Authors:J. ReuΒner, G. W. H. Höhne, H. Utschick, M. Arnold, T. Wegner, and L. Wohlfarth
Poly(butadiene-alt-1-olefin) copolymers and poly[(butadiene-alt-ethene)-co-(butadiene-alt-1lefin)] terpolymers, and the hydrogenated products too, has been characterized with the aid of differential scanning calorimetry (DSC). Both the glass transition and the melting behaviour of the partial crystallized products has been investigated. From the peak area the degree of crystallinity has been calculated in a first approximation. The results allow to draw conclusions about the crystallization behaviour in relation to the number and length of the side chains and about the course of the synthesis in question.
The thermal degradation behaviour of poly(ethyl methacrylate) homopolymers and poly(ethyl methacrylate) and poly(ethyl acrylate) copolymers synthesized by using the benzoyl peroxide-di-methyl aniline redox pair at different temperatures (18–35‡C) was investigated. Contrary to some reports in the literature, the thermal degradation of PEMA was observed to take place in multi steps. These are assigned to be loss of labile end groups, side chain scission, anhydride formation and main chain degradation steps. Dominating chemical formations at the end of these steps were characterized by FTIR spectroscopy.
Thermal characteristics of a new thiophene derivative, 2-(thiophen-3-yl-)ethyl octanoate (OTE), its homopolymer (POTE), and
copolymer with thiophene P(OTE-co-Th) were investigated via pyrolysis mass spectrometry. Thermal degradation of the copolymer
started by lose of side chains and thiophene involving products evolved almost in the same temperature range where PTh degradation
was detected, at slightly higher temperatures than PTh backbone decomposed during the pyrolysis of POTE. The extent of doping
and network structure decreased in the order POTE<P(OTE-co-Th)<PTh.
The thermal degradation of copolymers based on butyl acrylate-methyl acrylate-acrylic acid used as acrylic pressure-sensitive
adhesives, especially for bonding of plasticizer containing materials, has been investigated using thermogravimetry and pyrolysis-gas
chromatography at 250°C. It was observed that during the pyrolysis of butyl acrylate-methyl acrylate-acrylic acid copolymers
unsaturated monomers as methyl acrylate, methyl methacrylate, butyl acrylate and butyl methacrylate were formed. During the
side-chain butyl acrylate-methyl-acrylate-acrylic acid-copolymer degradation the presence of methyl alcohol and butyl alcohol
Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used to examine the thermal behavior of the multimonomer
poly[2-(10-undecenoyloxy)ethyl methacrylate] (PUDEM) within the temperature range from -80 to 400C. DSC measurements indicated
that the polymer side chains were able to crystallize in paraffinic phase. PUDEM, added to methyl methacrylate (MM), can effectively
copolymerize with essentially no homopolymer produced as shown by DSC (single Tg). The value of Tg depends on the PUDEM content, degree of cross-linking and the presence of free MM in the cross-linked product.
Two derivatives of cellulose were investigated by ESR method after gamma-irradiation. Irradiation of methylcellulose (MC)
and hydroxyethylcellulose (HEC) results in formation of radicals on these polysaccharides. Their transformations cause main-chain
scission or to the opposite effect, crosslinking of polymer. It was proposed that radicals placed on anhydroglucose repeating
unit contribute to degradation reactions, and those located on side chains of derivatives, i.e., methoxy group, -O-CH3 and hydroxyetyl ether group, -O-CH2-CH2-OH participate in crosslinking.
Authors:Kawthar Bouchemal, Patrick Couvreur, Samia Daoud-Mahammed, Jacques Poupaert, and Ruxandra Gref
In this study, the entrapment of benzophenone (BZ) into supramolecular nanoassemblies prepared by mixing two water-soluble
associative polymers (i.e. polymerized β-CD (pβ–CD) and dextran grafted with lauryl-side chains (MD)) has been investigated
by using isothermal titration microcalorimetry (ITC) and molecular modeling. ITC experiments have been performed at various
temperatures (4 °C (277 K), 25 °C (298 K), and 37 °C (310 K)) to evaluate the interaction of BZ with pβ–CD in comparison with
β-CD. The inclusion complexation for both β-CD/BZ and pβ–CD/BZ interactions was entropy-driven (|ΔH|<|TΔS|) when the temperature of the experiment was low (4 °C) and enthalpy-driven (|ΔH|>|TΔS|) with minor entropic contribution when the temperature was increased (25 and 37 °C). Using all the thermodynamic data obtained
for β-CD/BZ and pβ–CD/BZ interactions when the temperature of the experiment was varied, the
plot was perfectly linear, which reflected an enthalpy–entropy compensation process. Finally, the combination of ITC data
with molecular modeling provided consistent information in regard to the location of MD side chains and BZ inside the cyclodextrin
cavity, as well as concerning the stability of the nanoassemblies loaded with BZ.
Authors:C. Shimasaki, T. Kanaki, S. Takeuchi, K. Hasegawa, D. Horita, E. Tsukurimichi, and T. Yoshimura
The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG
curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition
by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination
of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and
side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time
in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose<ketohexose<aldohexose.
This result indicates that the trimethylsilyl derivatives are thermally stable. Subsequently, the pyrolysis regime for 1 obeyed
apparent 1/2-order kinetics and their apparent activation energy was estimated as 75–100 kJ/mole.
Living cells are able to respond to the surrounding environment. As a first step in this process, membrane receptors react with an extracellular ligand. There are three main families of cell-surface receptors: (1) Ion-channel-linked receptors, (2) G-protein-linked receptors, and (3) Enzyme-linked receptors that either act directly as enzymes or are associated with enzymes. These enzymes are oftenprotein kinasesthat phosphorylate specific proteins in the target cell. Through cascades of phosphorylations elaborate sets of proteins relay signals from the receptor to the nucleus regulating gene expression. There are two groups of protein kinases: tyrosine- and serine-threonine-specific protein kinases and there areprotein phosphataseswith specificity for the appropriate side chain to match each type of kinase. They can terminate an activation event reversing the phosphorylation caused by a protein kinase.
Authors:H. Bhalla, P. Vavia, G. Samuel, and N. Sivaprasad
Therapeutic monitoring of theophylline can be accurately performed by radioimmunoassay (RIA). It is radioactive tracer as an essential reagent for the development of very sensitive RIA. Direct radiolabeling of theophylline with125I is very difficult due to the absence of appropriate functional groups. Hence carboxylic acid of theophylline was tagged to tyrosine methyl ester and then radiolabeled. The derivatives of theophylline, bearing a propionic acid and butyric acid side chains at seventh and eight position of theophylline, were synthesised and coupled to tyrosine methyl ester. Theophylline-tyrosine methyl ester conjugates were labeled with125I using chlora mine—T. Radiolabeled theophylline was purified by solvent extraction followed by thin layer chromatography. The purified radiolabeled compound were assessed for their radiochemical purity, specific activity and immunoreactivity. Stability studies of radiolabeled compounds were performed with different solvents at different temperatures. Theophylline serum samples analysed using developed and commercial kits showed the correlation coefficient of 0.961 (n=9).