    

DOI:10.1080/00387019808003257

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Raman spectra, together with factor analysis and band deconvolution procedure, have been used to study formation of magnesium thiocyanate complexes in aqueous solutions at ambient and elevated temperatures. The total salt concentration in solutions, containing different mole ratio of Mg2+to SCN, varied between 3.4 and 7.5 mol dm−3. Factor analyses indicated that two linearly independent scattering components in the band envelopes, recorded in the V1and v3stretching regions of SCN, for all solutions with total salt concentration of 3.4 mol dm−3. The appearance of a pseudo-isosbestic point in the area normalized spectra supported this result, as well as the baud resolution procedure. The latter revealed the third scattering component in the spectra of solutions with total salt concentration above 3.5 mol dm−3Resolved components have been assigned to the free thiocyanate, the 1:1 and 1:2 magnesium thiocyanate complexes. The equilibrium constant Kcof the 1:1 complex is of an order of 10−1mol dm−3.

ISSN:0038-7010    

DOI:10.1080/00387019808003258

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The FTIR spectral measurements were carried out for native cytochromec(cytc) and its four platinum-modified derivatives. The influence of the platinum complex binding on the secondary structure of cytcwas discussed. It was found that the secondary structure of platinum-binded derivatives is similar to that of native cytcwhen the platinum complex is binding on or near the surface of the protein. While in the case of derivatives, in which the platinum complex interacts with the second axial ligand of cytc(Met 80) and causes the replacement of Met 80 by Lys 79 or solvent (H2O), great secondary structural changes were observed.

ISSN:0038-7010    

DOI:10.1080/00387019808003259

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The halochromic behaviour of the title dye (1) was studied in methanol, ethanol, 2-propanol, 1-butanol, 2-butanol, dimethyl acetamide, dimethyl sulfoxide, acetone and acetonitrile, in the presence of sodium iodide, potassium perchlorate and lithium perchlorate. The observed shifts of the charge-transfer band of 1, caused by the addition of increasing concentrations of the salts, was interpreted in terms of dye-salt and solvent-salt interactions and compared with the behaviour of other solvatochromic dyes which exhibit cationic halochromism.

ISSN:0038-7010    

DOI:10.1080/00387019808003260

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor