Efeito do sorbitol em relaxação estrutural de filmes de gelatina em estado vítreo

The objective of this work was to study the effect of sorbitol on the kinetic of enthalpy relaxation of gelatin films stored at temperatures below the glass transition temperature (Tg). Bovine gelatin and sorbitol films were prepared by cold casting method. Sorbitol was added at weight fraction (Qs) of 0.0, 0.06 and 0.10. Films were equilibrated in environment of 44% relative humidity using a saturated salt solution of potassium carbonate, giving a moisture weight fraction in samples (Qw) of 0.18, 0.16 and 0.18 respectively. Enthalpy relaxation (∆H) was measured by differential scanning calorimetry (DSC). Tg values of the samples tested were observed at 48ºC (Qs=0.0), 35ºC (Qs=0.06) and 30ºC (Qs=0.10). After the thermal history deletion (30ºC above Tg, 15 minutes), samples were annealed from 2 to 80 hours at 10ºC below Tgonset. The addition of sorbitol showed a significant reduction (p<0.05) in structural relaxation kinetic. The linearization of relaxation enthalpy (∆H) versus log of annealing time showed a reduction of the slope in samples plasticized with sorbitol. The reduction in structural relaxation kinetic could be related to the effect of molecular packing by the presence of polyol in polymer matrix as has been recently reported by Positron Annihilation Spectroscopy (PALS).O objetivo deste estudo foi avaliar o efeito do sorbitol sobre a cinética da relaxação estrutural de películas de gelatina armazenadas a temperatura inferior a temperatura de transição vítrea (Tg). Filmes de gelatina bovina e sorbitol foram preparados por moldagem a frio. O sorbitol foi adicionado em fracções de peso (QS), de 0,0, 0,06 e 0,10. Os filmes foram acondicionados em atmosfera de humidade relativa constante (44%), utilizando uma solução saturada de carbonato de potássio, obtendo-se de frações de teor de humidade de peso (Qw) de 0,18, 0,16 e 0,18, respectivamente. A entalpia de relaxação (DH) foi determinada por Calorimetria Diferencial de Varrimento (DSC). As amostras usadas neste estudo apresentaram valores de Tg de 48°C (Qs = 0,0), 35ºC (Qs = 0,06) e 30ºC (Qs = 0,10). Após eliminar historial térmico (30°C a Tg, 15 minutos), as amostras foram armazenadas isotermicamente a 10°C sob Tgonset entre 2 e 80 horas. A adição de sorbitol produziu uma redução significativa (p <0,05) na cinética da relaxação estrutural. A linearização do valor de entalpia de relaxação (DH) versus o logaritmo do tempo de armazenamento apresentou uma redução do declive nas amostras plastificados com sorbitol. A redução da cinética de relaxamento poderia estar relacionada com o efeito de empaquetamiento molecular associado à presença de polióis em matrizes em estado vítreo recentemente relatado pela espectroscopia de positroês (PALS).El objetivo de este trabajo fue evaluar el efecto del sorbitol sobre la cinética de relajación estructural de películas de gelatina almacenadas bajo la temperatura de transición vítrea (Tg). Películas de gelatina de bovino y sorbitol fueron preparadas mediante casting en frío. El sorbitol fue agregado en fracciones en peso (Qs) de 0,0, 0,06 y 0,10. Las películas fueron acondicionadas en un ambiente de humedad relativa constante (44%) utilizando una solución saturada de carbonato de potasio, obteniéndose fracciones de contenido de humedad en peso (Qw) de 0,18, 0,16 y 0,18 respectivamente. La entalpía de relajación (∆H) fue determinada mediante Calorimetría Diferencial de Barrido (DSC). Las muestras utilizadas en este estudio presentaron valores de Tg de 48ºC (Qs=0,0), 35ºC (Qs=0,06) y 30ºC (Qs=0,10). Luego de eliminar el historial térmico (30ºC sobre Tg, 15min), las muestras fueron almacenadas isotérmicamente a 10ºC bajo Tgonset entre 2 y 80 horas. La adición de sorbitol produjo una reducción significativa (p<0,05) en la cinética de relajación estructural. La linealización del valor de entalpía de relajación (∆H) en función del logaritmo del tiempo de almacenamiento mostró una reducción de la pendiente en las muestras plastificadas con sorbitol. La reducción en la cinética de relajación estaría relacionada con el efecto de empaquetamiento molecular asociado a la presencia de polioles en matrices en estado vítreo recientemente reportada mediante espectroscopía de positrones (PALS)

Efeito do sorbitol em relaxação estrutural de filmes de gelatina em estado vítreo

The objective of this work was to study the effect of sorbitol on the kinetic of enthalpy relaxation of gelatin films stored at temperatures below the glass transition temperature (Tg). Bovine gelatin and sorbitol films were prepared by cold casting method. Sorbitol was added at weight fraction (Qs) of 0.0, 0.06 and 0.10. Films were equilibrated in environment of 44% relative humidity using a saturated salt solution of potassium carbonate, giving a moisture weight fraction in samples (Qw) of 0.18, 0.16 and 0.18 respectively. Enthalpy relaxation (∆H) was measured by differential scanning calorimetry (DSC). Tg values of the samples tested were observed at 48ºC (Qs=0.0), 35ºC (Qs=0.06) and 30ºC (Qs=0.10). After the thermal history deletion (30ºC above Tg, 15 minutes), samples were annealed from 2 to 80 hours at 10ºC below Tgonset. The addition of sorbitol showed a significant reduction (p<0.05) in structural relaxation kinetic. The linearization of relaxation enthalpy (∆H) versus log of annealing time showed a reduction of the slope in samples plasticized with sorbitol. The reduction in structural relaxation kinetic could be related to the effect of molecular packing by the presence of polyol in polymer matrix as has been recently reported by Positron Annihilation Spectroscopy (PALS).O objetivo deste estudo foi avaliar o efeito do sorbitol sobre a cinética da relaxação estrutural de películas de gelatina armazenadas a temperatura inferior a temperatura de transição vítrea (Tg). Filmes de gelatina bovina e sorbitol foram preparados por moldagem a frio. O sorbitol foi adicionado em fracções de peso (QS), de 0,0, 0,06 e 0,10. Os filmes foram acondicionados em atmosfera de humidade relativa constante (44%), utilizando uma solução saturada de carbonato de potássio, obtendo-se de frações de teor de humidade de peso (Qw) de 0,18, 0,16 e 0,18, respectivamente. A entalpia de relaxação (DH) foi determinada por Calorimetria Diferencial de Varrimento (DSC). As amostras usadas neste estudo apresentaram valores de Tg de 48°C (Qs = 0,0), 35ºC (Qs = 0,06) e 30ºC (Qs = 0,10). Após eliminar historial térmico (30°C a Tg, 15 minutos), as amostras foram armazenadas isotermicamente a 10°C sob Tgonset entre 2 e 80 horas. A adição de sorbitol produziu uma redução significativa (p <0,05) na cinética da relaxação estrutural. A linearização do valor de entalpia de relaxação (DH) versus o logaritmo do tempo de armazenamento apresentou uma redução do declive nas amostras plastificados com sorbitol. A redução da cinética de relaxamento poderia estar relacionada com o efeito de empaquetamiento molecular associado à presença de polióis em matrizes em estado vítreo recentemente relatado pela espectroscopia de positroês (PALS).El objetivo de este trabajo fue evaluar el efecto del sorbitol sobre la cinética de relajación estructural de películas de gelatina almacenadas bajo la temperatura de transición vítrea (Tg). Películas de gelatina de bovino y sorbitol fueron preparadas mediante casting en frío. El sorbitol fue agregado en fracciones en peso (Qs) de 0,0, 0,06 y 0,10. Las películas fueron acondicionadas en un ambiente de humedad relativa constante (44%) utilizando una solución saturada de carbonato de potasio, obteniéndose fracciones de contenido de humedad en peso (Qw) de 0,18, 0,16 y 0,18 respectivamente. La entalpía de relajación (∆H) fue determinada mediante Calorimetría Diferencial de Barrido (DSC). Las muestras utilizadas en este estudio presentaron valores de Tg de 48ºC (Qs=0,0), 35ºC (Qs=0,06) y 30ºC (Qs=0,10). Luego de eliminar el historial térmico (30ºC sobre Tg, 15min), las muestras fueron almacenadas isotérmicamente a 10ºC bajo Tgonset entre 2 y 80 horas. La adición de sorbitol produjo una reducción significativa (p<0,05) en la cinética de relajación estructural. La linealización del valor de entalpía de relajación (∆H) en función del logaritmo del tiempo de almacenamiento mostró una reducción de la pendiente en las muestras plastificadas con sorbitol. La reducción en la cinética de relajación estaría relacionada con el efecto de empaquetamiento molecular asociado a la presencia de polioles en matrices en estado vítreo recientemente reportada mediante espectroscopía de positrones (PALS)

Effect of intermolecular interactions on the glass transition temperature of chemically modified alternating polyketones

Thermal properties of polymers depend on the chemical structure of the polymer chain and intermolecular forces arising from hydrogen bonding and π-π stacking. Here we analyzed the effect of increasing the amount of supramolecular interactions on the glass transition temperature of polyketones by chemically modifying the same polymer backbone with five amine derivatives, namely (1-(3-aminopropyl)-imidazole, 4-(aminomethyl) benzoic acid, 6-aminohexanoic acid, benzylamine or hexylamine, at various molar concentrations. The grafting was performed via the Paal-Knorr reaction and the interactions between the pyrrole backbone and different grafted functional groups were elucidated by proton nuclear magnetic resonance, Fourier transform infrared and X-ray photoelectron spectroscopy as well as differential scanning calorimetry and computational modeling. The modification of polyketone with 4-(aminomethyl) benzoic acid and 6-aminohexanoic acid, allowed for new possibilities of hydrogen bonding and led to a significant increase in the glass transition temperature as compared to the neat polymer and pyrrole-containing polymers that did not bear reactive side groups. In contrast, modification with the imidazole derivative was found to introduce new and more robust CH⋯π interactions between imidazole groups and the π-system of the pyrrole backbone chain, based on electrostatic effects. Both types of supramolecular interactions affect the mobility of the backbone chains and this systematic study demonstrates how the combined effect of π-π stacking and hydrogen bonding to carboxylate moieties can be used to tune the molecular mobility and phase transition temperature of these chemically modified polyketones.</p

Mechanical properties and electrical surface charges of microfibrillated cellulose/imidazole-modified polyketone composite membranes

In the present work, microfibrillated cellulose (MFC) suspensions were produced by high-pressure homogenization and subsequently used to fabricate MFC membranes (C-1) by vacuum filtration followed by hot-pressing. A polyketone (PK50) was chemically modified by Paal-Knorr reaction to graft imidazole (IM) functional groups along its backbone structure. The resulting polymer is referred to as PK50IM80. By solution impregnation, C-1 was immersed in an aqueous solution of PK50IM80 and subsequently hot pressed, resulting in the fabrication of MFC/PK50IM80 composite membranes (C-IMP). Another method, referred to as solution mixing, consisted in adding MFC into an aqueous solution of PK50IM80 followed by vacuum filtration and hot-pressing to obtain MFC/PK50IM80 composite membranes (C-MEZC). C-IMP and C-MEZC were characterized by a wide range of analytical techniques including, X-ray photoelectron spectroscopy, Fourier-transform infrared chemical imaging, scanning electron microscopy, atomic force microscopy, dynamical mechanical analysis, tensile testing as well as streaming zeta potential, and compared to C-1 (reference material). The results suggested that C-IMP possess a more homogeneous distribution of PK50IM80 at their surface compared to C-MEZC. C-IMP was found to possess significantly enhanced Young's modulus compared to C-1 and C-MEZC. The tensile strength of C-IMP was found to improve significantly compared to C-1, whereas C-1 possessed significantly higher tensile index than C-IMP and C-MEZC. Furthermore, the presence of PK50IM80 at the surface of MFC was found to significantly shift the isoelectric point (IEP) of the membranes from pH 2.3 to a maximum value of 4.5 for C-IMP. Above the IEP, C-IMP and C-MEZC were found to possess significantly less negative electrical surface charges (plateau value of -25 mV at pH 10) when compared to C-1 (plateau value of -42 mV at pH 10). Our approach may have implication to broaden the range of filtration applications of MFC-based membranes

Highly efficient multifunctional graphene/chitosan/magnetite nanocomposites for photocatalytic degradation of important dye molecules

Multifunctional chitosan/magnetite (CS/Fe3O4) and graphene/chitosan/magnetite (Gr/CS/Fe3O4) nanocomposites (NCs) were synthesized using a simple hydrothermal method. The NCs were subsequently evaluated as magnetic photocatalysts towards the photodegradation of dye molecules that are detrimental to the environment. In the present study, sphere shaped Fe3O4 nanoparticles (NPs) were found to uniformly decorate CS and Gr surfaces. The synthesized Fe3O4 NPs, CS/Fe(3)O(4 )and Gr/CS/Fe3O4 NCs were characterized by powder X-ray diffraction, Fourier-transform infrared and Raman spectroscopy, thermogravimetric analysis, UV-visible diffuse reflectance and photoluminescence spectroscopy, and field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The Gr/CS/Fe3O4 NCs showed 100% photocatalytic efficiency against rhodamine B (40 min), bromothymol blue (60 min), methylene blue (80 min) and methyl orange (100 min) compared to Fe3O4 NPs (100 min for Rh-B, 120 min for BTB, 160 min for MB and 180 min for MO) and CS/Fe3O4 NCs (90 min for Rh-B, 100 min for BTB, 140 min for MB and 150 min for MO). The photocatalytic irradiation efficiency of Fe3O4 NPs, CS/Fe3O4 and Gr/CS/Fe3O4 NCs, evaluated against visible light, was found to be significantly higher for Rh-B (100% within 40 min) compared to the other tested dyes.Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) CONICYT FONDECYT 3180128 CONICYT/FONDEQUIP EQM130149 FONDEQUIP EQM15010

Graphene/nickel oxide nanocomposites against isolated ESBL producing bacteria and A549 cancer cells

The synthesis of nickel oxide nanoparticles (NiO NPs)and graphene/nickel oxide nanocomposites (Gr/NiO NCs)was performed using a simple chemical reduction method. Powder X-ray diffraction (XRD)and thermogravimetric analysis (TGA)were used to examine the crystalline nature and thermal stability of the synthesized NiO NPs and Gr/NiO NCs, respectively. Scanning electron microscopy (SEM)and transmission electron microscopy (TEM)were utilized to observe the morphology of NiO NPs and Gr/NiO NCs and estimate their size range. TEM suggested that the NiO NPs were speared onto the surface of Gr nanosheet. The efficiency of NiO NPs and Gr/NiO NCs against extended spectrum β-lacamase (ESBL)producing bacteria, which was confirmed by specific HEXA disc Hexa G-minus 24 (HX-096)and MIC strip methods (CLSI); namely Escherichia coli (E. coli)and Pseudomonas aeruginosa (P. aeruginosa)was investigated using the minimal inhibitory concentration (MIC)and minimal bactericidal concentration (MBC)methods. MIC results suggested that the NiO NPs and Gr/NiO NCs possess maximum growth inhibition of 86%, 82% and 94%, 92% at 50 and 30 μg/mL concentrations, respectively. Similarly, both nanomaterials were found to inhibit the β-lacamase enzyme at concentrations of 60 μg/mL and 40 μg/mL, respectively. The cytotoxicity of NiO NPs and Gr/NiO NCs was quantified against A549 human lung cancer cells. Cell death percentage values of 52% at 50 μg/mL against NiO NPs and 54% at 20 μg/mL against Gr/NiO NCs were obtained, respectively. The NCs were found to reduce cell viability, increase the level of reactive oxygen species (ROS)and modify both the mitochondrial membrane permeability and cell cycle arrest

Anti-ESBL investigation of chitosan/silver nanocomposites against carbapenem resistant Pseudomonas aeruginosa

In the present investigation functional chitosan/silver nanocomposites (CS/Ag NCs) were successfully synthesized and found to possess favorable antibacterial activity against extended spectrum beta-lactasame (ESBL) producing Pseudomonas aeruginosa. Powder X-ray diffraction showed that the obtained CS/Ag NCs are constituted of highly crystalline Ag nanoparticles (NPs) embedded in an amorphous CS matrix material. Transmission electron microscopy (TEM) analysis provided structural information about CS/Ag NCs, revealing the formation of spherical cluster structures constituted of Ag NPs with size ranging from 6 to 18 nm embedded in the amorphous CS matrix. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Ag NPs and CS/Ag NCs were found to inhibit the ESBL producing P. aeruginosa at 80 μg/mL (76%) and 50 μg/mL (92%), respectively. Confocal laser scanning microscope (CLSM) and scanning electron microscopy (SEM) images revealed that P. aeruginosa experienced reduced cell viability and morphological cell membrane damage at desired MIC. The in-vivo toxicity effect of Ag NPs and CS/Ag NCs suggested an increased mortality rate when Artemia franciscana were exposed for 24 h to increasing concentrations of Ag NPs and CS/Ag NCs. Anti-ESBL activity and toxicity effect of CS/Ag NCs revealed that these NCs possess promising antibacterial properties to overcome numerous communicable bacterial strains

Chitosan/silver nanocomposites for colorimetric detection of glucose molecules

This study was about the simple method for the rapid colorimetric and visual detection of glucose molecules in water medium. Silver nanoparticles were spread on the chitosan surface (CS/Ag NCs) and it was characterized by UV–visible spectroscopy, fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The CS/Ag NCs displayed a strong surface plasmon resonance band at 429 nm which disappears in the addition of accelerative concentrations of glucose molecules and it was attended by color alteration from yellow to colorless. The interaction of glucose molecules on the CS/Ag NCs was displayed through TEM technique. Glucose molecules was detected not only by naked eyes (from yellow to purple grey) but also by UV–vis spectrophotometer in the concentration range between 0 and 100 μM, with limit detection of 5 μM and a good linear relationship of R2 value = 0.99. The proposed paper was used for the application of the detection of glucose molecules in water sample with adequate outcome. This CS/Ag NCs was very simple and low cost system without using any other enzymatic catalyst and organic chromogenic agents for glucose molecules detection