Fluid phase behavior modeling of CO2 + molten polymer systems using cubic and theoretically based equations of state

Phase equilibrium data of CO₂ + molten polymer systems are of great relevance for chemical engineers because these are necessary for the optimal design of polymer final‐treatment processes. This kind of processes needs information about gas solubilities in polymers at several temperatures and pressures. In this work, CO₂ solubilities in molten polymers were modeled by the perturbed chain‐statistical associating fluid theory (PC‐SAFT) equation of state (EoS). For comparison, the solubilities were also calculated by the lattice gas theory (LGT) EoS, and by the well‐known Peng‐Robinson (PR) cubic EoS. To adjust the interactions between segments of mixtures, there were used classical mixing rules, with one adjustable temperature‐dependent binary parameter for the PC‐SAFT and PR EoS, and two adjustable binary parameters for the LGT EoS. The results were compared with experimental data obtained from literature. The results in terms of solubility pressure deviations indicate that the vapor–liquid behavior for CO₂ + polymer systems is better predicted by the PC‐SAFT model than by LGT and PR models. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Strategies to Modulate Specialized Metabolism in Mediterranean Crops: From Molecular Aspects to Field

Plant specialized metabolites (SMs) play an important role in the interaction with the environment and are part of the plant defense response. These natural products are volatile, semi-volatile and non-volatile compounds produced from common building blocks deriving from primary metabolic pathways and rapidly evolved to allow a better adaptation of plants to environmental cues. Specialized metabolites include terpenes, flavonoids, alkaloids, glucosinolates, tannins, resins, etc. that can be used as phytochemicals, food additives, flavoring agents and pharmaceutical compounds. This review will be focused on Mediterranean crop plants as a source of SMs, with a special attention on the strategies that can be used to modulate their production, including abiotic stresses, interaction with beneficial soil microorganisms and novel genetic approaches.     

Implicit Riquier Bases for PDAE and their semi-discretizations

Complicated nonlinear systems of pde with constraints (called pdae) arise frequently in applications. Missing constraints arising by prolongation (differentiation) of the pdae need to be determined to consistently initialize and stabilize their numerical solution. In this article we review a fast prolongation method, a development of (explicit) symbolic Riquier Bases, suitable for such numerical applications. Our symbolic-numeric method to determine Riquier Bases in implicit form, without the unstable eliminations of the exact approaches, applies to square systems which are dominated by pure derivatives in one of the independent variables.     

Modelling the respiration rate of fresh-cut Annurca apples to develop modified atmosphere packaging

In this work, the effect of temperature, oxygen, red coloration process and post-harvest storage time on the respiration rate of fresh-cut Annurca apples was studied to properly develop modified atmosphere packaging. Our results showed that the red coloration process and the post-harvest storage time did not affect the respiration rate or the respiratory quotient of fresh-cut Annurca apples in the range of temperature studied (5–20 °C). A Michaelis–Menten-type equation, with the model constants described by means of an Arrhenius-type relationship, was used for predicting respiration rate on varying the temperature and O₂ concentration in the head space. The maximal respiration rate (mL kg h⁻¹) (RR_max) and the O₂% corresponding to     values estimated at the reference temperature (12.5 °C), i.e. the average of the experimental temperature ranges, were, respectively, 6.77 ± 0.1 mL kg⁻¹ h⁻¹ and 0.68 ± 0.07% v/v, and the activation energy of the aerobic respiration rate of fresh-cut Annurca apples was estimated at 51 ± 1 kJ mol⁻¹. The model works well to develop a modified atmosphere for fresh-cut Annurca apples.     

Correlation of analyte structures with biosensor responses using the detection of phenolic estrogens as a model

The apparent increase in hormone-induced cancers and disorders of the reproductive tract in wildlife and humans has led to a search for an accurate and reliable method for monitoring endocrine-disrupting chemicals (EDCs). This study presents a generic approach that may allow researchers to establish screening procedures for potential EDCs by correlating the analyte structures with biosensor responses and explain possible reaction mechanisms. A simple amperometric tyrosinase-based biosensor (Tyr-CPE) has been developed for the detection of phenolic EDCs. The investigation of the enzymatic oxidation of selected phenolic estrogens was first carried out using UV-vis spectroscopy. The result was used to correlate sensor responses to enzymatic activity. Natural phytoestrogen polyphenols, including resveratrol (RES), genistein (GEN), and quercetin (QRC), were compared with synthetic estrogens, for example, bisphenol A (BPhA), nonylphenol (NPh), and diethylstilbestrol (DES). The Tyr-CPE biosensor resulted in rapid, simple, and accurate measurement of phenolic estrogens with varying degrees of sensitivity, selectivity, and response times. The sensor responses have been evaluated for the detection of binary and tertiary mixtures of EDCs and natural estrogens. The results showed that BPhA could be successfully discriminated in a composite mixture containing NPh and DES at various ratios. In the case of natural phenolic estrogens GEN, RES, and QRC, the sensor allows the determination of a total phenolic content. The sensor was also validated for the detection of BPhA in a real environmental water sample, and the results was compared with standard ASTM method 9065. Mechanistically, our results indicated that the number of OH groups, the nature and the position of aryl ring substituents, or both could affect the detection limit and the biosensor sensitivity.     

Bonding ability of self-adhesive resin-cements after dentin biomodification with hyaluronic acid

Purpose: The present study evaluated the influence of the hyaluronic acid (HA) on the bonding ability of self-adhesive resin cements to dentin regarding the bond strength. Eighty bovine incisors were ground flat to obtain a 2-mm thick slices which received conical preparations. The specimens were randomly distributed into 4 groups (n = 15) according to the dentin pretreatment (1 – control: untreated dentin; 2 – application of HA) and the evaluation time (1 – control: immediate evaluation; 2 – hydrolytic degradation: 6 months of storage in water at 37 °C). Preparations received the application of a self-adhesive resin cement (RelyX U200 or MaxCem Elite). Push-out bond strength test was conducted (0.5 mm/min). The bond strength data was submitted to two-way ANOVA/Tukey’s test (α = 0.05). For U200, no significance was observed when comparing the immediate (24 h) and 6 months means for the control groups (unexposed specimens). Previous application of HA to dentin significantly reduced the bond strength of U200 to dentin in both evaluation times (p < 0.05). HA had no significant influence on the push-out bond strength means for the cement MAX in both evaluation times (p > 0.05). The type 1 failure mode (adhesive mode) occurred in 100% of the specimens, irrespective of the dentin treatment or evaluation times. Pretreatment of dentin with HA produces a material-dependent influence on the push-out bond strength. The bonding ability of RelyX U200 is negatively influenced by the pretreatment of dentin with HA, whereas the biomodification of dentin with this bioactive agent causes no impact for the cement MaxCem Elite.