Antonio Veloso

Distribution of lipids in human brain

The enormous abundance of lipid molecules in the central nervous system (CNS) suggests that their role is not limited to be structural and energetic components of cells. Over the last decades, some lipids in the CNS have been identified as intracellular signalers, while others are known to act as neuromodulators of neurotransmission through binding to specific receptors. Neurotransmitters of lipidic nature, currently known as neurolipids, are synthesized during the metabolism of phospholipid precursors present in cell membranes. Therefore, the anatomical identification of each of the different lipid species in human CNS by imaging mass spectrometry (IMS), in association with other biochemical techniques with spatial resolution, can increase our knowledge on the precise metabolic routes that synthesize these neurolipids and their localization. The present study shows the lipid distribution obtained by MALDI-TOF IMS in human frontal cortex, hippocampus, and striatal area, together with functional autoradiography of cannabinoid and LPA receptors. The combined application of these methods to postmortem human brain samples may be envisioned as critical to further understand neurological diseases, in general, and particularly, the neurodegeneration that accompanies Alzheimer’s disease.

Design of Stable and Powerful Nanobiocatalysts, Based on Enzyme Laccase Immobilized on Self-Assembled 3D Graphene/Polymer Composite Hydrogels

Graphene-based materials appear as a suitable answer to the demand for novel nanostructured materials for effective nanobiocatalytic systems design. In this work, a design of stable and efficient nanobiocatalysts made of enzyme laccase immobilized on composite hydrogels [reduced graphene oxide (rGO)/polymer] is presented. The composite hydrogel supports were synthesized by self-assembly of graphene oxide nanoplatelets in the frame of a polymer latex matrix, where the polymer nanoparticles were adsorbed onto the GO surface, creating hybrid nanoplatelets. These hybrids self-assembled when ascorbic acid was added as a GO reducing agent and formed three-dimensional porous structures, greatly swollen with water, e.g., the composite hydrogels. The hydrogels were used as a support for covalent immobilization of the laccase. The performance of the nanobiocatalysts was tested in the oxidative degradation of the recalcitrant synthetic dye Remazol Brilliant Blue R in aqueous solutions. The biocatalysts showed strong dye discoloration ability and high stability as they preserved their catalytic action in four successive batches of dye degradation. The presented biocatalysts offer possibilities for overcoming the main disadvantages of the enzyme catalysts (fragile nature, high cost, and high loading of the enzyme), which would lead to a step forward toward their industrial application.

Zwitterionic polymerization of glycidyl monomers to cyclic polyethers with B(C6F5)3

A new method of generating cyclic polyethers is reported. Glycidyl monomers react with B(C6F5)3 to generate cyclic polyethers under anhydrous conditions. In the presence of water, linear chains are formed. A zwitterionic ring-opening polymerization mechanism is postulated based on experimental evidence and DFT calculations. The obtained cyclic polyethers can be considered a new family of crown ethers, where peripheral functional groups such as phenyls, fluorinated aliphatic chains or hydroxyls decorate the rings.

Determining the effect of side reactions on product distributions in RAFT polymerization by MALDI-TOF MS

Reversible Addition–Fragmentation chain Transfer (RAFT) polymerization has emerged as one of the most versatile reversible deactivation radical polymerization techniques and is capable of polymerizing a wide range of monomers under various conditions. One of the most important factors governing the success of a RAFT polymerization is the fraction of living chains at the end of the reaction, which can be maximized by using a low amount of initiator. From the point of view of the process, it is tempting to perform the polymerization in solution, which allows a better mixing. However, in this work it is shown that this choice may be negative for the quality of the polymer. Detailed analysis using Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) of poly(n-butyl acrylate) (pBA) obtained at high conversion in the RAFT solution polymerization revealed that in addition to the polymer chains, formed by the RAFT mechanism, there were two distinct populations resulting from chain transfer to solvent and transfer to polymer followed by β-scission. Complementary results from Size Exclusion Chromatography coupled with Multi Angle Light Scattering detector (SEC/MALS), quantum chemical calculations, and a mathematical model that predicts product distributions, were also used to further confirm the assigned structures. The results highlight the scope and limitation on the living fraction of chains due to chain transfer events using RAFT polymerization and reversible deactivation radical polymerizations in general, and furthermore, yielded information about the fate of midchain radicals formed by intramolecular transfer to polymer.

Biodegradation of bisphenol A by the newly-isolated Enterobacter gergoviae strain BYK-7 enhanced using genetic manipulation

Endogenous bacterial strains possessing a high bisphenol A (BPA)-tolerance/degradation activity were isolated from different outlets of petrochemical wastewater in Iran using the enrichment cultivation approach. Two bacterial isolates with high efficiency for BPA degradation in basal medium and petrochemical wastewater were identified as Enterobacter gergoviae strain BYK-7 and Klebsiella pneumoniae strain BYK-9 using morphology, 16s rDNA analysis and MALDI-TOF mass spectrometry systems. Due to the pathogenicity of K. pneumoniae, the E. gergoviae strain was selected for further studies. This strain with very high BPA tolerance (up to 2000 mg L−1) degraded 23.10 ± 0.126 mg L−1 BPA in basal medium, 31.35 ± 4.05 mg L−1 BPA in petrochemical wastewater and 53.50 ± 0.153 mg L−1 BPA in nutritious medium within 8, 72 and 48 h, respectively. Biostimulation by mineral salts and ethanol was effective in the BPA-degradation activity of the E. gergoviae. In addition, recombinant E. gergoviae [pBRbisd] was able to degrade 45.02 ± 0.334 mg L−1 BPA in basal medium within 48 h. These results point out this strain as a very promising organism for BPA removal in industrial wastewater.

Enantioselective Ring-Opening Polymerization of rac-Lactide Dictated by Densely Substituted Amino Acids

Organocatalysis is becoming an important tool in polymer science because of its versatility and specificity. To date a limited number of organic catalysts have demonstrated the ability to promote stereocontrolled polymerizations. In this work we report one of the first examples of chirality transfer from a catalyst to a polymer in the organocatalyzed ring-opening polymerization (ROP) of rac-lactide (rac-LA). We have polymerized rac-LA using the diastereomeric densely substituted amino acids (2S,3R,4S,5S)-1-methyl-4-nitro-3,5-diphenylpyrrolidine-2-carboxylic acid (endo-6) and (2S,3S,4R,5S)-1-methyl-4-nitro-3,5-diphenylpyrrolidine-2-carboxylic acid (exo-6), combined with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a cocatalyst. Both diastereoisomers not only showed the ability to synthesize enriched isotactic polylactide with a Pm higher than 0.90 at room temperature but also were able to preferentially promote the polymerization of one of the isomers (l or d) with respect to the other. Thus, exo-6 preferentially polymerized l-lactide, whereas endo-6 preferred d-lactide as the substrate. Density functional theory calculations were conducted to investigate the origins of this unique stereocontrol in the polymerization, providing mechanistic insight and explaining why the chirality of the catalyst is able to define the stereochemistry of the monomer insertion.

Neurotransmitter receptor localization: from autoradiography to imaging mass spectrometry.

Autoradiography is used to determine the anatomical distribution of biological molecules in human tissue and experimental animal models. This method is based on the analysis of the specific binding of radiolabeled compounds to locate neurotransmitter receptors or transporters in fresh frozen tissue slices. The anatomical resolution obtained by quantification of the radioligands has allowed the density of receptor proteins to be mapped over the last 40 years. The data yielded by autoradiography identify the receptors at their specific microscopic localization in the tissues and also in their native microenvironment, the intact cell membrane. Furthermore, in functional autoradiography, the effects of small molecules on the activity of G protein-coupled receptors are evaluated. More recently, autoradiography has been combined with membrane microarrays to improve the high-throughput screening of compounds. These technical advances have made autoradiography an essential analytical method for the progress of drug discovery. We include the future prospects and some preliminary results for imaging mass spectrometry (IMS) as a useful new method in pharmacodynamic and pharmacokinetic studies, complementing autoradiographic studies. IMS results could also be presented as density maps of molecules, proteins, and metabolites in tissue sections that can be identified, localized, and quantified, with the advantage of avoiding any labeling of marker molecules. The limitations and future developments of these techniques are discussed here.

Novel alkoxyamines for the successful controlled polymerization of styrene and methacrylates

The design of alkoxyamine/nitroxide species capable of mediating the polymerization of both styrene and methacrylic monomers has been notoriously difficult. Herein, the nitroxide-mediated polymerization of styrene using a series of readily obtained alkoxyamines that were recently shown to control the polymerization of methyl methacrylate is presented. The robustness of the system is tested towards different temperatures and molecular weights. The influence of the substitution pattern in the nitroxide adducts on the polymerization of styrene is monitored through kinetic analyses. An alkoxyamine that can successfully mediate the homopolymerization of styrene and methyl methacrylate is presented. This alkoxyamine is subsequently utilized for the synthesis of PMMA-b-PS and PS-b-PBMA copolymers.

Mid-Chain Radical Migration in the Radical Polymerization of n-Butyl Acrylate

The occurrence of intramolecular transfer to polymer in the radical polymerization of acrylic monomers has been extensively documented in the literature. Whilst it has been largely assumed that intramolecular transfer to polymer leads to short chain branches, there has been some speculation over whether the mid-chain radical can migrate. Herein, by the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) of poly(n-butyl acrylate) synthesized by solution polymerization under a range of conditions, it is shown that this mid-chain radical migration does occur in the radical polymerization of acrylates conducted at high temperatures, as is evident from the shape of the molecular weight distribution. Using a mathematical model, an initial approximation of the rate at which migration occurs is made and the distribution of branching lengths formed in this scenario is explored. It is shown that the polymerizations carried out under a low monomer concentration and at high temperatures are particularly prone to radical migration reactions, which may affect the rheological properties of the polymer.

Efficient polymerization and post-modification of N-substituted eight-membered cyclic carbonates containing allyl groups

Aliphatic polycarbonates are promising materials in the biomedical field due to their low toxicity, biocompatibility, and biodegradability. A popular approach in obtaining these materials is through the organocatalyzed ring-opening polymerization (ROP) of cyclic carbonates. Functional polycarbonates can be obtained by (co)polymerizing allyl-functional cyclic monomers, which can be chemically modified via radical thiol–ene click reactions after the ROP process. To date, allyl-bearing 6-membered cyclic carbonates have been reported, however their polymerization kinetics are slow. In previous works, larger cyclic carbonates (e.g. N-substituted eight membered cyclic carbonates) have demonstrated superior reactivities over their smaller counterparts and hence, in this work, we investigated the preparation and ROP of two allyl bearing N-substituted eight membered cyclic carbonates. One of these monomers, with a pendent carbamate group, displayed substantially enhanced polymerization kinetics that allowed for efficient homopolymerizations and co-polymerizations with commercially available monomers (e.g. trimethylene carbonate, or TMC). Lastly, the polymers underwent almost quantitative post-polymerization modification via thiol–ene chemistry to yield different functionalized polycarbonates. We also demonstrated that the post-polymerization reaction could be used to form polycarbonate-based gels with multifunctional thiols.