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      Dynamic light scattering and viscosimetry of aqueous solutions of pectin, sodium alginate and their mixtures: effects of added salt, concentration, counterions, temperature and chelating agent

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          Abstract

          The effects of added salt, concentration, counterions, temperature and chelating agent on aqueous solutions of pectin, sodium alginate and their mixtures were analyzed by viscosimetry and dynamic light scattering (DLS) techniques. The intrinsic viscosity of the binary systems decreased with the addition of salt and with temperature, while it was found to be insensitive to the addition of NaEDTA. As expected the intrinsic viscosity of the ternary alginate/pectin/water system was equal to the average of the intrinsic viscosity for the binary systems. The DLS studies indicated a bimodal distribution (fast and slow relaxation modes) for both binary and ternary systems at 25 °C, reflecting aggregation. A significant increase in the hydrodynamic radius, in the case of the slow mode, was observed for the binary and ternary systems in the presence of NaCl and KCl at 25 °C. However, at 80 °C the hydrodynamic radius for the slow mode in KCl solutions was practically constant for all the studied systems, except for the alginate binary solutions in which were not observed.

          Translated abstract

          Efeitos de adição de sal, concentração, presença de contraíons, temperatura e agente quelante em soluções aquosas de pectina, alginato de sódio e misturas destes foram analisadas por viscosimetria e espalhamento de luz dinâmico (DLS). A viscosidade intrínseca dos sistemas binários diminuiu com a adição de sal e com o aumento da temperatura, porém, mostrou-se insensível à adição de NaEDTA. Como esperado, a viscosidade intrínseca do sistema ternário alginato/pectina/água foi igual a média da viscosidade intrínseca determinada para os sistemas binários. Estudos de DLS indicaram a ocorrência de uma distribuição bimodal (presença dos modos de relaxação rápido e lento) para ambos os sistemas binários e ternários a 25 °C, refletindo um processo de agregação. No caso do modo lento de relaxação, um aumento significativo do raio hidrodinâmico foi observado tanto para os sistemas binários como ternário, na presença de NaCl e KCl a 25 °C. No entanto, a 80 °C, o raio hidrodinâmico correspondente ao modo lento em soluções de KCl foi praticamente constante para todos os sistemas estudados e não foi observado para o sistema binário alginato/solução aquosa.

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          Most cited references60

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          Biopolymers from Renewable Resources

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            A molecular dynamics simulation of the flavin mononucleotide-RNA aptamer complex.

            We report on an unrestrained molecular dynamics simulation of the flavin mononucleotide (FMN)-RNA aptamer. The simulated average structure maintains both cross-strand and intermolecular FMN-RNA nuclear Overhauser effects from the nmr experiments and has all qualitative features of the nmr structure including the G10-U12-A25 base triple and the A13-G24, A8-G28, and G9-G27 mismatches. However, the relative orientation of the hairpin loop to the remaining part of the molecule differs from the nmr structure. The simulation predicts that the flexible phosphoglycerol part of FMN moves toward G27 and forms hydrogen bonds. There are structurally long-lived water molecules in the FMN binding pocket forming hydrogen bonds within FMN and between FMN and RNA. In addition, long-lived water is found bridging primarily RNA backbone atoms. A general feature of the environment of long-lived "structural" water is at least two and in most cases three or four potential acceptor atoms. The 2'-OH group of RNA usually acts as an acceptor in interactions with the solvent. There are almost no intrastrand O2'H(n) vertical ...O4'(n + 1) hydrogen bonds within the RNA backbone. In the standard case the preferred orientation of the 2'-OH hydrogen atoms is approximately toward O3' of the same nucleotide. However, a relatively large number of conformations with the backbone torsional angle gamma in the trans orientation is found. A survey of all experimental RNA x-ray structures shows that this backbone conformation occurs but is less frequent than found in the simulation. Experimental nmr RNA aptamer structures have a higher fraction of this conformation as compared to the x-ray structures. The backbone conformation of nucleotide n + 1 with the torsional angle gamma in the trans orientation leads to a relatively short distance between 2'-OH(n) and O5'(n + 1), enabling hydrogen-bond formation. In this case the preferred orientation of the 2'-OH hydrogen atom is approximately toward O5'(n + 1). We find two relatively short and dynamically stable types of backbone-backbone next-neighbor contacts, namely C2'(H)(n) vertical ...O4'(n + 1) and C5'(H)(n + 1) vertical ...O2'(n). These interactions may affect both backbone rigidity and thermodynamic stability of RNA helical structures.
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              Macromolecules in solution

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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                jbchs
                Journal of the Brazilian Chemical Society
                J. Braz. Chem. Soc.
                Sociedade Brasileira de Química (São Paulo )
                1678-4790
                2009
                : 20
                : 9
                : 1705-1714
                Affiliations
                [1 ] Universidade Federal de Santa Catarina Brazil
                [2 ] Joseph Fourier University France
                Article
                S0103-50532009000900020
                10.1590/S0103-50532009000900020
                0787f476-56c9-42e0-b1a4-afd0b29cb70d

                http://creativecommons.org/licenses/by/4.0/

                History
                Product

                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0103-5053&lng=en
                Categories
                CHEMISTRY, MULTIDISCIPLINARY

                General chemistry
                pectin,sodium alginate,viscosity,salt effect,dynamic light scattering
                General chemistry
                pectin, sodium alginate, viscosity, salt effect, dynamic light scattering

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