A.M. Ramos

Recovery of polyhydroxybutyrate (PHB) from Cupriavidus necator biomass by solvent extraction with 1,2-propylene carbonate

An integrated procedure for the recovery of polyhydroxybutyrate (PHB) produced by Cupriavidus necator based on the extraction with 1,2‐propylene carbonate was evaluated. The effect of temperature (100–145°C) and contact time (15–45 min), precipitation period, and biomass pretreatments (pH shock and/or thermal treatments) on PHB extraction efficiency and polymer properties was evaluated. The highest yield (95%) and purity (84%) were obtained with the combination of a temperature of 130°C and a contact time of 30 min, with a precipitation period of 48 h. Under these conditions, PHB had a molecular weight of 7.4×105, which was the highest value obtained. Lower values (2.2×105) were obtained for higher temperatures (145°C), while lower temperatures resulted in incomplete extraction yields (45–54%). No further yield improvement was achieved with the pH/heat pretreatments, but the polymers molecular weight was increased to 1.3×106. The PHB physical properties were not significantly affected by any of the tested procedures, as shown by the narrow ranges obtained for the glass transition temperature (4.8–5.0°C), melting temperature (170.1–180.1°C), melting enthalpy (77.8–88.5 J/g) and crystallinity (55–62%). 1,2‐Propylene carbonate was shown to be an efficient solvent for the extraction of PHB from biomass. The precipitation procedure was found to highly influence the polymer recovery and its molecular weight. Although polymer molecular weight and purity were improved by applying pH/heat pretreatment to the biomass, the procedure involves the use of large amounts of chemicals, which increases the recovery costs and makes the process environmentally unfriendly.

Hydration of α-pinene over zeolites and activated carbons dispersed in polymeric membranes

Abstract The acid catalysed hydration of α-pinene yields a complex mixture of monoterpenes, alcohols and hydrocarbons. By controlling the reaction variables is possible to make it selective to the terpenic alcohols, namely α-terpineol. In this paper the results of the hydration reaction of α-pinene catalysed by polydimethylsiloxane (PDMS) membranes filled with zeolite USY, zeolite beta or a surface modified activated carbon, are reported. The reaction is carried out at 50°C, using aqueous acetone as solvent. The activity and selectivity towards α-terpineol of the composite membranes are compared with those of the free catalysts.

The acid-catalysed reaction of α-pinene over molybdophosphoric acid immobilised in dense polymeric membranes

Abstract The α-pinene hydration to α-terpineol was studied using as catalysts polymeric catalytic membranes consisting of HPMo entrapped in polyvinyl alcohol (PVA) cross-linked with 10, 20 and 30% of succinic acid, and HPMo encaged in USY zeolites dispersed in a polydimethylsiloxane (PDMS) matrix. In the case of HPMo/PVA membranes it was observed that membrane activity increases with the polymer cross-linking, due to the increase in membrane hydrophobicity, up to the limit of the increasingly restrictions to the molecules mobility. The HPMo-USY/PDMS membrane shows a significantly higher activity for pinene hydration, which is even higher than that observed with USY encaged HPMo alone. However, selectivity to α-terpineol (65% at 80% conversion) is slightly lower than that obtained for the HPMo/PVA cross-linked with 20 or 30% of succinic acid (70–75% at 90% conversion). For both catalytic membranes, HPMo/PVA or HPMo-USY/PDMS, the stability is reasonable good and catalyst activity increases in the subsequent uses of the same membrane, probably due to the interaction between retained α-terpineol and the polymer matrix.

Response of a three-stage process for PHA production by mixed microbial cultures to feedstock shift: impact on polymer composition.

Polyhydroxyalkanoates (PHA) can be produced by mixed microbial cultures (MMC) using a three-stage process. An attractive feature of MMC for PHA production is the ability to use waste/surplus feedstocks. In this study, the effect of a feedstock shift, mimicking a seasonal feedstock scenario and/or as a strategy for controlling polymer composition, on a MMC PHA production process was assessed using cheese whey (CW) and sugar cane molasses (SCM) as model feedstocks. The acidogenic stage responded immediately to the feedstock shift by changing the fermented products profile, with acetate and butyrate being the main acids produced from CW, while for SCM propionate and valerate were the dominant products. The fermentation process was then quite stable during long term operation. The PHA culture selection stage also responded quickly to the fermented feestocks shift, generating a polymer whose composition was linearly dependent on the concentration of HV and HB precursors produced in the acidogenic stage. The selected culture reached a maximum PHA content of 56% and 65% with fermented SCM and CW, respectively. Mixing fermented CW and SCM, in equal volume proportions, demonstrated the possibility of using different fermented feedstocks for tailoring polymer composition.

The effect of α-terpineol on the hydration of α-pinene over zeolites dispersed in polymeric membranes

Abstract The hydration of α-pinene over catalytic PDMS membranes loaded with a USY zeolite is studied. The concentration profiles of reagent and products exhibited a pronounced initial induction period followed by a rapid increase of the reaction rate, suggesting an autocatalytic behaviour. The effects of the main reaction product, α-terpineol, on the membrane transport properties are investigated. A simple diffusion-kinetic model which fits experimental concentration data quite well has been developed.

Vanadium as a catalyst for NO, N2O and CO2 reaction with activated carbon

The kinetics of the reaction of NO, N 2 O and CO 2 with activated carbon without catalyst and impregnated with a precursor salt of vanadium (ammonium monovanadate) was investigated. The conversion of NO, N 2 O and CO 2 was studied (450-900°C) using a TGA apparatus and a fixed bed reactor. The reactor effluents were analysed using a GC/MS on line. The addition of vanadium increased carbon reactivity and adsorption at lower temperatures. For NO and N 2 O conversion the main products obtained were N 2 , N 2 O, CO and CO 2 but for CO 2 conversion only CO was detected. In situ XRD was a useful tool for interpreting catalyst behaviour and identifying phases present during reaction conditions. The catalytic effect of vanadium can be explained by the occurrence of redox processes in which the catalyst is reduced to lower oxidation states such as V 2 O 5 /V 6 O 13 .

Oxidation of pinane using transition metal acetylacetonate complexes immobilised on modified activated carbon

The performance of a new solid catalyst is studied. Copper and cobalt acetylacetonate complexes are chemically anchored to functionalised activated carbon. These catalysts are active and highly selective to 2-pinane hydroperoxide in the oxidation of pinane at room temperature and atmospheric pressure.

MMP-2 Selectivity in Hydroxamate-Type Inhibitors

Extracellular matrix metalloproteinases (MMPs) are a family of zinc-dependent neutral endopeptidases involved in physiological and pathological processes, through the cleavage of extracellular matrix. MMPs are capable of degrading essentially all matrix components, which is crucial for malignant tumor growth, invasion, metastasis and angiogenesis. The vertebrates MMP family includes at least 26 enzymes (23 have been known in humans) with only MMP-1, 2, and 7 experimentally validated as targets for antitumoral drug design. However, inhibition of MMP-1 has been hypothesized to be the cause of the clinically observed musculoskeletal syndrome when broad spectrum inhibitors are used. On the other hand, MMP-9 is a tricky enzyme, since its inhibition might be useful in treating patients with early-stage cancers, but MMP-9 is an anti-target in patients with advanced disease. So, MMP-9 inhibition should also be prevented. Therefore, selective MMP-2 inhibition arises as a pursued profile for MMP binders. Among them, hydroxamates have been extensively studied as small molecule drug candidates characterized by an effective zinc-binding group plus additional side chains responsible for the selectivity. This article pays particular attention to MMP-2 selectivity on hydroxamate-type inhibitors, especially against MMP-9, and their chemical structure, SAR, general synthetic methods, and molecular modelling studies are here reviewed in order to inspire further design of new effective anticancer agents.

Hydrolysis of sucrose using sulfonated poly(vinyl alcohol) as catalyst.

The hydrolysis of sucrose was carried out over poly(vinyl alcohol) (PVA) with sulfonic acid groups, at 80 degrees C. The products of sucrose hydrolysis were glucose and fructose. A series of PVA with different crosslinking degree were prepared. It was observed that the catalytic activity of PVA matrix increases with the crosslinking degree, due to the increases of the amount of sulfonic acid groups on PVA. Further, the influence of various reaction parameters, such as, catalyst loading, initial concentration of sucrose and temperature, on the hydrolysis of sucrose over PVA_40 was studied. It was found that at 80 degrees C, with 0.511 g of catalyst loading and with an initial concentration of sucrose of 0.6M, a sucrose conversion of about 90%, after 3h, could be obtained. The PVA_40 catalyst was recycled and reused with negligible loss in the activity. A simple kinetic model was developed assuming that the sucrose hydrolysis is an irreversible reaction and the first order with respect to the sucrose concentration. Since the concentration profiles of the reactant and the products do not exhibit any pronounced initial inductive period, the external and internal diffusion of the reactant and products on the catalyst were not considered. It was observed that the kinetic model fits experimental concentration data quite well.

Kinetics of production and characterization of the fucose-containing exopolysaccharide from Enterobacter A47

A fucose-containing exopolysaccharide (EPS) was produced by the bacterium Enterobacter A47 using glycerol byproduct from the biodiesel industry. The analysis of kinetic data suggested a partially growth associated EPS synthesis model. Although the EPS was composed of fucose, galactose and glucose at all cultivation stages, their relative proportion has varied considerably during the run. At the beginning (24h), glucose was the main component (82.4 wt.%), being fucose and galactose minor components (5.0 wt.% and 10.9 wt.%, respectively), while at the end (96 h) it was composed of 26.0 wt.% fucose, 28.9 wt.% galactose and 43.7 wt.% glucose. The acyl groups content and composition have also changed, reaching their maximum content (19.2wt.%) at the end of the run. Moreover, the molecular weight has increased linearly during the run (from 8×10(5) to 5×10(6)). The changes observed in EPS composition and molecular weight have also had an impact upon the polymers intrinsic viscosity, as shown by its linear increase from 3.95 to 10.72 dL g(-1). The results suggest that the culture might have synthesized at least two distinct EPS, with different sugar composition and average molecular weight, which predominated at different cultivation stages.