Fast and efficient synthesis of high molecular weight poly(epsilon‐caprolactone) diols by microwave‐assisted polymer synthesis

Because of advantageous features such as shorter reaction times, greater yields, limited generation of by‐products and relatively easy and straightforward scale‐up, microwave‐assisted synthesis has become a very appealing tool in organic synthesis. Conversely, its implementation in the context of the synthesis of biomaterials for biopharmaceutical applications has been more limited. The present work reports on the fast and efficient microwave‐assisted synthesis of poly(ethylene glycol) (PEG)‐initiated poly(ε‐caprolactone) diols (PCL) by the ring‐opening polymerization (ROP) of ε‐caprolactone using stannous octanoate as catalyst. Since the PEG content in the synthesized copolymers was extremely low (0.2–1.9%), products were highly hydrophobic and displayed the intrinsic thermal properties of pure PCL. As opposed to the more time‐consuming conventional thermally‐driven synthesis that usually demands 2–3 h, the microwave technique resulted in intermediate to high molecular weight PEG‐PCL derivatives within 10–15 min. The influence of different parameters affecting the synthetic process, namely monomer‐to‐initiator ratio, reaction time, catalyst concentration and the presence, type, and concentration of solvent were thoroughly investigated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fabrication of Arsenic Sulfide Optical Fiber with Low Hydrogen Impurities

Arsenic sulfide glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength region associated with residual hydrogen and oxygen related impurities, despite using purified precursors. We report a purification process based on the addition of tellurium tetrachloride (TeCl₄) to the glass. During melting, the chlorine from TeCl₄ reacts with the hydrogen impurities to produce volatile products (e.g., HCl) that can be removed by subsequent dynamic distillation. The processing conditions have been modified accordingly to produce optical fibers with significantly reduced loss due to hydrogen sulfide impurity content (1.5 dB/m).     

Variability of Phytosterols in Jatropha curcas Germplasm

Jatropha curcas L. has great potential for biofuel and phytosterol production. The objective of this research was to evaluate G × E variability for kernel phytosterol content and composition in Jatropha germplasm. Freshly matured seeds from 21 accessions grown in Málaga, Spain were collected at two stages of development. Significant genetic variation was detected for total kernel phytosterol content, which ranged from 2,246 to 2,883 mg kg^?1; and stigmasterol concentration, which ranged from 7.6 to 11.5 % of the total phytosterols. An accession with 9.2 % Δ⁵‐avenasterol was also identified. The coefficient of variation for kernel phytosterol content and stigmasterol concentration was 6.2 and 14.0 % respectively between accessions and 7.2 and 10.2 % respectively within accessions. Accordingly, evaluation of plant to plant variation is advisable. The existence of variability for kernel phytosterol content and composition in Jatropha will enable breeding for enhanced levels of these compounds.     

Cr(VI) removal from synthetic and real wastewaters: The use of the invasive biomass Sargassum muticum in batch and column experiments

The macroalgae Sargassum muticum was selected for the treatment of solutions containing Cr(VI). Very acidic pH values were established as optimal for Cr(VI) reduction. Algae chemical modification reduced equilibrium time to 4 h. First order kinetic model was used to describe the reduction kinetic of Cr(VI). A column experiment allowed to distinguish the processes occurring during Cr(VI) elimination: its reduction to Cr(III) and the subsequent adsorption of this species formed. Under the selected conditions the biomass was capable of reducing all the incoming Cr(VI) during 77 h. Industrial wastewaters from chrome plating industry were also tested for chromium removal.     

Noncanonical Reactions of Flavoenzymes

Enzymes containing flavin cofactors are predominantly involved in redox reactions in numerous cellular processes where the protein environment modulates the chemical reactivity of the flavin to either transfer one or two electrons. Some flavoenzymes catalyze reactions with no net redox change. In these reactions, the protein environment modulates the reactivity of the flavin to perform novel chemistries. Recent mechanistic and structural data supporting novel flavin functionalities in reactions catalyzed by chorismate synthase, type II isopentenyl diphosphate isomerase, UDP-galactopyranose mutase, and alkyl-dihydroxyacetonephosphate synthase are presented in this review. In these enzymes, the flavin plays either a direct role in acid/base reactions or as a nucleophile or electrophile. In addition, the flavin cofactor is proposed to function as a “molecular scaffold” in the formation of UDP-galactofuranose and alkyl-dihydroxyacetonephosphate by forming a covalent adduct with reaction intermediates.     

Modeling Alcohol Dehydrogenase Catalysis in Deep Eutectic Solvent/Water Mixtures

The use of oxidoreductases (EC1) in non-conventional reaction media has been increasingly explored. In particular, deep eutectic solvents (DESs) have emerged as a novel class of solvents. Herein, an in-depth study of bioreduction with an alcohol dehydrogenase (ADH) in the DES glyceline is presented. The activity and stability of ADH in mixtures of glyceline/water with varying water contents were measured. Furthermore, the thermodynamic water activity and viscosity of mixtures of glyceline/water have been determined. For a better understanding of the observations, molecular dynamics simulations were performed to quantify the molecular flexibility, hydration layer, and intraprotein hydrogen bonds of ADH. The behavior of the enzyme in DESs follows the classic dependence of water activity (a_W) in non-conventional media. At low a_W values (<0.2), ADH does not show any activity; at higher a_W values, the activity was still lower than that in pure water due to the high viscosities of the DES. These findings could be further explained by increased enzyme flexibility with increasing water content.     

Intersecting Xenobiology and Neometabolism To Bring Novel Chemistries to Life

The diversity of life relies on a handful of chemical elements (carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus) as part of essential building blocks; some other atoms are needed to a lesser extent, but most of the remaining elements are excluded from biology. This circumstance limits the scope of biochemical reactions in extant metabolism – yet it offers a phenomenal playground for synthetic biology. Xenobiology aims to bring novel bricks to life that could be exploited for (xeno)metabolite synthesis. In particular, the assembly of novel pathways engineered to handle nonbiological elements (neometabolism) will broaden chemical space beyond the reach of natural evolution. In this review, xeno-elements that could be blended into nature's biosynthetic portfolio are discussed together with their physicochemical properties and tools and strategies to incorporate them into biochemistry. We argue that current bioproduction methods can be revolutionized by bridging xenobiology and neometabolism for the synthesis of new-to-nature molecules, such as organohalides.     

Molecular Recognition in C-Type Lectins: The Cases of DC-SIGN,Langerin, MGL,and L-Sectin

Carbohydrates play a pivotal role in intercellular communication processes. In particular, glycan antigens are key for sustaining homeostasis, helping leukocytes to distinguish damaged tissues and invading pathogens from healthy tissues. From a structural perspective, this cross-talk is fairly complex, and multiple membrane proteins guide these recognition processes, including lectins and Toll-like receptors. Since the beginning of this century, lectins have become potential targets for therapeutics for controlling and/or avoiding the progression of pathologies derived from an incorrect immune outcome, including infectious processes, cancer, or autoimmune diseases. Therefore, a detailed knowledge of these receptors is mandatory for the development of specific treatments. In this review, we summarize the current knowledge about four key C-type lectins whose importance has been steadily growing in recent years, focusing in particular on how glycan recognition takes place at the molecular level, but also looking at recent progresses in the quest for therapeutics.     

Screening of lactic acid bacteria for fermentation of minced wastes of Argentinean hake (Merluccius hubbsi)

Sixteen strains of lactic acid bacteria were evaluated for their capacity of acidification of Merluccius hubbsi fish wastes obtained from a processing factory. Only three lactobacilli (Lactobacillus buchneri B-1837, Lactobacillus arizonensis B-14768 and Lactobacillus plantarum B-4496) were able to reduce the pH value to 4.0 or below when using glucose or sucrose as carbon source. Either with only 25 g l^?1 of glucose or sucrose, L. arizonensis B-14768 reduced the pH to 3.8 ± 0.2 within 24 h of fermentation. The acid tolerance test (pH 3.0 at 37 °C) for the strains presented D_pH3-values of 192, 383 and 767 min for L. buchneri, L. plantarum and L. arizonensis, respectively. However, at a lower pH value (pH 2.0) only L. arizonensis was significantly recovered after 45 min of exposure (D_pH2 68 min). Considering together the acidification capacity, the tolerance to other stresses (heat and bile salts) and the lower optimum temperature for the process, L. arizonensis is described as a suitable strain for M. hubbsi silage; constituting a promissory alternative for fish fermentation at location with temperate or cold climes.