Temperature-and pH-Sensitive Nanohydrogels of Poly(N-Isopropylacrylamide) for Food Packaging Applications: Modelling the Swelling-Collapse Behaviour

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

ph eta kontzentrazioaren eragina, erretxina kelanteen gainean egindako ioi trukaketa prozesuan

Azken urte hauetan industriak izan duen garapenak, onura asko ekarri ditu, hala nola, bizi maila eta kalitatea gora egin dute. Baina dena ez dira alde onak, izan ere, prozesu honek, kutsagarriak eta oso konplexuak diren hondakinak sortu ditu. Kutsadura hau ez du soilik oreka ekologikoa n kalte egiten, izan ere, kutsadura hau dagoen guneetan ere eragin handia dauka. Hori dela eta , ingurumenaren babesa gero eta garrantzi handiagoa hartzen ari da. Horretarako, industriak sortzen dituen hondakinen tratamendurako prozesuetan, inbertsio ekonomiko handiak egin behar dira. Hau ez da soilik legea betetzeko egin behar, baizik eta, indus tria merkatuan dagoen konpetentzian toki on bat lortzeko oso garrantzitsua da. Jariakinen tratamenduaren xedea dituzten araztegiak duten arazo printzipala, jariakin hauetan dauden metal astunen presentzia da. Metal hauek, araztegi hauetan ematen diren pro zesu biologikoen zai ltasuna bermatzen dute eta animali, landare eta giza osasunean efektu toxikoak izaten dituzte. Baimenduta dauden kontzentrazioen limitea betetzeko, industriak normalean isurketan egin baino lehen, aurretratamendu bat egitera behartuta ikusten dira, toxikoak diren edo oso oldarkorrak diren produktuak kentzeko. Adibidez, Industria Hidrometalurgiakoak , oso kontzentrazio baxuetan metal astunak isurtzen ditu, baina kantitate hauek baimenduta daude, industria hau erabiltzen dituen emari handiak direla eta. Normalean hondakin industrialetatik kanpora isurt zen diren metal astunak , kontzentrazio baxuetan eg ot en dira . Honek, errentagarritasun positiboa du ten araztegi tekniken aplikazioa ahalbideratzen du. Kutsadura hau sortzen dituzten prozesu industrial mota asko existitzen direnez, metal hauek, oso diluituak dauden disoluzioetatik banatu behar dira. Horretara ko, metal baliotsuen errekuperazioa eta isurketa industrialaren legeak betetzea bermatzen duten, banaketa prozesuak sortu behar izan d ira. Jarraian, helburu hau duten teknika batzuk azaltzen dira

Temperature-and pH-Sensitive Nanohydrogels of Poly(N-Isopropylacrylamide) for Food Packaging Applications: Modelling the Swelling-Collapse Behaviour

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

Estudio de la homodimerización del dominio PH de la quinasa PDK1 por espectroscopía por correlación de la emisión fluorescente (FCS)

El objetivo de este trabajo es comprobar la homodimerización del dominio PH de la PDK1 in vitro.

Photosynthetic responses of trees in high-elevation forests: comparing evergreen species along an elevation gradient in the Central Andes

Plant growth at extremely high elevations is constrained by high daily thermal amplitude, strong solar radiation and water scarcity. These conditions are particularly harsh in the tropics, where the highest elevation treelines occur. In this environment, the maintenance of a positive carbon balance involves protecting the photosynthetic apparatus and taking advantage of any climatically favourable periods. To characterize photoprotective mechanisms at such high elevations, and particularly to address the question of whether these mechanisms are the same as those previously described in woody plants along extratropical treelines, we have studied photosynthetic responses in Polylepis tarapacana Philippi in the central Andes (18 degrees S) along an elevational gradient from 4300 to 4900 m. For comparative purposes, this gradient has been complemented with a lower elevation site (3700 m) where another Polylepis species (P. rugulosa Bitter) occurs. During the daily cycle, two periods of photosynthetic activity were observed: one during the morning when, despite low temperatures, assimilation was high; and the second starting at noon when the stomata closed because of a rise in the vapour pressure deficit and thermal dissipation is prevalent over photosynthesis. From dawn to noon there was a decrease in the content of antenna pigments (chlorophyll b and neoxanthin), together with an increase in the content of xanthophyll cycle carotenoids. These results could be caused by a reduction in the antenna size along with an increase in photoprotection. Additionally, photoprotection was enhanced by a partial overnight retention of de-epoxized xanthophylls. The unique combination of all of these mechanisms made possible the efficient use of the favourable conditions during the morning while still providing enough protection for the rest of the day. This strategy differs completely from that of extratropical mountain trees, which uncouple light-harvesting and energy-use during long periods of unfavourable, winter conditions.