Formation Of Secondary Bonds Research Articles

ChemInform Abstract: Solvent Extraction: The Coordination Chemistry Behind Extractive Metallurgy

AbstractReview: 49 refs.

Solvent extraction: the coordination chemistry behind extractive metallurgy

The modes of action of the commercial solvent extractants used in extractive hydrometallurgy are classified according to whether the recovery process involves the transport of metal cations, M(n+), metalate anions, MXx(n-), or metal salts, MXx into a water-immiscible solvent. Well-established principles of coordination chemistry provide an explanation for the remarkable strengths and selectivities shown by most of these extractants. Reagents which achieve high selectivity when transporting metal cations or metal salts into a water-immiscible solvent usually operate in the inner coordination sphere of the metal and provide donor atom types or dispositions which favour the formation of particularly stable neutral complexes that have high solubility in the hydrocarbons commonly used in recovery processes. In the extraction of metalates, the structures of the neutral assemblies formed in the water-immiscible phase are usually not well defined and the cationic reagents can be assumed to operate in the outer coordination spheres. The formation of secondary bonds in the outer sphere using, for example, electrostatic or H-bonding interactions are favoured by the low polarity of the water-immiscible solvents.

Investigation of triacetin effect on indomethacin release from poly(methyl methacrylate) microspheres: Evaluation of interactions using FT-IR and NMR spectroscopies

The purpose of this study was to form indomethacin (IND)-loaded poly(methyl methacrylate) (PMMA) microspheres having an extended drug release profile over a period of 24h. Microspheres were prepared by solvent evaporation method using sucrose stearate as a droplet stabilizer. When PMMA was used alone for the preparation of microspheres, only 44% of IND could be released at the end of 8h. Triacetin was added to PMMA, as a minor phase, and the obtained microspheres showed a high yield process with recovery of 89.82% and incorporation efficiency of 102.3%. A desired release profile lasting 24h was achieved. Differential scanning calorimetry (DSC) analysis showed that IND was found to be in an amorphous state in the microspheres. Fourier transform infrared (FT-IR) and nuclear magnetic resonance (1H NMR) spectra suggested that there might be a hydrogen bond present between the IND hydroxyl group and PMMA. No interaction between triacetin and IND or PMMA as the formation of secondary bonds was observed. The release enhancement of IND from microspheres was attributed to the physical plasticization effect of triacetin on PMMA and, to some extent, the amorphous state of the drug.

MEASUREMENT OF FLOW ABILITY OF BUTTER BY CAPILLARY RHEOMETRY

ABSTRACTCapillary rheometry was used to study and compare the rheological behavior of butters made from supercritically fractionated high melting triglyceride (HMT) and anhydrous milk fat (AMF) at different temperatures. Application of shear rates in the range of 17.37 to 346.93 S−1 showed a strong dependency of flow behavior on the capillary diameter, indicating slippage at the walls. Shear rates were corrected for wall‐slippage using capillaries with different diameters but the same length, and for non‐Newtonian behavior using the Rabinowitsch procedure. Shear stresses were corrected for entrance effect using capillaries of the same diameter but different lengths. Power law consistency indices (K), determined from loglog plots of corrected shear stresses versus shear rates, were found to have a negative correlation with temperature. Higher K values were observed for HMT butter depicting its more solid‐like behavior due to greater concentration of high melting triglycerides. A slight increase in the K values was observed on storage probably due to rearrangement of fat crystals and formation of secondary bonds between them. Flow indices were found to be relatively insensitive to both time and temperature of storage. From the flow curves (apparent viscosity versus shear rates), master curves were generated using the time‐temperature superposition principle.

Three‐stage interaction of dimethyl phthalate, dibutyl phthalate, and poly(vinyl acetate) with poly(methyl methacrylate)

AbstractThe interaction of dimethyl phthalate (DMP), n‐dibutyl phthalate (DBP), and poly(vinyl acetate) (PVAc) with poly(methyl methacrylate) (PMMA) was studied. Changes in the tensile strength, elastic modulus, and percentage elongation at break of the PMMA‐additive films produced were followed using the Instron testing machine. The three additives produced (1) an initial plasticization, with a decrease in tensile strength and modulus and a possible increase in elongation; (2) an antiplasticization, with accompanying increase in tensile strength and modulus and an anomalous increase in elongation; and (3) a final plasticization, with a marked decrease in tensile strength and modulus and a definite increase in elongation of PMMA. The three effects were influenced by the molecular weight of the PMMA. A spacer effect by the interposition of the molecules of the additives between those of PMMA is proposed for the initial plasticization, while for the final plasticization, a lubrication action of the plasticizers on PMMA is suggested. Antiplasticization is explained by the formation of secondary bonds between the antiplasticizer and the PMMA molecules.