Browsing by Issue Date, starting with "2017-09-18"
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- Synthesis and characterization of ionic co-crystals of enantiopure and racemic prolinePublication . Tsenkova, Boryana Krasimirova; Cavaco, Isabel; Duarte, TeresaAn ionic co-crystal (ICC) is a multicomponent solid formed by at least an organic molecule and an inorganic salt in a defined stoichiometric ratio. ICCs have the potential to alter physicochemical properties (such as solubility and thermal stability) of a pure organic material of interest, and recent research has also highlighted the possibility of chiral resolution through ICC formation. The purpose of the current work was to synthesize and characterize novel ionic co-crystals of racemic proline with lithium halides using mechanochemical and solution techniques, and to investigate the solid-state chiral resolution ability of lithium. The synthesis of molecular and ionic co-crystals of enantiopure and racemic proline with different inorganic salts and organic co-formers was attempted in order to obtain novel compounds with modified properties. Powder and Single Crystal X-ray diffraction, TGA and DSC were the main techniques used for the characterization of the novel compounds. The results obtained confirm the potential for chiral resolution through ICC formation as conglomerate and racemate ICCs were obtained. In the racemate ICCs, at least in the 1:1 stoichiometry amino acid to lithium halide, a very consistent pattern was observed - the homochiral preference of Lithium resulted in the formation of homochiral columns. Previously described in the literature ICC of (DL-Proline)2•ZnCl2 with homochiral columns spiked our interest and a different synthesis procedure was followed, resulting in the formation of a (DL-Proline)2•ZnCl2 polymorph without the homochiral columns. These results encourage further studying the factors that promote homochiral column formation in the crystal packing - a possible precursor to conglomerate formation. Narrowing down these factors could allow us in the future to fine-tune the co-crystallization of chiral compounds as a conglomerate or a racemate ICC and pave the road towards novel methods for chiral resolution.
- Recovery of Pd as nanosized Pds by combining solvent extraction with biological strategies based on the use of sulphate-reducing bacteria communitiesPublication . Nanusha, Mulatu Yohannes; Costa, Maria ClaraPlatinum group metals (PGMs) are highly demanding metals in current high-techs. However, their supply is limited due to their scarcity in natural resources and expensive mining. Previously, several techniques proposed for the recovery of PGMs from secondary sources are still eco-unfriendly and expensive. In the present study, solvent extraction in combination with cheap, operationally easy and safe techniques involving microbial communities were employed for the recovery of Pd(II) from aqueous media. Accordingly, extraction of Pd(II) by N,N’- dimethyl-N,N’-dicyclohexylthiodiglycolamide (DMDCHTDGA) in toluene and subsequent stripping of Pd(II) with an acidic thiourea solution were performed, followed by bio-Pd recovery through the use of biogenic sulphide generated by a sulphate-reducing bacteria community. The results revealed that an excellent Pd(II) extraction performance of DMDCHTDGA from binary, tertiary and complex mixtures at 2, 4 and 6 M HCl feed solutions was observed. However, Fe(III) was co-extracted from 4 and 6 M HCl feed solutions, being completely removed with deionized water in the scrubbing stage. Regarding stripping, 94-99% of extracted Pd(II) were stripped using acidic thiourea solution. Concerning palladium biorecovery, over 99% of stripped Pd(II) were recovered using biogenic sulphide obtained from a bioremediation process and Postgate B medium, in batch assay. Similarly, > 99 % palladium recovery was achieved by directly connecting Pd(II) solution with effluent from bioremediation process. Likewise, 78-99% of scrubbed Fe(III) were bio-recovered. Analysis of the precipitate collected during palladium bio-recovery testified that the precipitate was composed by Pd and S, and consistent with the synthesis of PdS nanoparticles. The elemental analysis of iron precipitate showed the presence of other metals besides Fe and S. Henceforth, the method engaged is environmentally sustainable, safe and cheap, thus attractive to be employed aiming the recovery of Pd or Fe from wastes materials.
- Exploring the potentialities of waste plant materials for the production of gold nanoparticles and multi-metallic composite particles and its application in wastewater treatmentPublication . Abagero, Wubshet Belay; Costa, Maria Clara; Dandlen, AnahiBiosynthesis of metallic nanoparticles has been regarded as a green, environmentally friendly and efficient method for nanoparticles production that avoids the usage of toxic chemicals and generation of hazardous waste during the process. In this study we reported a green, facile and rapid biosynthesis method for the synthesis of gold nanoparticles (AuNPs) and multi-metallic composite particles using raspberry leave extract as both reductant and capping agent in a single-pot process. Various waste plant materials were collected from the Algarve region for extract preparation. The waste plant materials were selected based on the availability and the cost of the material. Reduction potential of each extract was determined using FRAP method. Optimization of the synthesis method (synthesis time and metal precursor concentration) was investigated to get the best synthesis conditions. Standard gold-(III) chloride solution for AuNPs and AMD wastewater from São Domingos mine site, southwest Portugal, for multi-metallic composite particles was used as source of the corresponding metal ions. The UV–Vis spectra showed a SPR peak at 560nm for the AuNPs that were synthesized using optimized synthesis conditions which were 15 min synthesis time, 100 mg/L gold-(III) solution concentration and 1:10 (v/v) extract to standard gold (III) solution ratio at room temperature. TEM images of the precipitates obtained from Au-(III) solution showed different shape and sizes which consist of spherical NPs (51–70 nm), along with few rods (71–80 nm), triangular (61-70 nm) and hexagonal (61-70 nm) particles. TEM images of multi-metallic composite particles revealed there were mostly composed of spherical particles with an approximate average size of 100 nm (range between 70-150 nm). In XRD pattern, the crystalline natures of the synthesized AuNPs showed sharp intense peaks of Bragg reflections corresponding to (111), (200), (220), (311) and (222) planes at 2θ values of 38.20, 44.50, 64.70, 77.70 and 81.20, respectively, displays the crystalline nature of AuNPs and no other peaks were observed due to impurities. These planes are assigned to cubic structure of the AuNPs according to the high-Score Plus software with the ICDD PDF-2 database. The AuNPs were further characterized by Energy dispersive X-ray spectra (EDS) analysis, which gives additional evidence for the reduction of Au-(III) solution to elemental gold thus confirming gold as the only element in the precipitate. The EDS analysis for multi-metallic composite particles suggested that the particles are mainly composed by iron, aluminum and copper, probably as oxides. The stability of AuNPs and multi-metallic composite particles were measured using zeta potential and both particles showed moderate to good stability at different pH range and lower stability at pH 1 and pH 2. The application of the synthesized multi-metallic particles as adsorbent was tested for the removal of phosphate from synthetic wastewater and it showed up to 70.0 ± 3.9 % removal efficiency. In conclusion, in this study suitable, eco-friendly, nontoxic, and single pot synthesis method was developed for the production of AuNPs and multi-metallic composite particles using raspberry leave extract. This study also revealed the potential utilization of acid mine drainage wastewater as a source of multi-metallic composite particles which has proven efficiency to remove phosphate from wastewater via adsorption.
- Micromedronho: design of microencapsulated arbutus unedo leaves and fruits by spray drying for supplements and functional foodsPublication . Nunes, Ricardo Jorge dos Santos; Carvalho, Isabel Saraiva deArbutus unedo is a common tree in the Mediterranean area. Its fruits are consumed fresh or transformed, leaves are rich in antioxidants and not much is known about flowers. In this work we conduct a bibliographic survey utilizing text mining coupled with bibliography management software to expedite the process. We then study the best conditions to extract antioxidants from leaves, fruits and flowers of A. unedo and we compare their antioxidant activity with other plants from Algarve. In this step we found A. unedo to be the best plant. We then investigate the antiproliferative and antimicrobial activities of A. unedo and other plants from Algarve and also explore their phenolic profile and zinc contents, where we find A. unedo has antibacterial activity and retards sw480 cell line growth. Next we determine the vitamin E contents and fatty acid profile of the A. unedo extracts and explore their potential use in the treatment of chronic diseases, namely diabetes, Alzheimer and Parkinson, using enzymatic assays. At this step we find that leaves and fruits are rich in vitamin E, mostly α-tocopherol, and have a ω3:ω6 ratio above 1. Additionally, leaf and flower extracts have the best potential to be used in diabetes control, mostly via α-glucosidase inhibition. We also find the extracts show strong potential to be used in Alzheimer’s control but not in Parkinson’s and that they inhibit acetylcholinesterase and butyrilcholinesterase differently and via difference mechanisms. Finally we expose the development and stability to storage of three new products using A. unedo leaves and fruits as basis. These include a beverage with antioxidant and anti-Alzheimer activity, macrocapsules rich in antioxidants and microcapsules obtained using a spray dryer, which even after in-vitro digestion present the potential to be used in the treatment of Alzheimer’s disease.