Showing papers by "Christian V. Stevens published in 2019"

Dialdehyde carboxymethyl cellulose cross-linked chitosan for the recovery of palladium and platinum from aqueous solution

Abstract: Platinum (Pt) and palladium (Pd) have widespread applications, such as in catalysts, jewelry, fuel cells, and electronics because of their favorable physical and chemical properties. Recovery of Pt and Pd from secondary sources is of great concern due to the increased market demand and limitation of the natural reserves of these precious metals. The aim of this research is to achieve recovery of Pt and Pd ions from dilute aqueous solution using dialdehyde of carboxymethyl cellulose (DCMC) crosslinked chitosan (Ch-DCMC). The DCMC was prepared by periodate oxidation of carboxymethyl cellulose (CMC). Both the DCMC and Ch-DCMC were characterized before and after Pt or Pd adsorption using Fourier-transformed infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The effect of cross-linking ratios of chitosan and DCMC (1:1, 1:0.8, 1:0.5, 1:0.25 and 1:0.1) on the Pt and Pd recovery was studied. The optimal cross-linking ratio was found to be 1:0.25 (chitosan: DCMC) with maximum adsorption capacity of 80.8 mg/g Pt and 89.4 mg/g Pd. High selectivity for Pt and Pd compared to base metals and common anions was achieved.

pH-Controlled self-assembled fibrillar network hydrogels : evidence of kinetic control of the mechanical properties

Abstract: Control of the nucleation and growth process in self-assembled fibrillary networks (SAFiN) with the goal of preparing physical hydrogels from low-molecular-weight gelators (LMWG) is well establishe...

Fundamental Study on the Salt Tolerance of Oregano Essential Oil-in-Water Nanoemulsions Containing Tween 80

Abstract: This study provides fundamental information about the influence of salt on the physicochemical stability of oregano essential oil (EO) and its main components incorporated in a nanoemulsion delivery system containing Tween 80 (T80) emulsifier. The emulsion stability was found to be strongly correlated with the lipid phase composition and the type of salts. The oregano essential oil nanoemulsions remained stable for several weeks in the absence of salts. Moreover, they were insensitive to tetrabutylammonium bromide, whereas similar to carvacrol emulsions, they exhibited a rapid phase separation and oiling-off in the presence of sodium chloride. On the other hand, high oleic sunflower oil (HOSO) and p-cymene emulsions remained stable in the presence of NaCl. Addition of 70 and 80% HOSO to the lipid phase of oregano EO and carvacrol, respectively, was found to be sufficient for the formation of emulsions with a high stability to 1.7 M NaCl. Hereby, the morphology of the oregano EO emulsions after 30 days of storage in the presence of NaCl was visualized using a transmission electron microscope. The determination of the surface load and area per surfactant molecule by interfacial tension (IFT) measurements and quartz crystal microbalance with dissipation revealed the dehydration of the polyoxyethylene groups of T80 in the presence of salt. The thickness of the T80 adsorbed layer onto solid hydrophobic and hydrophilic surfaces was significantly lower (p < 0.05) in the presence of sodium chloride. It is hypothesized that a combination of Ostwald ripening and coalescence due to an IFT increase and dehydration was responsible for the instability of the emulsions containing the more polar oregano EO and carvacrol in the presence of salt. The results obtained in this study could be useful for the formulation of essential oil nanoemulsions in the presence of salts applicable in food, pharmaceutical, and personal care products.

Nanoscale antiadhesion properties of sophorolipid-coated surfaces against pathogenic bacteria

Abstract: A current challenge in nanomedicine is to develop innovative strategies to fight infections caused by multiresistant bacterial pathogens. A striking example is antiadhesion therapy, which represents an attractive alternative to antibiotics to prevent and treat biofilm-associated infections on medical devices. By means of single-cell force nanoscopy, we demonstrate that sophorolipid (SL) biosurfactants feature unusually strong antiadhesion properties against Staphylococcus aureus and Escherichia coli, two nosocomial pathogens involved in catheter-related infections, which represent a major public health problem worldwide. We find that the nanoscale adhesion forces of single bacteria are much weaker on SL monolayers than on abiotic alkanethiol monolayers. The remarkable antifouling efficacy of SL-surfaces is likely to involve repulsive hydration forces associated with sophorose headgroups. We also show that, owing to their surfactant properties, soluble SLs block bacterial adhesion forces towards abiotic surfaces. Collectively, our single-cell experiments demonstrate that sophorolipids exhibit strong and versatile antiadhesion properties, making them promising candidates to design anti-infective biomaterials.

Enzymatic degumming of corn oil using phospholipase C from a selected strain of Pichia pastoris

Abstract: Degumming is a necessary refining step for all crude vegetable oils. Purifine® PLC is a new enzyme used for industrial oil degumming. In the present study, enzymatic degumming trials were performed on crude corn oil using a commercial phospholipase C enzyme Purifine® PLC with the aim of determining its optimum process conditions. Enzymatic degumming applying 200 mg/kg of Purifine® PLC during 120 min at 60 °C, and a pH of 5.7 using chemical conditioning, resulted in a residual phosphorus content of 27 mg/kg and an absolute diacylglycerol increase of 0.54 wt%. Compared to water degumming, enzymatic degumming with Purifine® PLC provided a better degumming (67 mg/kg versus 27 mg/kg) and an increase in the diacylglycerol content. The pH adjustment of crude corn oil performed by means of a caustic pretreatment was not able to keep the pH at an optimal stable value due to the continuous release of acidic phosphate groups. Analysis of the composition of remaining phospholipids in the gums fraction showed that Purifine® PLC could effectively convert phosphatidylcholine and phosphatidylethanolamine into diacylglycerols, whereas it could not convert phosphatidylinositol and phosphatidic acid. These results confirm that Purifine® PLC degumming is a commercially feasible alternative to traditional degumming processes.

Asymmetrical, Symmetrical, Divalent, and Y-Shaped (Bola)amphiphiles: The Relationship between the Molecular Structure and Self-Assembly in Amino Derivatives of Sophorolipid Biosurfactants.

Abstract: Conventional head-chain but also more exotic divalent, Gemini, or bolaform amphiphiles have in common well-defined hydrophilic and hydrophobic blocks with often a predictable self-assembly behavior. However, new categories of amphiphiles, such as microbial biosurfactants, challenge such conventional understanding because of the poorly defined boundaries between the hydrophilic and hydrophobic portions. Microbial glycolipids, such as sophorolipids, rhamnolipids, or cellobioselipids, interesting biodegradable, nontoxic, alternatives to synthetic surfactants, all represent interesting examples of atypical amphiphiles with partially predictable self-assembly properties. However, their limited molecular diversity strongly limits their application potential. For this reason, we used them as ready-made platform to prepare a whole class of new derivatives. In particular, a broad range of amino derivatives of sophorolipid biosurfactant was recently prepared with the goal of producing biobased antimicrobial and transfection agents, of which the efficiency strongly depends on their molecular structure and unpredictable self-assembly behavior. The new compounds contain a set of asymmetrical and symmetrical bolaamphiphiles, the latter with three or four hydrophilic centers, divalent amphiphiles with asymmetric polar headgroups and even Y-shaped amphiphiles, bearing two sophorose groups connected to one nitrogen atom. In this contribution, we employ small-angle X-ray scattering to establish a relationship between their peculiar molecular structures and the self-assembly properties in water. We find that all divalent and Y-shaped compounds form micelles, of which the hydrophilic shell is composed of a bulky sophorose-C x( x = 8,11)-amine moiety, with aggregation numbers between 30 and 100. On the contrary, most symmetrical and asymmetrical bolaamphiphiles display poor self-assembly properties, generally showing aggregation numbers below 20, especially in the presence of either short spacers or large spacers containing hydrophilic centers.

Lanthanide grafted phenanthroline-polymer for physiological temperature range sensing

Abstract: Accurate measurement of the temperature is crucial as it determines the dynamics of almost any system. Conventional contact thermometers are not well suited for small scale measurements. Temperature dependent luminescent materials, i.e. materials that emit light of different color at different temperature, are therefore of particular interest in the development of noncontact thermometers. Luminescent materials consisting of lanthanide ions feature high thermal sensitivity, high photostability and high quantum yields. These ions possess very interesting light emitting properties. By anchoring them onto different backbone materials, their light absorption is increased. The search for a backbone that allows the sensor to be active in a defined temperature range, with a high detection sensitivity is ongoing. This work reports the first insoluble phenanthroline-polymer (phen-polymer) backbone on which europium (Eu3+) and terbium (Tb3+) trifluoroacetylacetone (tfac) complexes are easily grafted in a 1 : 1 metal ratio in order to create a noncontact temperature sensor. Two clear, discriminable emission peaks were observed during the photoluminescence study at room temperature, demonstrating that this material can be used as a ratiometric thermometer. The characteristic emission peak correlated to Eu3+ transition is slightly stronger than the emission peak of Tb3+ transition, resulting in a yellow emission color. The maximum value of the relative temperature sensitivity was calculated to be 2.3404% K−1 (340 K), which indicated good thermometric behavior. The emission color of the designed phen-polymer@Eu,Tb_tfac changed from light green (260 K) to orange-red (460 K). The thermometer can therefore be used as a ratiometric noncontact temperature sensor in the broad physiological temperature range.

Electrophilic Bromination in Flow: A Safe and Sustainable Alternative to the Use of Molecular Bromine in Batch.

Abstract: Bromination reactions are crucial in today’s chemical industry since the versatility of the formed organobromides makes them suitable building blocks for numerous syntheses. However, the use of the toxic and highly reactive molecular bromine (Br2) makes these brominations very challenging and hazardous. We describe here a safe and straightforward protocol for bromination in continuous flow. The hazardous Br2 or KOBr is generated in situ by reacting an oxidant (NaOCl) with HBr or KBr, respectively, which is directly coupled to the bromination reaction and a quench of residual bromine. This protocol was demonstrated by polybrominating both alkenes and aromatic substrates in a wide variety of solvents, with yields ranging from 78% to 99%. The protocol can easily be adapted for the bromination of other substrates in an academic and industrial environment.

Lipid-Based Quaternary Ammonium Sophorolipid Amphiphiles with Antimicrobial and Transfection Activities.

Abstract: Twelve new quaternary ammonium sophorolipids with long alkyl chains on the nitrogen atom were synthesized starting from oleic and petroselinic acid-based sophorolipids. These novel derivatives were evaluated for their antimicrobial activity against selected Gram-negative and Gram-positive bacteria and their transfection efficacies on three different eukaryotic cell lines in vitro as good activities were demonstrated for previously synthesized derivatives. Self-assembly properties were also evaluated. All compounds proved to possess antimicrobial and transfection properties, and trends could be observed based on the length of the nitrogen substituent and the total length of the sophorolipid tail. Moreover, all long-chain quaternary ammonium sophorolipids form micelles, which proved to be a prerequisite to induce antimicrobial activity and transfection capacity. These results are promising for future healthcare applications of long-chained quaternary ammonium sophorolipids.

A review on nuclear overhauser enhancement (NOE) and rotating-frame overhauser effect (ROE) NMR techniques in food science: Basic principles and applications

Abstract: Background The characterization of the original chemical structure and induced changes of micro- and macro-molecules using analytical techniques with concise and detailed outcomes is potentially one of the major challenges for food scientists. To this end, the non-invasive nuclear magnetic resonance (NMR) technique can play a significant role through employment of different NMR methods. The Nuclear Overhauser effect (NOE) and rotating-frame Overhauser effect (ROE) techniques are powerful NMR methods that have attracted great interest because they provide precise information about the three dimensional spatial structure of the molecules, as well as about possible chemical reactions and interactions. Scope and approach In this article, we reviewed the basic principles as well as applications of two NMR techniques: Nuclear Overhauser effect spectroscopy (NOESY) and rotating-frame Overhauser effect spectroscopy (ROESY). Hereby, we focused mainly on the applications and importance of these techniques in food science research. Both the structural (configuration and conformation) changes and the complexes formed by interacting compounds could be better studied using these techniques. Key findings and conclusions The inter- and intra-molecular interactions within food-based ingredient mixtures, as well as configurational and conformational analyses can be more efficiently studied with the aid of NOESY and ROESY. These methods as complementary analysis tools can be exploited for the straightforward elucidation of the spatial proximity of either novel, native or modified compounds. In the future, these techniques may be helpful to better understand the interaction between polymers, such as protein-polysaccharide interactions.

Single-Molecule Lamellar Hydrogels from Bolaform Microbial Glucolipids

Abstract: Lipid lamellar hydrogels are rare soft fluids composed of a phospholipid lamellar phase instead of fibrillar networks. The mechanical properties of these materials are controlled by defects, induced by local accumulation of a polymer or surfactant in a classical lipid bilayer. Herein we report a new class of lipid lamellar hydrogels composed of one single bolaform glycosylated lipid obtained by fermentation. The lipid is self-organized into flat interdigitated membranes, stabilized by electrostatic repulsive forces and stacked in micrometer-sized lamellar domains. The defects in the membranes and the interconnection of the lamellar domains are responsible, from the nano- to the micrometer scales, for the elastic properties of the hydrogels. The lamellar structure is probed by combining small angle x-ray and neutron scattering (SAXS, SANS), the defect-rich lamellar domains are visualized by polarized light microscopy while the elastic properties are studied by oscillatory rheology. The latter show that both storage G' and loss G'' moduli scale as a weak power-law of the frequency, that can be fitted with fractional rheology models. The hydrogels possess rheo-thinning properties with second-scale recovery. We also show that ionic strength is not only necessary, as one could expect, to control the interactions in the lamellar phase but, most importantly, it directly controls the elastic properties of the lamellar gels.

Production of long-chain hydroxy fatty acids by Starmerella bombicola.

Abstract: To decrease our dependency for the diminishing source of fossils resources, bio-based alternatives are being explored for the synthesis of commodity and high-value molecules. One example in this ecological initiative is the microbial production of the biosurfactant sophorolipids by the yeast Starmerella bombicola. Sophorolipids are surface-active molecules mainly used as household and laundry detergents. Because S. bombicola is able to produce high titers of sophorolipids, the yeast is also used to increase the portfolio of lipophilic compounds through strain engineering. Here, the one-step microbial production of hydroxy fatty acids by S. bombicola was accomplished by the selective blockage of three catabolic pathways through metabolic engineering. Successful production of 17.39 g/l (ω-1) linked hydroxy fatty acids was obtained by the successive blockage of the sophorolipid biosynthesis, the β-oxidation and the ω-oxidation pathways. Minor contamination of dicarboxylic acids and fatty aldehydes were successfully removed using flash chromatography. This way, S. bombicola was further expanded into a flexible production platform of economical relevant compounds in the chemical, food and cosmetic industries.

Kinetic evaluation of chitosan-derived catalysts for the aldol reaction in water

Abstract: The site time yield (STY) and stability of the primary amine sites in low molecular weight chitosan have been quantified for the aldol reaction of acetone with 4-nitrobenzaldehyde in a mixture of water and acetone as a solvent. Crude chitosan with varying degrees of deacetylation (DDA), as well as chitosan in hydrogel and aerogel forms, was used. Apart from the main reaction, accumulation of an imine formed from 4-nitrobenzaldehyde occurred in the early stages of the reaction. This imine acted as an inhibitor of the primary amine sites and was formed until an equilibrium was reached, after which the catalytic activity remained constant. Chitosan with a DDA amounting to 70.4% exhibited a STY of 2.18 ± 0.05 × 10−5 molproduct molamine−1 s−1. This STY increased with decreasing DDA, as a direct result of an increase in amine pKa. No differences in activity were observed between the crude, hydrogel, and aerogel forms of chitosan with the same DDA. Recycling in a second batch experiment allowed reproducing the same performance as that in the first experiment. Under continuous-flow conditions, the activity of chitosan was found to stabilize as a function of the time on stream, after the imine formation has equilibrated. Even though the catalytic activity of these chitosan catalysts was found to be lower than those of the current state-of-the-art catalysts for the aldol reaction, their stability in an aqueous environment opens new perspectives for future catalyst development.

Gold and Palladium Mediated Bimetallic Catalysis:Mechanistic Investigation through the Isolation of the Organogold(I)Intermediates

Abstract: Au–Pd based catalytic systems are a unique couple due to the carbophilic Lewis acidity of Au and the redox properties of Pd. To gain more insight into this bimetallic couple, a synthetic and mechanistic investigation was conducted. As key substrates, ynamides (N-alkynyl allyloxycarbamates and N-alkynyl ethyloxycarbamates) were used. Essential for the mechanistic part was the isolation of the organogold(I) intermediate to validate the proposed mechanism. In total, 18 polysubstituted oxazolones and 12 organogold(I) complexes were synthesized.

Optical Properties of Isolated and Covalent Organic Framework-Embedded Ruthenium Complexes.

Abstract: Heterogenization of RuL3 complexes on a support with proper anchor points provides a route toward design of green catalysts. In this paper, Ru(II) polypyridyl complexes are investigated with the aim to unravel the influence on the photocatalytic properties of varying nitrogen content in the ligands and of embedding the complex in a triazine-based covalent organic framework. To provide fundamental insight into the electronic mechanisms underlying this behavior, a computational study is performed. Both the ground and excited state properties of isolated and anchored ruthenium complexes are theoretically investigated by means of density functional theory and time-dependent density functional theory. Varying the ligands among 2,2'-bipyridine, 2,2'-bipyrimidine, and 2,2'-bipyrazine allows us to tune to a certain extent the optical gaps and the metal to ligand charge transfer excitations. Heterogenization of the complex within a CTF support has a significant effect on the nature and energy of the electronic transitions. The allowed transitions are significantly red-shifted toward the near IR region and involve transitions from states localized on the CTF toward ligands attached to the ruthenium. The study shows how variations in ligands and anchoring on proper supports allows us to increase the range of wavelengths that may be exploited for photocatalysis.

Electronic properties of heterogenized Ru(II) polypyridyl photoredox complexes on covalent triazine frameworks

Abstract: Ru(II) polypyridyl complexes have been successful for a wide range of photoredox applications thanks to their efficient light-induced metal-to-ligand charge transfer. Using the computational framework of density-functional theory, we report how these complexes can be anchored onto covalent triazine frameworks while maintaining their favorable electronic properties. We moreover show that variation of the nitrogen content of the framework linkers or complex ligands endows the heterogenized catalyst with a unique versatility, spanning a wide range of absorption characteristics and redox potentials. By judiciously choosing the catalyst building blocks, it is even possible to selectively guide the charge transfer toward either the scaffold or the accessible pore sites. Rational design of sustainable and efficient photocatalysts thus comes within reach.

Design and visualization of second-generation cyanoisoindole-based fluorescent strigolactone analogs.

Abstract: Strigolactones (SLs) are a family of terpenoid allelochemicals that were recognized as plant hormones only a decade ago. They influence a myriad of both above- and belowground developmental processes, and are an important survival strategy for plants in nutrient-deprived soils. A rapidly emerging approach to gain knowledge on hormone signaling is the use of traceable analogs. A unique class of labeled SL analogs was constructed, where the original tricyclic lactone moiety of natural SLs is replaced by a fluorescent cyanoisoindole ring system. Biological evaluation as parasitic seed germination stimulant and hypocotyl elongation repressor proved the potency of the cyanoisoindole strigolactone analogs (CISA) to be comparable to the commonly accepted standard GR24. Additionally, via a SMXL6 protein degradation assay, we provided molecular evidence that the compounds elicit SL-like responses through the natural signaling cascade. All CISA analogs were shown to exhibit fluorescent properties, and the high quantum yield and Stokes shift of the pyrroloindole derivative CISA-7 also enabled in vivo visualization in plants. In contrast to the previously reported fluorescent analogs, CISA-7 displays a large similarity in shape and structure with natural SLs, which renders the analog a promising tracer to investigate the spatiotemporal distribution of SLs in plants and fungi.

Process for the manufacturing of an acid halide in a flow reactor

Abstract: The present disclosure relates to a process for the manufacturing of an acid halide, wherein the process comprises the steps of: a) providing a flow reactor comprising a reaction chamber; b) providing reactants comprising: i. a carboxylic acid; ii. a reaction co-agent selected from the group consisting of N,N- disubstituted amides; and iii. a phosphoryl halide; c) incorporating the reactants into the reaction chamber of the flow reactor, wherein the molar ratio of the carboxylic acid to the phosphoryl halide is 1 to at least 0.8, and the molar ratio of the carboxylic acid to the co-agent is 1 to at least 0.5; and d) producing a reaction product stream comprising the acid halide. In another aspect, the present disclosure is directed to the use of a phosphoryl halide for the manufacturing of an acid halide in a flow reactor.

Process for the manufacturing of a 3-halopropionyl halide in a flow reactor

Abstract: The present disclosure relates to a process for the manufacturing of a 3-5 halopropionylhalide, wherein the process comprises the steps of: a) providing a flow reactor comprising a reaction chamber; b) providing reactants comprising: i. acrylic acid; ii. a reaction co-agent selected from the group consisting of N,N-0 disubstituted amides; and iii. a halogenating agent; and c) incorporating the reactants into the reaction chamber of the flow reactor, thereby forming a reaction product stream comprising a 3-halopropionyl-halide; wherein the molar ratio of acrylic acid to the halogenating agent is 1 to at least 5 0.8; wherein the temperature of the reaction chamber of the flow reactor is greater than 60° C.; and wherein the residence time of the reaction product stream comprising the 3-halopropionylhalide in the reaction chamber of the flow reactor is greater than 10 minutes.