摘要:

The phase transitions ofN-octadecanoyl-L-alanine and zinc octadecanoyl-L-alaninate LB films have been investigated through variable temperature FTIR spectroscopy. Hydrogen-bonding interactions between the enantiomeric head-groups strengthens the interactions between the alkyl chains so that the transition temperature of theN-octadecanoyl-L-alanine LB film (Tc= 122 °C) is nearly twice as high as that of the same-chain-length stearic acid LB film (Tc= 65 °C). The intermolecular hydrogen-bonding interactions in the zinc octadecanoyl-L-alaninate LB film are greatly intensified in comparison to that in theN-octadecanoyl-L-alanine LB film; the relatively weak hydrogen-bonding interaction in the latter is easily disrupted around its transition temperature (Tc= 122 °C) together with an abrupt increase of va(CH2) stretching frequency, while the intensified intermolecular hydrogen-bonding interaction in the former weakens step by step with temperature along with a monotonic increase of va(CH2) stretching frequency, the zinc octadecanoyl-L-alaninate LB film thus exhibits a different phase behavior from the pure enantiomer LB film. Therefore, the strength of the intermolecular hydrogen bond is closely related to the interchain interaction and the film phase behavior.

ISSN:0038-7010    

DOI:10.1080/00387019909349962

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Spectrophotometric evidence for the formation of a short-lived Mn(VI) intermediate has been confirmed during the oxidation of pectin polysaccharide, a natural polymer, as well as poly (vinyl alcohol) [PVA], a synthetic polymer, by potassium permanganate in alkaline medium at pH's > 12. This Mn(VI) intermediate was characterized by a band at a wavelength of 606 nm an absorption maximum, with a molar extinction coefficient of 1200 ± 50 dm3mol−1cm−1

ISSN:0038-7010    

DOI:10.1080/00387019909349963

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The Franck-Condon (FC) factors (transition probabilities) and r-centroids have been evaluated by the reliable numerical integration procedure for the bands of the BO+→XO+system of BiD molecule, using a suitable potential. The dissociation energy for the electronic ground state of BiD has been estimated by fitting the empirical potential function to the experimental potential energy curve, using correlation coefficient.

ISSN:0038-7010    

DOI:10.1080/00387019909349964

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The title compound has been investigated by x-ray analysis and AM1 semi-empirical quantum mechanical method. The geometry of the two molecules in the asymmetric unit is different in terms of the torsion angle [C4-C5-C6-C10] between the two pryidne rings which is -34.1 (2)° and -17.9 (2)° in molecule I and II respectively. The conformation of the energy profile showed that the minimum energy conformation has the torsion angle near 35°. The crystal structure is stabilized by C-H … N hydrogen bonds.

ISSN:0038-7010    

DOI:10.1080/00387019909349965

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The FT-IR (from 50 to -180°C) and the FT-Raman spectra at 25°C of glutarimide in in the solid state are investigated. The data are compared with recent results of Bienko et al.(J.Phys.Chem.A 101, 7834 (1997) on glutarimide isolated in a low-temperature argon matrix. The vibrational changes induced by hydrogen bond formation in the crystalline state are discussed. The v(NH…O) vibration is observed at 3189 cm−1at 25°C and at 3163 cm−1at -180°C. These values correspond to a contraction of the N…O distance of 0.022 Å.

ISSN:0038-7010    

DOI:10.1080/00387019909349966

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A study was made of the solvent effects observed in the absorption spectra of N-(2-hydroxy-1-naphthylidene)anilines, N-(2-hydroxybenzylidene)amines and N-(4-hydroxybenzylidene)aniline in various solvents. It was established that the logarithm of the constant describing the equilibrium enol ⇔ keto tautomer correlates closely with the parametersENTand BKTcharacteristic of the acidity or basicity of the solvents.

ISSN:0038-7010    

DOI:10.1080/00387019909349967

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The fluorescence of the lithium-tetracycline system is studied and discussed in terms of several water-miscible solvents. The excitation and emission spectra of the system are compared with both corresponding lithium and tetracycline blanks. Only two different spectra patterns are found to be the most fluorescence enhanced in the presence of non-hydroxylic solvents.

ISSN:0038-7010    

DOI:10.1080/00387019909349968

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Three modifications of the sodium hydrogen sulphate (NaHSO4·H2O, A-NaHSO4, B-NaHSO4) have been prepared. Their vibrational spectra have been measured. The results are discussed in relation to the structures of crystals. The good agreement between the crystal structure, selection rules and vibrational spectra is observed for NaHSO4·H2O crystal. However, the careful analysis of the infrared spectra of both anhydrous modifications (A-NaHSO4, B-NaHSO4) show that neither of them correspond to β-NaHSO4form. On the other hand, the infrared spectra of A-NaHSO4and B-NaHSO4modifications show that each of them contain some amount of the α-NaHSO4phase.

ISSN:0038-7010    

DOI:10.1080/00387019909349969

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Surface enhanced Raman scattering studies are carried out for 1,4-diaminoanthraquinone dye [1,4-DAAQ] in Ag colloid in order to understand the enhancement effect and the nature of interaction between the dye molecule and Ag surface. Detailed analysis of the enhanced vibrational bands in the SERS spectrum shows that the 1,4-DAAQ molecule is not adsorbed through its coordinating sites, because of intramolecular hydrogen bond formation. The 1,4-DAAQ molecule is seen having 'flat on' orientation. Laser induced fluorescence measurements in different solvents and in different pH confirm the intramolecular hydrogen bond formation.

ISSN:0038-7010    

DOI:10.1080/00387019909349970

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The interaction of the cyclic base 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (TODACOD) with different π-electron acceptors have been studied spectrophotometrically in CHCl3. These π-electron acceptors are 1-chloro-2,4,6-trinitrobenzene (picryl chloride), 7,7', 8,8'-tetracyanoquinone (TCNQ) and tetrachloro-p-benzoquinone (chloranil). The results indicate the formation of 1:4 charge transfer complexes with the general structures [(TODACOD)(Accept)4]. The charge transfer absorptions as well as the infrared spectra of these complexes are obtained.

ISSN:0038-7010    

DOI:10.1080/00387019909349971

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor