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31.
Fernandes L. P. Éhen Zs. Moura T. F. Novák Cs. Sztatisz J. 《Journal of Thermal Analysis and Calorimetry》2004,78(2):557-573
Thermoanalytical techniques, being rapid and un-expensive have been used for the investigation of the cyclodextrin inclusion
complexes for three decades. The conventional thermoanalytical techniques (TG and DTA/DSC) follow the thermal properties of
the uncomplexed compounds. Consequently, the inclusion complex formation as well as the liberation of the entrapped guest
cannot be followed. Monitoring the products of the thermal fragmentation of parent cyclodextrin and the included molecule(s),
applying TG-MS combined technique provides evidence concerning the inclusion complex formation, and besides, gives selective
signal to follow the decomposition of the cyclodextrin inclusion complexes. b-cyclodextrin inclusion complexes of Thymol and
Lippia sidoides Cham essential oil extract have been prepared and investigated using conventional and combined (TG-MS) thermoanalytical techniques.
The evolved gas analysis proved the inclusion complex formation between the host and guests. By the evaluation of the experimental
results the elaboration of the entrapped guests from the cyclodextrin cavity could be followed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
32.
Fluoride ions and, in about 0.005M concentration, tungstate ions form gelatinous precipitates, poorly soluble in water, with calcium ions. The radiometric determinations
of the above ions are based on these reactions. Accurate radiometric determination can be carried out only if the gelatinous
precipitate formed during titration can be properly separated from the solution. It has been found that in the case of fluoride
ions the application of crystalline, easily filtrable Ca(COO)2·H2O or CaCO3, and in the case of tungstate ions the application of CaWO4 precipitate improves the filtration properties of45CaF2 and45CaWO4, respectively, formed during titration, whereby the radiometric determinations of the above ions become possible. Titrations
were carried out with 0.05M and 0.005M CaCl2 solutions, labelled with45Ca. 相似文献
33.
Summary The peroxidation of molybdenum(VI) was investigated in neutral and alkaline media. The stability constants of the peroxo complexes were determined by spectrophotometric measurement as (9.12±0.67)×10–7, (2.68±0.17) ×105, (1.26±0.06)×106 and (1.58±0.02) for the 11, 21 (yellow), 31 and 41 (red) species. The diperoxomolybdate disproportionates into the tetraperoxo derivative when treated with alkali. Formation of the tetraperoxo complex was found to be pH dependent according to a curve, with maximum at pH 10. Acidification of tetraperoxomolybdate solution results in the regeneration of hydrogen peroxide and the diperoxo complex is reformed. 相似文献
34.
J. Fekete M. Milen L. Hazai L. Poppe Cs. Szántay A. Kettrup I. Gebefügi 《Chromatographia》2003,57(3-4):147-153
Summary Reversed (RP-HPLC) and normal phase chromatographic (NP-HPLC) separations have been developed for diastereomers ofN-acyl-1-methyl-1,2,3,4-tetrahydo-β-carbolines which are acylated derivatives of simple natural β-carboline alkaloids. Separations
of derivatives having different acyl moieties in theO,O-diacyl-tartaric acid ester subtituent differed remarkably. Little or no resolution in either NP-HPLC or RP-HPLC could be
achieved with the diacetyl-tartrate derivative. Base-line separation by RP-HPLC but no separation by NP-HPLC was possible
with the bulkier and more apolar dipivaloyl derivative. Retention order of the bis-benzoylated diastereomers was reversed
and separation time increased dramatically by RP-HPLC. Good separation of the medium polarity, but rigid,N-camphanyl derivative by NP-HPLC has been achieved, whereas RP-HPLC could not be used for separation of these diastereomers.
Separability of different diastereomers was highly dependent on polarity and rigidity of the derivatizingN-acyl moieties. Conformational analysis by molecular mechanics and comparison of the lowest energy conformational states of
the diastereomers was applied to rationalise separation-retention behaviour of stereoisomers by RP-HPLC.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001 相似文献
35.
36.
Kassai Cs. Illés R. Pokol G. Sztatisz J. Fogassy E. Kozma D. 《Journal of Thermal Analysis and Calorimetry》2000,62(3):647-655
The resolution of three chiral alcohols with O,O'-dibenzoyl-(2R,3R)-tartaric acid (DBTA) via diastereoisomeric supramolecular
compound formation was investigated with thermoanalytical methods. On the basis of TG measurements the DBTA:chiral alcohol
molar ratio in the compounds is 1:1 which agrees with the results of single-crystal X-ray diffraction analysis. The DBTA –
chiral alcohol supramolecular compounds have different supramolecular structure than the DBTA – achiral alcohol supramolecular
compounds. The supramolecular compounds containing cyclohexanols have higher thermal stability than the compounds containing
acyclic aliphatic alcohols. The amount of unreacted DBTA monohydrate in the solid phase can be determined both with DSC and
with TG measurements.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
37.
J. Zsakó I. Ganescu Cs. Várhelyi L. Chirigiu 《Journal of Thermal Analysis and Calorimetry》1997,48(2):367-371
Thermal decomposition of 6 complexes of the type AH[Cr(NCS)4 (am)2]· nH2O is studied with derivatograph. The formation of Cr(NCS)3 as a labile intermediate is presumed. For some decomposition stages kinetic parameters are derived. The kinetic compensation effect is discussed. 相似文献
38.
Comparison
of the fragility index of different eudragit polymers determined by activation
enthalpies
Gabriella Csóka A. Gelencsér Dorottya Kiss Eszter Pásztor I. Klebovich Romána Zelkó 《Journal of Thermal Analysis and Calorimetry》2007,87(2):469-473
The present study aimed to apply fragility
index (m) of polymers in the determination
of the optimal amount of plasticizer in polymer films. The fragility index
of different Eudragit polymers (RS, RL, EPO) was assessed by differential
scanning calorimerty (DSC), applying the Arrhenius connection (logq–1/T
g).
The fragility of Eudragit EPO films proved to be the highest, while in the
case of RS and RL, the increase of the alkyl-chain length caused the increase
of fragility. Studying the effect of plasticizer (triethyl citrate, TEC) on
the m value of Eudragit RL and RS films,
a near linear reduction of the fragility index could be observed between 5–30%
TEC concentration, but above 30%, this value leveled out to constant. 相似文献
39.
Aacute;gnes Buvári-Barcza Antal Csámpai Lajos Barcza 《Journal of inclusion phenomena and macrocyclic chemistry》2002,42(3-4):209-212
Two guests reacting with cyclodextrins (CDs) may form ternary complexes, in addition to the common competition of 1:1 complexes. One of the guests can really be included into the cavity of the CD, while the second guest molecule is either inserted close to the first one or attached to the outer surface of the supramolecule by H-bonding. There is a further possibility when the included guest bears a substituent outside the cavity and the second guest can interact with it. The properties of the ternary species formed are highly influenced by the solely (or primarily) included guest. The changes are attributed to the altered properties of the hydrophilic domain of the CD. The phenomena can be proved by NMR data obtained for some binary systems of -CD inclusion complexes and acetic acid and by the stability constants of the ternary complexes formed. Allosteric effects as well as coenzyme/apoenzyme/substrate interactions could be well modelled by these types of CD complexes. 相似文献
40.
Thermal decomposition of 21 complexes of the type [Co(DH)2(amine)2]NCS has been studied under the conditions of thermogravimetric analysis, by using different heating rates. From the thermogravimetric curves apparent kinetic parameters of the pyrolysis reaction have been derived by means of the modified Doyle method. Apparent reaction order increases and apparent activation energy decreases with increasing heating rate. Thus, the obtained kinetic parameters do not characterize the purely chemical reaction, but the complex heterogeneous process as a whole. The explanation of the observed effect is discussed. Results are compared with those obtained with other analogous complexes.
Zusammenfassung Die thermische Zersetzung von 21 Komplexen des Typs [Co(DH)2(Amin)2]NCS wurde thermogravimetrisch bei verschiedenen Aufheizungsgeschwindigkeiten untersucht. Aus den TG-Kurven wurden die scheinbaren kinetischen Parameter der Reaktion mit Hilfe der Doyleschen Methode ermittelt. Bei zunehmender Aufheizungsgeschwindigkeit wächst die scheinbare Reaktionsordnung während die scheinbare Aktivierungsenergie abnimmt. Die erhaltenen chemischen Parameter kennzeichnen nicht die eigentliche chemische Reaktion, sondern den ganzen komplexen heterogenen Vorgang. Die beobachteten Effekte wurden diskutiert und die Ergebnisse verglichen mit Resultaten von Untersuchungen anderer analoger Komplexe.
Résumé On a étudié par thermogravimétrie, avec différentes vitesses d'échauffement, la décomposition thermique de 21 complexes du type [Co(DH)2(amine)2SCN. On a calculé suivant la méthode deDoyle les paramètres cinétiques apparents déduits des courbes d'ATG. L'ordre apparent de la réaction augmente si la vitesse d'échauffement croît, alors que l'énergie d'activation apparente décroît. Les paramètres cinétiques obtenus ne caractérisent que le processus hétérogène complexe et non la réaction chimique proprement dite. Les effets observés ont été discutés et comparés avec les résultats obtenus avec d'autres complexes analogues.
21 [(D)2()2]NS , . . . , , . . , .相似文献