Many of the isomers of polybutadiene and polyisoprene elastomers can be characterized by thermal analysis.Tg is sensitive to side chain units (1,2 or 3,4 structure) for both polymers. Crystallinity measurements can characterizecis andtrans isomers. DMA and DEA master curves provide an idea of the heterogeneity of the chain units from the width of the loss factor
curves in theTg region. Thermal and thermooxidative degradation, as followed by DSC and DTG, can differentiate specific natural and synthetic
isomers of polyisoprenes in raw and vulcanized states.
New polyurethanes with mesogenic units in the main chain due to the use of a liquid crystalline chain extender were synthesized
from 4,4'-methylenebis(cyclohexyl isocyanate) (HMDI)using diisocyanates of different trans, trans isomer content, a low molecular diol4,4'-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and a high molecular poly(hexyleneadipate)diol
(PHA). The growth of trans, trans isomer content in HMDI used to syntheses of PU induces monotonic growth of melting point, rectilinear growth of crystallization
temperatures and the growth of crystallization enthalpy, both for hard segment polyurethanes and block polyurethanes. The
increase of trans, trans isomer content in HMDI increases also glass transition temperatures and dynamic storage modulus of the polyurethanes.
Authors:Zsuzsa Király-Véghely, Ágnes Móricz, Klára Otta, and György Kátay
A method, including solid phase extraction sample preparation, overpressured layer chromatographic separation, and subsequent densitometric evaluation, was developed for measurement of total resveratrol (cis- and trans-isomers) content of wine. The amount of resveratrol was determined in wine samples from different winemaking regions of Hungary. The total resveratrol was high in Hungarian red wines (3.6–11 mg L−1), and much lower in white ones (0.04–1.5 mg L−1).
By comparing the composition of products formed during the -radiolysis of structural and geometrical /cis and trans/ isomers of dimethylcyclohexanes, the relationship between molecular structure and ring decomposition reactions was investigated. The yields of products that exist in geometrical isomeric forms /e.g. 2-butenes, 2-octenes/ were considerably different in the irradiation of cis- and transdimethylcyclohexanes: the products reflected the conformation of the decomposed molecule. It was assumed that the ring decomposition is a very fast process taking place within about 1 ps. If biradical intermediates are involved in the reactions, their further transformations occur before attaining conformational equilibrium.
Authors:L. Núńez-Regueira, S. Gómez-Barreiro, and C. A. Gracia-Fernández
Modulated differential scanning calorimetry (MDSC) and dielectric analysis (DEA) have been used to characterize the cure process
of the system diglycidyl ether of bisphenol A (DGEBA(n=0)/1,2 diaminocyclohexane (1,2 DCH). The trans isomer and a mixture cis/trans(30-70% respectively) of 1,2 DCH were used to find their different behaviour. The study allowed to check the influence of
the cisisomer on the thermoset curing process. Gelation times were obtained through the equation proposed by Johari and vitrification
times from the point of inflection of the complex calorific capacity modulus.
Authors:Sandra Šegan, Dejan Opsenica, Bogdan Šolaja, and Dušanka Milojković-Opsenica
Seven pairs of
isomers of bis-steroidal tetraoxanes have been examined by both normal-phase (NP) and reversed-phase (RP) planar chromatography. Unmodified silica gel was used with ethyl acetate-toluene and ethyl acetate-petroleum ether as mobile phases in typical normal-phase systems. CN-silica with the mobile phases methanol-water and acetone-water and RP-18 silica with water-organic modifier (methanol, acetone, or dioxane) mobile phases were used as reversed-phase systems. For the RP systems a good linear correlation was established between
values and amount ([%]
) of organic modifier in the mobile phase (usually
> 0.99). It was found that under both NP and RP conditions
isomers were more weakly retained than the corresponding
isomers. The only exception to this was the chromatographic behavior of C(24) methyl esters. It was established that increasing the polarity of substituents at C(24) and C(24a) led to stronger retention in NP systems, i.e. weaker retention in RP systems. Highly selective separation was achieved in all the chromatographic systems investigated. Possible separation mechanisms are discussed on the basis of the results obtained.
Authors:Jogender Lalla, Purnima Hamrapurkar, and Santosh Sacket
The oleo-gum-resin known as ‘guggul’, obtained from the plant
, Hook (family Burseraceae), is widely used, as a component of formulations containing other Ayurvedic drugs, for treatment of hypercholesterolemia, rheumatism, and arthritis. Chemically, guggul contains two active keto steroids, guggulsterones
, which are reported to be responsible for its antihyperlipidemic activity. These
isomers have been isolated, purified by TLC and column chromatography, and characterized by determination of melting point and by acquisition of UV, IR, and NMR spectra. After confirmation of their identity, they were used as biomarkers in HPTLC fingerprinting analysis of five commercial Ayurvedic formulations, four tablets and a capsule, all of which contain guggul as a constituent. The analytical method was fully validated. Extrapolation was used to calculate probable amounts of guggul added to the formulations on the basis of
Organic substances containing double bonds, e.g. allyl alcohol, and different medicaments (quinine, vasalgin), were determined with bromine water by direct injection enthalpimetry. Measurement of the reaction heat or the rate of evolution of heat permits simple and rapid distinction of cis and trans isomers: fumaric and maleic acid, or oleic and elaidinic acid.
Authors:B. Butinar, M. Bučar-Miklavčič, A. Krumpak, and P. Raspor
Olive and pumpkin seed oils play a specific role in Slovenian edible oil market. That is why exact and accurate tools for assessing the oils’ quality and purity (adulteration) are needed. One of the tools is registering certain names and foodstuffs in National registers and the Register of European Union. Another tool is the analysis which can help to assess the characteristics of the oil and to classify it in categories. In the field of olive oils, this has been done excellently with the European Commission regulations. In the present work we tried to test few pumpkin seed oils for fatty acids content, trans isomers of fatty acids, composition of sterols and tocopherols. The main goal was to check the purity of the oils and understand the present situation in the field. The analytical results show that some samples are adulterated with seed oils. What can consumers benefit? From the Slovenian olive oil experience it can be concluded that the path towards better quality oils does not strictly follow analytical methods but tries to track well-established rules and definitions of quality and purity. The consumers must learn and be aware that the quality and purity can be analytically proven.