The goal of the present study was to determine the potential use of thermal analysis for the measurement of the light crude oil (LCO) content of standard biodiesel mixtures. Standard samples of biodiesel/LCO blends were prepared with different ratios of biodiesel; LCO: 1:0 (biodiesel only), 1:3, 1:1, 3:1, 0:1 (LCO only). Thermogravimetry (TG) and differential scanning calorimetry were used to determine the usefulness of thermal analysis for quantification of the LCO in the mixtures. Proton nuclear magnetic resonance (1H NMR) spectroscopy was also used to confirm the composition of the samples. It was found that thermogravimetric curves were not appropriate for the LCO measurements. However, the DSC signal of wax crystallization exhibited a good linear (R2 = 0.99) correlation with the LCO content in the blend. Furthermore, it was shown that aliphatic protons (-CH2-)n in biodiesel and light crude oil can also be used to determine LCO in biodiesel/LCO blends.

Abstract Bioresorbable linear poly(ether-ester-urethane)s with different hydrophilic characteristics were synthesized from triblock copolymers of poly(ε-caprolactone)-poly(ethylene oxide)-poly(ε-caprolactone) (PCL-PEO) as macrodiols, and L-lysine diisocyanate (LDI) or hexamethylenediisocyanate (HDI) were used as the required diisocyanates. Macrodiols were obtained by ring-opening polymerization (ROP) of ε-caprolactone (CL). Polyurethanes were synthesized by the reaction of the triblock copolymers with LDI or HDI in solution using stannous 2-ethylhexanoate as catalyst. Polyurethane tablets were fabricated and investigated as prospective drug delivery systems. The effect of the PEO content on the polymers' performance as drug carriers was evaluated. It was found that water provoked more swelling and erosion of polymers with higher contents of PEO. The hydrocortisone release profiles were analyzed using the Ritger-Peppas approximation. An anomalous release behaviour (values of n higher than 0.5) was found for most of the analyzed samples.

In this paper a joint theoretical and experimental study examines the ability of diethyleneglycol as a ligand to form silicon complexes. Due to the known oxophilia of the silicon atom, it would be expected that in the reaction of this tridentate O,O,O-donor-ligand with a reagent such as SiCl4, the corresponding bis-chelate, hexacoordinated neutral silicon complex may be formed. However, a spirocyclic tetracoordinated silicon bis-chelate complex was isolated and no evidence of formation of any hypervalent alkoxysilane was observed. The tetracoordinated compound, 1,4,7,9,12,15-Hexaoxa-8-silaspiro[7.7]pentadecane (8CI,9CI), was crystallized in hexanes from an extract of the product of the aforementioned reaction in methylene chloride and its crystal structure has been determined by X-ray diffraction (C8H16O6Si; orthorhombic; α = 9.2892(3), b = 9.5845(3), c = 12.3748(4) A; space group P212121; Z = 4). From the same reaction, two other oligomeric tetracoordinated silicon compounds were detected spectroscopically. Furthermore, Density Functional calculations at the BP86/TZ2P level were performed for the bis-chelate compound. We obtained the condensed Fukui functions as well as theoretical NMR chemical shifts to rationalize why the diethyleneglycol acts only as a dianionic, bidentate ligand towards silicon. Our DFT results indicate that the tetracoordinated Si complex is a stable molecule (minimum energy point) whereas the hexacoordinated species is a first-order saddle point (transition state). These results are in agreement and rationalize the experimental findings.

Mediante un estudio teórico y experimental se analizó la capacidad ligante del dietilenglicol para formar complejos con el átomo de silicio. Debido a la bien conocida oxofilia del silicio, se esperaría que la reacción de este ligante tridentado O,O,O-donador con un reactivo tal como el SiCl4 daría lugar a la formación del correspondiente complejo bisquelato hexacoordinado neutro de silicio. En su lugar se aisló un complejo espirocíclico bisquelato tetracoordinado y no hubo evidencia de la formación de algún alcoxisilano hipervalente. El compuesto tetracoordinado, 1,4,7,9,12,15-Hexaoxa-8-silaespiro[7.7]pentadecano (8CI,9CI) fue cristalizado en hexano a partir de un extracto del producto de reacción en cloruro de metileno, y se determinó su estructura cristalina mediante difracción de rayos X de cristal único (C8H16O6Si; orto-rrómbico; α = 9.2892(3), b = 9.5845(3), c =12.3748(4) A; grupo espacial P212121; Z = 4). En la misma reacción se detectaron espectroscópicamente dos compuestos de silicio tetracoordinado y oligomérico. También se llevaron a cabo cálculos de Funcionales de la Densidad (DFT) al nivel BP86/TZ2P para el compuesto bisquelato. Se obtuvieron las funciones condensadas de Fukui así como los desplazamientos químicos teóricos de RMN para racionalizar porqué el dietilenglicol actúa como un ligante bidentado dianiónico frente al silicio. Los resultados de DFT indican que el compuesto de silicio tetracoordinado es una molécula estable (punto de mínima energía) mientras que la especie hexacoordinada es un punto silla de primer orden (estado de transición). Los resultados teóricos son consistentes con los hallazgos experimentales y permiten racionalizar estos últimos.