Ionically modified LCST polymers were synthesized by free radical copolymerization of N-isopropylacrylamide (NIPAM) with various cationic, anionic, and amphoteric comonomers, resulting in products with comparable molecular masses and charge concentrations. The temperature-dependent phase transition behavior of the copolymers was investigated in water, aqueous sodium chloride solutions, and mixtures of water with dimethylformamide (DMF) using light transmission measurements, static light scattering, viscometry, and sedimentation experiments in an analytical ultracentrifuge. The LCST of the cationic modified copolymers remains unchanged compared with the homopolymer, but it is increased as a result of an amphoteric or anionic modification. Phase transitions are accompanied by conformational changes followed by aggregation processes. These changes are enhanced in the presence of salt. The phase transition of poly-NIPAM-co-MADAMBQ ((methacryloyloxy)ethyl)dimethylbenzylammonium chloride) in 0.5 M NaCl was studied in detail investigating the temperature dependence of molecular parameters as intrinsic viscosity, particle mass, radius of gyration, second virial coefficient, and sedimentation coefficient.
The synthesis of defined polyelectrolyte models by radical copolymerization of diallyldimethylammonium chloride (DADMAC, M,) and acrylamide (AAM, M2) in aqueous solution is impeded by a large difference of the reactivity ratios (rl 4 r2) leading to a strong conversion dependence of the copolymer composition. For the synthesis of normally distributed polyelectrolytes of the same molecular weight with various charge densities, a general algorithm based on a feeded polymerization with dosage of the more reactive monomer was therefore developed.Various copolymer compositions predictable by the Mayo-Lewis equation and determined by chloride potentiometry were obtained. The sequence lengths distributions investigated by I3C NMR spectroscopy followed a Markov statistic of first order. The 13C NMR spectroscopy is shown as alternative method to gravimetry in determining reactivity ratios. The partial specific volumes and the refractive index increments of the copolymers correspond to the additivity principle. Further molecular and dynamic parameters are determined by membrane osmometry, static and dynamic light scattering, analytical ultracentrifugation, gel permeation chromatography, and viscometry. Monomodal molecular weight distributions, small polydispersities only for copolymers with high content of DADMAC are obtained at given comonomer and initiator concentration. The number-average molecular weight is almost constant for a broad copolymer composition range.R,-M and [q]-M relations could be established for practical use at high ionic strength, despite the various chemical compositions. Some indications for a higher stiffness of copolymers with high contents of DADMAC despite the shielding of the electrostatic interactions are, however, given. At low ionic strength the electrostatic interactions prevail. Their influence with increasing charge density is stronger on
Kinetics of the free radical polymerization of dimethyl diallyl ammonium chloride, 5" Kinetic model with persulfate as initiatorS20i-und C1-, der und mit Chloratomen.Konstanten und Parameter numerische Werte ermittelt wurden.
Radical copolymerization of maleic acid with allyl amine or diallyl amine derivatives results in regular polyampholytes which are completely or to high extent soluble in water. With equimolar amounts of both comonomers the rate of the alternating copolymerization runs through a minimum. The copolymers are thermally relatively stable and can be changed to water insoluble products by tempering.
Spodoptera frugiperda insect cells (Sf9) containing the stably integrated human P,-adrenergic receptor gene under the control of the baculovirus IE1 promoter expressed up to 350000 human receptorskell. The number of receptors did not change with cell density or age of culture. The adrenergic receptors overexpressed in the insect cells were functional with respect to their ligand binding and signalling properties. Coupling of the receptors to endogenous GTP-binding proteins is demonstrated by hormone-dependent stimulation of GTPase and adenylyl cyclase activity in the transformed insect cells. Western-blot analysis revealed that the endogenous GTP-binding protein appears to be of the heterotrimeric type. Antibodies raised against the mammalian a subunit of stimulatory GTP-binding proteins cross-react with the insect a subunit of GTP-binding proteins, which also exhibits the same apparent molecular mass as its mammalian counterpart. The p subunit of GTP-binding proteins from insect cells reacts with anti-peptide serum directed against the Cterminal amino acids of the mammalian / 3 subunit of GTP-binding proteins, but is about =2 kDa larger than that of the P subunit of GTP-binding proteins from bovine brain. Exposure of the transformed insect cells to L-isoproterenol rapidly induces uncoupling and internalization of 30 % of the heterologously expressed receptors. In contrast to the situation in mammalian cells, prolonged exposure of the agonist (24 h) does not result in down regulation of the remaining 70% of the receptors.Mammalian P-adrenergic receptors CB,AR) have been introduced into several heterologous expression systems for extensive pharmacological and biochemical analysis, including Escherichia coli (Marullo et al., 1989(Marullo et al., ,1990, yeast (King et al., 1990), Xenopus oocytes (Frielle et al., 1988;Kobilka et al., 1988), several mammalian cell lines Fraser et al., 1987;Hen et al., 1989;Lohse, 1992;Rands et al., 1990;Wang et al., 1989) and insect cells, using the baculovirus expression system (George et al., 1989;Reiliinder et al., 1991). Evidence has been presented that mammalian P,AR functionally couple to insect adenylyl cyclase in cells of Spodoptera frugiperda (Sf9) . However, little is known about the signal-transduction pathway in these invertebrate cells. Despite the several advantages which have made the baculovirus expression system a popular method of engineering richer sources of recombinant protein, analysis of insect proteins that are known to functionally interact with the foreign proteins has been hampered. This is because the transient expression that occurs after the cells have been infected with the recombi- nant baculovirus is a cytotoxic event that stops the transcription and translation of insect proteins and ultimately kills the cells. To facilitate further biochemical and biophysical characterization of P,AR, taking advantage of the stability and robust nature of insect ovarian cells, we have used the promoter of the IE1 gene (an immediate early gene of the baculovirus Aut...
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