Synthesis and characterization of liquid crystalline polymethacrylates,polyacrylates, and polysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene-based mesogenic groups

The synthesis and characterization of polymethacrylates and polyacrylates containing 4-methoxy-4′-hydroxy-α-methylstilbene side groups attached either directly or through flexible spacers containing eleven, eight, six, three, and respectively two methylenic units, and of the polysiloxanes containing the same mesogenic group connected through flexible spacers containing eleven, eight, six, and respectively three methylenic units are described. All polymers exhibit thermotropic liquid crystallinity. The nature of the mesophase is determined by the spacer length. However, the nature of the polymer backbone determines the thermal stability of the mesophase. That is, for the same spacer length and similar polymer molecular weight, the most flexible polymer backbone leads to the highest isotropization temperature.     

Alkyd resins derived from glycolized waste poly(ethylene terephthalate)

In this investigation the production of secondary value-added products, such as alkyd resins, derived from the glycolysis of poly(ethylene terephthalate) (PET) is examined as an effective way for its recycling. PET was taken from common soft-drink bottles and diethylene glycol (DEG) was used for the depolymerization at several initial molar ratios. The oligomers obtained were analyzed according to their average molecular weights. Furthermore, the glycolyzed PET products (oligomers) were reacted with maleic anhydride, phthalic anhydride and propylene glycol to form unsaturated polyester resins. These were subsequently mixed with styrene and cured using the benzoyl peroxide/amine initiator system to carry out the reaction in ambient temperature. The curing characteristics of the resins produced were investigated with respect to the initial molar ratio of DEG/PET as well as the initial initiator concentration. Finally, the mechanical properties (tensile strength and elongation at the break point) of the resins were compared with the conventional general purpose resin and were found to be comparable.     

Photochemically Induced Solid-State Degradation, Condensation, and Rearrangement Reactions in Lignin Model Compounds and Milled Wood Lignin

Abstract— Milled wood lignin produced from alkaline hydrogen peroxide-bleached softwood thermomechanical pulp (TMP) fibers was adsorbed on pure cellulose and irradiated for variable periods of time under oxygen and/or nitrogen. The absolute amounts of β-O-4 ethers, phenolic hydroxyl groups, carboxylic acids and various condensed phenolic units were quantified, nondestructively, using ³¹P NMR spectroscopy. Photoirradiation was found to severely cleave the β-O-4 ethers present in lignin with the concomitant formation of new phenolic units. The rate of this cleavage was found to be faster under oxygen than under nitrogen. The catalytic role of oxygen can be rationalized by invoking the formation of peroxy free radicals that may initiate new sites of radical generation ( e.g. ketyl radicals) within the lignin causing the subsequent breakdown of the β-O-4 linkage. The photoirradiation was found to cause a net increase of the C₅-related condensed phenolic units in lignin. Among these, C_α-C₅ and/ or C_β-C₅ phenolic moieties were found to predominate. Similar irradiation of a binary mixture of model compounds resembling structures present in softwood lignin resulted in 18 products that were identified and quantified using gas chromatography coupled to mass spectrometry. The photochemical products obtained supported the phenacyl and ketyl mechanistic pathways to pho-toyellowing, whereas the detection of β-5 coupling products (common in both the model compound and milled wood lignin studies) may point a new avenue toward the formation of light-induced products that has not been previously considered in the solid state.     

Phenotypic and Target-Directed Screening Yields New Acaricidal Alternatives for the Control of Ticks

Rhipicephalus microplus, the “common cattle tick”, is the most important ectoparasite in livestock worldwide due to the economic and health losses it produces. This tick is a vector for pathogens of several tick-borne diseases. In Latin American countries, damages reach approximately USD 500 million annually due to tick infections, as well as tick-borne diseases. Currently, resistant populations for every chemical group of acaricides have been reported, posing a serious problem for tick control. This study aims to find new alternatives for controlling resistant ticks with compounds derived from small synthetic organic molecules and natural origins. Using BME26 embryonic cells, we performed phenotypic screening of 44 natural extracts from 10 Mexican plants used in traditional medicine, and 33 compounds selected from our chemical collection. We found 10 extracts and 13 compounds that inhibited cell growth by 50% at 50 µg/mL and 100 µM, respectively; the dose-response profile of two of them was characterized, and these compounds were assayed in vitro against different life stages of Rhipicephalus microplus. We also performed a target-directed screening of the activity of triosephosphate isomerase, using 86 compounds selected from our chemical collection. In this collection, we found the most potent and selective inhibitor of tick triosephosphate isomerase reported until now. Two other compounds had a potent acaricidal effect in vitro using adults and larvae when compared with other acaricides such as ivermectin and Amitraz. Those compounds were also selective to the ticks compared with the cytotoxicity in mammalian cells like macrophages or bovine spermatozoids. They also had a good toxicological profile, resulting in promising acaricidal compounds for tick control in cattle raising.     

Study of the 'teaching system' according to systems theory

The traditional triadic 'Teaching System' (the teacher, the student and mathematics) and the new quaternary version (the teacher, the student, mathematics and new technologies), are studied according to Systems Theory. Systems Theory is described and the model of the traditional 'Teaching System' and that of the new system are analysed with the aid of this theory; that is the structure of each system (elements, interactions) and its function are described. Finally, comments are made about the application of the new system on didactic, on the one hand, and the philosophical background of the incorporation of the fourth element (new technologies) in the traditional system, on the other.     

Bootstrap robust prescriptive analytics

Mathematical Programming - We address the problem of prescribing an optimal decision in a framework where the cost function depends on uncertain problem parameters that need to be learned from...     

Ionic liquid crystals derived from the protonation of poly(propylene imine) dendrimers with a cholesterol-based carboxylic acid

The liquid crystalline character of salts resulting from the interaction of poly(propylene imine) dendrimers with 3-cholesteryloxycarbonylpropanoic acid has been studied. The supramolecular structure and consequently the observed liquid crystalline phases are dictated by the degree of protonation of primary amino groups as compared with that of tertiary ones, determined by FTIR spectroscopy in the bulk and by NMR spectroscopy in solution. Glass transition temperatures of the materials are about 38°C. At higher temperatures they are transformed to smectic C* phases while a second-order smectic C phase to smectic A phase transition is observed between 90 and 110°C depending on dendrimer generation. At about 150°C the onset of degradation is observed. The influence of the ionic dendrimeric scaffold on the thermotropic properties is discussed.