Browsing by Autor "Dimas Medina"

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    Cinética de la degradación enzimática de quitosano usando bromelina: un estudio viscosimétrico.
    (Universidad de Los Andes, 2007) Cristóbal Lárez Velásquez; Dimas Medina; Carlos Torres Guzmán; Enrique J. Millán Barrios
    Enzymatic degradation of chitosan (degree of acetylation (da) and average viscosimetric molecular weight (MV) of 0.85 and 310 kDa, respectively) was carried out using commercial bromelain. Decrease of the average viscosimetric polymerization degree (XV) was studied in a buffer solution of acetic acid (0.3 M)/sodium acetate (0.2 M) at 25 oC.Under these experimental conditions it is possible to relate the instantaneous intrinsic viscosity [?] with MV through the Mark-Houwink-Sakurada equation. Equations of Sano, Solomon-Ciuta, Deb-Chatterjee and Ram-Yaseen, whichallow to compute values of [?] with a single measurement of relative (?rel) and/or specific viscosity (?sp), were employed to obtain instantaneous values of [?]. Instantaneous values of [?] were also obtained through an iterative process using Huggins equation. Initial velocity of depolymerization (vo) was obtained from different concentration of chitosan solutions and a fixed bromelain concentration. Michaelis-Menten constant (kM) and maximum velocity(Vm) were obtained using the Lineweaver-Burk representation of the Michaelis-Menten equation for each set of [?]which were calculated employing all procedures mentioned. Best kinetic parameters for chitosan depolymerization(kM=3.92x10-7 mol.dL-1; Vm=9.09x10-8 mol.dL-1.s-1) were obtained when Sano`s equation was employed to calculate[?] values.
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    Síntesis y polimerización de bis-macromonómeros de poli(E-caprolactona)
    (2016) Jesús Contreras; Dimas Medina; Francisco López Carrasquero
    Poly(e-caprolactone) (PCL) bis -macromonomer was obtained by the esterification reaction of poly(e-caprolactone) diol with acryloyl chloride. The functionalization of the end-groups of the polymer chains was in the order of 40 % as determinate by proton nuclear magnetic resonance ( 1 H-NMR). Then, PCL networks synthesis was performed and theirs thermal behavior, swelling degree and hydrophilic and hydrophobic interactions were analyzed. The network swelling degree is depended on the degree of polymerization of the bis-macromonomer. The PCL networks swelled considerably in slightly polar and non-polar solvents.